This is gdb.info, produced by makeinfo version 4.8 from

This is gdb.info, produced by makeinfo version 4.8 from
/usr/src/tools/gdb/../../external/gpl3/gdb/dist/gdb/doc/gdb.texinfo.

INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb: (gdb). The GNU debugger.
* gdbserver: (gdb) Server. The GNU debugging server.
END-INFO-DIR-ENTRY

Copyright (C) 1988-2024 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual. Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."

This file documents the GNU debugger GDB.

This is the Tenth Edition, of `Debugging with GDB: the GNU
Source-Level Debugger' for GDB (GDB) Version 15.1.

Copyright (C) 1988-2024 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software" and "Free Software Needs Free
Documentation", with the Front-Cover Texts being "A GNU Manual," and
with the Back-Cover Texts as in (a) below.

(a) The FSF's Back-Cover Text is: "You are free to copy and modify
this GNU Manual. Buying copies from GNU Press supports the FSF in
developing GNU and promoting software freedom."

File: gdb.info, Node: Top, Next: Summary

Debugging with GDB
******************

This file describes GDB, the GNU symbolic debugger.

This is the Tenth Edition, for GDB (GDB) Version 15.1.

Copyright (C) 1988-2024 Free Software Foundation, Inc.

This edition of the GDB manual is dedicated to the memory of Fred
Fish. Fred was a long-standing contributor to GDB and to Free software
in general. We will miss him.

* Menu:

* Summary:: Summary of GDB
* Sample Session:: A sample GDB session

* Invocation:: Getting in and out of GDB
* Commands:: GDB commands
* Running:: Running programs under GDB
* Stopping:: Stopping and continuing
* Reverse Execution:: Running programs backward
* Process Record and Replay:: Recording inferior's execution and replaying it
* Stack:: Examining the stack
* Source:: Examining source files
* Data:: Examining data
* Optimized Code:: Debugging optimized code
* Macros:: Preprocessor Macros
* Tracepoints:: Debugging remote targets non-intrusively
* Overlays:: Debugging programs that use overlays

* Languages:: Using GDB with different languages

* Symbols:: Examining the symbol table
* Altering:: Altering execution
* GDB Files:: GDB files
* Targets:: Specifying a debugging target
* Remote Debugging:: Debugging remote programs
* Configurations:: Configuration-specific information
* Controlling GDB:: Controlling GDB
* Extending GDB:: Extending GDB
* Interpreters:: Command Interpreters
* TUI:: GDB Text User Interface
* Emacs:: Using GDB under GNU Emacs
* GDB/MI:: GDB's Machine Interface.
* Annotations:: GDB's annotation interface.
* Debugger Adapter Protocol:: The Debugger Adapter Protocol.
* JIT Interface:: Using the JIT debugging interface.
* In-Process Agent:: In-Process Agent

* GDB Bugs:: Reporting bugs in GDB

* Command Line Editing:: Command Line Editing
* Using History Interactively:: Using History Interactively
* In Memoriam:: In Memoriam
* Formatting Documentation:: How to format and print GDB documentation
* Installing GDB:: Installing GDB
* Maintenance Commands:: Maintenance Commands
* Remote Protocol:: GDB Remote Serial Protocol
* Agent Expressions:: The GDB Agent Expression Mechanism
* Target Descriptions:: How targets can describe themselves to
GDB
* Operating System Information:: Getting additional information from
the operating system
* Trace File Format:: GDB trace file format
* Index Section Format:: .gdb_index section format
* Debuginfod:: Download debugging resources with `debuginfod'
* Man Pages:: Manual pages
* Copying:: GNU General Public License says
how you can copy and share GDB
* GNU Free Documentation License:: The license for this documentation
* Concept Index:: Index of GDB concepts
* Command and Variable Index:: Index of GDB commands, variables,
functions, and Python data types

File: gdb.info, Node: Summary, Next: Sample Session, Prev: Top, Up: Top

Summary of GDB
**************

The purpose of a debugger such as GDB is to allow you to see what is
going on "inside" another program while it executes--or what another
program was doing at the moment it crashed.

GDB can do four main kinds of things (plus other things in support of
these) to help you catch bugs in the act:

* Start your program, specifying anything that might affect its
behavior.

* Make your program stop on specified conditions.

* Examine what has happened, when your program has stopped.

* Change things in your program, so you can experiment with
correcting the effects of one bug and go on to learn about another.

You can use GDB to debug programs written in C and C++. For more
information, see *Note Supported Languages: Supported Languages. For
more information, see *Note C and C++: C.

Support for D is partial. For information on D, see *Note D: D.

Support for Modula-2 is partial. For information on Modula-2, see
*Note Modula-2: Modula-2.

Support for OpenCL C is partial. For information on OpenCL C, see
*Note OpenCL C: OpenCL C.

Debugging Pascal programs which use sets, subranges, file variables,
or nested functions does not currently work. GDB does not support
entering expressions, printing values, or similar features using Pascal
syntax.

GDB can be used to debug programs written in Fortran, although it
may be necessary to refer to some variables with a trailing underscore.

GDB can be used to debug programs written in Objective-C, using
either the Apple/NeXT or the GNU Objective-C runtime.

* Menu:

* Free Software:: Freely redistributable software
* Free Documentation:: Free Software Needs Free Documentation
* Contributors:: Contributors to GDB

File: gdb.info, Node: Free Software, Next: Free Documentation, Up: Summary

Free Software
=============

GDB is "free software", protected by the GNU General Public License
(GPL). The GPL gives you the freedom to copy or adapt a licensed
program--but every person getting a copy also gets with it the freedom
to modify that copy (which means that they must get access to the
source code), and the freedom to distribute further copies. Typical
software companies use copyrights to limit your freedoms; the Free
Software Foundation uses the GPL to preserve these freedoms.

Fundamentally, the General Public License is a license which says
that you have these freedoms and that you cannot take these freedoms
away from anyone else.

File: gdb.info, Node: Free Documentation, Next: Contributors, Prev: Free Software, Up: Summary

Free Software Needs Free Documentation
======================================

The biggest deficiency in the free software community today is not in
the software--it is the lack of good free documentation that we can
include with the free software. Many of our most important programs do
not come with free reference manuals and free introductory texts.
Documentation is an essential part of any software package; when an
important free software package does not come with a free manual and a
free tutorial, that is a major gap. We have many such gaps today.

Consider Perl, for instance. The tutorial manuals that people
normally use are non-free. How did this come about? Because the
authors of those manuals published them with restrictive terms--no
copying, no modification, source files not available--which exclude
them from the free software world.

That wasn't the first time this sort of thing happened, and it was
far from the last. Many times we have heard a GNU user eagerly
describe a manual that he is writing, his intended contribution to the
community, only to learn that he had ruined everything by signing a
publication contract to make it non-free.

Free documentation, like free software, is a matter of freedom, not
price. The problem with the non-free manual is not that publishers
charge a price for printed copies--that in itself is fine. (The Free
Software Foundation sells printed copies of manuals, too.) The problem
is the restrictions on the use of the manual. Free manuals are
available in source code form, and give you permission to copy and
modify. Non-free manuals do not allow this.

The criteria of freedom for a free manual are roughly the same as for
free software. Redistribution (including the normal kinds of
commercial redistribution) must be permitted, so that the manual can
accompany every copy of the program, both on-line and on paper.

Permission for modification of the technical content is crucial too.
When people modify the software, adding or changing features, if they
are conscientious they will change the manual too--so they can provide
accurate and clear documentation for the modified program. A manual
that leaves you no choice but to write a new manual to document a
changed version of the program is not really available to our community.

Some kinds of limits on the way modification is handled are
acceptable. For example, requirements to preserve the original
author's copyright notice, the distribution terms, or the list of
authors, are ok. It is also no problem to require modified versions to
include notice that they were modified. Even entire sections that may
not be deleted or changed are acceptable, as long as they deal with
nontechnical topics (like this one). These kinds of restrictions are
acceptable because they don't obstruct the community's normal use of
the manual.

However, it must be possible to modify all the _technical_ content
of the manual, and then distribute the result in all the usual media,
through all the usual channels. Otherwise, the restrictions obstruct
the use of the manual, it is not free, and we need another manual to
replace it.

Please spread the word about this issue. Our community continues to
lose manuals to proprietary publishing. If we spread the word that
free software needs free reference manuals and free tutorials, perhaps
the next person who wants to contribute by writing documentation will
realize, before it is too late, that only free manuals contribute to
the free software community.

If you are writing documentation, please insist on publishing it
under the GNU Free Documentation License or another free documentation
license. Remember that this decision requires your approval--you don't
have to let the publisher decide. Some commercial publishers will use
a free license if you insist, but they will not propose the option; it
is up to you to raise the issue and say firmly that this is what you
want. If the publisher you are dealing with refuses, please try other
publishers. If you're not sure whether a proposed license is free,
write to <[email protected]>.

You can encourage commercial publishers to sell more free, copylefted
manuals and tutorials by buying them, and particularly by buying copies
from the publishers that paid for their writing or for major
improvements. Meanwhile, try to avoid buying non-free documentation at
all. Check the distribution terms of a manual before you buy it, and
insist that whoever seeks your business must respect your freedom.
Check the history of the book, and try to reward the publishers that
have paid or pay the authors to work on it.

The Free Software Foundation maintains a list of free documentation
published by other publishers, at
`http://www.fsf.org/doc/other-free-books.html'.

File: gdb.info, Node: Contributors, Prev: Free Documentation, Up: Summary

Contributors to GDB
===================

Richard Stallman was the original author of GDB, and of many other GNU
programs. Many others have contributed to its development. This
section attempts to credit major contributors. One of the virtues of
free software is that everyone is free to contribute to it; with
regret, we cannot actually acknowledge everyone here. The file
`ChangeLog' in the GDB distribution approximates a blow-by-blow account.

Changes much prior to version 2.0 are lost in the mists of time.

_Plea:_ Additions to this section are particularly welcome. If you
or your friends (or enemies, to be evenhanded) have been unfairly
omitted from this list, we would like to add your names!

So that they may not regard their many labors as thankless, we
particularly thank those who shepherded GDB through major releases:
Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim
Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs
(release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10,
and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5,
and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim
Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2,
3.1, and 3.0).

Richard Stallman, assisted at various times by Peter TerMaat, Chris
Hanson, and Richard Mlynarik, handled releases through 2.8.

Michael Tiemann is the author of most of the GNU C++ support in GDB,
with significant additional contributions from Per Bothner and Daniel
Berlin. James Clark wrote the GNU C++ demangler. Early work on C++
was by Peter TerMaat (who also did much general update work leading to
release 3.0).

GDB uses the BFD subroutine library to examine multiple object-file
formats; BFD was a joint project of David V. Henkel-Wallace, Rich
Pixley, Steve Chamberlain, and John Gilmore.

David Johnson wrote the original COFF support; Pace Willison did the
original support for encapsulated COFF.

Brent Benson of Harris Computer Systems contributed DWARF 2 support.

Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
support. Jean-Daniel Fekete contributed Sun 386i support. Chris
Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
Hasei contributed Sony/News OS 3 support. David Johnson contributed
Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
Jeff Law contributed HP PA and SOM support. Keith Packard contributed
NS32K support. Doug Rabson contributed Acorn Risc Machine support.
Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith
contributed Convex support (and Fortran debugging). Jonathan Stone
contributed Pyramid support. Michael Tiemann contributed SPARC support.
Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
Pace Willison contributed Intel 386 support. Jay Vosburgh contributed
Symmetry support. Marko Mlinar contributed OpenRISC 1000 support.

Andreas Schwab contributed M68K GNU/Linux support.

Rich Schaefer and Peter Schauer helped with support of SunOS shared
libraries.

Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
several machine instruction sets.

Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
develop remote debugging. Intel Corporation, Wind River Systems, AMD,
and ARM contributed remote debugging modules for the i960, VxWorks,
A29K UDI, and RDI targets, respectively.

Brian Fox is the author of the readline libraries providing
command-line editing and command history.

Andrew Beers of SUNY Buffalo wrote the language-switching code, the
Modula-2 support, and contributed the Languages chapter of this manual.

Fred Fish wrote most of the support for Unix System Vr4. He also
enhanced the command-completion support to cover C++ overloaded symbols.

Hitachi America (now Renesas America), Ltd. sponsored the support for
H8/300, H8/500, and Super-H processors.

NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx
processors.

Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and
M32R/D processors.

Toshiba sponsored the support for the TX39 Mips processor.

Matsushita sponsored the support for the MN10200 and MN10300
processors.

Fujitsu sponsored the support for SPARClite and FR30 processors.

Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
watchpoints.

Michael Snyder added support for tracepoints.

Stu Grossman wrote gdbserver.

Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly
innumerable bug fixes and cleanups throughout GDB.

The following people at the Hewlett-Packard Company contributed
support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
(narrow mode), HP's implementation of kernel threads, HP's aC++
compiler, and the Text User Interface (nee Terminal User Interface):
Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
provided HP-specific information in this manual.

DJ Delorie ported GDB to MS-DOS, for the DJGPP project. Robert
Hoehne made significant contributions to the DJGPP port.

Cygnus Solutions has sponsored GDB maintenance and much of its
development since 1991. Cygnus engineers who have worked on GDB
fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
Zuhn have made contributions both large and small.

Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
Cygnus Solutions, implemented the original GDB/MI interface.

Jim Blandy added support for preprocessor macros, while working for
Red Hat.

Andrew Cagney designed GDB's architecture vector. Many people
including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick Duffek,
Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto,
Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason Thorpe, Corinna
Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the migration
of old architectures to this new framework.

Andrew Cagney completely re-designed and re-implemented GDB's
unwinder framework, this consisting of a fresh new design featuring
frame IDs, independent frame sniffers, and the sentinel frame. Mark
Kettenis implemented the DWARF 2 unwinder, Jeff Johnston the libunwind
unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad
unwinders. The architecture-specific changes, each involving a
complete rewrite of the architecture's frame code, were carried out by
Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
Weigand.

Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
Tensilica, Inc. contributed support for Xtensa processors. Others who
have worked on the Xtensa port of GDB in the past include Steve Tjiang,
John Newlin, and Scott Foehner.

Michael Eager and staff of Xilinx, Inc., contributed support for the
Xilinx MicroBlaze architecture.

Initial support for the FreeBSD/mips target and native configuration
was developed by SRI International and the University of Cambridge
Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237
("CTSRD"), as part of the DARPA CRASH research programme.

Initial support for the FreeBSD/riscv target and native configuration
was developed by SRI International and the University of Cambridge
Computer Laboratory (Department of Computer Science and Technology)
under DARPA contract HR0011-18-C-0016 ("ECATS"), as part of the DARPA
SSITH research programme.

The original port to the OpenRISC 1000 is believed to be due to
Alessandro Forin and Per Bothner. More recent ports have been the work
of Jeremy Bennett, Franck Jullien, Stefan Wallentowitz and Stafford
Horne.

Weimin Pan, David Faust and Jose E. Marchesi contributed support for
the Linux kernel BPF virtual architecture. This work was sponsored by
Oracle.

File: gdb.info, Node: Sample Session, Next: Invocation, Prev: Summary, Up: Top

1 A Sample GDB Session
**********************

You can use this manual at your leisure to read all about GDB.
However, a handful of commands are enough to get started using the
debugger. This chapter illustrates those commands.

One of the preliminary versions of GNU `m4' (a generic macro
processor) exhibits the following bug: sometimes, when we change its
quote strings from the default, the commands used to capture one macro
definition within another stop working. In the following short `m4'
session, we define a macro `foo' which expands to `0000'; we then use
the `m4' built-in `defn' to define `bar' as the same thing. However,
when we change the open quote string to `<QUOTE>' and the close quote
string to `<UNQUOTE>', the same procedure fails to define a new synonym
`baz':

$ cd gnu/m4
$ ./m4
define(foo,0000)

foo
0000
define(bar,defn(`foo'))

bar
0000
changequote(<QUOTE>,<UNQUOTE>)

define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
Ctrl-d
m4: End of input: 0: fatal error: EOF in string

Let us use GDB to try to see what is going on.

$ gdb m4
GDB is free software and you are welcome to distribute copies
of it under certain conditions; type "show copying" to see
the conditions.
There is absolutely no warranty for GDB; type "show warranty"
for details.

GDB 15.1, Copyright 1999 Free Software Foundation, Inc...
(gdb)

GDB reads only enough symbol data to know where to find the rest when
needed; as a result, the first prompt comes up very quickly. We now
tell GDB to use a narrower display width than usual, so that examples
fit in this manual.

(gdb) set width 70

We need to see how the `m4' built-in `changequote' works. Having
looked at the source, we know the relevant subroutine is
`m4_changequote', so we set a breakpoint there with the GDB `break'
command.

(gdb) break m4_changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.

Using the `run' command, we start `m4' running under GDB control; as
long as control does not reach the `m4_changequote' subroutine, the
program runs as usual:

(gdb) run
Starting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)

foo
0000

To trigger the breakpoint, we call `changequote'. GDB suspends
execution of `m4', displaying information about the context where it
stops.

changequote(<QUOTE>,<UNQUOTE>)

Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
at builtin.c:879
879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))

Now we use the command `n' (`next') to advance execution to the next
line of the current function.

(gdb) n
882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
: nil,

`set_quotes' looks like a promising subroutine. We can go into it by
using the command `s' (`step') instead of `next'. `step' goes to the
next line to be executed in _any_ subroutine, so it steps into
`set_quotes'.

(gdb) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
530 if (lquote != def_lquote)

The display that shows the subroutine where `m4' is now suspended (and
its arguments) is called a stack frame display. It shows a summary of
the stack. We can use the `backtrace' command (which can also be
spelled `bt'), to see where we are in the stack as a whole: the
`backtrace' command displays a stack frame for each active subroutine.

(gdb) bt
#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
at input.c:530
#1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
at builtin.c:882
#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
at macro.c:71
#4 0x79dc in expand_input () at macro.c:40
#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195

We step through a few more lines to see what happens. The first two
times, we can use `s'; the next two times we use `n' to avoid falling
into the `xstrdup' subroutine.

(gdb) s
0x3b5c 532 if (rquote != def_rquote)
(gdb) s
0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
def_lquote : xstrdup(lq);
(gdb) n
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup(rq);
(gdb) n
538 len_lquote = strlen(rquote);

The last line displayed looks a little odd; we can examine the variables
`lquote' and `rquote' to see if they are in fact the new left and right
quotes we specified. We use the command `p' (`print') to see their
values.

(gdb) p lquote
$1 = 0x35d40 "<QUOTE>"
(gdb) p rquote
$2 = 0x35d50 "<UNQUOTE>"

`lquote' and `rquote' are indeed the new left and right quotes. To
look at some context, we can display ten lines of source surrounding
the current line with the `l' (`list') command.

(gdb) l
533 xfree(rquote);
534
535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
: xstrdup (lq);
536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
: xstrdup (rq);
537
538 len_lquote = strlen(rquote);
539 len_rquote = strlen(lquote);
540 }
541
542 void

Let us step past the two lines that set `len_lquote' and `len_rquote',
and then examine the values of those variables.

(gdb) n
539 len_rquote = strlen(lquote);
(gdb) n
540 }
(gdb) p len_lquote
$3 = 9
(gdb) p len_rquote
$4 = 7

That certainly looks wrong, assuming `len_lquote' and `len_rquote' are
meant to be the lengths of `lquote' and `rquote' respectively. We can
set them to better values using the `p' command, since it can print the
value of any expression--and that expression can include subroutine
calls and assignments.

(gdb) p len_lquote=strlen(lquote)
$5 = 7
(gdb) p len_rquote=strlen(rquote)
$6 = 9

Is that enough to fix the problem of using the new quotes with the `m4'
built-in `defn'? We can allow `m4' to continue executing with the `c'
(`continue') command, and then try the example that caused trouble
initially:

(gdb) c
Continuing.

define(baz,defn(<QUOTE>foo<UNQUOTE>))

baz
0000

Success! The new quotes now work just as well as the default ones. The
problem seems to have been just the two typos defining the wrong
lengths. We allow `m4' exit by giving it an EOF as input:

Ctrl-d
Program exited normally.

The message `Program exited normally.' is from GDB; it indicates `m4'
has finished executing. We can end our GDB session with the GDB `quit'
command.

(gdb) quit

File: gdb.info, Node: Invocation, Next: Commands, Prev: Sample Session, Up: Top

2 Getting In and Out of GDB
***************************

This chapter discusses how to start GDB, and how to get out of it. The
essentials are:
* type `gdb' to start GDB.

* type `quit', `exit' or `Ctrl-d' to exit.

* Menu:

* Invoking GDB:: How to start GDB
* Quitting GDB:: How to quit GDB
* Shell Commands:: How to use shell commands inside GDB
* Logging Output:: How to log GDB's output to a file

File: gdb.info, Node: Invoking GDB, Next: Quitting GDB, Up: Invocation

2.1 Invoking GDB
================

Invoke GDB by running the program `gdb'. Once started, GDB reads
commands from the terminal until you tell it to exit.

You can also run `gdb' with a variety of arguments and options, to
specify more of your debugging environment at the outset.

The command-line options described here are designed to cover a
variety of situations; in some environments, some of these options may
effectively be unavailable.

The most usual way to start GDB is with one argument, specifying an
executable program:

gdb PROGRAM

You can also start with both an executable program and a core file
specified:

gdb PROGRAM CORE

You can, instead, specify a process ID as a second argument or use
option `-p', if you want to debug a running process:

gdb PROGRAM 1234
gdb -p 1234

would attach GDB to process `1234'. With option `-p' you can omit the
PROGRAM filename.

Taking advantage of the second command-line argument requires a
fairly complete operating system; when you use GDB as a remote debugger
attached to a bare board, there may not be any notion of "process", and
there is often no way to get a core dump. GDB will warn you if it is
unable to attach or to read core dumps.

You can optionally have `gdb' pass any arguments after the
executable file to the inferior using `--args'. This option stops
option processing.
gdb --args gcc -O2 -c foo.c
This will cause `gdb' to debug `gcc', and to set `gcc''s
command-line arguments (*note Arguments::) to `-O2 -c foo.c'.

You can run `gdb' without printing the front material, which
describes GDB's non-warranty, by specifying `--silent' (or
`-q'/`--quiet'):

gdb --silent

You can further control how GDB starts up by using command-line
options. GDB itself can remind you of the options available.

Type

gdb -help

to display all available options and briefly describe their use (`gdb
-h' is a shorter equivalent).

All options and command line arguments you give are processed in
sequential order. The order makes a difference when the `-x' option is
used.

* Menu:

* File Options:: Choosing files
* Mode Options:: Choosing modes
* Startup:: What GDB does during startup
* Initialization Files:: Initialization Files

File: gdb.info, Node: File Options, Next: Mode Options, Up: Invoking GDB

2.1.1 Choosing Files
--------------------

When GDB starts, it reads any arguments other than options as
specifying an executable file and core file (or process ID). This is
the same as if the arguments were specified by the `-se' and `-c' (or
`-p') options respectively. (GDB reads the first argument that does
not have an associated option flag as equivalent to the `-se' option
followed by that argument; and the second argument that does not have
an associated option flag, if any, as equivalent to the `-c'/`-p'
option followed by that argument.) If the second argument begins with
a decimal digit, GDB will first attempt to attach to it as a process,
and if that fails, attempt to open it as a corefile. If you have a
corefile whose name begins with a digit, you can prevent GDB from
treating it as a pid by prefixing it with `./', e.g. `./12345'.

If GDB has not been configured to included core file support, such
as for most embedded targets, then it will complain about a second
argument and ignore it.

For the `-s', `-e', and `-se' options, and their long form
equivalents, the method used to search the file system for the symbol
and/or executable file is the same as that used by the `file' command.
*Note file: Files.

Many options have both long and short forms; both are shown in the
following list. GDB also recognizes the long forms if you truncate
them, so long as enough of the option is present to be unambiguous.
(If you prefer, you can flag option arguments with `--' rather than
`-', though we illustrate the more usual convention.)

`-symbols FILE'
`-s FILE'
Read symbol table from file FILE.

`-exec FILE'
`-e FILE'
Use file FILE as the executable file to execute when appropriate,
and for examining pure data in conjunction with a core dump.

`-se FILE'
Read symbol table from file FILE and use it as the executable file.

`-core FILE'
`-c FILE'
Use file FILE as a core dump to examine.

`-pid NUMBER'
`-p NUMBER'
Connect to process ID NUMBER, as with the `attach' command.

`-command FILE'
`-x FILE'
Execute commands from file FILE. The contents of this file is
evaluated exactly as the `source' command would. *Note Command
files: Command Files.

`-eval-command COMMAND'
`-ex COMMAND'
Execute a single GDB command.

This option may be used multiple times to call multiple commands.
It may also be interleaved with `-command' as required.

gdb -ex 'target sim' -ex 'load' \
-x setbreakpoints -ex 'run' a.out

`-init-command FILE'
`-ix FILE'
Execute commands from file FILE before loading the inferior (but
after loading gdbinit files). *Note Startup::.

`-init-eval-command COMMAND'
`-iex COMMAND'
Execute a single GDB command before loading the inferior (but
after loading gdbinit files). *Note Startup::.

`-early-init-command FILE'
`-eix FILE'
Execute commands from FILE very early in the initialization
process, before any output is produced. *Note Startup::.

`-early-init-eval-command COMMAND'
`-eiex COMMAND'
Execute a single GDB command very early in the initialization
process, before any output is produced.

`-directory DIRECTORY'
`-d DIRECTORY'
Add DIRECTORY to the path to search for source and script files.

`-r'
`-readnow'
Read each symbol file's entire symbol table immediately, rather
than the default, which is to read it incrementally as it is
needed. This makes startup slower, but makes future operations
faster.

`--readnever'
Do not read each symbol file's symbolic debug information. This
makes startup faster but at the expense of not being able to
perform symbolic debugging. DWARF unwind information is also not
read, meaning backtraces may become incomplete or inaccurate. One
use of this is when a user simply wants to do the following
sequence: attach, dump core, detach. Loading the debugging
information in this case is an unnecessary cause of delay.

File: gdb.info, Node: Mode Options, Next: Startup, Prev: File Options, Up: Invoking GDB

2.1.2 Choosing Modes
--------------------

You can run GDB in various alternative modes--for example, in batch
mode or quiet mode.

`-nx'
`-n'
Do not execute commands found in any initialization files (*note
Initialization Files::).

`-nh'
Do not execute commands found in any home directory initialization
file (*note Home directory initialization file: Initialization
Files.). The system wide and current directory initialization
files are still loaded.

`-quiet'
`-silent'
`-q'
"Quiet". Do not print the introductory and copyright messages.
These messages are also suppressed in batch mode.

This can also be enabled using `set startup-quietly on'. The
default is `off'. Use `show startup-quietly' to see the current
setting. Place `set startup-quietly on' into your early
initialization file (*note Initialization Files: Initialization
Files.) to have future GDB sessions startup quietly.

`-batch'
Run in batch mode. Exit with status `0' after processing all the
command files specified with `-x' (and all commands from
initialization files, if not inhibited with `-n'). Exit with
nonzero status if an error occurs in executing the GDB commands in
the command files. Batch mode also disables pagination, sets
unlimited terminal width and height *note Screen Size::, and acts
as if `set confirm off' were in effect (*note Messages/Warnings::).

Batch mode may be useful for running GDB as a filter, for example
to download and run a program on another computer; in order to
make this more useful, the message

Program exited normally.

(which is ordinarily issued whenever a program running under GDB
control terminates) is not issued when running in batch mode.

`-batch-silent'
Run in batch mode exactly like `-batch', but totally silently. All
GDB output to `stdout' is prevented (`stderr' is unaffected).
This is much quieter than `-silent' and would be useless for an
interactive session.

This is particularly useful when using targets that give `Loading
section' messages, for example.

Note that targets that give their output via GDB, as opposed to
writing directly to `stdout', will also be made silent.

`-return-child-result'
The return code from GDB will be the return code from the child
process (the process being debugged), with the following
exceptions:

* GDB exits abnormally. E.g., due to an incorrect argument or
an internal error. In this case the exit code is the same as
it would have been without `-return-child-result'.

* The user quits with an explicit value. E.g., `quit 1'.

* The child process never runs, or is not allowed to terminate,
in which case the exit code will be -1.

This option is useful in conjunction with `-batch' or
`-batch-silent', when GDB is being used as a remote program loader
or simulator interface.

`-nowindows'
`-nw'
"No windows". If GDB comes with a graphical user interface (GUI)
built in, then this option tells GDB to only use the command-line
interface. If no GUI is available, this option has no effect.

`-windows'
`-w'
If GDB includes a GUI, then this option requires it to be used if
possible.

`-cd DIRECTORY'
Run GDB using DIRECTORY as its working directory, instead of the
current directory.

`-data-directory DIRECTORY'
`-D DIRECTORY'
Run GDB using DIRECTORY as its data directory. The data directory
is where GDB searches for its auxiliary files. *Note Data Files::.

`-fullname'
`-f'
GNU Emacs sets this option when it runs GDB as a subprocess. It
tells GDB to output the full file name and line number in a
standard, recognizable fashion each time a stack frame is
displayed (which includes each time your program stops). This
recognizable format looks like two `\032' characters, followed by
the file name, line number and character position separated by
colons, and a newline. The Emacs-to-GDB interface program uses
the two `\032' characters as a signal to display the source code
for the frame.

`-annotate LEVEL'
This option sets the "annotation level" inside GDB. Its effect is
identical to using `set annotate LEVEL' (*note Annotations::).
The annotation LEVEL controls how much information GDB prints
together with its prompt, values of expressions, source lines, and
other types of output. Level 0 is the normal, level 1 is for use
when GDB is run as a subprocess of GNU Emacs, level 3 is the
maximum annotation suitable for programs that control GDB, and
level 2 has been deprecated.

The annotation mechanism has largely been superseded by GDB/MI
(*note GDB/MI::).

`--args'
Change interpretation of command line so that arguments following
the executable file are passed as command line arguments to the
inferior. This option stops option processing.

`-baud BPS'
`-b BPS'
Set the line speed (baud rate or bits per second) of any serial
interface used by GDB for remote debugging.

`-l TIMEOUT'
Set the timeout (in seconds) of any communication used by GDB for
remote debugging.

`-tty DEVICE'
`-t DEVICE'
Run using DEVICE for your program's standard input and output.

`-tui'
Activate the "Text User Interface" when starting. The Text User
Interface manages several text windows on the terminal, showing
source, assembly, registers and GDB command outputs (*note GDB
Text User Interface: TUI.). Do not use this option if you run GDB
from Emacs (*note Using GDB under GNU Emacs: Emacs.).

`-interpreter INTERP'
Use the interpreter INTERP for interface with the controlling
program or device. This option is meant to be set by programs
which communicate with GDB using it as a back end. *Note Command
Interpreters: Interpreters.

`--interpreter=mi' (or `--interpreter=mi3') causes GDB to use the
"GDB/MI interface" version 3 (*note The GDB/MI Interface: GDB/MI.)
included since GDB version 9.1. GDB/MI version 2 (`mi2'),
included in GDB 6.0 and version 1 (`mi1'), included in GDB 5.3,
are also available. Earlier GDB/MI interfaces are no longer
supported.

`-write'
Open the executable and core files for both reading and writing.
This is equivalent to the `set write on' command inside GDB (*note
Patching::).

`-statistics'
This option causes GDB to print statistics about time and memory
usage after it completes each command and returns to the prompt.

`-version'
This option causes GDB to print its version number and no-warranty
blurb, and exit.

`-configuration'
This option causes GDB to print details about its build-time
configuration parameters, and then exit. These details can be
important when reporting GDB bugs (*note GDB Bugs::).

File: gdb.info, Node: Startup, Next: Initialization Files, Prev: Mode Options, Up: Invoking GDB

2.1.3 What GDB Does During Startup
----------------------------------

Here's the description of what GDB does during session startup:

1. Performs minimal setup required to initialize basic internal state.

2. Reads commands from the early initialization file (if any) in your
home directory. Only a restricted set of commands can be placed
into an early initialization file, see *Note Initialization
Files::, for details.

3. Executes commands and command files specified by the `-eiex' and
`-eix' command line options in their specified order. Only a
restricted set of commands can be used with `-eiex' and `eix', see
*Note Initialization Files::, for details.

4. Sets up the command interpreter as specified by the command line
(*note interpreter: Mode Options.).

5. Reads the system wide initialization file and the files from the
system wide initialization directory, *note System Wide Init
Files::.

6. Reads the initialization file (if any) in your home directory and
executes all the commands in that file, *note Home Directory Init
File::.

7. Executes commands and command files specified by the `-iex' and
`-ix' options in their specified order. Usually you should use the
`-ex' and `-x' options instead, but this way you can apply
settings before GDB init files get executed and before inferior
gets loaded.

8. Processes command line options and operands.

9. Reads and executes the commands from the initialization file (if
any) in the current working directory as long as `set auto-load
local-gdbinit' is set to `on' (*note Init File in the Current
Directory::). This is only done if the current directory is
different from your home directory. Thus, you can have more than
one init file, one generic in your home directory, and another,
specific to the program you are debugging, in the directory where
you invoke GDB. *Note Init File in the Current Directory during
Startup::.

10. If the command line specified a program to debug, or a process to
attach to, or a core file, GDB loads any auto-loaded scripts
provided for the program or for its loaded shared libraries.
*Note Auto-loading::.

If you wish to disable the auto-loading during startup, you must
do something like the following:

$ gdb -iex "set auto-load python-scripts off" myprogram

Option `-ex' does not work because the auto-loading is then turned
off too late.

11. Executes commands and command files specified by the `-ex' and
`-x' options in their specified order. *Note Command Files::, for
more details about GDB command files.

12. Reads the command history recorded in the "history file". *Note
Command History::, for more details about the command history and
the files where GDB records it.

File: gdb.info, Node: Initialization Files, Prev: Startup, Up: Invoking GDB

2.1.4 Initialization Files
--------------------------

During startup (*note Startup::) GDB will execute commands from several
initialization files. These initialization files use the same syntax
as "command files" (*note Command Files::) and are processed by GDB in
the same way.

To display the list of initialization files loaded by GDB at
startup, in the order they will be loaded, you can use `gdb --help'.

The "early initialization" file is loaded very early in GDB's
initialization process, before the interpreter (*note Interpreters::)
has been initialized, and before the default target (*note Targets::)
is initialized. Only `set' or `source' commands should be placed into
an early initialization file, and the only `set' commands that can be
used are those that control how GDB starts up.

Commands that can be placed into an early initialization file will be
documented as such throughout this manual. Any command that is not
documented as being suitable for an early initialization file should
instead be placed into a general initialization file. Command files
passed to `--early-init-command' or `-eix' are also early
initialization files, with the same command restrictions. Only
commands that can appear in an early initialization file should be
passed to `--early-init-eval-command' or `-eiex'.

In contrast, the "general initialization" files are processed later,
after GDB has finished its own internal initialization process, any
valid command can be used in these files.

Throughout the rest of this document the term "initialization file"
refers to one of the general initialization files, not the early
initialization file. Any discussion of the early initialization file
will specifically mention that it is the early initialization file
being discussed.

As the system wide and home directory initialization files are
processed before most command line options, changes to settings (e.g.
`set complaints') can affect subsequent processing of command line
options and operands.

The following sections describe where GDB looks for the early
initialization and initialization files, and the order that the files
are searched for.

2.1.4.1 Home directory early initialization files
................................................

GDB initially looks for an early initialization file in the users home
directory(1). There are a number of locations that GDB will search in
the home directory, these locations are searched in order and GDB will
load the first file that it finds, and subsequent locations will not be
checked.

On non-macOS hosts the locations searched are:
* The file `gdb/gdbearlyinit' within the directory pointed to by the
environment variable `XDG_CONFIG_HOME', if it is defined.

* The file `.config/gdb/gdbearlyinit' within the directory pointed to
by the environment variable `HOME', if it is defined.

* The file `.gdbearlyinit' within the directory pointed to by the
environment variable `HOME', if it is defined.

By contrast, on macOS hosts the locations searched are:
* The file `Library/Preferences/gdb/gdbearlyinit' within the
directory pointed to by the environment variable `HOME', if it is
defined.

* The file `.gdbearlyinit' within the directory pointed to by the
environment variable `HOME', if it is defined.

It is possible to prevent the home directory early initialization
file from being loaded using the `-nx' or `-nh' command line options,
*note Choosing Modes: Mode Options.

2.1.4.2 System wide initialization files
.......................................

There are two locations that are searched for system wide
initialization files. Both of these locations are always checked:

``system.gdbinit''
This is a single system-wide initialization file. Its location is
specified with the `--with-system-gdbinit' configure option (*note
System-wide configuration::). It is loaded first when GDB starts,
before command line options have been processed.

``system.gdbinit.d''
This is the system-wide initialization directory. Its location is
specified with the `--with-system-gdbinit-dir' configure option
(*note System-wide configuration::). Files in this directory are
loaded in alphabetical order immediately after `system.gdbinit'
(if enabled) when GDB starts, before command line options have
been processed. Files need to have a recognized scripting
language extension (`.py'/`.scm') or be named with a `.gdb'
extension to be interpreted as regular GDB commands. GDB will not
recurse into any subdirectories of this directory.

It is possible to prevent the system wide initialization files from
being loaded using the `-nx' command line option, *note Choosing Modes:
Mode Options.

2.1.4.3 Home directory initialization file
.........................................

After loading the system wide initialization files GDB will look for an
initialization file in the users home directory(2). There are a number
of locations that GDB will search in the home directory, these
locations are searched in order and GDB will load the first file that
it finds, and subsequent locations will not be checked.

On non-Apple hosts the locations searched are:
`$XDG_CONFIG_HOME/gdb/gdbinit'

`$HOME/.config/gdb/gdbinit'

`$HOME/.gdbinit'

While on Apple hosts the locations searched are:
`$HOME/Library/Preferences/gdb/gdbinit'

`$HOME/.gdbinit'

It is possible to prevent the home directory initialization file from
being loaded using the `-nx' or `-nh' command line options, *note
Choosing Modes: Mode Options.

The DJGPP port of GDB uses the name `gdb.ini' instead of `.gdbinit'
or `gdbinit', due to the limitations of file names imposed by DOS
filesystems. The Windows port of GDB uses the standard name, but if it
finds a `gdb.ini' file in your home directory, it warns you about that
and suggests to rename the file to the standard name.

2.1.4.4 Local directory initialization file
..........................................

GDB will check the current directory for a file called `.gdbinit'. It
is loaded last, after command line options other than `-x' and `-ex'
have been processed. The command line options `-x' and `-ex' are
processed last, after `.gdbinit' has been loaded, *note Choosing Files:
File Options.

If the file in the current directory was already loaded as the home
directory initialization file then it will not be loaded a second time.

It is possible to prevent the local directory initialization file
from being loaded using the `-nx' command line option, *note Choosing
Modes: Mode Options.

---------- Footnotes ----------

(1) On DOS/Windows systems, the home directory is the one pointed to
by the `HOME' environment variable.

(2) On DOS/Windows systems, the home directory is the one pointed to
by the `HOME' environment variable.

File: gdb.info, Node: Quitting GDB, Next: Shell Commands, Prev: Invoking GDB, Up: Invocation

2.2 Quitting GDB
================

`quit [EXPRESSION]'
`exit [EXPRESSION]'
`q'
To exit GDB, use the `quit' command (abbreviated `q'), the `exit'
command, or type an end-of-file character (usually `Ctrl-d'). If
you do not supply EXPRESSION, GDB will terminate normally;
otherwise it will terminate using the result of EXPRESSION as the
error code.

An interrupt (often `Ctrl-c') does not exit from GDB, but rather
terminates the action of any GDB command that is in progress and
returns to GDB command level. It is safe to type the interrupt
character at any time because GDB does not allow it to take effect
until a time when it is safe.

If you have been using GDB to control an attached process or device,
you can release it with the `detach' command (*note Debugging an
Already-running Process: Attach.).

File: gdb.info, Node: Shell Commands, Next: Logging Output, Prev: Quitting GDB, Up: Invocation

2.3 Shell Commands
==================

If you need to execute occasional shell commands during your debugging
session, there is no need to leave or suspend GDB; you can just use the
`shell' command.

`shell COMMAND-STRING'
`!COMMAND-STRING'
Invoke a shell to execute COMMAND-STRING. Note that no space is
needed between `!' and COMMAND-STRING. On GNU and Unix systems,
the environment variable `SHELL', if it exists, determines which
shell to run. Otherwise GDB uses the default shell (`/bin/sh' on
GNU and Unix systems, `cmd.exe' on MS-Windows, `COMMAND.COM' on
MS-DOS, etc.).

You may also invoke shell commands from expressions, using the
`$_shell' convenience function. *Note $_shell convenience function::.

The utility `make' is often needed in development environments. You
do not have to use the `shell' command for this purpose in GDB:

`make MAKE-ARGS'
Execute the `make' program with the specified arguments. This is
equivalent to `shell make MAKE-ARGS'.

`pipe [COMMAND] | SHELL_COMMAND'
`| [COMMAND] | SHELL_COMMAND'
`pipe -d DELIM COMMAND DELIM SHELL_COMMAND'
`| -d DELIM COMMAND DELIM SHELL_COMMAND'
Executes COMMAND and sends its output to SHELL_COMMAND. Note that
no space is needed around `|'. If no COMMAND is provided, the
last command executed is repeated.

In case the COMMAND contains a `|', the option `-d DELIM' can be
used to specify an alternate delimiter string DELIM that separates
the COMMAND from the SHELL_COMMAND.

Example:
(gdb) p var
$1 = {
black = 144,
red = 233,
green = 377,
blue = 610,
white = 987
}
(gdb) pipe p var|wc
7 19 80
(gdb) |p var|wc -l
7
(gdb) p /x var
$4 = {
black = 0x90,
red = 0xe9,
green = 0x179,
blue = 0x262,
white = 0x3db
}
(gdb) ||grep red
red => 0xe9,
(gdb) | -d ! echo this contains a | char\n ! sed -e 's/|/PIPE/'
this contains a PIPE char
(gdb) | -d xxx echo this contains a | char!\n xxx sed -e 's/|/PIPE/'
this contains a PIPE char!
(gdb)

The convenience variables `$_shell_exitcode' and `$_shell_exitsignal'
can be used to examine the exit status of the last shell command
launched by `shell', `make', `pipe' and `|'. *Note Convenience
Variables: Convenience Vars.

File: gdb.info, Node: Logging Output, Prev: Shell Commands, Up: Invocation

2.4 Logging Output
==================

You may want to save the output of GDB commands to a file. There are
several commands to control GDB's logging.

`set logging enabled [on|off]'
Enable or disable logging.

`set logging file FILE'
Change the name of the current logfile. The default logfile is
`gdb.txt'.

`set logging overwrite [on|off]'
By default, GDB will append to the logfile. Set `overwrite' if
you want `set logging enabled on' to overwrite the logfile instead.

`set logging redirect [on|off]'
By default, GDB output will go to both the terminal and the
logfile. Set `redirect' if you want output to go only to the log
file.

`set logging debugredirect [on|off]'
By default, GDB debug output will go to both the terminal and the
logfile. Set `debugredirect' if you want debug output to go only
to the log file.

`show logging'
Show the current values of the logging settings.

You can also redirect the output of a GDB command to a shell
command. *Note pipe::.

File: gdb.info, Node: Commands, Next: Running, Prev: Invocation, Up: Top

3 GDB Commands
**************

You can abbreviate a GDB command to the first few letters of the command
name, if that abbreviation is unambiguous; and you can repeat certain
GDB commands by typing just <RET>. You can also use the <TAB> key to
get GDB to fill out the rest of a word in a command (or to show you the
alternatives available, if there is more than one possibility).

* Menu:

* Command Syntax:: How to give commands to GDB
* Command Settings:: How to change default behavior of commands
* Completion:: Command completion
* Filename Arguments:: Filenames As Command Arguments
* Command Options:: Command options
* Help:: How to ask GDB for help

File: gdb.info, Node: Command Syntax, Next: Command Settings, Up: Commands

3.1 Command Syntax
==================

A GDB command is a single line of input. There is no limit on how long
it can be. It starts with a command name, which is followed by
arguments whose meaning depends on the command name. For example, the
command `step' accepts an argument which is the number of times to
step, as in `step 5'. You can also use the `step' command with no
arguments. Some commands do not allow any arguments.

GDB command names may always be truncated if that abbreviation is
unambiguous. Other possible command abbreviations are listed in the
documentation for individual commands. In some cases, even ambiguous
abbreviations are allowed; for example, `s' is specially defined as
equivalent to `step' even though there are other commands whose names
start with `s'. You can test abbreviations by using them as arguments
to the `help' command.

A blank line as input to GDB (typing just <RET>) means to repeat the
previous command. Certain commands (for example, `run') will not
repeat this way; these are commands whose unintentional repetition
might cause trouble and which you are unlikely to want to repeat.
User-defined commands can disable this feature; see *Note dont-repeat:
Define.

The `list' and `x' commands, when you repeat them with <RET>,
construct new arguments rather than repeating exactly as typed. This
permits easy scanning of source or memory.

GDB can also use <RET> in another way: to partition lengthy output,
in a way similar to the common utility `more' (*note Screen Size:
Screen Size.). Since it is easy to press one <RET> too many in this
situation, GDB disables command repetition after any command that
generates this sort of display.

Any text from a `#' to the end of the line is a comment; it does
nothing. This is useful mainly in command files (*note Command Files:
Command Files.).

The `Ctrl-o' binding is useful for repeating a complex sequence of
commands. This command accepts the current line, like <RET>, and then
fetches the next line relative to the current line from the history for
editing.

File: gdb.info, Node: Command Settings, Next: Completion, Prev: Command Syntax, Up: Commands

3.2 Command Settings
====================

Many commands change their behavior according to command-specific
variables or settings. These settings can be changed with the `set'
subcommands. For example, the `print' command (*note Examining Data:
Data.) prints arrays differently depending on settings changeable with
the commands `set print elements NUMBER-OF-ELEMENTS' and `set print
array-indexes', among others.

You can change these settings to your preference in the gdbinit files
loaded at GDB startup. *Note Startup::.

The settings can also be changed interactively during the debugging
session. For example, to change the limit of array elements to print,
you can do the following:
(gdb) set print elements 10
(gdb) print some_array
$1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}

The above `set print elements 10' command changes the number of
elements to print from the default of 200 to 10. If you only intend
this limit of 10 to be used for printing `some_array', then you must
restore the limit back to 200, with `set print elements 200'.

Some commands allow overriding settings with command options. For
example, the `print' command supports a number of options that allow
overriding relevant global print settings as set by `set print'
subcommands. *Note print options::. The example above could be
rewritten as:
(gdb) print -elements 10 -- some_array
$1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}

Alternatively, you can use the `with' command to change a setting
temporarily, for the duration of a command invocation.

`with SETTING [VALUE] [-- COMMAND]'
`w SETTING [VALUE] [-- COMMAND]'
Temporarily set SETTING to VALUE for the duration of COMMAND.

SETTING is any setting you can change with the `set' subcommands.
VALUE is the value to assign to `setting' while running `command'.

If no COMMAND is provided, the last command executed is repeated.

If a COMMAND is provided, it must be preceded by a double dash
(`--') separator. This is required because some settings accept
free-form arguments, such as expressions or filenames.

For example, the command
(gdb) with print array on -- print some_array
is equivalent to the following 3 commands:
(gdb) set print array on
(gdb) print some_array
(gdb) set print array off

The `with' command is particularly useful when you want to
override a setting while running user-defined commands, or commands
defined in Python or Guile. *Note Extending GDB: Extending GDB.

(gdb) with print pretty on -- my_complex_command

To change several settings for the same command, you can nest
`with' commands. For example, `with language ada -- with print
elements 10' temporarily changes the language to Ada and sets a
limit of 10 elements to print for arrays and strings.

File: gdb.info, Node: Completion, Next: Filename Arguments, Prev: Command Settings, Up: Commands

3.3 Command Completion
======================

GDB can fill in the rest of a word in a command for you, if there is
only one possibility; it can also show you what the valid possibilities
are for the next word in a command, at any time. This works for GDB
commands, GDB subcommands, command options, and the names of symbols in
your program.

Press the <TAB> key whenever you want GDB to fill out the rest of a
word. If there is only one possibility, GDB fills in the word, and
waits for you to finish the command (or press <RET> to enter it). For
example, if you type

(gdb) info bre<TAB>

GDB fills in the rest of the word `breakpoints', since that is the only
`info' subcommand beginning with `bre':

(gdb) info breakpoints

You can either press <RET> at this point, to run the `info breakpoints'
command, or backspace and enter something else, if `breakpoints' does
not look like the command you expected. (If you were sure you wanted
`info breakpoints' in the first place, you might as well just type
<RET> immediately after `info bre', to exploit command abbreviations
rather than command completion).

If there is more than one possibility for the next word when you
press <TAB>, GDB sounds a bell. You can either supply more characters
and try again, or just press <TAB> a second time; GDB displays all the
possible completions for that word. For example, you might want to set
a breakpoint on a subroutine whose name begins with `make_', but when
you type `b make_<TAB>' GDB just sounds the bell. Typing <TAB> again
displays all the function names in your program that begin with those
characters, for example:

(gdb) b make_<TAB>
GDB sounds bell; press <TAB> again, to see:
make_a_section_from_file make_environ
make_abs_section make_function_type
make_blockvector make_pointer_type
make_cleanup make_reference_type
make_command make_symbol_completion_list
(gdb) b make_

After displaying the available possibilities, GDB copies your partial
input (`b make_' in the example) so you can finish the command.

If the command you are trying to complete expects either a keyword
or a number to follow, then `NUMBER' will be shown among the available
completions, for example:

(gdb) print -elements <TAB><TAB>
NUMBER unlimited
(gdb) print -elements

Here, the option expects a number (e.g., `100'), not literal `NUMBER'.
Such metasyntactical arguments are always presented in uppercase.

If you just want to see the list of alternatives in the first place,
you can press `M-?' rather than pressing <TAB> twice. `M-?' means
`<META> ?'. You can type this either by holding down a key designated
as the <META> shift on your keyboard (if there is one) while typing
`?', or as <ESC> followed by `?'.

If the number of possible completions is large, GDB will print as
much of the list as it has collected, as well as a message indicating
that the list may be truncated.

(gdb) b m<TAB><TAB>
main
<... the rest of the possible completions ...>
*** List may be truncated, max-completions reached. ***
(gdb) b m

This behavior can be controlled with the following commands:

`set max-completions LIMIT'
`set max-completions unlimited'
Set the maximum number of completion candidates. GDB will stop
looking for more completions once it collects this many candidates.
This is useful when completing on things like function names as
collecting all the possible candidates can be time consuming. The
default value is 200. A value of zero disables tab-completion.
Note that setting either no limit or a very large limit can make
completion slow.

`show max-completions'
Show the maximum number of candidates that GDB will collect and
show during completion.

Sometimes the string you need, while logically a "word", may contain
parentheses or other characters that GDB normally excludes from its
notion of a word. To permit word completion to work in this situation,
you may enclose words in `'' (single quote marks) in GDB commands.

A likely situation where you might need this is in typing an
expression that involves a C++ symbol name with template parameters.
This is because when completing expressions, GDB treats the `<'
character as word delimiter, assuming that it's the less-than
comparison operator (*note C and C++ Operators: C Operators.).

For example, when you want to call a C++ template function
interactively using the `print' or `call' commands, you may need to
distinguish whether you mean the version of `name' that was specialized
for `int', `name<int>()', or the version that was specialized for
`float', `name<float>()'. To use the word-completion facilities in
this situation, type a single quote `'' at the beginning of the
function name. This alerts GDB that it may need to consider more
information than usual when you press <TAB> or `M-?' to request word
completion:

(gdb) p 'func<M-?
func<int>() func<float>()
(gdb) p 'func<

When setting breakpoints however (*note Location Specifications::),
you don't usually need to type a quote before the function name, because
GDB understands that you want to set a breakpoint on a function:

(gdb) b func<M-?
func<int>() func<float>()
(gdb) b func<

This is true even in the case of typing the name of C++ overloaded
functions (multiple definitions of the same function, distinguished by
argument type). For example, when you want to set a breakpoint you
don't need to distinguish whether you mean the version of `name' that
takes an `int' parameter, `name(int)', or the version that takes a
`float' parameter, `name(float)'.

(gdb) b bubble(M-?
bubble(int) bubble(double)
(gdb) b bubble(douM-?
bubble(double)

See *Note quoting names:: for a description of other scenarios that
require quoting.

For more information about overloaded functions, see *Note C++
Expressions: C Plus Plus Expressions. You can use the command `set
overload-resolution off' to disable overload resolution; see *Note GDB
Features for C++: Debugging C Plus Plus.

When completing in an expression which looks up a field in a
structure, GDB also tries(1) to limit completions to the field names
available in the type of the left-hand-side:

(gdb) p gdb_stdout.M-?
magic to_fputs to_rewind
to_data to_isatty to_write
to_delete to_put to_write_async_safe
to_flush to_read

This is because the `gdb_stdout' is a variable of the type `struct
ui_file' that is defined in GDB sources as follows:

struct ui_file
{
int *magic;
ui_file_flush_ftype *to_flush;
ui_file_write_ftype *to_write;
ui_file_write_async_safe_ftype *to_write_async_safe;
ui_file_fputs_ftype *to_fputs;
ui_file_read_ftype *to_read;
ui_file_delete_ftype *to_delete;
ui_file_isatty_ftype *to_isatty;
ui_file_rewind_ftype *to_rewind;
ui_file_put_ftype *to_put;
void *to_data;
}

---------- Footnotes ----------

(1) The completer can be confused by certain kinds of invalid
expressions. Also, it only examines the static type of the expression,
not the dynamic type.

File: gdb.info, Node: Filename Arguments, Next: Command Options, Prev: Completion, Up: Commands

3.4 Filenames As Command Arguments
==================================

When passing filenames (or directory names) as arguments to a command,
if the filename argument does not include any whitespace, double
quotes, or single quotes, then for all commands the filename can be
written as a simple string, for example:

(gdb) file /path/to/some/file

If the filename does include whitespace, double quotes, or single
quotes, then GDB has two approaches for how these filenames should be
formatted; which format to use depends on which command is being used.

Most GDB commands don't require, or support, quoting and escaping.
These commands treat any text after the command name, that is not a
command option (*note Command Options::), as the filename, even if the
filename contains whitespace or quote characters. In the following
example the user is adding `/path/that contains/two spaces/' to the
auto-load safe-path (*note add-auto-load-safe-path::):

(gdb) add-auto-load-safe-path /path/that contains/two spaces/

A small number of commands require that filenames containing
whitespace or quote characters are either quoted, or have the special
characters escaped with a backslash. Commands that support this style
are marked as such in the manual, any command not marked as accepting
quoting and escaping of its filename argument, does not accept this
filename argument style.

For example, to load the file `/path/with spaces/to/a file' with the
`file' command (*note Commands to Specify Files: Files.), you can
escape the whitespace characters with a backslash:

(gdb) file /path/with\ spaces/to/a\ file

Alternatively the entire filename can be wrapped in either single or
double quotes, in which case no backlsashes are needed, for example:

(gdb) symbol-file "/path/with spaces/to/a file"
(gdb) exec-file '/path/with spaces/to/a file'

It is possible to include a quote character within a quoted filename
by escaping it with a backslash, for example, within a filename
surrounded by double quotes, a double quote character should be escaped
with a backslash, but a single quote character should not be escaped.
Within a single quoted string a single quote character needs to be
escaped, but a double quote character does not.

A literal backslash character can also be included by escaping it
with a backslash.

File: gdb.info, Node: Command Options, Next: Help, Prev: Filename Arguments, Up: Commands

3.5 Command options
===================

Some commands accept options starting with a leading dash. For
example, `print -pretty'. Similarly to command names, you can
abbreviate a GDB option to the first few letters of the option name, if
that abbreviation is unambiguous, and you can also use the <TAB> key to
get GDB to fill out the rest of a word in an option (or to show you the
alternatives available, if there is more than one possibility).

Some commands take raw input as argument. For example, the print
command processes arbitrary expressions in any of the languages
supported by GDB. With such commands, because raw input may start with
a leading dash that would be confused with an option or any of its
abbreviations, e.g. `print -p' (short for `print -pretty' or printing
negative `p'?), if you specify any command option, then you must use a
double-dash (`--') delimiter to indicate the end of options.

Some options are described as accepting an argument which can be
either `on' or `off'. These are known as "boolean options". Similarly
to boolean settings commands--`on' and `off' are the typical values,
but any of `1', `yes' and `enable' can also be used as "true" value,
and any of `0', `no' and `disable' can also be used as "false" value.
You can also omit a "true" value, as it is implied by default.

For example, these are equivalent:

(gdb) print -object on -pretty off -element unlimited -- *myptr
(gdb) p -o -p 0 -e u -- *myptr

You can discover the set of options some command accepts by
completing on `-' after the command name. For example:

(gdb) print -<TAB><TAB>
-address -max-depth -object -static-members
-array -memory-tag-violations -pretty -symbol
-array-indexes -nibbles -raw-values -union
-elements -null-stop -repeats -vtbl

Completion will in some cases guide you with a suggestion of what
kind of argument an option expects. For example:

(gdb) print -elements <TAB><TAB>
NUMBER unlimited

Here, the option expects a number (e.g., `100'), not literal `NUMBER'.
Such metasyntactical arguments are always presented in uppercase.

(For more on using the `print' command, see *Note Examining Data:
Data.)

File: gdb.info, Node: Help, Prev: Command Options, Up: Commands

3.6 Getting Help
================

You can always ask GDB itself for information on its commands, using
the command `help'.

`help'
`h'
You can use `help' (abbreviated `h') with no arguments to display
a short list of named classes of commands:

(gdb) help
List of classes of commands:

aliases -- User-defined aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of
commands in that class.
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

`help CLASS'
Using one of the general help classes as an argument, you can get a
list of the individual commands in that class. If a command has
aliases, the aliases are given after the command name, separated by
commas. If an alias has default arguments, the full definition of
the alias is given after the first line. For example, here is the
help display for the class `status':

(gdb) help status
Status inquiries.

List of commands:

info, inf, i -- Generic command for showing things
about the program being debugged
info address, iamain -- Describe where symbol SYM is stored.
alias iamain = info address main
info all-registers -- List of all registers and their contents,
for selected stack frame.
...
show, info set -- Generic command for showing things
about the debugger

Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

`help COMMAND'
With a command name as `help' argument, GDB displays a short
paragraph on how to use that command. If that command has one or
more aliases, GDB will display a first line with the command name
and all its aliases separated by commas. This first line will be
followed by the full definition of all aliases having default
arguments. When asking the help for an alias, the documentation
for the aliased command is shown.

A user-defined alias can optionally be documented using the
`document' command (*note document: Define.). GDB then considers
this alias as different from the aliased command: this alias is
not listed in the aliased command help output, and asking help for
this alias will show the documentation provided for the alias
instead of the documentation of the aliased command.

`apropos [-v] REGEXP'
The `apropos' command searches through all of the GDB commands and
aliases, and their documentation, for the regular expression
specified in ARGS. It prints out all matches found. The optional
flag `-v', which stands for `verbose', indicates to output the
full documentation of the matching commands and highlight the
parts of the documentation matching REGEXP. For example:

apropos alias

results in:

alias -- Define a new command that is an alias of an existing command
aliases -- User-defined aliases of other commands

while

apropos -v cut.*thread apply

results in the below output, where `cut for 'thread apply' is
highlighted if styling is enabled.

taas -- Apply a command to all threads (ignoring errors
and empty output).
Usage: taas COMMAND
shortcut for 'thread apply all -s COMMAND'

tfaas -- Apply a command to all frames of all threads
(ignoring errors and empty output).
Usage: tfaas COMMAND
shortcut for 'thread apply all -s frame apply all -s COMMAND'

`complete ARGS'
The `complete ARGS' command lists all the possible completions for
the beginning of a command. Use ARGS to specify the beginning of
the command you want completed. For example:

complete i

results in:

if
ignore
info
inspect

This is intended for use by GNU Emacs.

In addition to `help', you can use the GDB commands `info' and
`show' to inquire about the state of your program, or the state of GDB
itself. Each command supports many topics of inquiry; this manual
introduces each of them in the appropriate context. The listings under
`info' and under `show' in the Command, Variable, and Function Index
point to all the sub-commands. *Note Command and Variable Index::.

`info'
This command (abbreviated `i') is for describing the state of your
program. For example, you can show the arguments passed to a
function with `info args', list the registers currently in use
with `info registers', or list the breakpoints you have set with
`info breakpoints'. You can get a complete list of the `info'
sub-commands with `help info'.

`set'
You can assign the result of an expression to an environment
variable with `set'. For example, you can set the GDB prompt to a
$-sign with `set prompt $'.

`show'
In contrast to `info', `show' is for describing the state of GDB
itself. You can change most of the things you can `show', by
using the related command `set'; for example, you can control what
number system is used for displays with `set radix', or simply
inquire which is currently in use with `show radix'.

To display all the settable parameters and their current values,
you can use `show' with no arguments; you may also use `info set'.
Both commands produce the same display.

Here are several miscellaneous `show' subcommands, all of which are
exceptional in lacking corresponding `set' commands:

`show version'
Show what version of GDB is running. You should include this
information in GDB bug-reports. If multiple versions of GDB are
in use at your site, you may need to determine which version of
GDB you are running; as GDB evolves, new commands are introduced,
and old ones may wither away. Also, many system vendors ship
variant versions of GDB, and there are variant versions of GDB in
GNU/Linux distributions as well. The version number is the same
as the one announced when you start GDB.

`show copying'
`info copying'
Display information about permission for copying GDB.

`show warranty'
`info warranty'
Display the GNU "NO WARRANTY" statement, or a warranty, if your
version of GDB comes with one.

`show configuration'
Display detailed information about the way GDB was configured when
it was built. This displays the optional arguments passed to the
`configure' script and also configuration parameters detected
automatically by `configure'. When reporting a GDB bug (*note GDB
Bugs::), it is important to include this information in your
report.

File: gdb.info, Node: Running, Next: Stopping, Prev: Commands, Up: Top

4 Running Programs Under GDB
****************************

When you run a program under GDB, you must first generate debugging
information when you compile it.

You may start GDB with its arguments, if any, in an environment of
your choice. If you are doing native debugging, you may redirect your
program's input and output, debug an already running process, or kill a
child process.

* Menu:

* Compilation:: Compiling for debugging
* Starting:: Starting your program
* Arguments:: Your program's arguments
* Environment:: Your program's environment

* Working Directory:: Your program's working directory
* Input/Output:: Your program's input and output
* Attach:: Debugging an already-running process
* Kill Process:: Killing the child process
* Inferiors Connections and Programs:: Debugging multiple inferiors
connections and programs
* Threads:: Debugging programs with multiple threads
* Forks:: Debugging forks
* Checkpoint/Restart:: Setting a _bookmark_ to return to later

File: gdb.info, Node: Compilation, Next: Starting, Up: Running

4.1 Compiling for Debugging
===========================

In order to debug a program effectively, you need to generate debugging
information when you compile it. This debugging information is stored
in the object file; it describes the data type of each variable or
function and the correspondence between source line numbers and
addresses in the executable code.

To request debugging information, specify the `-g' option when you
run the compiler.

Programs that are to be shipped to your customers are compiled with
optimizations, using the `-O' compiler option. However, some compilers
are unable to handle the `-g' and `-O' options together. Using those
compilers, you cannot generate optimized executables containing
debugging information.

GCC, the GNU C/C++ compiler, supports `-g' with or without `-O',
making it possible to debug optimized code. We recommend that you
_always_ use `-g' whenever you compile a program. You may think your
program is correct, but there is no sense in pushing your luck. For
more information, see *Note Optimized Code::.

Older versions of the GNU C compiler permitted a variant option
`-gg' for debugging information. GDB no longer supports this format;
if your GNU C compiler has this option, do not use it.

GDB knows about preprocessor macros and can show you their expansion
(*note Macros::). Most compilers do not include information about
preprocessor macros in the debugging information if you specify the
`-g' flag alone. Version 3.1 and later of GCC, the GNU C compiler,
provides macro information if you are using the DWARF debugging format,
and specify the option `-g3'.

*Note Options for Debugging Your Program or GCC: (gcc)Debugging
Options, for more information on GCC options affecting debug
information.

You will have the best debugging experience if you use the latest
version of the DWARF debugging format that your compiler supports.
DWARF is currently the most expressive and best supported debugging
format in GDB.

File: gdb.info, Node: Starting, Next: Arguments, Prev: Compilation, Up: Running

4.2 Starting your Program
=========================

`run'
`r'
Use the `run' command to start your program under GDB. You must
first specify the program name with an argument to GDB (*note
Getting In and Out of GDB: Invocation.), or by using the `file' or
`exec-file' command (*note Commands to Specify Files: Files.).

If you are running your program in an execution environment that
supports processes, `run' creates an inferior process and makes that
process run your program. In some environments without processes,
`run' jumps to the start of your program. Other targets, like
`remote', are always running. If you get an error message like this
one:

The "remote" target does not support "run".
Try "help target" or "continue".

then use `continue' to run your program. You may need `load' first
(*note load::).

The execution of a program is affected by certain information it
receives from its superior. GDB provides ways to specify this
information, which you must do _before_ starting your program. (You
can change it after starting your program, but such changes only affect
your program the next time you start it.) This information may be
divided into four categories:

The _arguments._
Specify the arguments to give your program as the arguments of the
`run' command. If a shell is available on your target, the shell
is used to pass the arguments, so that you may use normal
conventions (such as wildcard expansion or variable substitution)
in describing the arguments. In Unix systems, you can control
which shell is used with the `SHELL' environment variable. If you
do not define `SHELL', GDB uses the default shell (`/bin/sh').
You can disable use of any shell with the `set startup-with-shell'
command (see below for details).

The _environment._
Your program normally inherits its environment from GDB, but you
can use the GDB commands `set environment' and `unset environment'
to change parts of the environment that affect your program.
*Note Your Program's Environment: Environment.

The _working directory._
You can set your program's working directory with the command `set
cwd'. If you do not set any working directory with this command,
your program will inherit GDB's working directory if native
debugging, or the remote server's working directory if remote
debugging. *Note Your Program's Working Directory: Working
Directory.

The _standard input and output._
Your program normally uses the same device for standard input and
standard output as GDB is using. You can redirect input and output
in the `run' command line, or you can use the `tty' command to set
a different device for your program. *Note Your Program's Input
and Output: Input/Output.

_Warning:_ While input and output redirection work, you cannot use
pipes to pass the output of the program you are debugging to
another program; if you attempt this, GDB is likely to wind up
debugging the wrong program.

When you issue the `run' command, your program begins to execute
immediately. *Note Stopping and Continuing: Stopping, for discussion
of how to arrange for your program to stop. Once your program has
stopped, you may call functions in your program, using the `print' or
`call' commands. *Note Examining Data: Data.

If the modification time of your symbol file has changed since the
last time GDB read its symbols, GDB discards its symbol table, and
reads it again. When it does this, GDB tries to retain your current
breakpoints.

`start'
The name of the main procedure can vary from language to language.
With C or C++, the main procedure name is always `main', but other
languages such as Ada do not require a specific name for their
main procedure. The debugger provides a convenient way to start
the execution of the program and to stop at the beginning of the
main procedure, depending on the language used.

The `start' command does the equivalent of setting a temporary
breakpoint at the beginning of the main procedure and then invoking
the `run' command.

Some programs contain an "elaboration" phase where some startup
code is executed before the main procedure is called. This
depends on the languages used to write your program. In C++, for
instance, constructors for static and global objects are executed
before `main' is called. It is therefore possible that the
debugger stops before reaching the main procedure. However, the
temporary breakpoint will remain to halt execution.

Specify the arguments to give to your program as arguments to the
`start' command. These arguments will be given verbatim to the
underlying `run' command. Note that the same arguments will be
reused if no argument is provided during subsequent calls to
`start' or `run'.

It is sometimes necessary to debug the program during elaboration.
In these cases, using the `start' command would stop the execution
of your program too late, as the program would have already
completed the elaboration phase. Under these circumstances,
either insert breakpoints in your elaboration code before running
your program or use the `starti' command.

`starti'
The `starti' command does the equivalent of setting a temporary
breakpoint at the first instruction of a program's execution and
then invoking the `run' command. For programs containing an
elaboration phase, the `starti' command will stop execution at the
start of the elaboration phase.

`set exec-wrapper WRAPPER'
`show exec-wrapper'
`unset exec-wrapper'
When `exec-wrapper' is set, the specified wrapper is used to
launch programs for debugging. GDB starts your program with a
shell command of the form `exec WRAPPER PROGRAM'. Quoting is
added to PROGRAM and its arguments, but not to WRAPPER, so you
should add quotes if appropriate for your shell. The wrapper runs
until it executes your program, and then GDB takes control.

You can use any program that eventually calls `execve' with its
arguments as a wrapper. Several standard Unix utilities do this,
e.g. `env' and `nohup'. Any Unix shell script ending with `exec
"$@"' will also work.

For example, you can use `env' to pass an environment variable to
the debugged program, without setting the variable in your shell's
environment:

(gdb) set exec-wrapper env 'LD_PRELOAD=libtest.so'
(gdb) run

This command is available when debugging locally on most targets,
excluding DJGPP, Cygwin, MS Windows, and QNX Neutrino.

`set startup-with-shell'
`set startup-with-shell on'
`set startup-with-shell off'
`show startup-with-shell'
On Unix systems, by default, if a shell is available on your
target, GDB) uses it to start your program. Arguments of the
`run' command are passed to the shell, which does variable
substitution, expands wildcard characters and performs redirection
of I/O. In some circumstances, it may be useful to disable such
use of a shell, for example, when debugging the shell itself or
diagnosing startup failures such as:

(gdb) run
Starting program: ./a.out
During startup program terminated with signal SIGSEGV, Segmentation fault.

which indicates the shell or the wrapper specified with
`exec-wrapper' crashed, not your program. Most often, this is
caused by something odd in your shell's non-interactive mode
initialization file--such as `.cshrc' for C-shell, $`.zshenv' for
the Z shell, or the file specified in the `BASH_ENV' environment
variable for BASH.

`set auto-connect-native-target'
`set auto-connect-native-target on'
`set auto-connect-native-target off'
`show auto-connect-native-target'
By default, if the current inferior is not connected to any target
yet (e.g., with `target remote'), the `run' command starts your
program as a native process under GDB, on your local machine. If
you're sure you don't want to debug programs on your local machine,
you can tell GDB to not connect to the native target automatically
with the `set auto-connect-native-target off' command.

If `on', which is the default, and if the current inferior is not
connected to a target already, the `run' command automatically
connects to the native target, if one is available.

If `off', and if the current inferior is not connected to a target
already, the `run' command fails with an error:

(gdb) run
Don't know how to run. Try "help target".

If the current inferior is already connected to a target, GDB
always uses it with the `run' command.

In any case, you can explicitly connect to the native target with
the `target native' command. For example,

(gdb) set auto-connect-native-target off
(gdb) run
Don't know how to run. Try "help target".
(gdb) target native
(gdb) run
Starting program: ./a.out
[Inferior 1 (process 10421) exited normally]

In case you connected explicitly to the `native' target, GDB
remains connected even if all inferiors exit, ready for the next
`run' command. Use the `disconnect' command to disconnect.

Examples of other commands that likewise respect the
`auto-connect-native-target' setting: `attach', `info proc', `info
os'.

`set disable-randomization'
`set disable-randomization on'
This option (enabled by default in GDB) will turn off the native
randomization of the virtual address space of the started program.
This option is useful for multiple debugging sessions to make the
execution better reproducible and memory addresses reusable across
debugging sessions.

This feature is implemented only on certain targets, including
GNU/Linux. On GNU/Linux you can get the same behavior using

(gdb) set exec-wrapper setarch `uname -m` -R

`set disable-randomization off'
Leave the behavior of the started executable unchanged. Some bugs
rear their ugly heads only when the program is loaded at certain
addresses. If your bug disappears when you run the program under
GDB, that might be because GDB by default disables the address
randomization on platforms, such as GNU/Linux, which do that for
stand-alone programs. Use `set disable-randomization off' to try
to reproduce such elusive bugs.

On targets where it is available, virtual address space
randomization protects the programs against certain kinds of
security attacks. In these cases the attacker needs to know the
exact location of a concrete executable code. Randomizing its
location makes it impossible to inject jumps misusing a code at
its expected addresses.

Prelinking shared libraries provides a startup performance
advantage but it makes addresses in these libraries predictable
for privileged processes by having just unprivileged access at the
target system. Reading the shared library binary gives enough
information for assembling the malicious code misusing it. Still
even a prelinked shared library can get loaded at a new random
address just requiring the regular relocation process during the
startup. Shared libraries not already prelinked are always loaded
at a randomly chosen address.

Position independent executables (PIE) contain position
independent code similar to the shared libraries and therefore
such executables get loaded at a randomly chosen address upon
startup. PIE executables always load even already prelinked
shared libraries at a random address. You can build such
executable using `gcc -fPIE -pie'.

Heap (malloc storage), stack and custom mmap areas are always
placed randomly (as long as the randomization is enabled).

`show disable-randomization'
Show the current setting of the explicit disable of the native
randomization of the virtual address space of the started program.

File: gdb.info, Node: Arguments, Next: Environment, Prev: Starting, Up: Running

4.3 Your Program's Arguments
============================

The arguments to your program can be specified by the arguments of the
`run' command. They are passed to a shell, which expands wildcard
characters and performs redirection of I/O, and thence to your program.
Your `SHELL' environment variable (if it exists) specifies what shell
GDB uses. If you do not define `SHELL', GDB uses the default shell
(`/bin/sh' on Unix).

On non-Unix systems, the program is usually invoked directly by GDB,
which emulates I/O redirection via the appropriate system calls, and
the wildcard characters are expanded by the startup code of the
program, not by the shell.

`run' with no arguments uses the same arguments used by the previous
`run', or those set by the `set args' command.

`set args'
Specify the arguments to be used the next time your program is
run. If `set args' has no arguments, `run' executes your program
with no arguments. Once you have run your program with arguments,
using `set args' before the next `run' is the only way to run it
again without arguments.

`show args'
Show the arguments to give your program when it is started.

File: gdb.info, Node: Environment, Next: Working Directory, Prev: Arguments, Up: Running

4.4 Your Program's Environment
==============================

The "environment" consists of a set of environment variables and their
values. Environment variables conventionally record such things as
your user name, your home directory, your terminal type, and your search
path for programs to run. Usually you set up environment variables with
the shell and they are inherited by all the other programs you run.
When debugging, it can be useful to try running your program with a
modified environment without having to start GDB over again.

`path DIRECTORY'
Add DIRECTORY to the front of the `PATH' environment variable (the
search path for executables) that will be passed to your program.
The value of `PATH' used by GDB does not change. You may specify
several directory names, separated by whitespace or by a
system-dependent separator character (`:' on Unix, `;' on MS-DOS
and MS-Windows). If DIRECTORY is already in the path, it is moved
to the front, so it is searched sooner.

You can use the string `$cwd' to refer to whatever is the current
working directory at the time GDB searches the path. If you use
`.' instead, it refers to the directory where you executed the
`path' command. GDB replaces `.' in the DIRECTORY argument (with
the current path) before adding DIRECTORY to the search path.

`show paths'
Display the list of search paths for executables (the `PATH'
environment variable).

`show environment [VARNAME]'
Print the value of environment variable VARNAME to be given to
your program when it starts. If you do not supply VARNAME, print
the names and values of all environment variables to be given to
your program. You can abbreviate `environment' as `env'.

`set environment VARNAME [=VALUE]'
Set environment variable VARNAME to VALUE. The value changes for
your program (and the shell GDB uses to launch it), not for GDB
itself. The VALUE may be any string; the values of environment
variables are just strings, and any interpretation is supplied by
your program itself. The VALUE parameter is optional; if it is
eliminated, the variable is set to a null value.

For example, this command:

set env USER = foo

tells the debugged program, when subsequently run, that its user
is named `foo'. (The spaces around `=' are used for clarity here;
they are not actually required.)

Note that on Unix systems, GDB runs your program via a shell,
which also inherits the environment set with `set environment'.
If necessary, you can avoid that by using the `env' program as a
wrapper instead of using `set environment'. *Note set
exec-wrapper::, for an example doing just that.

Environment variables that are set by the user are also
transmitted to `gdbserver' to be used when starting the remote
inferior. *note QEnvironmentHexEncoded::.

`unset environment VARNAME'
Remove variable VARNAME from the environment to be passed to your
program. This is different from `set env VARNAME ='; `unset
environment' removes the variable from the environment, rather
than assigning it an empty value.

Environment variables that are unset by the user are also unset on
`gdbserver' when starting the remote inferior. *note
QEnvironmentUnset::.

_Warning:_ On Unix systems, GDB runs your program using the shell
indicated by your `SHELL' environment variable if it exists (or
`/bin/sh' if not). If your `SHELL' variable names a shell that runs an
initialization file when started non-interactively--such as `.cshrc'
for C-shell, $`.zshenv' for the Z shell, or the file specified in the
`BASH_ENV' environment variable for BASH--any variables you set in that
file affect your program. You may wish to move setting of environment
variables to files that are only run when you sign on, such as `.login'
or `.profile'.

File: gdb.info, Node: Working Directory, Next: Input/Output, Prev: Environment, Up: Running

4.5 Your Program's Working Directory
====================================

Each time you start your program with `run', the inferior will be
initialized with the current working directory specified by the `set
cwd' command. If no directory has been specified by this command, then
the inferior will inherit GDB's current working directory as its
working directory if native debugging, or it will inherit the remote
server's current working directory if remote debugging.

`set cwd [DIRECTORY]'
Set the inferior's working directory to DIRECTORY, which will be
`glob'-expanded in order to resolve tildes (`~'). If no argument
has been specified, the command clears the setting and resets it
to an empty state. This setting has no effect on GDB's working
directory, and it only takes effect the next time you start the
inferior. The `~' in DIRECTORY is a short for the "home
directory", usually pointed to by the `HOME' environment variable.
On MS-Windows, if `HOME' is not defined, GDB uses the
concatenation of `HOMEDRIVE' and `HOMEPATH' as fallback.

You can also change GDB's current working directory by using the
`cd' command. *Note cd command::.

`show cwd'
Show the inferior's working directory. If no directory has been
specified by `set cwd', then the default inferior's working
directory is the same as GDB's working directory.

`cd [DIRECTORY]'
Set the GDB working directory to DIRECTORY. If not given,
DIRECTORY uses `'~''.

The GDB working directory serves as a default for the commands
that specify files for GDB to operate on. *Note Commands to
Specify Files: Files. *Note set cwd command::.

`pwd'
Print the GDB working directory.

It is generally impossible to find the current working directory of
the process being debugged (since a program can change its directory
during its run). If you work on a system where GDB supports the `info
proc' command (*note Process Information::), you can use the `info
proc' command to find out the current working directory of the debuggee.

File: gdb.info, Node: Input/Output, Next: Attach, Prev: Working Directory, Up: Running

4.6 Your Program's Input and Output
===================================

By default, the program you run under GDB does input and output to the
same terminal that GDB uses. GDB switches the terminal to its own
terminal modes to interact with you, but it records the terminal modes
your program was using and switches back to them when you continue
running your program.

`info terminal'
Displays information recorded by GDB about the terminal modes your
program is using.

You can redirect your program's input and/or output using shell
redirection with the `run' command. For example,

run > outfile

starts your program, diverting its output to the file `outfile'.

Another way to specify where your program should do input and output
is with the `tty' command. This command accepts a file name as
argument, and causes this file to be the default for future `run'
commands. It also resets the controlling terminal for the child
process, for future `run' commands. For example,

tty /dev/ttyb

directs that processes started with subsequent `run' commands default
to do input and output on the terminal `/dev/ttyb' and have that as
their controlling terminal.

An explicit redirection in `run' overrides the `tty' command's
effect on the input/output device, but not its effect on the controlling
terminal.

When you use the `tty' command or redirect input in the `run'
command, only the input _for your program_ is affected. The input for
GDB still comes from your terminal. `tty' is an alias for `set
inferior-tty'.

You can use the `show inferior-tty' command to tell GDB to display
the name of the terminal that will be used for future runs of your
program.

`set inferior-tty [ TTY ]'
Set the tty for the program being debugged to TTY. Omitting TTY
restores the default behavior, which is to use the same terminal as
GDB.

`show inferior-tty'
Show the current tty for the program being debugged.

File: gdb.info, Node: Attach, Next: Kill Process, Prev: Input/Output, Up: Running

4.7 Debugging an Already-running Process
========================================

`attach PROCESS-ID'
This command attaches to a running process--one that was started
outside GDB. (`info files' shows your active targets.) The
command takes as argument a process ID. The usual way to find out
the PROCESS-ID of a Unix process is with the `ps' utility, or with
the `jobs -l' shell command.

`attach' does not repeat if you press <RET> a second time after
executing the command.

To use `attach', your program must be running in an environment
which supports processes; for example, `attach' does not work for
programs on bare-board targets that lack an operating system. You must
also have permission to send the process a signal.

When you use `attach', the debugger finds the program running in the
process first by looking in the current working directory, then (if the
program is not found) by using the source file search path (*note
Specifying Source Directories: Source Path.). You can also use the
`file' command to load the program. *Note Commands to Specify Files:
Files.

If the debugger can determine that the executable file running in the
process it is attaching to does not match the current exec-file loaded
by GDB, the option `exec-file-mismatch' specifies how to handle the
mismatch. GDB tries to compare the files by comparing their build IDs
(*note build ID::), if available.

`set exec-file-mismatch `ask|warn|off''
Whether to detect mismatch between the current executable file
loaded by GDB and the executable file used to start the process.
If `ask', the default, display a warning and ask the user whether
to load the process executable file; if `warn', just display a
warning; if `off', don't attempt to detect a mismatch. If the
user confirms loading the process executable file, then its symbols
will be loaded as well.

`show exec-file-mismatch'
Show the current value of `exec-file-mismatch'.

The first thing GDB does after arranging to debug the specified
process is to stop it. You can examine and modify an attached process
with all the GDB commands that are ordinarily available when you start
processes with `run'. You can insert breakpoints; you can step and
continue; you can modify storage. If you would rather the process
continue running, you may use the `continue' command after attaching
GDB to the process.

`detach'
When you have finished debugging the attached process, you can use
the `detach' command to release it from GDB control. Detaching
the process continues its execution. After the `detach' command,
that process and GDB become completely independent once more, and
you are ready to `attach' another process or start one with `run'.
`detach' does not repeat if you press <RET> again after executing
the command.

If you exit GDB while you have an attached process, you detach that
process. If you use the `run' command, you kill that process. By
default, GDB asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the
`set confirm' command (*note Optional Warnings and Messages:
Messages/Warnings.).

File: gdb.info, Node: Kill Process, Next: Inferiors Connections and Programs, Prev: Attach, Up: Running

4.8 Killing the Child Process
=============================

`kill'
Kill the child process in which your program is running under GDB.

This command is useful if you wish to debug a core dump instead of a
running process. GDB ignores any core dump file while your program is
running.

On some operating systems, a program cannot be executed outside GDB
while you have breakpoints set on it inside GDB. You can use the
`kill' command in this situation to permit running your program outside
the debugger.

The `kill' command is also useful if you wish to recompile and
relink your program, since on many systems it is impossible to modify an
executable file while it is running in a process. In this case, when
you next type `run', GDB notices that the file has changed, and reads
the symbol table again (while trying to preserve your current
breakpoint settings).

File: gdb.info, Node: Inferiors Connections and Programs, Next: Threads, Prev: Kill Process, Up: Running

4.9 Debugging Multiple Inferiors Connections and Programs
=========================================================

GDB lets you run and debug multiple programs in a single session. In
addition, GDB on some systems may let you run several programs
simultaneously (otherwise you have to exit from one before starting
another). On some systems GDB may even let you debug several programs
simultaneously on different remote systems. In the most general case,
you can have multiple threads of execution in each of multiple
processes, launched from multiple executables, running on different
machines.

GDB represents the state of each program execution with an object
called an "inferior". An inferior typically corresponds to a process,
but is more general and applies also to targets that do not have
processes. Inferiors may be created before a process runs, and may be
retained after a process exits. Inferiors have unique identifiers that
are different from process ids. Usually each inferior will also have
its own distinct address space, although some embedded targets may have
several inferiors running in different parts of a single address space.
Each inferior may in turn have multiple threads running in it.

The commands `info inferiors' and `info connections', which will be
introduced below, accept a space-separated "ID list" as their argument
specifying one or more elements on which to operate. A list element
can be either a single non-negative number, like `5', or an ascending
range of such numbers, like `5-7'. A list can consist of any
combination of such elements, even duplicates or overlapping ranges are
valid. E.g. `1 4-6 5 4-4' or `1 2 4-7'.

To find out what inferiors exist at any moment, use `info inferiors':

`info inferiors'
Print a list of all inferiors currently being managed by GDB. By
default all inferiors are printed, but the ID list ID... can be
used to limit the display to just the requested inferiors.

GDB displays for each inferior (in this order):

1. the inferior number assigned by GDB

2. the target system's inferior identifier

3. the target connection the inferior is bound to, including the
unique connection number assigned by GDB, and the protocol
used by the connection.

4. the name of the executable the inferior is running.

An asterisk `*' preceding the GDB inferior number indicates the
current inferior.

For example,

(gdb) info inferiors
Num Description Connection Executable
* 1 process 3401 1 (native) goodbye
2 process 2307 2 (extended-remote host:10000) hello

To get information about the current inferior, use `inferior':

`inferior'
Shows information about the current inferior.

For example,

(gdb) inferior
[Current inferior is 1 [process 3401] (helloworld)]

To find out what open target connections exist at any moment, use
`info connections':

`info connections'
Print a list of all open target connections currently being
managed by GDB. By default all connections are printed, but the
ID list ID... can be used to limit the display to just the
requested connections.

GDB displays for each connection (in this order):

1. the connection number assigned by GDB.

2. the protocol used by the connection.

3. a textual description of the protocol used by the connection.

An asterisk `*' preceding the connection number indicates the
connection of the current inferior.

For example,

(gdb) info connections
Num What Description
* 1 extended-remote host:10000 Extended remote serial target in gdb-specific protocol
2 native Native process
3 core Local core dump file

To switch focus between inferiors, use the `inferior' command:

`inferior INFNO'
Make inferior number INFNO the current inferior. The argument
INFNO is the inferior number assigned by GDB, as shown in the
first field of the `info inferiors' display.

The debugger convenience variable `$_inferior' contains the number
of the current inferior. You may find this useful in writing
breakpoint conditional expressions, command scripts, and so forth.
*Note Convenience Variables: Convenience Vars, for general information
on convenience variables.

You can get multiple executables into a debugging session via the
`add-inferior' and `clone-inferior' commands. On some systems GDB can
add inferiors to the debug session automatically by following calls to
`fork' and `exec'. To remove inferiors from the debugging session use
the `remove-inferiors' command.

`add-inferior [ -copies N ] [ -exec EXECUTABLE ] [-no-connection ]'
Adds N inferiors to be run using EXECUTABLE as the executable; N
defaults to 1. If no executable is specified, the inferiors
begins empty, with no program. You can still assign or change the
program assigned to the inferior at any time by using the `file'
command with the executable name as its argument.

By default, the new inferior begins connected to the same target
connection as the current inferior. For example, if the current
inferior was connected to `gdbserver' with `target remote', then
the new inferior will be connected to the same `gdbserver'
instance. The `-no-connection' option starts the new inferior
with no connection yet. You can then for example use the `target
remote' command to connect to some other `gdbserver' instance, use
`run' to spawn a local program, etc.

`clone-inferior [ -copies N ] [ INFNO ]'
Adds N inferiors ready to execute the same program as inferior
INFNO; N defaults to 1, and INFNO defaults to the number of the
current inferior. This command copies the values of the ARGS,
INFERIOR-TTY and CWD properties from the current inferior to the
new one. It also propagates changes the user made to environment
variables using the `set environment' and `unset environment'
commands. This is a convenient command when you want to run
another instance of the inferior you are debugging.

(gdb) info inferiors
Num Description Connection Executable
* 1 process 29964 1 (native) helloworld
(gdb) clone-inferior
Added inferior 2.
1 inferiors added.
(gdb) info inferiors
Num Description Connection Executable
* 1 process 29964 1 (native) helloworld
2 <null> 1 (native) helloworld

You can now simply switch focus to inferior 2 and run it.

`remove-inferiors INFNO...'
Removes the inferior or inferiors INFNO.... It is not possible to
remove an inferior that is running with this command. For those,
use the `kill' or `detach' command first.

To quit debugging one of the running inferiors that is not the
current inferior, you can either detach from it by using the
`detach inferior' command (allowing it to run independently), or kill it
using the `kill inferiors' command:

`detach inferior INFNO...'
Detach from the inferior or inferiors identified by GDB inferior
number(s) INFNO.... Note that the inferior's entry still stays on
the list of inferiors shown by `info inferiors', but its
Description will show `<null>'.

`kill inferiors INFNO...'
Kill the inferior or inferiors identified by GDB inferior
number(s) INFNO.... Note that the inferior's entry still stays on
the list of inferiors shown by `info inferiors', but its
Description will show `<null>'.

After the successful completion of a command such as `detach',
`detach inferiors', `kill' or `kill inferiors', or after a normal
process exit, the inferior is still valid and listed with `info
inferiors', ready to be restarted.

To be notified when inferiors are started or exit under GDB's
control use `set print inferior-events':

`set print inferior-events'
`set print inferior-events on'
`set print inferior-events off'
The `set print inferior-events' command allows you to enable or
disable printing of messages when GDB notices that new inferiors
have started or that inferiors have exited or have been detached.
By default, these messages will be printed.

`show print inferior-events'
Show whether messages will be printed when GDB detects that
inferiors have started, exited or have been detached.

Many commands will work the same with multiple programs as with a
single program: e.g., `print myglobal' will simply display the value of
`myglobal' in the current inferior.

Occasionally, when debugging GDB itself, it may be useful to get
more info about the relationship of inferiors, programs, address spaces
in a debug session. You can do that with the
`maint info program-spaces' command.

`maint info program-spaces'
Print a list of all program spaces currently being managed by GDB.

GDB displays for each program space (in this order):

1. the program space number assigned by GDB

2. the name of the executable loaded into the program space,
with e.g., the `file' command.

3. the name of the core file loaded into the program space, with
e.g., the `core-file' command.

An asterisk `*' preceding the GDB program space number indicates
the current program space.

In addition, below each program space line, GDB prints extra
information that isn't suitable to display in tabular form. For
example, the list of inferiors bound to the program space.

(gdb) maint info program-spaces
Id Executable Core File
* 1 hello
2 goodbye
Bound inferiors: ID 1 (process 21561)

Here we can see that no inferior is running the program `hello',
while `process 21561' is running the program `goodbye'. On some
targets, it is possible that multiple inferiors are bound to the
same program space. The most common example is that of debugging
both the parent and child processes of a `vfork' call. For
example,

(gdb) maint info program-spaces
Id Executable Core File
* 1 vfork-test
Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)

Here, both inferior 2 and inferior 1 are running in the same
program space as a result of inferior 1 having executed a `vfork'
call.

* Menu:

* Inferior-Specific Breakpoints:: Controlling breakpoints

File: gdb.info, Node: Inferior-Specific Breakpoints, Up: Inferiors Connections and Programs

4.9.1 Inferior-Specific Breakpoints
-----------------------------------

When debugging multiple inferiors, you can choose whether to set
breakpoints for all inferiors, or for a particular inferior.

`break LOCSPEC inferior INFERIOR-ID'
`break LOCSPEC inferior INFERIOR-ID if ...'
LOCSPEC specifies a code location or locations in your program.
*Note Location Specifications::, for details.

Use the qualifier `inferior INFERIOR-ID' with a breakpoint command
to specify that you only want GDB to stop when a particular
inferior reaches this breakpoint. The INFERIOR-ID specifier is
one of the inferior identifiers assigned by GDB, shown in the
first column of the `info inferiors' output.

If you do not specify `inferior INFERIOR-ID' when you set a
breakpoint, the breakpoint applies to _all_ inferiors of your
program.

You can use the `inferior' qualifier on conditional breakpoints as
well; in this case, place `inferior INFERIOR-ID' before or after
the breakpoint condition, like this:

(gdb) break frik.c:13 inferior 2 if bartab > lim

Inferior-specific breakpoints are automatically deleted when the
corresponding inferior is removed from GDB. For example:

(gdb) remove-inferiors 2
Inferior-specific breakpoint 3 deleted - inferior 2 has been removed.

A breakpoint can't be both inferior-specific and thread-specific
(*note Thread-Specific Breakpoints::), or task-specific (*note Ada
Tasks::); using more than one of the `inferior', `thread', or `task'
keywords when creating a breakpoint will give an error.

File: gdb.info, Node: Threads, Next: Forks, Prev: Inferiors Connections and Programs, Up: Running

4.10 Debugging Programs with Multiple Threads
=============================================

In some operating systems, such as GNU/Linux and Solaris, a single
program may have more than one "thread" of execution. The precise
semantics of threads differ from one operating system to another, but
in general the threads of a single program are akin to multiple
processes--except that they share one address space (that is, they can
all examine and modify the same variables). On the other hand, each
thread has its own registers and execution stack, and perhaps private
memory.

GDB provides these facilities for debugging multi-thread programs:

* automatic notification of new threads

* `thread THREAD-ID', a command to switch among threads

* `info threads', a command to inquire about existing threads

* `thread apply [THREAD-ID-LIST | all] ARGS', a command to apply a
command to a list of threads

* thread-specific breakpoints

* `set print thread-events', which controls printing of messages on
thread start and exit.

* `set libthread-db-search-path PATH', which lets the user specify
which `libthread_db' to use if the default choice isn't compatible
with the program.

The GDB thread debugging facility allows you to observe all threads
while your program runs--but whenever GDB takes control, one thread in
particular is always the focus of debugging. This thread is called the
"current thread". Debugging commands show program information from the
perspective of the current thread.

Whenever GDB detects a new thread in your program, it displays the
target system's identification for the thread with a message in the
form `[New SYSTAG]', where SYSTAG is a thread identifier whose form
varies depending on the particular system. For example, on GNU/Linux,
you might see

[New Thread 0x41e02940 (LWP 25582)]

when GDB notices a new thread. In contrast, on other systems, the
SYSTAG is simply something like `process 368', with no further
qualifier.

For debugging purposes, GDB associates its own thread number
--always a single integer--with each thread of an inferior. This
number is unique between all threads of an inferior, but not unique
between threads of different inferiors.

You can refer to a given thread in an inferior using the qualified
INFERIOR-NUM.THREAD-NUM syntax, also known as "qualified thread ID",
with INFERIOR-NUM being the inferior number and THREAD-NUM being the
thread number of the given inferior. For example, thread `2.3' refers
to thread number 3 of inferior 2. If you omit INFERIOR-NUM (e.g.,
`thread 3'), then GDB infers you're referring to a thread of the current
inferior.

Until you create a second inferior, GDB does not show the
INFERIOR-NUM part of thread IDs, even though you can always use the
full INFERIOR-NUM.THREAD-NUM form to refer to threads of inferior 1,
the initial inferior.

Some commands accept a space-separated "thread ID list" as argument.
A list element can be:

1. A thread ID as shown in the first field of the `info threads'
display, with or without an inferior qualifier. E.g., `2.1' or
`1'.

2. A range of thread numbers, again with or without an inferior
qualifier, as in INF.THR1-THR2 or THR1-THR2. E.g., `1.2-4' or
`2-4'.

3. All threads of an inferior, specified with a star wildcard, with or
without an inferior qualifier, as in INF.`*' (e.g., `1.*') or `*'.
The former refers to all threads of the given inferior, and the
latter form without an inferior qualifier refers to all threads of
the current inferior.

For example, if the current inferior is 1, and inferior 7 has one
thread with ID 7.1, the thread list `1 2-3 4.5 6.7-9 7.*' includes
threads 1 to 3 of inferior 1, thread 5 of inferior 4, threads 7 to 9 of
inferior 6 and all threads of inferior 7. That is, in expanded
qualified form, the same as `1.1 1.2 1.3 4.5 6.7 6.8 6.9 7.1'.

In addition to a _per-inferior_ number, each thread is also assigned
a unique _global_ number, also known as "global thread ID", a single
integer. Unlike the thread number component of the thread ID, no two
threads have the same global ID, even when you're debugging multiple
inferiors.

From GDB's perspective, a process always has at least one thread.
In other words, GDB assigns a thread number to the program's "main
thread" even if the program is not multi-threaded.

The debugger convenience variables `$_thread' and `$_gthread'
contain, respectively, the per-inferior thread number and the global
thread number of the current thread. You may find this useful in
writing breakpoint conditional expressions, command scripts, and so
forth. The convenience variable `$_inferior_thread_count' contains the
number of live threads in the current inferior. *Note Convenience
Variables: Convenience Vars, for general information on convenience
variables.

When running in non-stop mode (*note Non-Stop Mode::), where new
threads can be created, and existing threads exit, at any time,
`$_inferior_thread_count' could return a different value each time it
is evaluated.

If GDB detects the program is multi-threaded, it augments the usual
message about stopping at a breakpoint with the ID and name of the
thread that hit the breakpoint.

Thread 2 "client" hit Breakpoint 1, send_message () at client.c:68

Likewise when the program receives a signal:

Thread 1 "main" received signal SIGINT, Interrupt.

`info threads [-gid] [THREAD-ID-LIST]'
Display information about one or more threads. With no arguments
displays information about all threads. You can specify the list
of threads that you want to display using the thread ID list syntax
(*note thread ID lists::).

GDB displays for each thread (in this order):

1. the per-inferior thread number assigned by GDB

2. the global thread number assigned by GDB, if the `-gid'
option was specified

3. the target system's thread identifier (SYSTAG)

4. the thread's name, if one is known. A thread can either be
named by the user (see `thread name', below), or, in some
cases, by the program itself.

5. the current stack frame summary for that thread

An asterisk `*' to the left of the GDB thread number indicates the
current thread.

For example,

(gdb) info threads
Id Target Id Frame
* 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2 process 35 thread 23 0x34e5 in sigpause ()
3 process 35 thread 27 0x34e5 in sigpause ()
at threadtest.c:68

If you're debugging multiple inferiors, GDB displays thread IDs
using the qualified INFERIOR-NUM.THREAD-NUM format. Otherwise, only
THREAD-NUM is shown.

If you specify the `-gid' option, GDB displays a column indicating
each thread's global thread ID:

(gdb) info threads
Id GId Target Id Frame
1.1 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1.2 3 process 35 thread 23 0x34e5 in sigpause ()
1.3 4 process 35 thread 27 0x34e5 in sigpause ()
* 2.1 2 process 65 thread 1 main (argc=1, argv=0x7ffffff8)

On Solaris, you can display more information about user threads with
a Solaris-specific command:

`maint info sol-threads'
Display info on Solaris user threads.

`thread THREAD-ID'
Make thread ID THREAD-ID the current thread. The command argument
THREAD-ID is the GDB thread ID, as shown in the first field of the
`info threads' display, with or without an inferior qualifier
(e.g., `2.1' or `1').

GDB responds by displaying the system identifier of the thread you
selected, and its current stack frame summary:

(gdb) thread 2
[Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))]
#0 some_function (ignore=0x0) at example.c:8
8 printf ("hello\n");

As with the `[New ...]' message, the form of the text after
`Switching to' depends on your system's conventions for identifying
threads.

`thread apply [THREAD-ID-LIST | all [-ascending]] [FLAG]... COMMAND'
The `thread apply' command allows you to apply the named COMMAND
to one or more threads. Specify the threads that you want
affected using the thread ID list syntax (*note thread ID
lists::), or specify `all' to apply to all threads. To apply a
command to all threads in descending order, type `thread apply all
COMMAND'. To apply a command to all threads in ascending order,
type `thread apply all -ascending COMMAND'.

The FLAG arguments control what output to produce and how to handle
errors raised when applying COMMAND to a thread. FLAG must start
with a `-' directly followed by one letter in `qcs'. If several
flags are provided, they must be given individually, such as `-c
-q'.

By default, GDB displays some thread information before the output
produced by COMMAND, and an error raised during the execution of a
COMMAND will abort `thread apply'. The following flags can be
used to fine-tune this behavior:

`-c'
The flag `-c', which stands for `continue', causes any errors
in COMMAND to be displayed, and the execution of `thread
apply' then continues.

`-s'
The flag `-s', which stands for `silent', causes any errors
or empty output produced by a COMMAND to be silently ignored.
That is, the execution continues, but the thread information
and errors are not printed.

`-q'
The flag `-q' (`quiet') disables printing the thread
information.

Flags `-c' and `-s' cannot be used together.

`taas [OPTION]... COMMAND'
Shortcut for `thread apply all -s [OPTION]... COMMAND'. Applies
COMMAND on all threads, ignoring errors and empty output.

The `taas' command accepts the same options as the `thread apply
all' command. *Note thread apply all::.

`tfaas [OPTION]... COMMAND'
Shortcut for `thread apply all -s -- frame apply all -s
[OPTION]... COMMAND'. Applies COMMAND on all frames of all
threads, ignoring errors and empty output. Note that the flag
`-s' is specified twice: The first `-s' ensures that `thread
apply' only shows the thread information of the threads for which
`frame apply' produces some output. The second `-s' is needed to
ensure that `frame apply' shows the frame information of a frame
only if the COMMAND successfully produced some output.

It can for example be used to print a local variable or a function
argument without knowing the thread or frame where this variable
or argument is, using:
(gdb) tfaas p some_local_var_i_do_not_remember_where_it_is

The `tfaas' command accepts the same options as the `frame apply'
command. *Note frame apply: Frame Apply.

`thread name [NAME]'
This command assigns a name to the current thread. If no argument
is given, any existing user-specified name is removed. The thread
name appears in the `info threads' display.

On some systems, such as GNU/Linux, GDB is able to determine the
name of the thread as given by the OS. On these systems, a name
specified with `thread name' will override the system-give name,
and removing the user-specified name will cause GDB to once again
display the system-specified name.

`thread find [REGEXP]'
Search for and display thread ids whose name or SYSTAG matches the
supplied regular expression.

As well as being the complement to the `thread name' command, this
command also allows you to identify a thread by its target SYSTAG.
For instance, on GNU/Linux, the target SYSTAG is the LWP id.

(gdb) thread find 26688
Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)'
(gdb) info thread 4
Id Target Id Frame
4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()

`set print thread-events'
`set print thread-events on'
`set print thread-events off'
The `set print thread-events' command allows you to enable or
disable printing of messages when GDB notices that new threads have
started or that threads have exited. By default, these messages
will be printed if detection of these events is supported by the
target. Note that these messages cannot be disabled on all
targets.

`show print thread-events'
Show whether messages will be printed when GDB detects that threads
have started and exited.

*Note Stopping and Starting Multi-thread Programs: Thread Stops, for
more information about how GDB behaves when you stop and start programs
with multiple threads.

*Note Setting Watchpoints: Set Watchpoints, for information about
watchpoints in programs with multiple threads.

`set libthread-db-search-path [PATH]'
If this variable is set, PATH is a colon-separated list of
directories GDB will use to search for `libthread_db'. If you
omit PATH, `libthread-db-search-path' will be reset to its default
value (`$sdir:$pdir' on GNU/Linux and Solaris systems).
Internally, the default value comes from the
`LIBTHREAD_DB_SEARCH_PATH' macro.

On GNU/Linux and Solaris systems, GDB uses a "helper"
`libthread_db' library to obtain information about threads in the
inferior process. GDB will use `libthread-db-search-path' to find
`libthread_db'. GDB also consults first if inferior specific
thread debugging library loading is enabled by `set auto-load
libthread-db' (*note libthread_db.so.1 file::).

A special entry `$sdir' for `libthread-db-search-path' refers to
the default system directories that are normally searched for
loading shared libraries. The `$sdir' entry is the only kind not
needing to be enabled by `set auto-load libthread-db' (*note
libthread_db.so.1 file::).

A special entry `$pdir' for `libthread-db-search-path' refers to
the directory from which `libpthread' was loaded in the inferior
process.

For any `libthread_db' library GDB finds in above directories, GDB
attempts to initialize it with the current inferior process. If
this initialization fails (which could happen because of a version
mismatch between `libthread_db' and `libpthread'), GDB will unload
`libthread_db', and continue with the next directory. If none of
`libthread_db' libraries initialize successfully, GDB will issue a
warning and thread debugging will be disabled.

Setting `libthread-db-search-path' is currently implemented only
on some platforms.

`show libthread-db-search-path'
Display current libthread_db search path.

`set debug libthread-db'
`show debug libthread-db'
Turns on or off display of `libthread_db'-related events. Use `1'
to enable, `0' to disable.

`set debug threads [on|off]'
`show debug threads'
When `on' GDB will print additional messages when threads are
created and deleted.

File: gdb.info, Node: Forks, Next: Checkpoint/Restart, Prev: Threads, Up: Running

4.11 Debugging Forks
====================

On most systems, GDB has no special support for debugging programs
which create additional processes using the `fork' function. When a
program forks, GDB will continue to debug the parent process and the
child process will run unimpeded. If you have set a breakpoint in any
code which the child then executes, the child will get a `SIGTRAP'
signal which (unless it catches the signal) will cause it to terminate.

However, if you want to debug the child process there is a workaround
which isn't too painful. Put a call to `sleep' in the code which the
child process executes after the fork. It may be useful to sleep only
if a certain environment variable is set, or a certain file exists, so
that the delay need not occur when you don't want to run GDB on the
child. While the child is sleeping, use the `ps' program to get its
process ID. Then tell GDB (a new invocation of GDB if you are also
debugging the parent process) to attach to the child process (*note
Attach::). From that point on you can debug the child process just
like any other process which you attached to.

On some systems, GDB provides support for debugging programs that
create additional processes using the `fork' or `vfork' functions. On
GNU/Linux platforms, this feature is supported with kernel version
2.5.46 and later.

The fork debugging commands are supported in native mode and when
connected to `gdbserver' in either `target remote' mode or `target
extended-remote' mode.

By default, when a program forks, GDB will continue to debug the
parent process and the child process will run unimpeded.

If you want to follow the child process instead of the parent
process, use the command `set follow-fork-mode'.

`set follow-fork-mode MODE'
Set the debugger response to a program call of `fork' or `vfork'.
A call to `fork' or `vfork' creates a new process. The MODE
argument can be:

`parent'
The original process is debugged after a fork. The child
process runs unimpeded. This is the default.

`child'
The new process is debugged after a fork. The parent process
runs unimpeded.

`show follow-fork-mode'
Display the current debugger response to a `fork' or `vfork' call.

On Linux, if you want to debug both the parent and child processes,
use the command `set detach-on-fork'.

`set detach-on-fork MODE'
Tells gdb whether to detach one of the processes after a fork, or
retain debugger control over them both.

`on'
The child process (or parent process, depending on the value
of `follow-fork-mode') will be detached and allowed to run
independently. This is the default.

`off'
Both processes will be held under the control of GDB. One
process (child or parent, depending on the value of
`follow-fork-mode') is debugged as usual, while the other is
held suspended.

`show detach-on-fork'
Show whether detach-on-fork mode is on/off.

If you choose to set `detach-on-fork' mode off, then GDB will retain
control of all forked processes (including nested forks). You can list
the forked processes under the control of GDB by using the
`info inferiors' command, and switch from one fork to another by using
the `inferior' command (*note Debugging Multiple Inferiors Connections
and Programs: Inferiors Connections and Programs.).

To quit debugging one of the forked processes, you can either detach
from it by using the `detach inferiors' command (allowing it to run
independently), or kill it using the `kill inferiors' command. *Note
Debugging Multiple Inferiors Connections and Programs: Inferiors
Connections and Programs.

If you ask to debug a child process and a `vfork' is followed by an
`exec', GDB executes the new target up to the first breakpoint in the
new target. If you have a breakpoint set on `main' in your original
program, the breakpoint will also be set on the child process's `main'.

On some systems, when a child process is spawned by `vfork', you
cannot debug the child or parent until an `exec' call completes.

If you issue a `run' command to GDB after an `exec' call executes,
the new target restarts. To restart the parent process, use the `file'
command with the parent executable name as its argument. By default,
after an `exec' call executes, GDB discards the symbols of the previous
executable image. You can change this behaviour with the
`set follow-exec-mode' command.

`set follow-exec-mode MODE'
Set debugger response to a program call of `exec'. An `exec' call
replaces the program image of a process.

`follow-exec-mode' can be:

`new'
GDB creates a new inferior and rebinds the process to this
new inferior. The program the process was running before the
`exec' call can be restarted afterwards by restarting the
original inferior.

For example:

(gdb) info inferiors
(gdb) info inferior
Id Description Executable
* 1 <null> prog1
(gdb) run
process 12020 is executing new program: prog2
Program exited normally.
(gdb) info inferiors
Id Description Executable
1 <null> prog1
* 2 <null> prog2

`same'
GDB keeps the process bound to the same inferior. The new
executable image replaces the previous executable loaded in
the inferior. Restarting the inferior after the `exec' call,
with e.g., the `run' command, restarts the executable the
process was running after the `exec' call. This is the
default mode.

For example:

(gdb) info inferiors
Id Description Executable
* 1 <null> prog1
(gdb) run
process 12020 is executing new program: prog2
Program exited normally.
(gdb) info inferiors
Id Description Executable
* 1 <null> prog2

`follow-exec-mode' is supported in native mode and `target
extended-remote' mode.

You can use the `catch' command to make GDB stop whenever a `fork',
`vfork', or `exec' call is made. *Note Setting Catchpoints: Set
Catchpoints.

File: gdb.info, Node: Checkpoint/Restart, Prev: Forks, Up: Running

4.12 Setting a _Bookmark_ to Return to Later
============================================

On certain operating systems(1), GDB is able to save a "snapshot" of a
program's state, called a "checkpoint", and come back to it later.

Returning to a checkpoint effectively undoes everything that has
happened in the program since the `checkpoint' was saved. This
includes changes in memory, registers, and even (within some limits)
system state. Effectively, it is like going back in time to the moment
when the checkpoint was saved.

Thus, if you're stepping thru a program and you think you're getting
close to the point where things go wrong, you can save a checkpoint.
Then, if you accidentally go too far and miss the critical statement,
instead of having to restart your program from the beginning, you can
just go back to the checkpoint and start again from there.

This can be especially useful if it takes a lot of time or steps to
reach the point where you think the bug occurs.

To use the `checkpoint'/`restart' method of debugging:

`checkpoint'
Save a snapshot of the debugged program's current execution state.
The `checkpoint' command takes no arguments, but each checkpoint
is assigned a small integer id, similar to a breakpoint id.

`info checkpoints'
List the checkpoints that have been saved in the current debugging
session. For each checkpoint, the following information will be
listed:

`Checkpoint ID'

`Process ID'

`Code Address'

`Source line, or label'

`restart CHECKPOINT-ID'
Restore the program state that was saved as checkpoint number
CHECKPOINT-ID. All program variables, registers, stack frames
etc. will be returned to the values that they had when the
checkpoint was saved. In essence, gdb will "wind back the clock"
to the point in time when the checkpoint was saved.

Note that breakpoints, GDB variables, command history etc. are
not affected by restoring a checkpoint. In general, a checkpoint
only restores things that reside in the program being debugged,
not in the debugger.

`delete checkpoint CHECKPOINT-ID'
Delete the previously-saved checkpoint identified by CHECKPOINT-ID.

Returning to a previously saved checkpoint will restore the user
state of the program being debugged, plus a significant subset of the
system (OS) state, including file pointers. It won't "un-write" data
from a file, but it will rewind the file pointer to the previous
location, so that the previously written data can be overwritten. For
files opened in read mode, the pointer will also be restored so that the
previously read data can be read again.

Of course, characters that have been sent to a printer (or other
external device) cannot be "snatched back", and characters received
from eg. a serial device can be removed from internal program buffers,
but they cannot be "pushed back" into the serial pipeline, ready to be
received again. Similarly, the actual contents of files that have been
changed cannot be restored (at this time).

However, within those constraints, you actually can "rewind" your
program to a previously saved point in time, and begin debugging it
again -- and you can change the course of events so as to debug a
different execution path this time.

Finally, there is one bit of internal program state that will be
different when you return to a checkpoint -- the program's process id.
Each checkpoint will have a unique process id (or PID), and each will
be different from the program's original PID. If your program has
saved a local copy of its process id, this could potentially pose a
problem.

4.12.1 A Non-obvious Benefit of Using Checkpoints
-------------------------------------------------

On some systems such as GNU/Linux, address space randomization is
performed on new processes for security reasons. This makes it
difficult or impossible to set a breakpoint, or watchpoint, on an
absolute address if you have to restart the program, since the absolute
location of a symbol will change from one execution to the next.

A checkpoint, however, is an _identical_ copy of a process.
Therefore if you create a checkpoint at (eg.) the start of main, and
simply return to that checkpoint instead of restarting the process, you
can avoid the effects of address randomization and your symbols will
all stay in the same place.

---------- Footnotes ----------

(1) Currently, only GNU/Linux.

File: gdb.info, Node: Stopping, Next: Reverse Execution, Prev: Running, Up: Top

5 Stopping and Continuing
*************************

The principal purposes of using a debugger are so that you can stop your
program before it terminates; or so that, if your program runs into
trouble, you can investigate and find out why.

Inside GDB, your program may stop for any of several reasons, such
as a signal, a breakpoint, or reaching a new line after a GDB command
such as `step'. You may then examine and change variables, set new
breakpoints or remove old ones, and then continue execution. Usually,
the messages shown by GDB provide ample explanation of the status of
your program--but you can also explicitly request this information at
any time.

`info program'
Display information about the status of your program: whether it is
running or not, what process it is, and why it stopped.

* Menu:

* Breakpoints:: Breakpoints, watchpoints, tracepoints,
and catchpoints
* Continuing and Stepping:: Resuming execution
* Skipping Over Functions and Files::
Skipping over functions and files
* Signals:: Signals
* Thread Stops:: Stopping and starting multi-thread programs

File: gdb.info, Node: Breakpoints, Next: Continuing and Stepping, Up: Stopping

5.1 Breakpoints, Watchpoints, and Catchpoints
=============================================

A "breakpoint" makes your program stop whenever a certain point in the
program is reached. For each breakpoint, you can add conditions to
control in finer detail whether your program stops. You can set
breakpoints with the `break' command and its variants (*note Setting
Breakpoints: Set Breaks.), to specify the place where your program
should stop by line number, function name or exact address in the
program.

On some systems, you can set breakpoints in shared libraries before
the executable is run.

A "watchpoint" is a special breakpoint that stops your program when
the value of an expression changes. The expression may be a value of a
variable, or it could involve values of one or more variables combined
by operators, such as `a + b'. This is sometimes called "data
breakpoints". You must use a different command to set watchpoints
(*note Setting Watchpoints: Set Watchpoints.), but aside from that, you
can manage a watchpoint like any other breakpoint: you enable, disable,
and delete both breakpoints and watchpoints using the same commands.

You can arrange to have values from your program displayed
automatically whenever GDB stops at a breakpoint. *Note Automatic
Display: Auto Display.

A "catchpoint" is another special breakpoint that stops your program
when a certain kind of event occurs, such as the throwing of a C++
exception or the loading of a library. As with watchpoints, you use a
different command to set a catchpoint (*note Setting Catchpoints: Set
Catchpoints.), but aside from that, you can manage a catchpoint like any
other breakpoint. (To stop when your program receives a signal, use the
`handle' command; see *Note Signals: Signals.)

GDB assigns a number to each breakpoint, watchpoint, or catchpoint
when you create it; these numbers are successive integers starting with
one. In many of the commands for controlling various features of
breakpoints you use the breakpoint number to say which breakpoint you
want to change. Each breakpoint may be "enabled" or "disabled"; if
disabled, it has no effect on your program until you enable it again.

Some GDB commands accept a space-separated list of breakpoints on
which to operate. A list element can be either a single breakpoint
number, like `5', or a range of such numbers, like `5-7'. When a
breakpoint list is given to a command, all breakpoints in that list are
operated on.

* Menu:

* Set Breaks:: Setting breakpoints
* Set Watchpoints:: Setting watchpoints
* Set Catchpoints:: Setting catchpoints
* Delete Breaks:: Deleting breakpoints
* Disabling:: Disabling breakpoints
* Conditions:: Break conditions
* Break Commands:: Breakpoint command lists
* Dynamic Printf:: Dynamic printf
* Save Breakpoints:: How to save breakpoints in a file
* Static Probe Points:: Listing static probe points
* Error in Breakpoints:: ``Cannot insert breakpoints''
* Breakpoint-related Warnings:: ``Breakpoint address adjusted...''

File: gdb.info, Node: Set Breaks, Next: Set Watchpoints, Up: Breakpoints

5.1.1 Setting Breakpoints
-------------------------

Breakpoints are set with the `break' command (abbreviated `b'). The
debugger convenience variable `$bpnum' records the number of the
breakpoint you've set most recently:
(gdb) b main
Breakpoint 1 at 0x11c6: file zeoes.c, line 24.
(gdb) p $bpnum
$1 = 1

A breakpoint may be mapped to multiple code locations for example
with inlined functions, Ada generics, C++ templates or overloaded
function names. GDB then indicates the number of code locations in the
breakpoint command output:
(gdb) b some_func
Breakpoint 2 at 0x1179: some_func. (3 locations)
(gdb) p $bpnum
$2 = 2
(gdb)

When your program stops on a breakpoint, the convenience variables
`$_hit_bpnum' and `$_hit_locno' are respectively set to the number of
the encountered breakpoint and the number of the breakpoint's code
location:
Thread 1 "zeoes" hit Breakpoint 2.1, some_func () at zeoes.c:8
8 printf("some func\n");
(gdb) p $_hit_bpnum
$5 = 2
(gdb) p $_hit_locno
$6 = 1
(gdb)

Note that `$_hit_bpnum' and `$bpnum' are not equivalent:
`$_hit_bpnum' is set to the breakpoint number last hit, while `$bpnum'
is set to the breakpoint number last set.

If the encountered breakpoint has only one code location,
`$_hit_locno' is set to 1:
Breakpoint 1, main (argc=1, argv=0x7fffffffe018) at zeoes.c:24
24 if (argc > 1)
(gdb) p $_hit_bpnum
$3 = 1
(gdb) p $_hit_locno
$4 = 1
(gdb)

The `$_hit_bpnum' and `$_hit_locno' variables can typically be used
in a breakpoint command list. (*note Breakpoint Command Lists: Break
Commands.). For example, as part of the breakpoint command list, you
can disable completely the encountered breakpoint using `disable
$_hit_bpnum' or disable the specific encountered breakpoint location
using `disable $_hit_bpnum.$_hit_locno'. If a breakpoint has only one
location, `$_hit_locno' is set to 1 and the commands `disable
$_hit_bpnum' and `disable $_hit_bpnum.$_hit_locno' both disable the
breakpoint.

You can also define aliases to easily disable the last hit location
or last hit breakpoint:
(gdb) alias lld = disable $_hit_bpnum.$_hit_locno
(gdb) alias lbd = disable $_hit_bpnum

`break LOCSPEC'
Set a breakpoint at all the code locations in your program that
result from resolving the given LOCSPEC. LOCSPEC can specify a
function name, a line number, an address of an instruction, and
more. *Note Location Specifications::, for the various forms of
LOCSPEC. The breakpoint will stop your program just before it
executes the instruction at the address of any of the breakpoint's
code locations.

When using source languages that permit overloading of symbols,
such as C++, a function name may refer to more than one symbol, and
thus more than one place to break. *Note Ambiguous Expressions:
Ambiguous Expressions, for a discussion of that situation.

It is also possible to insert a breakpoint that will stop the
program only if a specific thread (*note Thread-Specific
Breakpoints::), specific inferior (*note Inferior-Specific
Breakpoints::), or a specific task (*note Ada Tasks::) hits that
breakpoint.

`break'
When called without any arguments, `break' sets a breakpoint at
the next instruction to be executed in the selected stack frame
(*note Examining the Stack: Stack.). In any selected frame but the
innermost, this makes your program stop as soon as control returns
to that frame. This is similar to the effect of a `finish'
command in the frame inside the selected frame--except that
`finish' does not leave an active breakpoint. If you use `break'
without an argument in the innermost frame, GDB stops the next
time it reaches the current location; this may be useful inside
loops.

GDB normally ignores breakpoints when it resumes execution, until
at least one instruction has been executed. If it did not do
this, you would be unable to proceed past a breakpoint without
first disabling the breakpoint. This rule applies whether or not
the breakpoint already existed when your program stopped.

`break ... if COND'
Set a breakpoint with condition COND; evaluate the expression COND
each time the breakpoint is reached, and stop only if the value is
nonzero--that is, if COND evaluates as true. `...' stands for one
of the possible arguments described above (or no argument)
specifying where to break. *Note Break Conditions: Conditions,
for more information on breakpoint conditions.

The breakpoint may be mapped to multiple locations. If the
breakpoint condition COND is invalid at some but not all of the
locations, the locations for which the condition is invalid are
disabled. For example, GDB reports below that two of the three
locations are disabled.

(gdb) break func if a == 10
warning: failed to validate condition at location 0x11ce, disabling:
No symbol "a" in current context.
warning: failed to validate condition at location 0x11b6, disabling:
No symbol "a" in current context.
Breakpoint 1 at 0x11b6: func. (3 locations)

Locations that are disabled because of the condition are denoted
by an uppercase `N' in the output of the `info breakpoints'
command:

(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y <MULTIPLE>
stop only if a == 10
1.1 N* 0x00000000000011b6 in ...
1.2 y 0x00000000000011c2 in ...
1.3 N* 0x00000000000011ce in ...
(*): Breakpoint condition is invalid at this location.

If the breakpoint condition COND is invalid in the context of
_all_ the locations of the breakpoint, GDB refuses to define the
breakpoint. For example, if variable `foo' is an undefined
variable:

(gdb) break func if foo
No symbol "foo" in current context.

`break ... -force-condition if COND'
There may be cases where the condition COND is invalid at all the
current locations, but the user knows that it will be valid at a
future location; for example, because of a library load. In such
cases, by using the `-force-condition' keyword before `if', GDB
can be forced to define the breakpoint with the given condition
expression instead of refusing it.

(gdb) break func -force-condition if foo
warning: failed to validate condition at location 1, disabling:
No symbol "foo" in current context.
warning: failed to validate condition at location 2, disabling:
No symbol "foo" in current context.
warning: failed to validate condition at location 3, disabling:
No symbol "foo" in current context.
Breakpoint 1 at 0x1158: test.c:18. (3 locations)

This causes all the present locations where the breakpoint would
otherwise be inserted, to be disabled, as seen in the example
above. However, if there exist locations at which the condition
is valid, the `-force-condition' keyword has no effect.

`tbreak ARGS'
Set a breakpoint enabled only for one stop. The ARGS are the same
as for the `break' command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first
time your program stops there. *Note Disabling Breakpoints:
Disabling.

`hbreak ARGS'
Set a hardware-assisted breakpoint. The ARGS are the same as for
the `break' command and the breakpoint is set in the same way, but
the breakpoint requires hardware support and some target hardware
may not have this support. The main purpose of this is EPROM/ROM
code debugging, so you can set a breakpoint at an instruction
without changing the instruction. This can be used with the new
trap-generation provided by SPARClite DSU and most x86-based
targets. These targets will generate traps when a program
accesses some data or instruction address that is assigned to the
debug registers. However the hardware breakpoint registers can
take a limited number of breakpoints. For example, on the DSU,
only two data breakpoints can be set at a time, and GDB will
reject this command if more than two are used. Delete or disable
unused hardware breakpoints before setting new ones (*note
Disabling Breakpoints: Disabling.). *Note Break Conditions:
Conditions. For remote targets, you can restrict the number of
hardware breakpoints GDB will use, see *Note set remote
hardware-breakpoint-limit::.

`thbreak ARGS'
Set a hardware-assisted breakpoint enabled only for one stop. The
ARGS are the same as for the `hbreak' command and the breakpoint
is set in the same way. However, like the `tbreak' command, the
breakpoint is automatically deleted after the first time your
program stops there. Also, like the `hbreak' command, the
breakpoint requires hardware support and some target hardware may
not have this support. *Note Disabling Breakpoints: Disabling.
See also *Note Break Conditions: Conditions.

`rbreak REGEX'
Set breakpoints on all functions matching the regular expression
REGEX. This command sets an unconditional breakpoint on all
matches, printing a list of all breakpoints it set. Once these
breakpoints are set, they are treated just like the breakpoints
set with the `break' command. You can delete them, disable them,
or make them conditional the same way as any other breakpoint.

In programs using different languages, GDB chooses the syntax to
print the list of all breakpoints it sets according to the `set
language' value: using `set language auto' (see *Note Set Language
Automatically: Automatically.) means to use the language of the
breakpoint's function, other values mean to use the manually
specified language (see *Note Set Language Manually: Manually.).

The syntax of the regular expression is the standard one used with
tools like `grep'. Note that this is different from the syntax
used by shells, so for instance `foo*' matches all functions that
include an `fo' followed by zero or more `o's. There is an
implicit `.*' leading and trailing the regular expression you
supply, so to match only functions that begin with `foo', use
`^foo'.

When debugging C++ programs, `rbreak' is useful for setting
breakpoints on overloaded functions that are not members of any
special classes.

The `rbreak' command can be used to set breakpoints in *all* the
functions in a program, like this:

(gdb) rbreak .

`rbreak FILE:REGEX'
If `rbreak' is called with a filename qualification, it limits the
search for functions matching the given regular expression to the
specified FILE. This can be used, for example, to set breakpoints
on every function in a given file:

(gdb) rbreak file.c:.

The colon separating the filename qualifier from the regex may
optionally be surrounded by spaces.

`info breakpoints [LIST...]'
`info break [LIST...]'
Print a table of all breakpoints, watchpoints, tracepoints, and
catchpoints set and not deleted. Optional argument N means print
information only about the specified breakpoint(s) (or
watchpoint(s) or tracepoint(s) or catchpoint(s)). For each
breakpoint, following columns are printed:

_Breakpoint Numbers_

_Type_
Breakpoint, watchpoint, tracepoint, or catchpoint.

_Disposition_
Whether the breakpoint is marked to be disabled or deleted
when hit.

_Enabled or Disabled_
Enabled breakpoints are marked with `y'. `n' marks
breakpoints that are not enabled.

_Address_
Where the breakpoint is in your program, as a memory address.
For a pending breakpoint whose address is not yet known,
this field will contain `<PENDING>'. Such breakpoint won't
fire until a shared library that has the symbol or line
referred by breakpoint is loaded. See below for details. A
breakpoint with several locations will have `<MULTIPLE>' in
this field--see below for details.

_What_
Where the breakpoint is in the source for your program, as a
file and line number. For a pending breakpoint, the original
string passed to the breakpoint command will be listed as it
cannot be resolved until the appropriate shared library is
loaded in the future.

If a breakpoint is conditional, there are two evaluation modes:
"host" and "target". If mode is "host", breakpoint condition
evaluation is done by GDB on the host's side. If it is "target",
then the condition is evaluated by the target. The `info break'
command shows the condition on the line following the affected
breakpoint, together with its condition evaluation mode in between
parentheses.

Breakpoint commands, if any, are listed after that. A pending
breakpoint is allowed to have a condition specified for it. The
condition is not parsed for validity until a shared library is
loaded that allows the pending breakpoint to resolve to a valid
location.

`info break' with a breakpoint number N as argument lists only
that breakpoint. The convenience variable `$_' and the default
examining-address for the `x' command are set to the address of
the last breakpoint listed (*note Examining Memory: Memory.).

`info break' displays a count of the number of times the breakpoint
has been hit. This is especially useful in conjunction with the
`ignore' command. You can ignore a large number of breakpoint
hits, look at the breakpoint info to see how many times the
breakpoint was hit, and then run again, ignoring one less than
that number. This will get you quickly to the last hit of that
breakpoint.

For a breakpoints with an enable count (xref) greater than 1,
`info break' also displays that count.

GDB allows you to set any number of breakpoints at the same place in
your program. There is nothing silly or meaningless about this. When
the breakpoints are conditional, this is even useful (*note Break
Conditions: Conditions.).

It is possible that a single logical breakpoint is set at several
code locations in your program. *Note Location Specifications::, for
examples.

A breakpoint with multiple code locations is displayed in the
breakpoint table using several rows--one header row, followed by one
row for each code location. The header row has `<MULTIPLE>' in the
address column. Each code location row contains the actual address,
source file, source line and function of its code location. The number
column for a code location is of the form
BREAKPOINT-NUMBER.LOCATION-NUMBER.

For example:

Num Type Disp Enb Address What
1 breakpoint keep y <MULTIPLE>
stop only if i==1
breakpoint already hit 1 time
1.1 y 0x080486a2 in void foo<int>() at t.cc:8
1.2 y 0x080486ca in void foo<double>() at t.cc:8

You cannot delete the individual locations from a breakpoint.
However, each location can be individually enabled or disabled by
passing BREAKPOINT-NUMBER.LOCATION-NUMBER as argument to the `enable'
and `disable' commands. It's also possible to `enable' and `disable' a
range of LOCATION-NUMBER locations using a BREAKPOINT-NUMBER and two
LOCATION-NUMBERs, in increasing order, separated by a hyphen, like
`BREAKPOINT-NUMBER.LOCATION-NUMBER1-LOCATION-NUMBER2', in which case
GDB acts on all the locations in the range (inclusive). Disabling or
enabling the parent breakpoint (*note Disabling::) affects all of the
locations that belong to that breakpoint.

Locations that are enabled while their parent breakpoint is disabled
won't trigger a break, and are denoted by `y-' in the `Enb' column.
For example:

(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep n <MULTIPLE>
1.1 y- 0x00000000000011b6 in ...
1.2 y- 0x00000000000011c2 in ...
1.3 n 0x00000000000011ce in ...

It's quite common to have a breakpoint inside a shared library.
Shared libraries can be loaded and unloaded explicitly, and possibly
repeatedly, as the program is executed. To support this use case, GDB
updates breakpoint locations whenever any shared library is loaded or
unloaded. Typically, you would set a breakpoint in a shared library at
the beginning of your debugging session, when the library is not
loaded, and when the symbols from the library are not available. When
you try to set breakpoint, GDB will ask you if you want to set a so
called "pending breakpoint"--breakpoint whose address is not yet
resolved.

After the program is run, whenever a new shared library is loaded,
GDB reevaluates all the breakpoints. When a newly loaded shared
library contains the symbol or line referred to by some pending
breakpoint, that breakpoint is resolved and becomes an ordinary
breakpoint. When a library is unloaded, all breakpoints that refer to
its symbols or source lines become pending again.

This logic works for breakpoints with multiple locations, too. For
example, if you have a breakpoint in a C++ template function, and a
newly loaded shared library has an instantiation of that template, a
new location is added to the list of locations for the breakpoint.

Except for having unresolved address, pending breakpoints do not
differ from regular breakpoints. You can set conditions or commands,
enable and disable them and perform other breakpoint operations.

GDB provides some additional commands for controlling what happens
when the `break' command cannot resolve the location spec to any code
location in your program (*note Location Specifications::):

`set breakpoint pending auto'
This is the default behavior. When GDB cannot resolve the
location spec, it queries you whether a pending breakpoint should
be created.

`set breakpoint pending on'
This indicates that when GDB cannot resolve the location spec, it
should create a pending breakpoint without confirmation.

`set breakpoint pending off'
This indicates that pending breakpoints are not to be created. If
GDB cannot resolve the location spec, it aborts the breakpoint
creation with an error. This setting does not affect any pending
breakpoints previously created.

`show breakpoint pending'
Show the current behavior setting for creating pending breakpoints.

The settings above only affect the `break' command and its variants.
Once a breakpoint is set, it will be automatically updated as shared
libraries are loaded and unloaded.

For some targets, GDB can automatically decide if hardware or
software breakpoints should be used, depending on whether the
breakpoint address is read-only or read-write. This applies to
breakpoints set with the `break' command as well as to internal
breakpoints set by commands like `next' and `finish'. For breakpoints
set with `hbreak', GDB will always use hardware breakpoints.

You can control this automatic behaviour with the following commands:

`set breakpoint auto-hw on'
This is the default behavior. When GDB sets a breakpoint, it will
try to use the target memory map to decide if software or hardware
breakpoint must be used.

`set breakpoint auto-hw off'
This indicates GDB should not automatically select breakpoint
type. If the target provides a memory map, GDB will warn when
trying to set software breakpoint at a read-only address.

GDB normally implements breakpoints by replacing the program code at
the breakpoint address with a special instruction, which, when
executed, given control to the debugger. By default, the program code
is so modified only when the program is resumed. As soon as the
program stops, GDB restores the original instructions. This behaviour
guards against leaving breakpoints inserted in the target should gdb
abrubptly disconnect. However, with slow remote targets, inserting and
removing breakpoint can reduce the performance. This behavior can be
controlled with the following commands::

`set breakpoint always-inserted off'
All breakpoints, including newly added by the user, are inserted in
the target only when the target is resumed. All breakpoints are
removed from the target when it stops. This is the default mode.

`set breakpoint always-inserted on'
Causes all breakpoints to be inserted in the target at all times.
If the user adds a new breakpoint, or changes an existing
breakpoint, the breakpoints in the target are updated immediately.
A breakpoint is removed from the target only when breakpoint
itself is deleted.

GDB handles conditional breakpoints by evaluating these conditions
when a breakpoint breaks. If the condition is true, then the process
being debugged stops, otherwise the process is resumed.

If the target supports evaluating conditions on its end, GDB may
download the breakpoint, together with its conditions, to it.

This feature can be controlled via the following commands:

`set breakpoint condition-evaluation host'
This option commands GDB to evaluate the breakpoint conditions on
the host's side. Unconditional breakpoints are sent to the target
which in turn receives the triggers and reports them back to GDB
for condition evaluation. This is the standard evaluation mode.

`set breakpoint condition-evaluation target'
This option commands GDB to download breakpoint conditions to the
target at the moment of their insertion. The target is
responsible for evaluating the conditional expression and reporting
breakpoint stop events back to GDB whenever the condition is true.
Due to limitations of target-side evaluation, some conditions
cannot be evaluated there, e.g., conditions that depend on local
data that is only known to the host. Examples include conditional
expressions involving convenience variables, complex types that
cannot be handled by the agent expression parser and expressions
that are too long to be sent over to the target, specially when the
target is a remote system. In these cases, the conditions will be
evaluated by GDB.

`set breakpoint condition-evaluation auto'
This is the default mode. If the target supports evaluating
breakpoint conditions on its end, GDB will download breakpoint
conditions to the target (limitations mentioned previously apply).
If the target does not support breakpoint condition evaluation,
then GDB will fallback to evaluating all these conditions on the
host's side.

GDB itself sometimes sets breakpoints in your program for special
purposes, such as proper handling of `longjmp' (in C programs). These
internal breakpoints are assigned negative numbers, starting with `-1';
`info breakpoints' does not display them. You can see these
breakpoints with the GDB maintenance command `maint info breakpoints'
(*note maint info breakpoints::).

File: gdb.info, Node: Set Watchpoints, Next: Set Catchpoints, Prev: Set Breaks, Up: Breakpoints

5.1.2 Setting Watchpoints
-------------------------

You can use a watchpoint to stop execution whenever the value of an
expression changes, without having to predict a particular place where
this may happen. (This is sometimes called a "data breakpoint".) The
expression may be as simple as the value of a single variable, or as
complex as many variables combined by operators. Examples include:

* A reference to the value of a single variable.

* An address cast to an appropriate data type. For example, `*(int
*)0x12345678' will watch a 4-byte region at the specified address
(assuming an `int' occupies 4 bytes).

* An arbitrarily complex expression, such as `a*b + c/d'. The
expression can use any operators valid in the program's native
language (*note Languages::).

You can set a watchpoint on an expression even if the expression can
not be evaluated yet. For instance, you can set a watchpoint on
`*global_ptr' before `global_ptr' is initialized. GDB will stop when
your program sets `global_ptr' and the expression produces a valid
value. If the expression becomes valid in some other way than changing
a variable (e.g. if the memory pointed to by `*global_ptr' becomes
readable as the result of a `malloc' call), GDB may not stop until the
next time the expression changes.

Depending on your system, watchpoints may be implemented in software
or hardware. GDB does software watchpointing by single-stepping your
program and testing the variable's value each time, which is hundreds of
times slower than normal execution. (But this may still be worth it, to
catch errors where you have no clue what part of your program is the
culprit.)

On some systems, such as most PowerPC or x86-based targets, GDB
includes support for hardware watchpoints, which do not slow down the
running of your program.

`watch [-l|-location] EXPR [thread THREAD-ID] [mask MASKVALUE] [task TASK-ID]'
Set a watchpoint for an expression. GDB will break when the
expression EXPR is written into by the program and its value
changes. The simplest (and the most popular) use of this command
is to watch the value of a single variable:

(gdb) watch foo

If the command includes a `[thread THREAD-ID]' argument, GDB
breaks only when the thread identified by THREAD-ID changes the
value of EXPR. If any other threads change the value of EXPR, GDB
will not break. Note that watchpoints restricted to a single
thread in this way only work with Hardware Watchpoints.

Similarly, if the `task' argument is given, then the watchpoint
will be specific to the indicated Ada task (*note Ada Tasks::).

Ordinarily a watchpoint respects the scope of variables in EXPR
(see below). The `-location' argument tells GDB to instead watch
the memory referred to by EXPR. In this case, GDB will evaluate
EXPR, take the address of the result, and watch the memory at that
address. The type of the result is used to determine the size of
the watched memory. If the expression's result does not have an
address, then GDB will print an error.

The `[mask MASKVALUE]' argument allows creation of masked
watchpoints, if the current architecture supports this feature
(e.g., PowerPC Embedded architecture, see *Note PowerPC
Embedded::.) A "masked watchpoint" specifies a mask in addition
to an address to watch. The mask specifies that some bits of an
address (the bits which are reset in the mask) should be ignored
when matching the address accessed by the inferior against the
watchpoint address. Thus, a masked watchpoint watches many
addresses simultaneously--those addresses whose unmasked bits are
identical to the unmasked bits in the watchpoint address. The
`mask' argument implies `-location'. Examples:

(gdb) watch foo mask 0xffff00ff
(gdb) watch *0xdeadbeef mask 0xffffff00

`rwatch [-l|-location] EXPR [thread THREAD-ID] [mask MASKVALUE]'
Set a watchpoint that will break when the value of EXPR is read by
the program.

`awatch [-l|-location] EXPR [thread THREAD-ID] [mask MASKVALUE]'
Set a watchpoint that will break when EXPR is either read from or
written into by the program.

`info watchpoints [LIST...]'
This command prints a list of watchpoints, using the same format as
`info break' (*note Set Breaks::).

If you watch for a change in a numerically entered address you need
to dereference it, as the address itself is just a constant number
which will never change. GDB refuses to create a watchpoint that
watches a never-changing value:

(gdb) watch 0x600850
Cannot watch constant value 0x600850.
(gdb) watch *(int *) 0x600850
Watchpoint 1: *(int *) 6293584

GDB sets a "hardware watchpoint" if possible. Hardware watchpoints
execute very quickly, and the debugger reports a change in value at the
exact instruction where the change occurs. If GDB cannot set a
hardware watchpoint, it sets a software watchpoint, which executes more
slowly and reports the change in value at the next _statement_, not the
instruction, after the change occurs.

You can force GDB to use only software watchpoints with the `set
can-use-hw-watchpoints 0' command. With this variable set to zero, GDB
will never try to use hardware watchpoints, even if the underlying
system supports them. (Note that hardware-assisted watchpoints that
were set _before_ setting `can-use-hw-watchpoints' to zero will still
use the hardware mechanism of watching expression values.)

`set can-use-hw-watchpoints'
Set whether or not to use hardware watchpoints.

`show can-use-hw-watchpoints'
Show the current mode of using hardware watchpoints.

For remote targets, you can restrict the number of hardware
watchpoints GDB will use, see *Note set remote
hardware-breakpoint-limit::.

When you issue the `watch' command, GDB reports

Hardware watchpoint NUM: EXPR

if it was able to set a hardware watchpoint.

Currently, the `awatch' and `rwatch' commands can only set hardware
watchpoints, because accesses to data that don't change the value of
the watched expression cannot be detected without examining every
instruction as it is being executed, and GDB does not do that
currently. If GDB finds that it is unable to set a hardware breakpoint
with the `awatch' or `rwatch' command, it will print a message like
this:

Expression cannot be implemented with read/access watchpoint.

Sometimes, GDB cannot set a hardware watchpoint because the data
type of the watched expression is wider than what a hardware watchpoint
on the target machine can handle. For example, some systems can only
watch regions that are up to 4 bytes wide; on such systems you cannot
set hardware watchpoints for an expression that yields a
double-precision floating-point number (which is typically 8 bytes
wide). As a work-around, it might be possible to break the large region
into a series of smaller ones and watch them with separate watchpoints.

If you set too many hardware watchpoints, GDB might be unable to
insert all of them when you resume the execution of your program.
Since the precise number of active watchpoints is unknown until such
time as the program is about to be resumed, GDB might not be able to
warn you about this when you set the watchpoints, and the warning will
be printed only when the program is resumed:

Hardware watchpoint NUM: Could not insert watchpoint

If this happens, delete or disable some of the watchpoints.

Watching complex expressions that reference many variables can also
exhaust the resources available for hardware-assisted watchpoints.
That's because GDB needs to watch every variable in the expression with
separately allocated resources.

If you call a function interactively using `print' or `call', any
watchpoints you have set will be inactive until GDB reaches another
kind of breakpoint or the call completes.

GDB automatically deletes watchpoints that watch local (automatic)
variables, or expressions that involve such variables, when they go out
of scope, that is, when the execution leaves the block in which these
variables were defined. In particular, when the program being debugged
terminates, _all_ local variables go out of scope, and so only
watchpoints that watch global variables remain set. If you rerun the
program, you will need to set all such watchpoints again. One way of
doing that would be to set a code breakpoint at the entry to the `main'
function and when it breaks, set all the watchpoints.

In multi-threaded programs, watchpoints will detect changes to the
watched expression from every thread.

_Warning:_ In multi-threaded programs, software watchpoints have
only limited usefulness. If GDB creates a software watchpoint, it
can only watch the value of an expression _in a single thread_.
If you are confident that the expression can only change due to
the current thread's activity (and if you are also confident that
no other thread can become current), then you can use software
watchpoints as usual. However, GDB may not notice when a
non-current thread's activity changes the expression. (Hardware
watchpoints, in contrast, watch an expression in all threads.)

*Note set remote hardware-watchpoint-limit::.

File: gdb.info, Node: Set Catchpoints, Next: Delete Breaks, Prev: Set Watchpoints, Up: Breakpoints

5.1.3 Setting Catchpoints
-------------------------

You can use "catchpoints" to cause the debugger to stop for certain
kinds of program events, such as C++ exceptions or the loading of a
shared library. Use the `catch' command to set a catchpoint.

`catch EVENT'
Stop when EVENT occurs. The EVENT can be any of the following:

`throw [REGEXP]'
`rethrow [REGEXP]'
`catch [REGEXP]'
The throwing, re-throwing, or catching of a C++ exception.

If REGEXP is given, then only exceptions whose type matches
the regular expression will be caught.

The convenience variable `$_exception' is available at an
exception-related catchpoint, on some systems. This holds the
exception being thrown.

There are currently some limitations to C++ exception
handling in GDB:

* The support for these commands is system-dependent.
Currently, only systems using the `gnu-v3' C++ ABI
(*note ABI::) are supported.

* The regular expression feature and the `$_exception'
convenience variable rely on the presence of some SDT
probes in `libstdc++'. If these probes are not present,
then these features cannot be used. These probes were
first available in the GCC 4.8 release, but whether or
not they are available in your GCC also depends on how
it was built.

* The `$_exception' convenience variable is only valid at
the instruction at which an exception-related catchpoint
is set.

* When an exception-related catchpoint is hit, GDB stops
at a location in the system library which implements
runtime exception support for C++, usually `libstdc++'.
You can use `up' (*note Selection::) to get to your code.

* If you call a function interactively, GDB normally
returns control to you when the function has finished
executing. If the call raises an exception, however,
the call may bypass the mechanism that returns control
to you and cause your program either to abort or to
simply continue running until it hits a breakpoint,
catches a signal that GDB is listening for, or exits.
This is the case even if you set a catchpoint for the
exception; catchpoints on exceptions are disabled within
interactive calls. *Note Calling::, for information on
controlling this with `set
unwind-on-terminating-exception'.

* You cannot raise an exception interactively.

* You cannot install an exception handler interactively.

`exception [NAME]'
An Ada exception being raised. If an exception name is
specified at the end of the command (eg `catch exception
Program_Error'), the debugger will stop only when this
specific exception is raised. Otherwise, the debugger stops
execution when any Ada exception is raised.

When inserting an exception catchpoint on a user-defined
exception whose name is identical to one of the exceptions
defined by the language, the fully qualified name must be
used as the exception name. Otherwise, GDB will assume that
it should stop on the pre-defined exception rather than the
user-defined one. For instance, assuming an exception called
`Constraint_Error' is defined in package `Pck', then the
command to use to catch such exceptions is `catch exception
Pck.Constraint_Error'.

The convenience variable `$_ada_exception' holds the address
of the exception being thrown. This can be useful when
setting a condition for such a catchpoint.

`exception unhandled'
An exception that was raised but is not handled by the
program. The convenience variable `$_ada_exception' is set
as for `catch exception'.

`handlers [NAME]'
An Ada exception being handled. If an exception name is
specified at the end of the command (eg `catch handlers
Program_Error'), the debugger will stop only when this
specific exception is handled. Otherwise, the debugger stops
execution when any Ada exception is handled.

When inserting a handlers catchpoint on a user-defined
exception whose name is identical to one of the exceptions
defined by the language, the fully qualified name must be used
as the exception name. Otherwise, GDB will assume that it
should stop on the pre-defined exception rather than the
user-defined one. For instance, assuming an exception called
`Constraint_Error' is defined in package `Pck', then the
command to use to catch such exceptions handling is `catch
handlers Pck.Constraint_Error'.

The convenience variable `$_ada_exception' is set as for
`catch exception'.

`assert'
A failed Ada assertion. Note that the convenience variable
`$_ada_exception' is _not_ set by this catchpoint.

`exec'
A call to `exec'.

`syscall'
`syscall [NAME | NUMBER | group:GROUPNAME | g:GROUPNAME] ...'
A call to or return from a system call, a.k.a. "syscall". A
syscall is a mechanism for application programs to request a
service from the operating system (OS) or one of the OS
system services. GDB can catch some or all of the syscalls
issued by the debuggee, and show the related information for
each syscall. If no argument is specified, calls to and
returns from all system calls will be caught.

NAME can be any system call name that is valid for the
underlying OS. Just what syscalls are valid depends on the
OS. On GNU and Unix systems, you can find the full list of
valid syscall names on `/usr/include/asm/unistd.h'.

Normally, GDB knows in advance which syscalls are valid for
each OS, so you can use the GDB command-line completion
facilities (*note command completion: Completion.) to list the
available choices.

You may also specify the system call numerically. A syscall's
number is the value passed to the OS's syscall dispatcher to
identify the requested service. When you specify the syscall
by its name, GDB uses its database of syscalls to convert the
name into the corresponding numeric code, but using the
number directly may be useful if GDB's database does not have
the complete list of syscalls on your system (e.g., because
GDB lags behind the OS upgrades).

You may specify a group of related syscalls to be caught at
once using the `group:' syntax (`g:' is a shorter
equivalent). For instance, on some platforms GDB allows you
to catch all network related syscalls, by passing the
argument `group:network' to `catch syscall'. Note that not
all syscall groups are available in every system. You can
use the command completion facilities (*note command
completion: Completion.) to list the syscall groups available
on your environment.

The example below illustrates how this command works if you
don't provide arguments to it:

(gdb) catch syscall
Catchpoint 1 (syscall)
(gdb) r
Starting program: /tmp/catch-syscall

Catchpoint 1 (call to syscall 'close'), \
0xffffe424 in __kernel_vsyscall ()
(gdb) c
Continuing.

Catchpoint 1 (returned from syscall 'close'), \
0xffffe424 in __kernel_vsyscall ()
(gdb)

Here is an example of catching a system call by name:

(gdb) catch syscall chroot
Catchpoint 1 (syscall 'chroot' [61])
(gdb) r
Starting program: /tmp/catch-syscall

Catchpoint 1 (call to syscall 'chroot'), \
0xffffe424 in __kernel_vsyscall ()
(gdb) c
Continuing.

Catchpoint 1 (returned from syscall 'chroot'), \
0xffffe424 in __kernel_vsyscall ()
(gdb)

An example of specifying a system call numerically. In the
case below, the syscall number has a corresponding entry in
the XML file, so GDB finds its name and prints it:

(gdb) catch syscall 252
Catchpoint 1 (syscall(s) 'exit_group')
(gdb) r
Starting program: /tmp/catch-syscall

Catchpoint 1 (call to syscall 'exit_group'), \
0xffffe424 in __kernel_vsyscall ()
(gdb) c
Continuing.

Program exited normally.
(gdb)

Here is an example of catching a syscall group:

(gdb) catch syscall group:process
Catchpoint 1 (syscalls 'exit' [1] 'fork' [2] 'waitpid' [7]
'execve' [11] 'wait4' [114] 'clone' [120] 'vfork' [190]
'exit_group' [252] 'waitid' [284] 'unshare' [310])
(gdb) r
Starting program: /tmp/catch-syscall

Catchpoint 1 (call to syscall fork), 0x00007ffff7df4e27 in open64 ()
from /lib64/ld-linux-x86-64.so.2

(gdb) c
Continuing.

However, there can be situations when there is no
corresponding name in XML file for that syscall number. In
this case, GDB prints a warning message saying that it was
not able to find the syscall name, but the catchpoint will be
set anyway. See the example below:

(gdb) catch syscall 764
warning: The number '764' does not represent a known syscall.
Catchpoint 2 (syscall 764)
(gdb)

If you configure GDB using the `--without-expat' option, it
will not be able to display syscall names. Also, if your
architecture does not have an XML file describing its system
calls, you will not be able to see the syscall names. It is
important to notice that these two features are used for
accessing the syscall name database. In either case, you
will see a warning like this:

(gdb) catch syscall
warning: Could not open "syscalls/i386-linux.xml"
warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
GDB will not be able to display syscall names.
Catchpoint 1 (syscall)
(gdb)

Of course, the file name will change depending on your
architecture and system.

Still using the example above, you can also try to catch a
syscall by its number. In this case, you would see something
like:

(gdb) catch syscall 252
Catchpoint 1 (syscall(s) 252)

Again, in this case GDB would not be able to display
syscall's names.

`fork'
A call to `fork'.

`vfork'
A call to `vfork'.

`load [REGEXP]'
`unload [REGEXP]'
The loading or unloading of a shared library. If REGEXP is
given, then the catchpoint will stop only if the regular
expression matches one of the affected libraries.

`signal [SIGNAL... | `all']'
The delivery of a signal.

With no arguments, this catchpoint will catch any signal that
is not used internally by GDB, specifically, all signals
except `SIGTRAP' and `SIGINT'.

With the argument `all', all signals, including those used by
GDB, will be caught. This argument cannot be used with other
signal names.

Otherwise, the arguments are a list of signal names as given
to `handle' (*note Signals::). Only signals specified in
this list will be caught.

One reason that `catch signal' can be more useful than
`handle' is that you can attach commands and conditions to the
catchpoint.

When a signal is caught by a catchpoint, the signal's `stop'
and `print' settings, as specified by `handle', are ignored.
However, whether the signal is still delivered to the
inferior depends on the `pass' setting; this can be changed
in the catchpoint's commands.

`tcatch EVENT'
Set a catchpoint that is enabled only for one stop. The
catchpoint is automatically deleted after the first time the event
is caught.

Use the `info break' command to list the current catchpoints.

File: gdb.info, Node: Delete Breaks, Next: Disabling, Prev: Set Catchpoints, Up: Breakpoints

5.1.4 Deleting Breakpoints
--------------------------

It is often necessary to eliminate a breakpoint, watchpoint, or
catchpoint once it has done its job and you no longer want your program
to stop there. This is called "deleting" the breakpoint. A breakpoint
that has been deleted no longer exists; it is forgotten.

With the `clear' command you can delete breakpoints according to
where they are in your program. With the `delete' command you can
delete individual breakpoints, watchpoints, or catchpoints by specifying
their breakpoint numbers.

It is not necessary to delete a breakpoint to proceed past it. GDB
automatically ignores breakpoints on the first instruction to be
executed when you continue execution without changing the execution
address.

`clear'
Delete any breakpoints at the next instruction to be executed in
the selected stack frame (*note Selecting a Frame: Selection.).
When the innermost frame is selected, this is a good way to delete
a breakpoint where your program just stopped.

`clear LOCSPEC'
Delete any breakpoint with a code location that corresponds to
LOCSPEC. *Note Location Specifications::, for the various forms
of LOCSPEC. Which code locations correspond to LOCSPEC depends on
the form used in the location specification LOCSPEC:

`LINENUM'
`FILENAME:LINENUM'
`-line LINENUM'
`-source FILENAME -line LINENUM'
If LOCSPEC specifies a line number, with or without a file
name, the command deletes any breakpoint with a code location
that is at or within the specified line LINENUM in files that
match the specified FILENAME. If FILENAME is omitted, it
defaults to the current source file.

`*ADDRESS'
If LOCSPEC specifies an address, the command deletes any
breakpoint with a code location that is at the given ADDRESS.

`FUNCTION'
`-function FUNCTION'
If LOCSPEC specifies a function, the command deletes any
breakpoint with a code location that is at the entry to any
function whose name matches FUNCTION.

Ambiguity in names of files and functions can be resolved as
described in *Note Location Specifications::.

`delete [breakpoints] [LIST...]'
Delete the breakpoints, watchpoints, tracepoints, or catchpoints
of the breakpoint list specified as argument. If no argument is
specified, delete all breakpoints, watchpoints, tracepoints, and
catchpoints (GDB asks confirmation, unless you have `set confirm
off'). You can abbreviate this command as `d'.

File: gdb.info, Node: Disabling, Next: Conditions, Prev: Delete Breaks, Up: Breakpoints

5.1.5 Disabling Breakpoints
---------------------------

Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
prefer to "disable" it. This makes the breakpoint inoperative as if it
had been deleted, but remembers the information on the breakpoint so
that you can "enable" it again later.

You disable and enable breakpoints, watchpoints, tracepoints, and
catchpoints with the `enable' and `disable' commands, optionally
specifying one or more breakpoint numbers as arguments. Use `info
break' to print a list of all breakpoints, watchpoints, tracepoints,
and catchpoints if you do not know which numbers to use.

Disabling and enabling a breakpoint that has multiple locations
affects all of its locations.

A breakpoint, watchpoint, or catchpoint can have any of several
different states of enablement:

* Enabled. The breakpoint stops your program. A breakpoint set
with the `break' command starts out in this state.

* Disabled. The breakpoint has no effect on your program.

* Enabled once. The breakpoint stops your program, but then becomes
disabled.

* Enabled for a count. The breakpoint stops your program for the
next N times, then becomes disabled.

* Enabled for deletion. The breakpoint stops your program, but
immediately after it does so it is deleted permanently. A
breakpoint set with the `tbreak' command starts out in this state.

You can use the following commands to enable or disable breakpoints,
watchpoints, tracepoints, and catchpoints:

`disable [breakpoints] [LIST...]'
Disable the specified breakpoints--or all breakpoints, if none are
listed. A disabled breakpoint has no effect but is not forgotten.
All options such as ignore-counts, conditions and commands are
remembered in case the breakpoint is enabled again later. You may
abbreviate `disable' as `dis'.

`enable [breakpoints] [LIST...]'
Enable the specified breakpoints (or all defined breakpoints).
They become effective once again in stopping your program.

`enable [breakpoints] once LIST...'
Enable the specified breakpoints temporarily. GDB disables any of
these breakpoints immediately after stopping your program.

`enable [breakpoints] count COUNT LIST...'
Enable the specified breakpoints temporarily. GDB records COUNT
with each of the specified breakpoints, and decrements a
breakpoint's count when it is hit. When any count reaches 0, GDB
disables that breakpoint. If a breakpoint has an ignore count
(*note Break Conditions: Conditions.), that will be decremented to
0 before COUNT is affected.

`enable [breakpoints] delete LIST...'
Enable the specified breakpoints to work once, then die. GDB
deletes any of these breakpoints as soon as your program stops
there. Breakpoints set by the `tbreak' command start out in this
state.

Except for a breakpoint set with `tbreak' (*note Setting
Breakpoints: Set Breaks.), breakpoints that you set are initially
enabled; subsequently, they become disabled or enabled only when you
use one of the commands above. (The command `until' can set and delete
a breakpoint of its own, but it does not change the state of your other
breakpoints; see *Note Continuing and Stepping: Continuing and
Stepping.)

File: gdb.info, Node: Conditions, Next: Break Commands, Prev: Disabling, Up: Breakpoints

5.1.6 Break Conditions
----------------------

The simplest sort of breakpoint breaks every time your program reaches a
specified place. You can also specify a "condition" for a breakpoint.
A condition is just a Boolean expression in your programming language
(*note Expressions: Expressions.). A breakpoint with a condition
evaluates the expression each time your program reaches it, and your
program stops only if the condition is _true_.

This is the converse of using assertions for program validation; in
that situation, you want to stop when the assertion is violated--that
is, when the condition is false. In C, if you want to test an
assertion expressed by the condition ASSERT, you should set the
condition `! ASSERT' on the appropriate breakpoint.

Conditions are also accepted for watchpoints; you may not need them,
since a watchpoint is inspecting the value of an expression anyhow--but
it might be simpler, say, to just set a watchpoint on a variable name,
and specify a condition that tests whether the new value is an
interesting one.

Break conditions can have side effects, and may even call functions
in your program. This can be useful, for example, to activate functions
that log program progress, or to use your own print functions to format
special data structures. The effects are completely predictable unless
there is another enabled breakpoint at the same address. (In that
case, GDB might see the other breakpoint first and stop your program
without checking the condition of this one.) Note that breakpoint
commands are usually more convenient and flexible than break conditions
for the purpose of performing side effects when a breakpoint is reached
(*note Breakpoint Command Lists: Break Commands.).

Breakpoint conditions can also be evaluated on the target's side if
the target supports it. Instead of evaluating the conditions locally,
GDB encodes the expression into an agent expression (*note Agent
Expressions::) suitable for execution on the target, independently of
GDB. Global variables become raw memory locations, locals become stack
accesses, and so forth.

In this case, GDB will only be notified of a breakpoint trigger when
its condition evaluates to true. This mechanism may provide faster
response times depending on the performance characteristics of the
target since it does not need to keep GDB informed about every
breakpoint trigger, even those with false conditions.

Break conditions can be specified when a breakpoint is set, by using
`if' in the arguments to the `break' command. *Note Setting
Breakpoints: Set Breaks. They can also be changed at any time with the
`condition' command.

You can also use the `if' keyword with the `watch' command. The
`catch' command does not recognize the `if' keyword; `condition' is the
only way to impose a further condition on a catchpoint.

`condition BNUM EXPRESSION'
Specify EXPRESSION as the break condition for breakpoint,
watchpoint, or catchpoint number BNUM. After you set a condition,
breakpoint BNUM stops your program only if the value of EXPRESSION
is true (nonzero, in C). When you use `condition', GDB checks
EXPRESSION immediately for syntactic correctness, and to determine
whether symbols in it have referents in the context of your
breakpoint. If EXPRESSION uses symbols not referenced in the
context of the breakpoint, GDB prints an error message:

No symbol "foo" in current context.

GDB does not actually evaluate EXPRESSION at the time the
`condition' command (or a command that sets a breakpoint with a
condition, like `break if ...') is given, however. *Note
Expressions: Expressions.

`condition -force BNUM EXPRESSION'
When the `-force' flag is used, define the condition even if
EXPRESSION is invalid at all the current locations of breakpoint
BNUM. This is similar to the `-force-condition' option of the
`break' command.

`condition BNUM'
Remove the condition from breakpoint number BNUM. It becomes an
ordinary unconditional breakpoint.

A special case of a breakpoint condition is to stop only when the
breakpoint has been reached a certain number of times. This is so
useful that there is a special way to do it, using the "ignore count"
of the breakpoint. Every breakpoint has an ignore count, which is an
integer. Most of the time, the ignore count is zero, and therefore has
no effect. But if your program reaches a breakpoint whose ignore count
is positive, then instead of stopping, it just decrements the ignore
count by one and continues. As a result, if the ignore count value is
N, the breakpoint does not stop the next N times your program reaches
it.

`ignore BNUM COUNT'
Set the ignore count of breakpoint number BNUM to COUNT. The next
COUNT times the breakpoint is reached, your program's execution
does not stop; other than to decrement the ignore count, GDB takes
no action.

To make the breakpoint stop the next time it is reached, specify a
count of zero.

When you use `continue' to resume execution of your program from a
breakpoint, you can specify an ignore count directly as an
argument to `continue', rather than using `ignore'. *Note
Continuing and Stepping: Continuing and Stepping.

If a breakpoint has a positive ignore count and a condition, the
condition is not checked. Once the ignore count reaches zero, GDB
resumes checking the condition.

You could achieve the effect of the ignore count with a condition
such as `$foo-- <= 0' using a debugger convenience variable that
is decremented each time. *Note Convenience Variables:
Convenience Vars.

Ignore counts apply to breakpoints, watchpoints, tracepoints, and
catchpoints.

File: gdb.info, Node: Break Commands, Next: Dynamic Printf, Prev: Conditions, Up: Breakpoints

5.1.7 Breakpoint Command Lists
------------------------------

You can give any breakpoint (or watchpoint or catchpoint) a series of
commands to execute when your program stops due to that breakpoint. For
example, you might want to print the values of certain expressions, or
enable other breakpoints.

`commands [LIST...]'
`... COMMAND-LIST ...'
`end'
Specify a list of commands for the given breakpoints. The commands
themselves appear on the following lines. Type a line containing
just `end' to terminate the commands.

To remove all commands from a breakpoint, type `commands' and
follow it immediately with `end'; that is, give no commands.

With no argument, `commands' refers to the last breakpoint,
watchpoint, or catchpoint set (not to the breakpoint most recently
encountered). If the most recent breakpoints were set with a
single command, then the `commands' will apply to all the
breakpoints set by that command. This applies to breakpoints set
by `rbreak', and also applies when a single `break' command
creates multiple breakpoints (*note Ambiguous Expressions:
Ambiguous Expressions.).

Pressing <RET> as a means of repeating the last GDB command is
disabled within a COMMAND-LIST.

Inside a command list, you can use the command `disable $_hit_bpnum'
to disable the encountered breakpoint.

If your breakpoint has several code locations, the command `disable
$_hit_bpnum.$_hit_locno' will disable the specific breakpoint code
location encountered. If the breakpoint has only one location, this
command will disable the encountered breakpoint.

You can use breakpoint commands to start your program up again.
Simply use the `continue' command, or `step', or any other command that
resumes execution.

Any other commands in the command list, after a command that resumes
execution, are ignored. This is because any time you resume execution
(even with a simple `next' or `step'), you may encounter another
breakpoint--which could have its own command list, leading to
ambiguities about which list to execute.

If the first command you specify in a command list is `silent', the
usual message about stopping at a breakpoint is not printed. This may
be desirable for breakpoints that are to print a specific message and
then continue. If none of the remaining commands print anything, you
see no sign that the breakpoint was reached. `silent' is meaningful
only at the beginning of a breakpoint command list.

The commands `echo', `output', and `printf' allow you to print
precisely controlled output, and are often useful in silent
breakpoints. *Note Commands for Controlled Output: Output.

For example, here is how you could use breakpoint commands to print
the value of `x' at entry to `foo' whenever `x' is positive.

break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end

One application for breakpoint commands is to compensate for one bug
so you can test for another. Put a breakpoint just after the erroneous
line of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them. End with the `continue' command so
that your program does not stop, and start with the `silent' command so
that no output is produced. Here is an example:

break 403
commands
silent
set x = y + 4
cont
end

File: gdb.info, Node: Dynamic Printf, Next: Save Breakpoints, Prev: Break Commands, Up: Breakpoints

5.1.8 Dynamic Printf
--------------------

The dynamic printf command `dprintf' combines a breakpoint with
formatted printing of your program's data to give you the effect of
inserting `printf' calls into your program on-the-fly, without having
to recompile it.

In its most basic form, the output goes to the GDB console. However,
you can set the variable `dprintf-style' for alternate handling. For
instance, you can ask to format the output by calling your program's
`printf' function. This has the advantage that the characters go to
the program's output device, so they can recorded in redirects to files
and so forth.

If you are doing remote debugging with a stub or agent, you can also
ask to have the printf handled by the remote agent. In addition to
ensuring that the output goes to the remote program's device along with
any other output the program might produce, you can also ask that the
dprintf remain active even after disconnecting from the remote target.
Using the stub/agent is also more efficient, as it can do everything
without needing to communicate with GDB.

`dprintf LOCSPEC,TEMPLATE,EXPRESSION[,EXPRESSION...]'
Whenever execution reaches a code location that results from
resolving LOCSPEC, print the values of one or more EXPRESSIONS
under the control of the string TEMPLATE. To print several values,
separate them with commas.

`set dprintf-style STYLE'
Set the dprintf output to be handled in one of several different
styles enumerated below. A change of style affects all existing
dynamic printfs immediately. (If you need individual control over
the print commands, simply define normal breakpoints with
explicitly-supplied command lists.)

`gdb'
Handle the output using the GDB `printf' command. When using
this style, it is possible to use the `%V' format specifier
(*note %V Format Specifier::).

`call'
Handle the output by calling a function in your program
(normally `printf'). When using this style the supported
format specifiers depend entirely on the function being
called.

Most of GDB's format specifiers align with those supported by
the `printf' function, however, GDB's `%V' format specifier
extension is not supported by `printf'. When using `call'
style dprintf, care should be taken to ensure that only
format specifiers supported by the output function are used,
otherwise the results will be undefined.

`agent'
Have the remote debugging agent (such as `gdbserver') handle
the output itself. This style is only available for agents
that support running commands on the target. This style does
not support the `%V' format specifier.

`set dprintf-function FUNCTION'
Set the function to call if the dprintf style is `call'. By
default its value is `printf'. You may set it to any expression
that GDB can evaluate to a function, as per the `call' command.

`set dprintf-channel CHANNEL'
Set a "channel" for dprintf. If set to a non-empty value, GDB
will evaluate it as an expression and pass the result as a first
argument to the `dprintf-function', in the manner of `fprintf' and
similar functions. Otherwise, the dprintf format string will be
the first argument, in the manner of `printf'.

As an example, if you wanted `dprintf' output to go to a logfile
that is a standard I/O stream assigned to the variable `mylog',
you could do the following:

(gdb) set dprintf-style call
(gdb) set dprintf-function fprintf
(gdb) set dprintf-channel mylog
(gdb) dprintf 25,"at line 25, glob=%d\n",glob
Dprintf 1 at 0x123456: file main.c, line 25.
(gdb) info break
1 dprintf keep y 0x00123456 in main at main.c:25
call (void) fprintf (mylog,"at line 25, glob=%d\n",glob)
continue
(gdb)

Note that the `info break' displays the dynamic printf commands as
normal breakpoint commands; you can thus easily see the effect of
the variable settings.

`set disconnected-dprintf on'
`set disconnected-dprintf off'
Choose whether `dprintf' commands should continue to run if GDB
has disconnected from the target. This only applies if the
`dprintf-style' is `agent'.

`show disconnected-dprintf off'
Show the current choice for disconnected `dprintf'.

GDB does not check the validity of function and channel, relying on
you to supply values that are meaningful for the contexts in which they
are being used. For instance, the function and channel may be the
values of local variables, but if that is the case, then all enabled
dynamic prints must be at locations within the scope of those locals.
If evaluation fails, GDB will report an error.

File: gdb.info, Node: Save Breakpoints, Next: Static Probe Points, Prev: Dynamic Printf, Up: Breakpoints

5.1.9 How to save breakpoints to a file
---------------------------------------

To save breakpoint definitions to a file use the `save breakpoints'
command.

`save breakpoints [FILENAME]'
This command saves all current breakpoint definitions together with
their commands and ignore counts, into a file `FILENAME' suitable
for use in a later debugging session. This includes all types of
breakpoints (breakpoints, watchpoints, catchpoints, tracepoints).
To read the saved breakpoint definitions, use the `source' command
(*note Command Files::). Note that watchpoints with expressions
involving local variables may fail to be recreated because it may
not be possible to access the context where the watchpoint is
valid anymore. Because the saved breakpoint definitions are
simply a sequence of GDB commands that recreate the breakpoints,
you can edit the file in your favorite editing program, and remove
the breakpoint definitions you're not interested in, or that can
no longer be recreated.

File: gdb.info, Node: Static Probe Points, Next: Error in Breakpoints, Prev: Save Breakpoints, Up: Breakpoints

5.1.10 Static Probe Points
--------------------------

GDB supports "SDT" probes in the code. SDT stands for Statically
Defined Tracing, and the probes are designed to have a tiny runtime
code and data footprint, and no dynamic relocations.

Currently, the following types of probes are supported on
ELF-compatible systems:

* `SystemTap' (`http://sourceware.org/systemtap/') SDT probes(1).
`SystemTap' probes are usable from assembly, C and C++
languages(2).

* `DTrace' (`http://oss.oracle.com/projects/DTrace') USDT probes.
`DTrace' probes are usable from C and C++ languages.

Some `SystemTap' probes have an associated semaphore variable; for
instance, this happens automatically if you defined your probe using a
DTrace-style `.d' file. If your probe has a semaphore, GDB will
automatically enable it when you specify a breakpoint using the
`-probe-stap' notation. But, if you put a breakpoint at a probe's
location by some other method (e.g., `break file:line'), then GDB will
not automatically set the semaphore. `DTrace' probes do not support
semaphores.

You can examine the available static static probes using `info
probes', with optional arguments:

`info probes [TYPE] [PROVIDER [NAME [OBJFILE]]]'
If given, TYPE is either `stap' for listing `SystemTap' probes or
`dtrace' for listing `DTrace' probes. If omitted all probes are
listed regardless of their types.

If given, PROVIDER is a regular expression used to match against
provider names when selecting which probes to list. If omitted,
probes by all probes from all providers are listed.

If given, NAME is a regular expression to match against probe names
when selecting which probes to list. If omitted, probe names are
not considered when deciding whether to display them.

If given, OBJFILE is a regular expression used to select which
object files (executable or shared libraries) to examine. If not
given, all object files are considered.

`info probes all'
List the available static probes, from all types.

Some probe points can be enabled and/or disabled. The effect of
enabling or disabling a probe depends on the type of probe being
handled. Some `DTrace' probes can be enabled or disabled, but
`SystemTap' probes cannot be disabled.

You can enable (or disable) one or more probes using the following
commands, with optional arguments:

`enable probes [PROVIDER [NAME [OBJFILE]]]'
If given, PROVIDER is a regular expression used to match against
provider names when selecting which probes to enable. If omitted,
all probes from all providers are enabled.

If given, NAME is a regular expression to match against probe
names when selecting which probes to enable. If omitted, probe
names are not considered when deciding whether to enable them.

If given, OBJFILE is a regular expression used to select which
object files (executable or shared libraries) to examine. If not
given, all object files are considered.

`disable probes [PROVIDER [NAME [OBJFILE]]]'
See the `enable probes' command above for a description of the
optional arguments accepted by this command.

A probe may specify up to twelve arguments. These are available at
the point at which the probe is defined--that is, when the current PC is
at the probe's location. The arguments are available using the
convenience variables (*note Convenience Vars::)
`$_probe_arg0'...`$_probe_arg11'. In `SystemTap' probes each probe
argument is an integer of the appropriate size; types are not
preserved. In `DTrace' probes types are preserved provided that they
are recognized as such by GDB; otherwise the value of the probe
argument will be a long integer. The convenience variable
`$_probe_argc' holds the number of arguments at the current probe point.

These variables are always available, but attempts to access them at
any location other than a probe point will cause GDB to give an error
message.

---------- Footnotes ----------

(1) See
`http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps' for
more information on how to add `SystemTap' SDT probes in your
applications.

(2) See
`http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation' for
a good reference on how the SDT probes are implemented.

File: gdb.info, Node: Error in Breakpoints, Next: Breakpoint-related Warnings, Prev: Static Probe Points, Up: Breakpoints

5.1.11 "Cannot insert breakpoints"
----------------------------------

If you request too many active hardware-assisted breakpoints and
watchpoints, you will see this error message:

Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.

This message is printed when you attempt to resume the program, since
only then GDB knows exactly how many hardware breakpoints and
watchpoints it needs to insert.

When this message is printed, you need to disable or remove some of
the hardware-assisted breakpoints and watchpoints, and then continue.

File: gdb.info, Node: Breakpoint-related Warnings, Prev: Error in Breakpoints, Up: Breakpoints

5.1.12 "Breakpoint address adjusted..."
---------------------------------------

Some processor architectures place constraints on the addresses at
which breakpoints may be placed. For architectures thus constrained,
GDB will attempt to adjust the breakpoint's address to comply with the
constraints dictated by the architecture.

One example of such an architecture is the Fujitsu FR-V. The FR-V is
a VLIW architecture in which a number of RISC-like instructions may be
bundled together for parallel execution. The FR-V architecture
constrains the location of a breakpoint instruction within such a
bundle to the instruction with the lowest address. GDB honors this
constraint by adjusting a breakpoint's address to the first in the
bundle.

It is not uncommon for optimized code to have bundles which contain
instructions from different source statements, thus it may happen that
a breakpoint's address will be adjusted from one source statement to
another. Since this adjustment may significantly alter GDB's
breakpoint related behavior from what the user expects, a warning is
printed when the breakpoint is first set and also when the breakpoint
is hit.

A warning like the one below is printed when setting a breakpoint
that's been subject to address adjustment:

warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.

Such warnings are printed both for user settable and GDB's internal
breakpoints. If you see one of these warnings, you should verify that
a breakpoint set at the adjusted address will have the desired affect.
If not, the breakpoint in question may be removed and other breakpoints
may be set which will have the desired behavior. E.g., it may be
sufficient to place the breakpoint at a later instruction. A
conditional breakpoint may also be useful in some cases to prevent the
breakpoint from triggering too often.

GDB will also issue a warning when stopping at one of these adjusted
breakpoints:

warning: Breakpoint 1 address previously adjusted from 0x00010414
to 0x00010410.

When this warning is encountered, it may be too late to take remedial
action except in cases where the breakpoint is hit earlier or more
frequently than expected.

File: gdb.info, Node: Continuing and Stepping, Next: Skipping Over Functions and Files, Prev: Breakpoints, Up: Stopping

5.2 Continuing and Stepping
===========================

"Continuing" means resuming program execution until your program
completes normally. In contrast, "stepping" means executing just one
more "step" of your program, where "step" may mean either one line of
source code, or one machine instruction (depending on what particular
command you use). Either when continuing or when stepping, your
program may stop even sooner, due to a breakpoint or a signal. (If it
stops due to a signal, you may want to use `handle', or use `signal 0'
to resume execution (*note Signals: Signals.), or you may step into the
signal's handler (*note stepping and signal handlers::).)

`continue [IGNORE-COUNT]'
`c [IGNORE-COUNT]'
`fg [IGNORE-COUNT]'
Resume program execution, at the address where your program last
stopped; any breakpoints set at that address are bypassed. The
optional argument IGNORE-COUNT allows you to specify a further
number of times to ignore a breakpoint at this location; its
effect is like that of `ignore' (*note Break Conditions:
Conditions.).

The argument IGNORE-COUNT is meaningful only when your program
stopped due to a breakpoint. At other times, the argument to
`continue' is ignored.

The synonyms `c' and `fg' (for "foreground", as the debugged
program is deemed to be the foreground program) are provided
purely for convenience, and have exactly the same behavior as
`continue'.

To resume execution at a different place, you can use `return'
(*note Returning from a Function: Returning.) to go back to the calling
function; or `jump' (*note Continuing at a Different Address: Jumping.)
to go to an arbitrary location in your program.

A typical technique for using stepping is to set a breakpoint (*note
Breakpoints; Watchpoints; and Catchpoints: Breakpoints.) at the
beginning of the function or the section of your program where a problem
is believed to lie, run your program until it stops at that breakpoint,
and then step through the suspect area, examining the variables that are
interesting, until you see the problem happen.

`step'
Continue running your program until control reaches a different
source line, then stop it and return control to GDB. This command
is abbreviated `s'.

_Warning:_ If you use the `step' command while control is
within a function that was compiled without debugging
information, execution proceeds until control reaches a
function that does have debugging information. Likewise, it
will not step into a function which is compiled without
debugging information. To step through functions without
debugging information, use the `stepi' command, described
below.

The `step' command only stops at the first instruction of a source
line. This prevents the multiple stops that could otherwise occur
in `switch' statements, `for' loops, etc. `step' continues to
stop if a function that has debugging information is called within
the line. In other words, `step' _steps inside_ any functions
called within the line.

Also, the `step' command only enters a function if there is line
number information for the function. Otherwise it acts like the
`next' command. This avoids problems when using `cc -gl' on MIPS
machines. Previously, `step' entered subroutines if there was any
debugging information about the routine.

`step COUNT'
Continue running as in `step', but do so COUNT times. If a
breakpoint is reached, or a signal not related to stepping occurs
before COUNT steps, stepping stops right away.

`next [COUNT]'
Continue to the next source line in the current (innermost) stack
frame. This is similar to `step', but function calls that appear
within the line of code are executed without stopping. Execution
stops when control reaches a different line of code at the
original stack level that was executing when you gave the `next'
command. This command is abbreviated `n'.

An argument COUNT is a repeat count, as for `step'.

The `next' command only stops at the first instruction of a source
line. This prevents multiple stops that could otherwise occur in
`switch' statements, `for' loops, etc.

`set step-mode'
`set step-mode on'
The `set step-mode on' command causes the `step' command to stop
at the first instruction of a function which contains no debug line
information rather than stepping over it.

This is useful in cases where you may be interested in inspecting
the machine instructions of a function which has no symbolic info
and do not want GDB to automatically skip over this function.

`set step-mode off'
Causes the `step' command to step over any functions which
contains no debug information. This is the default.

`show step-mode'
Show whether GDB will stop in or step over functions without
source line debug information.

`finish'
Continue running until just after function in the selected stack
frame returns. Print the returned value (if any). This command
can be abbreviated as `fin'.

Contrast this with the `return' command (*note Returning from a
Function: Returning.).

`set print finish [on|off]'
`show print finish'
By default the `finish' command will show the value that is
returned by the function. This can be disabled using `set print
finish off'. When disabled, the value is still entered into the
value history (*note Value History::), but not displayed.

`until'
`u'
Continue running until a source line past the current line, in the
current stack frame, is reached. This command is used to avoid
single stepping through a loop more than once. It is like the
`next' command, except that when `until' encounters a jump, it
automatically continues execution until the program counter is
greater than the address of the jump.

This means that when you reach the end of a loop after single
stepping though it, `until' makes your program continue execution
until it exits the loop. In contrast, a `next' command at the end
of a loop simply steps back to the beginning of the loop, which
forces you to step through the next iteration.

`until' always stops your program if it attempts to exit the
current stack frame.

`until' may produce somewhat counterintuitive results if the order
of machine code does not match the order of the source lines. For
example, in the following excerpt from a debugging session, the `f'
(`frame') command shows that execution is stopped at line `206';
yet when we use `until', we get to line `195':

(gdb) f
#0 main (argc=4, argv=0xf7fffae8) at m4.c:206
206 expand_input();
(gdb) until
195 for ( ; argc > 0; NEXTARG) {

This happened because, for execution efficiency, the compiler had
generated code for the loop closure test at the end, rather than
the start, of the loop--even though the test in a C `for'-loop is
written before the body of the loop. The `until' command appeared
to step back to the beginning of the loop when it advanced to this
expression; however, it has not really gone to an earlier
statement--not in terms of the actual machine code.

`until' with no argument works by means of single instruction
stepping, and hence is slower than `until' with an argument.

`until LOCSPEC'
`u LOCSPEC'
Continue running your program until either it reaches a code
location that results from resolving LOCSPEC, or the current stack
frame returns. LOCSPEC is any of the forms described in *Note
Location Specifications::. This form of the command uses
temporary breakpoints, and hence is quicker than `until' without
an argument. The specified location is actually reached only if
it is in the current frame. This implies that `until' can be used
to skip over recursive function invocations. For instance in the
code below, if the current location is line `96', issuing `until
99' will execute the program up to line `99' in the same
invocation of factorial, i.e., after the inner invocations have
returned.

94 int factorial (int value)
95 {
96 if (value > 1) {
97 value *= factorial (value - 1);
98 }
99 return (value);
100 }

`advance LOCSPEC'
Continue running your program until either it reaches a code
location that results from resolving LOCSPEC, or the current stack
frame returns. LOCSPEC is any of the forms described in *Note
Location Specifications::. This command is similar to `until', but
`advance' will not skip over recursive function calls, and the
target code location doesn't have to be in the same frame as the
current one.

`stepi'
`stepi ARG'
`si'
Execute one machine instruction, then stop and return to the
debugger.

It is often useful to do `display/i $pc' when stepping by machine
instructions. This makes GDB automatically display the next
instruction to be executed, each time your program stops. *Note
Automatic Display: Auto Display.

An argument is a repeat count, as in `step'.

`nexti'
`nexti ARG'
`ni'
Execute one machine instruction, but if it is a function call,
proceed until the function returns.

An argument is a repeat count, as in `next'.

By default, and if available, GDB makes use of target-assisted
"range stepping". In other words, whenever you use a stepping command
(e.g., `step', `next'), GDB tells the target to step the corresponding
range of instruction addresses instead of issuing multiple
single-steps. This speeds up line stepping, particularly for remote
targets. Ideally, there should be no reason you would want to turn
range stepping off. However, it's possible that a bug in the debug
info, a bug in the remote stub (for remote targets), or even a bug in
GDB could make line stepping behave incorrectly when target-assisted
range stepping is enabled. You can use the following command to turn
off range stepping if necessary:

`set range-stepping'
`show range-stepping'
Control whether range stepping is enabled.

If `on', and the target supports it, GDB tells the target to step
a range of addresses itself, instead of issuing multiple
single-steps. If `off', GDB always issues single-steps, even if
range stepping is supported by the target. The default is `on'.

File: gdb.info, Node: Skipping Over Functions and Files, Next: Signals, Prev: Continuing and Stepping, Up: Stopping

5.3 Skipping Over Functions and Files
=====================================

The program you are debugging may contain some functions which are
uninteresting to debug. The `skip' command lets you tell GDB to skip a
function, all functions in a file or a particular function in a
particular file when stepping.

For example, consider the following C function:

101 int func()
102 {
103 foo(boring());
104 bar(boring());
105 }

Suppose you wish to step into the functions `foo' and `bar', but you
are not interested in stepping through `boring'. If you run `step' at
line 103, you'll enter `boring()', but if you run `next', you'll step
over both `foo' and `boring'!

One solution is to `step' into `boring' and use the `finish' command
to immediately exit it. But this can become tedious if `boring' is
called from many places.

A more flexible solution is to execute `skip boring'. This instructs
GDB never to step into `boring'. Now when you execute `step' at line
103, you'll step over `boring' and directly into `foo'.

Functions may be skipped by providing either a function name,
linespec (*note Location Specifications::), regular expression that
matches the function's name, file name or a `glob'-style pattern that
matches the file name.

On Posix systems the form of the regular expression is "Extended
Regular Expressions". See for example `man 7 regex' on GNU/Linux
systems. On non-Posix systems the form of the regular expression is
whatever is provided by the `regcomp' function of the underlying system.
See for example `man 7 glob' on GNU/Linux systems for a description of
`glob'-style patterns.

`skip [OPTIONS]'
The basic form of the `skip' command takes zero or more options
that specify what to skip. The OPTIONS argument is any useful
combination of the following:

`-file FILE'
`-fi FILE'
Functions in FILE will be skipped over when stepping.

`-gfile FILE-GLOB-PATTERN'
`-gfi FILE-GLOB-PATTERN'
Functions in files matching FILE-GLOB-PATTERN will be skipped
over when stepping.

(gdb) skip -gfi utils/*.c

`-function LINESPEC'
`-fu LINESPEC'
Functions named by LINESPEC or the function containing the
line named by LINESPEC will be skipped over when stepping.
*Note Location Specifications::.

`-rfunction REGEXP'
`-rfu REGEXP'
Functions whose name matches REGEXP will be skipped over when
stepping.

This form is useful for complex function names. For example,
there is generally no need to step into C++ `std::string'
constructors or destructors. Plus with C++ templates it can
be hard to write out the full name of the function, and often
it doesn't matter what the template arguments are.
Specifying the function to be skipped as a regular expression
makes this easier.

(gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\(

If you want to skip every templated C++ constructor and
destructor in the `std' namespace you can do:

(gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\(

If no options are specified, the function you're currently
debugging will be skipped.

`skip function [LINESPEC]'
After running this command, the function named by LINESPEC or the
function containing the line named by LINESPEC will be skipped
over when stepping. *Note Location Specifications::.

If you do not specify LINESPEC, the function you're currently
debugging will be skipped.

(If you have a function called `file' that you want to skip, use
`skip function file'.)

`skip file [FILENAME]'
After running this command, any function whose source lives in
FILENAME will be skipped over when stepping.

(gdb) skip file boring.c
File boring.c will be skipped when stepping.

If you do not specify FILENAME, functions whose source lives in
the file you're currently debugging will be skipped.

Skips can be listed, deleted, disabled, and enabled, much like
breakpoints. These are the commands for managing your list of skips:

`info skip [RANGE]'
Print details about the specified skip(s). If RANGE is not
specified, print a table with details about all functions and
files marked for skipping. `info skip' prints the following
information about each skip:

_Identifier_
A number identifying this skip.

_Enabled or Disabled_
Enabled skips are marked with `y'. Disabled skips are marked
with `n'.

_Glob_
If the file name is a `glob' pattern this is `y'. Otherwise
it is `n'.

_File_
The name or `glob' pattern of the file to be skipped. If no
file is specified this is `<none>'.

_RE_
If the function name is a `regular expression' this is `y'.
Otherwise it is `n'.

_Function_
The name or regular expression of the function to skip. If
no function is specified this is `<none>'.

`skip delete [RANGE]'
Delete the specified skip(s). If RANGE is not specified, delete
all skips.

`skip enable [RANGE]'
Enable the specified skip(s). If RANGE is not specified, enable
all skips.

`skip disable [RANGE]'
Disable the specified skip(s). If RANGE is not specified, disable
all skips.

`set debug skip [on|off]'
Set whether to print the debug output about skipping files and
functions.

`show debug skip'
Show whether the debug output about skipping files and functions
is printed.

File: gdb.info, Node: Signals, Next: Thread Stops, Prev: Skipping Over Functions and Files, Up: Stopping

5.4 Signals
===========

A signal is an asynchronous event that can happen in a program. The
operating system defines the possible kinds of signals, and gives each
kind a name and a number. For example, in Unix `SIGINT' is the signal
a program gets when you type an interrupt character (often `Ctrl-c');
`SIGSEGV' is the signal a program gets from referencing a place in
memory far away from all the areas in use; `SIGALRM' occurs when the
alarm clock timer goes off (which happens only if your program has
requested an alarm).

Some signals, including `SIGALRM', are a normal part of the
functioning of your program. Others, such as `SIGSEGV', indicate
errors; these signals are "fatal" (they kill your program immediately)
if the program has not specified in advance some other way to handle
the signal. `SIGINT' does not indicate an error in your program, but
it is normally fatal so it can carry out the purpose of the interrupt:
to kill the program.

GDB has the ability to detect any occurrence of a signal in your
program. You can tell GDB in advance what to do for each kind of
signal.

Normally, GDB is set up to let the non-erroneous signals like
`SIGALRM' be silently passed to your program (so as not to interfere
with their role in the program's functioning) but to stop your program
immediately whenever an error signal happens. You can change these
settings with the `handle' command.

`info signals'
`info handle'
Print a table of all the kinds of signals and how GDB has been
told to handle each one. You can use this to see the signal
numbers of all the defined types of signals.

`info signals SIG'
Similar, but print information only about the specified signal
number.

`info handle' is an alias for `info signals'.

`catch signal [SIGNAL... | `all']'
Set a catchpoint for the indicated signals. *Note Set
Catchpoints::, for details about this command.

`handle SIGNAL [ SIGNAL ... ] [KEYWORDS...]'
Change the way GDB handles each SIGNAL. Each SIGNAL can be the
number of a signal or its name (with or without the `SIG' at the
beginning); a list of signal numbers of the form `LOW-HIGH'; or
the word `all', meaning all the known signals, except `SIGINT' and
`SIGTRAP', which are used by GDB. Optional argument KEYWORDS,
described below, say what changes to make to all of the specified
signals.

The keywords allowed by the `handle' command can be abbreviated.
Their full names are:

`nostop'
GDB should not stop your program when this signal happens. It may
still print a message telling you that the signal has come in.

`stop'
GDB should stop your program when this signal happens. This
implies the `print' keyword as well.

`print'
GDB should print a message when this signal happens.

`noprint'
GDB should not mention the occurrence of the signal at all. This
implies the `nostop' keyword as well.

`pass'
`noignore'
GDB should allow your program to see this signal; your program can
handle the signal, or else it may terminate if the signal is fatal
and not handled. `pass' and `noignore' are synonyms.

`nopass'
`ignore'
GDB should not allow your program to see this signal. `nopass'
and `ignore' are synonyms.

When a signal stops your program, the signal is not visible to the
program until you continue. Your program sees the signal then, if
`pass' is in effect for the signal in question _at that time_. In
other words, after GDB reports a signal, you can use the `handle'
command with `pass' or `nopass' to control whether your program sees
that signal when you continue.

The default is set to `nostop', `noprint', `pass' for non-erroneous
signals such as `SIGALRM', `SIGWINCH' and `SIGCHLD', and to `stop',
`print', `pass' for the erroneous signals.

You can also use the `signal' command to prevent your program from
seeing a signal, or cause it to see a signal it normally would not see,
or to give it any signal at any time. For example, if your program
stopped due to some sort of memory reference error, you might store
correct values into the erroneous variables and continue, hoping to see
more execution; but your program would probably terminate immediately as
a result of the fatal signal once it saw the signal. To prevent this,
you can continue with `signal 0'. *Note Giving your Program a Signal:
Signaling.

GDB optimizes for stepping the mainline code. If a signal that has
`handle nostop' and `handle pass' set arrives while a stepping command
(e.g., `stepi', `step', `next') is in progress, GDB lets the signal
handler run and then resumes stepping the mainline code once the signal
handler returns. In other words, GDB steps over the signal handler.
This prevents signals that you've specified as not interesting (with
`handle nostop') from changing the focus of debugging unexpectedly.
Note that the signal handler itself may still hit a breakpoint, stop
for another signal that has `handle stop' in effect, or for any other
event that normally results in stopping the stepping command sooner.
Also note that GDB still informs you that the program received a signal
if `handle print' is set.

If you set `handle pass' for a signal, and your program sets up a
handler for it, then issuing a stepping command, such as `step' or
`stepi', when your program is stopped due to the signal will step
_into_ the signal handler (if the target supports that).

Likewise, if you use the `queue-signal' command to queue a signal to
be delivered to the current thread when execution of the thread resumes
(*note Giving your Program a Signal: Signaling.), then a stepping
command will step into the signal handler.

Here's an example, using `stepi' to step to the first instruction of
`SIGUSR1''s handler:

(gdb) handle SIGUSR1
Signal Stop Print Pass to program Description
SIGUSR1 Yes Yes Yes User defined signal 1
(gdb) c
Continuing.

Program received signal SIGUSR1, User defined signal 1.
main () sigusr1.c:28
28 p = 0;
(gdb) si
sigusr1_handler () at sigusr1.c:9
9 {

The same, but using `queue-signal' instead of waiting for the
program to receive the signal first:

(gdb) n
28 p = 0;
(gdb) queue-signal SIGUSR1
(gdb) si
sigusr1_handler () at sigusr1.c:9
9 {
(gdb)

On some targets, GDB can inspect extra signal information associated
with the intercepted signal, before it is actually delivered to the
program being debugged. This information is exported by the
convenience variable `$_siginfo', and consists of data that is passed
by the kernel to the signal handler at the time of the receipt of a
signal. The data type of the information itself is target dependent.
You can see the data type using the `ptype $_siginfo' command. On Unix
systems, it typically corresponds to the standard `siginfo_t' type, as
defined in the `signal.h' system header.

Here's an example, on a GNU/Linux system, printing the stray
referenced address that raised a segmentation fault.

(gdb) continue
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400766 in main ()
69 *(int *)p = 0;
(gdb) ptype $_siginfo
type = struct {
int si_signo;
int si_errno;
int si_code;
union {
int _pad[28];
struct {...} _kill;
struct {...} _timer;
struct {...} _rt;
struct {...} _sigchld;
struct {...} _sigfault;
struct {...} _sigpoll;
} _sifields;
}
(gdb) ptype $_siginfo._sifields._sigfault
type = struct {
void *si_addr;
}
(gdb) p $_siginfo._sifields._sigfault.si_addr
$1 = (void *) 0x7ffff7ff7000

Depending on target support, `$_siginfo' may also be writable.

On some targets, a `SIGSEGV' can be caused by a boundary violation,
i.e., accessing an address outside of the allowed range. In those
cases GDB may displays additional information, depending on how GDB has
been told to handle the signal. With `handle stop SIGSEGV', GDB
displays the violation kind: "Upper" or "Lower", the memory address
accessed and the bounds, while with `handle nostop SIGSEGV' no
additional information is displayed.

The usual output of a segfault is:
Program received signal SIGSEGV, Segmentation fault
0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68
68 value = *(p + len);

While a bound violation is presented as:
Program received signal SIGSEGV, Segmentation fault
Upper bound violation while accessing address 0x7fffffffc3b3
Bounds: [lower = 0x7fffffffc390, upper = 0x7fffffffc3a3]
0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68
68 value = *(p + len);

File: gdb.info, Node: Thread Stops, Prev: Signals, Up: Stopping

5.5 Stopping and Starting Multi-thread Programs
===============================================

GDB supports debugging programs with multiple threads (*note Debugging
Programs with Multiple Threads: Threads.). There are two modes of
controlling execution of your program within the debugger. In the
default mode, referred to as "all-stop mode", when any thread in your
program stops (for example, at a breakpoint or while being stepped),
all other threads in the program are also stopped by GDB. On some
targets, GDB also supports "non-stop mode", in which other threads can
continue to run freely while you examine the stopped thread in the
debugger.

* Menu:

* All-Stop Mode:: All threads stop when GDB takes control
* Non-Stop Mode:: Other threads continue to execute
* Background Execution:: Running your program asynchronously
* Thread-Specific Breakpoints:: Controlling breakpoints
* Interrupted System Calls:: GDB may interfere with system calls
* Observer Mode:: GDB does not alter program behavior

File: gdb.info, Node: All-Stop Mode, Next: Non-Stop Mode, Up: Thread Stops

5.5.1 All-Stop Mode
-------------------

In all-stop mode, whenever your program stops under GDB for any reason,
_all_ threads of execution stop, not just the current thread. This
allows you to examine the overall state of the program, including
switching between threads, without worrying that things may change
underfoot.

Conversely, whenever you restart the program, _all_ threads start
executing. _This is true even when single-stepping_ with commands like
`step' or `next'.

In particular, GDB cannot single-step all threads in lockstep.
Since thread scheduling is up to your debugging target's operating
system (not controlled by GDB), other threads may execute more than one
statement while the current thread completes a single step. Moreover,
in general other threads stop in the middle of a statement, rather than
at a clean statement boundary, when the program stops.

You might even find your program stopped in another thread after
continuing or even single-stepping. This happens whenever some other
thread runs into a breakpoint, a signal, or an exception before the
first thread completes whatever you requested.

Whenever GDB stops your program, due to a breakpoint or a signal, it
automatically selects the thread where that breakpoint or signal
happened. GDB alerts you to the context switch with a message such as
`[Switching to Thread N]' to identify the thread.

On some OSes, you can modify GDB's default behavior by locking the
OS scheduler to allow only a single thread to run.

`set scheduler-locking MODE'
Set the scheduler locking mode. It applies to normal execution,
record mode, and replay mode. MODE can be one of the following:

`off'
There is no locking and any thread may run at any time.

`on'
Only the current thread may run when the inferior is resumed.
New threads created by the resumed thread are held stopped
at their entry point, before they execute any instruction.

`step'
Behaves like `on' when stepping, and `off' otherwise.
Threads other than the current never get a chance to run when
you step, and they are completely free to run when you use
commands like `continue', `until', or `finish'.

This mode optimizes for single-stepping; it prevents other
threads from preempting the current thread while you are
stepping, so that the focus of debugging does not change
unexpectedly. However, unless another thread hits a
breakpoint during its timeslice, GDB does not change the
current thread away from the thread that you are debugging.

`replay'
Behaves like `on' in replay mode, and `off' in either record
mode or during normal execution. This is the default mode.

`show scheduler-locking'
Display the current scheduler locking mode.

By default, when you issue one of the execution commands such as
`continue', `next' or `step', GDB allows only threads of the current
inferior to run. For example, if GDB is attached to two inferiors,
each with two threads, the `continue' command resumes only the two
threads of the current inferior. This is useful, for example, when you
debug a program that forks and you want to hold the parent stopped (so
that, for instance, it doesn't run to exit), while you debug the child.
In other situations, you may not be interested in inspecting the
current state of any of the processes GDB is attached to, and you may
want to resume them all until some breakpoint is hit. In the latter
case, you can instruct GDB to allow all threads of all the inferiors to
run with the `set schedule-multiple' command.

`set schedule-multiple'
Set the mode for allowing threads of multiple processes to be
resumed when an execution command is issued. When `on', all
threads of all processes are allowed to run. When `off', only the
threads of the current process are resumed. The default is `off'.
The `scheduler-locking' mode takes precedence when set to `on',
or while you are stepping and set to `step'.

`show schedule-multiple'
Display the current mode for resuming the execution of threads of
multiple processes.

File: gdb.info, Node: Non-Stop Mode, Next: Background Execution, Prev: All-Stop Mode, Up: Thread Stops

5.5.2 Non-Stop Mode
-------------------

For some multi-threaded targets, GDB supports an optional mode of
operation in which you can examine stopped program threads in the
debugger while other threads continue to execute freely. This
minimizes intrusion when debugging live systems, such as programs where
some threads have real-time constraints or must continue to respond to
external events. This is referred to as "non-stop" mode.

In non-stop mode, when a thread stops to report a debugging event,
_only_ that thread is stopped; GDB does not stop other threads as well,
in contrast to the all-stop mode behavior. Additionally, execution
commands such as `continue' and `step' apply by default only to the
current thread in non-stop mode, rather than all threads as in all-stop
mode. This allows you to control threads explicitly in ways that are
not possible in all-stop mode -- for example, stepping one thread while
allowing others to run freely, stepping one thread while holding all
others stopped, or stepping several threads independently and
simultaneously.

To enter non-stop mode, use this sequence of commands before you run
or attach to your program:

# If using the CLI, pagination breaks non-stop.
set pagination off

# Finally, turn it on!
set non-stop on

You can use these commands to manipulate the non-stop mode setting:

`set non-stop on'
Enable selection of non-stop mode.

`set non-stop off'
Disable selection of non-stop mode.

`show non-stop'
Show the current non-stop enablement setting.

Note these commands only reflect whether non-stop mode is enabled,
not whether the currently-executing program is being run in non-stop
mode. In particular, the `set non-stop' preference is only consulted
when GDB starts or connects to the target program, and it is generally
not possible to switch modes once debugging has started. Furthermore,
since not all targets support non-stop mode, even when you have enabled
non-stop mode, GDB may still fall back to all-stop operation by default.

In non-stop mode, all execution commands apply only to the current
thread by default. That is, `continue' only continues one thread. To
continue all threads, issue `continue -a' or `c -a'.

You can use GDB's background execution commands (*note Background
Execution::) to run some threads in the background while you continue
to examine or step others from GDB. The MI execution commands (*note
GDB/MI Program Execution::) are always executed asynchronously in
non-stop mode.

Suspending execution is done with the `interrupt' command when
running in the background, or `Ctrl-c' during foreground execution. In
all-stop mode, this stops the whole process; but in non-stop mode the
interrupt applies only to the current thread. To stop the whole
program, use `interrupt -a'.

Other execution commands do not currently support the `-a' option.

In non-stop mode, when a thread stops, GDB doesn't automatically make
that thread current, as it does in all-stop mode. This is because the
thread stop notifications are asynchronous with respect to GDB's
command interpreter, and it would be confusing if GDB unexpectedly
changed to a different thread just as you entered a command to operate
on the previously current thread.

File: gdb.info, Node: Background Execution, Next: Thread-Specific Breakpoints, Prev: Non-Stop Mode, Up: Thread Stops

5.5.3 Background Execution
--------------------------

GDB's execution commands have two variants: the normal foreground
(synchronous) behavior, and a background (asynchronous) behavior. In
foreground execution, GDB waits for the program to report that some
thread has stopped before prompting for another command. In background
execution, GDB immediately gives a command prompt so that you can issue
other commands while your program runs.

If the target doesn't support async mode, GDB issues an error
message if you attempt to use the background execution commands.

To specify background execution, add a `&' to the command. For
example, the background form of the `continue' command is `continue&',
or just `c&'. The execution commands that accept background execution
are:

`run'
*Note Starting your Program: Starting.

`attach'
*Note Debugging an Already-running Process: Attach.

`step'
*Note step: Continuing and Stepping.

`stepi'
*Note stepi: Continuing and Stepping.

`next'
*Note next: Continuing and Stepping.

`nexti'
*Note nexti: Continuing and Stepping.

`continue'
*Note continue: Continuing and Stepping.

`finish'
*Note finish: Continuing and Stepping.

`until'
*Note until: Continuing and Stepping.

Background execution is especially useful in conjunction with
non-stop mode for debugging programs with multiple threads; see *Note
Non-Stop Mode::. However, you can also use these commands in the
normal all-stop mode with the restriction that you cannot issue another
execution command until the previous one finishes. Examples of
commands that are valid in all-stop mode while the program is running
include `help' and `info break'.

You can interrupt your program while it is running in the background
by using the `interrupt' command.

`interrupt'
`interrupt -a'
Suspend execution of the running program. In all-stop mode,
`interrupt' stops the whole process, but in non-stop mode, it stops
only the current thread. To stop the whole program in non-stop
mode, use `interrupt -a'.

File: gdb.info, Node: Thread-Specific Breakpoints, Next: Interrupted System Calls, Prev: Background Execution, Up: Thread Stops

5.5.4 Thread-Specific Breakpoints
---------------------------------

When your program has multiple threads (*note Debugging Programs with
Multiple Threads: Threads.), you can choose whether to set breakpoints
on all threads, or on a particular thread.

`break LOCSPEC thread THREAD-ID'
`break LOCSPEC thread THREAD-ID if ...'
LOCSPEC specifies a code location or locations in your program.
*Note Location Specifications::, for details.

Use the qualifier `thread THREAD-ID' with a breakpoint command to
specify that you only want GDB to stop the program when a
particular thread reaches this breakpoint. The THREAD-ID specifier
is one of the thread identifiers assigned by GDB, shown in the
first column of the `info threads' display.

If you do not specify `thread THREAD-ID' when you set a
breakpoint, the breakpoint applies to _all_ threads of your
program.

You can use the `thread' qualifier on conditional breakpoints as
well; in this case, place `thread THREAD-ID' before or after the
breakpoint condition, like this:

(gdb) break frik.c:13 thread 28 if bartab > lim

Thread-specific breakpoints are automatically deleted when GDB
detects the corresponding thread is no longer in the thread list. For
example:

(gdb) c
Thread-specific breakpoint 3 deleted - thread 28 no longer in the thread list.

There are several ways for a thread to disappear, such as a regular
thread exit, but also when you detach from the process with the
`detach' command (*note Debugging an Already-running Process: Attach.),
or if GDB loses the remote connection (*note Remote Debugging::), etc.
Note that with some targets, GDB is only able to detect a thread has
exited when the user explicitly asks for the thread list with the `info
threads' command.

A breakpoint can't be both thread-specific and inferior-specific
(*note Inferior-Specific Breakpoints::), or task-specific (*note Ada
Tasks::); using more than one of the `thread', `inferior', or `task'
keywords when creating a breakpoint will give an error.

File: gdb.info, Node: Interrupted System Calls, Next: Observer Mode, Prev: Thread-Specific Breakpoints, Up: Thread Stops

5.5.5 Interrupted System Calls
------------------------------

There is an unfortunate side effect when using GDB to debug
multi-threaded programs. If one thread stops for a breakpoint, or for
some other reason, and another thread is blocked in a system call, then
the system call may return prematurely. This is a consequence of the
interaction between multiple threads and the signals that GDB uses to
implement breakpoints and other events that stop execution.

To handle this problem, your program should check the return value of
each system call and react appropriately. This is good programming
style anyways.

For example, do not write code like this:

sleep (10);

The call to `sleep' will return early if a different thread stops at
a breakpoint or for some other reason.

Instead, write this:

int unslept = 10;
while (unslept > 0)
unslept = sleep (unslept);

A system call is allowed to return early, so the system is still
conforming to its specification. But GDB does cause your
multi-threaded program to behave differently than it would without GDB.

Also, GDB uses internal breakpoints in the thread library to monitor
certain events such as thread creation and thread destruction. When
such an event happens, a system call in another thread may return
prematurely, even though your program does not appear to stop.

File: gdb.info, Node: Observer Mode, Prev: Interrupted System Calls, Up: Thread Stops

5.5.6 Observer Mode
-------------------

If you want to build on non-stop mode and observe program behavior
without any chance of disruption by GDB, you can set variables to
disable all of the debugger's attempts to modify state, whether by
writing memory, inserting breakpoints, etc. These operate at a low
level, intercepting operations from all commands.

When all of these are set to `off', then GDB is said to be "observer
mode". As a convenience, the variable `observer' can be set to disable
these, plus enable non-stop mode.

Note that GDB will not prevent you from making nonsensical
combinations of these settings. For instance, if you have enabled
`may-insert-breakpoints' but disabled `may-write-memory', then
breakpoints that work by writing trap instructions into the code stream
will still not be able to be placed.

`set observer on'
`set observer off'
When set to `on', this disables all the permission variables below
(except for `insert-fast-tracepoints'), plus enables non-stop
debugging. Setting this to `off' switches back to normal
debugging, though remaining in non-stop mode.

`show observer'
Show whether observer mode is on or off.

`set may-write-registers on'
`set may-write-registers off'
This controls whether GDB will attempt to alter the values of
registers, such as with assignment expressions in `print', or the
`jump' command. It defaults to `on'.

`show may-write-registers'
Show the current permission to write registers.

`set may-write-memory on'
`set may-write-memory off'
This controls whether GDB will attempt to alter the contents of
memory, such as with assignment expressions in `print'. It
defaults to `on'.

`show may-write-memory'
Show the current permission to write memory.

`set may-insert-breakpoints on'
`set may-insert-breakpoints off'
This controls whether GDB will attempt to insert breakpoints.
This affects all breakpoints, including internal breakpoints
defined by GDB. It defaults to `on'.

`show may-insert-breakpoints'
Show the current permission to insert breakpoints.

`set may-insert-tracepoints on'
`set may-insert-tracepoints off'
This controls whether GDB will attempt to insert (regular)
tracepoints at the beginning of a tracing experiment. It affects
only non-fast tracepoints, fast tracepoints being under the
control of `may-insert-fast-tracepoints'. It defaults to `on'.

`show may-insert-tracepoints'
Show the current permission to insert tracepoints.

`set may-insert-fast-tracepoints on'
`set may-insert-fast-tracepoints off'
This controls whether GDB will attempt to insert fast tracepoints
at the beginning of a tracing experiment. It affects only fast
tracepoints, regular (non-fast) tracepoints being under the
control of `may-insert-tracepoints'. It defaults to `on'.

`show may-insert-fast-tracepoints'
Show the current permission to insert fast tracepoints.

`set may-interrupt on'
`set may-interrupt off'
This controls whether GDB will attempt to interrupt or stop
program execution. When this variable is `off', the `interrupt'
command will have no effect, nor will `Ctrl-c'. It defaults to
`on'.

`show may-interrupt'
Show the current permission to interrupt or stop the program.

File: gdb.info, Node: Reverse Execution, Next: Process Record and Replay, Prev: Stopping, Up: Top

6 Running programs backward
***************************

When you are debugging a program, it is not unusual to realize that you
have gone too far, and some event of interest has already happened. If
the target environment supports it, GDB can allow you to "rewind" the
program by running it backward.

A target environment that supports reverse execution should be able
to "undo" the changes in machine state that have taken place as the
program was executing normally. Variables, registers etc. should
revert to their previous values. Obviously this requires a great deal
of sophistication on the part of the target environment; not all target
environments can support reverse execution.

When a program is executed in reverse, the instructions that have
most recently been executed are "un-executed", in reverse order. The
program counter runs backward, following the previous thread of
execution in reverse. As each instruction is "un-executed", the values
of memory and/or registers that were changed by that instruction are
reverted to their previous states. After executing a piece of source
code in reverse, all side effects of that code should be "undone", and
all variables should be returned to their prior values(1).

On some platforms, GDB has built-in support for reverse execution,
activated with the `record' or `record btrace' commands. *Note Process
Record and Replay::. Some remote targets, typically full system
emulators, support reverse execution directly without requiring any
special command.

If you are debugging in a target environment that supports reverse
execution, GDB provides the following commands.

`reverse-continue [IGNORE-COUNT]'
`rc [IGNORE-COUNT]'
Beginning at the point where your program last stopped, start
executing in reverse. Reverse execution will stop for breakpoints
and synchronous exceptions (signals), just like normal execution.
Behavior of asynchronous signals depends on the target environment.

`reverse-step [COUNT]'
Run the program backward until control reaches the start of a
different source line; then stop it, and return control to GDB.

Like the `step' command, `reverse-step' will only stop at the
beginning of a source line. It "un-executes" the previously
executed source line. If the previous source line included calls
to debuggable functions, `reverse-step' will step (backward) into
the called function, stopping at the beginning of the _last_
statement in the called function (typically a return statement).

Also, as with the `step' command, if non-debuggable functions are
called, `reverse-step' will run thru them backward without
stopping.

`reverse-stepi [COUNT]'
Reverse-execute one machine instruction. Note that the instruction
to be reverse-executed is _not_ the one pointed to by the program
counter, but the instruction executed prior to that one. For
instance, if the last instruction was a jump, `reverse-stepi' will
take you back from the destination of the jump to the jump
instruction itself.

`reverse-next [COUNT]'
Run backward to the beginning of the previous line executed in the
current (innermost) stack frame. If the line contains function
calls, they will be "un-executed" without stopping. Starting from
the first line of a function, `reverse-next' will take you back to
the caller of that function, _before_ the function was called,
just as the normal `next' command would take you from the last
line of a function back to its return to its caller (2).

`reverse-nexti [COUNT]'
Like `nexti', `reverse-nexti' executes a single instruction in
reverse, except that called functions are "un-executed" atomically.
That is, if the previously executed instruction was a return from
another function, `reverse-nexti' will continue to execute in
reverse until the call to that function (from the current stack
frame) is reached.

`reverse-finish'
Just as the `finish' command takes you to the point where the
current function returns, `reverse-finish' takes you to the point
where it was called. Instead of ending up at the end of the
current function invocation, you end up at the beginning.

`set exec-direction'
Set the direction of target execution.

`set exec-direction reverse'
GDB will perform all execution commands in reverse, until the
exec-direction mode is changed to "forward". Affected commands
include `step, stepi, next, nexti, continue, and finish'. The
`return' command cannot be used in reverse mode.

`set exec-direction forward'
GDB will perform all execution commands in the normal fashion.
This is the default.

---------- Footnotes ----------

(1) Note that some side effects are easier to undo than others. For
instance, memory and registers are relatively easy, but device I/O is
hard. Some targets may be able undo things like device I/O, and some
may not.

The contract between GDB and the reverse executing target requires
only that the target do something reasonable when GDB tells it to
execute backwards, and then report the results back to GDB. Whatever
the target reports back to GDB, GDB will report back to the user. GDB
assumes that the memory and registers that the target reports are in a
consistent state, but GDB accepts whatever it is given.

(2) Unless the code is too heavily optimized.

File: gdb.info, Node: Process Record and Replay, Next: Stack, Prev: Reverse Execution, Up: Top

7 Recording Inferior's Execution and Replaying It
*************************************************

On some platforms, GDB provides a special "process record and replay"
target that can record a log of the process execution, and replay it
later with both forward and reverse execution commands.

When this target is in use, if the execution log includes the record
for the next instruction, GDB will debug in "replay mode". In the
replay mode, the inferior does not really execute code instructions.
Instead, all the events that normally happen during code execution are
taken from the execution log. While code is not really executed in
replay mode, the values of registers (including the program counter
register) and the memory of the inferior are still changed as they
normally would. Their contents are taken from the execution log.

If the record for the next instruction is not in the execution log,
GDB will debug in "record mode". In this mode, the inferior executes
normally, and GDB records the execution log for future replay.

The process record and replay target supports reverse execution
(*note Reverse Execution::), even if the platform on which the inferior
runs does not. However, the reverse execution is limited in this case
by the range of the instructions recorded in the execution log. In
other words, reverse execution on platforms that don't support it
directly can only be done in the replay mode.

When debugging in the reverse direction, GDB will work in replay
mode as long as the execution log includes the record for the previous
instruction; otherwise, it will work in record mode, if the platform
supports reverse execution, or stop if not.

Currently, process record and replay is supported on ARM, Aarch64,
Moxie, PowerPC, PowerPC64, S/390, and x86 (i386/amd64) running
GNU/Linux. Process record and replay can be used both when native
debugging, and when remote debugging via `gdbserver'.

For architecture environments that support process record and replay,
GDB provides the following commands:

`record METHOD'
This command starts the process record and replay target. The
recording method can be specified as parameter. Without a
parameter the command uses the `full' recording method. The
following recording methods are available:

`full'
Full record/replay recording using GDB's software record and
replay implementation. This method allows replaying and
reverse execution.

`btrace FORMAT'
Hardware-supported instruction recording, supported on Intel
processors. This method does not record data. Further, the
data is collected in a ring buffer so old data will be
overwritten when the buffer is full. It allows limited
reverse execution. Variables and registers are not available
during reverse execution. In remote debugging, recording
continues on disconnect. Recorded data can be inspected
after reconnecting. The recording may be stopped using
`record stop'.

The recording format can be specified as parameter. Without
a parameter the command chooses the recording format. The
following recording formats are available:

`bts'
Use the "Branch Trace Store" (BTS) recording format. In
this format, the processor stores a from/to record for
each executed branch in the btrace ring buffer.

`pt'
Use the "Intel Processor Trace" recording format. In
this format, the processor stores the execution trace in
a compressed form that is afterwards decoded by GDB.

The trace can be recorded with very low overhead. The
compressed trace format also allows small trace buffers
to already contain a big number of instructions compared
to BTS.

Decoding the recorded execution trace, on the other
hand, is more expensive than decoding BTS trace. This
is mostly due to the increased number of instructions to
process. You should increase the buffer-size with care.

Not all recording formats may be available on all processors.

The process record and replay target can only debug a process that
is already running. Therefore, you need first to start the
process with the `run' or `start' commands, and then start the
recording with the `record METHOD' command.

Displaced stepping (*note displaced stepping: Maintenance
Commands.) will be automatically disabled when process record and
replay target is started. That's because the process record and
replay target doesn't support displaced stepping.

If the inferior is in the non-stop mode (*note Non-Stop Mode::) or
in the asynchronous execution mode (*note Background Execution::),
not all recording methods are available. The `full' recording
method does not support these two modes.

`record stop'
Stop the process record and replay target. When process record and
replay target stops, the entire execution log will be deleted and
the inferior will either be terminated, or will remain in its
final state.

When you stop the process record and replay target in record mode
(at the end of the execution log), the inferior will be stopped at
the next instruction that would have been recorded. In other
words, if you record for a while and then stop recording, the
inferior process will be left in the same state as if the
recording never happened.

On the other hand, if the process record and replay target is
stopped while in replay mode (that is, not at the end of the
execution log, but at some earlier point), the inferior process
will become "live" at that earlier state, and it will then be
possible to continue the usual "live" debugging of the process
from that state.

When the inferior process exits, or GDB detaches from it, process
record and replay target will automatically stop itself.

`record goto'
Go to a specific location in the execution log. There are several
ways to specify the location to go to:

`record goto begin'
`record goto start'
Go to the beginning of the execution log.

`record goto end'
Go to the end of the execution log.

`record goto N'
Go to instruction number N in the execution log.

`record save FILENAME'
Save the execution log to a file `FILENAME'. Default filename is
`gdb_record.PROCESS_ID', where PROCESS_ID is the process ID of the
inferior.

This command may not be available for all recording methods.

`record restore FILENAME'
Restore the execution log from a file `FILENAME'. File must have
been created with `record save'.

`set record full insn-number-max LIMIT'
`set record full insn-number-max unlimited'
Set the limit of instructions to be recorded for the `full'
recording method. Default value is 200000.

If LIMIT is a positive number, then GDB will start deleting
instructions from the log once the number of the record
instructions becomes greater than LIMIT. For every new recorded
instruction, GDB will delete the earliest recorded instruction to
keep the number of recorded instructions at the limit. (Since
deleting recorded instructions loses information, GDB lets you
control what happens when the limit is reached, by means of the
`stop-at-limit' option, described below.)

If LIMIT is `unlimited' or zero, GDB will never delete recorded
instructions from the execution log. The number of recorded
instructions is limited only by the available memory.

`show record full insn-number-max'
Show the limit of instructions to be recorded with the `full'
recording method.

`set record full stop-at-limit'
Control the behavior of the `full' recording method when the
number of recorded instructions reaches the limit. If ON (the
default), GDB will stop when the limit is reached for the first
time and ask you whether you want to stop the inferior or continue
running it and recording the execution log. If you decide to
continue recording, each new recorded instruction will cause the
oldest one to be deleted.

If this option is OFF, GDB will automatically delete the oldest
record to make room for each new one, without asking.

`show record full stop-at-limit'
Show the current setting of `stop-at-limit'.

`set record full memory-query'
Control the behavior when GDB is unable to record memory changes
caused by an instruction for the `full' recording method. If ON,
GDB will query whether to stop the inferior in that case.

If this option is OFF (the default), GDB will automatically ignore
the effect of such instructions on memory. Later, when GDB
replays this execution log, it will mark the log of this
instruction as not accessible, and it will not affect the replay
results.

`show record full memory-query'
Show the current setting of `memory-query'.

The `btrace' record target does not trace data. As a convenience,
when replaying, GDB reads read-only memory off the live program
directly, assuming that the addresses of the read-only areas don't
change. This for example makes it possible to disassemble code
while replaying, but not to print variables. In some cases, being
able to inspect variables might be useful. You can use the
following command for that:

`set record btrace replay-memory-access'
Control the behavior of the `btrace' recording method when
accessing memory during replay. If `read-only' (the default), GDB
will only allow accesses to read-only memory. If `read-write',
GDB will allow accesses to read-only and to read-write memory.
Beware that the accessed memory corresponds to the live target and
not necessarily to the current replay position.

`set record btrace cpu IDENTIFIER'
Set the processor to be used for enabling workarounds for processor
errata when decoding the trace.

Processor errata are defects in processor operation, caused by its
design or manufacture. They can cause a trace not to match the
specification. This, in turn, may cause trace decode to fail.
GDB can detect erroneous trace packets and correct them, thus
avoiding the decoding failures. These corrections are known as
"errata workarounds", and are enabled based on the processor on
which the trace was recorded.

By default, GDB attempts to detect the processor automatically,
and apply the necessary workarounds for it. However, you may need
to specify the processor if GDB does not yet support it. This
command allows you to do that, and also allows to disable the
workarounds.

The argument IDENTIFIER identifies the CPU and is of the form:
`VENDOR:PROCESSOR IDENTIFIER'. In addition, there are two special
identifiers, `none' and `auto' (default).

The following vendor identifiers and corresponding processor
identifiers are currently supported:

`intel' FAMILY/MODEL[/STEPPING]

On GNU/Linux systems, the processor FAMILY, MODEL, and STEPPING
can be obtained from `/proc/cpuinfo'.

If IDENTIFIER is `auto', enable errata workarounds for the
processor on which the trace was recorded. If IDENTIFIER is
`none', errata workarounds are disabled.

For example, when using an old GDB on a new system, decode may
fail because GDB does not support the new processor. It often
suffices to specify an older processor that GDB supports.

(gdb) info record
Active record target: record-btrace
Recording format: Intel Processor Trace.
Buffer size: 16kB.
Failed to configure the Intel Processor Trace decoder: unknown cpu.
(gdb) set record btrace cpu intel:6/158
(gdb) info record
Active record target: record-btrace
Recording format: Intel Processor Trace.
Buffer size: 16kB.
Recorded 84872 instructions in 3189 functions (0 gaps) for thread 1 (...).

`show record btrace replay-memory-access'
Show the current setting of `replay-memory-access'.

`show record btrace cpu'
Show the processor to be used for enabling trace decode errata
workarounds.

`set record btrace bts buffer-size SIZE'
`set record btrace bts buffer-size unlimited'
Set the requested ring buffer size for branch tracing in BTS
format. Default is 64KB.

If SIZE is a positive number, then GDB will try to allocate a
buffer of at least SIZE bytes for each new thread that uses the
btrace recording method and the BTS format. The actually obtained
buffer size may differ from the requested SIZE. Use the `info
record' command to see the actual buffer size for each thread that
uses the btrace recording method and the BTS format.

If LIMIT is `unlimited' or zero, GDB will try to allocate a buffer
of 4MB.

Bigger buffers mean longer traces. On the other hand, GDB will
also need longer to process the branch trace data before it can be
used.

`show record btrace bts buffer-size SIZE'
Show the current setting of the requested ring buffer size for
branch tracing in BTS format.

`set record btrace pt buffer-size SIZE'
`set record btrace pt buffer-size unlimited'
Set the requested ring buffer size for branch tracing in Intel
Processor Trace format. Default is 16KB.

If SIZE is a positive number, then GDB will try to allocate a
buffer of at least SIZE bytes for each new thread that uses the
btrace recording method and the Intel Processor Trace format. The
actually obtained buffer size may differ from the requested SIZE.
Use the `info record' command to see the actual buffer size for
each thread.

If LIMIT is `unlimited' or zero, GDB will try to allocate a buffer
of 4MB.

Bigger buffers mean longer traces. On the other hand, GDB will
also need longer to process the branch trace data before it can be
used.

`show record btrace pt buffer-size SIZE'
Show the current setting of the requested ring buffer size for
branch tracing in Intel Processor Trace format.

`info record'
Show various statistics about the recording depending on the
recording method:

`full'
For the `full' recording method, it shows the state of process
record and its in-memory execution log buffer, including:

* Whether in record mode or replay mode.

* Lowest recorded instruction number (counting from when
the current execution log started recording
instructions).

* Highest recorded instruction number.

* Current instruction about to be replayed (if in replay
mode).

* Number of instructions contained in the execution log.

* Maximum number of instructions that may be contained in
the execution log.

`btrace'
For the `btrace' recording method, it shows:

* Recording format.

* Number of instructions that have been recorded.

* Number of blocks of sequential control-flow formed by
the recorded instructions.

* Whether in record mode or replay mode.

For the `bts' recording format, it also shows:
* Size of the perf ring buffer.

For the `pt' recording format, it also shows:
* Size of the perf ring buffer.

`record delete'
When record target runs in replay mode ("in the past"), delete the
subsequent execution log and begin to record a new execution log
starting from the current address. This means you will abandon
the previously recorded "future" and begin recording a new
"future".

`record instruction-history'
Disassembles instructions from the recorded execution log. By
default, ten instructions are disassembled. This can be changed
using the `set record instruction-history-size' command.
Instructions are printed in execution order.

It can also print mixed source+disassembly if you specify the the
`/m' or `/s' modifier, and print the raw instructions in hex as
well as in symbolic form by specifying the `/r' or `/b' modifier.
The behaviour of the `/m', `/s', `/r', and `/b' modifiers are the
same as for the `disassemble' command (*note `disassemble':
disassemble.).

The current position marker is printed for the instruction at the
current program counter value. This instruction can appear
multiple times in the trace and the current position marker will
be printed every time. To omit the current position marker,
specify the `/p' modifier.

To better align the printed instructions when the trace contains
instructions from more than one function, the function name may be
omitted by specifying the `/f' modifier.

Speculatively executed instructions are prefixed with `?'. This
feature is not available for all recording formats.

There are several ways to specify what part of the execution log to
disassemble:

`record instruction-history INSN'
Disassembles ten instructions starting from instruction number
INSN.

`record instruction-history INSN, +/-N'
Disassembles N instructions around instruction number INSN.
If N is preceded with `+', disassembles N instructions after
instruction number INSN. If N is preceded with `-',
disassembles N instructions before instruction number INSN.

`record instruction-history'
Disassembles ten more instructions after the last disassembly.

`record instruction-history -'
Disassembles ten more instructions before the last
disassembly.

`record instruction-history BEGIN, END'
Disassembles instructions beginning with instruction number
BEGIN until instruction number END. The instruction number
END is included.

This command may not be available for all recording methods.

`set record instruction-history-size SIZE'
`set record instruction-history-size unlimited'
Define how many instructions to disassemble in the `record
instruction-history' command. The default value is 10. A SIZE of
`unlimited' means unlimited instructions.

`show record instruction-history-size'
Show how many instructions to disassemble in the `record
instruction-history' command.

`record function-call-history'
Prints the execution history at function granularity. For each
sequence of instructions that belong to the same function, it
prints the name of that function, the source lines for this
instruction sequence (if the `/l' modifier is specified), and the
instructions numbers that form the sequence (if the `/i' modifier
is specified). The function names are indented to reflect the
call stack depth if the `/c' modifier is specified. The `/l',
`/i', and `/c' modifiers can be given together.

(gdb) list 1, 10
1 void foo (void)
2 {
3 }
4
5 void bar (void)
6 {
7 ...
8 foo ();
9 ...
10 }
(gdb) record function-call-history /ilc
1 bar inst 1,4 at foo.c:6,8
2 foo inst 5,10 at foo.c:2,3
3 bar inst 11,13 at foo.c:9,10

By default, ten functions are printed. This can be changed using
the `set record function-call-history-size' command. Functions are
printed in execution order. There are several ways to specify what
to print:

`record function-call-history FUNC'
Prints ten functions starting from function number FUNC.

`record function-call-history FUNC, +/-N'
Prints N functions around function number FUNC. If N is
preceded with `+', prints N functions after function number
FUNC. If N is preceded with `-', prints N functions before
function number FUNC.

`record function-call-history'
Prints ten more functions after the last ten-function print.

`record function-call-history -'
Prints ten more functions before the last ten-function print.

`record function-call-history BEGIN, END'
Prints functions beginning with function number BEGIN until
function number END. The function number END is included.

This command may not be available for all recording methods.

`set record function-call-history-size SIZE'
`set record function-call-history-size unlimited'
Define how many functions to print in the `record
function-call-history' command. The default value is 10. A size
of `unlimited' means unlimited functions.

`show record function-call-history-size'
Show how many functions to print in the `record
function-call-history' command.

File: gdb.info, Node: Stack, Next: Source, Prev: Process Record and Replay, Up: Top

8 Examining the Stack
*********************

When your program has stopped, the first thing you need to know is
where it stopped and how it got there.

Each time your program performs a function call, information about
the call is generated. That information includes the location of the
call in your program, the arguments of the call, and the local
variables of the function being called. The information is saved in a
block of data called a "stack frame". The stack frames are allocated
in a region of memory called the "call stack".

When your program stops, the GDB commands for examining the stack
allow you to see all of this information.

One of the stack frames is "selected" by GDB and many GDB commands
refer implicitly to the selected frame. In particular, whenever you
ask GDB for the value of a variable in your program, the value is found
in the selected frame. There are special GDB commands to select
whichever frame you are interested in. *Note Selecting a Frame:
Selection.

When your program stops, GDB automatically selects the currently
executing frame and describes it briefly, similar to the `frame'
command (*note Information about a Frame: Frame Info.).

* Menu:

* Frames:: Stack frames
* Backtrace:: Backtraces
* Selection:: Selecting a frame
* Frame Info:: Information on a frame
* Frame Apply:: Applying a command to several frames
* Frame Filter Management:: Managing frame filters

File: gdb.info, Node: Frames, Next: Backtrace, Up: Stack

8.1 Stack Frames
================

The call stack is divided up into contiguous pieces called "stack
frames", or "frames" for short; each frame is the data associated with
one call to one function. The frame contains the arguments given to
the function, the function's local variables, and the address at which
the function is executing.

When your program is started, the stack has only one frame, that of
the function `main'. This is called the "initial" frame or the
"outermost" frame. Each time a function is called, a new frame is
made. Each time a function returns, the frame for that function
invocation is eliminated. If a function is recursive, there can be
many frames for the same function. The frame for the function in which
execution is actually occurring is called the "innermost" frame. This
is the most recently created of all the stack frames that still exist.

Inside your program, stack frames are identified by their addresses.
A stack frame consists of many bytes, each of which has its own
address; each kind of computer has a convention for choosing one byte
whose address serves as the address of the frame. Usually this address
is kept in a register called the "frame pointer register" (*note $fp:
Registers.) while execution is going on in that frame.

GDB labels each existing stack frame with a "level", a number that
is zero for the innermost frame, one for the frame that called it, and
so on upward. These level numbers give you a way of designating stack
frames in GDB commands. The terms "frame number" and "frame level" can
be used interchangeably to describe this number.

Some compilers provide a way to compile functions so that they
operate without stack frames. (For example, the GCC option
`-fomit-frame-pointer'
generates functions without a frame.) This is occasionally done
with heavily used library functions to save the frame setup time. GDB
has limited facilities for dealing with these function invocations. If
the innermost function invocation has no stack frame, GDB nevertheless
regards it as though it had a separate frame, which is numbered zero as
usual, allowing correct tracing of the function call chain. However,
GDB has no provision for frameless functions elsewhere in the stack.

File: gdb.info, Node: Backtrace, Next: Selection, Prev: Frames, Up: Stack

8.2 Backtraces
==============

A backtrace is a summary of how your program got where it is. It shows
one line per frame, for many frames, starting with the currently
executing frame (frame zero), followed by its caller (frame one), and
on up the stack.

To print a backtrace of the entire stack, use the `backtrace'
command, or its alias `bt'. This command will print one line per frame
for frames in the stack. By default, all stack frames are printed.
You can stop the backtrace at any time by typing the system interrupt
character, normally `Ctrl-c'.

`backtrace [OPTION]... [QUALIFIER]... [COUNT]'
`bt [OPTION]... [QUALIFIER]... [COUNT]'
Print the backtrace of the entire stack.

The optional COUNT can be one of the following:

`N'
`N'
Print only the innermost N frames, where N is a positive
number.

`-N'
`-N'
Print only the outermost N frames, where N is a positive
number.

Options:

`-full'
Print the values of the local variables also. This can be
combined with the optional COUNT to limit the number of
frames shown.

`-no-filters'
Do not run Python frame filters on this backtrace. *Note
Frame Filter API::, for more information. Additionally use
*Note disable frame-filter all:: to turn off all frame
filters. This is only relevant when GDB has been configured
with `Python' support.

`-hide'
A Python frame filter might decide to "elide" some frames.
Normally such elided frames are still printed, but they are
indented relative to the filtered frames that cause them to
be elided. The `-hide' option causes elided frames to not be
printed at all.

The `backtrace' command also supports a number of options that
allow overriding relevant global print settings as set by `set
backtrace' and `set print' subcommands:

`-past-main [`on'|`off']'
Set whether backtraces should continue past `main'. Related
setting: *Note set backtrace past-main::.

`-past-entry [`on'|`off']'
Set whether backtraces should continue past the entry point
of a program. Related setting: *Note set backtrace
past-entry::.

`-entry-values `no'|`only'|`preferred'|`if-needed'|`both'|`compact'|`default''
Set printing of function arguments at function entry.
Related setting: *Note set print entry-values::.

`-frame-arguments `all'|`scalars'|`none''
Set printing of non-scalar frame arguments. Related setting:
*Note set print frame-arguments::.

`-raw-frame-arguments [`on'|`off']'
Set whether to print frame arguments in raw form. Related
setting: *Note set print raw-frame-arguments::.

`-frame-info `auto'|`source-line'|`location'|`source-and-location'|`location-and-address'|`short-location''
Set printing of frame information. Related setting: *Note
set print frame-info::.

The optional QUALIFIER is maintained for backward compatibility.
It can be one of the following:

`full'
Equivalent to the `-full' option.

`no-filters'
Equivalent to the `-no-filters' option.

`hide'
Equivalent to the `-hide' option.

The names `where' and `info stack' (abbreviated `info s') are
additional aliases for `backtrace'.

In a multi-threaded program, GDB by default shows the backtrace only
for the current thread. To display the backtrace for several or all of
the threads, use the command `thread apply' (*note thread apply:
Threads.). For example, if you type `thread apply all backtrace', GDB
will display the backtrace for all the threads; this is handy when you
debug a core dump of a multi-threaded program.

Each line in the backtrace shows the frame number and the function
name. The program counter value is also shown--unless you use `set
print address off'. The backtrace also shows the source file name and
line number, as well as the arguments to the function. The program
counter value is omitted if it is at the beginning of the code for that
line number.

Here is an example of a backtrace. It was made with the command `bt
3', so it shows the innermost three frames.

#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)

The display for frame zero does not begin with a program counter value,
indicating that your program has stopped at the beginning of the code
for line `993' of `builtin.c'.

The value of parameter `data' in frame 1 has been replaced by `...'.
By default, GDB prints the value of a parameter only if it is a scalar
(integer, pointer, enumeration, etc). See command `set print
frame-arguments' in *Note Print Settings:: for more details on how to
configure the way function parameter values are printed. The command
`set print frame-info' (*note Print Settings::) controls what frame
information is printed.

If your program was compiled with optimizations, some compilers will
optimize away arguments passed to functions if those arguments are
never used after the call. Such optimizations generate code that
passes arguments through registers, but doesn't store those arguments
in the stack frame. GDB has no way of displaying such arguments in
stack frames other than the innermost one. Here's what such a
backtrace might look like:

#0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242
#2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)

The values of arguments that were not saved in their stack frames are
shown as `<optimized out>'.

If you need to display the values of such optimized-out arguments,
either deduce that from other variables whose values depend on the one
you are interested in, or recompile without optimizations.

Most programs have a standard user entry point--a place where system
libraries and startup code transition into user code. For C this is
`main'(1). When GDB finds the entry function in a backtrace it will
terminate the backtrace, to avoid tracing into highly system-specific
(and generally uninteresting) code.

If you need to examine the startup code, or limit the number of
levels in a backtrace, you can change this behavior:

`set backtrace past-main'
`set backtrace past-main on'
Backtraces will continue past the user entry point.

`set backtrace past-main off'
Backtraces will stop when they encounter the user entry point.
This is the default.

`show backtrace past-main'
Display the current user entry point backtrace policy.

`set backtrace past-entry'
`set backtrace past-entry on'
Backtraces will continue past the internal entry point of an
application. This entry point is encoded by the linker when the
application is built, and is likely before the user entry point
`main' (or equivalent) is called.

`set backtrace past-entry off'
Backtraces will stop when they encounter the internal entry point
of an application. This is the default.

`show backtrace past-entry'
Display the current internal entry point backtrace policy.

`set backtrace limit N'
`set backtrace limit 0'
`set backtrace limit unlimited'
Limit the backtrace to N levels. A value of `unlimited' or zero
means unlimited levels.

`show backtrace limit'
Display the current limit on backtrace levels.

You can control how file names are displayed.

`set filename-display'
`set filename-display relative'
Display file names relative to the compilation directory. This is
the default.

`set filename-display basename'
Display only basename of a filename.

`set filename-display absolute'
Display an absolute filename.

`show filename-display'
Show the current way to display filenames.

---------- Footnotes ----------

(1) Note that embedded programs (the so-called "free-standing"
environment) are not required to have a `main' function as the entry
point. They could even have multiple entry points.

File: gdb.info, Node: Selection, Next: Frame Info, Prev: Backtrace, Up: Stack

8.3 Selecting a Frame
=====================

Most commands for examining the stack and other data in your program
work on whichever stack frame is selected at the moment. Here are the
commands for selecting a stack frame; all of them finish by printing a
brief description of the stack frame just selected.

`frame [ FRAME-SELECTION-SPEC ]'

`f [ FRAME-SELECTION-SPEC ]'
The `frame' command allows different stack frames to be selected.
The FRAME-SELECTION-SPEC can be any of the following:

`NUM'

`level NUM'
Select frame level NUM. Recall that frame zero is the
innermost (currently executing) frame, frame one is the frame
that called the innermost one, and so on. The highest level
frame is usually the one for `main'.

As this is the most common method of navigating the frame
stack, the string `level' can be omitted. For example, the
following two commands are equivalent:

(gdb) frame 3
(gdb) frame level 3

`address STACK-ADDRESS'
Select the frame with stack address STACK-ADDRESS. The
STACK-ADDRESS for a frame can be seen in the output of `info
frame', for example:

(gdb) info frame
Stack level 1, frame at 0x7fffffffda30:
rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
tail call frame, caller of frame at 0x7fffffffda30
source language c++.
Arglist at unknown address.
Locals at unknown address, Previous frame's sp is 0x7fffffffda30

The STACK-ADDRESS for this frame is `0x7fffffffda30' as
indicated by the line:

Stack level 1, frame at 0x7fffffffda30:

`function FUNCTION-NAME'
Select the stack frame for function FUNCTION-NAME. If there
are multiple stack frames for function FUNCTION-NAME then the
inner most stack frame is selected.

`view STACK-ADDRESS [ PC-ADDR ]'
View a frame that is not part of GDB's backtrace. The frame
viewed has stack address STACK-ADDR, and optionally, a program
counter address of PC-ADDR.

This is useful mainly if the chaining of stack frames has been
damaged by a bug, making it impossible for GDB to assign
numbers properly to all frames. In addition, this can be
useful when your program has multiple stacks and switches
between them.

When viewing a frame outside the current backtrace using
`frame view' then you can always return to the original stack
using one of the previous stack frame selection instructions,
for example `frame level 0'.

`up N'
Move N frames up the stack; N defaults to 1. For positive numbers
N, this advances toward the outermost frame, to higher frame
numbers, to frames that have existed longer.

`down N'
Move N frames down the stack; N defaults to 1. For positive
numbers N, this advances toward the innermost frame, to lower
frame numbers, to frames that were created more recently. You may
abbreviate `down' as `do'.

All of these commands end by printing two lines of output describing
the frame. The first line shows the frame number, the function name,
the arguments, and the source file and line number of execution in that
frame. The second line shows the text of that source line.

For example:

(gdb) up
#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
at env.c:10
10 read_input_file (argv[i]);

After such a printout, the `list' command with no arguments prints
ten lines centered on the point of execution in the frame. You can
also edit the program at the point of execution with your favorite
editing program by typing `edit'. *Note Printing Source Lines: List,
for details.

`select-frame [ FRAME-SELECTION-SPEC ]'
The `select-frame' command is a variant of `frame' that does not
display the new frame after selecting it. This command is
intended primarily for use in GDB command scripts, where the
output might be unnecessary and distracting. The
FRAME-SELECTION-SPEC is as for the `frame' command described in
*Note Selecting a Frame: Selection.

`up-silently N'
`down-silently N'
These two commands are variants of `up' and `down', respectively;
they differ in that they do their work silently, without causing
display of the new frame. They are intended primarily for use in
GDB command scripts, where the output might be unnecessary and
distracting.

File: gdb.info, Node: Frame Info, Next: Frame Apply, Prev: Selection, Up: Stack

8.4 Information About a Frame
=============================

There are several other commands to print information about the selected
stack frame.

`frame'
`f'
When used without any argument, this command does not change which
frame is selected, but prints a brief description of the currently
selected stack frame. It can be abbreviated `f'. With an
argument, this command is used to select a stack frame. *Note
Selecting a Frame: Selection.

`info frame'
`info f'
This command prints a verbose description of the selected stack
frame, including:

* the address of the frame

* the address of the next frame down (called by this frame)

* the address of the next frame up (caller of this frame)

* the language in which the source code corresponding to this
frame is written

* the address of the frame's arguments

* the address of the frame's local variables

* the program counter saved in it (the address of execution in
the caller frame)

* which registers were saved in the frame

The verbose description is useful when something has gone wrong
that has made the stack format fail to fit the usual conventions.

`info frame [ FRAME-SELECTION-SPEC ]'
`info f [ FRAME-SELECTION-SPEC ]'
Print a verbose description of the frame selected by
FRAME-SELECTION-SPEC. The FRAME-SELECTION-SPEC is the same as for
the `frame' command (*note Selecting a Frame: Selection.). The
selected frame remains unchanged by this command.

`info args [-q]'
Print the arguments of the selected frame, each on a separate line.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no argument
have been printed.

`info args [-q] [-t TYPE_REGEXP] [REGEXP]'
Like `info args', but only print the arguments selected with the
provided regexp(s).

If REGEXP is provided, print only the arguments whose names match
the regular expression REGEXP.

If TYPE_REGEXP is provided, print only the arguments whose types,
as printed by the `whatis' command, match the regular expression
TYPE_REGEXP. If TYPE_REGEXP contains space(s), it should be
enclosed in quote characters. If needed, use backslash to escape
the meaning of special characters or quotes.

If both REGEXP and TYPE_REGEXP are provided, an argument is
printed only if its name matches REGEXP and its type matches
TYPE_REGEXP.

`info locals [-q]'
Print the local variables of the selected frame, each on a separate
line. These are all variables (declared either static or
automatic) accessible at the point of execution of the selected
frame.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no local
variables have been printed.

`info locals [-q] [-t TYPE_REGEXP] [REGEXP]'
Like `info locals', but only print the local variables selected
with the provided regexp(s).

If REGEXP is provided, print only the local variables whose names
match the regular expression REGEXP.

If TYPE_REGEXP is provided, print only the local variables whose
types, as printed by the `whatis' command, match the regular
expression TYPE_REGEXP. If TYPE_REGEXP contains space(s), it
should be enclosed in quote characters. If needed, use backslash
to escape the meaning of special characters or quotes.

If both REGEXP and TYPE_REGEXP are provided, a local variable is
printed only if its name matches REGEXP and its type matches
TYPE_REGEXP.

The command `info locals -q -t TYPE_REGEXP' can usefully be
combined with the commands `frame apply' and `thread apply'. For
example, your program might use Resource Acquisition Is
Initialization types (RAII) such as `lock_something_t': each local
variable of type `lock_something_t' automatically places a lock
that is destroyed when the variable goes out of scope. You can
then list all acquired locks in your program by doing
thread apply all -s frame apply all -s info locals -q -t lock_something_t
or the equivalent shorter form
tfaas i lo -q -t lock_something_t

File: gdb.info, Node: Frame Apply, Next: Frame Filter Management, Prev: Frame Info, Up: Stack

8.5 Applying a Command to Several Frames.
=========================================

`frame apply [all | COUNT | -COUNT | level LEVEL...] [OPTION]... COMMAND'
The `frame apply' command allows you to apply the named COMMAND to
one or more frames.

``all''
Specify `all' to apply COMMAND to all frames.

`COUNT'
Use COUNT to apply COMMAND to the innermost COUNT frames,
where COUNT is a positive number.

`-COUNT'
Use -COUNT to apply COMMAND to the outermost COUNT frames,
where COUNT is a positive number.

``level''
Use `level' to apply COMMAND to the set of frames identified
by the LEVEL list. LEVEL is a frame level or a range of frame
levels as LEVEL1-LEVEL2. The frame level is the number shown
in the first field of the `backtrace' command output. E.g.,
`2-4 6-8 3' indicates to apply COMMAND for the frames at
levels 2, 3, 4, 6, 7, 8, and then again on frame at level 3.

Note that the frames on which `frame apply' applies a command are
also influenced by the `set backtrace' settings such as `set
backtrace past-main' and `set backtrace limit N'. *Note
Backtraces: Backtrace.

The `frame apply' command also supports a number of options that
allow overriding relevant `set backtrace' settings:

`-past-main [`on'|`off']'
Whether backtraces should continue past `main'. Related
setting: *Note set backtrace past-main::.

`-past-entry [`on'|`off']'
Whether backtraces should continue past the entry point of a
program. Related setting: *Note set backtrace past-entry::.

By default, GDB displays some frame information before the output
produced by COMMAND, and an error raised during the execution of a
COMMAND will abort `frame apply'. The following options can be
used to fine-tune these behaviors:

`-c'
The flag `-c', which stands for `continue', causes any errors
in COMMAND to be displayed, and the execution of `frame
apply' then continues.

`-s'
The flag `-s', which stands for `silent', causes any errors
or empty output produced by a COMMAND to be silently ignored.
That is, the execution continues, but the frame information
and errors are not printed.

`-q'
The flag `-q' (`quiet') disables printing the frame
information.

The following example shows how the flags `-c' and `-s' are
working when applying the command `p j' to all frames, where
variable `j' can only be successfully printed in the outermost `#1
main' frame.

(gdb) frame apply all p j
#0 some_function (i=5) at fun.c:4
No symbol "j" in current context.
(gdb) frame apply all -c p j
#0 some_function (i=5) at fun.c:4
No symbol "j" in current context.
#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11
$1 = 5
(gdb) frame apply all -s p j
#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11
$2 = 5
(gdb)

By default, `frame apply', prints the frame location information
before the command output:

(gdb) frame apply all p $sp
#0 some_function (i=5) at fun.c:4
$4 = (void *) 0xffffd1e0
#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11
$5 = (void *) 0xffffd1f0
(gdb)

If the flag `-q' is given, no frame information is printed:
(gdb) frame apply all -q p $sp
$12 = (void *) 0xffffd1e0
$13 = (void *) 0xffffd1f0
(gdb)

`faas COMMAND'
Shortcut for `frame apply all -s COMMAND'. Applies COMMAND on all
frames, ignoring errors and empty output.

It can for example be used to print a local variable or a function
argument without knowing the frame where this variable or argument
is, using:
(gdb) faas p some_local_var_i_do_not_remember_where_it_is

The `faas' command accepts the same options as the `frame apply'
command. *Note frame apply: Frame Apply.

Note that the command `tfaas COMMAND' applies COMMAND on all
frames of all threads. See *Note Threads: Threads.

File: gdb.info, Node: Frame Filter Management, Prev: Frame Apply, Up: Stack

8.6 Management of Frame Filters.
================================

Frame filters are Python based utilities to manage and decorate the
output of frames. *Note Frame Filter API::, for further information.

Managing frame filters is performed by several commands available
within GDB, detailed here.

`info frame-filter'
Print a list of installed frame filters from all dictionaries,
showing their name, priority and enabled status.

`disable frame-filter FILTER-DICTIONARY FILTER-NAME'
Disable a frame filter in the dictionary matching
FILTER-DICTIONARY and FILTER-NAME. The FILTER-DICTIONARY may be
`all', `global', `progspace', or the name of the object file where
the frame filter dictionary resides. When `all' is specified, all
frame filters across all dictionaries are disabled. The
FILTER-NAME is the name of the frame filter and is used when `all'
is not the option for FILTER-DICTIONARY. A disabled frame-filter
is not deleted, it may be enabled again later.

`enable frame-filter FILTER-DICTIONARY FILTER-NAME'
Enable a frame filter in the dictionary matching FILTER-DICTIONARY
and FILTER-NAME. The FILTER-DICTIONARY may be `all', `global',
`progspace' or the name of the object file where the frame filter
dictionary resides. When `all' is specified, all frame filters
across all dictionaries are enabled. The FILTER-NAME is the name
of the frame filter and is used when `all' is not the option for
FILTER-DICTIONARY.

Example:

(gdb) info frame-filter

global frame-filters:
Priority Enabled Name
1000 No PrimaryFunctionFilter
100 Yes Reverse

progspace /build/test frame-filters:
Priority Enabled Name
100 Yes ProgspaceFilter

objfile /build/test frame-filters:
Priority Enabled Name
999 Yes BuildProgramFilter

(gdb) disable frame-filter /build/test BuildProgramFilter
(gdb) info frame-filter

global frame-filters:
Priority Enabled Name
1000 No PrimaryFunctionFilter
100 Yes Reverse

progspace /build/test frame-filters:
Priority Enabled Name
100 Yes ProgspaceFilter

objfile /build/test frame-filters:
Priority Enabled Name
999 No BuildProgramFilter

(gdb) enable frame-filter global PrimaryFunctionFilter
(gdb) info frame-filter

global frame-filters:
Priority Enabled Name
1000 Yes PrimaryFunctionFilter
100 Yes Reverse

progspace /build/test frame-filters:
Priority Enabled Name
100 Yes ProgspaceFilter

objfile /build/test frame-filters:
Priority Enabled Name
999 No BuildProgramFilter

`set frame-filter priority FILTER-DICTIONARY FILTER-NAME PRIORITY'
Set the PRIORITY of a frame filter in the dictionary matching
FILTER-DICTIONARY, and the frame filter name matching FILTER-NAME.
The FILTER-DICTIONARY may be `global', `progspace' or the name of
the object file where the frame filter dictionary resides. The
PRIORITY is an integer.

`show frame-filter priority FILTER-DICTIONARY FILTER-NAME'
Show the PRIORITY of a frame filter in the dictionary matching
FILTER-DICTIONARY, and the frame filter name matching FILTER-NAME.
The FILTER-DICTIONARY may be `global', `progspace' or the name of
the object file where the frame filter dictionary resides.

Example:

(gdb) info frame-filter

global frame-filters:
Priority Enabled Name
1000 Yes PrimaryFunctionFilter
100 Yes Reverse

progspace /build/test frame-filters:
Priority Enabled Name
100 Yes ProgspaceFilter

objfile /build/test frame-filters:
Priority Enabled Name
999 No BuildProgramFilter

(gdb) set frame-filter priority global Reverse 50
(gdb) info frame-filter

global frame-filters:
Priority Enabled Name
1000 Yes PrimaryFunctionFilter
50 Yes Reverse

progspace /build/test frame-filters:
Priority Enabled Name
100 Yes ProgspaceFilter

objfile /build/test frame-filters:
Priority Enabled Name
999 No BuildProgramFilter

File: gdb.info, Node: Source, Next: Data, Prev: Stack, Up: Top

9 Examining Source Files
************************

GDB can print parts of your program's source, since the debugging
information recorded in the program tells GDB what source files were
used to build it. When your program stops, GDB spontaneously prints
the line where it stopped. Likewise, when you select a stack frame
(*note Selecting a Frame: Selection.), GDB prints the line where
execution in that frame has stopped. You can print other portions of
source files by explicit command.

If you use GDB through its GNU Emacs interface, you may prefer to
use Emacs facilities to view source; see *Note Using GDB under GNU
Emacs: Emacs.

* Menu:

* List:: Printing source lines
* Location Specifications:: How to specify code locations
* Edit:: Editing source files
* Search:: Searching source files
* Source Path:: Specifying source directories
* Machine Code:: Source and machine code
* Disable Reading Source:: Disable Reading Source Code

File: gdb.info, Node: List, Next: Location Specifications, Up: Source

9.1 Printing Source Lines
=========================

To print lines from a source file, use the `list' command (abbreviated
`l'). By default, ten lines are printed. There are several ways to
specify what part of the file you want to print; see *Note Location
Specifications::, for the full list.

Here are the forms of the `list' command most commonly used:

`list LINENUM'
Print lines centered around line number LINENUM in the current
source file.

`list FUNCTION'
Print lines centered around the beginning of function FUNCTION.

`list'
Print more lines. If the last lines printed were printed with a
`list' command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line
printed as part of displaying a stack frame (*note Examining the
Stack: Stack.), this prints lines centered around that line. If no
`list' command has been used and no solitary line was printed, it
prints the lines around the function `main'.

`list +'
Same as using with no arguments.

`list -'
Print lines just before the lines last printed.

`list .'
Print the lines surrounding the point of execution within the
currently selected frame. If the inferior is not running, print
lines around the start of the main function instead.

By default, GDB prints ten source lines with any of these forms of
the `list' command. You can change this using `set listsize':

`set listsize COUNT'
`set listsize unlimited'
Make the `list' command display COUNT source lines (unless the
`list' argument explicitly specifies some other number). Setting
COUNT to `unlimited' or 0 means there's no limit.

`show listsize'
Display the number of lines that `list' prints.

Repeating a `list' command with <RET> discards the argument, so it
is equivalent to typing just `list'. This is more useful than listing
the same lines again. An exception is made for an argument of `-';
that argument is preserved in repetition so that each repetition moves
up in the source file.

In general, the `list' command expects you to supply zero, one or
two location specs. These location specs are interpreted to resolve to
source code lines; there are several ways of writing them (*note
Location Specifications::), but the effect is always to resolve to some
source lines to display.

Here is a complete description of the possible arguments for `list':

`list LOCSPEC'
Print lines centered around the line or lines of all the code
locations that result from resolving LOCSPEC.

`list FIRST,LAST'
Print lines from FIRST to LAST. Both arguments are location
specs. When a `list' command has two location specs, and the
source file of the second location spec is omitted, this refers to
the same source file as the first location spec. If either FIRST
or LAST resolve to more than one source line in the program, then
the list command shows the list of resolved source lines and does
not proceed with the source code listing.

`list ,LAST'
Print lines ending with LAST.

Likewise, if LAST resolves to more than one source line in the
program, then the list command prints the list of resolved source
lines and does not proceed with the source code listing.

`list FIRST,'
Print lines starting with FIRST.

`list +'
Print lines just after the lines last printed.

`list -'
Print lines just before the lines last printed.

`list'
As described in the preceding table.

File: gdb.info, Node: Location Specifications, Next: Edit, Prev: List, Up: Source

9.2 Location Specifications
===========================

Several GDB commands accept arguments that specify a location or
locations of your program's code. Many times locations are specified
using a source line number, but they can also be specified by a
function name, an address, a label, etc. The different forms of
specifying a location that GDB recognizes are collectively known as
forms of "location specification", or "location spec". This section
documents the forms of specifying locations that GDB recognizes.

When you specify a location, GDB needs to find the place in your
program, known as "code location", that corresponds to the given
location spec. We call this process of finding actual code locations
corresponding to a location spec "location resolution".

A concrete code location in your program is uniquely identifiable by
a set of several attributes: its source line number, the name of its
source file, the fully-qualified and prototyped function in which it is
defined, and an instruction address. Because each inferior has its own
address space, the inferior number is also a necessary part of these
attributes.

By contrast, location specs you type will many times omit some of
these attributes. For example, it is customary to specify just the
source line number to mean a line in the current source file, or
specify just the basename of the file, omitting its directories. In
other words, a location spec is usually incomplete, a kind of
blueprint, and GDB needs to complete the missing attributes by using
the implied defaults, and by considering the source code and the debug
information available to it. This is what location resolution is about.

The resolution of an incomplete location spec can produce more than a
single code location, if the spec doesn't allow distinguishing between
them. Here are some examples of situations that result in a location
spec matching multiple code locations in your program:

* The location spec specifies a function name, and there are several
functions in the program which have that name. (To distinguish
between them, you can specify a fully-qualified and prototyped
function name, such as `A::func(int)' instead of just `func'.)

* The location spec specifies a source file name, and there are
several source files in the program that share the same name, for
example several files with the same basename in different
subdirectories. (To distinguish between them, specify enough
leading directories with the file name.)

* For a C++ constructor, the GCC compiler generates several
instances of the function body, used in different cases, but their
source-level names are identical.

* For a C++ template function, a given line in the function can
correspond to any number of instantiations.

* For an inlined function, a given source line can correspond to
several actual code locations with that function's inlined code.

Resolution of a location spec can also fail to produce a complete
code location, or even fail to produce any code location. Here are some
examples of such situations:

* Some parts of the program lack detailed enough debug info, so the
resolved code location lacks some attributes, like source file name
and line number, leaving just the instruction address and perhaps
also a function name. Such an incomplete code location is only
usable in contexts that work with addresses and/or function names.
Some commands can only work with complete code locations.

* The location spec specifies a function name, and there are no
functions in the program by that name, or they only exist in a
yet-unloaded shared library.

* The location spec specifies a source file name, and there are no
source files in the program by that name, or they only exist in a
yet-unloaded shared library.

* The location spec specifies both a source file name and a source
line number, and even though there are source files in the program
that match the file name, none of those files has the specified
line number.

Locations may be specified using three different formats: linespec
locations, explicit locations, or address locations. The following
subsections describe these formats.

* Menu:

* Linespec Locations:: Linespec locations
* Explicit Locations:: Explicit locations
* Address Locations:: Address locations

File: gdb.info, Node: Linespec Locations, Next: Explicit Locations, Up: Location Specifications

9.2.1 Linespec Locations
------------------------

A "linespec" is a colon-separated list of source location parameters
such as file name, function name, etc. Here are all the different ways
of specifying a linespec:

`LINENUM'
Specifies the line number LINENUM of the current source file.

`-OFFSET'
`+OFFSET'
Specifies the line OFFSET lines before or after the "current
line". For the `list' command, the current line is the last one
printed; for the breakpoint commands, this is the line at which
execution stopped in the currently selected "stack frame" (*note
Frames: Frames, for a description of stack frames.) When used as
the second of the two linespecs in a `list' command, this
specifies the line OFFSET lines up or down from the first linespec.

`FILENAME:LINENUM'
Specifies the line LINENUM in the source file FILENAME. If
FILENAME is a relative file name, then it will match any source
file name with the same trailing components. For example, if
FILENAME is `gcc/expr.c', then it will match source file name of
`/build/trunk/gcc/expr.c', but not `/build/trunk/libcpp/expr.c' or
`/build/trunk/gcc/x-expr.c'.

`FUNCTION'
Specifies the line that begins the body of the function FUNCTION.
For example, in C, this is the line with the open brace.

By default, in C++ and Ada, FUNCTION is interpreted as specifying
all functions named FUNCTION in all scopes. For C++, this means
in all namespaces and classes. For Ada, this means in all
packages.

For example, assuming a program with C++ symbols named
`A::B::func' and `B::func', both commands `break func' and
`break B::func' set a breakpoint on both symbols.

Commands that accept a linespec let you override this with the
`-qualified' option. For example, `break -qualified func' sets a
breakpoint on a free-function named `func' ignoring any C++ class
methods and namespace functions called `func'.

*Note Explicit Locations::.

`FUNCTION:LABEL'
Specifies the line where LABEL appears in FUNCTION.

`FILENAME:FUNCTION'
Specifies the line that begins the body of the function FUNCTION
in the file FILENAME. You only need the file name with a function
name to avoid ambiguity when there are identically named functions
in different source files.

`LABEL'
Specifies the line at which the label named LABEL appears in the
function corresponding to the currently selected stack frame. If
there is no current selected stack frame (for instance, if the
inferior is not running), then GDB will not search for a label.

`-pstap|-probe-stap [OBJFILE:[PROVIDER:]]NAME'
The GNU/Linux tool `SystemTap' provides a way for applications to
embed static probes. *Note Static Probe Points::, for more
information on finding and using static probes. This form of
linespec specifies the location of such a static probe.

If OBJFILE is given, only probes coming from that shared library
or executable matching OBJFILE as a regular expression are
considered. If PROVIDER is given, then only probes from that
provider are considered. If several probes match the spec, GDB
will insert a breakpoint at each one of those probes.

File: gdb.info, Node: Explicit Locations, Next: Address Locations, Prev: Linespec Locations, Up: Location Specifications

9.2.2 Explicit Locations
------------------------

"Explicit locations" allow the user to directly specify the source
location's parameters using option-value pairs.

Explicit locations are useful when several functions, labels, or
file names have the same name (base name for files) in the program's
sources. In these cases, explicit locations point to the source line
you meant more accurately and unambiguously. Also, using explicit
locations might be faster in large programs.

For example, the linespec `foo:bar' may refer to a function `bar'
defined in the file named `foo' or the label `bar' in a function named
`foo'. GDB must search either the file system or the symbol table to
know.

The list of valid explicit location options is summarized in the
following table:

`-source FILENAME'
The value specifies the source file name. To differentiate between
files with the same base name, prepend as many directories as is
necessary to uniquely identify the desired file, e.g.,
`foo/bar/baz.c'. Otherwise GDB will use the first file it finds
with the given base name. This option requires the use of either
`-function' or `-line'.

`-function FUNCTION'
The value specifies the name of a function. Operations on
function locations unmodified by other options (such as `-label'
or `-line') refer to the line that begins the body of the function.
In C, for example, this is the line with the open brace.

By default, in C++ and Ada, FUNCTION is interpreted as specifying
all functions named FUNCTION in all scopes. For C++, this means
in all namespaces and classes. For Ada, this means in all
packages.

For example, assuming a program with C++ symbols named
`A::B::func' and `B::func', both commands `break -function func'
and `break -function B::func' set a breakpoint on both symbols.

You can use the `-qualified' flag to override this (see below).

`-qualified'
This flag makes GDB interpret a function name specified with
`-function' as a complete fully-qualified name.

For example, assuming a C++ program with symbols named
`A::B::func' and `B::func', the
`break -qualified -function B::func' command sets a breakpoint on
`B::func', only.

(Note: the `-qualified' option can precede a linespec as well
(*note Linespec Locations::), so the particular example above
could be simplified as `break -qualified B::func'.)

`-label LABEL'
The value specifies the name of a label. When the function name
is not specified, the label is searched in the function of the
currently selected stack frame.

`-line NUMBER'
The value specifies a line offset for the location. The offset
may either be absolute (`-line 3') or relative (`-line +3'),
depending on the command. When specified without any other
options, the line offset is relative to the current line.

Explicit location options may be abbreviated by omitting any
non-unique trailing characters from the option name, e.g.,
`break -s main.c -li 3'.

File: gdb.info, Node: Address Locations, Prev: Explicit Locations, Up: Location Specifications

9.2.3 Address Locations
-----------------------

"Address locations" indicate a specific program address. They have the
generalized form *ADDRESS.

For line-oriented commands, such as `list' and `edit', this
specifies a source line that contains ADDRESS. For `break' and other
breakpoint-oriented commands, this can be used to set breakpoints in
parts of your program which do not have debugging information or source
files.

Here ADDRESS may be any expression valid in the current working
language (*note working language: Languages.) that specifies a code
address. In addition, as a convenience, GDB extends the semantics of
expressions used in locations to cover several situations that
frequently occur during debugging. Here are the various forms of
ADDRESS:

`EXPRESSION'
Any expression valid in the current working language.

`FUNCADDR'
An address of a function or procedure derived from its name. In C,
C++, Objective-C, Fortran, minimal, and assembly, this is simply
the function's name FUNCTION (and actually a special case of a
valid expression). In Pascal and Modula-2, this is `&FUNCTION'.
In Ada, this is `FUNCTION'Address' (although the Pascal form also
works).

This form specifies the address of the function's first
instruction, before the stack frame and arguments have been set up.

`'FILENAME':FUNCADDR'
Like FUNCADDR above, but also specifies the name of the source
file explicitly. This is useful if the name of the function does
not specify the function unambiguously, e.g., if there are several
functions with identical names in different source files.

File: gdb.info, Node: Edit, Next: Search, Prev: Location Specifications, Up: Source

9.3 Editing Source Files
========================

To edit the lines in a source file, use the `edit' command. The
editing program of your choice is invoked with the current line set to
the active line in the program. Alternatively, there are several ways
to specify what part of the file you want to print if you want to see
other parts of the program:

`edit LOCSPEC'
Edit the source file of the code location that results from
resolving `locspec'. Editing starts at the source file and source
line `locspec' resolves to. *Note Location Specifications::, for
all the possible forms of the LOCSPEC argument.

If `locspec' resolves to more than one source line in your
program, then the command prints the list of resolved source lines
and does not proceed with the editing.

Here are the forms of the `edit' command most commonly used:

`edit NUMBER'
Edit the current source file with NUMBER as the active line
number.

`edit FUNCTION'
Edit the file containing FUNCTION at the beginning of its
definition.

9.3.1 Choosing your Editor
--------------------------

You can customize GDB to use any editor you want (1). By default, it
is `/bin/ex', but you can change this by setting the environment
variable `EDITOR' before using GDB. For example, to configure GDB to
use the `vi' editor, you could use these commands with the `sh' shell:
EDITOR=/usr/bin/vi
export EDITOR
gdb ...
or in the `csh' shell,
setenv EDITOR /usr/bin/vi
gdb ...

---------- Footnotes ----------

(1) The only restriction is that your editor (say `ex'), recognizes
the following command-line syntax:
ex +NUMBER file
The optional numeric value +NUMBER specifies the number of the line
in the file where to start editing.

File: gdb.info, Node: Search, Next: Source Path, Prev: Edit, Up: Source

9.4 Searching Source Files
==========================

There are two commands for searching through the current source file
for a regular expression.

`forward-search REGEXP'
`search REGEXP'
The command `forward-search REGEXP' checks each line, starting
with the one following the last line listed, for a match for
REGEXP. It lists the line that is found. You can use the synonym
`search REGEXP' or abbreviate the command name as `fo'.

`reverse-search REGEXP'
The command `reverse-search REGEXP' checks each line, starting
with the one before the last line listed and going backward, for a
match for REGEXP. It lists the line that is found. You can
abbreviate this command as `rev'.

File: gdb.info, Node: Source Path, Next: Machine Code, Prev: Search, Up: Source

9.5 Specifying Source Directories
=================================

Executable programs sometimes do not record the directories of the
source files from which they were compiled, just the names. Even when
they do, the directories could be moved between the compilation and
your debugging session. GDB has a list of directories to search for
source files; this is called the "source path". Each time GDB wants a
source file, it tries all the directories in the list, in the order
they are present in the list, until it finds a file with the desired
name.

For example, suppose an executable references the file
`/usr/src/foo-1.0/lib/foo.c', does not record a compilation directory,
and the "source path" is `/mnt/cross'. GDB would look for the source
file in the following locations:

1. `/usr/src/foo-1.0/lib/foo.c'

2. `/mnt/cross/usr/src/foo-1.0/lib/foo.c'

3. `/mnt/cross/foo.c'

If the source file is not present at any of the above locations then
an error is printed. GDB does not look up the parts of the source file
name, such as `/mnt/cross/src/foo-1.0/lib/foo.c'. Likewise, the
subdirectories of the source path are not searched: if the source path
is `/mnt/cross', and the binary refers to `foo.c', GDB would not find
it under `/mnt/cross/usr/src/foo-1.0/lib'.

Plain file names, relative file names with leading directories, file
names containing dots, etc. are all treated as described above, except
that non-absolute file names are not looked up literally. If the
"source path" is `/mnt/cross', the source file is recorded as
`../lib/foo.c', and no compilation directory is recorded, then GDB will
search in the following locations:

1. `/mnt/cross/../lib/foo.c'

2. `/mnt/cross/foo.c'

The "source path" will always include two special entries `$cdir'
and `$cwd', these refer to the compilation directory (if one is
recorded) and the current working directory respectively.

`$cdir' causes GDB to search within the compilation directory, if
one is recorded in the debug information. If no compilation directory
is recorded in the debug information then `$cdir' is ignored.

`$cwd' is not the same as `.'--the former tracks the current working
directory as it changes during your GDB session, while the latter is
immediately expanded to the current directory at the time you add an
entry to the source path.

If a compilation directory is recorded in the debug information, and
GDB has not found the source file after the first search using "source
path", then GDB will combine the compilation directory and the
filename, and then search for the source file again using the "source
path".

For example, if the executable records the source file as
`/usr/src/foo-1.0/lib/foo.c', the compilation directory is recorded as
`/project/build', and the "source path" is `/mnt/cross:$cdir:$cwd'
while the current working directory of the GDB session is `/home/user',
then GDB will search for the source file in the following locations:

1. `/usr/src/foo-1.0/lib/foo.c'

2. `/mnt/cross/usr/src/foo-1.0/lib/foo.c'

3. `/project/build/usr/src/foo-1.0/lib/foo.c'

4. `/home/user/usr/src/foo-1.0/lib/foo.c'

5. `/mnt/cross/project/build/usr/src/foo-1.0/lib/foo.c'

6. `/project/build/project/build/usr/src/foo-1.0/lib/foo.c'

7. `/home/user/project/build/usr/src/foo-1.0/lib/foo.c'

8. `/mnt/cross/foo.c'

9. `/project/build/foo.c'

10. `/home/user/foo.c'

If the file name in the previous example had been recorded in the
executable as a relative path rather than an absolute path, then the
first look up would not have occurred, but all of the remaining steps
would be similar.

When searching for source files on MS-DOS and MS-Windows, where
absolute paths start with a drive letter (e.g. `C:/project/foo.c'),
GDB will remove the drive letter from the file name before appending it
to a search directory from "source path"; for instance if the
executable references the source file `C:/project/foo.c' and "source
path" is set to `D:/mnt/cross', then GDB will search in the following
locations for the source file:

1. `C:/project/foo.c'

2. `D:/mnt/cross/project/foo.c'

3. `D:/mnt/cross/foo.c'

Note that the executable search path is _not_ used to locate the
source files.

Whenever you reset or rearrange the source path, GDB clears out any
information it has cached about where source files are found and where
each line is in the file.

When you start GDB, its source path includes only `$cdir' and
`$cwd', in that order. To add other directories, use the `directory'
command.

The search path is used to find both program source files and GDB
script files (read using the `-command' option and `source' command).

In addition to the source path, GDB provides a set of commands that
manage a list of source path substitution rules. A "substitution rule"
specifies how to rewrite source directories stored in the program's
debug information in case the sources were moved to a different
directory between compilation and debugging. A rule is made of two
strings, the first specifying what needs to be rewritten in the path,
and the second specifying how it should be rewritten. In *Note set
substitute-path::, we name these two parts FROM and TO respectively.
GDB does a simple string replacement of FROM with TO at the start of
the directory part of the source file name, and uses that result
instead of the original file name to look up the sources.

Using the previous example, suppose the `foo-1.0' tree has been
moved from `/usr/src' to `/mnt/cross', then you can tell GDB to replace
`/usr/src' in all source path names with `/mnt/cross'. The first
lookup will then be `/mnt/cross/foo-1.0/lib/foo.c' in place of the
original location of `/usr/src/foo-1.0/lib/foo.c'. To define a source
path substitution rule, use the `set substitute-path' command (*note
set substitute-path::).

To avoid unexpected substitution results, a rule is applied only if
the FROM part of the directory name ends at a directory separator. For
instance, a rule substituting `/usr/source' into `/mnt/cross' will be
applied to `/usr/source/foo-1.0' but not to `/usr/sourceware/foo-2.0'.
And because the substitution is applied only at the beginning of the
directory name, this rule will not be applied to
`/root/usr/source/baz.c' either.

In many cases, you can achieve the same result using the `directory'
command. However, `set substitute-path' can be more efficient in the
case where the sources are organized in a complex tree with multiple
subdirectories. With the `directory' command, you need to add each
subdirectory of your project. If you moved the entire tree while
preserving its internal organization, then `set substitute-path' allows
you to direct the debugger to all the sources with one single command.

`set substitute-path' is also more than just a shortcut command.
The source path is only used if the file at the original location no
longer exists. On the other hand, `set substitute-path' modifies the
debugger behavior to look at the rewritten location instead. So, if
for any reason a source file that is not relevant to your executable is
located at the original location, a substitution rule is the only
method available to point GDB at the new location.

You can configure a default source path substitution rule by
configuring GDB with the `--with-relocated-sources=DIR' option. The DIR
should be the name of a directory under GDB's configured prefix (set
with `--prefix' or `--exec-prefix'), and directory names in debug
information under DIR will be adjusted automatically if the installed
GDB is moved to a new location. This is useful if GDB, libraries or
executables with debug information and corresponding source code are
being moved together.

`directory DIRNAME ...'

`dir DIRNAME ...'
Add directory DIRNAME to the front of the source path. Several
directory names may be given to this command, separated by `:'
(`;' on MS-DOS and MS-Windows, where `:' usually appears as part
of absolute file names) or whitespace. You may specify a
directory that is already in the source path; this moves it
forward, so GDB searches it sooner.

The special strings `$cdir' (to refer to the compilation
directory, if one is recorded), and `$cwd' (to refer to the
current working directory) can also be included in the list of
directories DIRNAME. Though these will already be in the source
path they will be moved forward in the list so GDB searches them
sooner.

`directory'
Reset the source path to its default value (`$cdir:$cwd' on Unix
systems). This requires confirmation.

`set directories PATH-LIST'
Set the source path to PATH-LIST. `$cdir:$cwd' are added if
missing.

`show directories'
Print the source path: show which directories it contains.

`set substitute-path FROM TO'
Define a source path substitution rule, and add it at the end of
the current list of existing substitution rules. If a rule with
the same FROM was already defined, then the old rule is also
deleted.

For example, if the file `/foo/bar/baz.c' was moved to
`/mnt/cross/baz.c', then the command

(gdb) set substitute-path /foo/bar /mnt/cross

will tell GDB to replace `/foo/bar' with `/mnt/cross', which will
allow GDB to find the file `baz.c' even though it was moved.

In the case when more than one substitution rule have been defined,
the rules are evaluated one by one in the order where they have
been defined. The first one matching, if any, is selected to
perform the substitution.

For instance, if we had entered the following commands:

(gdb) set substitute-path /usr/src/include /mnt/include
(gdb) set substitute-path /usr/src /mnt/src

GDB would then rewrite `/usr/src/include/defs.h' into
`/mnt/include/defs.h' by using the first rule. However, it would
use the second rule to rewrite `/usr/src/lib/foo.c' into
`/mnt/src/lib/foo.c'.

`unset substitute-path [path]'
If a path is specified, search the current list of substitution
rules for a rule that would rewrite that path. Delete that rule
if found. A warning is emitted by the debugger if no rule could
be found.

If no path is specified, then all substitution rules are deleted.

`show substitute-path [path]'
If a path is specified, then print the source path substitution
rule which would rewrite that path, if any.

If no path is specified, then print all existing source path
substitution rules.

If your source path is cluttered with directories that are no longer
of interest, GDB may sometimes cause confusion by finding the wrong
versions of source. You can correct the situation as follows:

1. Use `directory' with no argument to reset the source path to its
default value.

2. Use `directory' with suitable arguments to reinstall the
directories you want in the source path. You can add all the
directories in one command.

File: gdb.info, Node: Machine Code, Next: Disable Reading Source, Prev: Source Path, Up: Source

9.6 Source and Machine Code
===========================

You can use the command `info line' to map source lines to program
addresses (and vice versa), and the command `disassemble' to display a
range of addresses as machine instructions. You can use the command
`set disassemble-next-line' to set whether to disassemble next source
line when execution stops. When run under GNU Emacs mode, the `info
line' command causes the arrow to point to the line specified. Also,
`info line' prints addresses in symbolic form as well as hex.

`info line'
`info line LOCSPEC'
Print the starting and ending addresses of the compiled code for
the source lines of the code locations that result from resolving
LOCSPEC. *Note Location Specifications::, for the various forms
of LOCSPEC. With no LOCSPEC, information about the current source
line is printed.

For example, we can use `info line' to discover the location of the
object code for the first line of function `m4_changequote':

(gdb) info line m4_changequote
Line 895 of "builtin.c" starts at pc 0x634c <m4_changequote> and \
ends at 0x6350 <m4_changequote+4>.

We can also inquire, using `*ADDR' as the form for LOCSPEC, what source
line covers a particular address ADDR:
(gdb) info line *0x63ff
Line 926 of "builtin.c" starts at pc 0x63e4 <m4_changequote+152> and \
ends at 0x6404 <m4_changequote+184>.

After `info line', the default address for the `x' command is
changed to the starting address of the line, so that `x/i' is
sufficient to begin examining the machine code (*note Examining Memory:
Memory.). Also, this address is saved as the value of the convenience
variable `$_' (*note Convenience Variables: Convenience Vars.).

After `info line', using `info line' again without specifying a
location will display information about the next source line.

`disassemble'
`disassemble /m'
`disassemble /s'
`disassemble /r'
`disassemble /b'
This specialized command dumps a range of memory as machine
instructions. It can also print mixed source+disassembly by
specifying the `/m' or `/s' modifier and print the raw
instructions in hex as well as in symbolic form by specifying the
`/r' or `/b' modifier.

Only one of `/m' and `/s' can be used, attempting to use both flag
will give an error.

Only one of `/r' and `/b' can be used, attempting to use both flag
will give an error.

The default memory range is the function surrounding the program
counter of the selected frame. A single argument to this command
is a program counter value; GDB dumps the function surrounding
this value. When two arguments are given, they should be
separated by a comma, possibly surrounded by whitespace. The
arguments specify a range of addresses to dump, in one of two
forms:

`START,END'
the addresses from START (inclusive) to END (exclusive)

`START,+LENGTH'
the addresses from START (inclusive) to `START+LENGTH'
(exclusive).

When 2 arguments are specified, the name of the function is also
printed (since there could be several functions in the given
range).

The argument(s) can be any expression yielding a numeric value,
such as `0x32c4', `&main+10' or `$pc - 8'.

If the range of memory being disassembled contains current program
counter, the instruction at that location is shown with a `=>'
marker.

The following example shows the disassembly of a range of addresses
of HP PA-RISC 2.0 code:

(gdb) disas 0x32c4, 0x32e4
Dump of assembler code from 0x32c4 to 0x32e4:
0x32c4 <main+204>: addil 0,dp
0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
0x32cc <main+212>: ldil 0x3000,r31
0x32d0 <main+216>: ble 0x3f8(sr4,r31)
0x32d4 <main+220>: ldo 0(r31),rp
0x32d8 <main+224>: addil -0x800,dp
0x32dc <main+228>: ldo 0x588(r1),r26
0x32e0 <main+232>: ldil 0x3000,r31
End of assembler dump.

The following two examples are for RISC-V, and demonstrates the
difference between the `/r' and `/b' modifiers. First with `/b', the
bytes of the instruction are printed, in hex, in memory order:

(gdb) disassemble /b 0x00010150,0x0001015c
Dump of assembler code from 0x10150 to 0x1015c:
0x00010150 <call_me+4>: 22 dc sw s0,56(sp)
0x00010152 <call_me+6>: 80 00 addi s0,sp,64
0x00010154 <call_me+8>: 23 26 a4 fe sw a0,-20(s0)
0x00010158 <call_me+12>: 23 24 b4 fe sw a1,-24(s0)
End of assembler dump.

In contrast, with `/r' the bytes of the instruction are displayed in
the instruction order, for RISC-V this means that the bytes have been
swapped to little-endian order:

(gdb) disassemble /r 0x00010150,0x0001015c
Dump of assembler code from 0x10150 to 0x1015c:
0x00010150 <call_me+4>: dc22 sw s0,56(sp)
0x00010152 <call_me+6>: 0080 addi s0,sp,64
0x00010154 <call_me+8>: fea42623 sw a0,-20(s0)
0x00010158 <call_me+12>: feb42423 sw a1,-24(s0)
End of assembler dump.

Here is an example showing mixed source+assembly for Intel x86 with
`/m' or `/s', when the program is stopped just after function prologue
in a non-optimized function with no inline code.

(gdb) disas /m main
Dump of assembler code for function main:
5 {
0x08048330 <+0>: push %ebp
0x08048331 <+1>: mov %esp,%ebp
0x08048333 <+3>: sub $0x8,%esp
0x08048336 <+6>: and $0xfffffff0,%esp
0x08048339 <+9>: sub $0x10,%esp

6 printf ("Hello.\n");
=> 0x0804833c <+12>: movl $0x8048440,(%esp)
0x08048343 <+19>: call 0x8048284 <puts@plt>

7 return 0;
8 }
0x08048348 <+24>: mov $0x0,%eax
0x0804834d <+29>: leave
0x0804834e <+30>: ret

End of assembler dump.

The `/m' option is deprecated as its output is not useful when there
is either inlined code or re-ordered code. The `/s' option is the
preferred choice. Here is an example for AMD x86-64 showing the
difference between `/m' output and `/s' output. This example has one
inline function defined in a header file, and the code is compiled with
`-O2' optimization. Note how the `/m' output is missing the
disassembly of several instructions that are present in the `/s' output.

`foo.h':

int
foo (int a)
{
if (a < 0)
return a * 2;
if (a == 0)
return 1;
return a + 10;
}

`foo.c':

#include "foo.h"
volatile int x, y;
int
main ()
{
x = foo (y);
return 0;
}

(gdb) disas /m main
Dump of assembler code for function main:
5 {

6 x = foo (y);
0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y>
0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x>

7 return 0;
8 }
0x000000000040041d <+29>: xor %eax,%eax
0x000000000040041f <+31>: retq
0x0000000000400420 <+32>: add %eax,%eax
0x0000000000400422 <+34>: jmp 0x400417 <main+23>

End of assembler dump.
(gdb) disas /s main
Dump of assembler code for function main:
foo.c:
5 {
6 x = foo (y);
0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y>

foo.h:
4 if (a < 0)
0x0000000000400406 <+6>: test %eax,%eax
0x0000000000400408 <+8>: js 0x400420 <main+32>

6 if (a == 0)
7 return 1;
8 return a + 10;
0x000000000040040a <+10>: lea 0xa(%rax),%edx
0x000000000040040d <+13>: test %eax,%eax
0x000000000040040f <+15>: mov $0x1,%eax
0x0000000000400414 <+20>: cmovne %edx,%eax

foo.c:
6 x = foo (y);
0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x>

7 return 0;
8 }
0x000000000040041d <+29>: xor %eax,%eax
0x000000000040041f <+31>: retq

foo.h:
5 return a * 2;
0x0000000000400420 <+32>: add %eax,%eax
0x0000000000400422 <+34>: jmp 0x400417 <main+23>
End of assembler dump.

Here is another example showing raw instructions in hex for AMD
x86-64,

(gdb) disas /r 0x400281,+10
Dump of assembler code from 0x400281 to 0x40028b:
0x0000000000400281: 38 36 cmp %dh,(%rsi)
0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax
0x0000000000400288: 6f outsl %ds:(%rsi),(%dx)
0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al
End of assembler dump.

Note that the `disassemble' command's address arguments are
specified using expressions in your programming language (*note
Expressions: Expressions.), not location specs (*note Location
Specifications::). So, for example, if you want to disassemble
function `bar' in file `foo.c', you must type `disassemble
'foo.c'::bar' and not `disassemble foo.c:bar'.

Some architectures have more than one commonly-used set of
instruction mnemonics or other syntax.

For programs that were dynamically linked and use shared libraries,
instructions that call functions or branch to locations in the shared
libraries might show a seemingly bogus location--it's actually a
location of the relocation table. On some architectures, GDB might be
able to resolve these to actual function names.

`set disassembler-options OPTION1[,OPTION2...]'
This command controls the passing of target specific information to
the disassembler. For a list of valid options, please refer to the
`-M'/`--disassembler-options' section of the `objdump' manual
and/or the output of `objdump --help' (*note objdump:
(binutils)objdump.). The default value is the empty string.

If it is necessary to specify more than one disassembler option,
then multiple options can be placed together into a comma
separated list. Currently this command is only supported on
targets ARC, ARM, MIPS, PowerPC and S/390.

`show disassembler-options'
Show the current setting of the disassembler options.

`set disassembly-flavor INSTRUCTION-SET'
Select the instruction set to use when disassembling the program
via the `disassemble' or `x/i' commands.

Currently this command is only defined for the Intel x86 family.
You can set INSTRUCTION-SET to either `intel' or `att'. The
default is `att', the AT&T flavor used by default by Unix
assemblers for x86-based targets.

`show disassembly-flavor'
Show the current setting of the disassembly flavor.

`set disassemble-next-line'
`show disassemble-next-line'
Control whether or not GDB will disassemble the next source line
or instruction when execution stops. If ON, GDB will display
disassembly of the next source line when execution of the program
being debugged stops. This is _in addition_ to displaying the
source line itself, which GDB always does if possible. If the
next source line cannot be displayed for some reason (e.g., if GDB
cannot find the source file, or there's no line info in the debug
info), GDB will display disassembly of the next _instruction_
instead of showing the next source line. If AUTO, GDB will
display disassembly of next instruction only if the source line
cannot be displayed. This setting causes GDB to display some
feedback when you step through a function with no line info or
whose source file is unavailable. The default is OFF, which means
never display the disassembly of the next line or instruction.

File: gdb.info, Node: Disable Reading Source, Prev: Machine Code, Up: Source

9.7 Disable Reading Source Code
===============================

In some cases it can be desirable to prevent GDB from accessing source
code files. One case where this might be desirable is if the source
code files are located over a slow network connection.

The following command can be used to control whether GDB should
access source code files or not:

`set source open [on|off]'
`show source open'
When this option is `on', which is the default, GDB will access
source code files when needed, for example to print source lines
when GDB stops, or in response to the `list' command.

When this option is `off', GDB will not access source code files.

File: gdb.info, Node: Data, Next: Optimized Code, Prev: Source, Up: Top

10 Examining Data
*****************

The usual way to examine data in your program is with the `print'
command (abbreviated `p'), or its synonym `inspect'. It evaluates and
prints the value of an expression of the language your program is
written in (*note Using GDB with Different Languages: Languages.). It
may also print the expression using a Python-based pretty-printer
(*note Pretty Printing::).

`print [[OPTIONS] --] EXPR'
`print [[OPTIONS] --] /F EXPR'
EXPR is an expression (in the source language). By default the
value of EXPR is printed in a format appropriate to its data type;
you can choose a different format by specifying `/F', where F is a
letter specifying the format; see *Note Output Formats: Output
Formats.

The `print' command supports a number of options that allow
overriding relevant global print settings as set by `set print'
subcommands:

`-address [`on'|`off']'
Set printing of addresses. Related setting: *Note set print
address::.

`-array [`on'|`off']'
Pretty formatting of arrays. Related setting: *Note set
print array::.

`-array-indexes [`on'|`off']'
Set printing of array indexes. Related setting: *Note set
print array-indexes::.

`-characters NUMBER-OF-CHARACTERS|`elements'|`unlimited''
Set limit on string characters to print. The value `elements'
causes the limit on array elements to print to be used. The
value `unlimited' causes there to be no limit. Related
setting: *Note set print characters::.

`-elements NUMBER-OF-ELEMENTS|`unlimited''
Set limit on array elements and optionally string characters
to print. See *Note set print characters::, and the
`-characters' option above for when this option applies to
strings. The value `unlimited' causes there to be no limit.
*Note set print elements::, for a related CLI command.

`-max-depth DEPTH|`unlimited''
Set the threshold after which nested structures are replaced
with ellipsis. Related setting: *Note set print max-depth::.

`-nibbles [`on'|`off']'
Set whether to print binary values in groups of four bits,
known as "nibbles". *Note set print nibbles::.

`-memory-tag-violations [`on'|`off']'
Set printing of additional information about memory tag
violations. *Note set print memory-tag-violations::.

`-null-stop [`on'|`off']'
Set printing of char arrays to stop at first null char.
Related setting: *Note set print null-stop::.

`-object [`on'|`off']'
Set printing C++ virtual function tables. Related setting:
*Note set print object::.

`-pretty [`on'|`off']'
Set pretty formatting of structures. Related setting: *Note
set print pretty::.

`-raw-values [`on'|`off']'
Set whether to print values in raw form, bypassing any
pretty-printers for that value. Related setting: *Note set
print raw-values::.

`-repeats NUMBER-OF-REPEATS|`unlimited''
Set threshold for repeated print elements. `unlimited' causes
all elements to be individually printed. Related setting:
*Note set print repeats::.

`-static-members [`on'|`off']'
Set printing C++ static members. Related setting: *Note set
print static-members::.

`-symbol [`on'|`off']'
Set printing of symbol names when printing pointers. Related
setting: *Note set print symbol::.

`-union [`on'|`off']'
Set printing of unions interior to structures. Related
setting: *Note set print union::.

`-vtbl [`on'|`off']'
Set printing of C++ virtual function tables. Related setting:
*Note set print vtbl::.

Because the `print' command accepts arbitrary expressions which
may look like options (including abbreviations), if you specify any
command option, then you must use a double dash (`--') to mark the
end of option processing.

For example, this prints the value of the `-p' expression:

(gdb) print -p

While this repeats the last value in the value history (see below)
with the `-pretty' option in effect:

(gdb) print -p --

Here is an example including both on option and an expression:

(gdb) print -pretty -- *myptr
$1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
},
meat = 0x54 "Pork"
}

`print [OPTIONS]'
`print [OPTIONS] /F'
If you omit EXPR, GDB displays the last value again (from the
"value history"; *note Value History: Value History.). This
allows you to conveniently inspect the same value in an
alternative format.

If the architecture supports memory tagging, the `print' command will
display pointer/memory tag mismatches if what is being printed is a
pointer or reference type. *Note Memory Tagging::.

A more low-level way of examining data is with the `x' command. It
examines data in memory at a specified address and prints it in a
specified format. *Note Examining Memory: Memory.

If you are interested in information about types, or about how the
fields of a struct or a class are declared, use the `ptype EXPR'
command rather than `print'. *Note Examining the Symbol Table: Symbols.

Another way of examining values of expressions and type information
is through the Python extension command `explore' (available only if
the GDB build is configured with `--with-python'). It offers an
interactive way to start at the highest level (or, the most abstract
level) of the data type of an expression (or, the data type itself) and
explore all the way down to leaf scalar values/fields embedded in the
higher level data types.

`explore ARG'
ARG is either an expression (in the source language), or a type
visible in the current context of the program being debugged.

The working of the `explore' command can be illustrated with an
example. If a data type `struct ComplexStruct' is defined in your C
program as

struct SimpleStruct
{
int i;
double d;
};

struct ComplexStruct
{
struct SimpleStruct *ss_p;
int arr[10];
};

followed by variable declarations as

struct SimpleStruct ss = { 10, 1.11 };
struct ComplexStruct cs = { &ss, { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 } };

then, the value of the variable `cs' can be explored using the
`explore' command as follows.

(gdb) explore cs
The value of `cs' is a struct/class of type `struct ComplexStruct' with
the following fields:

ss_p = <Enter 0 to explore this field of type `struct SimpleStruct *'>
arr = <Enter 1 to explore this field of type `int [10]'>

Enter the field number of choice:

Since the fields of `cs' are not scalar values, you are being prompted
to chose the field you want to explore. Let's say you choose the field
`ss_p' by entering `0'. Then, since this field is a pointer, you will
be asked if it is pointing to a single value. From the declaration of
`cs' above, it is indeed pointing to a single value, hence you enter
`y'. If you enter `n', then you will be asked if it were pointing to
an array of values, in which case this field will be explored as if it
were an array.

`cs.ss_p' is a pointer to a value of type `struct SimpleStruct'
Continue exploring it as a pointer to a single value [y/n]: y
The value of `*(cs.ss_p)' is a struct/class of type `struct
SimpleStruct' with the following fields:

i = 10 .. (Value of type `int')
d = 1.1100000000000001 .. (Value of type `double')

Press enter to return to parent value:

If the field `arr' of `cs' was chosen for exploration by entering `1'
earlier, then since it is as array, you will be prompted to enter the
index of the element in the array that you want to explore.

`cs.arr' is an array of `int'.
Enter the index of the element you want to explore in `cs.arr': 5

`(cs.arr)[5]' is a scalar value of type `int'.

(cs.arr)[5] = 4

Press enter to return to parent value:

In general, at any stage of exploration, you can go deeper towards
the leaf values by responding to the prompts appropriately, or hit the
return key to return to the enclosing data structure (the higher level
data structure).

Similar to exploring values, you can use the `explore' command to
explore types. Instead of specifying a value (which is typically a
variable name or an expression valid in the current context of the
program being debugged), you specify a type name. If you consider the
same example as above, your can explore the type `struct ComplexStruct'
by passing the argument `struct ComplexStruct' to the `explore' command.

(gdb) explore struct ComplexStruct

By responding to the prompts appropriately in the subsequent interactive
session, you can explore the type `struct ComplexStruct' in a manner
similar to how the value `cs' was explored in the above example.

The `explore' command also has two sub-commands, `explore value' and
`explore type'. The former sub-command is a way to explicitly specify
that value exploration of the argument is being invoked, while the
latter is a way to explicitly specify that type exploration of the
argument is being invoked.

`explore value EXPR'
This sub-command of `explore' explores the value of the expression
EXPR (if EXPR is an expression valid in the current context of the
program being debugged). The behavior of this command is
identical to that of the behavior of the `explore' command being
passed the argument EXPR.

`explore type ARG'
This sub-command of `explore' explores the type of ARG (if ARG is
a type visible in the current context of program being debugged),
or the type of the value/expression ARG (if ARG is an expression
valid in the current context of the program being debugged). If
ARG is a type, then the behavior of this command is identical to
that of the `explore' command being passed the argument ARG. If
ARG is an expression, then the behavior of this command will be
identical to that of the `explore' command being passed the type
of ARG as the argument.

* Menu:

* Expressions:: Expressions
* Ambiguous Expressions:: Ambiguous Expressions
* Variables:: Program variables
* Arrays:: Artificial arrays
* Output Formats:: Output formats
* Memory:: Examining memory
* Memory Tagging:: Memory Tagging
* Auto Display:: Automatic display
* Print Settings:: Print settings
* Pretty Printing:: Python pretty printing
* Value History:: Value history
* Convenience Vars:: Convenience variables
* Convenience Funs:: Convenience functions
* Registers:: Registers
* Floating Point Hardware:: Floating point hardware
* Vector Unit:: Vector Unit
* OS Information:: Auxiliary data provided by operating system
* Memory Region Attributes:: Memory region attributes
* Dump/Restore Files:: Copy between memory and a file
* Core File Generation:: Cause a program dump its core
* Character Sets:: Debugging programs that use a different
character set than GDB does
* Caching Target Data:: Data caching for targets
* Searching Memory:: Searching memory for a sequence of bytes
* Value Sizes:: Managing memory allocated for values

File: gdb.info, Node: Expressions, Next: Ambiguous Expressions, Up: Data

10.1 Expressions
================

`print' and many other GDB commands accept an expression and compute
its value. Any kind of constant, variable or operator defined by the
programming language you are using is valid in an expression in GDB.
This includes conditional expressions, function calls, casts, and
string constants. It also includes preprocessor macros, if you
compiled your program to include this information; see *Note
Compilation::.

GDB supports array constants in expressions input by the user. The
syntax is {ELEMENT, ELEMENT...}. For example, you can use the command
`print {1, 2, 3}' to create an array of three integers. If you pass an
array to a function or assign it to a program variable, GDB copies the
array to memory that is `malloc'ed in the target program.

Because C is so widespread, most of the expressions shown in
examples in this manual are in C. *Note Using GDB with Different
Languages: Languages, for information on how to use expressions in other
languages.

In this section, we discuss operators that you can use in GDB
expressions regardless of your programming language.

Casts are supported in all languages, not just in C, because it is so
useful to cast a number into a pointer in order to examine a structure
at that address in memory.

GDB supports these operators, in addition to those common to
programming languages:

`@'
`@' is a binary operator for treating parts of memory as arrays.
*Note Artificial Arrays: Arrays, for more information.

`::'
`::' allows you to specify a variable in terms of the file or
function where it is defined. *Note Program Variables: Variables.

`{TYPE} ADDR'
Refers to an object of type TYPE stored at address ADDR in memory.
The address ADDR may be any expression whose value is an integer
or pointer (but parentheses are required around binary operators,
just as in a cast). This construct is allowed regardless of what
kind of data is normally supposed to reside at ADDR.

File: gdb.info, Node: Ambiguous Expressions, Next: Variables, Prev: Expressions, Up: Data

10.2 Ambiguous Expressions
==========================

Expressions can sometimes contain some ambiguous elements. For
instance, some programming languages (notably Ada, C++ and Objective-C)
permit a single function name to be defined several times, for
application in different contexts. This is called "overloading".
Another example involving Ada is generics. A "generic package" is
similar to C++ templates and is typically instantiated several times,
resulting in the same function name being defined in different contexts.

In some cases and depending on the language, it is possible to adjust
the expression to remove the ambiguity. For instance in C++, you can
specify the signature of the function you want to break on, as in
`break FUNCTION(TYPES)'. In Ada, using the fully qualified name of
your function often makes the expression unambiguous as well.

When an ambiguity that needs to be resolved is detected, the debugger
has the capability to display a menu of numbered choices for each
possibility, and then waits for the selection with the prompt `>'. The
first option is always `[0] cancel', and typing `0 <RET>' aborts the
current command. If the command in which the expression was used
allows more than one choice to be selected, the next option in the menu
is `[1] all', and typing `1 <RET>' selects all possible choices.

For example, the following session excerpt shows an attempt to set a
breakpoint at the overloaded symbol `String::after'. We choose three
particular definitions of that function name:

(gdb) b String::after
[0] cancel
[1] all
[2] file:String.cc; line number:867
[3] file:String.cc; line number:860
[4] file:String.cc; line number:875
[5] file:String.cc; line number:853
[6] file:String.cc; line number:846
[7] file:String.cc; line number:735
> 2 4 6
Breakpoint 1 at 0xb26c: file String.cc, line 867.
Breakpoint 2 at 0xb344: file String.cc, line 875.
Breakpoint 3 at 0xafcc: file String.cc, line 846.
Multiple breakpoints were set.
Use the "delete" command to delete unwanted
breakpoints.
(gdb)

`set multiple-symbols MODE'
This option allows you to adjust the debugger behavior when an
expression is ambiguous.

By default, MODE is set to `all'. If the command with which the
expression is used allows more than one choice, then GDB
automatically selects all possible choices. For instance,
inserting a breakpoint on a function using an ambiguous name
results in a breakpoint inserted on each possible match. However,
if a unique choice must be made, then GDB uses the menu to help
you disambiguate the expression. For instance, printing the
address of an overloaded function will result in the use of the
menu.

When MODE is set to `ask', the debugger always uses the menu when
an ambiguity is detected.

Finally, when MODE is set to `cancel', the debugger reports an
error due to the ambiguity and the command is aborted.

`show multiple-symbols'
Show the current value of the `multiple-symbols' setting.

File: gdb.info, Node: Variables, Next: Arrays, Prev: Ambiguous Expressions, Up: Data

10.3 Program Variables
======================

The most common kind of expression to use is the name of a variable in
your program.

Variables in expressions are understood in the selected stack frame
(*note Selecting a Frame: Selection.); they must be either:

* global (or file-static)

or

* visible according to the scope rules of the programming language
from the point of execution in that frame

This means that in the function

foo (a)
int a;
{
bar (a);
{
int b = test ();
bar (b);
}
}

you can examine and use the variable `a' whenever your program is
executing within the function `foo', but you can only use or examine
the variable `b' while your program is executing inside the block where
`b' is declared.

There is an exception: you can refer to a variable or function whose
scope is a single source file even if the current execution point is not
in this file. But it is possible to have more than one such variable or
function with the same name (in different source files). If that
happens, referring to that name has unpredictable effects. If you wish,
you can specify a static variable in a particular function or file by
using the colon-colon (`::') notation:

FILE::VARIABLE
FUNCTION::VARIABLE

Here FILE or FUNCTION is the name of the context for the static
VARIABLE. In the case of file names, you can use quotes to make sure
GDB parses the file name as a single word--for example, to print a
global value of `x' defined in `f2.c':

(gdb) p 'f2.c'::x

The `::' notation is normally used for referring to static
variables, since you typically disambiguate uses of local variables in
functions by selecting the appropriate frame and using the simple name
of the variable. However, you may also use this notation to refer to
local variables in frames enclosing the selected frame:

void
foo (int a)
{
if (a < 10)
bar (a);
else
process (a); /* Stop here */
}

int
bar (int a)
{
foo (a + 5);
}

For example, if there is a breakpoint at the commented line, here is
what you might see when the program stops after executing the call
`bar(0)':

(gdb) p a
$1 = 10
(gdb) p bar::a
$2 = 5
(gdb) up 2
#2 0x080483d0 in foo (a=5) at foobar.c:12
(gdb) p a
$3 = 5
(gdb) p bar::a
$4 = 0

These uses of `::' are very rarely in conflict with the very similar
use of the same notation in C++. When they are in conflict, the C++
meaning takes precedence; however, this can be overridden by quoting
the file or function name with single quotes.

For example, suppose the program is stopped in a method of a class
that has a field named `includefile', and there is also an include file
named `includefile' that defines a variable, `some_global'.

(gdb) p includefile
$1 = 23
(gdb) p includefile::some_global
A syntax error in expression, near `'.
(gdb) p 'includefile'::some_global
$2 = 27

_Warning:_ Occasionally, a local variable may appear to have the
wrong value at certain points in a function--just after entry to a
new scope, and just before exit.
You may see this problem when you are stepping by machine
instructions. This is because, on most machines, it takes more than
one instruction to set up a stack frame (including local variable
definitions); if you are stepping by machine instructions, variables
may appear to have the wrong values until the stack frame is completely
built. On exit, it usually also takes more than one machine
instruction to destroy a stack frame; after you begin stepping through
that group of instructions, local variable definitions may be gone.

This may also happen when the compiler does significant
optimizations. To be sure of always seeing accurate values, turn off
all optimization when compiling.

Another possible effect of compiler optimizations is to optimize
unused variables out of existence, or assign variables to registers (as
opposed to memory addresses). Depending on the support for such cases
offered by the debug info format used by the compiler, GDB might not be
able to display values for such local variables. If that happens, GDB
will print a message like this:

No symbol "foo" in current context.

To solve such problems, either recompile without optimizations, or
use a different debug info format, if the compiler supports several such
formats. *Note Compilation::, for more information on choosing compiler
options. *Note C and C++: C, for more information about debug info
formats that are best suited to C++ programs.

If you ask to print an object whose contents are unknown to GDB,
e.g., because its data type is not completely specified by the debug
information, GDB will say `<incomplete type>'. *Note incomplete type:
Symbols, for more about this.

If you try to examine or use the value of a (global) variable for
which GDB has no type information, e.g., because the program includes
no debug information, GDB displays an error message. *Note unknown
type: Symbols, for more about unknown types. If you cast the variable
to its declared type, GDB gets the variable's value using the cast-to
type as the variable's type. For example, in a C program:

(gdb) p var
'var' has unknown type; cast it to its declared type
(gdb) p (float) var
$1 = 3.14

If you append `@entry' string to a function parameter name you get
its value at the time the function got called. If the value is not
available an error message is printed. Entry values are available only
with some compilers. Entry values are normally also printed at the
function parameter list according to *Note set print entry-values::.

Breakpoint 1, d (i=30) at gdb.base/entry-value.c:29
29 i++;
(gdb) next
30 e (i);
(gdb) print i
$1 = 31
(gdb) print i@entry
$2 = 30

Strings are identified as arrays of `char' values without specified
signedness. Arrays of either `signed char' or `unsigned char' get
printed as arrays of 1 byte sized integers. `-fsigned-char' or
`-funsigned-char' GCC options have no effect as GDB defines literal
string type `"char"' as `char' without a sign. For program code

char var0[] = "A";
signed char var1[] = "A";

You get during debugging
(gdb) print var0
$1 = "A"
(gdb) print var1
$2 = {65 'A', 0 '\0'}

File: gdb.info, Node: Arrays, Next: Output Formats, Prev: Variables, Up: Data

10.4 Artificial Arrays
======================

It is often useful to print out several successive objects of the same
type in memory; a section of an array, or an array of dynamically
determined size for which only a pointer exists in the program.

You can do this by referring to a contiguous span of memory as an
"artificial array", using the binary operator `@'. The left operand of
`@' should be the first element of the desired array and be an
individual object. The right operand should be the desired length of
the array. The result is an array value whose elements are all of the
type of the left argument. The first element is actually the left
argument; the second element comes from bytes of memory immediately
following those that hold the first element, and so on. Here is an
example. If a program says

int *array = (int *) malloc (len * sizeof (int));

you can print the contents of `array' with

p *array@len

The left operand of `@' must reside in memory. Array values made
with `@' in this way behave just like other arrays in terms of
subscripting, and are coerced to pointers when used in expressions.
Artificial arrays most often appear in expressions via the value history
(*note Value History: Value History.), after printing one out.

Another way to create an artificial array is to use a cast. This
re-interprets a value as if it were an array. The value need not be in
memory:
(gdb) p/x (short[2])0x12345678
$1 = {0x1234, 0x5678}

As a convenience, if you leave the array length out (as in
`(TYPE[])VALUE') GDB calculates the size to fill the value (as
`sizeof(VALUE)/sizeof(TYPE)':
(gdb) p/x (short[])0x12345678
$2 = {0x1234, 0x5678}

Sometimes the artificial array mechanism is not quite enough; in
moderately complex data structures, the elements of interest may not
actually be adjacent--for example, if you are interested in the values
of pointers in an array. One useful work-around in this situation is
to use a convenience variable (*note Convenience Variables: Convenience
Vars.) as a counter in an expression that prints the first interesting
value, and then repeat that expression via <RET>. For instance,
suppose you have an array `dtab' of pointers to structures, and you are
interested in the values of a field `fv' in each structure. Here is an
example of what you might type:

set $i = 0
p dtab[$i++]->fv
<RET>
<RET>
...

File: gdb.info, Node: Output Formats, Next: Memory, Prev: Arrays, Up: Data

10.5 Output Formats
===================

By default, GDB prints a value according to its data type. Sometimes
this is not what you want. For example, you might want to print a
number in hex, or a pointer in decimal. Or you might want to view data
in memory at a certain address as a character string or as an
instruction. To do these things, specify an "output format" when you
print a value.

The simplest use of output formats is to say how to print a value
already computed. This is done by starting the arguments of the
`print' command with a slash and a format letter. The format letters
supported are:

`x'
Print the binary representation of the value in hexadecimal.

`d'
Print the binary representation of the value in decimal.

`u'
Print the binary representation of the value as an decimal, as if
it were unsigned.

`o'
Print the binary representation of the value in octal.

`t'
Print the binary representation of the value in binary. The letter
`t' stands for "two". (1)

`a'
Print as an address, both absolute in hexadecimal and as an offset
from the nearest preceding symbol. You can use this format used
to discover where (in what function) an unknown address is located:

(gdb) p/a 0x54320
$3 = 0x54320 <_initialize_vx+396>

The command `info symbol 0x54320' yields similar results. *Note
info symbol: Symbols.

`c'
Cast the value to an integer (unlike other formats, this does not
just reinterpret the underlying bits) and print it as a character
constant. This prints both the numerical value and its character
representation. The character representation is replaced with the
octal escape `\nnn' for characters outside the 7-bit ASCII range.

Without this format, GDB displays `char', `unsigned char', and
`signed char' data as character constants. Single-byte members of
vectors are displayed as integer data.

`f'
Regard the bits of the value as a floating point number and print
using typical floating point syntax.

`s'
Regard as a string, if possible. With this format, pointers to
single-byte data are displayed as null-terminated strings and
arrays of single-byte data are displayed as fixed-length strings.
Other values are displayed in their natural types.

Without this format, GDB displays pointers to and arrays of
`char', `unsigned char', and `signed char' as strings.
Single-byte members of a vector are displayed as an integer array.

`z'
Like `x' formatting, the value is treated as an integer and
printed as hexadecimal, but leading zeros are printed to pad the
value to the size of the integer type.

`r'
Print using the `raw' formatting. By default, GDB will use a
Python-based pretty-printer, if one is available (*note Pretty
Printing::). This typically results in a higher-level display of
the value's contents. The `r' format bypasses any Python
pretty-printer which might exist.

For example, to print the program counter in hex (*note
Registers::), type

p/x $pc

Note that no space is required before the slash; this is because command
names in GDB cannot contain a slash.

To reprint the last value in the value history with a different
format, you can use the `print' command with just a format and no
expression. For example, `p/x' reprints the last value in hex.

---------- Footnotes ----------

(1) `b' cannot be used because these format letters are also used
with the `x' command, where `b' stands for "byte"; see *Note Examining
Memory: Memory.

File: gdb.info, Node: Memory, Next: Memory Tagging, Prev: Output Formats, Up: Data

10.6 Examining Memory
=====================

You can use the command `x' (for "examine") to examine memory in any of
several formats, independently of your program's data types.

`x/NFU ADDR'
`x ADDR'
`x'
Use the `x' command to examine memory.

N, F, and U are all optional parameters that specify how much memory
to display and how to format it; ADDR is an expression giving the
address where you want to start displaying memory. If you use defaults
for NFU, you need not type the slash `/'. Several commands set
convenient defaults for ADDR.

N, the repeat count
The repeat count is a decimal integer; the default is 1. It
specifies how much memory (counting by units U) to display. If a
negative number is specified, memory is examined backward from
ADDR.

F, the display format
The display format is one of the formats used by `print' (`x',
`d', `u', `o', `t', `a', `c', `f', `s'), `i' (for machine
instructions) and `m' (for displaying memory tags). The default
is `x' (hexadecimal) initially. The default changes each time you
use either `x' or `print'.

U, the unit size
The unit size is any of

`b'
Bytes.

`h'
Halfwords (two bytes).

`w'
Words (four bytes). This is the initial default.

`g'
Giant words (eight bytes).

Each time you specify a unit size with `x', that size becomes the
default unit the next time you use `x'. For the `i' format, the
unit size is ignored and is normally not written. For the `s'
format, the unit size defaults to `b', unless it is explicitly
given. Use `x /hs' to display 16-bit char strings and `x /ws' to
display 32-bit strings. The next use of `x /s' will again display
8-bit strings. Note that the results depend on the programming
language of the current compilation unit. If the language is C,
the `s' modifier will use the UTF-16 encoding while `w' will use
UTF-32. The encoding is set by the programming language and cannot
be altered.

ADDR, starting display address
ADDR is the address where you want GDB to begin displaying memory.
The expression need not have a pointer value (though it may); it
is always interpreted as an integer address of a byte of memory.
*Note Expressions: Expressions, for more information on
expressions. The default for ADDR is usually just after the last
address examined--but several other commands also set the default
address: `info breakpoints' (to the address of the last breakpoint
listed), `info line' (to the starting address of a line), and
`print' (if you use it to display a value from memory).

For example, `x/3uh 0x54320' is a request to display three halfwords
(`h') of memory, formatted as unsigned decimal integers (`u'), starting
at address `0x54320'. `x/4xw $sp' prints the four words (`w') of
memory above the stack pointer (here, `$sp'; *note Registers:
Registers.) in hexadecimal (`x').

You can also specify a negative repeat count to examine memory
backward from the given address. For example, `x/-3uh 0x54320' prints
three halfwords (`h') at `0x5431a', `0x5431c', and `0x5431e'.

Since the letters indicating unit sizes are all distinct from the
letters specifying output formats, you do not have to remember whether
unit size or format comes first; either order works. The output
specifications `4xw' and `4wx' mean exactly the same thing. (However,
the count N must come first; `wx4' does not work.)

Even though the unit size U is ignored for the formats `s' and `i',
you might still want to use a count N; for example, `3i' specifies that
you want to see three machine instructions, including any operands.
For convenience, especially when used with the `display' command, the
`i' format also prints branch delay slot instructions, if any, beyond
the count specified, which immediately follow the last instruction that
is within the count. The command `disassemble' gives an alternative
way of inspecting machine instructions; see *Note Source and Machine
Code: Machine Code.

If a negative repeat count is specified for the formats `s' or `i',
the command displays null-terminated strings or instructions before the
given address as many as the absolute value of the given number. For
the `i' format, we use line number information in the debug info to
accurately locate instruction boundaries while disassembling backward.
If line info is not available, the command stops examining memory with
an error message.

All the defaults for the arguments to `x' are designed to make it
easy to continue scanning memory with minimal specifications each time
you use `x'. For example, after you have inspected three machine
instructions with `x/3i ADDR', you can inspect the next seven with just
`x/7'. If you use <RET> to repeat the `x' command, the repeat count N
is used again; the other arguments default as for successive uses of
`x'.

When examining machine instructions, the instruction at current
program counter is shown with a `=>' marker. For example:

(gdb) x/5i $pc-6
0x804837f <main+11>: mov %esp,%ebp
0x8048381 <main+13>: push %ecx
0x8048382 <main+14>: sub $0x4,%esp
=> 0x8048385 <main+17>: movl $0x8048460,(%esp)
0x804838c <main+24>: call 0x80482d4 <puts@plt>

If the architecture supports memory tagging, the tags can be
displayed by using `m'. *Note Memory Tagging::.

The information will be displayed once per granule size (the amount
of bytes a particular memory tag covers). For example, AArch64 has a
granule size of 16 bytes, so it will display a tag every 16 bytes.

Due to the way GDB prints information with the `x' command (not
aligned to a particular boundary), the tag information will refer to the
initial address displayed on a particular line. If a memory tag
boundary is crossed in the middle of a line displayed by the `x'
command, it will be displayed on the next line.

The `m' format doesn't affect any other specified formats that were
passed to the `x' command.

The addresses and contents printed by the `x' command are not saved
in the value history because there is often too much of them and they
would get in the way. Instead, GDB makes these values available for
subsequent use in expressions as values of the convenience variables
`$_' and `$__'. After an `x' command, the last address examined is
available for use in expressions in the convenience variable `$_'. The
contents of that address, as examined, are available in the convenience
variable `$__'.

If the `x' command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of
output.

Most targets have an addressable memory unit size of 8 bits. This
means that to each memory address are associated 8 bits of data. Some
targets, however, have other addressable memory unit sizes. Within GDB
and this document, the term "addressable memory unit" (or "memory unit"
for short) is used when explicitly referring to a chunk of data of that
size. The word "byte" is used to refer to a chunk of data of 8 bits,
regardless of the addressable memory unit size of the target. For most
systems, addressable memory unit is a synonym of byte.

When you are debugging a program running on a remote target machine
(*note Remote Debugging::), you may wish to verify the program's image
in the remote machine's memory against the executable file you
downloaded to the target. Or, on any target, you may want to check
whether the program has corrupted its own read-only sections. The
`compare-sections' command is provided for such situations.

`compare-sections [SECTION-NAME|`-r']'
Compare the data of a loadable section SECTION-NAME in the
executable file of the program being debugged with the same
section in the target machine's memory, and report any mismatches.
With no arguments, compares all loadable sections. With an
argument of `-r', compares all loadable read-only sections.

Note: for remote targets, this command can be accelerated if the
target supports computing the CRC checksum of a block of memory
(*note qCRC packet::).

File: gdb.info, Node: Memory Tagging, Next: Auto Display, Prev: Memory, Up: Data

10.7 Memory Tagging
===================

Memory tagging is a memory protection technology that uses a pair of
tags to validate memory accesses through pointers. The tags are
integer values usually comprised of a few bits, depending on the
architecture.

There are two types of tags that are used in this setup: logical and
allocation. A logical tag is stored in the pointers themselves,
usually at the higher bits of the pointers. An allocation tag is the
tag associated with particular ranges of memory in the physical address
space, against which the logical tags from pointers are compared.

The pointer tag (logical tag) must match the memory tag (allocation
tag) for the memory access to be valid. If the logical tag does not
match the allocation tag, that will raise a memory violation.

Allocation tags cover multiple contiguous bytes of physical memory.
This range of bytes is called a memory tag granule and is
architecture-specific. For example, AArch64 has a tag granule of 16
bytes, meaning each allocation tag spans 16 bytes of memory.

If the underlying architecture supports memory tagging, like AArch64
MTE or SPARC ADI do, GDB can make use of it to validate pointers
against memory allocation tags.

The `print' (*note Data::) and `x' (*note Memory::) commands will
display tag information when appropriate, and a command prefix of
`memory-tag' gives access to the various memory tagging commands.

The `memory-tag' commands are the following:

`memory-tag print-logical-tag POINTER_EXPRESSION'
Print the logical tag stored in POINTER_EXPRESSION.

`memory-tag with-logical-tag POINTER_EXPRESSION TAG_BYTES'
Print the pointer given by POINTER_EXPRESSION, augmented with a
logical tag of TAG_BYTES.

`memory-tag print-allocation-tag ADDRESS_EXPRESSION'
Print the allocation tag associated with the memory address given
by ADDRESS_EXPRESSION.

`memory-tag setatag STARTING_ADDRESS LENGTH TAG_BYTES'
Set the allocation tag(s) for memory range [STARTING_ADDRESS,
STARTING_ADDRESS + LENGTH) to TAG_BYTES.

`memory-tag check POINTER_EXPRESSION'
Check if the logical tag in the pointer given by POINTER_EXPRESSION
matches the allocation tag for the memory referenced by the
pointer.

This essentially emulates the hardware validation that is done
when tagged memory is accessed through a pointer, but does not
cause a memory fault as it would during hardware validation.

It can be used to inspect potential memory tagging violations in
the running process, before any faults get triggered.

File: gdb.info, Node: Auto Display, Next: Print Settings, Prev: Memory Tagging, Up: Data

10.8 Automatic Display
======================

If you find that you want to print the value of an expression frequently
(to see how it changes), you might want to add it to the "automatic
display list" so that GDB prints its value each time your program stops.
Each expression added to the list is given a number to identify it; to
remove an expression from the list, you specify that number. The
automatic display looks like this:

2: foo = 38
3: bar[5] = (struct hack *) 0x3804

This display shows item numbers, expressions and their current values.
As with displays you request manually using `x' or `print', you can
specify the output format you prefer; in fact, `display' decides
whether to use `print' or `x' depending your format specification--it
uses `x' if you specify either the `i' or `s' format, or a unit size;
otherwise it uses `print'.

`display EXPR'
Add the expression EXPR to the list of expressions to display each
time your program stops. *Note Expressions: Expressions.

`display' does not repeat if you press <RET> again after using it.

`display/FMT EXPR'
For FMT specifying only a display format and not a size or count,
add the expression EXPR to the auto-display list but arrange to
display it each time in the specified format FMT. *Note Output
Formats: Output Formats.

`display/FMT ADDR'
For FMT `i' or `s', or including a unit-size or a number of units,
add the expression ADDR as a memory address to be examined each
time your program stops. Examining means in effect doing `x/FMT
ADDR'. *Note Examining Memory: Memory.

For example, `display/i $pc' can be helpful, to see the machine
instruction about to be executed each time execution stops (`$pc' is a
common name for the program counter; *note Registers: Registers.).

`undisplay DNUMS...'
`delete display DNUMS...'
Remove items from the list of expressions to display. Specify the
numbers of the displays that you want affected with the command
argument DNUMS. It can be a single display number, one of the
numbers shown in the first field of the `info display' display; or
it could be a range of display numbers, as in `2-4'.

`undisplay' does not repeat if you press <RET> after using it.
(Otherwise you would just get the error `No display number ...'.)

`disable display DNUMS...'
Disable the display of item numbers DNUMS. A disabled display
item is not printed automatically, but is not forgotten. It may be
enabled again later. Specify the numbers of the displays that you
want affected with the command argument DNUMS. It can be a single
display number, one of the numbers shown in the first field of the
`info display' display; or it could be a range of display numbers,
as in `2-4'.

`enable display DNUMS...'
Enable display of item numbers DNUMS. It becomes effective once
again in auto display of its expression, until you specify
otherwise. Specify the numbers of the displays that you want
affected with the command argument DNUMS. It can be a single
display number, one of the numbers shown in the first field of the
`info display' display; or it could be a range of display numbers,
as in `2-4'.

`display'
Display the current values of the expressions on the list, just as
is done when your program stops.

`info display'
Print the list of expressions previously set up to display
automatically, each one with its item number, but without showing
the values. This includes disabled expressions, which are marked
as such. It also includes expressions which would not be
displayed right now because they refer to automatic variables not
currently available.

If a display expression refers to local variables, then it does not
make sense outside the lexical context for which it was set up. Such an
expression is disabled when execution enters a context where one of its
variables is not defined. For example, if you give the command
`display last_char' while inside a function with an argument
`last_char', GDB displays this argument while your program continues to
stop inside that function. When it stops elsewhere--where there is no
variable `last_char'--the display is disabled automatically. The next
time your program stops where `last_char' is meaningful, you can enable
the display expression once again.

File: gdb.info, Node: Print Settings, Next: Pretty Printing, Prev: Auto Display, Up: Data

10.9 Print Settings
===================

GDB provides the following ways to control how arrays, structures, and
symbols are printed.

These settings are useful for debugging programs in any language:

`set print address'
`set print address on'
GDB prints memory addresses showing the location of stack traces,
structure values, pointer values, breakpoints, and so forth, even
when it also displays the contents of those addresses. The default
is `on'. For example, this is what a stack frame display looks
like with `set print address on':

(gdb) f
#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
at input.c:530
530 if (lquote != def_lquote)

`set print address off'
Do not print addresses when displaying their contents. For
example, this is the same stack frame displayed with `set print
address off':

(gdb) set print addr off
(gdb) f
#0 set_quotes (lq="<<", rq=">>") at input.c:530
530 if (lquote != def_lquote)

You can use `set print address off' to eliminate all machine
dependent displays from the GDB interface. For example, with
`print address off', you should get the same text for backtraces on
all machines--whether or not they involve pointer arguments.

`show print address'
Show whether or not addresses are to be printed.

When GDB prints a symbolic address, it normally prints the closest
earlier symbol plus an offset. If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify. One way to do this is with
`info line', for example `info line *0x4537'. Alternately, you can set
GDB to print the source file and line number when it prints a symbolic
address:

`set print symbol-filename on'
Tell GDB to print the source file name and line number of a symbol
in the symbolic form of an address.

`set print symbol-filename off'
Do not print source file name and line number of a symbol. This
is the default.

`show print symbol-filename'
Show whether or not GDB will print the source file name and line
number of a symbol in the symbolic form of an address.

Another situation where it is helpful to show symbol filenames and
line numbers is when disassembling code; GDB shows you the line number
and source file that corresponds to each instruction.

Also, you may wish to see the symbolic form only if the address being
printed is reasonably close to the closest earlier symbol:

`set print max-symbolic-offset MAX-OFFSET'
`set print max-symbolic-offset unlimited'
Tell GDB to only display the symbolic form of an address if the
offset between the closest earlier symbol and the address is less
than MAX-OFFSET. The default is `unlimited', which tells GDB to
always print the symbolic form of an address if any symbol precedes
it. Zero is equivalent to `unlimited'.

`show print max-symbolic-offset'
Ask how large the maximum offset is that GDB prints in a symbolic
address.

If you have a pointer and you are not sure where it points, try `set
print symbol-filename on'. Then you can determine the name and source
file location of the variable where it points, using `p/a POINTER'.
This interprets the address in symbolic form. For example, here GDB
shows that a variable `ptt' points at another variable `t', defined in
`hi2.c':

(gdb) set print symbol-filename on
(gdb) p/a ptt
$4 = 0xe008 <t in hi2.c>

_Warning:_ For pointers that point to a local variable, `p/a' does
not show the symbol name and filename of the referent, even with
the appropriate `set print' options turned on.

You can also enable `/a'-like formatting all the time using `set
print symbol on':

`set print symbol on'
Tell GDB to print the symbol corresponding to an address, if one
exists.

`set print symbol off'
Tell GDB not to print the symbol corresponding to an address. In
this mode, GDB will still print the symbol corresponding to
pointers to functions. This is the default.

`show print symbol'
Show whether GDB will display the symbol corresponding to an
address.

Other settings control how different kinds of objects are printed:

`set print array'
`set print array on'
Pretty print arrays. This format is more convenient to read, but
uses more space. The default is off.

`set print array off'
Return to compressed format for arrays.

`show print array'
Show whether compressed or pretty format is selected for displaying
arrays.

`set print array-indexes'
`set print array-indexes on'
Print the index of each element when displaying arrays. May be
more convenient to locate a given element in the array or quickly
find the index of a given element in that printed array. The
default is off.

`set print array-indexes off'
Stop printing element indexes when displaying arrays.

`show print array-indexes'
Show whether the index of each element is printed when displaying
arrays.

`set print nibbles'
`set print nibbles on'
Print binary values in groups of four bits, known as "nibbles",
when using the print command of GDB with the option `/t'. For
example, this is what it looks like with `set print nibbles on':

(gdb) print val_flags
$1 = 1230
(gdb) print/t val_flags
$2 = 0100 1100 1110

`set print nibbles off'
Don't printing binary values in groups. This is the default.

`show print nibbles'
Show whether to print binary values in groups of four bits.

`set print characters NUMBER-OF-CHARACTERS'
`set print characters elements'
`set print characters unlimited'
Set a limit on how many characters of a string GDB will print. If
GDB is printing a large string, it stops printing after it has
printed the number of characters set by the `set print characters'
command. This equally applies to multi-byte and wide character
strings, that is for strings whose character type is `wchar_t',
`char16_t', or `char32_t' it is the number of actual characters
rather than underlying bytes the encoding uses that this setting
controls. Setting NUMBER-OF-CHARACTERS to `elements' means that
the limit on the number of characters to print follows one for
array elements; see *Note set print elements::. Setting
NUMBER-OF-CHARACTERS to `unlimited' means that the number of
characters to print is unlimited. When GDB starts, this limit is
set to `elements'.

`show print characters'
Display the number of characters of a large string that GDB will
print.

`set print elements NUMBER-OF-ELEMENTS'
`set print elements unlimited'
Set a limit on how many elements of an array GDB will print. If
GDB is printing a large array, it stops printing after it has
printed the number of elements set by the `set print elements'
command. By default this limit also applies to the display of
strings; see *Note set print characters::. When GDB starts, this
limit is set to 200. Setting NUMBER-OF-ELEMENTS to `unlimited' or
zero means that the number of elements to print is unlimited.

When printing very large arrays, whose size is greater than
`max-value-size' (*note max-value-size: set max-value-size.), if
the `print elements' is set such that the size of the elements
being printed is less than or equal to `max-value-size', then GDB
will print the array (up to the `print elements' limit), and only
`max-value-size' worth of data will be added into the value
history (*note Value History: Value History.).

`show print elements'
Display the number of elements of a large array that GDB will
print.

`set print frame-arguments VALUE'
This command allows to control how the values of arguments are
printed when the debugger prints a frame (*note Frames::). The
possible values are:

`all'
The values of all arguments are printed.

`scalars'
Print the value of an argument only if it is a scalar. The
value of more complex arguments such as arrays, structures,
unions, etc, is replaced by `...'. This is the default.
Here is an example where only scalar arguments are shown:

#1 0x08048361 in call_me (i=3, s=..., ss=0xbf8d508c, u=..., e=green)
at frame-args.c:23

`none'
None of the argument values are printed. Instead, the value
of each argument is replaced by `...'. In this case, the
example above now becomes:

#1 0x08048361 in call_me (i=..., s=..., ss=..., u=..., e=...)
at frame-args.c:23

`presence'
Only the presence of arguments is indicated by `...'. The
`...' are not printed for function without any arguments.
None of the argument names and values are printed. In this
case, the example above now becomes:

#1 0x08048361 in call_me (...) at frame-args.c:23

By default, only scalar arguments are printed. This command can
be used to configure the debugger to print the value of all
arguments, regardless of their type. However, it is often
advantageous to not print the value of more complex parameters.
For instance, it reduces the amount of information printed in each
frame, making the backtrace more readable. Also, it improves
performance when displaying Ada frames, because the computation of
large arguments can sometimes be CPU-intensive, especially in
large applications. Setting `print frame-arguments' to `scalars'
(the default), `none' or `presence' avoids this computation, thus
speeding up the display of each Ada frame.

`show print frame-arguments'
Show how the value of arguments should be displayed when printing
a frame.

`set print raw-frame-arguments on'
Print frame arguments in raw, non pretty-printed, form.

`set print raw-frame-arguments off'
Print frame arguments in pretty-printed form, if there is a
pretty-printer for the value (*note Pretty Printing::), otherwise
print the value in raw form. This is the default.

`show print raw-frame-arguments'
Show whether to print frame arguments in raw form.

`set print entry-values VALUE'
Set printing of frame argument values at function entry. In some
cases GDB can determine the value of function argument which was
passed by the function caller, even if the value was modified
inside the called function and therefore is different. With
optimized code, the current value could be unavailable, but the
entry value may still be known.

The default value is `default' (see below for its description).
Older GDB behaved as with the setting `no'. Compilers not
supporting this feature will behave in the `default' setting the
same way as with the `no' setting.

This functionality is currently supported only by DWARF 2
debugging format and the compiler has to produce
`DW_TAG_call_site' tags. With GCC, you need to specify `-O -g'
during compilation, to get this information.

The VALUE parameter can be one of the following:

`no'
Print only actual parameter values, never print values from
function entry point.
#0 equal (val=5)
#0 different (val=6)
#0 lost (val=<optimized out>)
#0 born (val=10)
#0 invalid (val=<optimized out>)

`only'
Print only parameter values from function entry point. The
actual parameter values are never printed.
#0 equal (val@entry=5)
#0 different (val@entry=5)
#0 lost (val@entry=5)
#0 born (val@entry=<optimized out>)
#0 invalid (val@entry=<optimized out>)

`preferred'
Print only parameter values from function entry point. If
value from function entry point is not known while the actual
value is known, print the actual value for such parameter.
#0 equal (val@entry=5)
#0 different (val@entry=5)
#0 lost (val@entry=5)
#0 born (val=10)
#0 invalid (val@entry=<optimized out>)

`if-needed'
Print actual parameter values. If actual parameter value is
not known while value from function entry point is known,
print the entry point value for such parameter.
#0 equal (val=5)
#0 different (val=6)
#0 lost (val@entry=5)
#0 born (val=10)
#0 invalid (val=<optimized out>)

`both'
Always print both the actual parameter value and its value
from function entry point, even if values of one or both are
not available due to compiler optimizations.
#0 equal (val=5, val@entry=5)
#0 different (val=6, val@entry=5)
#0 lost (val=<optimized out>, val@entry=5)
#0 born (val=10, val@entry=<optimized out>)
#0 invalid (val=<optimized out>, val@entry=<optimized out>)

`compact'
Print the actual parameter value if it is known and also its
value from function entry point if it is known. If neither
is known, print for the actual value `<optimized out>'. If
not in MI mode (*note GDB/MI::) and if both values are known
and identical, print the shortened `param=param@entry=VALUE'
notation.
#0 equal (val=val@entry=5)
#0 different (val=6, val@entry=5)
#0 lost (val@entry=5)
#0 born (val=10)
#0 invalid (val=<optimized out>)

`default'
Always print the actual parameter value. Print also its
value from function entry point, but only if it is known. If
not in MI mode (*note GDB/MI::) and if both values are known
and identical, print the shortened `param=param@entry=VALUE'
notation.
#0 equal (val=val@entry=5)
#0 different (val=6, val@entry=5)
#0 lost (val=<optimized out>, val@entry=5)
#0 born (val=10)
#0 invalid (val=<optimized out>)

For analysis messages on possible failures of frame argument
values at function entry resolution see *Note set debug
entry-values::.

`show print entry-values'
Show the method being used for printing of frame argument values
at function entry.

`set print frame-info VALUE'
This command allows to control the information printed when the
debugger prints a frame. See *Note Frames::, *Note Backtrace::,
for a general explanation about frames and frame information.
Note that some other settings (such as `set print frame-arguments'
and `set print address') are also influencing if and how some frame
information is displayed. In particular, the frame program
counter is never printed if `set print address' is off.

The possible values for `set print frame-info' are:
`short-location'
Print the frame level, the program counter (if not at the
beginning of the location source line), the function, the
function arguments.

`location'
Same as `short-location' but also print the source file and
source line number.

`location-and-address'
Same as `location' but print the program counter even if
located at the beginning of the location source line.

`source-line'
Print the program counter (if not at the beginning of the
location source line), the line number and the source line.

`source-and-location'
Print what `location' and `source-line' are printing.

`auto'
The information printed for a frame is decided automatically
by the GDB command that prints a frame. For example, `frame'
prints the information printed by `source-and-location' while
`stepi' will switch between `source-line' and
`source-and-location' depending on the program counter. The
default value is `auto'.

`set print repeats NUMBER-OF-REPEATS'
`set print repeats unlimited'
Set the threshold for suppressing display of repeated array
elements. When the number of consecutive identical elements of an
array exceeds the threshold, GDB prints the string `"<repeats N
times>"', where N is the number of identical repetitions, instead
of displaying the identical elements themselves. Setting the
threshold to `unlimited' or zero will cause all elements to be
individually printed. The default threshold is 10.

`show print repeats'
Display the current threshold for printing repeated identical
elements.

`set print max-depth DEPTH'

`set print max-depth unlimited'
Set the threshold after which nested structures are replaced with
ellipsis, this can make visualising deeply nested structures
easier.

For example, given this C code

typedef struct s1 { int a; } s1;
typedef struct s2 { s1 b; } s2;
typedef struct s3 { s2 c; } s3;
typedef struct s4 { s3 d; } s4;

s4 var = { { { { 3 } } } };

The following table shows how different values of DEPTH will
effect how `var' is printed by GDB:

DEPTH setting Result of `p var'
---------------------------------------------------------------------
unlimited `$1 = {d = {c = {b = {a = 3}}}}'
`0' `$1 = {...}'
`1' `$1 = {d = {...}}'
`2' `$1 = {d = {c = {...}}}'
`3' `$1 = {d = {c = {b = {...}}}}'
`4' `$1 = {d = {c = {b = {a = 3}}}}'

To see the contents of structures that have been hidden the user
can either increase the print max-depth, or they can print the
elements of the structure that are visible, for example

(gdb) set print max-depth 2
(gdb) p var
$1 = {d = {c = {...}}}
(gdb) p var.d
$2 = {c = {b = {...}}}
(gdb) p var.d.c
$3 = {b = {a = 3}}

The pattern used to replace nested structures varies based on
language, for most languages `{...}' is used, but Fortran uses
`(...)'.

`show print max-depth'
Display the current threshold after which nested structures are
replaces with ellipsis.

`set print memory-tag-violations'
`set print memory-tag-violations on'
Cause GDB to display additional information about memory tag
violations when printing pointers and addresses.

`set print memory-tag-violations off'
Stop printing memory tag violation information.

`show print memory-tag-violations'
Show whether memory tag violation information is displayed when
printing pointers and addresses.

`set print null-stop'
Cause GDB to stop printing the characters of an array when the
first NULL is encountered. This is useful when large arrays
actually contain only short strings. The default is off.

`show print null-stop'
Show whether GDB stops printing an array on the first NULL
character.

`set print pretty on'
Cause GDB to print structures in an indented format with one member
per line, like this:

$1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
},
meat = 0x54 "Pork"
}

`set print pretty off'
Cause GDB to print structures in a compact format, like this:

$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \
meat = 0x54 "Pork"}

This is the default format.

`show print pretty'
Show which format GDB is using to print structures.

`set print raw-values on'
Print values in raw form, without applying the pretty printers for
the value.

`set print raw-values off'
Print values in pretty-printed form, if there is a pretty-printer
for the value (*note Pretty Printing::), otherwise print the value
in raw form.

The default setting is "off".

`show print raw-values'
Show whether to print values in raw form.

`set print sevenbit-strings on'
Print using only seven-bit characters; if this option is set, GDB
displays any eight-bit characters (in strings or character values)
using the notation `\'NNN. This setting is best if you are
working in English (ASCII) and you use the high-order bit of
characters as a marker or "meta" bit.

`set print sevenbit-strings off'
Print full eight-bit characters. This allows the use of more
international character sets, and is the default.

`show print sevenbit-strings'
Show whether or not GDB is printing only seven-bit characters.

`set print union on'
Tell GDB to print unions which are contained in structures and
other unions. This is the default setting.

`set print union off'
Tell GDB not to print unions which are contained in structures and
other unions. GDB will print `"{...}"' instead.

`show print union'
Ask GDB whether or not it will print unions which are contained in
structures and other unions.

For example, given the declarations

typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling} Tree_forms;
typedef enum {Caterpillar, Cocoon, Butterfly}
Bug_forms;

struct thing {
Species it;
union {
Tree_forms tree;
Bug_forms bug;
} form;
};

struct thing foo = {Tree, {Acorn}};

with `set print union on' in effect `p foo' would print

$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}

and with `set print union off' in effect it would print

$1 = {it = Tree, form = {...}}

`set print union' affects programs written in C-like languages and
in Pascal.

These settings are of interest when debugging C++ programs:

`set print demangle'
`set print demangle on'
Print C++ names in their source form rather than in the encoded
("mangled") form passed to the assembler and linker for type-safe
linkage. The default is on.

`show print demangle'
Show whether C++ names are printed in mangled or demangled form.

`set print asm-demangle'
`set print asm-demangle on'
Print C++ names in their source form rather than their mangled
form, even in assembler code printouts such as instruction
disassemblies. The default is off.

`show print asm-demangle'
Show whether C++ names in assembly listings are printed in mangled
or demangled form.

`set demangle-style STYLE'
Choose among several encoding schemes used by different compilers
to represent C++ names. If you omit STYLE, you will see a list of
possible formats. The default value is AUTO, which lets GDB
choose a decoding style by inspecting your program.

`show demangle-style'
Display the encoding style currently in use for decoding C++
symbols.

`set print object'
`set print object on'
When displaying a pointer to an object, identify the _actual_
(derived) type of the object rather than the _declared_ type, using
the virtual function table. Note that the virtual function table
is required--this feature can only work for objects that have
run-time type identification; a single virtual method in the
object's declared type is sufficient. Note that this setting is
also taken into account when working with variable objects via MI
(*note GDB/MI::).

`set print object off'
Display only the declared type of objects, without reference to the
virtual function table. This is the default setting.

`show print object'
Show whether actual, or declared, object types are displayed.

`set print static-members'
`set print static-members on'
Print static members when displaying a C++ object. The default is
on.

`set print static-members off'
Do not print static members when displaying a C++ object.

`show print static-members'
Show whether C++ static members are printed or not.

`set print pascal_static-members'
`set print pascal_static-members on'
Print static members when displaying a Pascal object. The default
is on.

`set print pascal_static-members off'
Do not print static members when displaying a Pascal object.

`show print pascal_static-members'
Show whether Pascal static members are printed or not.

`set print vtbl'
`set print vtbl on'
Pretty print C++ virtual function tables. The default is off.
(The `vtbl' commands do not work on programs compiled with the HP
ANSI C++ compiler (`aCC').)

`set print vtbl off'
Do not pretty print C++ virtual function tables.

`show print vtbl'
Show whether C++ virtual function tables are pretty printed, or
not.

File: gdb.info, Node: Pretty Printing, Next: Value History, Prev: Print Settings, Up: Data

10.10 Pretty Printing
=====================

GDB provides a mechanism to allow pretty-printing of values using
Python code. It greatly simplifies the display of complex objects.
This mechanism works for both MI and the CLI.

* Menu:

* Pretty-Printer Introduction:: Introduction to pretty-printers
* Pretty-Printer Example:: An example pretty-printer
* Pretty-Printer Commands:: Pretty-printer commands

File: gdb.info, Node: Pretty-Printer Introduction, Next: Pretty-Printer Example, Up: Pretty Printing

10.10.1 Pretty-Printer Introduction
-----------------------------------

When GDB prints a value, it first sees if there is a pretty-printer
registered for the value. If there is then GDB invokes the
pretty-printer to print the value. Otherwise the value is printed
normally.

Pretty-printers are normally named. This makes them easy to manage.
The `info pretty-printer' command will list all the installed
pretty-printers with their names. If a pretty-printer can handle
multiple data types, then its "subprinters" are the printers for the
individual data types. Each such subprinter has its own name. The
format of the name is PRINTER-NAME;SUBPRINTER-NAME.

Pretty-printers are installed by "registering" them with GDB.
Typically they are automatically loaded and registered when the
corresponding debug information is loaded, thus making them available
without having to do anything special.

There are three places where a pretty-printer can be registered.

* Pretty-printers registered globally are available when debugging
all inferiors.

* Pretty-printers registered with a program space are available only
when debugging that program. *Note Progspaces In Python::, for
more details on program spaces in Python.

* Pretty-printers registered with an objfile are loaded and unloaded
with the corresponding objfile (e.g., shared library). *Note
Objfiles In Python::, for more details on objfiles in Python.

*Note Selecting Pretty-Printers::, for further information on how
pretty-printers are selected,

*Note Writing a Pretty-Printer::, for implementing pretty printers
for new types.

File: gdb.info, Node: Pretty-Printer Example, Next: Pretty-Printer Commands, Prev: Pretty-Printer Introduction, Up: Pretty Printing

10.10.2 Pretty-Printer Example
------------------------------

Here is how a C++ `std::string' looks without a pretty-printer:

(gdb) print s
$1 = {
static npos = 4294967295,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::new_allocator<char>> = {
<No data fields>}, <No data fields>
},
members of std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::_Alloc_hider:
_M_p = 0x804a014 "abcd"
}
}

With a pretty-printer for `std::string' only the contents are
printed:

(gdb) print s
$2 = "abcd"

File: gdb.info, Node: Pretty-Printer Commands, Prev: Pretty-Printer Example, Up: Pretty Printing

10.10.3 Pretty-Printer Commands
-------------------------------

`info pretty-printer [OBJECT-REGEXP [NAME-REGEXP]]'
Print the list of installed pretty-printers. This includes
disabled pretty-printers, which are marked as such.

OBJECT-REGEXP is a regular expression matching the objects whose
pretty-printers to list. Objects can be `global', the program
space's file (*note Progspaces In Python::), and the object files
within that program space (*note Objfiles In Python::). *Note
Selecting Pretty-Printers::, for details on how GDB looks up a
printer from these three objects.

NAME-REGEXP is a regular expression matching the name of the
printers to list.

`disable pretty-printer [OBJECT-REGEXP [NAME-REGEXP]]'
Disable pretty-printers matching OBJECT-REGEXP and NAME-REGEXP. A
disabled pretty-printer is not forgotten, it may be enabled again
later.

`enable pretty-printer [OBJECT-REGEXP [NAME-REGEXP]]'
Enable pretty-printers matching OBJECT-REGEXP and NAME-REGEXP.

Example:

Suppose we have three pretty-printers installed: one from library1.so
named `foo' that prints objects of type `foo', and another from
library2.so named `bar' that prints two types of objects, `bar1' and
`bar2'.

(gdb) info pretty-printer
library1.so:
foo
library2.so:
bar
bar1
bar2
(gdb) info pretty-printer library2
library2.so:
bar
bar1
bar2
(gdb) disable pretty-printer library1
1 printer disabled
2 of 3 printers enabled
(gdb) info pretty-printer
library1.so:
foo [disabled]
library2.so:
bar
bar1
bar2
(gdb) disable pretty-printer library2 bar;bar1
1 printer disabled
1 of 3 printers enabled
(gdb) info pretty-printer library2
library2.so:
bar
bar1 [disabled]
bar2
(gdb) disable pretty-printer library2 bar
1 printer disabled
0 of 3 printers enabled
(gdb) info pretty-printer
library1.so:
foo [disabled]
library2.so:
bar [disabled]
bar1 [disabled]
bar2

Note that for `bar' the entire printer can be disabled, as can each
individual subprinter.

Printing values and frame arguments is done by default using the
enabled pretty printers.

The print option `-raw-values' and GDB setting `set print
raw-values' (*note set print raw-values::) can be used to print values
without applying the enabled pretty printers.

Similarly, the backtrace option `-raw-frame-arguments' and GDB
setting `set print raw-frame-arguments' (*note set print
raw-frame-arguments::) can be used to ignore the enabled pretty
printers when printing frame argument values.

File: gdb.info, Node: Value History, Next: Convenience Vars, Prev: Pretty Printing, Up: Data

10.11 Value History
===================

Values printed by the `print' command are saved in the GDB "value
history". This allows you to refer to them in other expressions.
Values are kept until the symbol table is re-read or discarded (for
example with the `file' or `symbol-file' commands). When the symbol
table changes, the value history is discarded, since the values may
contain pointers back to the types defined in the symbol table.

The values printed are given "history numbers" by which you can
refer to them. These are successive integers starting with one.
`print' shows you the history number assigned to a value by printing
`$NUM = ' before the value; here NUM is the history number.

To refer to any previous value, use `$' followed by the value's
history number. The way `print' labels its output is designed to
remind you of this. Just `$' refers to the most recent value in the
history, and `$$' refers to the value before that. `$$N' refers to the
Nth value from the end; `$$2' is the value just prior to `$$', `$$1' is
equivalent to `$$', and `$$0' is equivalent to `$'.

For example, suppose you have just printed a pointer to a structure
and want to see the contents of the structure. It suffices to type

p *$

If you have a chain of structures where the component `next' points
to the next one, you can print the contents of the next one with this:

p *$.next

You can print successive links in the chain by repeating this
command--which you can do by just typing <RET>.

Note that the history records values, not expressions. If the value
of `x' is 4 and you type these commands:

print x
set x=5

then the value recorded in the value history by the `print' command
remains 4 even though the value of `x' has changed.

`show values'
Print the last ten values in the value history, with their item
numbers. This is like `p $$9' repeated ten times, except that
`show values' does not change the history.

`show values N'
Print ten history values centered on history item number N.

`show values +'
Print ten history values just after the values last printed. If
no more values are available, `show values +' produces no display.

Pressing <RET> to repeat `show values N' has exactly the same effect
as `show values +'.

File: gdb.info, Node: Convenience Vars, Next: Convenience Funs, Prev: Value History, Up: Data

10.12 Convenience Variables
===========================

GDB provides "convenience variables" that you can use within GDB to
hold on to a value and refer to it later. These variables exist
entirely within GDB; they are not part of your program, and setting a
convenience variable has no direct effect on further execution of your
program. That is why you can use them freely.

Convenience variables are prefixed with `$'. Any name preceded by
`$' can be used for a convenience variable, unless it is one of the
predefined machine-specific register names (*note Registers:
Registers.). (Value history references, in contrast, are _numbers_
preceded by `$'. *Note Value History: Value History.)

You can save a value in a convenience variable with an assignment
expression, just as you would set a variable in your program. For
example:

set $foo = *object_ptr

would save in `$foo' the value contained in the object pointed to by
`object_ptr'.

Using a convenience variable for the first time creates it, but its
value is `void' until you assign a new value. You can alter the value
with another assignment at any time.

Convenience variables have no fixed types. You can assign a
convenience variable any type of value, including structures and
arrays, even if that variable already has a value of a different type.
The convenience variable, when used as an expression, has the type of
its current value.

`show convenience'
Print a list of convenience variables used so far, and their
values, as well as a list of the convenience functions.
Abbreviated `show conv'.

`init-if-undefined $VARIABLE = EXPRESSION'
Set a convenience variable if it has not already been set. This
is useful for user-defined commands that keep some state. It is
similar, in concept, to using local static variables with
initializers in C (except that convenience variables are global).
It can also be used to allow users to override default values used
in a command script.

If the variable is already defined then the expression is not
evaluated so any side-effects do not occur.

One of the ways to use a convenience variable is as a counter to be
incremented or a pointer to be advanced. For example, to print a field
from successive elements of an array of structures:

set $i = 0
print bar[$i++]->contents

Repeat that command by typing <RET>.

Some convenience variables are created automatically by GDB and given
values likely to be useful.

`$_'
The variable `$_' is automatically set by the `x' command to the
last address examined (*note Examining Memory: Memory.). Other
commands which provide a default address for `x' to examine also
set `$_' to that address; these commands include `info line' and
`info breakpoint'. The type of `$_' is `void *' except when set
by the `x' command, in which case it is a pointer to the type of
`$__'.

`$__'
The variable `$__' is automatically set by the `x' command to the
value found in the last address examined. Its type is chosen to
match the format in which the data was printed.

`$_exitcode'
When the program being debugged terminates normally, GDB
automatically sets this variable to the exit code of the program,
and resets `$_exitsignal' to `void'.

`$_exitsignal'
When the program being debugged dies due to an uncaught signal,
GDB automatically sets this variable to that signal's number, and
resets `$_exitcode' to `void'.

To distinguish between whether the program being debugged has
exited (i.e., `$_exitcode' is not `void') or signalled (i.e.,
`$_exitsignal' is not `void'), the convenience function `$_isvoid'
can be used (*note Convenience Functions: Convenience Funs.). For
example, considering the following source code:

#include <signal.h>

int
main (int argc, char *argv[])
{
raise (SIGALRM);
return 0;
}

A valid way of telling whether the program being debugged has
exited or signalled would be:

(gdb) define has_exited_or_signalled
Type commands for definition of ``has_exited_or_signalled''.
End with a line saying just ``end''.
>if $_isvoid ($_exitsignal)
>echo The program has exited\n
>else
>echo The program has signalled\n
>end
>end
(gdb) run
Starting program:

Program terminated with signal SIGALRM, Alarm clock.
The program no longer exists.
(gdb) has_exited_or_signalled
The program has signalled

As can be seen, GDB correctly informs that the program being
debugged has signalled, since it calls `raise' and raises a
`SIGALRM' signal. If the program being debugged had not called
`raise', then GDB would report a normal exit:

(gdb) has_exited_or_signalled
The program has exited

`$_exception'
The variable `$_exception' is set to the exception object being
thrown at an exception-related catchpoint. *Note Set
Catchpoints::.

`$_ada_exception'
The variable `$_ada_exception' is set to the address of the
exception being caught or thrown at an Ada exception-related
catchpoint. *Note Set Catchpoints::.

`$_probe_argc'
`$_probe_arg0...$_probe_arg11'
Arguments to a static probe. *Note Static Probe Points::.

`$_sdata'
The variable `$_sdata' contains extra collected static tracepoint
data. *Note Tracepoint Action Lists: Tracepoint Actions. Note
that `$_sdata' could be empty, if not inspecting a trace buffer, or
if extra static tracepoint data has not been collected.

`$_siginfo'
The variable `$_siginfo' contains extra signal information (*note
extra signal information::). Note that `$_siginfo' could be
empty, if the application has not yet received any signals. For
example, it will be empty before you execute the `run' command.

`$_tlb'
The variable `$_tlb' is automatically set when debugging
applications running on MS-Windows in native mode or connected to
gdbserver that supports the `qGetTIBAddr' request. *Note General
Query Packets::. This variable contains the address of the thread
information block.

`$_inferior'
The number of the current inferior. *Note Debugging Multiple
Inferiors Connections and Programs: Inferiors Connections and
Programs.

`$_thread'
The thread number of the current thread. *Note thread numbers::.

`$_gthread'
The global number of the current thread. *Note global thread
numbers::.

`$_inferior_thread_count'
The number of live threads in the current inferior. *Note
Threads::.

`$_gdb_major'
`$_gdb_minor'
The major and minor version numbers of the running GDB.
Development snapshots and pretest versions have their minor version
incremented by one; thus, GDB pretest 9.11.90 will produce the
value 12 for `$_gdb_minor'. These variables allow you to write
scripts that work with different versions of GDB without errors
caused by features unavailable in some of those versions.

`$_shell_exitcode'
`$_shell_exitsignal'
GDB commands such as `shell' and `|' are launching shell commands.
When a launched command terminates, GDB automatically maintains
the variables `$_shell_exitcode' and `$_shell_exitsignal'
according to the exit status of the last launched command. These
variables are set and used similarly to the variables `$_exitcode'
and `$_exitsignal'.

File: gdb.info, Node: Convenience Funs, Next: Registers, Prev: Convenience Vars, Up: Data

10.13 Convenience Functions
===========================

GDB also supplies some "convenience functions". These have a syntax
similar to convenience variables. A convenience function can be used
in an expression just like an ordinary function; however, a convenience
function is implemented internally to GDB.

These functions do not require GDB to be configured with `Python'
support, which means that they are always available.

`$_isvoid (EXPR)'
Return one if the expression EXPR is `void'. Otherwise it returns
zero.

A `void' expression is an expression where the type of the result
is `void'. For example, you can examine a convenience variable
(see *Note Convenience Variables: Convenience Vars.) to check
whether it is `void':

(gdb) print $_exitcode
$1 = void
(gdb) print $_isvoid ($_exitcode)
$2 = 1
(gdb) run
Starting program: ./a.out
[Inferior 1 (process 29572) exited normally]
(gdb) print $_exitcode
$3 = 0
(gdb) print $_isvoid ($_exitcode)
$4 = 0

In the example above, we used `$_isvoid' to check whether
`$_exitcode' is `void' before and after the execution of the
program being debugged. Before the execution there is no exit
code to be examined, therefore `$_exitcode' is `void'. After the
execution the program being debugged returned zero, therefore
`$_exitcode' is zero, which means that it is not `void' anymore.

The `void' expression can also be a call of a function from the
program being debugged. For example, given the following function:

void
foo (void)
{
}

The result of calling it inside GDB is `void':

(gdb) print foo ()
$1 = void
(gdb) print $_isvoid (foo ())
$2 = 1
(gdb) set $v = foo ()
(gdb) print $v
$3 = void
(gdb) print $_isvoid ($v)
$4 = 1

`$_gdb_setting_str (SETTING)'
Return the value of the GDB SETTING as a string. SETTING is any
setting that can be used in a `set' or `show' command (*note
Controlling GDB::).

(gdb) show print frame-arguments
Printing of non-scalar frame arguments is "scalars".
(gdb) p $_gdb_setting_str("print frame-arguments")
$1 = "scalars"
(gdb) p $_gdb_setting_str("height")
$2 = "30"
(gdb)

`$_gdb_setting (SETTING)'
Return the value of the GDB SETTING. The type of the returned
value depends on the setting.

The value type for boolean and auto boolean settings is `int'.
The boolean values `off' and `on' are converted to the integer
values `0' and `1'. The value `auto' is converted to the value
`-1'.

The value type for integer settings is either `unsigned int' or
`int', depending on the setting.

Some integer settings accept an `unlimited' value. Depending on
the setting, the `set' command also accepts the value `0' or the
value `-1' as a synonym for `unlimited'. For example, `set height
unlimited' is equivalent to `set height 0'.

Some other settings that accept the `unlimited' value use the
value `0' to literally mean zero. For example, `set history size
0' indicates to not record any GDB commands in the command history.
For such settings, `-1' is the synonym for `unlimited'.

See the documentation of the corresponding `set' command for the
numerical value equivalent to `unlimited'.

The `$_gdb_setting' function converts the unlimited value to a `0'
or a `-1' value according to what the `set' command uses.

(gdb) p $_gdb_setting_str("height")
$1 = "30"
(gdb) p $_gdb_setting("height")
$2 = 30
(gdb) set height unlimited
(gdb) p $_gdb_setting_str("height")
$3 = "unlimited"
(gdb) p $_gdb_setting("height")
$4 = 0
(gdb) p $_gdb_setting_str("history size")
$5 = "unlimited"
(gdb) p $_gdb_setting("history size")
$6 = -1
(gdb) p $_gdb_setting_str("disassemble-next-line")
$7 = "auto"
(gdb) p $_gdb_setting("disassemble-next-line")
$8 = -1
(gdb)

Other setting types (enum, filename, optional filename, string,
string noescape) are returned as string values.

`$_gdb_maint_setting_str (SETTING)'
Like the `$_gdb_setting_str' function, but works with `maintenance
set' variables.

`$_gdb_maint_setting (SETTING)'
Like the `$_gdb_setting' function, but works with `maintenance
set' variables.

`$_shell (COMMAND-STRING)'
Invoke a shell to execute COMMAND-STRING. COMMAND-STRING must be
a string. The shell runs on the host machine, the machine GDB is
running on. Returns the command's exit status. On Unix systems,
a command which exits with a zero exit status has succeeded, and
non-zero exit status indicates failure. When a command terminates
on a fatal signal whose number is N, GDB uses the value 128+N as
the exit status, as is standard in Unix shells. Note that N is a
host signal number, not a target signal number. If you're native
debugging, they will be the same, but if cross debugging, the host
vs target signal numbers may be completely unrelated. Please
consult your host operating system's documentation for the mapping
between host signal numbers and signal names. The shell to run is
determined in the same way as for the `shell' command. *Note
Shell Commands: Shell Commands.

(gdb) print $_shell("true")
$1 = 0
(gdb) print $_shell("false")
$2 = 1
(gdb) p $_shell("echo hello")
hello
$3 = 0
(gdb) p $_shell("foobar")
bash: line 1: foobar: command not found
$4 = 127

This may also be useful in breakpoint conditions. For example:

(gdb) break function if $_shell("some command") == 0

In this scenario, you'll want to make sure that the shell command
you run in the breakpoint condition takes the least amount of time
possible. For example, avoid running a command that may block
indefinitely, or that sleeps for a while before exiting. Prefer a
command or script which analyzes some state and exits immediately.
This is important because the debugged program stops for the
breakpoint every time, and then GDB evaluates the breakpoint
condition. If the condition is false, the program is re-resumed
transparently, without informing you of the stop. A quick shell
command thus avoids significantly slowing down the debugged program
unnecessarily.

Note: unlike the `shell' command, the `$_shell' convenience
function does not affect the `$_shell_exitcode' and
`$_shell_exitsignal' convenience variables.

The following functions require GDB to be configured with `Python'
support.

`$_memeq(BUF1, BUF2, LENGTH)'
Returns one if the LENGTH bytes at the addresses given by BUF1 and
BUF2 are equal. Otherwise it returns zero.

`$_regex(STR, REGEX)'
Returns one if the string STR matches the regular expression
REGEX. Otherwise it returns zero. The syntax of the regular
expression is that specified by `Python''s regular expression
support.

`$_streq(STR1, STR2)'
Returns one if the strings STR1 and STR2 are equal. Otherwise it
returns zero.

`$_strlen(STR)'
Returns the length of string STR.

`$_caller_is(NAME[, NUMBER_OF_FRAMES])'
Returns one if the calling function's name is equal to NAME.
Otherwise it returns zero.

If the optional argument NUMBER_OF_FRAMES is provided, it is the
number of frames up in the stack to look. The default is 1.

Example:

(gdb) backtrace
#0 bottom_func ()
at testsuite/gdb.python/py-caller-is.c:21
#1 0x00000000004005a0 in middle_func ()
at testsuite/gdb.python/py-caller-is.c:27
#2 0x00000000004005ab in top_func ()
at testsuite/gdb.python/py-caller-is.c:33
#3 0x00000000004005b6 in main ()
at testsuite/gdb.python/py-caller-is.c:39
(gdb) print $_caller_is ("middle_func")
$1 = 1
(gdb) print $_caller_is ("top_func", 2)
$1 = 1

`$_caller_matches(REGEXP[, NUMBER_OF_FRAMES])'
Returns one if the calling function's name matches the regular
expression REGEXP. Otherwise it returns zero.

If the optional argument NUMBER_OF_FRAMES is provided, it is the
number of frames up in the stack to look. The default is 1.

`$_any_caller_is(NAME[, NUMBER_OF_FRAMES])'
Returns one if any calling function's name is equal to NAME.
Otherwise it returns zero.

If the optional argument NUMBER_OF_FRAMES is provided, it is the
number of frames up in the stack to look. The default is 1.

This function differs from `$_caller_is' in that this function
checks all stack frames from the immediate caller to the frame
specified by NUMBER_OF_FRAMES, whereas `$_caller_is' only checks
the frame specified by NUMBER_OF_FRAMES.

`$_any_caller_matches(REGEXP[, NUMBER_OF_FRAMES])'
Returns one if any calling function's name matches the regular
expression REGEXP. Otherwise it returns zero.

If the optional argument NUMBER_OF_FRAMES is provided, it is the
number of frames up in the stack to look. The default is 1.

This function differs from `$_caller_matches' in that this function
checks all stack frames from the immediate caller to the frame
specified by NUMBER_OF_FRAMES, whereas `$_caller_matches' only
checks the frame specified by NUMBER_OF_FRAMES.

`$_as_string(VALUE)'
This convenience function is considered deprecated, and could be
removed from future versions of GDB. Use the `%V' format
specifier instead (*note %V Format Specifier::).

Return the string representation of VALUE.

This function is useful to obtain the textual label (enumerator)
of an enumeration value. For example, assuming the variable NODE
is of an enumerated type:

(gdb) printf "Visiting node of type %s\n", $_as_string(node)
Visiting node of type NODE_INTEGER

`$_cimag(VALUE)'
`$_creal(VALUE)'
Return the imaginary (`$_cimag') or real (`$_creal') part of the
complex number VALUE.

The type of the imaginary or real part depends on the type of the
complex number, e.g., using `$_cimag' on a `float complex' will
return an imaginary part of type `float'.

GDB provides the ability to list and get help on convenience
functions.

`help function'
Print a list of all convenience functions.

File: gdb.info, Node: Registers, Next: Floating Point Hardware, Prev: Convenience Funs, Up: Data

10.14 Registers
===============

You can refer to machine register contents, in expressions, as variables
with names starting with `$'. The names of registers are different for
each machine; use `info registers' to see the names used on your
machine.

`info registers'
Print the names and values of all registers except floating-point
and vector registers (in the selected stack frame).

`info all-registers'
Print the names and values of all registers, including
floating-point and vector registers (in the selected stack frame).

`info registers REGGROUP ...'
Print the name and value of the registers in each of the specified
REGGROUPs. The REGGROUP can be any of those returned by `maint
print reggroups' (*note Maintenance Commands::).

`info registers REGNAME ...'
Print the "relativized" value of each specified register REGNAME.
As discussed in detail below, register values are normally
relative to the selected stack frame. The REGNAME may be any
register name valid on the machine you are using, with or without
the initial `$'.

GDB has four "standard" register names that are available (in
expressions) on most machines--whenever they do not conflict with an
architecture's canonical mnemonics for registers. The register names
`$pc' and `$sp' are used for the program counter register and the stack
pointer. `$fp' is used for a register that contains a pointer to the
current stack frame, and `$ps' is used for a register that contains the
processor status. For example, you could print the program counter in
hex with

p/x $pc

or print the instruction to be executed next with

x/i $pc

or add four to the stack pointer(1) with

set $sp += 4

Whenever possible, these four standard register names are available
on your machine even though the machine has different canonical
mnemonics, so long as there is no conflict. The `info registers'
command shows the canonical names. For example, on the SPARC, `info
registers' displays the processor status register as `$psr' but you can
also refer to it as `$ps'; and on x86-based machines `$ps' is an alias
for the EFLAGS register.

GDB always considers the contents of an ordinary register as an
integer when the register is examined in this way. Some machines have
special registers which can hold nothing but floating point; these
registers are considered to have floating point values. There is no way
to refer to the contents of an ordinary register as floating point value
(although you can _print_ it as a floating point value with `print/f
$REGNAME').

Some registers have distinct "raw" and "virtual" data formats. This
means that the data format in which the register contents are saved by
the operating system is not the same one that your program normally
sees. For example, the registers of the 68881 floating point
coprocessor are always saved in "extended" (raw) format, but all C
programs expect to work with "double" (virtual) format. In such cases,
GDB normally works with the virtual format only (the format that makes
sense for your program), but the `info registers' command prints the
data in both formats.

Some machines have special registers whose contents can be
interpreted in several different ways. For example, modern x86-based
machines have SSE and MMX registers that can hold several values packed
together in several different formats. GDB refers to such registers in
`struct' notation:

(gdb) print $xmm1
$1 = {
v4_float = {0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044},
v2_double = {9.92129282474342e-303, 2.7585945287983262e-313},
v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
v8_int16 = {0, 0, 14072, 315, 11, 0, 13, 0},
v4_int32 = {0, 20657912, 11, 13},
v2_int64 = {88725056443645952, 55834574859},
uint128 = 0x0000000d0000000b013b36f800000000
}

To set values of such registers, you need to tell GDB which view of the
register you wish to change, as if you were assigning value to a
`struct' member:

(gdb) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF

Normally, register values are relative to the selected stack frame
(*note Selecting a Frame: Selection.). This means that you get the
value that the register would contain if all stack frames farther in
were exited and their saved registers restored. In order to see the
true contents of hardware registers, you must select the innermost
frame (with `frame 0').

Usually ABIs reserve some registers as not needed to be saved by the
callee (a.k.a.: "caller-saved", "call-clobbered" or "volatile"
registers). It may therefore not be possible for GDB to know the value
a register had before the call (in other words, in the outer frame), if
the register value has since been changed by the callee. GDB tries to
deduce where the inner frame saved ("callee-saved") registers, from the
debug info, unwind info, or the machine code generated by your
compiler. If some register is not saved, and GDB knows the register is
"caller-saved" (via its own knowledge of the ABI, or because the
debug/unwind info explicitly says the register's value is undefined),
GDB displays `<not saved>' as the register's value. With targets that
GDB has no knowledge of the register saving convention, if a register
was not saved by the callee, then its value and location in the outer
frame are assumed to be the same of the inner frame. This is usually
harmless, because if the register is call-clobbered, the caller either
does not care what is in the register after the call, or has code to
restore the value that it does care about. Note, however, that if you
change such a register in the outer frame, you may also be affecting
the inner frame. Also, the more "outer" the frame is you're looking
at, the more likely a call-clobbered register's value is to be wrong,
in the sense that it doesn't actually represent the value the register
had just before the call.

---------- Footnotes ----------

(1) This is a way of removing one word from the stack, on machines
where stacks grow downward in memory (most machines, nowadays). This
assumes that the innermost stack frame is selected; setting `$sp' is
not allowed when other stack frames are selected. To pop entire frames
off the stack, regardless of machine architecture, use `return'; see
*Note Returning from a Function: Returning.

File: gdb.info, Node: Floating Point Hardware, Next: Vector Unit, Prev: Registers, Up: Data

10.15 Floating Point Hardware
=============================

Depending on the configuration, GDB may be able to give you more
information about the status of the floating point hardware.

`info float'
Display hardware-dependent information about the floating point
unit. The exact contents and layout vary depending on the
floating point chip. Currently, `info float' is supported on the
ARM and x86 machines.

File: gdb.info, Node: Vector Unit, Next: OS Information, Prev: Floating Point Hardware, Up: Data

10.16 Vector Unit
=================

Depending on the configuration, GDB may be able to give you more
information about the status of the vector unit.

`info vector'
Display information about the vector unit. The exact contents and
layout vary depending on the hardware.

File: gdb.info, Node: OS Information, Next: Memory Region Attributes, Prev: Vector Unit, Up: Data

10.17 Operating System Auxiliary Information
============================================

GDB provides interfaces to useful OS facilities that can help you debug
your program.

Some operating systems supply an "auxiliary vector" to programs at
startup. This is akin to the arguments and environment that you
specify for a program, but contains a system-dependent variety of
binary values that tell system libraries important details about the
hardware, operating system, and process. Each value's purpose is
identified by an integer tag; the meanings are well-known but
system-specific. Depending on the configuration and operating system
facilities, GDB may be able to show you this information. For remote
targets, this functionality may further depend on the remote stub's
support of the `qXfer:auxv:read' packet, see *Note qXfer auxiliary
vector read::.

`info auxv'
Display the auxiliary vector of the inferior, which can be either a
live process or a core dump file. GDB prints each tag value
numerically, and also shows names and text descriptions for
recognized tags. Some values in the vector are numbers, some bit
masks, and some pointers to strings or other data. GDB displays
each value in the most appropriate form for a recognized tag, and
in hexadecimal for an unrecognized tag.

On some targets, GDB can access operating system-specific
information and show it to you. The types of information available
will differ depending on the type of operating system running on the
target. The mechanism used to fetch the data is described in *Note
Operating System Information::. For remote targets, this functionality
depends on the remote stub's support of the `qXfer:osdata:read' packet,
see *Note qXfer osdata read::.

`info os INFOTYPE'
Display OS information of the requested type.

On GNU/Linux, the following values of INFOTYPE are valid:

`cpus'
Display the list of all CPUs/cores. For each CPU/core, GDB
prints the available fields from /proc/cpuinfo. For each
supported architecture different fields are available. Two
common entries are processor which gives CPU number and
bogomips; a system constant that is calculated during kernel
initialization.

`files'
Display the list of open file descriptors on the target. For
each file descriptor, GDB prints the identifier of the process
owning the descriptor, the command of the owning process, the
value of the descriptor, and the target of the descriptor.

`modules'
Display the list of all loaded kernel modules on the target.
For each module, GDB prints the module name, the size of the
module in bytes, the number of times the module is used, the
dependencies of the module, the status of the module, and the
address of the loaded module in memory.

`msg'
Display the list of all System V message queues on the
target. For each message queue, GDB prints the message queue
key, the message queue identifier, the access permissions,
the current number of bytes on the queue, the current number
of messages on the queue, the processes that last sent and
received a message on the queue, the user and group of the
owner and creator of the message queue, the times at which a
message was last sent and received on the queue, and the time
at which the message queue was last changed.

`processes'
Display the list of processes on the target. For each
process, GDB prints the process identifier, the name of the
user, the command corresponding to the process, and the list
of processor cores that the process is currently running on.
(To understand what these properties mean, for this and the
following info types, please consult the general GNU/Linux
documentation.)

`procgroups'
Display the list of process groups on the target. For each
process, GDB prints the identifier of the process group that
it belongs to, the command corresponding to the process group
leader, the process identifier, and the command line of the
process. The list is sorted first by the process group
identifier, then by the process identifier, so that processes
belonging to the same process group are grouped together and
the process group leader is listed first.

`semaphores'
Display the list of all System V semaphore sets on the
target. For each semaphore set, GDB prints the semaphore set
key, the semaphore set identifier, the access permissions,
the number of semaphores in the set, the user and group of
the owner and creator of the semaphore set, and the times at
which the semaphore set was operated upon and changed.

`shm'
Display the list of all System V shared-memory regions on the
target. For each shared-memory region, GDB prints the region
key, the shared-memory identifier, the access permissions,
the size of the region, the process that created the region,
the process that last attached to or detached from the
region, the current number of live attaches to the region,
and the times at which the region was last attached to,
detach from, and changed.

`sockets'
Display the list of Internet-domain sockets on the target.
For each socket, GDB prints the address and port of the local
and remote endpoints, the current state of the connection,
the creator of the socket, the IP address family of the
socket, and the type of the connection.

`threads'
Display the list of threads running on the target. For each
thread, GDB prints the identifier of the process that the
thread belongs to, the command of the process, the thread
identifier, and the processor core that it is currently
running on. The main thread of a process is not listed.

`info os'
If INFOTYPE is omitted, then list the possible values for INFOTYPE
and the kind of OS information available for each INFOTYPE. If
the target does not return a list of possible types, this command
will report an error.

File: gdb.info, Node: Memory Region Attributes, Next: Dump/Restore Files, Prev: OS Information, Up: Data

10.18 Memory Region Attributes
==============================

"Memory region attributes" allow you to describe special handling
required by regions of your target's memory. GDB uses attributes to
determine whether to allow certain types of memory accesses; whether to
use specific width accesses; and whether to cache target memory. By
default the description of memory regions is fetched from the target
(if the current target supports this), but the user can override the
fetched regions.

Defined memory regions can be individually enabled and disabled.
When a memory region is disabled, GDB uses the default attributes when
accessing memory in that region. Similarly, if no memory regions have
been defined, GDB uses the default attributes when accessing all memory.

When a memory region is defined, it is given a number to identify it;
to enable, disable, or remove a memory region, you specify that number.

`mem LOWER UPPER ATTRIBUTES...'
Define a memory region bounded by LOWER and UPPER with attributes
ATTRIBUTES..., and add it to the list of regions monitored by GDB.
Note that UPPER == 0 is a special case: it is treated as the
target's maximum memory address. (0xffff on 16 bit targets,
0xffffffff on 32 bit targets, etc.)

`mem auto'
Discard any user changes to the memory regions and use
target-supplied regions, if available, or no regions if the target
does not support.

`delete mem NUMS...'
Remove memory regions NUMS... from the list of regions monitored
by GDB.

`disable mem NUMS...'
Disable monitoring of memory regions NUMS.... A disabled memory
region is not forgotten. It may be enabled again later.

`enable mem NUMS...'
Enable monitoring of memory regions NUMS....

`info mem'
Print a table of all defined memory regions, with the following
columns for each region:

_Memory Region Number_

_Enabled or Disabled._
Enabled memory regions are marked with `y'. Disabled memory
regions are marked with `n'.

_Lo Address_
The address defining the inclusive lower bound of the memory
region.

_Hi Address_
The address defining the exclusive upper bound of the memory
region.

_Attributes_
The list of attributes set for this memory region.

10.18.1 Attributes
------------------

10.18.1.1 Memory Access Mode
...........................

The access mode attributes set whether GDB may make read or write
accesses to a memory region.

While these attributes prevent GDB from performing invalid memory
accesses, they do nothing to prevent the target system, I/O DMA, etc.
from accessing memory.

`ro'
Memory is read only.

`wo'
Memory is write only.

`rw'
Memory is read/write. This is the default.

10.18.1.2 Memory Access Size
...........................

The access size attribute tells GDB to use specific sized accesses in
the memory region. Often memory mapped device registers require
specific sized accesses. If no access size attribute is specified, GDB
may use accesses of any size.

`8'
Use 8 bit memory accesses.

`16'
Use 16 bit memory accesses.

`32'
Use 32 bit memory accesses.

`64'
Use 64 bit memory accesses.

10.18.1.3 Data Cache
...................

The data cache attributes set whether GDB will cache target memory.
While this generally improves performance by reducing debug protocol
overhead, it can lead to incorrect results because GDB does not know
about volatile variables or memory mapped device registers.

`cache'
Enable GDB to cache target memory.

`nocache'
Disable GDB from caching target memory. This is the default.

10.18.2 Memory Access Checking
------------------------------

GDB can be instructed to refuse accesses to memory that is not
explicitly described. This can be useful if accessing such regions has
undesired effects for a specific target, or to provide better error
checking. The following commands control this behaviour.

`set mem inaccessible-by-default [on|off]'
If `on' is specified, make GDB treat memory not explicitly
described by the memory ranges as non-existent and refuse accesses
to such memory. The checks are only performed if there's at least
one memory range defined. If `off' is specified, make GDB treat
the memory not explicitly described by the memory ranges as RAM.
The default value is `on'.

`show mem inaccessible-by-default'
Show the current handling of accesses to unknown memory.

File: gdb.info, Node: Dump/Restore Files, Next: Core File Generation, Prev: Memory Region Attributes, Up: Data

10.19 Copy Between Memory and a File
====================================

You can use the commands `dump', `append', and `restore' to copy data
between target memory and a file. The `dump' and `append' commands
write data to a file, and the `restore' command reads data from a file
back into the inferior's memory. Files may be in binary, Motorola
S-record, Intel hex, Tektronix Hex, or Verilog Hex format; however, GDB
can only append to binary files, and cannot read from Verilog Hex files.

`dump [FORMAT] memory FILENAME START_ADDR END_ADDR'
`dump [FORMAT] value FILENAME EXPR'
Dump the contents of memory from START_ADDR to END_ADDR, or the
value of EXPR, to FILENAME in the given format.

The FORMAT parameter may be any one of:
`binary'
Raw binary form.

`ihex'
Intel hex format.

`srec'
Motorola S-record format.

`tekhex'
Tektronix Hex format.

`verilog'
Verilog Hex format.

GDB uses the same definitions of these formats as the GNU binary
utilities, like `objdump' and `objcopy'. If FORMAT is omitted,
GDB dumps the data in raw binary form.

`append [binary] memory FILENAME START_ADDR END_ADDR'
`append [binary] value FILENAME EXPR'
Append the contents of memory from START_ADDR to END_ADDR, or the
value of EXPR, to the file FILENAME, in raw binary form. (GDB can
only append data to files in raw binary form.)

`restore FILENAME [binary] BIAS START END'
Restore the contents of file FILENAME into memory. The `restore'
command can automatically recognize any known BFD file format,
except for raw binary. To restore a raw binary file you must
specify the optional keyword `binary' after the filename.

If BIAS is non-zero, its value will be added to the addresses
contained in the file. Binary files always start at address zero,
so they will be restored at address BIAS. Other bfd files have a
built-in location; they will be restored at offset BIAS from that
location.

If START and/or END are non-zero, then only data between file
offset START and file offset END will be restored. These offsets
are relative to the addresses in the file, before the BIAS
argument is applied.

File: gdb.info, Node: Core File Generation, Next: Character Sets, Prev: Dump/Restore Files, Up: Data

10.20 How to Produce a Core File from Your Program
==================================================

A "core file" or "core dump" is a file that records the memory image of
a running process and its process status (register values etc.). Its
primary use is post-mortem debugging of a program that crashed while it
ran outside a debugger. A program that crashes automatically produces
a core file, unless this feature is disabled by the user. *Note
Files::, for information on invoking GDB in the post-mortem debugging
mode.

Occasionally, you may wish to produce a core file of the program you
are debugging in order to preserve a snapshot of its state. GDB has a
special command for that.

`generate-core-file [FILE]'
`gcore [FILE]'
Produce a core dump of the inferior process. The optional argument
FILE specifies the file name where to put the core dump. If not
specified, the file name defaults to `core.PID', where PID is the
inferior process ID.

If supported by the filesystem where the core is written to, GDB
generates a sparse core dump file.

Note that this command is implemented only for some systems (as of
this writing, GNU/Linux, FreeBSD, Solaris, and S390).

On GNU/Linux, this command can take into account the value of the
file `/proc/PID/coredump_filter' when generating the core dump
(*note set use-coredump-filter::), and by default honors the
`VM_DONTDUMP' flag for mappings where it is present in the file
`/proc/PID/smaps' (*note set dump-excluded-mappings::).

`set use-coredump-filter on'
`set use-coredump-filter off'
Enable or disable the use of the file `/proc/PID/coredump_filter'
when generating core dump files. This file is used by the Linux
kernel to decide what types of memory mappings will be dumped or
ignored when generating a core dump file. PID is the process ID
of a currently running process.

To make use of this feature, you have to write in the
`/proc/PID/coredump_filter' file a value, in hexadecimal, which is
a bit mask representing the memory mapping types. If a bit is set
in the bit mask, then the memory mappings of the corresponding
types will be dumped; otherwise, they will be ignored. This
configuration is inherited by child processes. For more
information about the bits that can be set in the
`/proc/PID/coredump_filter' file, please refer to the manpage of
`core(5)'.

By default, this option is `on'. If this option is turned `off',
GDB does not read the `coredump_filter' file and instead uses the
same default value as the Linux kernel in order to decide which
pages will be dumped in the core dump file. This value is
currently `0x33', which means that bits `0' (anonymous private
mappings), `1' (anonymous shared mappings), `4' (ELF headers) and
`5' (private huge pages) are active. This will cause these memory
mappings to be dumped automatically.

`set dump-excluded-mappings on'
`set dump-excluded-mappings off'
If `on' is specified, GDB will dump memory mappings marked with
the `VM_DONTDUMP' flag. This flag is represented in the file
`/proc/PID/smaps' with the acronym `dd'.

The default value is `off'.

File: gdb.info, Node: Character Sets, Next: Caching Target Data, Prev: Core File Generation, Up: Data

10.21 Character Sets
====================

If the program you are debugging uses a different character set to
represent characters and strings than the one GDB uses itself, GDB can
automatically translate between the character sets for you. The
character set GDB uses we call the "host character set"; the one the
inferior program uses we call the "target character set".

For example, if you are running GDB on a GNU/Linux system, which
uses the ISO Latin 1 character set, but you are using GDB's remote
protocol (*note Remote Debugging::) to debug a program running on an
IBM mainframe, which uses the EBCDIC character set, then the host
character set is Latin-1, and the target character set is EBCDIC. If
you give GDB the command `set target-charset EBCDIC-US', then GDB
translates between EBCDIC and Latin 1 as you print character or string
values, or use character and string literals in expressions.

GDB has no way to automatically recognize which character set the
inferior program uses; you must tell it, using the `set target-charset'
command, described below.

Here are the commands for controlling GDB's character set support:

`set target-charset CHARSET'
Set the current target character set to CHARSET. To display the
list of supported target character sets, type
`set target-charset <TAB><TAB>'.

`set host-charset CHARSET'
Set the current host character set to CHARSET.

By default, GDB uses a host character set appropriate to the
system it is running on; you can override that default using the
`set host-charset' command. On some systems, GDB cannot
automatically determine the appropriate host character set. In
this case, GDB uses `UTF-8'.

GDB can only use certain character sets as its host character set.
If you type `set host-charset <TAB><TAB>', GDB will list the host
character sets it supports.

`set charset CHARSET'
Set the current host and target character sets to CHARSET. As
above, if you type `set charset <TAB><TAB>', GDB will list the
names of the character sets that can be used for both host and
target.

`show charset'
Show the names of the current host and target character sets.

`show host-charset'
Show the name of the current host character set.

`show target-charset'
Show the name of the current target character set.

`set target-wide-charset CHARSET'
Set the current target's wide character set to CHARSET. This is
the character set used by the target's `wchar_t' type. To display
the list of supported wide character sets, type
`set target-wide-charset <TAB><TAB>'.

`show target-wide-charset'
Show the name of the current target's wide character set.

Here is an example of GDB's character set support in action. Assume
that the following source code has been placed in the file
`charset-test.c':

#include <stdio.h>

char ascii_hello[]
= {72, 101, 108, 108, 111, 44, 32, 119,
111, 114, 108, 100, 33, 10, 0};
char ibm1047_hello[]
= {200, 133, 147, 147, 150, 107, 64, 166,
150, 153, 147, 132, 90, 37, 0};

main ()
{
printf ("Hello, world!\n");
}

In this program, `ascii_hello' and `ibm1047_hello' are arrays
containing the string `Hello, world!' followed by a newline, encoded in
the ASCII and IBM1047 character sets.

We compile the program, and invoke the debugger on it:

$ gcc -g charset-test.c -o charset-test
$ gdb -nw charset-test
GNU gdb 2001-12-19-cvs
Copyright 2001 Free Software Foundation, Inc.
...
(gdb)

We can use the `show charset' command to see what character sets GDB
is currently using to interpret and display characters and strings:

(gdb) show charset
The current host and target character set is `ISO-8859-1'.
(gdb)

For the sake of printing this manual, let's use ASCII as our initial
character set:
(gdb) set charset ASCII
(gdb) show charset
The current host and target character set is `ASCII'.
(gdb)

Let's assume that ASCII is indeed the correct character set for our
host system -- in other words, let's assume that if GDB prints
characters using the ASCII character set, our terminal will display
them properly. Since our current target character set is also ASCII,
the contents of `ascii_hello' print legibly:

(gdb) print ascii_hello
$1 = 0x401698 "Hello, world!\n"
(gdb) print ascii_hello[0]
$2 = 72 'H'
(gdb)

GDB uses the target character set for character and string literals
you use in expressions:

(gdb) print '+'
$3 = 43 '+'
(gdb)

The ASCII character set uses the number 43 to encode the `+'
character.

GDB relies on the user to tell it which character set the target
program uses. If we print `ibm1047_hello' while our target character
set is still ASCII, we get jibberish:

(gdb) print ibm1047_hello
$4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%"
(gdb) print ibm1047_hello[0]
$5 = 200 '\310'
(gdb)

If we invoke the `set target-charset' followed by <TAB><TAB>, GDB
tells us the character sets it supports:

(gdb) set target-charset
ASCII EBCDIC-US IBM1047 ISO-8859-1
(gdb) set target-charset

We can select IBM1047 as our target character set, and examine the
program's strings again. Now the ASCII string is wrong, but GDB
translates the contents of `ibm1047_hello' from the target character
set, IBM1047, to the host character set, ASCII, and they display
correctly:

(gdb) set target-charset IBM1047
(gdb) show charset
The current host character set is `ASCII'.
The current target character set is `IBM1047'.
(gdb) print ascii_hello
$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
(gdb) print ascii_hello[0]
$7 = 72 '\110'
(gdb) print ibm1047_hello
$8 = 0x4016a8 "Hello, world!\n"
(gdb) print ibm1047_hello[0]
$9 = 200 'H'
(gdb)

As above, GDB uses the target character set for character and string
literals you use in expressions:

(gdb) print '+'
$10 = 78 '+'
(gdb)

The IBM1047 character set uses the number 78 to encode the `+'
character.

File: gdb.info, Node: Caching Target Data, Next: Searching Memory, Prev: Character Sets, Up: Data

10.22 Caching Data of Targets
=============================

GDB caches data exchanged between the debugger and a target. Each
cache is associated with the address space of the inferior. *Note
Inferiors Connections and Programs::, about inferior and address space.
Such caching generally improves performance in remote debugging (*note
Remote Debugging::), because it reduces the overhead of the remote
protocol by bundling memory reads and writes into large chunks.
Unfortunately, simply caching everything would lead to incorrect
results, since GDB does not necessarily know anything about volatile
values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode
(*note Non-Stop Mode::) memory can be changed _while_ a gdb command is
executing. Therefore, by default, GDB only caches data known to be on
the stack(1) or in the code segment. Other regions of memory can be
explicitly marked as cacheable; *note Memory Region Attributes::.

`set remotecache on'
`set remotecache off'
This option no longer does anything; it exists for compatibility
with old scripts.

`show remotecache'
Show the current state of the obsolete remotecache flag.

`set stack-cache on'
`set stack-cache off'
Enable or disable caching of stack accesses. When `on', use
caching. By default, this option is `on'.

`show stack-cache'
Show the current state of data caching for memory accesses.

`set code-cache on'
`set code-cache off'
Enable or disable caching of code segment accesses. When `on',
use caching. By default, this option is `on'. This improves
performance of disassembly in remote debugging.

`show code-cache'
Show the current state of target memory cache for code segment
accesses.

`info dcache [line]'
Print the information about the performance of data cache of the
current inferior's address space. The information displayed
includes the dcache width and depth, and for each cache line, its
number, address, and how many times it was referenced. This
command is useful for debugging the data cache operation.

If a line number is specified, the contents of that line will be
printed in hex.

`set dcache size SIZE'
Set maximum number of entries in dcache (dcache depth above).

`set dcache line-size LINE-SIZE'
Set number of bytes each dcache entry caches (dcache width above).
Must be a power of 2.

`show dcache size'
Show maximum number of dcache entries. *Note info dcache: Caching
Target Data.

`show dcache line-size'
Show default size of dcache lines.

`maint flush dcache'
Flush the contents (if any) of the dcache. This maintainer
command is useful when debugging the dcache implementation.

---------- Footnotes ----------

(1) In non-stop mode, it is moderately rare for a running thread to
modify the stack of a stopped thread in a way that would interfere with
a backtrace, and caching of stack reads provides a significant speed up
of remote backtraces.

File: gdb.info, Node: Searching Memory, Next: Value Sizes, Prev: Caching Target Data, Up: Data

10.23 Search Memory
===================

Memory can be searched for a particular sequence of bytes with the
`find' command.

`find [/SN] START_ADDR, +LEN, VAL1 [, VAL2, ...]'
`find [/SN] START_ADDR, END_ADDR, VAL1 [, VAL2, ...]'
Search memory for the sequence of bytes specified by VAL1, VAL2,
etc. The search begins at address START_ADDR and continues for
either LEN bytes or through to END_ADDR inclusive.

S and N are optional parameters. They may be specified in either
order, apart or together.

S, search query size
The size of each search query value.

`b'
bytes

`h'
halfwords (two bytes)

`w'
words (four bytes)

`g'
giant words (eight bytes)

All values are interpreted in the current language. This means,
for example, that if the current source language is C/C++ then
searching for the string "hello" includes the trailing '\0'. The
null terminator can be removed from searching by using casts,
e.g.: `{char[5]}"hello"'.

If the value size is not specified, it is taken from the value's
type in the current language. This is useful when one wants to
specify the search pattern as a mixture of types. Note that this
means, for example, that in the case of C-like languages a search
for an untyped 0x42 will search for `(int) 0x42' which is
typically four bytes.

N, maximum number of finds
The maximum number of matches to print. The default is to print
all finds.

You can use strings as search values. Quote them with double-quotes
(`"'). The string value is copied into the search pattern byte by
byte, regardless of the endianness of the target and the size
specification.

The address of each match found is printed as well as a count of the
number of matches found.

The address of the last value found is stored in convenience variable
`$_'. A count of the number of matches is stored in `$numfound'.

For example, if stopped at the `printf' in this function:

void
hello ()
{
static char hello[] = "hello-hello";
static struct { char c; short s; int i; }
__attribute__ ((packed)) mixed
= { 'c', 0x1234, 0x87654321 };
printf ("%s\n", hello);
}

you get during debugging:

(gdb) find &hello[0], +sizeof(hello), "hello"
0x804956d <hello.1620+6>
1 pattern found
(gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find &hello[0], +sizeof(hello), {char[5]}"hello"
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
0x8049567 <hello.1620>
1 pattern found
(gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
0x8049560 <mixed.1625>
1 pattern found
(gdb) print $numfound
$1 = 1
(gdb) print $_
$2 = (void *) 0x8049560

File: gdb.info, Node: Value Sizes, Prev: Searching Memory, Up: Data

10.24 Value Sizes
=================

Whenever GDB prints a value memory will be allocated within GDB to hold
the contents of the value. It is possible in some languages with
dynamic typing systems, that an invalid program may indicate a value
that is incorrectly large, this in turn may cause GDB to try and
allocate an overly large amount of memory.

`set max-value-size BYTES'
`set max-value-size unlimited'
Set the maximum size of memory that GDB will allocate for the
contents of a value to BYTES, trying to display a value that
requires more memory than that will result in an error.

Setting this variable does not effect values that have already been
allocated within GDB, only future allocations.

There's a minimum size that `max-value-size' can be set to in
order that GDB can still operate correctly, this minimum is
currently 16 bytes.

The limit applies to the results of some subexpressions as well as
to complete expressions. For example, an expression denoting a
simple integer component, such as `x.y.z', may fail if the size of
X.Y is dynamic and exceeds BYTES. On the other hand, GDB is
sometimes clever; the expression `A[i]', where A is an array
variable with non-constant size, will generally succeed regardless
of the bounds on A, as long as the component size is less than
BYTES.

The default value of `max-value-size' is currently 64k.

`show max-value-size'
Show the maximum size of memory, in bytes, that GDB will allocate
for the contents of a value.

File: gdb.info, Node: Optimized Code, Next: Macros, Prev: Data, Up: Top

11 Debugging Optimized Code
***************************

Almost all compilers support optimization. With optimization disabled,
the compiler generates assembly code that corresponds directly to your
source code, in a simplistic way. As the compiler applies more
powerful optimizations, the generated assembly code diverges from your
original source code. With help from debugging information generated
by the compiler, GDB can map from the running program back to
constructs from your original source.

GDB is more accurate with optimization disabled. If you can
recompile without optimization, it is easier to follow the progress of
your program during debugging. But, there are many cases where you may
need to debug an optimized version.

When you debug a program compiled with `-g -O', remember that the
optimizer has rearranged your code; the debugger shows you what is
really there. Do not be too surprised when the execution path does not
exactly match your source file! An extreme example: if you define a
variable, but never use it, GDB never sees that variable--because the
compiler optimizes it out of existence.

Some things do not work as well with `-g -O' as with just `-g',
particularly on machines with instruction scheduling. If in doubt,
recompile with `-g' alone, and if this fixes the problem, please report
it to us as a bug (including a test case!). *Note Variables::, for
more information about debugging optimized code.

* Menu:

* Inline Functions:: How GDB presents inlining
* Tail Call Frames:: GDB analysis of jumps to functions

File: gdb.info, Node: Inline Functions, Next: Tail Call Frames, Up: Optimized Code

11.1 Inline Functions
=====================

"Inlining" is an optimization that inserts a copy of the function body
directly at each call site, instead of jumping to a shared routine.
GDB displays inlined functions just like non-inlined functions. They
appear in backtraces. You can view their arguments and local
variables, step into them with `step', skip them with `next', and
escape from them with `finish'. You can check whether a function was
inlined by using the `info frame' command.

For GDB to support inlined functions, the compiler must record
information about inlining in the debug information -- GCC using the
DWARF 2 format does this, and several other compilers do also. GDB
only supports inlined functions when using DWARF 2. Versions of GCC
before 4.1 do not emit two required attributes (`DW_AT_call_file' and
`DW_AT_call_line'); GDB does not display inlined function calls with
earlier versions of GCC. It instead displays the arguments and local
variables of inlined functions as local variables in the caller.

The body of an inlined function is directly included at its call
site; unlike a non-inlined function, there are no instructions devoted
to the call. GDB still pretends that the call site and the start of
the inlined function are different instructions. Stepping to the call
site shows the call site, and then stepping again shows the first line
of the inlined function, even though no additional instructions are
executed.

This makes source-level debugging much clearer; you can see both the
context of the call and then the effect of the call. Only stepping by
a single instruction using `stepi' or `nexti' does not do this; single
instruction steps always show the inlined body.

There are some ways that GDB does not pretend that inlined function
calls are the same as normal calls:

* Setting breakpoints at the call site of an inlined function may not
work, because the call site does not contain any code. GDB may
incorrectly move the breakpoint to the next line of the enclosing
function, after the call. This limitation will be removed in a
future version of GDB; until then, set a breakpoint on an earlier
line or inside the inlined function instead.

* GDB cannot locate the return value of inlined calls after using
the `finish' command. This is a limitation of compiler-generated
debugging information; after `finish', you can step to the next
line and print a variable where your program stored the return
value.

File: gdb.info, Node: Tail Call Frames, Prev: Inline Functions, Up: Optimized Code

11.2 Tail Call Frames
=====================

Function `B' can call function `C' in its very last statement. In
unoptimized compilation the call of `C' is immediately followed by
return instruction at the end of `B' code. Optimizing compiler may
replace the call and return in function `B' into one jump to function
`C' instead. Such use of a jump instruction is called "tail call".

During execution of function `C', there will be no indication in the
function call stack frames that it was tail-called from `B'. If
function `A' regularly calls function `B' which tail-calls function `C',
then GDB will see `A' as the caller of `C'. However, in some cases GDB
can determine that `C' was tail-called from `B', and it will then
create fictitious call frame for that, with the return address set up
as if `B' called `C' normally.

This functionality is currently supported only by DWARF 2 debugging
format and the compiler has to produce `DW_TAG_call_site' tags. With
GCC, you need to specify `-O -g' during compilation, to get this
information.

`info frame' command (*note Frame Info::) will indicate the tail
call frame kind by text `tail call frame' such as in this sample GDB
output:

(gdb) x/i $pc - 2
0x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)>
(gdb) info frame
Stack level 1, frame at 0x7fffffffda30:
rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
tail call frame, caller of frame at 0x7fffffffda30
source language c++.
Arglist at unknown address.
Locals at unknown address, Previous frame's sp is 0x7fffffffda30

The detection of all the possible code path executions can find them
ambiguous. There is no execution history stored (possible *Note
Reverse Execution:: is never used for this purpose) and the last known
caller could have reached the known callee by multiple different jump
sequences. In such case GDB still tries to show at least all the
unambiguous top tail callers and all the unambiguous bottom tail
callees, if any.

`set debug entry-values'
When set to on, enables printing of analysis messages for both
frame argument values at function entry and tail calls. It will
show all the possible valid tail calls code paths it has
considered. It will also print the intersection of them with the
final unambiguous (possibly partial or even empty) code path
result.

`show debug entry-values'
Show the current state of analysis messages printing for both
frame argument values at function entry and tail calls.

The analysis messages for tail calls can for example show why the
virtual tail call frame for function `c' has not been recognized (due
to the indirect reference by variable `x'):

static void __attribute__((noinline, noclone)) c (void);
void (*x) (void) = c;
static void __attribute__((noinline, noclone)) a (void) { x++; }
static void __attribute__((noinline, noclone)) c (void) { a (); }
int main (void) { x (); return 0; }

Breakpoint 1, DW_OP_entry_value resolving cannot find
DW_TAG_call_site 0x40039a in main
a () at t.c:3
3 static void __attribute__((noinline, noclone)) a (void) { x++; }
(gdb) bt
#0 a () at t.c:3
#1 0x000000000040039a in main () at t.c:5

Another possibility is an ambiguous virtual tail call frames
resolution:

int i;
static void __attribute__((noinline, noclone)) f (void) { i++; }
static void __attribute__((noinline, noclone)) e (void) { f (); }
static void __attribute__((noinline, noclone)) d (void) { f (); }
static void __attribute__((noinline, noclone)) c (void) { d (); }
static void __attribute__((noinline, noclone)) b (void)
{ if (i) c (); else e (); }
static void __attribute__((noinline, noclone)) a (void) { b (); }
int main (void) { a (); return 0; }

tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d)
tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e)
tailcall: reduced: 0x4004d2(a) |
(gdb) bt
#0 f () at t.c:2
#1 0x00000000004004d2 in a () at t.c:8
#2 0x0000000000400395 in main () at t.c:9

Frames #0 and #2 are real, #1 is a virtual tail call frame. The
code can have possible execution paths `main->a->b->c->d->f' or
`main->a->b->e->f', GDB cannot find which one from the inferior state.

`initial:' state shows some random possible calling sequence GDB has
found. It then finds another possible calling sequence - that one is
prefixed by `compare:'. The non-ambiguous intersection of these two is
printed as the `reduced:' calling sequence. That one could have many
further `compare:' and `reduced:' statements as long as there remain
any non-ambiguous sequence entries.

For the frame of function `b' in both cases there are different
possible `$pc' values (`0x4004cc' or `0x4004ce'), therefore this frame
is also ambiguous. The only non-ambiguous frame is the one for
function `a', therefore this one is displayed to the user while the
ambiguous frames are omitted.

There can be also reasons why printing of frame argument values at
function entry may fail:

int v;
static void __attribute__((noinline, noclone)) c (int i) { v++; }
static void __attribute__((noinline, noclone)) a (int i);
static void __attribute__((noinline, noclone)) b (int i) { a (i); }
static void __attribute__((noinline, noclone)) a (int i)
{ if (i) b (i - 1); else c (0); }
int main (void) { a (5); return 0; }

(gdb) bt
#0 c (i=i@entry=0) at t.c:2
#1 0x0000000000400428 in a (DW_OP_entry_value resolving has found
function "a" at 0x400420 can call itself via tail calls
i=<optimized out>) at t.c:6
#2 0x000000000040036e in main () at t.c:7

GDB cannot find out from the inferior state if and how many times did
function `a' call itself (via function `b') as these calls would be
tail calls. Such tail calls would modify the `i' variable, therefore
GDB cannot be sure the value it knows would be right - GDB prints
`<optimized out>' instead.

File: gdb.info, Node: Macros, Next: Tracepoints, Prev: Optimized Code, Up: Top

12 C Preprocessor Macros
************************

Some languages, such as C and C++, provide a way to define and invoke
"preprocessor macros" which expand into strings of tokens. GDB can
evaluate expressions containing macro invocations, show the result of
macro expansion, and show a macro's definition, including where it was
defined.

You may need to compile your program specially to provide GDB with
information about preprocessor macros. Most compilers do not include
macros in their debugging information, even when you compile with the
`-g' flag. *Note Compilation::.

A program may define a macro at one point, remove that definition
later, and then provide a different definition after that. Thus, at
different points in the program, a macro may have different
definitions, or have no definition at all. If there is a current stack
frame, GDB uses the macros in scope at that frame's source code line.
Otherwise, GDB uses the macros in scope at the current listing location;
see *Note List::.

Whenever GDB evaluates an expression, it always expands any macro
invocations present in the expression. GDB also provides the following
commands for working with macros explicitly.

`macro expand EXPRESSION'
`macro exp EXPRESSION'
Show the results of expanding all preprocessor macro invocations in
EXPRESSION. Since GDB simply expands macros, but does not parse
the result, EXPRESSION need not be a valid expression; it can be
any string of tokens.

`macro expand-once EXPRESSION'
`macro exp1 EXPRESSION'
(This command is not yet implemented.) Show the results of
expanding those preprocessor macro invocations that appear
explicitly in EXPRESSION. Macro invocations appearing in that
expansion are left unchanged. This command allows you to see the
effect of a particular macro more clearly, without being confused
by further expansions. Since GDB simply expands macros, but does
not parse the result, EXPRESSION need not be a valid expression; it
can be any string of tokens.

`info macro [-a|-all] [--] MACRO'
Show the current definition or all definitions of the named MACRO,
and describe the source location or compiler command-line where
that definition was established. The optional double dash is to
signify the end of argument processing and the beginning of MACRO
for non C-like macros where the macro may begin with a hyphen.

`info macros LOCSPEC'
Show all macro definitions that are in effect at the source line of
the code location that results from resolving LOCSPEC, and
describe the source location or compiler command-line where those
definitions were established.

`macro define MACRO REPLACEMENT-LIST'
`macro define MACRO(ARGLIST) REPLACEMENT-LIST'
Introduce a definition for a preprocessor macro named MACRO,
invocations of which are replaced by the tokens given in
REPLACEMENT-LIST. The first form of this command defines an
"object-like" macro, which takes no arguments; the second form
defines a "function-like" macro, which takes the arguments given in
ARGLIST.

A definition introduced by this command is in scope in every
expression evaluated in GDB, until it is removed with the `macro
undef' command, described below. The definition overrides all
definitions for MACRO present in the program being debugged, as
well as any previous user-supplied definition.

`macro undef MACRO'
Remove any user-supplied definition for the macro named MACRO.
This command only affects definitions provided with the `macro
define' command, described above; it cannot remove definitions
present in the program being debugged.

`macro list'
List all the macros defined using the `macro define' command.

Here is a transcript showing the above commands in action. First, we
show our source files:

$ cat sample.c
#include <stdio.h>
#include "sample.h"

#define M 42
#define ADD(x) (M + x)

main ()
{
#define N 28
printf ("Hello, world!\n");
#undef N
printf ("We're so creative.\n");
#define N 1729
printf ("Goodbye, world!\n");
}
$ cat sample.h
#define Q <
$

Now, we compile the program using the GNU C compiler, GCC. We pass
the `-gdwarf-2'(1) _and_ `-g3' flags to ensure the compiler includes
information about preprocessor macros in the debugging information.

$ gcc -gdwarf-2 -g3 sample.c -o sample
$

Now, we start GDB on our sample program:

$ gdb -nw sample
GNU gdb 2002-05-06-cvs
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, ...
(gdb)

We can expand macros and examine their definitions, even when the
program is not running. GDB uses the current listing position to
decide which macro definitions are in scope:

(gdb) list main
3
4 #define M 42
5 #define ADD(x) (M + x)
6
7 main ()
8 {
9 #define N 28
10 printf ("Hello, world!\n");
11 #undef N
12 printf ("We're so creative.\n");
(gdb) info macro ADD
Defined at /home/jimb/gdb/macros/play/sample.c:5
#define ADD(x) (M + x)
(gdb) info macro Q
Defined at /home/jimb/gdb/macros/play/sample.h:1
included at /home/jimb/gdb/macros/play/sample.c:2
#define Q <
(gdb) macro expand ADD(1)
expands to: (42 + 1)
(gdb) macro expand-once ADD(1)
expands to: once (M + 1)
(gdb)

In the example above, note that `macro expand-once' expands only the
macro invocation explicit in the original text -- the invocation of
`ADD' -- but does not expand the invocation of the macro `M', which was
introduced by `ADD'.

Once the program is running, GDB uses the macro definitions in force
at the source line of the current stack frame:

(gdb) break main
Breakpoint 1 at 0x8048370: file sample.c, line 10.
(gdb) run
Starting program: /home/jimb/gdb/macros/play/sample

Breakpoint 1, main () at sample.c:10
10 printf ("Hello, world!\n");
(gdb)

At line 10, the definition of the macro `N' at line 9 is in force:

(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:9
#define N 28
(gdb) macro expand N Q M
expands to: 28 < 42
(gdb) print N Q M
$1 = 1
(gdb)

As we step over directives that remove `N''s definition, and then
give it a new definition, GDB finds the definition (or lack thereof) in
force at each point:

(gdb) next
Hello, world!
12 printf ("We're so creative.\n");
(gdb) info macro N
The symbol `N' has no definition as a C/C++ preprocessor macro
at /home/jimb/gdb/macros/play/sample.c:12
(gdb) next
We're so creative.
14 printf ("Goodbye, world!\n");
(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:13
#define N 1729
(gdb) macro expand N Q M
expands to: 1729 < 42
(gdb) print N Q M
$2 = 0
(gdb)

In addition to source files, macros can be defined on the
compilation command line using the `-DNAME=VALUE' syntax. For macros
defined in such a way, GDB displays the location of their definition as
line zero of the source file submitted to the compiler.

(gdb) info macro __STDC__
Defined at /home/jimb/gdb/macros/play/sample.c:0
-D__STDC__=1
(gdb)

---------- Footnotes ----------

(1) This is the minimum. Recent versions of GCC support `-gdwarf-3'
and `-gdwarf-4'; we recommend always choosing the most recent version
of DWARF.

File: gdb.info, Node: Tracepoints, Next: Overlays, Prev: Macros, Up: Top

13 Tracepoints
**************

In some applications, it is not feasible for the debugger to interrupt
the program's execution long enough for the developer to learn anything
helpful about its behavior. If the program's correctness depends on
its real-time behavior, delays introduced by a debugger might cause the
program to change its behavior drastically, or perhaps fail, even when
the code itself is correct. It is useful to be able to observe the
program's behavior without interrupting it.

Using GDB's `trace' and `collect' commands, you can specify
locations in the program, called "tracepoints", and arbitrary
expressions to evaluate when those tracepoints are reached. Later,
using the `tfind' command, you can examine the values those expressions
had when the program hit the tracepoints. The expressions may also
denote objects in memory--structures or arrays, for example--whose
values GDB should record; while visiting a particular tracepoint, you
may inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with you,
it can do so quickly and unobtrusively, hopefully not disturbing the
program's behavior.

The tracepoint facility is currently available only for remote
targets. *Note Targets::. In addition, your remote target must know
how to collect trace data. This functionality is implemented in the
remote stub; however, none of the stubs distributed with GDB support
tracepoints as of this writing. The format of the remote packets used
to implement tracepoints are described in *Note Tracepoint Packets::.

It is also possible to get trace data from a file, in a manner
reminiscent of corefiles; you specify the filename, and use `tfind' to
search through the file. *Note Trace Files::, for more details.

This chapter describes the tracepoint commands and features.

* Menu:

* Set Tracepoints::
* Analyze Collected Data::
* Tracepoint Variables::
* Trace Files::

File: gdb.info, Node: Set Tracepoints, Next: Analyze Collected Data, Up: Tracepoints

13.1 Commands to Set Tracepoints
================================

Before running such a "trace experiment", an arbitrary number of
tracepoints can be set. A tracepoint is actually a special type of
breakpoint (*note Set Breaks::), so you can manipulate it using
standard breakpoint commands. For instance, as with breakpoints,
tracepoint numbers are successive integers starting from one, and many
of the commands associated with tracepoints take the tracepoint number
as their argument, to identify which tracepoint to work on.

For each tracepoint, you can specify, in advance, some arbitrary set
of data that you want the target to collect in the trace buffer when it
hits that tracepoint. The collected data can include registers, local
variables, or global data. Later, you can use GDB commands to examine
the values these data had at the time the tracepoint was hit.

Tracepoints do not support every breakpoint feature. Ignore counts
on tracepoints have no effect, and tracepoints cannot run GDB commands
when they are hit. Tracepoints may not be thread-specific either.

Some targets may support "fast tracepoints", which are inserted in a
different way (such as with a jump instead of a trap), that is faster
but possibly restricted in where they may be installed.

Regular and fast tracepoints are dynamic tracing facilities, meaning
that they can be used to insert tracepoints at (almost) any location in
the target. Some targets may also support controlling "static
tracepoints" from GDB. With static tracing, a set of instrumentation
points, also known as "markers", are embedded in the target program,
and can be activated or deactivated by name or address. These are
usually placed at locations which facilitate investigating what the
target is actually doing. GDB's support for static tracing includes
being able to list instrumentation points, and attach them with GDB
defined high level tracepoints that expose the whole range of
convenience of GDB's tracepoints support. Namely, support for
collecting registers values and values of global or local (to the
instrumentation point) variables; tracepoint conditions and trace state
variables. The act of installing a GDB static tracepoint on an
instrumentation point, or marker, is referred to as "probing" a static
tracepoint marker.

`gdbserver' supports tracepoints on some target systems. *Note
Tracepoints support in `gdbserver': Server.

This section describes commands to set tracepoints and associated
conditions and actions.

* Menu:

* Create and Delete Tracepoints::
* Enable and Disable Tracepoints::
* Tracepoint Passcounts::
* Tracepoint Conditions::
* Trace State Variables::
* Tracepoint Actions::
* Listing Tracepoints::
* Listing Static Tracepoint Markers::
* Starting and Stopping Trace Experiments::
* Tracepoint Restrictions::

File: gdb.info, Node: Create and Delete Tracepoints, Next: Enable and Disable Tracepoints, Up: Set Tracepoints

13.1.1 Create and Delete Tracepoints
------------------------------------

`trace LOCSPEC'
The `trace' command is very similar to the `break' command. Its
argument LOCSPEC can be any valid location specification. *Note
Location Specifications::. The `trace' command defines a
tracepoint, which is a point in the target program where the
debugger will briefly stop, collect some data, and then allow the
program to continue. Setting a tracepoint or changing its actions
takes effect immediately if the remote stub supports the
`InstallInTrace' feature (*note install tracepoint in tracing::).
If remote stub doesn't support the `InstallInTrace' feature, all
these changes don't take effect until the next `tstart' command,
and once a trace experiment is running, further changes will not
have any effect until the next trace experiment starts. In
addition, GDB supports "pending tracepoints"--tracepoints whose
address is not yet resolved. (This is similar to pending
breakpoints.) Pending tracepoints are not downloaded to the
target and not installed until they are resolved. The resolution
of pending tracepoints requires GDB support--when debugging with
the remote target, and GDB disconnects from the remote stub (*note
disconnected tracing::), pending tracepoints can not be resolved
(and downloaded to the remote stub) while GDB is disconnected.

Here are some examples of using the `trace' command:

(gdb) trace foo.c:121 // a source file and line number

(gdb) trace +2 // 2 lines forward

(gdb) trace my_function // first source line of function

(gdb) trace *my_function // EXACT start address of function

(gdb) trace *0x2117c4 // an address

You can abbreviate `trace' as `tr'.

`trace LOCSPEC if COND'
Set a tracepoint with condition COND; evaluate the expression COND
each time the tracepoint is reached, and collect data only if the
value is nonzero--that is, if COND evaluates as true. *Note
Tracepoint Conditions: Tracepoint Conditions, for more information
on tracepoint conditions.

`ftrace LOCSPEC [ if COND ]'
The `ftrace' command sets a fast tracepoint. For targets that
support them, fast tracepoints will use a more efficient but
possibly less general technique to trigger data collection, such
as a jump instruction instead of a trap, or some sort of hardware
support. It may not be possible to create a fast tracepoint at
the desired location, in which case the command will exit with an
explanatory message.

GDB handles arguments to `ftrace' exactly as for `trace'.

On 32-bit x86-architecture systems, fast tracepoints normally need
to be placed at an instruction that is 5 bytes or longer, but can
be placed at 4-byte instructions if the low 64K of memory of the
target program is available to install trampolines. Some
Unix-type systems, such as GNU/Linux, exclude low addresses from
the program's address space; but for instance with the Linux
kernel it is possible to let GDB use this area by doing a `sysctl'
command to set the `mmap_min_addr' kernel parameter, as in

sudo sysctl -w vm.mmap_min_addr=32768

which sets the low address to 32K, which leaves plenty of room for
trampolines. The minimum address should be set to a page boundary.

`strace [LOCSPEC | -m MARKER] [ if COND ]'
The `strace' command sets a static tracepoint. For targets that
support it, setting a static tracepoint probes a static
instrumentation point, or marker, found at the code locations that
result from resolving LOCSPEC. It may not be possible to set a
static tracepoint at the desired code location, in which case the
command will exit with an explanatory message.

GDB handles arguments to `strace' exactly as for `trace', with the
addition that the user can also specify `-m MARKER' instead of a
location spec. This probes the marker identified by the MARKER
string identifier. This identifier depends on the static
tracepoint backend library your program is using. You can find
all the marker identifiers in the `ID' field of the `info
static-tracepoint-markers' command output. *Note Listing Static
Tracepoint Markers: Listing Static Tracepoint Markers. For
example, in the following small program using the UST tracing
engine:

main ()
{
trace_mark(ust, bar33, "str %s", "FOOBAZ");
}

the marker id is composed of joining the first two arguments to the
`trace_mark' call with a slash, which translates to:

(gdb) info static-tracepoint-markers
Cnt Enb ID Address What
1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22
Data: "str %s"
[etc...]

so you may probe the marker above with:

(gdb) strace -m ust/bar33

Static tracepoints accept an extra collect action -- `collect
$_sdata'. This collects arbitrary user data passed in the probe
point call to the tracing library. In the UST example above,
you'll see that the third argument to `trace_mark' is a
printf-like format string. The user data is then the result of
running that formatting string against the following arguments.
Note that `info static-tracepoint-markers' command output lists
that format string in the `Data:' field.

You can inspect this data when analyzing the trace buffer, by
printing the $_sdata variable like any other variable available to
GDB. *Note Tracepoint Action Lists: Tracepoint Actions.

The convenience variable `$tpnum' records the tracepoint number of
the most recently set tracepoint.

`delete tracepoint [NUM]'
Permanently delete one or more tracepoints. With no argument, the
default is to delete all tracepoints. Note that the regular
`delete' command can remove tracepoints also.

Examples:

(gdb) delete trace 1 2 3 // remove three tracepoints

(gdb) delete trace // remove all tracepoints

You can abbreviate this command as `del tr'.

File: gdb.info, Node: Enable and Disable Tracepoints, Next: Tracepoint Passcounts, Prev: Create and Delete Tracepoints, Up: Set Tracepoints

13.1.2 Enable and Disable Tracepoints
-------------------------------------

These commands are deprecated; they are equivalent to plain `disable'
and `enable'.

`disable tracepoint [NUM]'
Disable tracepoint NUM, or all tracepoints if no argument NUM is
given. A disabled tracepoint will have no effect during a trace
experiment, but it is not forgotten. You can re-enable a disabled
tracepoint using the `enable tracepoint' command. If the command
is issued during a trace experiment and the debug target has
support for disabling tracepoints during a trace experiment, then
the change will be effective immediately. Otherwise, it will be
applied to the next trace experiment.

`enable tracepoint [NUM]'
Enable tracepoint NUM, or all tracepoints. If this command is
issued during a trace experiment and the debug target supports
enabling tracepoints during a trace experiment, then the enabled
tracepoints will become effective immediately. Otherwise, they
will become effective the next time a trace experiment is run.

File: gdb.info, Node: Tracepoint Passcounts, Next: Tracepoint Conditions, Prev: Enable and Disable Tracepoints, Up: Set Tracepoints

13.1.3 Tracepoint Passcounts
----------------------------

`passcount [N [NUM]]'
Set the "passcount" of a tracepoint. The passcount is a way to
automatically stop a trace experiment. If a tracepoint's
passcount is N, then the trace experiment will be automatically
stopped on the N'th time that tracepoint is hit. If the
tracepoint number NUM is not specified, the `passcount' command
sets the passcount of the most recently defined tracepoint. If no
passcount is given, the trace experiment will run until stopped
explicitly by the user.

Examples:

(gdb) passcount 5 2 // Stop on the 5th execution of
`// tracepoint 2'

(gdb) passcount 12 // Stop on the 12th execution of the
`// most recently defined tracepoint.'
(gdb) trace foo
(gdb) pass 3
(gdb) trace bar
(gdb) pass 2
(gdb) trace baz
(gdb) pass 1 // Stop tracing when foo has been
`// executed 3 times OR when bar has'
`// been executed 2 times'
`// OR when baz has been executed 1 time.'

File: gdb.info, Node: Tracepoint Conditions, Next: Trace State Variables, Prev: Tracepoint Passcounts, Up: Set Tracepoints

13.1.4 Tracepoint Conditions
----------------------------

The simplest sort of tracepoint collects data every time your program
reaches a specified place. You can also specify a "condition" for a
tracepoint. A condition is just a Boolean expression in your
programming language (*note Expressions: Expressions.). A tracepoint
with a condition evaluates the expression each time your program
reaches it, and data collection happens only if the condition is true.

Tracepoint conditions can be specified when a tracepoint is set, by
using `if' in the arguments to the `trace' command. *Note Setting
Tracepoints: Create and Delete Tracepoints. They can also be set or
changed at any time with the `condition' command, just as with
breakpoints.

Unlike breakpoint conditions, GDB does not actually evaluate the
conditional expression itself. Instead, GDB encodes the expression
into an agent expression (*note Agent Expressions::) suitable for
execution on the target, independently of GDB. Global variables become
raw memory locations, locals become stack accesses, and so forth.

For instance, suppose you have a function that is usually called
frequently, but should not be called after an error has occurred. You
could use the following tracepoint command to collect data about calls
of that function that happen while the error code is propagating
through the program; an unconditional tracepoint could end up
collecting thousands of useless trace frames that you would have to
search through.

(gdb) trace normal_operation if errcode > 0

File: gdb.info, Node: Trace State Variables, Next: Tracepoint Actions, Prev: Tracepoint Conditions, Up: Set Tracepoints

13.1.5 Trace State Variables
----------------------------

A "trace state variable" is a special type of variable that is created
and managed by target-side code. The syntax is the same as that for
GDB's convenience variables (a string prefixed with "$"), but they are
stored on the target. They must be created explicitly, using a
`tvariable' command. They are always 64-bit signed integers.

Trace state variables are remembered by GDB, and downloaded to the
target along with tracepoint information when the trace experiment
starts. There are no intrinsic limits on the number of trace state
variables, beyond memory limitations of the target.

Although trace state variables are managed by the target, you can use
them in print commands and expressions as if they were convenience
variables; GDB will get the current value from the target while the
trace experiment is running. Trace state variables share the same
namespace as other "$" variables, which means that you cannot have
trace state variables with names like `$23' or `$pc', nor can you have
a trace state variable and a convenience variable with the same name.

`tvariable $NAME [ = EXPRESSION ]'
The `tvariable' command creates a new trace state variable named
`$NAME', and optionally gives it an initial value of EXPRESSION.
The EXPRESSION is evaluated when this command is entered; the
result will be converted to an integer if possible, otherwise GDB
will report an error. A subsequent `tvariable' command specifying
the same name does not create a variable, but instead assigns the
supplied initial value to the existing variable of that name,
overwriting any previous initial value. The default initial value
is 0.

`info tvariables'
List all the trace state variables along with their initial values.
Their current values may also be displayed, if the trace
experiment is currently running.

`delete tvariable [ $NAME ... ]'
Delete the given trace state variables, or all of them if no
arguments are specified.

File: gdb.info, Node: Tracepoint Actions, Next: Listing Tracepoints, Prev: Trace State Variables, Up: Set Tracepoints

13.1.6 Tracepoint Action Lists
------------------------------

`actions [NUM]'
This command will prompt for a list of actions to be taken when the
tracepoint is hit. If the tracepoint number NUM is not specified,
this command sets the actions for the one that was most recently
defined (so that you can define a tracepoint and then say
`actions' without bothering about its number). You specify the
actions themselves on the following lines, one action at a time,
and terminate the actions list with a line containing just `end'.
So far, the only defined actions are `collect', `teval', and
`while-stepping'.

`actions' is actually equivalent to `commands' (*note Breakpoint
Command Lists: Break Commands.), except that only the defined
actions are allowed; any other GDB command is rejected.

To remove all actions from a tracepoint, type `actions NUM' and
follow it immediately with `end'.

(gdb) collect DATA // collect some data

(gdb) while-stepping 5 // single-step 5 times, collect data

(gdb) end // signals the end of actions.

In the following example, the action list begins with `collect'
commands indicating the things to be collected when the tracepoint
is hit. Then, in order to single-step and collect additional data
following the tracepoint, a `while-stepping' command is used,
followed by the list of things to be collected after each step in a
sequence of single steps. The `while-stepping' command is
terminated by its own separate `end' command. Lastly, the action
list is terminated by an `end' command.

(gdb) trace foo
(gdb) actions
Enter actions for tracepoint 1, one per line:
> collect bar,baz
> collect $regs
> while-stepping 12
> collect $pc, arr[i]
> end
end

`collect[/MODS] EXPR1, EXPR2, ...'
Collect values of the given expressions when the tracepoint is hit.
This command accepts a comma-separated list of any valid
expressions. In addition to global, static, or local variables,
the following special arguments are supported:

`$regs'
Collect all registers.

`$args'
Collect all function arguments.

`$locals'
Collect all local variables.

`$_ret'
Collect the return address. This is helpful if you want to
see more of a backtrace.

_Note:_ The return address location can not always be reliably
determined up front, and the wrong address / registers may
end up collected instead. On some architectures the
reliability is higher for tracepoints at function entry,
while on others it's the opposite. When this happens,
backtracing will stop because the return address is found
unavailable (unless another collect rule happened to match
it).

`$_probe_argc'
Collects the number of arguments from the static probe at
which the tracepoint is located. *Note Static Probe Points::.

`$_probe_argN'
N is an integer between 0 and 11. Collects the Nth argument
from the static probe at which the tracepoint is located.
*Note Static Probe Points::.

`$_sdata'
Collect static tracepoint marker specific data. Only
available for static tracepoints. *Note Tracepoint Action
Lists: Tracepoint Actions. On the UST static tracepoints
library backend, an instrumentation point resembles a
`printf' function call. The tracing library is able to
collect user specified data formatted to a character string
using the format provided by the programmer that instrumented
the program. Other backends have similar mechanisms. Here's
an example of a UST marker call:

const char master_name[] = "$your_name";
trace_mark(channel1, marker1, "hello %s", master_name)

In this case, collecting `$_sdata' collects the string `hello
$yourname'. When analyzing the trace buffer, you can inspect
`$_sdata' like any other variable available to GDB.

You can give several consecutive `collect' commands, each one with
a single argument, or one `collect' command with several arguments
separated by commas; the effect is the same.

The optional MODS changes the usual handling of the arguments.
`s' requests that pointers to chars be handled as strings, in
particular collecting the contents of the memory being pointed at,
up to the first zero. The upper bound is by default the value of
the `print characters' variable; if `s' is followed by a decimal
number, that is the upper bound instead. So for instance
`collect/s25 mystr' collects as many as 25 characters at `mystr'.

The command `info scope' (*note info scope: Symbols.) is
particularly useful for figuring out what data to collect.

`teval EXPR1, EXPR2, ...'
Evaluate the given expressions when the tracepoint is hit. This
command accepts a comma-separated list of expressions. The results
are discarded, so this is mainly useful for assigning values to
trace state variables (*note Trace State Variables::) without
adding those values to the trace buffer, as would be the case if
the `collect' action were used.

`while-stepping N'
Perform N single-step instruction traces after the tracepoint,
collecting new data after each step. The `while-stepping' command
is followed by the list of what to collect while stepping
(followed by its own `end' command):

> while-stepping 12
> collect $regs, myglobal
> end
>

Note that `$pc' is not automatically collected by
`while-stepping'; you need to explicitly collect that register if
you need it. You may abbreviate `while-stepping' as `ws' or
`stepping'.

`set default-collect EXPR1, EXPR2, ...'
This variable is a list of expressions to collect at each
tracepoint hit. It is effectively an additional `collect' action
prepended to every tracepoint action list. The expressions are
parsed individually for each tracepoint, so for instance a
variable named `xyz' may be interpreted as a global for one
tracepoint, and a local for another, as appropriate to the
tracepoint's location.

`show default-collect'
Show the list of expressions that are collected by default at each
tracepoint hit.

File: gdb.info, Node: Listing Tracepoints, Next: Listing Static Tracepoint Markers, Prev: Tracepoint Actions, Up: Set Tracepoints

13.1.7 Listing Tracepoints
--------------------------

`info tracepoints [NUM...]'
Display information about the tracepoint NUM. If you don't
specify a tracepoint number, displays information about all the
tracepoints defined so far. The format is similar to that used for
`info breakpoints'; in fact, `info tracepoints' is the same
command, simply restricting itself to tracepoints.

A tracepoint's listing may include additional information specific
to tracing:

* its passcount as given by the `passcount N' command

* the state about installed on target of each location

(gdb) info trace
Num Type Disp Enb Address What
1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
while-stepping 20
collect globfoo, $regs
end
collect globfoo2
end
pass count 1200
2 tracepoint keep y <MULTIPLE>
collect $eip
2.1 y 0x0804859c in func4 at change-loc.h:35
installed on target
2.2 y 0xb7ffc480 in func4 at change-loc.h:35
installed on target
2.3 y <PENDING> set_tracepoint
3 tracepoint keep y 0x080485b1 in foo at change-loc.c:29
not installed on target
(gdb)

This command can be abbreviated `info tp'.

File: gdb.info, Node: Listing Static Tracepoint Markers, Next: Starting and Stopping Trace Experiments, Prev: Listing Tracepoints, Up: Set Tracepoints

13.1.8 Listing Static Tracepoint Markers
----------------------------------------

`info static-tracepoint-markers'
Display information about all static tracepoint markers defined in
the program.

For each marker, the following columns are printed:

_Count_
An incrementing counter, output to help readability. This is
not a stable identifier.

_ID_
The marker ID, as reported by the target.

_Enabled or Disabled_
Probed markers are tagged with `y'. `n' identifies marks
that are not enabled.

_Address_
Where the marker is in your program, as a memory address.

_What_
Where the marker is in the source for your program, as a file
and line number. If the debug information included in the
program does not allow GDB to locate the source of the
marker, this column will be left blank.

In addition, the following information may be printed for each
marker:

_Data_
User data passed to the tracing library by the marker call.
In the UST backend, this is the format string passed as
argument to the marker call.

_Static tracepoints probing the marker_
The list of static tracepoints attached to the marker.

(gdb) info static-tracepoint-markers
Cnt ID Enb Address What
1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25
Data: number1 %d number2 %d
Probed by static tracepoints: #2
2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24
Data: str %s
(gdb)

File: gdb.info, Node: Starting and Stopping Trace Experiments, Next: Tracepoint Restrictions, Prev: Listing Static Tracepoint Markers, Up: Set Tracepoints

13.1.9 Starting and Stopping Trace Experiments
----------------------------------------------

`tstart'
This command starts the trace experiment, and begins collecting
data. It has the side effect of discarding all the data collected
in the trace buffer during the previous trace experiment. If any
arguments are supplied, they are taken as a note and stored with
the trace experiment's state. The notes may be arbitrary text,
and are especially useful with disconnected tracing in a
multi-user context; the notes can explain what the trace is doing,
supply user contact information, and so forth.

`tstop'
This command stops the trace experiment. If any arguments are
supplied, they are recorded with the experiment as a note. This is
useful if you are stopping a trace started by someone else, for
instance if the trace is interfering with the system's behavior and
needs to be stopped quickly.

*Note*: a trace experiment and data collection may stop
automatically if any tracepoint's passcount is reached (*note
Tracepoint Passcounts::), or if the trace buffer becomes full.

`tstatus'
This command displays the status of the current trace data
collection.

Here is an example of the commands we described so far:

(gdb) trace gdb_c_test
(gdb) actions
Enter actions for tracepoint #1, one per line.
> collect $regs,$locals,$args
> while-stepping 11
> collect $regs
> end
> end
(gdb) tstart
[time passes ...]
(gdb) tstop

You can choose to continue running the trace experiment even if GDB
disconnects from the target, voluntarily or involuntarily. For
commands such as `detach', the debugger will ask what you want to do
with the trace. But for unexpected terminations (GDB crash, network
outage), it would be unfortunate to lose hard-won trace data, so the
variable `disconnected-tracing' lets you decide whether the trace should
continue running without GDB.

`set disconnected-tracing on'
`set disconnected-tracing off'
Choose whether a tracing run should continue to run if GDB has
disconnected from the target. Note that `detach' or `quit' will
ask you directly what to do about a running trace no matter what
this variable's setting, so the variable is mainly useful for
handling unexpected situations, such as loss of the network.

`show disconnected-tracing'
Show the current choice for disconnected tracing.

When you reconnect to the target, the trace experiment may or may not
still be running; it might have filled the trace buffer in the
meantime, or stopped for one of the other reasons. If it is running,
it will continue after reconnection.

Upon reconnection, the target will upload information about the
tracepoints in effect. GDB will then compare that information to the
set of tracepoints currently defined, and attempt to match them up,
allowing for the possibility that the numbers may have changed due to
creation and deletion in the meantime. If one of the target's
tracepoints does not match any in GDB, the debugger will create a new
tracepoint, so that you have a number with which to specify that
tracepoint. This matching-up process is necessarily heuristic, and it
may result in useless tracepoints being created; you may simply delete
them if they are of no use.

If your target agent supports a "circular trace buffer", then you
can run a trace experiment indefinitely without filling the trace
buffer; when space runs out, the agent deletes already-collected trace
frames, oldest first, until there is enough room to continue
collecting. This is especially useful if your tracepoints are being
hit too often, and your trace gets terminated prematurely because the
buffer is full. To ask for a circular trace buffer, simply set
`circular-trace-buffer' to on. You can set this at any time, including
during tracing; if the agent can do it, it will change buffer handling
on the fly, otherwise it will not take effect until the next run.

`set circular-trace-buffer on'
`set circular-trace-buffer off'
Choose whether a tracing run should use a linear or circular buffer
for trace data. A linear buffer will not lose any trace data, but
may fill up prematurely, while a circular buffer will discard old
trace data, but it will have always room for the latest tracepoint
hits.

`show circular-trace-buffer'
Show the current choice for the trace buffer. Note that this may
not match the agent's current buffer handling, nor is it
guaranteed to match the setting that might have been in effect
during a past run, for instance if you are looking at frames from
a trace file.

`set trace-buffer-size N'
`set trace-buffer-size unlimited'
Request that the target use a trace buffer of N bytes. Not all
targets will honor the request; they may have a compiled-in size
for the trace buffer, or some other limitation. Set to a value of
`unlimited' or `-1' to let the target use whatever size it likes.
This is also the default.

`show trace-buffer-size'
Show the current requested size for the trace buffer. Note that
this will only match the actual size if the target supports
size-setting, and was able to handle the requested size. For
instance, if the target can only change buffer size between runs,
this variable will not reflect the change until the next run
starts. Use `tstatus' to get a report of the actual buffer size.

`set trace-user TEXT'

`show trace-user'

`set trace-notes TEXT'
Set the trace run's notes.

`show trace-notes'
Show the trace run's notes.

`set trace-stop-notes TEXT'
Set the trace run's stop notes. The handling of the note is as for
`tstop' arguments; the set command is convenient way to fix a stop
note that is mistaken or incomplete.

`show trace-stop-notes'
Show the trace run's stop notes.

File: gdb.info, Node: Tracepoint Restrictions, Prev: Starting and Stopping Trace Experiments, Up: Set Tracepoints

13.1.10 Tracepoint Restrictions
-------------------------------

There are a number of restrictions on the use of tracepoints. As
described above, tracepoint data gathering occurs on the target without
interaction from GDB. Thus the full capabilities of the debugger are
not available during data gathering, and then at data examination time,
you will be limited by only having what was collected. The following
items describe some common problems, but it is not exhaustive, and you
may run into additional difficulties not mentioned here.

* Tracepoint expressions are intended to gather objects (lvalues).
Thus the full flexibility of GDB's expression evaluator is not
available. You cannot call functions, cast objects to aggregate
types, access convenience variables or modify values (except by
assignment to trace state variables). Some language features may
implicitly call functions (for instance Objective-C fields with
accessors), and therefore cannot be collected either.

* Collection of local variables, either individually or in bulk with
`$locals' or `$args', during `while-stepping' may behave
erratically. The stepping action may enter a new scope (for
instance by stepping into a function), or the location of the
variable may change (for instance it is loaded into a register).
The tracepoint data recorded uses the location information for the
variables that is correct for the tracepoint location. When the
tracepoint is created, it is not possible, in general, to determine
where the steps of a `while-stepping' sequence will advance the
program--particularly if a conditional branch is stepped.

* Collection of an incompletely-initialized or partially-destroyed
object may result in something that GDB cannot display, or displays
in a misleading way.

* When GDB displays a pointer to character it automatically
dereferences the pointer to also display characters of the string
being pointed to. However, collecting the pointer during tracing
does not automatically collect the string. You need to explicitly
dereference the pointer and provide size information if you want to
collect not only the pointer, but the memory pointed to. For
example, `*ptr@50' can be used to collect the 50 element array
pointed to by `ptr'.

* It is not possible to collect a complete stack backtrace at a
tracepoint. Instead, you may collect the registers and a few
hundred bytes from the stack pointer with something like
`*(unsigned char *)$esp@300' (adjust to use the name of the actual
stack pointer register on your target architecture, and the amount
of stack you wish to capture). Then the `backtrace' command will
show a partial backtrace when using a trace frame. The number of
stack frames that can be examined depends on the sizes of the
frames in the collected stack. Note that if you ask for a block
so large that it goes past the bottom of the stack, the target
agent may report an error trying to read from an invalid address.

* If you do not collect registers at a tracepoint, GDB can infer
that the value of `$pc' must be the same as the address of the
tracepoint and use that when you are looking at a trace frame for
that tracepoint. However, this cannot work if the tracepoint has
multiple locations (for instance if it was set in a function that
was inlined), or if it has a `while-stepping' loop. In those cases
GDB will warn you that it can't infer `$pc', and default it to
zero.

File: gdb.info, Node: Analyze Collected Data, Next: Tracepoint Variables, Prev: Set Tracepoints, Up: Tracepoints

13.2 Using the Collected Data
=============================

After the tracepoint experiment ends, you use GDB commands for
examining the trace data. The basic idea is that each tracepoint
collects a trace "snapshot" every time it is hit and another snapshot
every time it single-steps. All these snapshots are consecutively
numbered from zero and go into a buffer, and you can examine them
later. The way you examine them is to "focus" on a specific trace
snapshot. When the remote stub is focused on a trace snapshot, it will
respond to all GDB requests for memory and registers by reading from
the buffer which belongs to that snapshot, rather than from _real_
memory or registers of the program being debugged. This means that
*all* GDB commands (`print', `info registers', `backtrace', etc.) will
behave as if we were currently debugging the program state as it was
when the tracepoint occurred. Any requests for data that are not in
the buffer will fail.

* Menu:

* tfind:: How to select a trace snapshot
* tdump:: How to display all data for a snapshot
* save tracepoints:: How to save tracepoints for a future run

File: gdb.info, Node: tfind, Next: tdump, Up: Analyze Collected Data

13.2.1 `tfind N'
----------------

The basic command for selecting a trace snapshot from the buffer is
`tfind N', which finds trace snapshot number N, counting from zero. If
no argument N is given, the next snapshot is selected.

Here are the various forms of using the `tfind' command.

`tfind start'
Find the first snapshot in the buffer. This is a synonym for
`tfind 0' (since 0 is the number of the first snapshot).

`tfind none'
Stop debugging trace snapshots, resume _live_ debugging.

`tfind end'
Same as `tfind none'.

`tfind'
No argument means find the next trace snapshot or find the first
one if no trace snapshot is selected.

`tfind -'
Find the previous trace snapshot before the current one. This
permits retracing earlier steps.

`tfind tracepoint NUM'
Find the next snapshot associated with tracepoint NUM. Search
proceeds forward from the last examined trace snapshot. If no
argument NUM is given, it means find the next snapshot collected
for the same tracepoint as the current snapshot.

`tfind pc ADDR'
Find the next snapshot associated with the value ADDR of the
program counter. Search proceeds forward from the last examined
trace snapshot. If no argument ADDR is given, it means find the
next snapshot with the same value of PC as the current snapshot.

`tfind outside ADDR1, ADDR2'
Find the next snapshot whose PC is outside the given range of
addresses (exclusive).

`tfind range ADDR1, ADDR2'
Find the next snapshot whose PC is between ADDR1 and ADDR2
(inclusive).

`tfind line [FILE:]N'
Find the next snapshot associated with the source line N. If the
optional argument FILE is given, refer to line N in that source
file. Search proceeds forward from the last examined trace
snapshot. If no argument N is given, it means find the next line
other than the one currently being examined; thus saying `tfind
line' repeatedly can appear to have the same effect as stepping
from line to line in a _live_ debugging session.

The default arguments for the `tfind' commands are specifically
designed to make it easy to scan through the trace buffer. For
instance, `tfind' with no argument selects the next trace snapshot, and
`tfind -' with no argument selects the previous trace snapshot. So, by
giving one `tfind' command, and then simply hitting <RET> repeatedly
you can examine all the trace snapshots in order. Or, by saying `tfind
-' and then hitting <RET> repeatedly you can examine the snapshots in
reverse order. The `tfind line' command with no argument selects the
snapshot for the next source line executed. The `tfind pc' command with
no argument selects the next snapshot with the same program counter
(PC) as the current frame. The `tfind tracepoint' command with no
argument selects the next trace snapshot collected by the same
tracepoint as the current one.

In addition to letting you scan through the trace buffer manually,
these commands make it easy to construct GDB scripts that scan through
the trace buffer and print out whatever collected data you are
interested in. Thus, if we want to examine the PC, FP, and SP
registers from each trace frame in the buffer, we can say this:

(gdb) tfind start
(gdb) while ($trace_frame != -1)
> printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
$trace_frame, $pc, $sp, $fp
> tfind
> end

Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14

Or, if we want to examine the variable `X' at each source line in
the buffer:

(gdb) tfind start
(gdb) while ($trace_frame != -1)
> printf "Frame %d, X == %d\n", $trace_frame, X
> tfind line
> end

Frame 0, X = 1
Frame 7, X = 2
Frame 13, X = 255

File: gdb.info, Node: tdump, Next: save tracepoints, Prev: tfind, Up: Analyze Collected Data

13.2.2 `tdump'
--------------

This command takes no arguments. It prints all the data collected at
the current trace snapshot.

(gdb) trace 444
(gdb) actions
Enter actions for tracepoint #2, one per line:
> collect $regs, $locals, $args, gdb_long_test
> end

(gdb) tstart

(gdb) tfind line 444
#0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
at gdb_test.c:444
444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )

(gdb) tdump
Data collected at tracepoint 2, trace frame 1:
d0 0xc4aa0085 -995491707
d1 0x18 24
d2 0x80 128
d3 0x33 51
d4 0x71aea3d 119204413
d5 0x22 34
d6 0xe0 224
d7 0x380035 3670069
a0 0x19e24a 1696330
a1 0x3000668 50333288
a2 0x100 256
a3 0x322000 3284992
a4 0x3000698 50333336
a5 0x1ad3cc 1758156
fp 0x30bf3c 0x30bf3c
sp 0x30bf34 0x30bf34
ps 0x0 0
pc 0x20b2c8 0x20b2c8
fpcontrol 0x0 0
fpstatus 0x0 0
fpiaddr 0x0 0
p = 0x20e5b4 "gdb-test"
p1 = (void *) 0x11
p2 = (void *) 0x22
p3 = (void *) 0x33
p4 = (void *) 0x44
p5 = (void *) 0x55
p6 = (void *) 0x66
gdb_long_test = 17 '\021'

(gdb)

`tdump' works by scanning the tracepoint's current collection
actions and printing the value of each expression listed. So `tdump'
can fail, if after a run, you change the tracepoint's actions to
mention variables that were not collected during the run.

Also, for tracepoints with `while-stepping' loops, `tdump' uses the
collected value of `$pc' to distinguish between trace frames that were
collected at the tracepoint hit, and frames that were collected while
stepping. This allows it to correctly choose whether to display the
basic list of collections, or the collections from the body of the
while-stepping loop. However, if `$pc' was not collected, then `tdump'
will always attempt to dump using the basic collection list, and may
fail if a while-stepping frame does not include all the same data that
is collected at the tracepoint hit.

File: gdb.info, Node: save tracepoints, Prev: tdump, Up: Analyze Collected Data

13.2.3 `save tracepoints FILENAME'
----------------------------------

This command saves all current tracepoint definitions together with
their actions and passcounts, into a file `FILENAME' suitable for use
in a later debugging session. To read the saved tracepoint
definitions, use the `source' command (*note Command Files::). The
`save-tracepoints' command is a deprecated alias for `save tracepoints'

File: gdb.info, Node: Tracepoint Variables, Next: Trace Files, Prev: Analyze Collected Data, Up: Tracepoints

13.3 Convenience Variables for Tracepoints
==========================================

`(int) $trace_frame'
The current trace snapshot (a.k.a. "frame") number, or -1 if no
snapshot is selected.

`(int) $tracepoint'
The tracepoint for the current trace snapshot.

`(int) $trace_line'
The line number for the current trace snapshot.

`(char []) $trace_file'
The source file for the current trace snapshot.

`(char []) $trace_func'
The name of the function containing `$tracepoint'.

Note: `$trace_file' is not suitable for use in `printf', use
`output' instead.

Here's a simple example of using these convenience variables for
stepping through all the trace snapshots and printing some of their
data. Note that these are not the same as trace state variables, which
are managed by the target.

(gdb) tfind start

(gdb) while $trace_frame != -1
> output $trace_file
> printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
> tfind
> end

File: gdb.info, Node: Trace Files, Prev: Tracepoint Variables, Up: Tracepoints

13.4 Using Trace Files
======================

In some situations, the target running a trace experiment may no longer
be available; perhaps it crashed, or the hardware was needed for a
different activity. To handle these cases, you can arrange to dump the
trace data into a file, and later use that file as a source of trace
data, via the `target tfile' command.

`tsave [ -r ] FILENAME'
`tsave [-ctf] DIRNAME'
Save the trace data to FILENAME. By default, this command assumes
that FILENAME refers to the host filesystem, so if necessary GDB
will copy raw trace data up from the target and then save it. If
the target supports it, you can also supply the optional argument
`-r' ("remote") to direct the target to save the data directly
into FILENAME in its own filesystem, which may be more efficient
if the trace buffer is very large. (Note, however, that `target
tfile' can only read from files accessible to the host.) By
default, this command will save trace frame in tfile format. You
can supply the optional argument `-ctf' to save data in CTF
format. The "Common Trace Format" (CTF) is proposed as a trace
format that can be shared by multiple debugging and tracing tools.
Please go to <http://www.efficios.com/ctf> to get more
information.

`target tfile FILENAME'
`target ctf DIRNAME'
Use the file named FILENAME or directory named DIRNAME as a source
of trace data. Commands that examine data work as they do with a
live target, but it is not possible to run any new trace
experiments. `tstatus' will report the state of the trace run at
the moment the data was saved, as well as the current trace frame
you are examining. Both FILENAME and DIRNAME must be on a
filesystem accessible to the host.

(gdb) target ctf ctf.ctf
(gdb) tfind
Found trace frame 0, tracepoint 2
39 ++a; /* set tracepoint 1 here */
(gdb) tdump
Data collected at tracepoint 2, trace frame 0:
i = 0
a = 0
b = 1 '\001'
c = {"123", "456", "789", "123", "456", "789"}
d = {{{a = 1, b = 2}, {a = 3, b = 4}}, {{a = 5, b = 6}, {a = 7, b = 8}}}
(gdb) p b
$1 = 1

File: gdb.info, Node: Overlays, Next: Languages, Prev: Tracepoints, Up: Top

14 Debugging Programs That Use Overlays
***************************************

If your program is too large to fit completely in your target system's
memory, you can sometimes use "overlays" to work around this problem.
GDB provides some support for debugging programs that use overlays.

* Menu:

* How Overlays Work:: A general explanation of overlays.
* Overlay Commands:: Managing overlays in GDB.
* Automatic Overlay Debugging:: GDB can find out which overlays are
mapped by asking the inferior.
* Overlay Sample Program:: A sample program using overlays.

File: gdb.info, Node: How Overlays Work, Next: Overlay Commands, Up: Overlays

14.1 How Overlays Work
======================

Suppose you have a computer whose instruction address space is only 64
kilobytes long, but which has much more memory which can be accessed by
other means: special instructions, segment registers, or memory
management hardware, for example. Suppose further that you want to
adapt a program which is larger than 64 kilobytes to run on this system.

One solution is to identify modules of your program which are
relatively independent, and need not call each other directly; call
these modules "overlays". Separate the overlays from the main program,
and place their machine code in the larger memory. Place your main
program in instruction memory, but leave at least enough space there to
hold the largest overlay as well.

Now, to call a function located in an overlay, you must first copy
that overlay's machine code from the large memory into the space set
aside for it in the instruction memory, and then jump to its entry point
there.

Data Instruction Larger
Address Space Address Space Address Space
+-----------+ +-----------+ +-----------+
| | | | | |
+-----------+ +-----------+ +-----------+<-- overlay 1
| program | | main | .----| overlay 1 | load address
| variables | | program | | +-----------+
| and heap | | | | | |
+-----------+ | | | +-----------+<-- overlay 2
| | +-----------+ | | | load address
+-----------+ | | | .-| overlay 2 |
| | | | | |
mapped --->+-----------+ | | +-----------+
address | | | | | |
| overlay | <-' | | |
| area | <---' +-----------+<-- overlay 3
| | <---. | | load address
+-----------+ `--| overlay 3 |
| | | |
+-----------+ | |
+-----------+
| |
+-----------+

A code overlay

The diagram (*note A code overlay::) shows a system with separate
data and instruction address spaces. To map an overlay, the program
copies its code from the larger address space to the instruction
address space. Since the overlays shown here all use the same mapped
address, only one may be mapped at a time. For a system with a single
address space for data and instructions, the diagram would be similar,
except that the program variables and heap would share an address space
with the main program and the overlay area.

An overlay loaded into instruction memory and ready for use is
called a "mapped" overlay; its "mapped address" is its address in the
instruction memory. An overlay not present (or only partially present)
in instruction memory is called "unmapped"; its "load address" is its
address in the larger memory. The mapped address is also called the
"virtual memory address", or "VMA"; the load address is also called the
"load memory address", or "LMA".

Unfortunately, overlays are not a completely transparent way to
adapt a program to limited instruction memory. They introduce a new
set of global constraints you must keep in mind as you design your
program:

* Before calling or returning to a function in an overlay, your
program must make sure that overlay is actually mapped.
Otherwise, the call or return will transfer control to the right
address, but in the wrong overlay, and your program will probably
crash.

* If the process of mapping an overlay is expensive on your system,
you will need to choose your overlays carefully to minimize their
effect on your program's performance.

* The executable file you load onto your system must contain each
overlay's instructions, appearing at the overlay's load address,
not its mapped address. However, each overlay's instructions must
be relocated and its symbols defined as if the overlay were at its
mapped address. You can use GNU linker scripts to specify
different load and relocation addresses for pieces of your
program; see *Note Overlay Description: (ld.info)Overlay
Description.

* The procedure for loading executable files onto your system must
be able to load their contents into the larger address space as
well as the instruction and data spaces.

The overlay system described above is rather simple, and could be
improved in many ways:

* If your system has suitable bank switch registers or memory
management hardware, you could use those facilities to make an
overlay's load area contents simply appear at their mapped address
in instruction space. This would probably be faster than copying
the overlay to its mapped area in the usual way.

* If your overlays are small enough, you could set aside more than
one overlay area, and have more than one overlay mapped at a time.

* You can use overlays to manage data, as well as instructions. In
general, data overlays are even less transparent to your design
than code overlays: whereas code overlays only require care when
you call or return to functions, data overlays require care every
time you access the data. Also, if you change the contents of a
data overlay, you must copy its contents back out to its load
address before you can copy a different data overlay into the same
mapped area.

File: gdb.info, Node: Overlay Commands, Next: Automatic Overlay Debugging, Prev: How Overlays Work, Up: Overlays

14.2 Overlay Commands
=====================

To use GDB's overlay support, each overlay in your program must
correspond to a separate section of the executable file. The section's
virtual memory address and load memory address must be the overlay's
mapped and load addresses. Identifying overlays with sections allows
GDB to determine the appropriate address of a function or variable,
depending on whether the overlay is mapped or not.

GDB's overlay commands all start with the word `overlay'; you can
abbreviate this as `ov' or `ovly'. The commands are:

`overlay off'
Disable GDB's overlay support. When overlay support is disabled,
GDB assumes that all functions and variables are always present at
their mapped addresses. By default, GDB's overlay support is
disabled.

`overlay manual'
Enable "manual" overlay debugging. In this mode, GDB relies on
you to tell it which overlays are mapped, and which are not, using
the `overlay map-overlay' and `overlay unmap-overlay' commands
described below.

`overlay map-overlay OVERLAY'
`overlay map OVERLAY'
Tell GDB that OVERLAY is now mapped; OVERLAY must be the name of
the object file section containing the overlay. When an overlay
is mapped, GDB assumes it can find the overlay's functions and
variables at their mapped addresses. GDB assumes that any other
overlays whose mapped ranges overlap that of OVERLAY are now
unmapped.

`overlay unmap-overlay OVERLAY'
`overlay unmap OVERLAY'
Tell GDB that OVERLAY is no longer mapped; OVERLAY must be the
name of the object file section containing the overlay. When an
overlay is unmapped, GDB assumes it can find the overlay's
functions and variables at their load addresses.

`overlay auto'
Enable "automatic" overlay debugging. In this mode, GDB consults
a data structure the overlay manager maintains in the inferior to
see which overlays are mapped. For details, see *Note Automatic
Overlay Debugging::.

`overlay load-target'
`overlay load'
Re-read the overlay table from the inferior. Normally, GDB
re-reads the table GDB automatically each time the inferior stops,
so this command should only be necessary if you have changed the
overlay mapping yourself using GDB. This command is only useful
when using automatic overlay debugging.

`overlay list-overlays'
`overlay list'
Display a list of the overlays currently mapped, along with their
mapped addresses, load addresses, and sizes.

Normally, when GDB prints a code address, it includes the name of
the function the address falls in:

(gdb) print main
$3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, GDB recognizes code in unmapped
overlays, and prints the names of unmapped functions with asterisks
around them. For example, if `foo' is a function in an unmapped
overlay, GDB prints it this way:

(gdb) overlay list
No sections are mapped.
(gdb) print foo
$5 = {int (int)} 0x100000 <*foo*>
When `foo''s overlay is mapped, GDB prints the function's name
normally:

(gdb) overlay list
Section .ov.foo.text, loaded at 0x100000 - 0x100034,
mapped at 0x1016 - 0x104a
(gdb) print foo
$6 = {int (int)} 0x1016 <foo>

When overlay debugging is enabled, GDB can find the correct address
for functions and variables in an overlay, whether or not the overlay
is mapped. This allows most GDB commands, like `break' and
`disassemble', to work normally, even on unmapped code. However, GDB's
breakpoint support has some limitations:

* You can set breakpoints in functions in unmapped overlays, as long
as GDB can write to the overlay at its load address.

* GDB can not set hardware or simulator-based breakpoints in
unmapped overlays. However, if you set a breakpoint at the end of
your overlay manager (and tell GDB which overlays are now mapped,
if you are using manual overlay management), GDB will re-set its
breakpoints properly.

File: gdb.info, Node: Automatic Overlay Debugging, Next: Overlay Sample Program, Prev: Overlay Commands, Up: Overlays

14.3 Automatic Overlay Debugging
================================

GDB can automatically track which overlays are mapped and which are
not, given some simple co-operation from the overlay manager in the
inferior. If you enable automatic overlay debugging with the `overlay
auto' command (*note Overlay Commands::), GDB looks in the inferior's
memory for certain variables describing the current state of the
overlays.

Here are the variables your overlay manager must define to support
GDB's automatic overlay debugging:

`_ovly_table':
This variable must be an array of the following structures:

struct
{
/* The overlay's mapped address. */
unsigned long vma;

/* The size of the overlay, in bytes. */
unsigned long size;

/* The overlay's load address. */
unsigned long lma;

/* Non-zero if the overlay is currently mapped;
zero otherwise. */
unsigned long mapped;
}

`_novlys':
This variable must be a four-byte signed integer, holding the total
number of elements in `_ovly_table'.

To decide whether a particular overlay is mapped or not, GDB looks
for an entry in `_ovly_table' whose `vma' and `lma' members equal the
VMA and LMA of the overlay's section in the executable file. When GDB
finds a matching entry, it consults the entry's `mapped' member to
determine whether the overlay is currently mapped.

In addition, your overlay manager may define a function called
`_ovly_debug_event'. If this function is defined, GDB will silently
set a breakpoint there. If the overlay manager then calls this
function whenever it has changed the overlay table, this will enable
GDB to accurately keep track of which overlays are in program memory,
and update any breakpoints that may be set in overlays. This will
allow breakpoints to work even if the overlays are kept in ROM or other
non-writable memory while they are not being executed.

File: gdb.info, Node: Overlay Sample Program, Prev: Automatic Overlay Debugging, Up: Overlays

14.4 Overlay Sample Program
===========================

When linking a program which uses overlays, you must place the overlays
at their load addresses, while relocating them to run at their mapped
addresses. To do this, you must write a linker script (*note Overlay
Description: (ld.info)Overlay Description.). Unfortunately, since
linker scripts are specific to a particular host system, target
architecture, and target memory layout, this manual cannot provide
portable sample code demonstrating GDB's overlay support.

However, the GDB source distribution does contain an overlaid
program, with linker scripts for a few systems, as part of its test
suite. The program consists of the following files from
`gdb/testsuite/gdb.base':

`overlays.c'
The main program file.

`ovlymgr.c'
A simple overlay manager, used by `overlays.c'.

`foo.c'
`bar.c'
`baz.c'
`grbx.c'
Overlay modules, loaded and used by `overlays.c'.

`d10v.ld'
`m32r.ld'
Linker scripts for linking the test program on the `d10v-elf' and
`m32r-elf' targets.

You can build the test program using the `d10v-elf' GCC
cross-compiler like this:

$ d10v-elf-gcc -g -c overlays.c
$ d10v-elf-gcc -g -c ovlymgr.c
$ d10v-elf-gcc -g -c foo.c
$ d10v-elf-gcc -g -c bar.c
$ d10v-elf-gcc -g -c baz.c
$ d10v-elf-gcc -g -c grbx.c
$ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
baz.o grbx.o -Wl,-Td10v.ld -o overlays

The build process is identical for any other architecture, except
that you must substitute the appropriate compiler and linker script for
the target system for `d10v-elf-gcc' and `d10v.ld'.

File: gdb.info, Node: Languages, Next: Symbols, Prev: Overlays, Up: Top

15 Using GDB with Different Languages
*************************************

Although programming languages generally have common aspects, they are
rarely expressed in the same manner. For instance, in ANSI C,
dereferencing a pointer `p' is accomplished by `*p', but in Modula-2,
it is accomplished by `p^'. Values can also be represented (and
displayed) differently. Hex numbers in C appear as `0x1ae', while in
Modula-2 they appear as `1AEH'.

Language-specific information is built into GDB for some languages,
allowing you to express operations like the above in your program's
native language, and allowing GDB to output values in a manner
consistent with the syntax of your program's native language. The
language you use to build expressions is called the "working language".

* Menu:

* Setting:: Switching between source languages
* Show:: Displaying the language
* Checks:: Type and range checks
* Supported Languages:: Supported languages
* Unsupported Languages:: Unsupported languages

File: gdb.info, Node: Setting, Next: Show, Up: Languages

15.1 Switching Between Source Languages
=======================================

There are two ways to control the working language--either have GDB set
it automatically, or select it manually yourself. You can use the `set
language' command for either purpose. On startup, GDB defaults to
setting the language automatically. The working language is used to
determine how expressions you type are interpreted, how values are
printed, etc.

In addition to the working language, every source file that GDB
knows about has its own working language. For some object file
formats, the compiler might indicate which language a particular source
file is in. However, most of the time GDB infers the language from the
name of the file. The language of a source file controls whether C++
names are demangled--this way `backtrace' can show each frame
appropriately for its own language. There is no way to set the
language of a source file from within GDB, but you can set the language
associated with a filename extension. *Note Displaying the Language:
Show.

This is most commonly a problem when you use a program, such as
`cfront' or `f2c', that generates C but is written in another language.
In that case, make the program use `#line' directives in its C output;
that way GDB will know the correct language of the source code of the
original program, and will display that source code, not the generated
C code.

* Menu:

* Filenames:: Filename extensions and languages.
* Manually:: Setting the working language manually
* Automatically:: Having GDB infer the source language

File: gdb.info, Node: Filenames, Next: Manually, Up: Setting

15.1.1 List of Filename Extensions and Languages
------------------------------------------------

If a source file name ends in one of the following extensions, then GDB
infers that its language is the one indicated.

`.ada'
`.ads'
`.adb'
`.a'
Ada source file.

`.c'
C source file

`.C'
`.cc'
`.cp'
`.cpp'
`.cxx'
`.c++'
C++ source file

`.d'
D source file

`.m'
Objective-C source file

`.f'
`.F'
Fortran source file

`.mod'
Modula-2 source file

`.s'
`.S'
Assembler source file. This actually behaves almost like C, but
GDB does not skip over function prologues when stepping.

In addition, you may set the language associated with a filename
extension. *Note Displaying the Language: Show.

File: gdb.info, Node: Manually, Next: Automatically, Prev: Filenames, Up: Setting

15.1.2 Setting the Working Language
-----------------------------------

If you allow GDB to set the language automatically, expressions are
interpreted the same way in your debugging session and your program.

If you wish, you may set the language manually. To do this, issue
the command `set language LANG', where LANG is the name of a language,
such as `c' or `modula-2'. For a list of the supported languages, type
`set language'.

Setting the language manually prevents GDB from updating the working
language automatically. This can lead to confusion if you try to debug
a program when the working language is not the same as the source
language, when an expression is acceptable to both languages--but means
different things. For instance, if the current source file were
written in C, and GDB was parsing Modula-2, a command such as:

print a = b + c

might not have the effect you intended. In C, this means to add `b'
and `c' and place the result in `a'. The result printed would be the
value of `a'. In Modula-2, this means to compare `a' to the result of
`b+c', yielding a `BOOLEAN' value.

File: gdb.info, Node: Automatically, Prev: Manually, Up: Setting

15.1.3 Having GDB Infer the Source Language
-------------------------------------------

To have GDB set the working language automatically, use `set language
local' or `set language auto'. GDB then infers the working language.
That is, when your program stops in a frame (usually by encountering a
breakpoint), GDB sets the working language to the language recorded for
the function in that frame. If the language for a frame is unknown
(that is, if the function or block corresponding to the frame was
defined in a source file that does not have a recognized extension),
the current working language is not changed, and GDB issues a warning.

This may not seem necessary for most programs, which are written
entirely in one source language. However, program modules and libraries
written in one source language can be used by a main program written in
a different source language. Using `set language auto' in this case
frees you from having to set the working language manually.

File: gdb.info, Node: Show, Next: Checks, Prev: Setting, Up: Languages

15.2 Displaying the Language
============================

The following commands help you find out which language is the working
language, and also what language source files were written in.

`show language'
Display the current working language. This is the language you
can use with commands such as `print' to build and compute
expressions that may involve variables in your program.

`info frame'
Display the source language for this frame. This language becomes
the working language if you use an identifier from this frame.
*Note Information about a Frame: Frame Info, to identify the other
information listed here.

`info source'
Display the source language of this source file. *Note Examining
the Symbol Table: Symbols, to identify the other information
listed here.

In unusual circumstances, you may have source files with extensions
not in the standard list. You can then set the extension associated
with a language explicitly:

`set extension-language EXT LANGUAGE'
Tell GDB that source files with extension EXT are to be assumed as
written in the source language LANGUAGE.

`info extensions'
List all the filename extensions and the associated languages.

File: gdb.info, Node: Checks, Next: Supported Languages, Prev: Show, Up: Languages

15.3 Type and Range Checking
============================

Some languages are designed to guard you against making seemingly common
errors through a series of compile- and run-time checks. These include
checking the type of arguments to functions and operators and making
sure mathematical overflows are caught at run time. Checks such as
these help to ensure a program's correctness once it has been compiled
by eliminating type mismatches and providing active checks for range
errors when your program is running.

By default GDB checks for these errors according to the rules of the
current source language. Although GDB does not check the statements in
your program, it can check expressions entered directly into GDB for
evaluation via the `print' command, for example.

* Menu:

* Type Checking:: An overview of type checking
* Range Checking:: An overview of range checking

File: gdb.info, Node: Type Checking, Next: Range Checking, Up: Checks

15.3.1 An Overview of Type Checking
-----------------------------------

Some languages, such as C and C++, are strongly typed, meaning that the
arguments to operators and functions have to be of the correct type,
otherwise an error occurs. These checks prevent type mismatch errors
from ever causing any run-time problems. For example,

int klass::my_method(char *b) { return b ? 1 : 2; }

(gdb) print obj.my_method (0)
$1 = 2
but
(gdb) print obj.my_method (0x1234)
Cannot resolve method klass::my_method to any overloaded instance

The second example fails because in C++ the integer constant
`0x1234' is not type-compatible with the pointer parameter type.

For the expressions you use in GDB commands, you can tell GDB to not
enforce strict type checking or to treat any mismatches as errors and
abandon the expression; When type checking is disabled, GDB
successfully evaluates expressions like the second example above.

Even if type checking is off, there may be other reasons related to
type that prevent GDB from evaluating an expression. For instance, GDB
does not know how to add an `int' and a `struct foo'. These particular
type errors have nothing to do with the language in use and usually
arise from expressions which make little sense to evaluate anyway.

GDB provides some additional commands for controlling type checking:

`set check type on'
`set check type off'
Set strict type checking on or off. If any type mismatches occur
in evaluating an expression while type checking is on, GDB prints a
message and aborts evaluation of the expression.

`show check type'
Show the current setting of type checking and whether GDB is
enforcing strict type checking rules.

File: gdb.info, Node: Range Checking, Prev: Type Checking, Up: Checks

15.3.2 An Overview of Range Checking
------------------------------------

In some languages (such as Modula-2), it is an error to exceed the
bounds of a type; this is enforced with run-time checks. Such range
checking is meant to ensure program correctness by making sure
computations do not overflow, or indices on an array element access do
not exceed the bounds of the array.

For expressions you use in GDB commands, you can tell GDB to treat
range errors in one of three ways: ignore them, always treat them as
errors and abandon the expression, or issue warnings but evaluate the
expression anyway.

A range error can result from numerical overflow, from exceeding an
array index bound, or when you type a constant that is not a member of
any type. Some languages, however, do not treat overflows as an error.
In many implementations of C, mathematical overflow causes the result
to "wrap around" to lower values--for example, if M is the largest
integer value, and S is the smallest, then

M + 1 => S

This, too, is specific to individual languages, and in some cases
specific to individual compilers or machines. *Note Supported
Languages: Supported Languages, for further details on specific
languages.

GDB provides some additional commands for controlling the range
checker:

`set check range auto'
Set range checking on or off based on the current working language.
*Note Supported Languages: Supported Languages, for the default
settings for each language.

`set check range on'
`set check range off'
Set range checking on or off, overriding the default setting for
the current working language. A warning is issued if the setting
does not match the language default. If a range error occurs and
range checking is on, then a message is printed and evaluation of
the expression is aborted.

`set check range warn'
Output messages when the GDB range checker detects a range error,
but attempt to evaluate the expression anyway. Evaluating the
expression may still be impossible for other reasons, such as
accessing memory that the process does not own (a typical example
from many Unix systems).

`show check range'
Show the current setting of the range checker, and whether or not
it is being set automatically by GDB.

File: gdb.info, Node: Supported Languages, Next: Unsupported Languages, Prev: Checks, Up: Languages

15.4 Supported Languages
========================

GDB supports C, C++, D, Go, Objective-C, Fortran, OpenCL C, Pascal,
Rust, assembly, Modula-2, and Ada. Some GDB features may be used in
expressions regardless of the language you use: the GDB `@' and `::'
operators, and the `{type}addr' construct (*note Expressions:
Expressions.) can be used with the constructs of any supported language.

The following sections detail to what degree each source language is
supported by GDB. These sections are not meant to be language
tutorials or references, but serve only as a reference guide to what the
GDB expression parser accepts, and what input and output formats should
look like for different languages. There are many good books written
on each of these languages; please look to these for a language
reference or tutorial.

* Menu:

* C:: C and C++
* D:: D
* Go:: Go
* Objective-C:: Objective-C
* OpenCL C:: OpenCL C
* Fortran:: Fortran
* Pascal:: Pascal
* Rust:: Rust
* Modula-2:: Modula-2
* Ada:: Ada

File: gdb.info, Node: C, Next: D, Up: Supported Languages

15.4.1 C and C++
----------------

Since C and C++ are so closely related, many features of GDB apply to
both languages. Whenever this is the case, we discuss those languages
together.

The C++ debugging facilities are jointly implemented by the C++
compiler and GDB. Therefore, to debug your C++ code effectively, you
must compile your C++ programs with a supported C++ compiler, such as
GNU `g++', or the HP ANSI C++ compiler (`aCC').

* Menu:

* C Operators:: C and C++ operators
* C Constants:: C and C++ constants
* C Plus Plus Expressions:: C++ expressions
* C Defaults:: Default settings for C and C++
* C Checks:: C and C++ type and range checks
* Debugging C:: GDB and C
* Debugging C Plus Plus:: GDB features for C++
* Decimal Floating Point:: Numbers in Decimal Floating Point format

File: gdb.info, Node: C Operators, Next: C Constants, Up: C

15.4.1.1 C and C++ Operators
...........................

Operators must be defined on values of specific types. For instance,
`+' is defined on numbers, but not on structures. Operators are often
defined on groups of types.

For the purposes of C and C++, the following definitions hold:

* _Integral types_ include `int' with any of its storage-class
specifiers; `char'; `enum'; and, for C++, `bool'.

* _Floating-point types_ include `float', `double', and `long
double' (if supported by the target platform).

* _Pointer types_ include all types defined as `(TYPE *)'.

* _Scalar types_ include all of the above.

The following operators are supported. They are listed here in order
of increasing precedence:

`,'
The comma or sequencing operator. Expressions in a
comma-separated list are evaluated from left to right, with the
result of the entire expression being the last expression
evaluated.

`='
Assignment. The value of an assignment expression is the value
assigned. Defined on scalar types.

`OP='
Used in an expression of the form `A OP= B', and translated to
`A = A OP B'. `OP=' and `=' have the same precedence. The
operator OP is any one of the operators `|', `^', `&', `<<', `>>',
`+', `-', `*', `/', `%'.

`?:'
The ternary operator. `A ? B : C' can be thought of as: if A
then B else C. The argument A should be of an integral type.

`||'
Logical OR. Defined on integral types.

`&&'
Logical AND. Defined on integral types.

`|'
Bitwise OR. Defined on integral types.

`^'
Bitwise exclusive-OR. Defined on integral types.

`&'
Bitwise AND. Defined on integral types.

`==, !='
Equality and inequality. Defined on scalar types. The value of
these expressions is 0 for false and non-zero for true.

`<, >, <=, >='
Less than, greater than, less than or equal, greater than or equal.
Defined on scalar types. The value of these expressions is 0 for
false and non-zero for true.

`<<, >>'
left shift, and right shift. Defined on integral types.

`@'
The GDB "artificial array" operator (*note Expressions:
Expressions.).

`+, -'
Addition and subtraction. Defined on integral types,
floating-point types and pointer types.

`*, /, %'
Multiplication, division, and modulus. Multiplication and
division are defined on integral and floating-point types.
Modulus is defined on integral types.

`++, --'
Increment and decrement. When appearing before a variable, the
operation is performed before the variable is used in an
expression; when appearing after it, the variable's value is used
before the operation takes place.

`*'
Pointer dereferencing. Defined on pointer types. Same precedence
as `++'.

`&'
Address operator. Defined on variables. Same precedence as `++'.

For debugging C++, GDB implements a use of `&' beyond what is
allowed in the C++ language itself: you can use `&(&REF)' to
examine the address where a C++ reference variable (declared with
`&REF') is stored.

`-'
Negative. Defined on integral and floating-point types. Same
precedence as `++'.

`!'
Logical negation. Defined on integral types. Same precedence as
`++'.

`~'
Bitwise complement operator. Defined on integral types. Same
precedence as `++'.

`., ->'
Structure member, and pointer-to-structure member. For
convenience, GDB regards the two as equivalent, choosing whether
to dereference a pointer based on the stored type information.
Defined on `struct' and `union' data.

`.*, ->*'
Dereferences of pointers to members.

`[]'
Array indexing. `A[I]' is defined as `*(A+I)'. Same precedence
as `->'.

`()'
Function parameter list. Same precedence as `->'.

`::'
C++ scope resolution operator. Defined on `struct', `union', and
`class' types.

`::'
Doubled colons also represent the GDB scope operator (*note
Expressions: Expressions.). Same precedence as `::', above.

If an operator is redefined in the user code, GDB usually attempts
to invoke the redefined version instead of using the operator's
predefined meaning.

File: gdb.info, Node: C Constants, Next: C Plus Plus Expressions, Prev: C Operators, Up: C

15.4.1.2 C and C++ Constants
...........................

GDB allows you to express the constants of C and C++ in the following
ways:

* Integer constants are a sequence of digits. Octal constants are
specified by a leading `0' (i.e. zero), and hexadecimal constants
by a leading `0x' or `0X'. Constants may also end with a letter
`l', specifying that the constant should be treated as a `long'
value.

* Floating point constants are a sequence of digits, followed by a
decimal point, followed by a sequence of digits, and optionally
followed by an exponent. An exponent is of the form:
`e[[+]|-]NNN', where NNN is another sequence of digits. The `+'
is optional for positive exponents. A floating-point constant may
also end with a letter `f' or `F', specifying that the constant
should be treated as being of the `float' (as opposed to the
default `double') type; or with a letter `l' or `L', which
specifies a `long double' constant.

* Enumerated constants consist of enumerated identifiers, or their
integral equivalents.

* Character constants are a single character surrounded by single
quotes (`''), or a number--the ordinal value of the corresponding
character (usually its ASCII value). Within quotes, the single
character may be represented by a letter or by "escape sequences",
which are of the form `\NNN', where NNN is the octal representation
of the character's ordinal value; or of the form `\X', where `X'
is a predefined special character--for example, `\n' for newline.

Wide character constants can be written by prefixing a character
constant with `L', as in C. For example, `L'x'' is the wide form
of `x'. The target wide character set is used when computing the
value of this constant (*note Character Sets::).

* String constants are a sequence of character constants surrounded
by double quotes (`"'). Any valid character constant (as described
above) may appear. Double quotes within the string must be
preceded by a backslash, so for instance `"a\"b'c"' is a string of
five characters.

Wide string constants can be written by prefixing a string constant
with `L', as in C. The target wide character set is used when
computing the value of this constant (*note Character Sets::).

* Pointer constants are an integral value. You can also write
pointers to constants using the C operator `&'.

* Array constants are comma-separated lists surrounded by braces `{'
and `}'; for example, `{1,2,3}' is a three-element array of
integers, `{{1,2}, {3,4}, {5,6}}' is a three-by-two array, and
`{&"hi", &"there", &"fred"}' is a three-element array of pointers.

File: gdb.info, Node: C Plus Plus Expressions, Next: C Defaults, Prev: C Constants, Up: C

15.4.1.3 C++ Expressions
.......................

GDB expression handling can interpret most C++ expressions.

_Warning:_ GDB can only debug C++ code if you use the proper
compiler and the proper debug format. Currently, GDB works best
when debugging C++ code that is compiled with the most recent
version of GCC possible. The DWARF debugging format is preferred;
GCC defaults to this on most popular platforms. Other compilers
and/or debug formats are likely to work badly or not at all when
using GDB to debug C++ code. *Note Compilation::.

1. Member function calls are allowed; you can use expressions like

count = aml->GetOriginal(x, y)

2. While a member function is active (in the selected stack frame),
your expressions have the same namespace available as the member
function; that is, GDB allows implicit references to the class
instance pointer `this' following the same rules as C++. `using'
declarations in the current scope are also respected by GDB.

3. You can call overloaded functions; GDB resolves the function call
to the right definition, with some restrictions. GDB does not
perform overload resolution involving user-defined type
conversions, calls to constructors, or instantiations of templates
that do not exist in the program. It also cannot handle ellipsis
argument lists or default arguments.

It does perform integral conversions and promotions, floating-point
promotions, arithmetic conversions, pointer conversions,
conversions of class objects to base classes, and standard
conversions such as those of functions or arrays to pointers; it
requires an exact match on the number of function arguments.

Overload resolution is always performed, unless you have specified
`set overload-resolution off'. *Note GDB Features for C++:
Debugging C Plus Plus.

You must specify `set overload-resolution off' in order to use an
explicit function signature to call an overloaded function, as in
p 'foo(char,int)'('x', 13)

The GDB command-completion facility can simplify this; see *Note
Command Completion: Completion.

4. GDB understands variables declared as C++ lvalue or rvalue
references; you can use them in expressions just as you do in C++
source--they are automatically dereferenced.

In the parameter list shown when GDB displays a frame, the values
of reference variables are not displayed (unlike other variables);
this avoids clutter, since references are often used for large
structures. The _address_ of a reference variable is always
shown, unless you have specified `set print address off'.

5. GDB supports the C++ name resolution operator `::'--your
expressions can use it just as expressions in your program do.
Since one scope may be defined in another, you can use `::'
repeatedly if necessary, for example in an expression like
`SCOPE1::SCOPE2::NAME'. GDB also allows resolving name scope by
reference to source files, in both C and C++ debugging (*note
Program Variables: Variables.).

6. GDB performs argument-dependent lookup, following the C++
specification.

File: gdb.info, Node: C Defaults, Next: C Checks, Prev: C Plus Plus Expressions, Up: C

15.4.1.4 C and C++ Defaults
..........................

If you allow GDB to set range checking automatically, it defaults to
`off' whenever the working language changes to C or C++. This happens
regardless of whether you or GDB selects the working language.

If you allow GDB to set the language automatically, it recognizes
source files whose names end with `.c', `.C', or `.cc', etc, and when
GDB enters code compiled from one of these files, it sets the working
language to C or C++. *Note Having GDB Infer the Source Language:
Automatically, for further details.

File: gdb.info, Node: C Checks, Next: Debugging C, Prev: C Defaults, Up: C

15.4.1.5 C and C++ Type and Range Checks
.......................................

By default, when GDB parses C or C++ expressions, strict type checking
is used. However, if you turn type checking off, GDB will allow
certain non-standard conversions, such as promoting integer constants
to pointers.

Range checking, if turned on, is done on mathematical operations.
Array indices are not checked, since they are often used to index a
pointer that is not itself an array.

File: gdb.info, Node: Debugging C, Next: Debugging C Plus Plus, Prev: C Checks, Up: C

15.4.1.6 GDB and C
.................

The `set print union' and `show print union' commands apply to the
`union' type. When set to `on', any `union' that is inside a `struct'
or `class' is also printed. Otherwise, it appears as `{...}'.

The `@' operator aids in the debugging of dynamic arrays, formed
with pointers and a memory allocation function. *Note Expressions:
Expressions.

File: gdb.info, Node: Debugging C Plus Plus, Next: Decimal Floating Point, Prev: Debugging C, Up: C

15.4.1.7 GDB Features for C++
............................

Some GDB commands are particularly useful with C++, and some are
designed specifically for use with C++. Here is a summary:

`breakpoint menus'
When you want a breakpoint in a function whose name is overloaded,
GDB has the capability to display a menu of possible breakpoint
locations to help you specify which function definition you want.
*Note Ambiguous Expressions: Ambiguous Expressions.

`rbreak REGEX'
Setting breakpoints using regular expressions is helpful for
setting breakpoints on overloaded functions that are not members
of any special classes. *Note Setting Breakpoints: Set Breaks.

`catch throw'
`catch rethrow'
`catch catch'
Debug C++ exception handling using these commands. *Note Setting
Catchpoints: Set Catchpoints.

`ptype TYPENAME'
Print inheritance relationships as well as other information for
type TYPENAME. *Note Examining the Symbol Table: Symbols.

`info vtbl EXPRESSION.'
The `info vtbl' command can be used to display the virtual method
tables of the object computed by EXPRESSION. This shows one entry
per virtual table; there may be multiple virtual tables when
multiple inheritance is in use.

`demangle NAME'
Demangle NAME. *Note Symbols::, for a more complete description
of the `demangle' command.

`set print demangle'
`show print demangle'
`set print asm-demangle'
`show print asm-demangle'
Control whether C++ symbols display in their source form, both when
displaying code as C++ source and when displaying disassemblies.
*Note Print Settings: Print Settings.

`set print object'
`show print object'
Choose whether to print derived (actual) or declared types of
objects. *Note Print Settings: Print Settings.

`set print vtbl'
`show print vtbl'
Control the format for printing virtual function tables. *Note
Print Settings: Print Settings. (The `vtbl' commands do not work
on programs compiled with the HP ANSI C++ compiler (`aCC').)

`set overload-resolution on'
Enable overload resolution for C++ expression evaluation. The
default is on. For overloaded functions, GDB evaluates the
arguments and searches for a function whose signature matches the
argument types, using the standard C++ conversion rules (see *Note
C++ Expressions: C Plus Plus Expressions, for details). If it
cannot find a match, it emits a message.

`set overload-resolution off'
Disable overload resolution for C++ expression evaluation. For
overloaded functions that are not class member functions, GDB
chooses the first function of the specified name that it finds in
the symbol table, whether or not its arguments are of the correct
type. For overloaded functions that are class member functions,
GDB searches for a function whose signature _exactly_ matches the
argument types.

`show overload-resolution'
Show the current setting of overload resolution.

`Overloaded symbol names'
You can specify a particular definition of an overloaded symbol,
using the same notation that is used to declare such symbols in
C++: type `SYMBOL(TYPES)' rather than just SYMBOL. You can also
use the GDB command-line word completion facilities to list the
available choices, or to finish the type list for you. *Note
Command Completion: Completion, for details on how to do this.

`Breakpoints in template functions'
Similar to how overloaded symbols are handled, GDB will ignore
template parameter lists when it encounters a symbol which
includes a C++ template. This permits setting breakpoints on
families of template functions or functions whose parameters
include template types.

The `-qualified' flag may be used to override this behavior,
causing GDB to search for a specific function or type.

The GDB command-line word completion facility also understands
template parameters and may be used to list available choices or
finish template parameter lists for you. *Note Command Completion:
Completion, for details on how to do this.

`Breakpoints in functions with ABI tags'
The GNU C++ compiler introduced the notion of ABI "tags", which
correspond to changes in the ABI of a type, function, or variable
that would not otherwise be reflected in a mangled name. See
`https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/'
for more detail.

The ABI tags are visible in C++ demangled names. For example, a
function that returns a std::string:

std::string function(int);

when compiled for the C++11 ABI is marked with the `cxx11' ABI
tag, and GDB displays the symbol like this:

function[abi:cxx11](int)

You can set a breakpoint on such functions simply as if they had no
tag. For example:

(gdb) b function(int)
Breakpoint 2 at 0x40060d: file main.cc, line 10.
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x0040060d in function[abi:cxx11](int)
at main.cc:10

On the rare occasion you need to disambiguate between different ABI
tags, you can do so by simply including the ABI tag in the function
name, like:

(gdb) b ambiguous[abi:other_tag](int)

File: gdb.info, Node: Decimal Floating Point, Prev: Debugging C Plus Plus, Up: C

15.4.1.8 Decimal Floating Point format
.....................................

GDB can examine, set and perform computations with numbers in decimal
floating point format, which in the C language correspond to the
`_Decimal32', `_Decimal64' and `_Decimal128' types as specified by the
extension to support decimal floating-point arithmetic.

There are two encodings in use, depending on the architecture: BID
(Binary Integer Decimal) for x86 and x86-64, and DPD (Densely Packed
Decimal) for PowerPC and S/390. GDB will use the appropriate encoding
for the configured target.

Because of a limitation in `libdecnumber', the library used by GDB
to manipulate decimal floating point numbers, it is not possible to
convert (using a cast, for example) integers wider than 32-bit to
decimal float.

In addition, in order to imitate GDB's behaviour with binary floating
point computations, error checking in decimal float operations ignores
underflow, overflow and divide by zero exceptions.

In the PowerPC architecture, GDB provides a set of pseudo-registers
to inspect `_Decimal128' values stored in floating point registers.
See *Note PowerPC: PowerPC. for more details.

File: gdb.info, Node: D, Next: Go, Prev: C, Up: Supported Languages

15.4.2 D
--------

GDB can be used to debug programs written in D and compiled with GDC,
LDC or DMD compilers. Currently GDB supports only one D specific
feature -- dynamic arrays.

File: gdb.info, Node: Go, Next: Objective-C, Prev: D, Up: Supported Languages

15.4.3 Go
---------

GDB can be used to debug programs written in Go and compiled with
`gccgo' or `6g' compilers.

Here is a summary of the Go-specific features and restrictions:

`The current Go package'
The name of the current package does not need to be specified when
specifying global variables and functions.

For example, given the program:

package main
var myglob = "Shall we?"
func main () {
// ...
}

When stopped inside `main' either of these work:

(gdb) p myglob
(gdb) p main.myglob

`Builtin Go types'
The `string' type is recognized by GDB and is printed as a string.

`Builtin Go functions'
The GDB expression parser recognizes the `unsafe.Sizeof' function
and handles it internally.

`Restrictions on Go expressions'
All Go operators are supported except `&^'. The Go `_' "blank
identifier" is not supported. Automatic dereferencing of pointers
is not supported.

File: gdb.info, Node: Objective-C, Next: OpenCL C, Prev: Go, Up: Supported Languages

15.4.4 Objective-C
------------------

This section provides information about some commands and command
options that are useful for debugging Objective-C code. See also *Note
info classes: Symbols, and *Note info selectors: Symbols, for a few
more commands specific to Objective-C support.

* Menu:

* Method Names in Commands::
* The Print Command with Objective-C::

File: gdb.info, Node: Method Names in Commands, Next: The Print Command with Objective-C, Up: Objective-C

15.4.4.1 Method Names in Commands
................................

The following commands have been extended to accept Objective-C method
names as line specifications:

* `clear'

* `break'

* `info line'

* `jump'

* `list'

A fully qualified Objective-C method name is specified as

-[CLASS METHODNAME]

where the minus sign is used to indicate an instance method and a
plus sign (not shown) is used to indicate a class method. The class
name CLASS and method name METHODNAME are enclosed in brackets, similar
to the way messages are specified in Objective-C source code. For
example, to set a breakpoint at the `create' instance method of class
`Fruit' in the program currently being debugged, enter:

break -[Fruit create]

To list ten program lines around the `initialize' class method,
enter:

list +[NSText initialize]

In the current version of GDB, the plus or minus sign is required.
In future versions of GDB, the plus or minus sign will be optional, but
you can use it to narrow the search. It is also possible to specify
just a method name:

break create

You must specify the complete method name, including any colons. If
your program's source files contain more than one `create' method,
you'll be presented with a numbered list of classes that implement that
method. Indicate your choice by number, or type `0' to exit if none
apply.

As another example, to clear a breakpoint established at the
`makeKeyAndOrderFront:' method of the `NSWindow' class, enter:

clear -[NSWindow makeKeyAndOrderFront:]

File: gdb.info, Node: The Print Command with Objective-C, Prev: Method Names in Commands, Up: Objective-C

15.4.4.2 The Print Command With Objective-C
..........................................

The print command has also been extended to accept methods. For
example:

print -[OBJECT hash]

will tell GDB to send the `hash' message to OBJECT and print the
result. Also, an additional command has been added, `print-object' or
`po' for short, which is meant to print the description of an object.
However, this command may only work with certain Objective-C libraries
that have a particular hook function, `_NSPrintForDebugger', defined.

File: gdb.info, Node: OpenCL C, Next: Fortran, Prev: Objective-C, Up: Supported Languages

15.4.5 OpenCL C
---------------

This section provides information about GDBs OpenCL C support.

* Menu:

* OpenCL C Datatypes::
* OpenCL C Expressions::
* OpenCL C Operators::

File: gdb.info, Node: OpenCL C Datatypes, Next: OpenCL C Expressions, Up: OpenCL C

15.4.5.1 OpenCL C Datatypes
..........................

GDB supports the builtin scalar and vector datatypes specified by
OpenCL 1.1. In addition the half- and double-precision floating point
data types of the `cl_khr_fp16' and `cl_khr_fp64' OpenCL extensions are
also known to GDB.

File: gdb.info, Node: OpenCL C Expressions, Next: OpenCL C Operators, Prev: OpenCL C Datatypes, Up: OpenCL C

15.4.5.2 OpenCL C Expressions
............................

GDB supports accesses to vector components including the access as
lvalue where possible. Since OpenCL C is based on C99 most C
expressions supported by GDB can be used as well.

File: gdb.info, Node: OpenCL C Operators, Prev: OpenCL C Expressions, Up: OpenCL C

15.4.5.3 OpenCL C Operators
..........................

GDB supports the operators specified by OpenCL 1.1 for scalar and
vector data types.

File: gdb.info, Node: Fortran, Next: Pascal, Prev: OpenCL C, Up: Supported Languages

15.4.6 Fortran
--------------

GDB can be used to debug programs written in Fortran. Note, that not
all Fortran language features are available yet.

Some Fortran compilers (GNU Fortran 77 and Fortran 95 compilers
among them) append an underscore to the names of variables and
functions. When you debug programs compiled by those compilers, you
will need to refer to variables and functions with a trailing
underscore.

Fortran symbols are usually case-insensitive, so GDB by default uses
case-insensitive matching for Fortran symbols. You can change that
with the `set case-insensitive' command, see *Note Symbols::, for the
details.

* Menu:

* Fortran Types:: Fortran builtin types
* Fortran Operators:: Fortran operators and expressions
* Fortran Intrinsics:: Fortran intrinsic functions
* Special Fortran Commands:: Special GDB commands for Fortran

File: gdb.info, Node: Fortran Types, Next: Fortran Operators, Up: Fortran

15.4.6.1 Fortran Types
.....................

In Fortran the primitive data-types have an associated `KIND' type
parameter, written as `TYPE*KINDPARAM', `TYPE*KINDPARAM', or in the
GDB-only dialect `TYPE_KINDPARAM'. A concrete example would be
``Real*4'', ``Real(kind=4)'', and ``Real_4''. The kind of a type can
be retrieved by using the intrinsic function `KIND', see *Note Fortran
Intrinsics::.

Generally, the actual implementation of the `KIND' type parameter is
compiler specific. In GDB the kind parameter is implemented in
accordance with its use in the GNU `gfortran' compiler. Here, the kind
parameter for a given TYPE specifies its size in memory -- a Fortran
`Integer*4' or `Integer(kind=4)' would be an integer type occupying 4
bytes of memory. An exception to this rule is the `Complex' type for
which the kind of the type does not specify its entire size, but the
size of each of the two `Real''s it is composed of. A `Complex*4'
would thus consist of two `Real*4's and occupy 8 bytes of memory.

For every type there is also a default kind associated with it, e.g.
`Integer' in GDB will internally be an `Integer*4' (see the table below
for default types). The default types are the same as in GNU compilers
but note, that the GNU default types can actually be changed by
compiler flags such as `-fdefault-integer-8' and `-fdefault-real-8'.

Not every kind parameter is valid for every type and in GDB the
following type kinds are available.

`Integer'
`Integer*1', `Integer*2', `Integer*4', `Integer*8', and `Integer'
= `Integer*4'.

`Logical'
`Logical*1', `Logical*2', `Logical*4', `Logical*8', and `Logical'
= `Logical*4'.

`Real'
`Real*4', `Real*8', `Real*16', and `Real' = `Real*4'.

`Complex'
`Complex*4', `Complex*8', `Complex*16', and `Complex' =
`Complex*4'.

File: gdb.info, Node: Fortran Operators, Next: Fortran Intrinsics, Prev: Fortran Types, Up: Fortran

15.4.6.2 Fortran Operators and Expressions
.........................................

Operators must be defined on values of specific types. For instance,
`+' is defined on numbers, but not on characters or other non-
arithmetic types. Operators are often defined on groups of types.

`**'
The exponentiation operator. It raises the first operand to the
power of the second one.

`:'
The range operator. Normally used in the form of array(low:high)
to represent a section of array.

`%'
The access component operator. Normally used to access elements
in derived types. Also suitable for unions. As unions aren't
part of regular Fortran, this can only happen when accessing a
register that uses a gdbarch-defined union type.

`::'
The scope operator. Normally used to access variables in modules
or to set breakpoints on subroutines nested in modules or in other
subroutines (internal subroutines).

File: gdb.info, Node: Fortran Intrinsics, Next: Special Fortran Commands, Prev: Fortran Operators, Up: Fortran

15.4.6.3 Fortran Intrinsics
..........................

Fortran provides a large set of intrinsic procedures. GDB implements
an incomplete subset of those procedures and their overloads. Some of
these procedures take an optional `KIND' parameter, see *Note Fortran
Types::.

`ABS(A)'
Computes the absolute value of its argument A. Currently not
supported for `Complex' arguments.

`ALLOCATE(ARRAY)'
Returns whether ARRAY is allocated or not.

`ASSOCIATED(POINTER [, TARGET])'
Returns the association status of the pointer POINTER or, if TARGET
is present, whether POINTER is associated with the target TARGET.

`CEILING(A [, KIND])'
Computes the least integer greater than or equal to A. The
optional parameter KIND specifies the kind of the return type
`Integer(KIND)'.

`CMPLX(X [, Y [, KIND]])'
Returns a complex number where X is converted to the real
component. If Y is present it is converted to the imaginary
component. If Y is not present then the imaginary component is
set to `0.0' except if X itself is of `Complex' type. The
optional parameter KIND specifies the kind of the return type
`Complex(KIND)'.

`FLOOR(A [, KIND])'
Computes the greatest integer less than or equal to A. The
optional parameter KIND specifies the kind of the return type
`Integer(KIND)'.

`KIND(A)'
Returns the kind value of the argument A, see *Note Fortran
Types::.

`LBOUND(ARRAY [, DIM [, KIND]])'
Returns the lower bounds of an ARRAY, or a single lower bound
along the DIM dimension if present. The optional parameter KIND
specifies the kind of the return type `Integer(KIND)'.

`LOC(X)'
Returns the address of X as an `Integer'.

`MOD(A, P)'
Computes the remainder of the division of A by P.

`MODULO(A, P)'
Computes the A modulo P.

`RANK(A)'
Returns the rank of a scalar or array (scalars have rank `0').

`SHAPE(A)'
Returns the shape of a scalar or array (scalars have shape `()').

`SIZE(ARRAY[, DIM [, KIND]])'
Returns the extent of ARRAY along a specified dimension DIM, or the
total number of elements in ARRAY if DIM is absent. The optional
parameter KIND specifies the kind of the return type
`Integer(KIND)'.

`UBOUND(ARRAY [, DIM [, KIND]])'
Returns the upper bounds of an ARRAY, or a single upper bound
along the DIM dimension if present. The optional parameter KIND
specifies the kind of the return type `Integer(KIND)'.

File: gdb.info, Node: Special Fortran Commands, Prev: Fortran Intrinsics, Up: Fortran

15.4.6.4 Special Fortran Commands
................................

GDB has some commands to support Fortran-specific features, such as
displaying common blocks.

`info common [COMMON-NAME]'
This command prints the values contained in the Fortran `COMMON'
block whose name is COMMON-NAME. With no argument, the names of
all `COMMON' blocks visible at the current program location are
printed.

`set fortran repack-array-slices [on|off]'

`show fortran repack-array-slices'
When taking a slice from an array, a Fortran compiler can choose to
either produce an array descriptor that describes the slice in
place, or it may repack the slice, copying the elements of the
slice into a new region of memory.

When this setting is on, then GDB will also repack array slices in
some situations. When this setting is off, then GDB will create
array descriptors for slices that reference the original data in
place.

GDB will never repack an array slice if the data for the slice is
contiguous within the original array.

GDB will always repack string slices if the data for the slice is
non-contiguous within the original string as GDB does not support
printing non-contiguous strings.

The default for this setting is `off'.

File: gdb.info, Node: Pascal, Next: Rust, Prev: Fortran, Up: Supported Languages

15.4.7 Pascal
-------------

Debugging Pascal programs which use sets, subranges, file variables, or
nested functions does not currently work. GDB does not support
entering expressions, printing values, or similar features using Pascal
syntax.

The Pascal-specific command `set print pascal_static-members'
controls whether static members of Pascal objects are displayed. *Note
pascal_static-members: Print Settings.

File: gdb.info, Node: Rust, Next: Modula-2, Prev: Pascal, Up: Supported Languages

15.4.8 Rust
-----------

GDB supports the Rust Programming Language
(https://www.rust-lang.org/). Type- and value-printing, and expression
parsing, are reasonably complete. However, there are a few
peculiarities and holes to be aware of.

* Linespecs (*note Location Specifications::) are never relative to
the current crate. Instead, they act as if there were a global
namespace of crates, somewhat similar to the way `extern crate'
behaves.

That is, if GDB is stopped at a breakpoint in a function in crate
`A', module `B', then `break B::f' will attempt to set a
breakpoint in a function named `f' in a crate named `B'.

As a consequence of this approach, linespecs also cannot refer to
items using `self::' or `super::'.

* Because GDB implements Rust name-lookup semantics in expressions,
it will sometimes prepend the current crate to a name. For
example, if GDB is stopped at a breakpoint in the crate `K', then
`print ::x::y' will try to find the symbol `K::x::y'.

However, since it is useful to be able to refer to other crates
when debugging, GDB provides the `extern' extension to circumvent
this. To use the extension, just put `extern' before a path
expression to refer to the otherwise unavailable "global" scope.

In the above example, if you wanted to refer to the symbol `y' in
the crate `x', you would use `print extern x::y'.

* The Rust expression evaluator does not support "statement-like"
expressions such as `if' or `match', or lambda expressions.

* Tuple expressions are not implemented.

* The Rust expression evaluator does not currently implement the
`Drop' trait. Objects that may be created by the evaluator will
never be destroyed.

* GDB does not implement type inference for generics. In order to
call generic functions or otherwise refer to generic items, you
will have to specify the type parameters manually.

* GDB currently uses the C++ demangler for Rust. In most cases this
does not cause any problems. However, in an expression context,
completing a generic function name will give syntactically invalid
results. This happens because Rust requires the `::' operator
between the function name and its generic arguments. For example,
GDB might provide a completion like `crate::f<u32>', where the
parser would require `crate::f::<u32>'.

* As of this writing, the Rust compiler (version 1.8) has a few
holes in the debugging information it generates. These holes
prevent certain features from being implemented by GDB:
* Method calls cannot be made via traits.

* Operator overloading is not implemented.

* When debugging in a monomorphized function, you cannot use
the generic type names.

* The type `Self' is not available.

* `use' statements are not available, so some names may not be
available in the crate.

File: gdb.info, Node: Modula-2, Next: Ada, Prev: Rust, Up: Supported Languages

15.4.9 Modula-2
---------------

The extensions made to GDB to support Modula-2 only support output from
the GNU Modula-2 compiler (which is currently being developed). Other
Modula-2 compilers are not currently supported, and attempting to debug
executables produced by them is most likely to give an error as GDB
reads in the executable's symbol table.

* Menu:

* M2 Operators:: Built-in operators
* Built-In Func/Proc:: Built-in functions and procedures
* M2 Constants:: Modula-2 constants
* M2 Types:: Modula-2 types
* M2 Defaults:: Default settings for Modula-2
* Deviations:: Deviations from standard Modula-2
* M2 Checks:: Modula-2 type and range checks
* M2 Scope:: The scope operators `::' and `.'
* GDB/M2:: GDB and Modula-2

File: gdb.info, Node: M2 Operators, Next: Built-In Func/Proc, Up: Modula-2

15.4.9.1 Operators
.................

Operators must be defined on values of specific types. For instance,
`+' is defined on numbers, but not on structures. Operators are often
defined on groups of types. For the purposes of Modula-2, the
following definitions hold:

* _Integral types_ consist of `INTEGER', `CARDINAL', and their
subranges.

* _Character types_ consist of `CHAR' and its subranges.

* _Floating-point types_ consist of `REAL'.

* _Pointer types_ consist of anything declared as `POINTER TO TYPE'.

* _Scalar types_ consist of all of the above.

* _Set types_ consist of `SET' and `BITSET' types.

* _Boolean types_ consist of `BOOLEAN'.

The following operators are supported, and appear in order of
increasing precedence:

`,'
Function argument or array index separator.

`:='
Assignment. The value of VAR `:=' VALUE is VALUE.

`<, >'
Less than, greater than on integral, floating-point, or enumerated
types.

`<=, >='
Less than or equal to, greater than or equal to on integral,
floating-point and enumerated types, or set inclusion on set
types. Same precedence as `<'.

`=, <>, #'
Equality and two ways of expressing inequality, valid on scalar
types. Same precedence as `<'. In GDB scripts, only `<>' is
available for inequality, since `#' conflicts with the script
comment character.

`IN'
Set membership. Defined on set types and the types of their
members. Same precedence as `<'.

`OR'
Boolean disjunction. Defined on boolean types.

`AND, &'
Boolean conjunction. Defined on boolean types.

`@'
The GDB "artificial array" operator (*note Expressions:
Expressions.).

`+, -'
Addition and subtraction on integral and floating-point types, or
union and difference on set types.

`*'
Multiplication on integral and floating-point types, or set
intersection on set types.

`/'
Division on floating-point types, or symmetric set difference on
set types. Same precedence as `*'.

`DIV, MOD'
Integer division and remainder. Defined on integral types. Same
precedence as `*'.

`-'
Negative. Defined on `INTEGER' and `REAL' data.

`^'
Pointer dereferencing. Defined on pointer types.

`NOT'
Boolean negation. Defined on boolean types. Same precedence as
`^'.

`.'
`RECORD' field selector. Defined on `RECORD' data. Same
precedence as `^'.

`[]'
Array indexing. Defined on `ARRAY' data. Same precedence as `^'.

`()'
Procedure argument list. Defined on `PROCEDURE' objects. Same
precedence as `^'.

`::, .'
GDB and Modula-2 scope operators.

_Warning:_ Set expressions and their operations are not yet
supported, so GDB treats the use of the operator `IN', or the use
of operators `+', `-', `*', `/', `=', , `<>', `#', `<=', and `>='
on sets as an error.

File: gdb.info, Node: Built-In Func/Proc, Next: M2 Constants, Prev: M2 Operators, Up: Modula-2

15.4.9.2 Built-in Functions and Procedures
.........................................

Modula-2 also makes available several built-in procedures and functions.
In describing these, the following metavariables are used:

A
represents an `ARRAY' variable.

C
represents a `CHAR' constant or variable.

I
represents a variable or constant of integral type.

M
represents an identifier that belongs to a set. Generally used in
the same function with the metavariable S. The type of S should
be `SET OF MTYPE' (where MTYPE is the type of M).

N
represents a variable or constant of integral or floating-point
type.

R
represents a variable or constant of floating-point type.

T
represents a type.

V
represents a variable.

X
represents a variable or constant of one of many types. See the
explanation of the function for details.

All Modula-2 built-in procedures also return a result, described
below.

`ABS(N)'
Returns the absolute value of N.

`CAP(C)'
If C is a lower case letter, it returns its upper case equivalent,
otherwise it returns its argument.

`CHR(I)'
Returns the character whose ordinal value is I.

`DEC(V)'
Decrements the value in the variable V by one. Returns the new
value.

`DEC(V,I)'
Decrements the value in the variable V by I. Returns the new
value.

`EXCL(M,S)'
Removes the element M from the set S. Returns the new set.

`FLOAT(I)'
Returns the floating point equivalent of the integer I.

`HIGH(A)'
Returns the index of the last member of A.

`INC(V)'
Increments the value in the variable V by one. Returns the new
value.

`INC(V,I)'
Increments the value in the variable V by I. Returns the new
value.

`INCL(M,S)'
Adds the element M to the set S if it is not already there.
Returns the new set.

`MAX(T)'
Returns the maximum value of the type T.

`MIN(T)'
Returns the minimum value of the type T.

`ODD(I)'
Returns boolean TRUE if I is an odd number.

`ORD(X)'
Returns the ordinal value of its argument. For example, the
ordinal value of a character is its ASCII value (on machines
supporting the ASCII character set). The argument X must be of an
ordered type, which include integral, character and enumerated
types.

`SIZE(X)'
Returns the size of its argument. The argument X can be a
variable or a type.

`TRUNC(R)'
Returns the integral part of R.

`TSIZE(X)'
Returns the size of its argument. The argument X can be a
variable or a type.

`VAL(T,I)'
Returns the member of the type T whose ordinal value is I.

_Warning:_ Sets and their operations are not yet supported, so
GDB treats the use of procedures `INCL' and `EXCL' as an error.

File: gdb.info, Node: M2 Constants, Next: M2 Types, Prev: Built-In Func/Proc, Up: Modula-2

15.4.9.3 Constants
.................

GDB allows you to express the constants of Modula-2 in the following
ways:

* Integer constants are simply a sequence of digits. When used in an
expression, a constant is interpreted to be type-compatible with
the rest of the expression. Hexadecimal integers are specified by
a trailing `H', and octal integers by a trailing `B'.

* Floating point constants appear as a sequence of digits, followed
by a decimal point and another sequence of digits. An optional
exponent can then be specified, in the form `E[+|-]NNN', where
`[+|-]NNN' is the desired exponent. All of the digits of the
floating point constant must be valid decimal (base 10) digits.

* Character constants consist of a single character enclosed by a
pair of like quotes, either single (`'') or double (`"'). They may
also be expressed by their ordinal value (their ASCII value,
usually) followed by a `C'.

* String constants consist of a sequence of characters enclosed by a
pair of like quotes, either single (`'') or double (`"'). Escape
sequences in the style of C are also allowed. *Note C and C++
Constants: C Constants, for a brief explanation of escape
sequences.

* Enumerated constants consist of an enumerated identifier.

* Boolean constants consist of the identifiers `TRUE' and `FALSE'.

* Pointer constants consist of integral values only.

* Set constants are not yet supported.

File: gdb.info, Node: M2 Types, Next: M2 Defaults, Prev: M2 Constants, Up: Modula-2

15.4.9.4 Modula-2 Types
......................

Currently GDB can print the following data types in Modula-2 syntax:
array types, record types, set types, pointer types, procedure types,
enumerated types, subrange types and base types. You can also print
the contents of variables declared using these type. This section
gives a number of simple source code examples together with sample GDB
sessions.

The first example contains the following section of code:

VAR
s: SET OF CHAR ;
r: [20..40] ;

and you can request GDB to interrogate the type and value of `r' and
`s'.

(gdb) print s
{'A'..'C', 'Z'}
(gdb) ptype s
SET OF CHAR
(gdb) print r
21
(gdb) ptype r
[20..40]

Likewise if your source code declares `s' as:

VAR
s: SET ['A'..'Z'] ;

then you may query the type of `s' by:

(gdb) ptype s
type = SET ['A'..'Z']

Note that at present you cannot interactively manipulate set
expressions using the debugger.

The following example shows how you might declare an array in
Modula-2 and how you can interact with GDB to print its type and
contents:

VAR
s: ARRAY [-10..10] OF CHAR ;

(gdb) ptype s
ARRAY [-10..10] OF CHAR

Note that the array handling is not yet complete and although the
type is printed correctly, expression handling still assumes that all
arrays have a lower bound of zero and not `-10' as in the example above.

Here are some more type related Modula-2 examples:

TYPE
colour = (blue, red, yellow, green) ;
t = [blue..yellow] ;
VAR
s: t ;
BEGIN
s := blue ;

The GDB interaction shows how you can query the data type and value of
a variable.

(gdb) print s
$1 = blue
(gdb) ptype t
type = [blue..yellow]

In this example a Modula-2 array is declared and its contents
displayed. Observe that the contents are written in the same way as
their `C' counterparts.

VAR
s: ARRAY [1..5] OF CARDINAL ;
BEGIN
s[1] := 1 ;

(gdb) print s
$1 = {1, 0, 0, 0, 0}
(gdb) ptype s
type = ARRAY [1..5] OF CARDINAL

The Modula-2 language interface to GDB also understands pointer
types as shown in this example:

VAR
s: POINTER TO ARRAY [1..5] OF CARDINAL ;
BEGIN
NEW(s) ;
s^[1] := 1 ;

and you can request that GDB describes the type of `s'.

(gdb) ptype s
type = POINTER TO ARRAY [1..5] OF CARDINAL

GDB handles compound types as we can see in this example. Here we
combine array types, record types, pointer types and subrange types:

TYPE
foo = RECORD
f1: CARDINAL ;
f2: CHAR ;
f3: myarray ;
END ;

myarray = ARRAY myrange OF CARDINAL ;
myrange = [-2..2] ;
VAR
s: POINTER TO ARRAY myrange OF foo ;

and you can ask GDB to describe the type of `s' as shown below.

(gdb) ptype s
type = POINTER TO ARRAY [-2..2] OF foo = RECORD
f1 : CARDINAL;
f2 : CHAR;
f3 : ARRAY [-2..2] OF CARDINAL;
END

File: gdb.info, Node: M2 Defaults, Next: Deviations, Prev: M2 Types, Up: Modula-2

15.4.9.5 Modula-2 Defaults
.........................

If type and range checking are set automatically by GDB, they both
default to `on' whenever the working language changes to Modula-2.
This happens regardless of whether you or GDB selected the working
language.

If you allow GDB to set the language automatically, then entering
code compiled from a file whose name ends with `.mod' sets the working
language to Modula-2. *Note Having GDB Infer the Source Language:
Automatically, for further details.

File: gdb.info, Node: Deviations, Next: M2 Checks, Prev: M2 Defaults, Up: Modula-2

15.4.9.6 Deviations from Standard Modula-2
.........................................

A few changes have been made to make Modula-2 programs easier to debug.
This is done primarily via loosening its type strictness:

* Unlike in standard Modula-2, pointer constants can be formed by
integers. This allows you to modify pointer variables during
debugging. (In standard Modula-2, the actual address contained in
a pointer variable is hidden from you; it can only be modified
through direct assignment to another pointer variable or
expression that returned a pointer.)

* C escape sequences can be used in strings and characters to
represent non-printable characters. GDB prints out strings with
these escape sequences embedded. Single non-printable characters
are printed using the `CHR(NNN)' format.

* The assignment operator (`:=') returns the value of its right-hand
argument.

* All built-in procedures both modify _and_ return their argument.

File: gdb.info, Node: M2 Checks, Next: M2 Scope, Prev: Deviations, Up: Modula-2

15.4.9.7 Modula-2 Type and Range Checks
......................................

_Warning:_ in this release, GDB does not yet perform type or range
checking.

GDB considers two Modula-2 variables type equivalent if:

* They are of types that have been declared equivalent via a `TYPE
T1 = T2' statement

* They have been declared on the same line. (Note: This is true of
the GNU Modula-2 compiler, but it may not be true of other
compilers.)

As long as type checking is enabled, any attempt to combine variables
whose types are not equivalent is an error.

Range checking is done on all mathematical operations, assignment,
array index bounds, and all built-in functions and procedures.

File: gdb.info, Node: M2 Scope, Next: GDB/M2, Prev: M2 Checks, Up: Modula-2

15.4.9.8 The Scope Operators `::' and `.'
........................................

There are a few subtle differences between the Modula-2 scope operator
(`.') and the GDB scope operator (`::'). The two have similar syntax:

MODULE . ID
SCOPE :: ID

where SCOPE is the name of a module or a procedure, MODULE the name of
a module, and ID is any declared identifier within your program, except
another module.

Using the `::' operator makes GDB search the scope specified by
SCOPE for the identifier ID. If it is not found in the specified
scope, then GDB searches all scopes enclosing the one specified by
SCOPE.

Using the `.' operator makes GDB search the current scope for the
identifier specified by ID that was imported from the definition module
specified by MODULE. With this operator, it is an error if the
identifier ID was not imported from definition module MODULE, or if ID
is not an identifier in MODULE.

File: gdb.info, Node: GDB/M2, Prev: M2 Scope, Up: Modula-2

15.4.9.9 GDB and Modula-2
........................

Some GDB commands have little use when debugging Modula-2 programs.
Five subcommands of `set print' and `show print' apply specifically to
C and C++: `vtbl', `demangle', `asm-demangle', `object', and `union'.
The first four apply to C++, and the last to the C `union' type, which
has no direct analogue in Modula-2.

The `@' operator (*note Expressions: Expressions.), while available
with any language, is not useful with Modula-2. Its intent is to aid
the debugging of "dynamic arrays", which cannot be created in Modula-2
as they can in C or C++. However, because an address can be specified
by an integral constant, the construct `{TYPE}ADREXP' is still useful.

In GDB scripts, the Modula-2 inequality operator `#' is interpreted
as the beginning of a comment. Use `<>' instead.

File: gdb.info, Node: Ada, Prev: Modula-2, Up: Supported Languages

15.4.10 Ada
-----------

The extensions made to GDB for Ada only support output from the GNU Ada
(GNAT) compiler. Other Ada compilers are not currently supported, and
attempting to debug executables produced by them is most likely to be
difficult.

* Menu:

* Ada Mode Intro:: General remarks on the Ada syntax
and semantics supported by Ada mode
in GDB.
* Omissions from Ada:: Restrictions on the Ada expression syntax.
* Additions to Ada:: Extensions of the Ada expression syntax.
* Overloading support for Ada:: Support for expressions involving overloaded
subprograms.
* Stopping Before Main Program:: Debugging the program during elaboration.
* Ada Exceptions:: Ada Exceptions
* Ada Tasks:: Listing and setting breakpoints in tasks.
* Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
* Ravenscar Profile:: Tasking Support when using the Ravenscar
Profile
* Ada Source Character Set:: Character set of Ada source files.
* Ada Glitches:: Known peculiarities of Ada mode.

File: gdb.info, Node: Ada Mode Intro, Next: Omissions from Ada, Up: Ada

15.4.10.1 Introduction
.....................

The Ada mode of GDB supports a fairly large subset of Ada expression
syntax, with some extensions. The philosophy behind the design of this
subset is

* That GDB should provide basic literals and access to operations for
arithmetic, dereferencing, field selection, indexing, and
subprogram calls, leaving more sophisticated computations to
subprograms written into the program (which therefore may be
called from GDB).

* That type safety and strict adherence to Ada language restrictions
are not particularly important to the GDB user.

* That brevity is important to the GDB user.

Thus, for brevity, the debugger acts as if all names declared in
user-written packages are directly visible, even if they are not visible
according to Ada rules, thus making it unnecessary to fully qualify most
names with their packages, regardless of context. Where this causes
ambiguity, GDB asks the user's intent.

The debugger will start in Ada mode if it detects an Ada main
program. As for other languages, it will enter Ada mode when stopped
in a program that was translated from an Ada source file.

While in Ada mode, you may use `-' for comments. This is useful
mostly for documenting command files. The standard GDB comment (`#')
still works at the beginning of a line in Ada mode, but not in the
middle (to allow based literals).

File: gdb.info, Node: Omissions from Ada, Next: Additions to Ada, Prev: Ada Mode Intro, Up: Ada

15.4.10.2 Omissions from Ada
...........................

Here are the notable omissions from the subset:

* Only a subset of the attributes are supported:

- 'First, 'Last, and 'Length on array objects (not on types
and subtypes).

- 'Min and 'Max.

- 'Pos and 'Val.

- 'Tag.

- 'Range on array objects (not subtypes), but only as the right
operand of the membership (`in') operator.

- 'Access, 'Unchecked_Access, and 'Unrestricted_Access (a GNAT
extension).

- 'Address.

* The names in `Characters.Latin_1' are not available.

* Equality tests (`=' and `/=') on arrays test for bitwise equality
of representations. They will generally work correctly for
strings and arrays whose elements have integer or enumeration
types. They may not work correctly for arrays whose element types
have user-defined equality, for arrays of real values (in
particular, IEEE-conformant floating point, because of negative
zeroes and NaNs), and for arrays whose elements contain unused
bits with indeterminate values.

* The other component-by-component array operations (`and', `or',
`xor', `not', and relational tests other than equality) are not
implemented.

* There is limited support for array and record aggregates. They are
permitted only on the right sides of assignments, as in these
examples:

(gdb) set An_Array := (1, 2, 3, 4, 5, 6)
(gdb) set An_Array := (1, others => 0)
(gdb) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
(gdb) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
(gdb) set A_Record := (1, "Peter", True);
(gdb) set A_Record := (Name => "Peter", Id => 1, Alive => True)

Changing a discriminant's value by assigning an aggregate has an
undefined effect if that discriminant is used within the record.
However, you can first modify discriminants by directly assigning
to them (which normally would not be allowed in Ada), and then
performing an aggregate assignment. For example, given a variable
`A_Rec' declared to have a type such as:

type Rec (Len : Small_Integer := 0) is record
Id : Integer;
Vals : IntArray (1 .. Len);
end record;

you can assign a value with a different size of `Vals' with two
assignments:

(gdb) set A_Rec.Len := 4
(gdb) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))

As this example also illustrates, GDB is very loose about the usual
rules concerning aggregates. You may leave out some of the
components of an array or record aggregate (such as the `Len'
component in the assignment to `A_Rec' above); they will retain
their original values upon assignment. You may freely use dynamic
values as indices in component associations. You may even use
overlapping or redundant component associations, although which
component values are assigned in such cases is not defined.

* Calls to dispatching subprograms are not implemented.

* The overloading algorithm is much more limited (i.e., less
selective) than that of real Ada. It makes only limited use of
the context in which a subexpression appears to resolve its
meaning, and it is much looser in its rules for allowing type
matches. As a result, some function calls will be ambiguous, and
the user will be asked to choose the proper resolution.

* The `new' operator is not implemented.

* Entry calls are not implemented.

* Aside from printing, arithmetic operations on the native VAX
floating-point formats are not supported.

* It is not possible to slice a packed array.

* The names `True' and `False', when not part of a qualified name,
are interpreted as if implicitly prefixed by `Standard',
regardless of context. Should your program redefine these names
in a package or procedure (at best a dubious practice), you will
have to use fully qualified names to access their new definitions.

* Based real literals are not implemented.

File: gdb.info, Node: Additions to Ada, Next: Overloading support for Ada, Prev: Omissions from Ada, Up: Ada

15.4.10.3 Additions to Ada
.........................

As it does for other languages, GDB makes certain generic extensions to
Ada (*note Expressions::):

* If the expression E is a variable residing in memory (typically a
local variable or array element) and N is a positive integer, then
`E@N' displays the values of E and the N-1 adjacent variables
following it in memory as an array. In Ada, this operator is
generally not necessary, since its prime use is in displaying
parts of an array, and slicing will usually do this in Ada.
However, there are occasional uses when debugging programs in
which certain debugging information has been optimized away.

* `B::VAR' means "the variable named VAR that appears in function or
file B." When B is a file name, you must typically surround it in
single quotes.

* The expression `{TYPE} ADDR' means "the variable of type TYPE that
appears at address ADDR."

* A name starting with `$' is a convenience variable (*note
Convenience Vars::) or a machine register (*note Registers::).

In addition, GDB provides a few other shortcuts and outright
additions specific to Ada:

* The assignment statement is allowed as an expression, returning
its right-hand operand as its value. Thus, you may enter

(gdb) set x := y + 3
(gdb) print A(tmp := y + 1)

* The semicolon is allowed as an "operator," returning as its value
the value of its right-hand operand. This allows, for example,
complex conditional breaks:

(gdb) break f
(gdb) condition 1 (report(i); k += 1; A(k) > 100)

* An extension to based literals can be used to specify the exact
byte contents of a floating-point literal. After the base, you
can use from zero to two `l' characters, followed by an `f'. The
number of `l' characters controls the width of the resulting real
constant: zero means `Float' is used, one means `Long_Float', and
two means `Long_Long_Float'.

(gdb) print 16f#41b80000#
$1 = 23.0

* Rather than use catenation and symbolic character names to
introduce special characters into strings, one may instead use a
special bracket notation, which is also used to print strings. A
sequence of characters of the form `["XX"]' within a string or
character literal denotes the (single) character whose numeric
encoding is XX in hexadecimal. The sequence of characters `["""]'
also denotes a single quotation mark in strings. For example,
"One line.["0a"]Next line.["0a"]"
contains an ASCII newline character (`Ada.Characters.Latin_1.LF')
after each period.

* The subtype used as a prefix for the attributes 'Pos, 'Min, and
'Max is optional (and is ignored in any case). For example, it is
valid to write

(gdb) print 'max(x, y)

* When printing arrays, GDB uses positional notation when the array
has a lower bound of 1, and uses a modified named notation
otherwise. For example, a one-dimensional array of three integers
with a lower bound of 3 might print as

(3 => 10, 17, 1)

That is, in contrast to valid Ada, only the first component has a
`=>' clause.

* You may abbreviate attributes in expressions with any unique,
multi-character subsequence of their names (an exact match gets
preference). For example, you may use a'len, a'gth, or a'lh in
place of a'length.

* Since Ada is case-insensitive, the debugger normally maps
identifiers you type to lower case. The GNAT compiler uses
upper-case characters for some of its internal identifiers, which
are normally of no interest to users. For the rare occasions when
you actually have to look at them, enclose them in angle brackets
to avoid the lower-case mapping. For example,
(gdb) print <JMPBUF_SAVE>[0]

* Printing an object of class-wide type or dereferencing an
access-to-class-wide value will display all the components of the
object's specific type (as indicated by its run-time tag).
Likewise, component selection on such a value will operate on the
specific type of the object.

File: gdb.info, Node: Overloading support for Ada, Next: Stopping Before Main Program, Prev: Additions to Ada, Up: Ada

15.4.10.4 Overloading support for Ada
....................................

The debugger supports limited overloading. Given a subprogram call in
which the function symbol has multiple definitions, it will use the
number of actual parameters and some information about their types to
attempt to narrow the set of definitions. It also makes very limited
use of context, preferring procedures to functions in the context of
the `call' command, and functions to procedures elsewhere.

If, after narrowing, the set of matching definitions still contains
more than one definition, GDB will display a menu to query which one it
should use, for instance:

(gdb) print f(1)
Multiple matches for f
[0] cancel
[1] foo.f (integer) return boolean at foo.adb:23
[2] foo.f (foo.new_integer) return boolean at foo.adb:28
>

In this case, just select one menu entry either to cancel expression
evaluation (type `0' and press <RET>) or to continue evaluation with a
specific instance (type the corresponding number and press <RET>).

Here are a couple of commands to customize GDB's behavior in this
case:

`set ada print-signatures'
Control whether parameter types and return types are displayed in
overloads selection menus. It is `on' by default. *Note
Overloading support for Ada::.

`show ada print-signatures'
Show the current setting for displaying parameter types and return
types in overloads selection menu. *Note Overloading support for
Ada::.

File: gdb.info, Node: Stopping Before Main Program, Next: Ada Exceptions, Prev: Overloading support for Ada, Up: Ada

15.4.10.5 Stopping at the Very Beginning
.......................................

It is sometimes necessary to debug the program during elaboration, and
before reaching the main procedure. As defined in the Ada Reference
Manual, the elaboration code is invoked from a procedure called
`adainit'. To run your program up to the beginning of elaboration,
simply use the following two commands: `tbreak adainit' and `run'.

File: gdb.info, Node: Ada Exceptions, Next: Ada Tasks, Prev: Stopping Before Main Program, Up: Ada

15.4.10.6 Ada Exceptions
.......................

A command is provided to list all Ada exceptions:

`info exceptions'
`info exceptions REGEXP'
The `info exceptions' command allows you to list all Ada exceptions
defined within the program being debugged, as well as their
addresses. With a regular expression, REGEXP, as argument, only
those exceptions whose names match REGEXP are listed.

Below is a small example, showing how the command can be used, first
without argument, and next with a regular expression passed as an
argument.

(gdb) info exceptions
All defined Ada exceptions:
constraint_error: 0x613da0
program_error: 0x613d20
storage_error: 0x613ce0
tasking_error: 0x613ca0
const.aint_global_e: 0x613b00
(gdb) info exceptions const.aint
All Ada exceptions matching regular expression "const.aint":
constraint_error: 0x613da0
const.aint_global_e: 0x613b00

It is also possible to ask GDB to stop your program's execution when
an exception is raised. For more details, see *Note Set Catchpoints::.

File: gdb.info, Node: Ada Tasks, Next: Ada Tasks and Core Files, Prev: Ada Exceptions, Up: Ada

15.4.10.7 Extensions for Ada Tasks
.................................

Support for Ada tasks is analogous to that for threads (*note
Threads::). GDB provides the following task-related commands:

`info tasks'
This command shows a list of current Ada tasks, as in the
following example:

(gdb) info tasks
ID TID P-ID Pri State Name
1 8088000 0 15 Child Activation Wait main_task
2 80a4000 1 15 Accept Statement b
3 809a800 1 15 Child Activation Wait a
* 4 80ae800 3 15 Runnable c

In this listing, the asterisk before the last task indicates it to
be the task currently being inspected.

ID
Represents GDB's internal task number.

TID
The Ada task ID.

P-ID
The parent's task ID (GDB's internal task number).

Pri
The base priority of the task.

State
Current state of the task.

`Unactivated'
The task has been created but has not been activated.
It cannot be executing.

`Runnable'
The task is not blocked for any reason known to Ada.
(It may be waiting for a mutex, though.) It is
conceptually "executing" in normal mode.

`Terminated'
The task is terminated, in the sense of ARM 9.3 (5).
Any dependents that were waiting on terminate
alternatives have been awakened and have terminated
themselves.

`Child Activation Wait'
The task is waiting for created tasks to complete
activation.

`Accept or Select Term'
The task is waiting on an accept or selective wait
statement.

`Waiting on entry call'
The task is waiting on an entry call.

`Async Select Wait'
The task is waiting to start the abortable part of an
asynchronous select statement.

`Delay Sleep'
The task is waiting on a select statement with only a
delay alternative open.

`Child Termination Wait'
The task is sleeping having completed a master within
itself, and is waiting for the tasks dependent on that
master to become terminated or waiting on a terminate
Phase.

`Wait Child in Term Alt'
The task is sleeping waiting for tasks on terminate
alternatives to finish terminating.

`Asynchronous Hold'
The task has been held by
`Ada.Asynchronous_Task_Control.Hold_Task'.

`Activating'
The task has been created and is being made runnable.

`Selective Wait'
The task is waiting in a selective wait statement.

`Accepting RV with TASKNO'
The task is accepting a rendez-vous with the task TASKNO.

`Waiting on RV with TASKNO'
The task is waiting for a rendez-vous with the task
TASKNO.

Name
Name of the task in the program.

`info task TASKNO'
This command shows detailed information on the specified task, as
in the following example:
(gdb) info tasks
ID TID P-ID Pri State Name
1 8077880 0 15 Child Activation Wait main_task
* 2 807c468 1 15 Runnable task_1
(gdb) info task 2
Ada Task: 0x807c468
Name: "task_1"
Thread: 0
LWP: 0x1fac
Parent: 1 ("main_task")
Base Priority: 15
State: Runnable

`task'
This command prints the ID and name of the current task.

(gdb) info tasks
ID TID P-ID Pri State Name
1 8077870 0 15 Child Activation Wait main_task
* 2 807c458 1 15 Runnable some_task
(gdb) task
[Current task is 2 "some_task"]

`task TASKNO'
This command is like the `thread THREAD-ID' command (*note
Threads::). It switches the context of debugging from the current
task to the given task.

(gdb) info tasks
ID TID P-ID Pri State Name
1 8077870 0 15 Child Activation Wait main_task
* 2 807c458 1 15 Runnable some_task
(gdb) task 1
[Switching to task 1 "main_task"]
#0 0x8067726 in pthread_cond_wait ()
(gdb) bt
#0 0x8067726 in pthread_cond_wait ()
#1 0x8056714 in system.os_interface.pthread_cond_wait ()
#2 0x805cb63 in system.task_primitives.operations.sleep ()
#3 0x806153e in system.tasking.stages.activate_tasks ()
#4 0x804aacc in un () at un.adb:5

`task apply [TASK-ID-LIST | all] [FLAG]... COMMAND'
The `task apply' command is the Ada tasking analogue of `thread
apply' (*note Threads::). It allows you to apply the named
COMMAND to one or more tasks. Specify the tasks that you want
affected using a list of task IDs, or specify `all' to apply to
all tasks.

The FLAG arguments control what output to produce and how to
handle errors raised when applying COMMAND to a task. FLAG must
start with a `-' directly followed by one letter in `qcs'. If
several flags are provided, they must be given individually, such
as `-c -q'.

By default, GDB displays some task information before the output
produced by COMMAND, and an error raised during the execution of a
COMMAND will abort `task apply'. The following flags can be used
to fine-tune this behavior:

`-c'
The flag `-c', which stands for `continue', causes any errors
in COMMAND to be displayed, and the execution of `task apply'
then continues.

`-s'
The flag `-s', which stands for `silent', causes any errors
or empty output produced by a COMMAND to be silently ignored.
That is, the execution continues, but the task information
and errors are not printed.

`-q'
The flag `-q' (`quiet') disables printing the task
information.

Flags `-c' and `-s' cannot be used together.

`break LOCSPEC task TASKNO'
`break LOCSPEC task TASKNO if ...'
These commands are like the `break ... thread ...' command (*note
Thread Stops::). *Note Location Specifications::, for the various
forms of LOCSPEC.

Use the qualifier `task TASKNO' with a breakpoint command to
specify that you only want GDB to stop the program when a
particular Ada task reaches this breakpoint. The TASKNO is one of
the numeric task identifiers assigned by GDB, shown in the first
column of the `info tasks' display.

If you do not specify `task TASKNO' when you set a breakpoint, the
breakpoint applies to _all_ tasks of your program.

You can use the `task' qualifier on conditional breakpoints as
well; in this case, place `task TASKNO' before the breakpoint
condition (before the `if').

For example,

(gdb) info tasks
ID TID P-ID Pri State Name
1 140022020 0 15 Child Activation Wait main_task
2 140045060 1 15 Accept/Select Wait t2
3 140044840 1 15 Runnable t1
* 4 140056040 1 15 Runnable t3
(gdb) b 15 task 2
Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
(gdb) cont
Continuing.
task # 1 running
task # 2 running

Breakpoint 5, test_task_debug () at test_task_debug.adb:15
15 flush;
(gdb) info tasks
ID TID P-ID Pri State Name
1 140022020 0 15 Child Activation Wait main_task
* 2 140045060 1 15 Runnable t2
3 140044840 1 15 Runnable t1
4 140056040 1 15 Delay Sleep t3

File: gdb.info, Node: Ada Tasks and Core Files, Next: Ravenscar Profile, Prev: Ada Tasks, Up: Ada

15.4.10.8 Tasking Support when Debugging Core Files
..................................................

When inspecting a core file, as opposed to debugging a live program,
tasking support may be limited or even unavailable, depending on the
platform being used. For instance, on x86-linux, the list of tasks is
available, but task switching is not supported.

On certain platforms, the debugger needs to perform some memory
writes in order to provide Ada tasking support. When inspecting a core
file, this means that the core file must be opened with read-write
privileges, using the command `"set write on"' (*note Patching::).
Under these circumstances, you should make a backup copy of the core
file before inspecting it with GDB.

File: gdb.info, Node: Ravenscar Profile, Next: Ada Source Character Set, Prev: Ada Tasks and Core Files, Up: Ada

15.4.10.9 Tasking Support when using the Ravenscar Profile
.........................................................

The "Ravenscar Profile" is a subset of the Ada tasking features,
specifically designed for systems with safety-critical real-time
requirements.

`set ravenscar task-switching on'
Allows task switching when debugging a program that uses the
Ravenscar Profile. This is the default.

`set ravenscar task-switching off'
Turn off task switching when debugging a program that uses the
Ravenscar Profile. This is mostly intended to disable the code
that adds support for the Ravenscar Profile, in case a bug in
either GDB or in the Ravenscar runtime is preventing GDB from
working properly. To be effective, this command should be run
before the program is started.

`show ravenscar task-switching'
Show whether it is possible to switch from task to task in a
program using the Ravenscar Profile.

When Ravenscar task-switching is enabled, Ravenscar tasks are
announced by GDB as if they were threads:

(gdb) continue
[New Ravenscar Thread 0x2b8f0]

Both Ravenscar tasks and the underlying CPU threads will show up in
the output of `info threads':

(gdb) info threads
Id Target Id Frame
1 Thread 1 (CPU#0 [running]) simple () at simple.adb:10
2 Thread 2 (CPU#1 [running]) 0x0000000000003d34 in __gnat_initialize_cpu_devices ()
3 Thread 3 (CPU#2 [running]) 0x0000000000003d28 in __gnat_initialize_cpu_devices ()
4 Thread 4 (CPU#3 [halted ]) 0x000000000000c6ec in system.task_primitives.operations.idle ()
* 5 Ravenscar Thread 0x2b8f0 simple () at simple.adb:10
6 Ravenscar Thread 0x2f150 0x000000000000c6ec in system.task_primitives.operations.idle ()

One known limitation of the Ravenscar support in GDB is that it
isn't currently possible to single-step through the runtime
initialization sequence. If you need to debug this code, you should
use `set ravenscar task-switching off'.

File: gdb.info, Node: Ada Source Character Set, Next: Ada Glitches, Prev: Ravenscar Profile, Up: Ada

15.4.10.10 Ada Source Character Set
..................................

The GNAT compiler supports a number of character sets for source files.
*Note Character Set Control: (gnat_ugn)Character Set Control. GDB
includes support for this as well.

`set ada source-charset CHARSET'
Set the source character set for Ada. The character set must be
supported by GNAT. Because this setting affects the decoding of
symbols coming from the debug information in your program, the
setting should be set as early as possible. The default is
`ISO-8859-1', because that is also GNAT's default.

`show ada source-charset'
Show the current source character set for Ada.

File: gdb.info, Node: Ada Glitches, Prev: Ada Source Character Set, Up: Ada

15.4.10.11 Known Peculiarities of Ada Mode
.........................................

Besides the omissions listed previously (*note Omissions from Ada::),
we know of several problems with and limitations of Ada mode in GDB,
some of which will be fixed with planned future releases of the debugger
and the GNU Ada compiler.

* Static constants that the compiler chooses not to materialize as
objects in storage are invisible to the debugger.

* Named parameter associations in function argument lists are
ignored (the argument lists are treated as positional).

* Many useful library packages are currently invisible to the
debugger.

* Fixed-point arithmetic, conversions, input, and output is carried
out using floating-point arithmetic, and may give results that
only approximate those on the host machine.

* The GNAT compiler never generates the prefix `Standard' for any of
the standard symbols defined by the Ada language. GDB knows about
this: it will strip the prefix from names when you use it, and
will never look for a name you have so qualified among local
symbols, nor match against symbols in other packages or
subprograms. If you have defined entities anywhere in your
program other than parameters and local variables whose simple
names match names in `Standard', GNAT's lack of qualification here
can cause confusion. When this happens, you can usually resolve
the confusion by qualifying the problematic names with package
`Standard' explicitly.

Older versions of the compiler sometimes generate erroneous debugging
information, resulting in the debugger incorrectly printing the value
of affected entities. In some cases, the debugger is able to work
around an issue automatically. In other cases, the debugger is able to
work around the issue, but the work-around has to be specifically
enabled.

`set ada trust-PAD-over-XVS on'
Configure GDB to strictly follow the GNAT encoding when computing
the value of Ada entities, particularly when `PAD' and `PAD___XVS'
types are involved (see `ada/exp_dbug.ads' in the GCC sources for
a complete description of the encoding used by the GNAT compiler).
This is the default.

`set ada trust-PAD-over-XVS off'
This is related to the encoding using by the GNAT compiler. If
GDB sometimes prints the wrong value for certain entities,
changing `ada trust-PAD-over-XVS' to `off' activates a work-around
which may fix the issue. It is always safe to set `ada
trust-PAD-over-XVS' to `off', but this incurs a slight performance
penalty, so it is recommended to leave this setting to `on' unless
necessary.

Internally, the debugger also relies on the compiler following a
number of conventions known as the `GNAT Encoding', all documented in
`gcc/ada/exp_dbug.ads' in the GCC sources. This encoding describes how
the debugging information should be generated for certain types. In
particular, this convention makes use of "descriptive types", which are
artificial types generated purely to help the debugger.

These encodings were defined at a time when the debugging information
format used was not powerful enough to describe some of the more complex
types available in Ada. Since DWARF allows us to express nearly all
Ada features, the long-term goal is to slowly replace these descriptive
types by their pure DWARF equivalent. To facilitate that transition, a
new maintenance option is available to force the debugger to ignore
those descriptive types. It allows the user to quickly evaluate how
well GDB works without them.

`maintenance ada set ignore-descriptive-types [on|off]'
Control whether the debugger should ignore descriptive types. The
default is not to ignore descriptives types (`off').

`maintenance ada show ignore-descriptive-types'
Show if descriptive types are ignored by GDB.

File: gdb.info, Node: Unsupported Languages, Prev: Supported Languages, Up: Languages

15.5 Unsupported Languages
==========================

In addition to the other fully-supported programming languages, GDB
also provides a pseudo-language, called `minimal'. It does not
represent a real programming language, but provides a set of
capabilities close to what the C or assembly languages provide. This
should allow most simple operations to be performed while debugging an
application that uses a language currently not supported by GDB.

If the language is set to `auto', GDB will automatically select this
language if the current frame corresponds to an unsupported language.

File: gdb.info, Node: Symbols, Next: Altering, Prev: Languages, Up: Top

16 Examining the Symbol Table
*****************************

The commands described in this chapter allow you to inquire about the
symbols (names of variables, functions and types) defined in your
program. This information is inherent in the text of your program and
does not change as your program executes. GDB finds it in your
program's symbol table, in the file indicated when you started GDB
(*note Choosing Files: File Options.), or by one of the file-management
commands (*note Commands to Specify Files: Files.).

Occasionally, you may need to refer to symbols that contain unusual
characters, which GDB ordinarily treats as word delimiters. The most
frequent case is in referring to static variables in other source files
(*note Program Variables: Variables.). File names are recorded in
object files as debugging symbols, but GDB would ordinarily parse a
typical file name, like `foo.c', as the three words `foo' `.' `c'. To
allow GDB to recognize `foo.c' as a single symbol, enclose it in single
quotes; for example,

p 'foo.c'::x

looks up the value of `x' in the scope of the file `foo.c'.

`set case-sensitive on'
`set case-sensitive off'
`set case-sensitive auto'
Normally, when GDB looks up symbols, it matches their names with
case sensitivity determined by the current source language.
Occasionally, you may wish to control that. The command `set
case-sensitive' lets you do that by specifying `on' for
case-sensitive matches or `off' for case-insensitive ones. If you
specify `auto', case sensitivity is reset to the default suitable
for the source language. The default is case-sensitive matches
for all languages except for Fortran, for which the default is
case-insensitive matches.

`show case-sensitive'
This command shows the current setting of case sensitivity for
symbols lookups.

`set print type methods'
`set print type methods on'
`set print type methods off'
Normally, when GDB prints a class, it displays any methods
declared in that class. You can control this behavior either by
passing the appropriate flag to `ptype', or using `set print type
methods'. Specifying `on' will cause GDB to display the methods;
this is the default. Specifying `off' will cause GDB to omit the
methods.

`show print type methods'
This command shows the current setting of method display when
printing classes.

`set print type nested-type-limit LIMIT'
`set print type nested-type-limit unlimited'
Set the limit of displayed nested types that the type printer will
show. A LIMIT of `unlimited' or `-1' will show all nested
definitions. By default, the type printer will not show any nested
types defined in classes.

`show print type nested-type-limit'
This command shows the current display limit of nested types when
printing classes.

`set print type typedefs'
`set print type typedefs on'
`set print type typedefs off'
Normally, when GDB prints a class, it displays any typedefs
defined in that class. You can control this behavior either by
passing the appropriate flag to `ptype', or using `set print type
typedefs'. Specifying `on' will cause GDB to display the typedef
definitions; this is the default. Specifying `off' will cause GDB
to omit the typedef definitions. Note that this controls whether
the typedef definition itself is printed, not whether typedef
names are substituted when printing other types.

`show print type typedefs'
This command shows the current setting of typedef display when
printing classes.

`set print type hex'
`set print type hex on'
`set print type hex off'
When GDB prints sizes and offsets of struct members, it can use
either the decimal or hexadecimal notation. You can select one or
the other either by passing the appropriate flag to `ptype', or by
using the `set print type hex' command.

`show print type hex'
This command shows whether the sizes and offsets of struct members
are printed in decimal or hexadecimal notation.

`info address SYMBOL'
Describe where the data for SYMBOL is stored. For a register
variable, this says which register it is kept in. For a
non-register local variable, this prints the stack-frame offset at
which the variable is always stored.

Note the contrast with `print &SYMBOL', which does not work at all
for a register variable, and for a stack local variable prints the
exact address of the current instantiation of the variable.

`info symbol ADDR'
Print the name of a symbol which is stored at the address ADDR.
If no symbol is stored exactly at ADDR, GDB prints the nearest
symbol and an offset from it:

(gdb) info symbol 0x54320
_initialize_vx + 396 in section .text

This is the opposite of the `info address' command. You can use
it to find out the name of a variable or a function given its
address.

For dynamically linked executables, the name of executable or
shared library containing the symbol is also printed:

(gdb) info symbol 0x400225
_start + 5 in section .text of /tmp/a.out
(gdb) info symbol 0x2aaaac2811cf
__read_nocancel + 6 in section .text of /usr/lib64/libc.so.6

`demangle [-l LANGUAGE] [-] NAME'
Demangle NAME. If LANGUAGE is provided it is the name of the
language to demangle NAME in. Otherwise NAME is demangled in the
current language.

The `--' option specifies the end of options, and is useful when
NAME begins with a dash.

The parameter `demangle-style' specifies how to interpret the kind
of mangling used. *Note Print Settings::.

`whatis[/FLAGS] [ARG]'
Print the data type of ARG, which can be either an expression or a
name of a data type. With no argument, print the data type of
`$', the last value in the value history.

If ARG is an expression (*note Expressions: Expressions.), it is
not actually evaluated, and any side-effecting operations (such as
assignments or function calls) inside it do not take place.

If ARG is a variable or an expression, `whatis' prints its literal
type as it is used in the source code. If the type was defined
using a `typedef', `whatis' will _not_ print the data type
underlying the `typedef'. If the type of the variable or the
expression is a compound data type, such as `struct' or `class',
`whatis' never prints their fields or methods. It just prints the
`struct'/`class' name (a.k.a. its "tag"). If you want to see the
members of such a compound data type, use `ptype'.

If ARG is a type name that was defined using `typedef', `whatis'
"unrolls" only one level of that `typedef'. Unrolling means that
`whatis' will show the underlying type used in the `typedef'
declaration of ARG. However, if that underlying type is also a
`typedef', `whatis' will not unroll it.

For C code, the type names may also have the form `class
CLASS-NAME', `struct STRUCT-TAG', `union UNION-TAG' or `enum
ENUM-TAG'.

FLAGS can be used to modify how the type is displayed. Available
flags are:

`r'
Display in "raw" form. Normally, GDB substitutes template
parameters and typedefs defined in a class when printing the
class' members. The `/r' flag disables this.

`m'
Do not print methods defined in the class.

`M'
Print methods defined in the class. This is the default, but
the flag exists in case you change the default with `set
print type methods'.

`t'
Do not print typedefs defined in the class. Note that this
controls whether the typedef definition itself is printed,
not whether typedef names are substituted when printing other
types.

`T'
Print typedefs defined in the class. This is the default,
but the flag exists in case you change the default with `set
print type typedefs'.

`o'
Print the offsets and sizes of fields in a struct, similar to
what the `pahole' tool does. This option implies the `/tm'
flags.

`x'
Use hexadecimal notation when printing offsets and sizes of
fields in a struct.

`d'
Use decimal notation when printing offsets and sizes of
fields in a struct.

For example, given the following declarations:

struct tuv
{
int a1;
char *a2;
int a3;
};

struct xyz
{
int f1;
char f2;
void *f3;
struct tuv f4;
};

union qwe
{
struct tuv fff1;
struct xyz fff2;
};

struct tyu
{
int a1 : 1;
int a2 : 3;
int a3 : 23;
char a4 : 2;
int64_t a5;
int a6 : 5;
int64_t a7 : 3;
};

Issuing a `ptype /o struct tuv' command would print:

(gdb) ptype /o struct tuv
/* offset | size */ type = struct tuv {
/* 0 | 4 */ int a1;
/* XXX 4-byte hole */
/* 8 | 8 */ char *a2;
/* 16 | 4 */ int a3;

/* total size (bytes): 24 */
}

Notice the format of the first column of comments. There,
you can find two parts separated by the `|' character: the
_offset_, which indicates where the field is located inside
the struct, in bytes, and the _size_ of the field. Another
interesting line is the marker of a _hole_ in the struct,
indicating that it may be possible to pack the struct and
make it use less space by reorganizing its fields.

It is also possible to print offsets inside an union:

(gdb) ptype /o union qwe
/* offset | size */ type = union qwe {
/* 24 */ struct tuv {
/* 0 | 4 */ int a1;
/* XXX 4-byte hole */
/* 8 | 8 */ char *a2;
/* 16 | 4 */ int a3;

/* total size (bytes): 24 */
} fff1;
/* 40 */ struct xyz {
/* 0 | 4 */ int f1;
/* 4 | 1 */ char f2;
/* XXX 3-byte hole */
/* 8 | 8 */ void *f3;
/* 16 | 24 */ struct tuv {
/* 16 | 4 */ int a1;
/* XXX 4-byte hole */
/* 24 | 8 */ char *a2;
/* 32 | 4 */ int a3;

/* total size (bytes): 24 */
} f4;

/* total size (bytes): 40 */
} fff2;

/* total size (bytes): 40 */
}

In this case, since `struct tuv' and `struct xyz' occupy the
same space (because we are dealing with an union), the offset
is not printed for them. However, you can still examine the
offset of each of these structures' fields.

Another useful scenario is printing the offsets of a struct
containing bitfields:

(gdb) ptype /o struct tyu
/* offset | size */ type = struct tyu {
/* 0:31 | 4 */ int a1 : 1;
/* 0:28 | 4 */ int a2 : 3;
/* 0: 5 | 4 */ int a3 : 23;
/* 3: 3 | 1 */ signed char a4 : 2;
/* XXX 3-bit hole */
/* XXX 4-byte hole */
/* 8 | 8 */ int64_t a5;
/* 16: 0 | 4 */ int a6 : 5;
/* 16: 5 | 8 */ int64_t a7 : 3;
/* XXX 7-byte padding */

/* total size (bytes): 24 */
}

Note how the offset information is now extended to also
include the first bit of the bitfield.

`ptype[/FLAGS] [ARG]'
`ptype' accepts the same arguments as `whatis', but prints a
detailed description of the type, instead of just the name of the
type. *Note Expressions: Expressions.

Contrary to `whatis', `ptype' always unrolls any `typedef's in its
argument declaration, whether the argument is a variable,
expression, or a data type. This means that `ptype' of a variable
or an expression will not print literally its type as present in
the source code--use `whatis' for that. `typedef's at the pointer
or reference targets are also unrolled. Only `typedef's of
fields, methods and inner `class typedef's of `struct's, `class'es
and `union's are not unrolled even with `ptype'.

For example, for this variable declaration:

typedef double real_t;
struct complex { real_t real; double imag; };
typedef struct complex complex_t;
complex_t var;
real_t *real_pointer_var;

the two commands give this output:

(gdb) whatis var
type = complex_t
(gdb) ptype var
type = struct complex {
real_t real;
double imag;
}
(gdb) whatis complex_t
type = struct complex
(gdb) whatis struct complex
type = struct complex
(gdb) ptype struct complex
type = struct complex {
real_t real;
double imag;
}
(gdb) whatis real_pointer_var
type = real_t *
(gdb) ptype real_pointer_var
type = double *

As with `whatis', using `ptype' without an argument refers to the
type of `$', the last value in the value history.

Sometimes, programs use opaque data types or incomplete
specifications of complex data structure. If the debug
information included in the program does not allow GDB to display
a full declaration of the data type, it will say `<incomplete
type>'. For example, given these declarations:

struct foo;
struct foo *fooptr;

but no definition for `struct foo' itself, GDB will say:

(gdb) ptype foo
$1 = <incomplete type>

"Incomplete type" is C terminology for data types that are not
completely specified.

Othertimes, information about a variable's type is completely
absent from the debug information included in the program. This
most often happens when the program or library where the variable
is defined includes no debug information at all. GDB knows the
variable exists from inspecting the linker/loader symbol table
(e.g., the ELF dynamic symbol table), but such symbols do not
contain type information. Inspecting the type of a (global)
variable for which GDB has no type information shows:

(gdb) ptype var
type = <data variable, no debug info>

*Note no debug info variables: Variables, for how to print the
values of such variables.

`info types [-q] [REGEXP]'
Print a brief description of all types whose names match the
regular expression REGEXP (or all types in your program, if you
supply no argument). Each complete typename is matched as though
it were a complete line; thus, `i type value' gives information on
all types in your program whose names include the string `value',
but `i type ^value$' gives information only on types whose complete
name is `value'.

In programs using different languages, GDB chooses the syntax to
print the type description according to the `set language' value:
using `set language auto' (see *Note Set Language Automatically:
Automatically.) means to use the language of the type, other
values mean to use the manually specified language (see *Note Set
Language Manually: Manually.).

This command differs from `ptype' in two ways: first, like
`whatis', it does not print a detailed description; second, it
lists all source files and line numbers where a type is defined.

The output from `into types' is proceeded with a header line
describing what types are being listed. The optional flag `-q',
which stands for `quiet', disables printing this header
information.

`info type-printers'
Versions of GDB that ship with Python scripting enabled may have
"type printers" available. When using `ptype' or `whatis', these
printers are consulted when the name of a type is needed. *Note
Type Printing API::, for more information on writing type printers.

`info type-printers' displays all the available type printers.

`enable type-printer NAME...'

`disable type-printer NAME...'
These commands can be used to enable or disable type printers.

`info scope LOCSPEC'
List all the variables local to the lexical scope of the code
location that results from resolving LOCSPEC. *Note Location
Specifications::, for details about supported forms of LOCSPEC.
For example:

(gdb) info scope command_line_handler
Scope for command_line_handler:
Symbol rl is an argument at stack/frame offset 8, length 4.
Symbol linebuffer is in static storage at address 0x150a18, length 4.
Symbol linelength is in static storage at address 0x150a1c, length 4.
Symbol p is a local variable in register $esi, length 4.
Symbol p1 is a local variable in register $ebx, length 4.
Symbol nline is a local variable in register $edx, length 4.
Symbol repeat is a local variable at frame offset -8, length 4.

This command is especially useful for determining what data to
collect during a "trace experiment", see *Note collect: Tracepoint
Actions.

`info source'
Show information about the current source file--that is, the
source file for the function containing the current point of
execution:
* the name of the source file, and the directory containing it,

* the directory it was compiled in,

* its length, in lines,

* which programming language it is written in,

* if the debug information provides it, the program that
compiled the file (which may include, e.g., the compiler
version and command line arguments),

* whether the executable includes debugging information for
that file, and if so, what format the information is in
(e.g., STABS, Dwarf 2, etc.), and

* whether the debugging information includes information about
preprocessor macros.

`info sources [-dirname | -basename] [--] [REGEXP]'
With no options `info sources' prints the names of all source
files in your program for which there is debugging information.
The source files are presented based on a list of object files
(executables and libraries) currently loaded into GDB. For each
object file all of the associated source files are listed.

Each source file will only be printed once for each object file,
but a single source file can be repeated in the output if it is
part of multiple object files.

If the optional REGEXP is provided, then only source files that
match the regular expression will be printed. The matching is
case-sensitive, except on operating systems that have
case-insensitive filesystem (e.g., MS-Windows). `--' can be used
before REGEXP to prevent GDB interpreting REGEXP as a command
option (e.g. if REGEXP starts with `-').

By default, the REGEXP is used to match anywhere in the filename.
If `-dirname', only files having a dirname matching REGEXP are
shown. If `-basename', only files having a basename matching
REGEXP are shown.

It is possible that an object file may be printed in the list with
no associated source files. This can happen when either no source
files match REGEXP, or, the object file was compiled without debug
information and so GDB is unable to find any source file names.

`info functions [-q] [-n]'
Print the names and data types of all defined functions.
Similarly to `info types', this command groups its output by source
files and annotates each function definition with its source line
number.

In programs using different languages, GDB chooses the syntax to
print the function name and type according to the `set language'
value: using `set language auto' (see *Note Set Language
Automatically: Automatically.) means to use the language of the
function, other values mean to use the manually specified language
(see *Note Set Language Manually: Manually.).

The `-n' flag excludes "non-debugging symbols" from the results.
A non-debugging symbol is a symbol that comes from the
executable's symbol table, not from the debug information (for
example, DWARF) associated with the executable.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no
functions have been printed.

`info functions [-q] [-n] [-t TYPE_REGEXP] [REGEXP]'
Like `info functions', but only print the names and data types of
the functions selected with the provided regexp(s).

If REGEXP is provided, print only the functions whose names match
the regular expression REGEXP. Thus, `info fun step' finds all
functions whose names include `step'; `info fun ^step' finds those
whose names start with `step'. If a function name contains
characters that conflict with the regular expression language (e.g.
`operator*()'), they may be quoted with a backslash.

If TYPE_REGEXP is provided, print only the functions whose types,
as printed by the `whatis' command, match the regular expression
TYPE_REGEXP. If TYPE_REGEXP contains space(s), it should be
enclosed in quote characters. If needed, use backslash to escape
the meaning of special characters or quotes. Thus, `info fun -t
'^int ('' finds the functions that return an integer; `info fun -t
'(.*int.*'' finds the functions that have an argument type
containing int; `info fun -t '^int (' ^step' finds the functions
whose names start with `step' and that return int.

If both REGEXP and TYPE_REGEXP are provided, a function is printed
only if its name matches REGEXP and its type matches TYPE_REGEXP.

`info variables [-q] [-n]'
Print the names and data types of all variables that are defined
outside of functions (i.e. excluding local variables). The
printed variables are grouped by source files and annotated with
their respective source line numbers.

In programs using different languages, GDB chooses the syntax to
print the variable name and type according to the `set language'
value: using `set language auto' (see *Note Set Language
Automatically: Automatically.) means to use the language of the
variable, other values mean to use the manually specified language
(see *Note Set Language Manually: Manually.).

The `-n' flag excludes non-debugging symbols from the results.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no
variables have been printed.

`info variables [-q] [-n] [-t TYPE_REGEXP] [REGEXP]'
Like `info variables', but only print the variables selected with
the provided regexp(s).

If REGEXP is provided, print only the variables whose names match
the regular expression REGEXP.

If TYPE_REGEXP is provided, print only the variables whose types,
as printed by the `whatis' command, match the regular expression
TYPE_REGEXP. If TYPE_REGEXP contains space(s), it should be
enclosed in quote characters. If needed, use backslash to escape
the meaning of special characters or quotes.

If both REGEXP and TYPE_REGEXP are provided, an argument is
printed only if its name matches REGEXP and its type matches
TYPE_REGEXP.

`info modules [-q] [REGEXP]'
List all Fortran modules in the program, or all modules matching
the optional regular expression REGEXP.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no modules
have been printed.

`info module functions [-q] [-m MODULE-REGEXP] [-t TYPE-REGEXP] [REGEXP]'
`info module variables [-q] [-m MODULE-REGEXP] [-t TYPE-REGEXP] [REGEXP]'
List all functions or variables within all Fortran modules. The
set of functions or variables listed can be limited by providing
some or all of the optional regular expressions. If MODULE-REGEXP
is provided, then only Fortran modules matching MODULE-REGEXP will
be searched. Only functions or variables whose type matches the
optional regular expression TYPE-REGEXP will be listed. And only
functions or variables whose name matches the optional regular
expression REGEXP will be listed.

The optional flag `-q', which stands for `quiet', disables
printing header information and messages explaining why no
functions or variables have been printed.

`info main'
Print the name of the starting function of the program. This
serves primarily Fortran programs, which have a user-supplied name
for the main subroutine.

`info classes'
`info classes REGEXP'
Display all Objective-C classes in your program, or (with the
REGEXP argument) all those matching a particular regular
expression.

`info selectors'
`info selectors REGEXP'
Display all Objective-C selectors in your program, or (with the
REGEXP argument) all those matching a particular regular
expression.

`set opaque-type-resolution on'
Tell GDB to resolve opaque types. An opaque type is a type
declared as a pointer to a `struct', `class', or `union'--for
example, `struct MyType *'--that is used in one source file
although the full declaration of `struct MyType' is in another
source file. The default is on.

A change in the setting of this subcommand will not take effect
until the next time symbols for a file are loaded.

`set opaque-type-resolution off'
Tell GDB not to resolve opaque types. In this case, the type is
printed as follows:
{<no data fields>}

`show opaque-type-resolution'
Show whether opaque types are resolved or not.

`set print symbol-loading'
`set print symbol-loading full'
`set print symbol-loading brief'
`set print symbol-loading off'
The `set print symbol-loading' command allows you to control the
printing of messages when GDB loads symbol information. By
default a message is printed for the executable and one for each
shared library, and normally this is what you want. However, when
debugging apps with large numbers of shared libraries these
messages can be annoying. When set to `brief' a message is
printed for each executable, and when GDB loads a collection of
shared libraries at once it will only print one message regardless
of the number of shared libraries. When set to `off' no messages
are printed.

`show print symbol-loading'
Show whether messages will be printed when a GDB command entered
from the keyboard causes symbol information to be loaded.

`maint print symbols [-pc ADDRESS] [FILENAME]'
`maint print symbols [-objfile OBJFILE] [-source SOURCE] [--] [FILENAME]'
`maint print psymbols [-objfile OBJFILE] [-pc ADDRESS] [--] [FILENAME]'
`maint print psymbols [-objfile OBJFILE] [-source SOURCE] [--] [FILENAME]'
`maint print msymbols [-objfile OBJFILE] [--] [FILENAME]'
Write a dump of debugging symbol data into the file FILENAME or
the terminal if FILENAME is unspecified. If `-objfile OBJFILE' is
specified, only dump symbols for that objfile. If `-pc ADDRESS'
is specified, only dump symbols for the file with code at that
address. Note that ADDRESS may be a symbol like `main'. If
`-source SOURCE' is specified, only dump symbols for that source
file.

These commands are used to debug the GDB symbol-reading code.
These commands do not modify internal GDB state, therefore `maint
print symbols' will only print symbols for already expanded symbol
tables. You can use the command `info sources' to find out which
files these are. If you use `maint print psymbols' instead, the
dump shows information about symbols that GDB only knows
partially--that is, symbols defined in files that GDB has skimmed,
but not yet read completely. Finally, `maint print msymbols' just
dumps "minimal symbols", e.g., "ELF symbols".

*Note Commands to Specify Files: Files, for a discussion of how
GDB reads symbols (in the description of `symbol-file').

`maint info symtabs [ REGEXP ]'
`maint info psymtabs [ REGEXP ]'
List the `struct symtab' or `struct partial_symtab' structures
whose names match REGEXP. If REGEXP is not given, list them all.
The output includes expressions which you can copy into a GDB
debugging this one to examine a particular structure in more
detail. For example:

(gdb) maint info psymtabs dwarf2read
{ objfile /home/gnu/build/gdb/gdb
((struct objfile *) 0x82e69d0)
{ psymtab /home/gnu/src/gdb/dwarf2read.c
((struct partial_symtab *) 0x8474b10)
readin no
fullname (null)
text addresses 0x814d3c8 -- 0x8158074
globals (* (struct partial_symbol **) 0x8507a08 @ 9)
statics (* (struct partial_symbol **) 0x40e95b78 @ 2882)
dependencies (none)
}
}
(gdb) maint info symtabs
(gdb)
We see that there is one partial symbol table whose filename
contains the string `dwarf2read', belonging to the `gdb'
executable; and we see that GDB has not read in any symtabs yet at
all. If we set a breakpoint on a function, that will cause GDB to
read the symtab for the compilation unit containing that function:

(gdb) break dwarf2_psymtab_to_symtab
Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
line 1574.
(gdb) maint info symtabs
{ objfile /home/gnu/build/gdb/gdb
((struct objfile *) 0x82e69d0)
{ symtab /home/gnu/src/gdb/dwarf2read.c
((struct symtab *) 0x86c1f38)
dirname (null)
fullname (null)
blockvector ((struct blockvector *) 0x86c1bd0) (primary)
linetable ((struct linetable *) 0x8370fa0)
debugformat DWARF 2
}
}
(gdb)

`maint info line-table [ REGEXP ]'
List the `struct linetable' from all `struct symtab' instances
whose name matches REGEXP. If REGEXP is not given, list the
`struct linetable' from all `struct symtab'. For example:

(gdb) maint info line-table
objfile: /home/gnu/build/a.out ((struct objfile *) 0x6120000e0d40)
compunit_symtab: simple.cpp ((struct compunit_symtab *) 0x6210000ff450)
symtab: /home/gnu/src/simple.cpp ((struct symtab *) 0x6210000ff4d0)
linetable: ((struct linetable *) 0x62100012b760):
INDEX LINE ADDRESS IS-STMT PROLOGUE-END EPILOGUE-BEGIN
0 3 0x0000000000401110 Y
1 4 0x0000000000401114 Y Y Y
2 9 0x0000000000401120 Y
3 10 0x0000000000401124 Y Y
4 10 0x0000000000401129 Y Y
5 15 0x0000000000401130 Y
6 16 0x0000000000401134 Y Y
7 16 0x0000000000401139
8 21 0x0000000000401140 Y Y
9 22 0x000000000040114f Y Y
10 22 0x0000000000401154 Y
11 END 0x000000000040115a Y
The `IS-STMT' column indicates if the address is a recommended
breakpoint location to represent a line or a statement. The
`PROLOGUE-END' column indicates that a given address is an
adequate place to set a breakpoint at the first instruction
following a function prologue. The `EPILOGUE-BEGIN' column
indicates that a given address marks the point where a block's
frame is destroyed, making local variables hard or impossible to
find.

`set always-read-ctf [on|off]'
`show always-read-ctf'
When off, CTF debug info is only read if DWARF debug info is not
present. When on, CTF debug info is read regardless of whether
DWARF debug info is present. The default value is off.

`maint set symbol-cache-size SIZE'
Set the size of the symbol cache to SIZE. The default size is
intended to be good enough for debugging most applications. This
option exists to allow for experimenting with different sizes.

`maint show symbol-cache-size'
Show the size of the symbol cache.

`maint print symbol-cache'
Print the contents of the symbol cache. This is useful when
debugging symbol cache issues.

`maint print symbol-cache-statistics'
Print symbol cache usage statistics. This helps determine how
well the cache is being utilized.

`maint flush symbol-cache'
`maint flush-symbol-cache'
Flush the contents of the symbol cache, all entries are removed.
This command is useful when debugging the symbol cache. It is
also useful when collecting performance data. The command `maint
flush-symbol-cache' is deprecated in favor of `maint flush
symbol-cache'..

`maint set ignore-prologue-end-flag [on|off]'
Enable or disable the use of the `PROLOGUE-END' flag from the
line-table. When `off' (the default), GDB uses the `PROLOGUE-END'
flag to place breakpoints past the end of a function prologue.
When `on', GDB ignores the flag and relies on prologue analyzers
to skip function prologues.

`maint show ignore-prologue-end-flag'
Show whether GDB will ignore the `PROLOGUE-END' flag.

File: gdb.info, Node: Altering, Next: GDB Files, Prev: Symbols, Up: Top

17 Altering Execution
*********************

Once you think you have found an error in your program, you might want
to find out for certain whether correcting the apparent error would
lead to correct results in the rest of the run. You can find the
answer by experiment, using the GDB features for altering execution of
the program.

For example, you can store new values into variables or memory
locations, give your program a signal, restart it at a different
address, or even return prematurely from a function.

* Menu:

* Assignment:: Assignment to variables
* Jumping:: Continuing at a different address
* Signaling:: Giving your program a signal
* Returning:: Returning from a function
* Calling:: Calling your program's functions
* Patching:: Patching your program
* Compiling and Injecting Code:: Compiling and injecting code in GDB

File: gdb.info, Node: Assignment, Next: Jumping, Up: Altering

17.1 Assignment to Variables
============================

To alter the value of a variable, evaluate an assignment expression.
*Note Expressions: Expressions. For example,

print x=4

stores the value 4 into the variable `x', and then prints the value of
the assignment expression (which is 4). *Note Using GDB with Different
Languages: Languages, for more information on operators in supported
languages.

If you are not interested in seeing the value of the assignment, use
the `set' command instead of the `print' command. `set' is really the
same as `print' except that the expression's value is not printed and
is not put in the value history (*note Value History: Value History.).
The expression is evaluated only for its effects.

If the beginning of the argument string of the `set' command appears
identical to a `set' subcommand, use the `set variable' command instead
of just `set'. This command is identical to `set' except for its lack
of subcommands. For example, if your program has a variable `width',
you get an error if you try to set a new value with just `set
width=13', because GDB has the command `set width':

(gdb) whatis width
type = double
(gdb) p width
$4 = 13
(gdb) set width=47
Invalid syntax in expression.

The invalid expression, of course, is `=47'. In order to actually set
the program's variable `width', use

(gdb) set var width=47

Because the `set' command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the `set
variable' command instead of just `set'. For example, if your program
has a variable `g', you run into problems if you try to set a new value
with just `set g=4', because GDB has the command `set gnutarget',
abbreviated `set g':

(gdb) whatis g
type = double
(gdb) p g
$1 = 1
(gdb) set g=4
(gdb) p g
$2 = 1
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/smith/cc_progs/a.out
"/home/smith/cc_progs/a.out": can't open to read symbols:
Invalid bfd target.
(gdb) show g
The current BFD target is "=4".

The program variable `g' did not change, and you silently set the
`gnutarget' to an invalid value. In order to set the variable `g', use

(gdb) set var g=4

GDB allows more implicit conversions in assignments than C; you can
freely store an integer value into a pointer variable or vice versa,
and you can convert any structure to any other structure that is the
same length or shorter.

To store values into arbitrary places in memory, use the `{...}'
construct to generate a value of specified type at a specified address
(*note Expressions: Expressions.). For example, `{int}0x83040' refers
to memory location `0x83040' as an integer (which implies a certain size
and representation in memory), and

set {int}0x83040 = 4

stores the value 4 into that memory location.

File: gdb.info, Node: Jumping, Next: Signaling, Prev: Assignment, Up: Altering

17.2 Continuing at a Different Address
======================================

Ordinarily, when you continue your program, you do so at the place where
it stopped, with the `continue' command. You can instead continue at
an address of your own choosing, with the following commands:

`jump LOCSPEC'
`j LOCSPEC'
Resume execution at the address of the code location that results
from resolving LOCSPEC. *Note Location Specifications::, for a
description of the different forms of LOCSPEC. If LOCSPEC
resolves to more than one address, those outside the current
compilation unit are ignored. If considering just the addresses
in the current compilation unit still doesn't yield a unique
address, the command aborts before jumping. Execution stops again
immediately if there is a breakpoint there. It is common practice
to use the `tbreak' command in conjunction with `jump'. *Note
Setting Breakpoints: Set Breaks.

The `jump' command does not change the current stack frame, or the
stack pointer, or the contents of any memory location or any
register other than the program counter. If LOCSPEC resolves to
an address in a different function from the one currently
executing, the results may be bizarre if the two functions expect
different patterns of arguments or of local variables. For this
reason, the `jump' command requests confirmation if the jump
address is not in the function currently executing. However, even
bizarre results are predictable if you are well acquainted with
the machine-language code of your program.

On many systems, you can get much the same effect as the `jump'
command by storing a new value into the register `$pc'. The difference
is that this does not start your program running; it only changes the
address of where it _will_ run when you continue. For example,

set $pc = 0x485

makes the next `continue' command or stepping command execute at
address `0x485', rather than at the address where your program stopped.
*Note Continuing and Stepping: Continuing and Stepping.

However, writing directly to `$pc' will only change the value of the
program-counter register, while using `jump' will ensure that any
additional auxiliary state is also updated. For example, on SPARC,
`jump' will update both `$pc' and `$npc' registers prior to resuming
execution. When using the approach of writing directly to `$pc' it is
your job to also update the `$npc' register.

The most common occasion to use the `jump' command is to back
up--perhaps with more breakpoints set--over a portion of a program that
has already executed, in order to examine its execution in more detail.

File: gdb.info, Node: Signaling, Next: Returning, Prev: Jumping, Up: Altering

17.3 Giving your Program a Signal
=================================

`signal SIGNAL'
Resume execution where your program is stopped, but immediately
give it the signal SIGNAL. The SIGNAL can be the name or the
number of a signal. For example, on many systems `signal 2' and
`signal SIGINT' are both ways of sending an interrupt signal.

Alternatively, if SIGNAL is zero, continue execution without
giving a signal. This is useful when your program stopped on
account of a signal and would ordinarily see the signal when
resumed with the `continue' command; `signal 0' causes it to
resume without a signal.

_Note:_ When resuming a multi-threaded program, SIGNAL is
delivered to the currently selected thread, not the thread that
last reported a stop. This includes the situation where a thread
was stopped due to a signal. So if you want to continue execution
suppressing the signal that stopped a thread, you should select
that same thread before issuing the `signal 0' command. If you
issue the `signal 0' command with another thread as the selected
one, GDB detects that and asks for confirmation.

Invoking the `signal' command is not the same as invoking the
`kill' utility from the shell. Sending a signal with `kill'
causes GDB to decide what to do with the signal depending on the
signal handling tables (*note Signals::). The `signal' command
passes the signal directly to your program.

`signal' does not repeat when you press <RET> a second time after
executing the command.

`queue-signal SIGNAL'
Queue SIGNAL to be delivered immediately to the current thread
when execution of the thread resumes. The SIGNAL can be the name
or the number of a signal. For example, on many systems `signal
2' and `signal SIGINT' are both ways of sending an interrupt
signal. The handling of the signal must be set to pass the signal
to the program, otherwise GDB will report an error. You can
control the handling of signals from GDB with the `handle' command
(*note Signals::).

Alternatively, if SIGNAL is zero, any currently queued signal for
the current thread is discarded and when execution resumes no
signal will be delivered. This is useful when your program
stopped on account of a signal and would ordinarily see the signal
when resumed with the `continue' command.

This command differs from the `signal' command in that the signal
is just queued, execution is not resumed. And `queue-signal'
cannot be used to pass a signal whose handling state has been set
to `nopass' (*note Signals::).

*Note stepping into signal handlers::, for information on how
stepping commands behave when the thread has a signal queued.

File: gdb.info, Node: Returning, Next: Calling, Prev: Signaling, Up: Altering

17.4 Returning from a Function
==============================

`return'
`return EXPRESSION'
You can cancel execution of a function call with the `return'
command. If you give an EXPRESSION argument, its value is used as
the function's return value.

When you use `return', GDB discards the selected stack frame (and
all frames within it). You can think of this as making the discarded
frame return prematurely. If you wish to specify a value to be
returned, give that value as the argument to `return'.

This pops the selected stack frame (*note Selecting a Frame:
Selection.), and any other frames inside of it, leaving its caller as
the innermost remaining frame. That frame becomes selected. The
specified value is stored in the registers used for returning values of
functions.

The `return' command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned. In contrast, the `finish' command (*note Continuing and
Stepping: Continuing and Stepping.) resumes execution until the
selected stack frame returns naturally.

GDB needs to know how the EXPRESSION argument should be set for the
inferior. The concrete registers assignment depends on the OS ABI and
the type being returned by the selected stack frame. For example it is
common for OS ABI to return floating point values in FPU registers
while integer values in CPU registers. Still some ABIs return even
floating point values in CPU registers. Larger integer widths (such as
`long long int') also have specific placement rules. GDB already knows
the OS ABI from its current target so it needs to find out also the
type being returned to make the assignment into the right register(s).

Normally, the selected stack frame has debug info. GDB will always
use the debug info instead of the implicit type of EXPRESSION when the
debug info is available. For example, if you type `return -1', and the
function in the current stack frame is declared to return a `long long
int', GDB transparently converts the implicit `int' value of -1 into a
`long long int':

Breakpoint 1, func () at gdb.base/return-nodebug.c:29
29 return 31;
(gdb) return -1
Make func return now? (y or n) y
#0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
43 printf ("result=%lld\n", func ());
(gdb)

However, if the selected stack frame does not have a debug info,
e.g., if the function was compiled without debug info, GDB has to find
out the type to return from user. Specifying a different type by
mistake may set the value in different inferior registers than the
caller code expects. For example, typing `return -1' with its implicit
type `int' would set only a part of a `long long int' result for a
debug info less function (on 32-bit architectures). Therefore the user
is required to specify the return type by an appropriate cast
explicitly:

Breakpoint 2, 0x0040050b in func ()
(gdb) return -1
Return value type not available for selected stack frame.
Please use an explicit cast of the value to return.
(gdb) return (long long int) -1
Make selected stack frame return now? (y or n) y
#0 0x00400526 in main ()
(gdb)

File: gdb.info, Node: Calling, Next: Patching, Prev: Returning, Up: Altering

17.5 Calling Program Functions
==============================

`print EXPR'
Evaluate the expression EXPR and display the resulting value. The
expression may include calls to functions in the program being
debugged.

`call EXPR'
Evaluate the expression EXPR without displaying `void' returned
values.

You can use this variant of the `print' command if you want to
execute a function from your program that does not return anything
(a.k.a. "a void function"), but without cluttering the output with
`void' returned values that GDB will otherwise print. If the
result is not void, it is printed and saved in the value history.

It is possible for the function you call via the `print' or `call'
command to generate a signal (e.g., if there's a bug in the function,
or if you passed it incorrect arguments). What happens in that case is
controlled by the `set unwind-on-signal' command.

Similarly, with a C++ program it is possible for the function you
call via the `print' or `call' command to generate an exception that is
not handled due to the constraints of the dummy frame. In this case,
any exception that is raised in the frame, but has an out-of-frame
exception handler will not be found. GDB builds a dummy-frame for the
inferior function call, and the unwinder cannot seek for exception
handlers outside of this dummy-frame. What happens in that case is
controlled by the `set unwind-on-terminating-exception' command.

`set unwind-on-signal'
Set unwinding of the stack if a signal is received while in a
function that GDB called in the program being debugged. If set to
on, GDB unwinds the stack it created for the call and restores the
context to what it was before the call. If set to off (the
default), GDB stops in the frame where the signal was received.

The command `set unwindonsignal' is an alias for this command, and
is maintained for backward compatibility.

`show unwind-on-signal'
Show the current setting of stack unwinding in the functions
called by GDB.

The command `show unwindonsignal' is an alias for this command,
and is maintained for backward compatibility.

`set unwind-on-terminating-exception'
Set unwinding of the stack if a C++ exception is raised, but left
unhandled while in a function that GDB called in the program being
debugged. If set to on (the default), GDB unwinds the stack it
created for the call and restores the context to what it was before
the call. If set to off, GDB the exception is delivered to the
default C++ exception handler and the inferior terminated.

`show unwind-on-terminating-exception'
Show the current setting of stack unwinding in the functions
called by GDB.

`set unwind-on-timeout'
Set unwinding of the stack if a function called from GDB times
out. If set to `off' (the default), GDB stops in the frame where
the timeout occurred. If set to `on', GDB unwinds the stack it
created for the call and restores the context to what it was
before the call.

`show unwind-on-timeout'
Show whether GDB will unwind the stack if a function called from
GDB times out.

`set may-call-functions'
Set permission to call functions in the program. This controls
whether GDB will attempt to call functions in the program, such as
with expressions in the `print' command. It defaults to `on'.

To call a function in the program, GDB has to temporarily modify
the state of the inferior. This has potentially undesired side
effects. Also, having GDB call nested functions is likely to be
erroneous and may even crash the program being debugged. You can
avoid such hazards by forbidding GDB from calling functions in the
program being debugged. If calling functions in the program is
forbidden, GDB will throw an error when a command (such as printing
an expression) starts a function call in the program.

`show may-call-functions'
Show permission to call functions in the program.

When calling a function within a program, it is possible that the
program could enter a state from which the called function may never
return. If this happens then it is possible to interrupt the function
call by typing the interrupt character (often `Ctrl-c').

If a called function is interrupted for any reason, including hitting
a breakpoint, or triggering a watchpoint, and the stack is not unwound
due to `set unwind-on-terminating-exception on', `set unwind-on-timeout
on', or `set unwind-on-signal on' (*note stack unwind settings::), then
the dummy-frame, created by GDB to facilitate the call to the program
function, will be visible in the backtrace, for example frame `#3' in
the following backtrace:

(gdb) backtrace
#0 0x00007ffff7b3d1e7 in nanosleep () from /lib64/libc.so.6
#1 0x00007ffff7b3d11e in sleep () from /lib64/libc.so.6
#2 0x000000000040113f in deadlock () at test.cc:13
#3 <function called from gdb>
#4 breakpt () at test.cc:20
#5 0x0000000000401151 in main () at test.cc:25

At this point it is possible to examine the state of the inferior
just like any other stop.

Depending on why the function was interrupted then it may be possible
to resume the inferior (using commands like `continue', `step', etc).
In this case, when the inferior finally returns to the dummy-frame, GDB
will once again halt the inferior.

On targets that support asynchronous execution (*note Background
Execution::) GDB can place a timeout on any functions called from GDB.
If the timeout expires and the function call is still ongoing, then GDB
will interrupt the program.

If a function called from GDB is interrupted by a timeout, then by
default the inferior is left in the frame where the timeout occurred,
this behaviour can be adjusted with `set unwind-on-timeout' (*note set
unwind-on-timeout::).

For targets that don't support asynchronous execution (*note
Background Execution::) then timeouts for functions called from GDB are
not supported, the timeout settings described below will be treated as
`unlimited', meaning GDB will wait indefinitely for function call to
complete, unless interrupted by the user using `Ctrl-C'.

`set direct-call-timeout SECONDS'
Set the timeout used when calling functions in the program to
SECONDS, which should be an integer greater than zero, or the
special value `unlimited', which indicates no timeout should be
used. The default for this setting is `unlimited'.

This setting is used when the user calls a function directly from
the command prompt, for example with a `call' or `print' command.

This setting only works for targets that support asynchronous
execution (*note Background Execution::), for any other target the
setting is treated as `unlimited'.

`show direct-call-timeout'
Show the timeout used when calling functions in the program with a
`call' or `print' command.

It is also possible to call functions within the program from the
condition of a conditional breakpoint (*note Break Conditions:
Conditions.). A different setting controls the timeout used for
function calls made from a breakpoint condition.

`set indirect-call-timeout SECONDS'
Set the timeout used when calling functions in the program from a
breakpoint or watchpoint condition to SECONDS, which should be an
integer greater than zero, or the special value `unlimited', which
indicates no timeout should be used. The default for this setting
is `30' seconds.

This setting only works for targets that support asynchronous
execution (*note Background Execution::), for any other target the
setting is treated as `unlimited'.

If a function called from a breakpoint or watchpoint condition
times out, then GDB will stop at the point where the timeout
occurred. The breakpoint condition evaluation will be abandoned.

`show indirect-call-timeout'
Show the timeout used when calling functions in the program from a
breakpoint or watchpoint condition.

17.5.1 Calling functions with no debug info
-------------------------------------------

Sometimes, a function you wish to call is missing debug information.
In such case, GDB does not know the type of the function, including the
types of the function's parameters. To avoid calling the inferior
function incorrectly, which could result in the called function
functioning erroneously and even crash, GDB refuses to call the
function unless you tell it the type of the function.

For prototyped (i.e. ANSI/ISO style) functions, there are two ways
to do that. The simplest is to cast the call to the function's
declared return type. For example:

(gdb) p getenv ("PATH")
'getenv' has unknown return type; cast the call to its declared return type
(gdb) p (char *) getenv ("PATH")
$1 = 0x7fffffffe7ba "/usr/local/bin:/"...

Casting the return type of a no-debug function is equivalent to
casting the function to a pointer to a prototyped function that has a
prototype that matches the types of the passed-in arguments, and
calling that. I.e., the call above is equivalent to:

(gdb) p ((char * (*) (const char *)) getenv) ("PATH")

and given this prototyped C or C++ function with float parameters:

float multiply (float v1, float v2) { return v1 * v2; }

these calls are equivalent:

(gdb) p (float) multiply (2.0f, 3.0f)
(gdb) p ((float (*) (float, float)) multiply) (2.0f, 3.0f)

If the function you wish to call is declared as unprototyped (i.e.
old K&R style), you must use the cast-to-function-pointer syntax, so
that GDB knows that it needs to apply default argument promotions
(promote float arguments to double). *Note float promotion: ABI. For
example, given this unprototyped C function with float parameters, and
no debug info:

float
multiply_noproto (v1, v2)
float v1, v2;
{
return v1 * v2;
}

you call it like this:

(gdb) p ((float (*) ()) multiply_noproto) (2.0f, 3.0f)

File: gdb.info, Node: Patching, Next: Compiling and Injecting Code, Prev: Calling, Up: Altering

17.6 Patching Programs
======================

By default, GDB opens the file containing your program's executable
code (or the corefile) read-only. This prevents accidental alterations
to machine code; but it also prevents you from intentionally patching
your program's binary.

If you'd like to be able to patch the binary, you can specify that
explicitly with the `set write' command. For example, you might want
to turn on internal debugging flags, or even to make emergency repairs.

`set write on'
`set write off'
If you specify `set write on', GDB opens executable and core files
for both reading and writing; if you specify `set write off' (the
default), GDB opens them read-only.

If you have already loaded a file, you must load it again (using
the `exec-file' or `core-file' command) after changing `set
write', for your new setting to take effect.

`show write'
Display whether executable files and core files are opened for
writing as well as reading.

File: gdb.info, Node: Compiling and Injecting Code, Prev: Patching, Up: Altering

17.7 Compiling and injecting code in GDB
========================================

GDB supports on-demand compilation and code injection into programs
running under GDB. GCC 5.0 or higher built with `libcc1.so' must be
installed for this functionality to be enabled. This functionality is
implemented with the following commands.

`compile code SOURCE-CODE'
`compile code -raw - SOURCE-CODE'
Compile SOURCE-CODE with the compiler language found as the current
language in GDB (*note Languages::). If compilation and injection
is not supported with the current language specified in GDB, or
the compiler does not support this feature, an error message will
be printed. If SOURCE-CODE compiles and links successfully, GDB
will load the object-code emitted, and execute it within the
context of the currently selected inferior. It is important to
note that the compiled code is executed immediately. After
execution, the compiled code is removed from GDB and any new types
or variables you have defined will be deleted.

The command allows you to specify SOURCE-CODE in two ways. The
simplest method is to provide a single line of code to the command.
E.g.:

compile code printf ("hello world\n");

If you specify options on the command line as well as source code,
they may conflict. The `--' delimiter can be used to separate
options from actual source code. E.g.:

compile code -r -- printf ("hello world\n");

Alternatively you can enter source code as multiple lines of text.
To enter this mode, invoke the `compile code' command without any
text following the command. This will start the multiple-line
editor and allow you to type as many lines of source code as
required. When you have completed typing, enter `end' on its own
line to exit the editor.

compile code
>printf ("hello\n");
>printf ("world\n");
>end

Specifying `-raw', prohibits GDB from wrapping the provided
SOURCE-CODE in a callable scope. In this case, you must specify
the entry point of the code by defining a function named
`_gdb_expr_'. The `-raw' code cannot access variables of the
inferior. Using `-raw' option may be needed for example when
SOURCE-CODE requires `#include' lines which may conflict with
inferior symbols otherwise.

`compile file FILENAME'
`compile file -raw FILENAME'
Like `compile code', but take the source code from FILENAME.

compile file /home/user/example.c

`compile print [[OPTIONS] --] EXPR'
`compile print [[OPTIONS] --] /F EXPR'
Compile and execute EXPR with the compiler language found as the
current language in GDB (*note Languages::). By default the value
of EXPR is printed in a format appropriate to its data type; you
can choose a different format by specifying `/F', where F is a
letter specifying the format; see *Note Output Formats: Output
Formats. The `compile print' command accepts the same options as
the `print' command; see *Note print options::.

`compile print [[OPTIONS] --]'
`compile print [[OPTIONS] --] /F'
Alternatively you can enter the expression (source code producing
it) as multiple lines of text. To enter this mode, invoke the
`compile print' command without any text following the command.
This will start the multiple-line editor.

The process of compiling and injecting the code can be inspected using:

`set debug compile'
Turns on or off display of GDB process of compiling and injecting
the code. The default is off.

`show debug compile'
Displays the current state of displaying GDB process of compiling
and injecting the code.

`set debug compile-cplus-types'
Turns on or off the display of C++ type conversion debugging
information. The default is off.

`show debug compile-cplus-types'
Displays the current state of displaying debugging information for
C++ type conversion.

17.7.1 Compilation options for the `compile' command
----------------------------------------------------

GDB needs to specify the right compilation options for the code to be
injected, in part to make its ABI compatible with the inferior and in
part to make the injected code compatible with GDB's injecting process.

The options used, in increasing precedence:

target architecture and OS options (`gdbarch')
These options depend on target processor type and target operating
system, usually they specify at least 32-bit (`-m32') or 64-bit
(`-m64') compilation option.

compilation options recorded in the target
GCC (since version 4.7) stores the options used for compilation
into `DW_AT_producer' part of DWARF debugging information according
to the GCC option `-grecord-gcc-switches'. One has to explicitly
specify `-g' during inferior compilation otherwise GCC produces no
DWARF. This feature is only relevant for platforms where `-g'
produces DWARF by default, otherwise one may try to enforce DWARF
by using `-gdwarf-4'.

compilation options set by `set compile-args'

You can override compilation options using the following command:

`set compile-args'
Set compilation options used for compiling and injecting code with
the `compile' commands. These options override any conflicting
ones from the target architecture and/or options stored during
inferior compilation.

`show compile-args'
Displays the current state of compilation options override. This
does not show all the options actually used during compilation,
use *Note set debug compile:: for that.

17.7.2 Caveats when using the `compile' command
-----------------------------------------------

There are a few caveats to keep in mind when using the `compile'
command. As the caveats are different per language, the table below
highlights specific issues on a per language basis.

C code examples and caveats
When the language in GDB is set to `C', the compiler will attempt
to compile the source code with a `C' compiler. The source code
provided to the `compile' command will have much the same access
to variables and types as it normally would if it were part of the
program currently being debugged in GDB.

Below is a sample program that forms the basis of the examples that
follow. This program has been compiled and loaded into GDB, much
like any other normal debugging session.

void function1 (void)
{
int i = 42;
printf ("function 1\n");
}

void function2 (void)
{
int j = 12;
function1 ();
}

int main(void)
{
int k = 6;
int *p;
function2 ();
return 0;
}

For the purposes of the examples in this section, the program
above has been compiled, loaded into GDB, stopped at the function
`main', and GDB is awaiting input from the user.

To access variables and types for any program in GDB, the program
must be compiled and packaged with debug information. The
`compile' command is not an exception to this rule. Without debug
information, you can still use the `compile' command, but you will
be very limited in what variables and types you can access.

So with that in mind, the example above has been compiled with
debug information enabled. The `compile' command will have access
to all variables and types (except those that may have been
optimized out). Currently, as GDB has stopped the program in the
`main' function, the `compile' command would have access to the
variable `k'. You could invoke the `compile' command and type
some source code to set the value of `k'. You can also read it,
or do anything with that variable you would normally do in `C'.
Be aware that changes to inferior variables in the `compile'
command are persistent. In the following example:

compile code k = 3;

the variable `k' is now 3. It will retain that value until
something else in the example program changes it, or another
`compile' command changes it.

Normal scope and access rules apply to source code compiled and
injected by the `compile' command. In the example, the variables
`j' and `k' are not accessible yet, because the program is
currently stopped in the `main' function, where these variables
are not in scope. Therefore, the following command

compile code j = 3;

will result in a compilation error message.

Once the program is continued, execution will bring these
variables in scope, and they will become accessible; then the code
you specify via the `compile' command will be able to access them.

You can create variables and types with the `compile' command as
part of your source code. Variables and types that are created as
part of the `compile' command are not visible to the rest of the
program for the duration of its run. This example is valid:

compile code int ff = 5; printf ("ff is %d\n", ff);

However, if you were to type the following into GDB after that
command has completed:

compile code printf ("ff is %d\n'', ff);

a compiler error would be raised as the variable `ff' no longer
exists. Object code generated and injected by the `compile'
command is removed when its execution ends. Caution is advised
when assigning to program variables values of variables created by
the code submitted to the `compile' command. This example is
valid:

compile code int ff = 5; k = ff;

The value of the variable `ff' is assigned to `k'. The variable
`k' does not require the existence of `ff' to maintain the value
it has been assigned. However, pointers require particular care in
assignment. If the source code compiled with the `compile' command
changed the address of a pointer in the example program, perhaps
to a variable created in the `compile' command, that pointer would
point to an invalid location when the command exits. The
following example would likely cause issues with your debugged
program:

compile code int ff = 5; p = &ff;

In this example, `p' would point to `ff' when the `compile'
command is executing the source code provided to it. However, as
variables in the (example) program persist with their assigned
values, the variable `p' would point to an invalid location when
the command exists. A general rule should be followed in that you
should either assign `NULL' to any assigned pointers, or restore a
valid location to the pointer before the command exits.

Similar caution must be exercised with any structs, unions, and
typedefs defined in `compile' command. Types defined in the
`compile' command will no longer be available in the next
`compile' command. Therefore, if you cast a variable to a type
defined in the `compile' command, care must be taken to ensure
that any future need to resolve the type can be achieved.

(gdb) compile code static struct a { int a; } v = { 42 }; argv = &v;
(gdb) compile code printf ("%d\n", ((struct a *) argv)->a);
gdb command line:1:36: error: dereferencing pointer to incomplete type ‘struct a’
Compilation failed.
(gdb) compile code struct a { int a; }; printf ("%d\n", ((struct a *) argv)->a);
42

Variables that have been optimized away by the compiler are not
accessible to the code submitted to the `compile' command. Access
to those variables will generate a compiler error which GDB will
print to the console.

17.7.3 Compiler search for the `compile' command
------------------------------------------------

GDB needs to find GCC for the inferior being debugged which may not be
obvious for remote targets of different architecture than where GDB is
running. Environment variable `PATH' on GDB host is searched for GCC
binary matching the target architecture and operating system. This
search can be overridden by `set compile-gcc' GDB command below.
`PATH' is taken from shell that executed GDB, it is not the value set by
GDB command `set environment'). *Note Environment::.

Specifically `PATH' is searched for binaries matching regular
expression `ARCH(-[^-]*)?-OS-gcc' according to the inferior target being
debugged. ARCH is processor name -- multiarch is supported, so for
example both `i386' and `x86_64' targets look for pattern
`(x86_64|i.86)' and both `s390' and `s390x' targets look for pattern
`s390x?'. OS is currently supported only for pattern `linux(-gnu)?'.

On Posix hosts the compiler driver GDB needs to find also shared
library `libcc1.so' from the compiler. It is searched in default
shared library search path (overridable with usual environment variable
`LD_LIBRARY_PATH'), unrelated to `PATH' or `set compile-gcc' settings.
Contrary to it `libcc1plugin.so' is found according to the installation
of the found compiler -- as possibly specified by the `set compile-gcc'
command.

`set compile-gcc'
Set compilation command used for compiling and injecting code with
the `compile' commands. If this option is not set (it is set to
an empty string), the search described above will occur -- that is
the default.

`show compile-gcc'
Displays the current compile command GCC driver filename. If set,
it is the main command `gcc', found usually for example under name
`x86_64-linux-gnu-gcc'.

File: gdb.info, Node: GDB Files, Next: Targets, Prev: Altering, Up: Top

18 GDB Files
************

GDB needs to know the file name of the program to be debugged, both in
order to read its symbol table and in order to start your program. To
debug a core dump of a previous run, you must also tell GDB the name of
the core dump file.

* Menu:

* Files:: Commands to specify files
* File Caching:: Information about GDB's file caching
* Separate Debug Files:: Debugging information in separate files
* MiniDebugInfo:: Debugging information in a special section
* Index Files:: Index files speed up GDB
* Debug Names:: Extensions to .debug_names
* Symbol Errors:: Errors reading symbol files
* Data Files:: GDB data files

File: gdb.info, Node: Files, Next: File Caching, Up: GDB Files

18.1 Commands to Specify Files
==============================

You may want to specify executable and core dump file names. The usual
way to do this is at start-up time, using the arguments to GDB's
start-up commands (*note Getting In and Out of GDB: Invocation.).

Occasionally it is necessary to change to a different file during a
GDB session. Or you may run GDB and forget to specify a file you want
to use. Or you are debugging a remote target via `gdbserver' (*note
file: Server.). In these situations the GDB commands to specify new
files are useful.

`file FILENAME'
Use FILENAME as the program to be debugged. It is read for its
symbols and for the contents of pure memory. It is also the
program executed when you use the `run' command. If you do not
specify a directory and the file is not found in the GDB working
directory, GDB uses the environment variable `PATH' as a list of
directories to search, just as the shell does when looking for a
program to run. You can change the value of this variable, for
both GDB and your program, using the `path' command.

The FILENAME argument supports escaping and quoting, see *Note
Filenames As Command Arguments: Filename Arguments.

You can load unlinked object `.o' files into GDB using the `file'
command. You will not be able to "run" an object file, but you
can disassemble functions and inspect variables. Also, if the
underlying BFD functionality supports it, you could use `gdb
-write' to patch object files using this technique. Note that GDB
can neither interpret nor modify relocations in this case, so
branches and some initialized variables will appear to go to the
wrong place. But this feature is still handy from time to time.

`file'
`file' with no argument makes GDB discard any information it has
on both executable file and the symbol table.

`exec-file [ FILENAME ]'
Specify that the program to be run (but not the symbol table) is
found in FILENAME. GDB searches the environment variable `PATH'
if necessary to locate your program. Omitting FILENAME means to
discard information on the executable file.

The FILENAME argument supports escaping and quoting, see *Note
Filenames As Command Arguments: Filename Arguments.

`symbol-file [ FILENAME [ -o OFFSET ]]'
Read symbol table information from file FILENAME. `PATH' is
searched when necessary. Use the `file' command to get both symbol
table and program to run from the same file.

If an optional OFFSET is specified, it is added to the start
address of each section in the symbol file. This is useful if the
program is relocated at runtime, such as the Linux kernel with
kASLR enabled.

`symbol-file' with no argument clears out GDB information on your
program's symbol table.

The `symbol-file' command causes GDB to forget the contents of
some breakpoints and auto-display expressions. This is because
they may contain pointers to the internal data recording symbols
and data types, which are part of the old symbol table data being
discarded inside GDB.

`symbol-file' does not repeat if you press <RET> again after
executing it once.

The FILENAME argument supports escaping and quoting, see *Note
Filenames As Command Arguments: Filename Arguments.

When GDB is configured for a particular environment, it
understands debugging information in whatever format is the
standard generated for that environment; you may use either a GNU
compiler, or other compilers that adhere to the local conventions.
Best results are usually obtained from GNU compilers; for example,
using `GCC' you can generate debugging information for optimized
code.

For most kinds of object files, with the exception of old SVR3
systems using COFF, the `symbol-file' command does not normally
read the symbol table in full right away. Instead, it scans the
symbol table quickly to find which source files and which symbols
are present. The details are read later, one source file at a
time, as they are needed.

The purpose of this two-stage reading strategy is to make GDB
start up faster. For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular
source file are being read. (The `set verbose' command can turn
these pauses into messages if desired. *Note Optional Warnings
and Messages: Messages/Warnings.)

We have not implemented the two-stage strategy for COFF yet. When
the symbol table is stored in COFF format, `symbol-file' reads the
symbol table data in full right away. Note that "stabs-in-COFF"
still does the two-stage strategy, since the debug info is actually
in stabs format.

`symbol-file [ -readnow ] FILENAME'
`file [ -readnow ] FILENAME'
You can override the GDB two-stage strategy for reading symbol
tables by using the `-readnow' option with any of the commands that
load symbol table information, if you want to be sure GDB has the
entire symbol table available.

`symbol-file [ -readnever ] FILENAME'
`file [ -readnever ] FILENAME'
You can instruct GDB to never read the symbolic information
contained in FILENAME by using the `-readnever' option. *Note
--readnever::.

`core-file [FILENAME]'
`core'
Specify the whereabouts of a core dump file to be used as the
"contents of memory". Traditionally, core files contain only some
parts of the address space of the process that generated them; GDB
can access the executable file itself for other parts.

`core-file' with no argument specifies that no core file is to be
used.

Note that the core file is ignored when your program is actually
running under GDB. So, if you have been running your program and
you wish to debug a core file instead, you must kill the
subprocess in which the program is running. To do this, use the
`kill' command (*note Killing the Child Process: Kill Process.).

`add-symbol-file FILENAME [ -readnow | -readnever ] [ -o OFFSET ] [ TEXTADDRESS ] [ -s SECTION ADDRESS ... ]'
The `add-symbol-file' command reads additional symbol table
information from the file FILENAME. You would use this command
when FILENAME has been dynamically loaded (by some other means)
into the program that is running. The TEXTADDRESS parameter gives
the memory address at which the file's text section has been
loaded. You can additionally specify the base address of other
sections using an arbitrary number of `-s SECTION ADDRESS' pairs.
If a section is omitted, GDB will use its default addresses as
found in FILENAME. Any ADDRESS or TEXTADDRESS can be given as an
expression.

If an optional OFFSET is specified, it is added to the start
address of each section, except those for which the address was
specified explicitly.

The symbol table of the file FILENAME is added to the symbol table
originally read with the `symbol-file' command. You can use the
`add-symbol-file' command any number of times; the new symbol data
thus read is kept in addition to the old.

The FILENAME argument supports escaping and quoting, see *Note
Filenames As Command Arguments: Filename Arguments.

Changes can be reverted using the command `remove-symbol-file'.

Although FILENAME is typically a shared library file, an
executable file, or some other object file which has been fully
relocated for loading into a process, you can also load symbolic
information from relocatable `.o' files, as long as:

* the file's symbolic information refers only to linker symbols
defined in that file, not to symbols defined by other object
files,

* every section the file's symbolic information refers to has
actually been loaded into the inferior, as it appears in the
file, and

* you can determine the address at which every section was
loaded, and provide these to the `add-symbol-file' command.

Some embedded operating systems, like Sun Chorus and VxWorks, can
load relocatable files into an already running program; such
systems typically make the requirements above easy to meet.
However, it's important to recognize that many native systems use
complex link procedures (`.linkonce' section factoring and C++
constructor table assembly, for example) that make the
requirements difficult to meet. In general, one cannot assume
that using `add-symbol-file' to read a relocatable object file's
symbolic information will have the same effect as linking the
relocatable object file into the program in the normal way.

`add-symbol-file' does not repeat if you press <RET> after using
it.

`remove-symbol-file FILENAME'

`remove-symbol-file -a ADDRESS'
Remove a symbol file added via the `add-symbol-file' command. The
file to remove can be identified by its FILENAME or by an ADDRESS
that lies within the boundaries of this symbol file in memory.
Example:

(gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480
add symbol table from file "/home/user/gdb/mylib.so" at
.text_addr = 0x7ffff7ff9480
(y or n) y
Reading symbols from /home/user/gdb/mylib.so...
(gdb) remove-symbol-file -a 0x7ffff7ff9480
Remove symbol table from file "/home/user/gdb/mylib.so"? (y or n) y
(gdb)

`remove-symbol-file' does not repeat if you press <RET> after
using it.

The FILENAME argument supports escaping and quoting, see *Note
Filenames As Command Arguments: Filename Arguments.

`add-symbol-file-from-memory ADDRESS'
Load symbols from the given ADDRESS in a dynamically loaded object
file whose image is mapped directly into the inferior's memory.
For example, the Linux kernel maps a `syscall DSO' into each
process's address space; this DSO provides kernel-specific code for
some system calls. The argument can be any expression whose
evaluation yields the address of the file's shared object file
header. For this command to work, you must have used
`symbol-file' or `exec-file' commands in advance.

`section SECTION ADDR'
The `section' command changes the base address of the named
SECTION of the exec file to ADDR. This can be used if the exec
file does not contain section addresses, (such as in the `a.out'
format), or when the addresses specified in the file itself are
wrong. Each section must be changed separately. The `info files'
command, described below, lists all the sections and their
addresses.

`info files'
`info target'
`info files' and `info target' are synonymous; both print the
current target (*note Specifying a Debugging Target: Targets.),
including the names of the executable and core dump files
currently in use by GDB, and the files from which symbols were
loaded. The command `help target' lists all possible targets
rather than current ones.

`maint info sections [-all-objects] [FILTER-LIST]'
Another command that can give you extra information about program
sections is `maint info sections'. In addition to the section
information displayed by `info files', this command displays the
flags and file offset of each section in the executable and core
dump files.

When `-all-objects' is passed then sections from all loaded object
files, including shared libraries, are printed.

The optional FILTER-LIST is a space separated list of filter
keywords. Sections that match any one of the filter criteria will
be printed. There are two types of filter:

`SECTION-NAME'
Display information about any section named SECTION-NAME.

`SECTION-FLAG'
Display information for any section with SECTION-FLAG. The
section flags that GDB currently knows about are:
`ALLOC'
Section will have space allocated in the process when
loaded. Set for all sections except those containing
debug information.

`LOAD'
Section will be loaded from the file into the child
process memory. Set for pre-initialized code and data,
clear for `.bss' sections.

`RELOC'
Section needs to be relocated before loading.

`READONLY'
Section cannot be modified by the child process.

`CODE'
Section contains executable code only.

`DATA'
Section contains data only (no executable code).

`ROM'
Section will reside in ROM.

`CONSTRUCTOR'
Section contains data for constructor/destructor lists.

`HAS_CONTENTS'
Section is not empty.

`NEVER_LOAD'
An instruction to the linker to not output the section.

`COFF_SHARED_LIBRARY'
A notification to the linker that the section contains
COFF shared library information.

`IS_COMMON'
Section contains common symbols.

`maint info target-sections'
This command prints GDB's internal section table. For each target
GDB maintains a table containing the allocatable sections from all
currently mapped objects, along with information about where the
section is mapped.

`set trust-readonly-sections on'
Tell GDB that readonly sections in your object file really are
read-only (i.e. that their contents will not change). In that
case, GDB can fetch values from these sections out of the object
file, rather than from the target program. For some targets
(notably embedded ones), this can be a significant enhancement to
debugging performance.

The default is off.

`set trust-readonly-sections off'
Tell GDB not to trust readonly sections. This means that the
contents of the section might change while the program is running,
and must therefore be fetched from the target when needed.

`show trust-readonly-sections'
Show the current setting of trusting readonly sections.

All file-specifying commands allow both absolute and relative file
names as arguments. GDB always converts the file name to an absolute
file name and remembers it that way.

GDB supports GNU/Linux, MS-Windows, SunOS, Darwin/Mach-O, SVr4, IBM
RS/6000 AIX, QNX Neutrino, FDPIC (FR-V), and DSBT (TIC6X) shared
libraries.

On MS-Windows GDB must be linked with the Expat library to support
shared libraries. *Note Expat::.

GDB automatically loads symbol definitions from shared libraries
when you use the `run' command, or when you examine a core file.
(Before you issue the `run' command, GDB does not understand references
to a function in a shared library, however--unless you are debugging a
core file).

There are times, however, when you may wish to not automatically load
symbol definitions from shared libraries, such as when they are
particularly large or there are many of them.

To control the automatic loading of shared library symbols, use the
commands:

`set auto-solib-add MODE'
If MODE is `on', symbols from all shared object libraries will be
loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic
linker informs GDB that a new library has been loaded. If MODE is
`off', symbols must be loaded manually, using the `sharedlibrary'
command. The default value is `on'.

If your program uses lots of shared libraries with debug info that
takes large amounts of memory, you can decrease the GDB memory
footprint by preventing it from automatically loading the symbols
from shared libraries. To that end, type `set auto-solib-add off'
before running the inferior, then load each library whose debug
symbols you do need with `sharedlibrary REGEXP', where REGEXP is a
regular expression that matches the libraries whose symbols you
want to be loaded.

`show auto-solib-add'
Display the current autoloading mode.

To explicitly load shared library symbols, use the `sharedlibrary'
command:

`info share REGEX'
`info sharedlibrary REGEX'
Print the names of the shared libraries which are currently loaded
that match REGEX. If REGEX is omitted then print all shared
libraries that are loaded.

`info dll REGEX'
This is an alias of `info sharedlibrary'.

`sharedlibrary REGEX'
`share REGEX'
Load shared object library symbols for files matching a Unix
regular expression. As with files loaded automatically, it only
loads shared libraries required by your program for a core file or
after typing `run'. If REGEX is omitted all shared libraries
required by your program are loaded.

`nosharedlibrary'
Unload all shared object library symbols. This discards all
symbols that have been loaded from all shared libraries. Symbols
from shared libraries that were loaded by explicit user requests
are not discarded.

Sometimes you may wish that GDB stops and gives you control when any
of shared library events happen. The best way to do this is to use
`catch load' and `catch unload' (*note Set Catchpoints::).

GDB also supports the `set stop-on-solib-events' command for this.
This command exists for historical reasons. It is less useful than
setting a catchpoint, because it does not allow for conditions or
commands as a catchpoint does.

`set stop-on-solib-events'
This command controls whether GDB should give you control when the
dynamic linker notifies it about some shared library event. The
most common event of interest is loading or unloading of a new
shared library.

`show stop-on-solib-events'
Show whether GDB stops and gives you control when shared library
events happen.

Shared libraries are also supported in many cross or remote debugging
configurations. GDB needs to have access to the target's libraries;
this can be accomplished either by providing copies of the libraries on
the host system, or by asking GDB to automatically retrieve the
libraries from the target. If copies of the target libraries are
provided, they need to be the same as the target libraries, although the
copies on the target can be stripped as long as the copies on the host
are not.

For remote debugging, you need to tell GDB where the target
libraries are, so that it can load the correct copies--otherwise, it
may try to load the host's libraries. GDB has two variables to specify
the search directories for target libraries.

`set sysroot PATH'
Use PATH as the system root for the program being debugged. Any
absolute shared library paths will be prefixed with PATH; many
runtime loaders store the absolute paths to the shared library in
the target program's memory. When starting processes remotely,
and when attaching to already-running processes (local or remote),
their executable filenames will be prefixed with PATH if reported
to GDB as absolute by the operating system. If you use `set
sysroot' to find executables and shared libraries, they need to be
laid out in the same way that they are on the target, with e.g. a
`/bin', `/lib' and `/usr/lib' hierarchy under PATH.

If PATH starts with the sequence `target:' and the target system
is remote then GDB will retrieve the target binaries from the
remote system. This is only supported when using a remote target
that supports the `remote get' command (*note Sending files to a
remote system: File Transfer.). The part of PATH following the
initial `target:' (if present) is used as system root prefix on
the remote file system. If PATH starts with the sequence
`remote:' this is converted to the sequence `target:' by `set
sysroot'(1). If you want to specify a local system root using a
directory that happens to be named `target:' or `remote:', you
need to use some equivalent variant of the name like `./target:'.

For targets with an MS-DOS based filesystem, such as MS-Windows,
GDB tries prefixing a few variants of the target absolute file
name with PATH. But first, on Unix hosts, GDB converts all
backslash directory separators into forward slashes, because the
backslash is not a directory separator on Unix:

c:\foo\bar.dll => c:/foo/bar.dll

Then, GDB attempts prefixing the target file name with PATH, and
looks for the resulting file name in the host file system:

c:/foo/bar.dll => /path/to/sysroot/c:/foo/bar.dll

If that does not find the binary, GDB tries removing the `:'
character from the drive spec, both for convenience, and, for the
case of the host file system not supporting file names with colons:

c:/foo/bar.dll => /path/to/sysroot/c/foo/bar.dll

This makes it possible to have a system root that mirrors a target
with more than one drive. E.g., you may want to setup your local
copies of the target system shared libraries like so (note `c' vs
`z'):

`/path/to/sysroot/c/sys/bin/foo.dll'
`/path/to/sysroot/c/sys/bin/bar.dll'
`/path/to/sysroot/z/sys/bin/bar.dll'

and point the system root at `/path/to/sysroot', so that GDB can
find the correct copies of both `c:\sys\bin\foo.dll', and
`z:\sys\bin\bar.dll'.

If that still does not find the binary, GDB tries removing the
whole drive spec from the target file name:

c:/foo/bar.dll => /path/to/sysroot/foo/bar.dll

This last lookup makes it possible to not care about the drive
name, if you don't want or need to.

The `set solib-absolute-prefix' command is an alias for `set
sysroot'.

You can set the default system root by using the configure-time
`--with-sysroot' option. If the system root is inside GDB's
configured binary prefix (set with `--prefix' or `--exec-prefix'),
then the default system root will be updated automatically if the
installed GDB is moved to a new location.

`show sysroot'
Display the current executable and shared library prefix.

`set solib-search-path PATH'
If this variable is set, PATH is a colon-separated list of
directories to search for shared libraries. `solib-search-path'
is used after `sysroot' fails to locate the library, or if the
path to the library is relative instead of absolute. If you want
to use `solib-search-path' instead of `sysroot', be sure to set
`sysroot' to a nonexistent directory to prevent GDB from finding
your host's libraries. `sysroot' is preferred; setting it to a
nonexistent directory may interfere with automatic loading of
shared library symbols.

`show solib-search-path'
Display the current shared library search path.

`set target-file-system-kind KIND'
Set assumed file system kind for target reported file names.

Shared library file names as reported by the target system may not
make sense as is on the system GDB is running on. For example,
when remote debugging a target that has MS-DOS based file system
semantics, from a Unix host, the target may be reporting to GDB a
list of loaded shared libraries with file names such as
`c:\Windows\kernel32.dll'. On Unix hosts, there's no concept of
drive letters, so the `c:\' prefix is not normally understood as
indicating an absolute file name, and neither is the backslash
normally considered a directory separator character. In that case,
the native file system would interpret this whole absolute file
name as a relative file name with no directory components. This
would make it impossible to point GDB at a copy of the remote
target's shared libraries on the host using `set sysroot', and
impractical with `set solib-search-path'. Setting
`target-file-system-kind' to `dos-based' tells GDB to interpret
such file names similarly to how the target would, and to map them
to file names valid on GDB's native file system semantics. The
value of KIND can be `"auto"', in addition to one of the supported
file system kinds. In that case, GDB tries to determine the
appropriate file system variant based on the current target's
operating system (*note Configuring the Current ABI: ABI.). The
supported file system settings are:

`unix'
Instruct GDB to assume the target file system is of Unix
kind. Only file names starting the forward slash (`/')
character are considered absolute, and the directory
separator character is also the forward slash.

`dos-based'
Instruct GDB to assume the target file system is DOS based.
File names starting with either a forward slash, or a drive
letter followed by a colon (e.g., `c:'), are considered
absolute, and both the slash (`/') and the backslash (`\\')
characters are considered directory separators.

`auto'
Instruct GDB to use the file system kind associated with the
target operating system (*note Configuring the Current ABI:
ABI.). This is the default.

When processing file names provided by the user, GDB frequently
needs to compare them to the file names recorded in the program's debug
info. Normally, GDB compares just the "base names" of the files as
strings, which is reasonably fast even for very large programs. (The
base name of a file is the last portion of its name, after stripping
all the leading directories.) This shortcut in comparison is based
upon the assumption that files cannot have more than one base name.
This is usually true, but references to files that use symlinks or
similar filesystem facilities violate that assumption. If your program
records files using such facilities, or if you provide file names to
GDB using symlinks etc., you can set `basenames-may-differ' to `true'
to instruct GDB to completely canonicalize each pair of file names it
needs to compare. This will make file-name comparisons accurate, but
at a price of a significant slowdown.

`set basenames-may-differ'
Set whether a source file may have multiple base names.

`show basenames-may-differ'
Show whether a source file may have multiple base names.

---------- Footnotes ----------

(1) Historically the functionality to retrieve binaries from the
remote system was provided by prefixing PATH with `remote:'

File: gdb.info, Node: File Caching, Next: Separate Debug Files, Prev: Files, Up: GDB Files

18.2 File Caching
=================

To speed up file loading, and reduce memory usage, GDB will reuse the
`bfd' objects used to track open files. *Note BFD: (bfd)Top. The
following commands allow visibility and control of the caching behavior.

`maint info bfds'
This prints information about each `bfd' object that is known to
GDB.

`maint set bfd-sharing'

`maint show bfd-sharing'
Control whether `bfd' objects can be shared. When sharing is
enabled GDB reuses already open `bfd' objects rather than
reopening the same file. Turning sharing off does not cause
already shared `bfd' objects to be unshared, but all future files
that are opened will create a new `bfd' object. Similarly,
re-enabling sharing does not cause multiple existing `bfd' objects
to be collapsed into a single shared `bfd' object.

`set debug bfd-cache LEVEL'
Turns on debugging of the bfd cache, setting the level to LEVEL.

`show debug bfd-cache'
Show the current debugging level of the bfd cache.

File: gdb.info, Node: Separate Debug Files, Next: MiniDebugInfo, Prev: File Caching, Up: GDB Files

18.3 Debugging Information in Separate Files
============================================

GDB allows you to put a program's debugging information in a file
separate from the executable itself, in a way that allows GDB to find
and load the debugging information automatically. Since debugging
information can be very large--sometimes larger than the executable
code itself--some systems distribute debugging information for their
executables in separate files, which users can install only when they
need to debug a problem.

GDB supports two ways of specifying the separate debug info file:

* The executable contains a "debug link" that specifies the name of
the separate debug info file. The separate debug file's name is
usually `EXECUTABLE.debug', where EXECUTABLE is the name of the
corresponding executable file without leading directories (e.g.,
`ls.debug' for `/usr/bin/ls'). In addition, the debug link
specifies a 32-bit "Cyclic Redundancy Check" (CRC) checksum for
the debug file, which GDB uses to validate that the executable and
the debug file came from the same build.

* The executable contains a "build ID", a unique bit string that is
also present in the corresponding debug info file. (This is
supported only on some operating systems, when using the ELF or PE
file formats for binary files and the GNU Binutils.) For more
details about this feature, see the description of the `--build-id'
command-line option in *Note Command Line Options: (ld)Options.
The debug info file's name is not specified explicitly by the
build ID, but can be computed from the build ID, see below.

Depending on the way the debug info file is specified, GDB uses two
different methods of looking for the debug file:

* For the "debug link" method, GDB looks up the named file in the
directory of the executable file, then in a subdirectory of that
directory named `.debug', and finally under each one of the global
debug directories, in a subdirectory whose name is identical to
the leading directories of the executable's absolute file name.
(On MS-Windows/MS-DOS, the drive letter of the executable's leading
directories is converted to a one-letter subdirectory, i.e.
`d:/usr/bin/' is converted to `/d/usr/bin/', because Windows
filesystems disallow colons in file names.)

* For the "build ID" method, GDB looks in the `.build-id'
subdirectory of each one of the global debug directories for a
file named `NN/NNNNNNNN.debug', where NN are the first 2 hex
characters of the build ID bit string, and NNNNNNNN are the rest
of the bit string. (Real build ID strings are 32 or more hex
characters, not 10.) GDB can automatically query `debuginfod'
servers using build IDs in order to download separate debug files
that cannot be found locally. For more information see *Note
Debuginfod::.

So, for example, suppose you ask GDB to debug `/usr/bin/ls', which
has a debug link that specifies the file `ls.debug', and a build ID
whose value in hex is `abcdef1234'. If the list of the global debug
directories includes `/usr/lib/debug', then GDB will look for the
following debug information files, in the indicated order:

- `/usr/lib/debug/.build-id/ab/cdef1234.debug'

- `/usr/bin/ls.debug'

- `/usr/bin/.debug/ls.debug'

- `/usr/lib/debug/usr/bin/ls.debug'.

If the debug file still has not been found and `debuginfod' (*note
Debuginfod::) is enabled, GDB will attempt to download the file from
`debuginfod' servers.

Global debugging info directories default to what is set by GDB
configure option `--with-separate-debug-dir' and augmented by the
colon-separated list of directories provided via GDB configure option
`--additional-debug-dirs'. During GDB run you can also set the global
debugging info directories, and view the list GDB is currently using.

`set debug-file-directory DIRECTORIES'
Set the directories which GDB searches for separate debugging
information files to DIRECTORY. Multiple path components can be
set concatenating them by a path separator.

`show debug-file-directory'
Show the directories GDB searches for separate debugging
information files.

A debug link is a special section of the executable file named
`.gnu_debuglink'. The section must contain:

* A filename, with any leading directory components removed,
followed by a zero byte,

* zero to three bytes of padding, as needed to reach the next
four-byte boundary within the section, and

* a four-byte CRC checksum, stored in the same endianness used for
the executable file itself. The checksum is computed on the
debugging information file's full contents by the function given
below, passing zero as the CRC argument.

Any executable file format can carry a debug link, as long as it can
contain a section named `.gnu_debuglink' with the contents described
above.

The build ID is a special section in the executable file (and in
other ELF binary files that GDB may consider). This section is often
named `.note.gnu.build-id', but that name is not mandatory. It
contains unique identification for the built files--the ID remains the
same across multiple builds of the same build tree. The default
algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
content for the build ID string. The same section with an identical
value is present in the original built binary with symbols, in its
stripped variant, and in the separate debugging information file.

The debugging information file itself should be an ordinary
executable, containing a full set of linker symbols, sections, and
debugging information. The sections of the debugging information file
should have the same names, addresses, and sizes as the original file,
but they need not contain any data--much like a `.bss' section in an
ordinary executable.

The GNU binary utilities (Binutils) package includes the `objcopy'
utility that can produce the separated executable / debugging
information file pairs using the following commands:

objcopy --only-keep-debug foo foo.debug
strip -g foo

These commands remove the debugging information from the executable
file `foo' and place it in the file `foo.debug'. You can use the
first, second or both methods to link the two files:

* The debug link method needs the following additional command to
also leave behind a debug link in `foo':

objcopy --add-gnu-debuglink=foo.debug foo

Ulrich Drepper's `elfutils' package, starting with version 0.53,
contains a version of the `strip' command such that the command
`strip foo -f foo.debug' has the same functionality as the two
`objcopy' commands and the `ln -s' command above, together.

* Build ID gets embedded into the main executable using `ld
--build-id' or the GCC counterpart `gcc -Wl,--build-id'. Build ID
support plus compatibility fixes for debug files separation are
present in GNU binary utilities (Binutils) package since version
2.18.

The CRC used in `.gnu_debuglink' is the CRC-32 defined in IEEE 802.3
using the polynomial:

x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11
+ x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1

The function is computed byte at a time, taking the least
significant bit of each byte first. The initial pattern `0xffffffff'
is used, to ensure leading zeros affect the CRC and the final result is
inverted to ensure trailing zeros also affect the CRC.

_Note:_ This is the same CRC polynomial as used in handling the
"Remote Serial Protocol" `qCRC' packet (*note qCRC packet::). However
in the case of the Remote Serial Protocol, the CRC is computed _most_
significant bit first, and the result is not inverted, so trailing
zeros have no effect on the CRC value.

To complete the description, we show below the code of the function
which produces the CRC used in `.gnu_debuglink'. Inverting the
initially supplied `crc' argument means that an initial call to this
function passing in zero will start computing the CRC using
`0xffffffff'.

unsigned long
gnu_debuglink_crc32 (unsigned long crc,
unsigned char *buf, size_t len)
{
static const unsigned long crc32_table[256] =
{
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
0x2d02ef8d
};
unsigned char *end;

crc = ~crc & 0xffffffff;
for (end = buf + len; buf < end; ++buf)
crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
return ~crc & 0xffffffff;
}

This computation does not apply to the "build ID" method.

File: gdb.info, Node: MiniDebugInfo, Next: Index Files, Prev: Separate Debug Files, Up: GDB Files

18.4 Debugging information in a special section
===============================================

Some systems ship pre-built executables and libraries that have a
special `.gnu_debugdata' section. This feature is called
"MiniDebugInfo". This section holds an LZMA-compressed object and is
used to supply extra symbols for backtraces.

The intent of this section is to provide extra minimal debugging
information for use in simple backtraces. It is not intended to be a
replacement for full separate debugging information (*note Separate
Debug Files::). The example below shows the intended use; however, GDB
does not currently put restrictions on what sort of debugging
information might be included in the section.

GDB has support for this extension. If the section exists, then it
is used provided that no other source of debugging information can be
found, and that GDB was configured with LZMA support.

This section can be easily created using `objcopy' and other
standard utilities:

# Extract the dynamic symbols from the main binary, there is no need
# to also have these in the normal symbol table.
nm -D BINARY --format=posix --defined-only \
| awk '{ print $1 }' | sort > dynsyms

# Extract all the text (i.e. function) symbols from the debuginfo.
# (Note that we actually also accept "D" symbols, for the benefit
# of platforms like PowerPC64 that use function descriptors.)
nm BINARY --format=posix --defined-only \
| awk '{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }' \
| sort > funcsyms

# Keep all the function symbols not already in the dynamic symbol
# table.
comm -13 dynsyms funcsyms > keep_symbols

# Separate full debug info into debug binary.
objcopy --only-keep-debug BINARY debug

# Copy the full debuginfo, keeping only a minimal set of symbols and
# removing some unnecessary sections.
objcopy -S --remove-section .gdb_index --remove-section .comment \
--keep-symbols=keep_symbols debug mini_debuginfo

# Drop the full debug info from the original binary.
strip --strip-all -R .comment BINARY

# Inject the compressed data into the .gnu_debugdata section of the
# original binary.
xz mini_debuginfo
objcopy --add-section .gnu_debugdata=mini_debuginfo.xz BINARY

File: gdb.info, Node: Index Files, Next: Debug Names, Prev: MiniDebugInfo, Up: GDB Files

18.5 Index Files Speed Up GDB
=============================

When GDB finds a symbol file, it scans the symbols in the file in order
to construct an internal symbol table. This lets most GDB operations
work quickly--at the cost of a delay early on. For large programs,
this delay can be quite lengthy, so GDB provides a way to build an
index, which speeds up startup.

For convenience, GDB comes with a program, `gdb-add-index', which
can be used to add the index to a symbol file. It takes the symbol
file as its only argument:

$ gdb-add-index symfile

*Note gdb-add-index::.

It is also possible to do the work manually. Here is what
`gdb-add-index' does behind the curtains.

The index is stored as a section in the symbol file. GDB can write
the index to a file, then you can put it into the symbol file using
`objcopy'.

To create an index file, use the `save gdb-index' command:

`save gdb-index [-dwarf-5] DIRECTORY'
Create index files for all symbol files currently known by GDB.
For each known SYMBOL-FILE, this command by default creates it
produces a single file `SYMBOL-FILE.gdb-index'. If you invoke
this command with the `-dwarf-5' option, it produces 2 files:
`SYMBOL-FILE.debug_names' and `SYMBOL-FILE.debug_str'. The files
are created in the given DIRECTORY.

Once you have created an index file you can merge it into your symbol
file, here named `symfile', using `objcopy':

$ objcopy --add-section .gdb_index=symfile.gdb-index \
--set-section-flags .gdb_index=readonly symfile symfile

Or for `-dwarf-5':

$ objcopy --dump-section .debug_str=symfile.debug_str.new symfile
$ cat symfile.debug_str >>symfile.debug_str.new
$ objcopy --add-section .debug_names=symfile.gdb-index \
--set-section-flags .debug_names=readonly \
--update-section .debug_str=symfile.debug_str.new symfile symfile

GDB will normally ignore older versions of `.gdb_index' sections
that have been deprecated. Usually they are deprecated because they
are missing a new feature or have performance issues. To tell GDB to
use a deprecated index section anyway specify `set
use-deprecated-index-sections on'. The default is `off'. This can
speed up startup, but may result in some functionality being lost.
*Note Index Section Format::.

_Warning:_ Setting `use-deprecated-index-sections' to `on' must be
done before gdb reads the file. The following will not work:

$ gdb -ex "set use-deprecated-index-sections on" <program>

Instead you must do, for example,

$ gdb -iex "set use-deprecated-index-sections on" <program>

Indices only work when using DWARF debugging information, not stabs.

18.5.1 Automatic symbol index cache
-----------------------------------

It is possible for GDB to automatically save a copy of this index in a
cache on disk and retrieve it from there when loading the same binary
in the future. This feature can be turned on with `set index-cache
enabled on'. The following commands can be used to tweak the behavior
of the index cache.

`set index-cache enabled on'
`set index-cache enabled off'
Enable or disable the use of the symbol index cache.

`set index-cache directory DIRECTORY'
`show index-cache directory'
Set/show the directory where index files will be saved.

The default value for this directory depends on the host platform.
On most systems, the index is cached in the `gdb' subdirectory of
the directory pointed to by the `XDG_CACHE_HOME' environment
variable, if it is defined, else in the `.cache/gdb' subdirectory
of your home directory. However, on some systems, the default may
differ according to local convention.

There is no limit on the disk space used by index cache. It is
perfectly safe to delete the content of that directory to free up
disk space.

`show index-cache stats'
Print the number of cache hits and misses since the launch of GDB.

File: gdb.info, Node: Debug Names, Next: Symbol Errors, Prev: Index Files, Up: GDB Files

18.6 Extensions to `.debug_names'
=================================

The DWARF specification documents an optional index section called
`.debug_names'. GDB can both read and create this section. However,
in order to work with GDB, some extensions were necessary.

GDB uses the augmentation string `GDB2'. Earlier versions used the
string `GDB', but these versions of the index are no longer supported.

GDB does not use the specified hash table. Therefore, because this
hash table is optional, GDB also does not write it.

GDB also generates and uses some extra index attributes:
`DW_IDX_GNU_internal'
This has the value `0x2000'. It is a flag that, when set,
indicates that the associated entry has `static' linkage.

`DW_IDX_GNU_main'
This has the value `0x2002'. It is a flag that, when set,
indicates that the associated entry is the program's `main'.

`DW_IDX_GNU_language'
This has the value `0x2003'. It is `DW_LANG_' constant,
indicating the language of the associated entry.

`DW_IDX_GNU_linkage_name'
This has the value `0x2004'. It is a flag that, when set,
indicates that the associated entry is a linkage name, and not a
source name.

File: gdb.info, Node: Symbol Errors, Next: Data Files, Prev: Debug Names, Up: GDB Files

18.7 Errors Reading Symbol Files
================================

While reading a symbol file, GDB occasionally encounters problems, such
as symbol types it does not recognize, or known bugs in compiler
output. By default, GDB does not notify you of such problems, since
they are relatively common and primarily of interest to people
debugging compilers. If you are interested in seeing information about
ill-constructed symbol tables, you can either ask GDB to print only one
message about each such type of problem, no matter how many times the
problem occurs; or you can ask GDB to print more messages, to see how
many times the problems occur, with the `set complaints' command (*note
Optional Warnings and Messages: Messages/Warnings.).

The messages currently printed, and their meanings, include:

`inner block not inside outer block in SYMBOL'
The symbol information shows where symbol scopes begin and end
(such as at the start of a function or a block of statements).
This error indicates that an inner scope block is not fully
contained in its outer scope blocks.

GDB circumvents the problem by treating the inner block as if it
had the same scope as the outer block. In the error message,
SYMBOL may be shown as "`(don't know)'" if the outer block is not a
function.

`block at ADDRESS out of order'
The symbol information for symbol scope blocks should occur in
order of increasing addresses. This error indicates that it does
not do so.

GDB does not circumvent this problem, and has trouble locating
symbols in the source file whose symbols it is reading. (You can
often determine what source file is affected by specifying `set
verbose on'. *Note Optional Warnings and Messages:
Messages/Warnings.)

`bad block start address patched'
The symbol information for a symbol scope block has a start address
smaller than the address of the preceding source line. This is
known to occur in the SunOS 4.1.1 (and earlier) C compiler.

GDB circumvents the problem by treating the symbol scope block as
starting on the previous source line.

`bad string table offset in symbol N'
Symbol number N contains a pointer into the string table which is
larger than the size of the string table.

GDB circumvents the problem by considering the symbol to have the
name `foo', which may cause other problems if many symbols end up
with this name.

`unknown symbol type `0xNN''
The symbol information contains new data types that GDB does not
yet know how to read. `0xNN' is the symbol type of the
uncomprehended information, in hexadecimal.

GDB circumvents the error by ignoring this symbol information.
This usually allows you to debug your program, though certain
symbols are not accessible. If you encounter such a problem and
feel like debugging it, you can debug `gdb' with itself, breakpoint
on `complain', then go up to the function `read_dbx_symtab' and
examine `*bufp' to see the symbol.

`stub type has NULL name'
GDB could not find the full definition for a struct or class.

`const/volatile indicator missing (ok if using g++ v1.x), got...'
The symbol information for a C++ member function is missing some
information that recent versions of the compiler should have
output for it.

`info mismatch between compiler and debugger'
GDB could not parse a type specification output by the compiler.

File: gdb.info, Node: Data Files, Prev: Symbol Errors, Up: GDB Files

18.8 GDB Data Files
===================

GDB will sometimes read an auxiliary data file. These files are kept
in a directory known as the "data directory".

You can set the data directory's name, and view the name GDB is
currently using.

`set data-directory DIRECTORY'
Set the directory which GDB searches for auxiliary data files to
DIRECTORY.

`show data-directory'
Show the directory GDB searches for auxiliary data files.

You can set the default data directory by using the configure-time
`--with-gdb-datadir' option. If the data directory is inside GDB's
configured binary prefix (set with `--prefix' or `--exec-prefix'), then
the default data directory will be updated automatically if the
installed GDB is moved to a new location.

The data directory may also be specified with the `--data-directory'
command line option. *Note Mode Options::.

File: gdb.info, Node: Targets, Next: Remote Debugging, Prev: GDB Files, Up: Top

19 Specifying a Debugging Target
********************************

A "target" is the execution environment occupied by your program.

Often, GDB runs in the same host environment as your program; in
that case, the debugging target is specified as a side effect when you
use the `file' or `core' commands. When you need more flexibility--for
example, running GDB on a physically separate host, or controlling a
standalone system over a serial port or a realtime system over a TCP/IP
connection--you can use the `target' command to specify one of the
target types configured for GDB (*note Commands for Managing Targets:
Target Commands.).

It is possible to build GDB for several different "target
architectures". When GDB is built like that, you can choose one of the
available architectures with the `set architecture' command.

`set architecture ARCH'
This command sets the current target architecture to ARCH. The
value of ARCH can be `"auto"', in addition to one of the supported
architectures.

`show architecture'
Show the current target architecture.

`set processor'
`processor'
These are alias commands for, respectively, `set architecture' and
`show architecture'.

* Menu:

* Active Targets:: Active targets
* Target Commands:: Commands for managing targets
* Byte Order:: Choosing target byte order

File: gdb.info, Node: Active Targets, Next: Target Commands, Up: Targets

19.1 Active Targets
===================

There are multiple classes of targets such as: processes, executable
files or recording sessions. Core files belong to the process class,
making core file and process mutually exclusive. Otherwise, GDB can
work concurrently on multiple active targets, one in each class. This
allows you to (for example) start a process and inspect its activity,
while still having access to the executable file after the process
finishes. Or if you start process recording (*note Reverse
Execution::) and `reverse-step' there, you are presented a virtual
layer of the recording target, while the process target remains stopped
at the chronologically last point of the process execution.

Use the `core-file' and `exec-file' commands to select a new core
file or executable target (*note Commands to Specify Files: Files.). To
specify as a target a process that is already running, use the `attach'
command (*note Debugging an Already-running Process: Attach.).

File: gdb.info, Node: Target Commands, Next: Byte Order, Prev: Active Targets, Up: Targets

19.2 Commands for Managing Targets
==================================

`target TYPE PARAMETERS'
Connects the GDB host environment to a target machine or process.
A target is typically a protocol for talking to debugging
facilities. You use the argument TYPE to specify the type or
protocol of the target machine.

Further PARAMETERS are interpreted by the target protocol, but
typically include things like device names or host names to connect
with, process numbers, and baud rates.

The `target' command does not repeat if you press <RET> again
after executing the command.

`help target'
Displays the names of all targets available. To display targets
currently selected, use either `info target' or `info files'
(*note Commands to Specify Files: Files.).

`help target NAME'
Describe a particular target, including any parameters necessary to
select it.

`set gnutarget ARGS'
GDB uses its own library BFD to read your files. GDB knows
whether it is reading an "executable", a "core", or a ".o" file;
however, you can specify the file format with the `set gnutarget'
command. Unlike most `target' commands, with `gnutarget' the
`target' refers to a program, not a machine.

_Warning:_ To specify a file format with `set gnutarget', you
must know the actual BFD name.

*Note Commands to Specify Files: Files.

`show gnutarget'
Use the `show gnutarget' command to display what file format
`gnutarget' is set to read. If you have not set `gnutarget', GDB
will determine the file format for each file automatically, and
`show gnutarget' displays `The current BFD target is "auto"'.

Here are some common targets (available, or not, depending on the GDB
configuration):

`target exec PROGRAM'
An executable file. `target exec PROGRAM' is the same as
`exec-file PROGRAM'.

`target core FILENAME'
A core dump file. `target core FILENAME' is the same as
`core-file FILENAME'.

`target remote MEDIUM'
A remote system connected to GDB via a serial line or network
connection. This command tells GDB to use its own remote protocol
over MEDIUM for debugging. *Note Remote Debugging::.

For example, if you have a board connected to `/dev/ttya' on the
machine running GDB, you could say:

target remote /dev/ttya

`target remote' supports the `load' command. This is only useful
if you have some other way of getting the stub to the target
system, and you can put it somewhere in memory where it won't get
clobbered by the download.

`target sim [SIMARGS] ...'
Builtin CPU simulator. GDB includes simulators for most
architectures. In general,
target sim
load
run
works; however, you cannot assume that a specific memory map,
device drivers, or even basic I/O is available, although some
simulators do provide these. For info about any
processor-specific simulator details, see the appropriate section
in *Note Embedded Processors: Embedded Processors.

`target native'
Setup for local/native process debugging. Useful to make the
`run' command spawn native processes (likewise `attach', etc.)
even when `set auto-connect-native-target' is `off' (*note set
auto-connect-native-target::).

Different targets are available on different configurations of GDB;
your configuration may have more or fewer targets.

Many remote targets require you to download the executable's code
once you've successfully established a connection. You may wish to
control various aspects of this process.

`set hash'
This command controls whether a hash mark `#' is displayed while
downloading a file to the remote monitor. If on, a hash mark is
displayed after each S-record is successfully downloaded to the
monitor.

`show hash'
Show the current status of displaying the hash mark.

`set debug monitor'
Enable or disable display of communications messages between GDB
and the remote monitor.

`show debug monitor'
Show the current status of displaying communications between GDB
and the remote monitor.

`load FILENAME OFFSET'
Depending on what remote debugging facilities are configured into
GDB, the `load' command may be available. Where it exists, it is
meant to make FILENAME (an executable) available for debugging on
the remote system--by downloading, or dynamic linking, for example.
`load' also records the FILENAME symbol table in GDB, like the
`add-symbol-file' command.

If your GDB does not have a `load' command, attempting to execute
it gets the error message "`You can't do that when your target is
...'"

The file is loaded at whatever address is specified in the
executable. For some object file formats, you can specify the
load address when you link the program; for other formats, like
a.out, the object file format specifies a fixed address.

It is also possible to tell GDB to load the executable file at a
specific offset described by the optional argument OFFSET. When
OFFSET is provided, FILENAME must also be provided.

Depending on the remote side capabilities, GDB may be able to load
programs into flash memory.

`load' does not repeat if you press <RET> again after using it.

`flash-erase'
Erases all known flash memory regions on the target.

File: gdb.info, Node: Byte Order, Prev: Target Commands, Up: Targets

19.3 Choosing Target Byte Order
===============================

Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
offer the ability to run either big-endian or little-endian byte
orders. Usually the executable or symbol will include a bit to
designate the endian-ness, and you will not need to worry about which
to use. However, you may still find it useful to adjust GDB's idea of
processor endian-ness manually.

`set endian big'
Instruct GDB to assume the target is big-endian.

`set endian little'
Instruct GDB to assume the target is little-endian.

`set endian auto'
Instruct GDB to use the byte order associated with the executable.

`show endian'
Display GDB's current idea of the target byte order.

If the `set endian auto' mode is in effect and no executable has
been selected, then the endianness used is the last one chosen either
by one of the `set endian big' and `set endian little' commands or by
inferring from the last executable used. If no endianness has been
previously chosen, then the default for this mode is inferred from the
target GDB has been built for, and is `little' if the name of the
target CPU has an `el' suffix and `big' otherwise.

Note that these commands merely adjust interpretation of symbolic
data on the host, and that they have absolutely no effect on the target
system.

File: gdb.info, Node: Remote Debugging, Next: Configurations, Prev: Targets, Up: Top

20 Debugging Remote Programs
****************************

If you are trying to debug a program running on a machine that cannot
run GDB in the usual way, it is often useful to use remote debugging.
For example, you might use remote debugging on an operating system
kernel, or on a small system which does not have a general purpose
operating system powerful enough to run a full-featured debugger.

Some configurations of GDB have special serial or TCP/IP interfaces
to make this work with particular debugging targets. In addition, GDB
comes with a generic serial protocol (specific to GDB, but not specific
to any particular target system) which you can use if you write the
remote stubs--the code that runs on the remote system to communicate
with GDB.

Other remote targets may be available in your configuration of GDB;
use `help target' to list them.

* Menu:

* Connecting:: Connecting to a remote target
* File Transfer:: Sending files to a remote system
* Server:: Using the gdbserver program
* Remote Configuration:: Remote configuration
* Remote Stub:: Implementing a remote stub

File: gdb.info, Node: Connecting, Next: File Transfer, Up: Remote Debugging

20.1 Connecting to a Remote Target
==================================

This section describes how to connect to a remote target, including the
types of connections and their differences, how to set up executable and
symbol files on the host and target, and the commands used for
connecting to and disconnecting from the remote target.

20.1.1 Types of Remote Connections
----------------------------------

GDB supports two types of remote connections, `target remote' mode and
`target extended-remote' mode. Note that many remote targets support
only `target remote' mode. There are several major differences between
the two types of connections, enumerated here:

Result of detach or program exit
*With target remote mode:* When the debugged program exits or you
detach from it, GDB disconnects from the target. When using
`gdbserver', `gdbserver' will exit.

*With target extended-remote mode:* When the debugged program
exits or you detach from it, GDB remains connected to the target,
even though no program is running. You can rerun the program,
attach to a running program, or use `monitor' commands specific to
the target.

When using `gdbserver' in this case, it does not exit unless it was
invoked using the `--once' option. If the `--once' option was not
used, you can ask `gdbserver' to exit using the `monitor exit'
command (*note Monitor Commands for gdbserver::).

Specifying the program to debug
For both connection types you use the `file' command to specify the
program on the host system. If you are using `gdbserver' there are
some differences in how to specify the location of the program on
the target.

*With target remote mode:* You must either specify the program to
debug on the `gdbserver' command line or use the `--attach' option
(*note Attaching to a Running Program: Attaching to a program.).

*With target extended-remote mode:* You may specify the program to
debug on the `gdbserver' command line, or you can load the program
or attach to it using GDB commands after connecting to `gdbserver'.

You can start `gdbserver' without supplying an initial command to
run or process ID to attach. To do this, use the `--multi'
command line option. Then you can connect using `target
extended-remote' and start the program you want to debug (see
below for details on using the `run' command in this scenario).
Note that the conditions under which `gdbserver' terminates depend
on how GDB connects to it (`target remote' or `target
extended-remote'). The `--multi' option to `gdbserver' has no
influence on that.

The `run' command
*With target remote mode:* The `run' command is not supported.
Once a connection has been established, you can use all the usual
GDB commands to examine and change data. The remote program is
already running, so you can use commands like `step' and
`continue'.

*With target extended-remote mode:* The `run' command is
supported. The `run' command uses the value set by `set remote
exec-file' (*note set remote exec-file::) to select the program to
run. Command line arguments are supported, except for wildcard
expansion and I/O redirection (*note Arguments::).

If you specify the program to debug on the command line, then the
`run' command is not required to start execution, and you can
resume using commands like `step' and `continue' as with `target
remote' mode.

Attaching
*With target remote mode:* The GDB command `attach' is not
supported. To attach to a running program using `gdbserver', you
must use the `--attach' option (*note Running gdbserver::).

*With target extended-remote mode:* To attach to a running program,
you may use the `attach' command after the connection has been
established. If you are using `gdbserver', you may also invoke
`gdbserver' using the `--attach' option (*note Running
gdbserver::).

Some remote targets allow GDB to determine the executable file
running in the process the debugger is attaching to. In such a
case, GDB uses the value of `exec-file-mismatch' to handle a
possible mismatch between the executable file name running in the
process and the name of the current exec-file loaded by GDB (*note
set exec-file-mismatch::).

20.1.2 Host and Target Files
----------------------------

GDB, running on the host, needs access to symbol and debugging
information for your program running on the target. This requires
access to an unstripped copy of your program, and possibly any
associated symbol files. Note that this section applies equally to
both `target remote' mode and `target extended-remote' mode.

Some remote targets (*note qXfer executable filename read::, and
*note Host I/O Packets::) allow GDB to access program files over the
same connection used to communicate with GDB. With such a target, if
the remote program is unstripped, the only command you need is `target
remote' (or `target extended-remote').

If the remote program is stripped, or the target does not support
remote program file access, start up GDB using the name of the local
unstripped copy of your program as the first argument, or use the
`file' command. Use `set sysroot' to specify the location (on the
host) of target libraries (unless your GDB was compiled with the
correct sysroot using `--with-sysroot'). Alternatively, you may use
`set solib-search-path' to specify how GDB locates target libraries.

The symbol file and target libraries must exactly match the
executable and libraries on the target, with one exception: the files
on the host system should not be stripped, even if the files on the
target system are. Mismatched or missing files will lead to confusing
results during debugging. On GNU/Linux targets, mismatched or missing
files may also prevent `gdbserver' from debugging multi-threaded
programs.

20.1.3 Remote Connection Commands
---------------------------------

GDB can communicate with the target over a serial line, a local Unix
domain socket, or over an IP network using TCP or UDP. In each case,
GDB uses the same protocol for debugging your program; only the medium
carrying the debugging packets varies. The `target remote' and `target
extended-remote' commands establish a connection to the target. Both
commands accept the same arguments, which indicate the medium to use:

`target remote SERIAL-DEVICE'
`target extended-remote SERIAL-DEVICE'
Use SERIAL-DEVICE to communicate with the target. For example, to
use a serial line connected to the device named `/dev/ttyb':

target remote /dev/ttyb

If you're using a serial line, you may want to give GDB the
`--baud' option, or use the `set serial baud' command (*note set
serial baud: Remote Configuration.) before the `target' command.

`target remote LOCAL-SOCKET'
`target extended-remote LOCAL-SOCKET'
Use LOCAL-SOCKET to communicate with the target. For example, to
use a local Unix domain socket bound to the file system entry
`/tmp/gdb-socket0':

target remote /tmp/gdb-socket0

Note that this command has the same form as the command to connect
to a serial line. GDB will automatically determine which kind of
file you have specified and will make the appropriate kind of
connection. This feature is not available if the host system does
not support Unix domain sockets.

`target remote `HOST:PORT''
`target remote `[HOST]:PORT''
`target remote `tcp:HOST:PORT''
`target remote `tcp:[HOST]:PORT''
`target remote `tcp4:HOST:PORT''
`target remote `tcp6:HOST:PORT''
`target remote `tcp6:[HOST]:PORT''
`target extended-remote `HOST:PORT''
`target extended-remote `[HOST]:PORT''
`target extended-remote `tcp:HOST:PORT''
`target extended-remote `tcp:[HOST]:PORT''
`target extended-remote `tcp4:HOST:PORT''
`target extended-remote `tcp6:HOST:PORT''
`target extended-remote `tcp6:[HOST]:PORT''
Debug using a TCP connection to PORT on HOST. The HOST may be
either a host name, a numeric IPv4 address, or a numeric IPv6
address (with or without the square brackets to separate the
address from the port); PORT must be a decimal number. The HOST
could be the target machine itself, if it is directly connected to
the net, or it might be a terminal server which in turn has a
serial line to the target.

For example, to connect to port 2828 on a terminal server named
`manyfarms':

target remote manyfarms:2828

To connect to port 2828 on a terminal server whose address is
`2001:0db8:85a3:0000:0000:8a2e:0370:7334', you can either use the
square bracket syntax:

target remote [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:2828

or explicitly specify the IPv6 protocol:

target remote tcp6:2001:0db8:85a3:0000:0000:8a2e:0370:7334:2828

This last example may be confusing to the reader, because there is
no visible separation between the hostname and the port number.
Therefore, we recommend the user to provide IPv6 addresses using
square brackets for clarity. However, it is important to mention
that for GDB there is no ambiguity: the number after the last
colon is considered to be the port number.

If your remote target is actually running on the same machine as
your debugger session (e.g. a simulator for your target running on
the same host), you can omit the hostname. For example, to
connect to port 1234 on your local machine:

target remote :1234
Note that the colon is still required here.

`target remote `udp:HOST:PORT''
`target remote `udp:[HOST]:PORT''
`target remote `udp4:HOST:PORT''
`target remote `udp6:[HOST]:PORT''
`target extended-remote `udp:HOST:PORT''
`target extended-remote `udp:HOST:PORT''
`target extended-remote `udp:[HOST]:PORT''
`target extended-remote `udp4:HOST:PORT''
`target extended-remote `udp6:HOST:PORT''
`target extended-remote `udp6:[HOST]:PORT''
Debug using UDP packets to PORT on HOST. For example, to connect
to UDP port 2828 on a terminal server named `manyfarms':

target remote udp:manyfarms:2828

When using a UDP connection for remote debugging, you should keep
in mind that the `U' stands for "Unreliable". UDP can silently
drop packets on busy or unreliable networks, which will cause
havoc with your debugging session.

`target remote | COMMAND'
`target extended-remote | COMMAND'
Run COMMAND in the background and communicate with it using a
pipe. The COMMAND is a shell command, to be parsed and expanded
by the system's command shell, `/bin/sh'; it should expect remote
protocol packets on its standard input, and send replies on its
standard output. You could use this to run a stand-alone simulator
that speaks the remote debugging protocol, to make net connections
using programs like `ssh', or for other similar tricks.

If COMMAND closes its standard output (perhaps by exiting), GDB
will try to send it a `SIGTERM' signal. (If the program has
already exited, this will have no effect.)

Whenever GDB is waiting for the remote program, if you type the
interrupt character (often `Ctrl-c'), GDB attempts to stop the program.
This may or may not succeed, depending in part on the hardware and the
serial drivers the remote system uses. If you type the interrupt
character once again, GDB displays this prompt:

Interrupted while waiting for the program.
Give up (and stop debugging it)? (y or n)

In `target remote' mode, if you type `y', GDB abandons the remote
debugging session. (If you decide you want to try again later, you can
use `target remote' again to connect once more.) If you type `n', GDB
goes back to waiting.

In `target extended-remote' mode, typing `n' will leave GDB
connected to the target.

`detach'
When you have finished debugging the remote program, you can use
the `detach' command to release it from GDB control. Detaching
from the target normally resumes its execution, but the results
will depend on your particular remote stub. After the `detach'
command in `target remote' mode, GDB is free to connect to another
target. In `target extended-remote' mode, GDB is still connected
to the target.

`disconnect'
The `disconnect' command closes the connection to the target, and
the target is generally not resumed. It will wait for GDB (this
instance or another one) to connect and continue debugging. After
the `disconnect' command, GDB is again free to connect to another
target.

`monitor CMD'
This command allows you to send arbitrary commands directly to the
remote monitor. Since GDB doesn't care about the commands it
sends like this, this command is the way to extend GDB--you can
add new commands that only the external monitor will understand
and implement.

File: gdb.info, Node: File Transfer, Next: Server, Prev: Connecting, Up: Remote Debugging

20.2 Sending files to a remote system
=====================================

Some remote targets offer the ability to transfer files over the same
connection used to communicate with GDB. This is convenient for
targets accessible through other means, e.g. GNU/Linux systems running
`gdbserver' over a network interface. For other targets, e.g. embedded
devices with only a single serial port, this may be the only way to
upload or download files.

Not all remote targets support these commands.

`remote put HOSTFILE TARGETFILE'
Copy file HOSTFILE from the host system (the machine running GDB)
to TARGETFILE on the target system.

`remote get TARGETFILE HOSTFILE'
Copy file TARGETFILE from the target system to HOSTFILE on the
host system.

`remote delete TARGETFILE'
Delete TARGETFILE from the target system.

File: gdb.info, Node: Server, Next: Remote Configuration, Prev: File Transfer, Up: Remote Debugging

20.3 Using the `gdbserver' Program
==================================

`gdbserver' is a control program for Unix-like systems, which allows
you to connect your program with a remote GDB via `target remote' or
`target extended-remote'--but without linking in the usual debugging
stub.

`gdbserver' is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that GDB itself does. In fact, a system that can run `gdbserver' to
connect to a remote GDB could also run GDB locally! `gdbserver' is
sometimes useful nevertheless, because it is a much smaller program
than GDB itself. It is also easier to port than all of GDB, so you may
be able to get started more quickly on a new system by using
`gdbserver'. Finally, if you develop code for real-time systems, you
may find that the tradeoffs involved in real-time operation make it
more convenient to do as much development work as possible on another
system, for example by cross-compiling. You can use `gdbserver' to
make a similar choice for debugging.

GDB and `gdbserver' communicate via either a serial line or a TCP
connection, using the standard GDB remote serial protocol.

_Warning:_ `gdbserver' does not have any built-in security. Do
not run `gdbserver' connected to any public network; a GDB
connection to `gdbserver' provides access to the target system
with the same privileges as the user running `gdbserver'.

20.3.1 Running `gdbserver'
--------------------------

Run `gdbserver' on the target system. You need a copy of the program
you want to debug, including any libraries it requires. `gdbserver'
does not need your program's symbol table, so you can strip the program
if necessary to save space. GDB on the host system does all the symbol
handling.

To use the server, you must tell it how to communicate with GDB; the
name of your program; and the arguments for your program. The usual
syntax is:

target> gdbserver COMM PROGRAM [ ARGS ... ]

COMM is either a device name (to use a serial line), or a TCP
hostname and portnumber, or `-' or `stdio' to use stdin/stdout of
`gdbserver'. For example, to debug Emacs with the argument `foo.txt'
and communicate with GDB over the serial port `/dev/com1':

target> gdbserver /dev/com1 emacs foo.txt

`gdbserver' waits passively for the host GDB to communicate with it.

To use a TCP connection instead of a serial line:

target> gdbserver host:2345 emacs foo.txt

The only difference from the previous example is the first argument,
specifying that you are communicating with the host GDB via TCP. The
`host:2345' argument means that `gdbserver' is to expect a TCP
connection from machine `host' to local TCP port 2345. (Currently, the
`host' part is ignored.) You can choose any number you want for the
port number as long as it does not conflict with any TCP ports already
in use on the target system (for example, `23' is reserved for
`telnet').(1) You must use the same port number with the host GDB
`target remote' command.

The `stdio' connection is useful when starting `gdbserver' with ssh:

(gdb) target remote | ssh -T hostname gdbserver - hello

The `-T' option to ssh is provided because we don't need a remote
pty, and we don't want escape-character handling. Ssh does this by
default when a command is provided, the flag is provided to make it
explicit. You could elide it if you want to.

Programs started with stdio-connected gdbserver have `/dev/null' for
`stdin', and `stdout',`stderr' are sent back to gdb for display through
a pipe connected to gdbserver. Both `stdout' and `stderr' use the same
pipe.

20.3.1.1 Attaching to a Running Program
......................................

On some targets, `gdbserver' can also attach to running programs. This
is accomplished via the `--attach' argument. The syntax is:

target> gdbserver --attach COMM PID

PID is the process ID of a currently running process. It isn't
necessary to point `gdbserver' at a binary for the running process.

In `target extended-remote' mode, you can also attach using the GDB
attach command (*note Attaching in Types of Remote Connections::).

You can debug processes by name instead of process ID if your target
has the `pidof' utility:

target> gdbserver --attach COMM `pidof PROGRAM`

In case more than one copy of PROGRAM is running, or PROGRAM has
multiple threads, most versions of `pidof' support the `-s' option to
only return the first process ID.

20.3.1.2 TCP port allocation lifecycle of `gdbserver'
....................................................

This section applies only when `gdbserver' is run to listen on a TCP
port.

`gdbserver' normally terminates after all of its debugged processes
have terminated in `target remote' mode. On the other hand, for `target
extended-remote', `gdbserver' stays running even with no processes left.
GDB normally terminates the spawned debugged process on its exit, which
normally also terminates `gdbserver' in the `target remote' mode.
Therefore, when the connection drops unexpectedly, and GDB cannot ask
`gdbserver' to kill its debugged processes, `gdbserver' stays running
even in the `target remote' mode.

When `gdbserver' stays running, GDB can connect to it again later.
Such reconnecting is useful for features like *Note disconnected
tracing::. For completeness, at most one GDB can be connected at a
time.

By default, `gdbserver' keeps the listening TCP port open, so that
subsequent connections are possible. However, if you start `gdbserver'
with the `--once' option, it will stop listening for any further
connection attempts after connecting to the first GDB session. This
means no further connections to `gdbserver' will be possible after the
first one. It also means `gdbserver' will terminate after the first
connection with remote GDB has closed, even for unexpectedly closed
connections and even in the `target extended-remote' mode. The
`--once' option allows reusing the same port number for connecting to
multiple instances of `gdbserver' running on the same host, since each
instance closes its port after the first connection.

20.3.1.3 Other Command-Line Arguments for `gdbserver'
....................................................

You can use the `--multi' option to start `gdbserver' without
specifying a program to debug or a process to attach to. Then you can
attach in `target extended-remote' mode and run or attach to a program.
For more information, *note --multi Option in Types of Remote
Connnections::.

The `--debug[=option1,option2,...]' option tells `gdbserver' to
display extra diagnostic information about the debugging process. The
options (OPTION1, OPTION2, etc) control for which areas of `gdbserver'
additional information will be displayed, possible values are:

`all'
This enables all available diagnostic output.

`threads'
This enables diagnostic output related to threading. Currently
other general diagnostic output is included in this category, but
this could change in future releases of `gdbserver'.

`event-loop'
This enables event-loop specific diagnostic output.

`remote'
This enables diagnostic output related to the transfer of remote
protocol packets too and from the debugger.

If no options are passed to `--debug' then this is treated as
equivalent to `--debug=threads'. This could change in future releases
of `gdbserver'. The options passed to `--debug' are processed left to
right, and individual options can be prefixed with the `-' (minus)
character to disable diagnostic output from this area, so it is
possible to use:

target> gdbserver --debug=all,-event-loop

In order to enable all diagnostic output except that for the event-loop.

The `--debug-file=FILENAME' option tells `gdbserver' to write any
debug output to the given FILENAME. These options are intended for
`gdbserver' development and for bug reports to the developers.

The `--debug-format=option1[,option2,...]' option tells `gdbserver'
to include additional information in each output. Possible options are:

`none'
Turn off all extra information in debugging output.

`all'
Turn on all extra information in debugging output.

`timestamps'
Include a timestamp in each line of debugging output.

Options are processed in order. Thus, for example, if `none'
appears last then no additional information is added to debugging
output.

The `--wrapper' option specifies a wrapper to launch programs for
debugging. The option should be followed by the name of the wrapper,
then any command-line arguments to pass to the wrapper, then `--'
indicating the end of the wrapper arguments.

`gdbserver' runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program. The wrapper runs
until it executes your program, and then GDB gains control.

You can use any program that eventually calls `execve' with its
arguments as a wrapper. Several standard Unix utilities do this, e.g.
`env' and `nohup'. Any Unix shell script ending with `exec "$@"' will
also work.

For example, you can use `env' to pass an environment variable to
the debugged program, without setting the variable in `gdbserver''s
environment:

$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog

The `--selftest' option runs the self tests in `gdbserver':

$ gdbserver --selftest
Ran 2 unit tests, 0 failed

These tests are disabled in release.

20.3.2 Connecting to `gdbserver'
--------------------------------

The basic procedure for connecting to the remote target is:
* Run GDB on the host system.

* Make sure you have the necessary symbol files (*note Host and
target files::). Load symbols for your application using the
`file' command before you connect. Use `set sysroot' to locate
target libraries (unless your GDB was compiled with the correct
sysroot using `--with-sysroot').

* Connect to your target (*note Connecting to a Remote Target:
Connecting.). For TCP connections, you must start up `gdbserver'
prior to using the `target' command. Otherwise you may get an
error whose text depends on the host system, but which usually
looks something like `Connection refused'. Don't use the `load'
command in GDB when using `target remote' mode, since the program
is already on the target.

20.3.3 Monitor Commands for `gdbserver'
---------------------------------------

During a GDB session using `gdbserver', you can use the `monitor'
command to send special requests to `gdbserver'. Here are the
available commands.

`monitor help'
List the available monitor commands.

`monitor set debug off'
Disable all internal logging from gdbserver.

`monitor set debug on'
Enable some general logging from within gdbserver. Currently this
is equivalent to `monitor set debug threads on', but this might
change in future releases of gdbserver.

`monitor set debug threads off'
`monitor set debug threads on'
Disable or enable specific logging messages associated with thread
handling in gdbserver. Currently this category also includes
additional output not specifically related to thread handling, this
could change in future releases of gdbserver.

`monitor set debug remote off'
`monitor set debug remote on'
Disable or enable specific logging messages associated with the
remote protocol (*note Remote Protocol::).

`monitor set debug event-loop off'
`monitor set debug event-loop on'
Disable or enable specific logging messages associated with
gdbserver's event-loop.

`monitor set debug-file filename'
`monitor set debug-file'
Send any debug output to the given file, or to stderr.

`monitor set debug-format option1[,option2,...]'
Specify additional text to add to debugging messages. Possible
options are:

`none'
Turn off all extra information in debugging output.

`all'
Turn on all extra information in debugging output.

`timestamps'
Include a timestamp in each line of debugging output.

Options are processed in order. Thus, for example, if `none'
appears last then no additional information is added to debugging
output.

`monitor set libthread-db-search-path [PATH]'
When this command is issued, PATH is a colon-separated list of
directories to search for `libthread_db' (*note set
libthread-db-search-path: Threads.). If you omit PATH,
`libthread-db-search-path' will be reset to its default value.

The special entry `$pdir' for `libthread-db-search-path' is not
supported in `gdbserver'.

`monitor exit'
Tell gdbserver to exit immediately. This command should be
followed by `disconnect' to close the debugging session.
`gdbserver' will detach from any attached processes and kill any
processes it created. Use `monitor exit' to terminate `gdbserver'
at the end of a multi-process mode debug session.

20.3.4 Tracepoints support in `gdbserver'
-----------------------------------------

On some targets, `gdbserver' supports tracepoints, fast tracepoints and
static tracepoints.

For fast or static tracepoints to work, a special library called the
"in-process agent" (IPA), must be loaded in the inferior process. This
library is built and distributed as an integral part of `gdbserver'.
In addition, support for static tracepoints requires building the
in-process agent library with static tracepoints support. At present,
the UST (LTTng Userspace Tracer, `http://lttng.org/ust') tracing engine
is supported. This support is automatically available if UST
development headers are found in the standard include path when
`gdbserver' is built, or if `gdbserver' was explicitly configured using
`--with-ust' to point at such headers. You can explicitly disable the
support using `--with-ust=no'.

There are several ways to load the in-process agent in your program:

`Specifying it as dependency at link time'
You can link your program dynamically with the in-process agent
library. On most systems, this is accomplished by adding
`-linproctrace' to the link command.

`Using the system's preloading mechanisms'
You can force loading the in-process agent at startup time by using
your system's support for preloading shared libraries. Many Unixes
support the concept of preloading user defined libraries. In most
cases, you do that by specifying `LD_PRELOAD=libinproctrace.so' in
the environment. See also the description of `gdbserver''s
`--wrapper' command line option.

`Using GDB to force loading the agent at run time'
On some systems, you can force the inferior to load a shared
library, by calling a dynamic loader function in the inferior that
takes care of dynamically looking up and loading a shared library.
On most Unix systems, the function is `dlopen'. You'll use the
`call' command for that. For example:

(gdb) call dlopen ("libinproctrace.so", ...)

Note that on most Unix systems, for the `dlopen' function to be
available, the program needs to be linked with `-ldl'.

On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to `gdbserver' using `target remote', you'll
find that the program is stopped at the dynamic loader's entry point,
and no shared library has been loaded in the program's address space
yet, including the in-process agent. In that case, before being able
to use any of the fast or static tracepoints features, you need to let
the loader run and load the shared libraries. The simplest way to do
that is to run the program to the main procedure. E.g., if debugging a
C or C++ program, start `gdbserver' like so:

$ gdbserver :9999 myprogram

Start GDB and connect to `gdbserver' like so, and run to main:

$ gdb myprogram
(gdb) target remote myhost:9999
0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
(gdb) b main
(gdb) continue

The in-process tracing agent library should now be loaded into the
process; you can confirm it with the `info sharedlibrary' command,
which will list `libinproctrace.so' as loaded in the process. You are
now ready to install fast tracepoints, list static tracepoint markers,
probe static tracepoints markers, and start tracing.

---------- Footnotes ----------

(1) If you choose a port number that conflicts with another service,
`gdbserver' prints an error message and exits.

File: gdb.info, Node: Remote Configuration, Next: Remote Stub, Prev: Server, Up: Remote Debugging

20.4 Remote Configuration
=========================

This section documents the configuration options available when
debugging remote programs. For the options related to the File I/O
extensions of the remote protocol, see *Note system-call-allowed:
system.

`set remoteaddresssize BITS'
Set the maximum size of address in a memory packet to the specified
number of bits. GDB will mask off the address bits above that
number, when it passes addresses to the remote target. The
default value is the number of bits in the target's address.

`show remoteaddresssize'
Show the current value of remote address size in bits.

`set serial baud N'
Set the baud rate for the remote serial I/O to N baud. The value
is used to set the speed of the serial port used for debugging
remote targets.

`show serial baud'
Show the current speed of the remote connection.

`set serial parity PARITY'
Set the parity for the remote serial I/O. Supported values of
PARITY are: `even', `none', and `odd'. The default is `none'.

`show serial parity'
Show the current parity of the serial port.

`set remotebreak'
If set to on, GDB sends a `BREAK' signal to the remote when you
type `Ctrl-c' to interrupt the program running on the remote. If
set to off, GDB sends the `Ctrl-C' character instead. The default
is off, since most remote systems expect to see `Ctrl-C' as the
interrupt signal.

`show remotebreak'
Show whether GDB sends `BREAK' or `Ctrl-C' to interrupt the remote
program.

`set remoteflow on'
`set remoteflow off'
Enable or disable hardware flow control (`RTS'/`CTS') on the
serial port used to communicate to the remote target.

`show remoteflow'
Show the current setting of hardware flow control.

`set remotelogbase BASE'
Set the base (a.k.a. radix) of logging serial protocol
communications to BASE. Supported values of BASE are: `ascii',
`octal', and `hex'. The default is `ascii'.

`show remotelogbase'
Show the current setting of the radix for logging remote serial
protocol.

`set remotelogfile FILE'
Record remote serial communications on the named FILE. The
default is not to record at all.

`show remotelogfile'
Show the current setting of the file name on which to record the
serial communications.

`set remotetimeout NUM'
Set the timeout limit to wait for the remote target to respond to
NUM seconds. The default is 2 seconds.

`show remotetimeout'
Show the current number of seconds to wait for the remote target
responses.

`set remote hardware-watchpoint-limit LIMIT'
`set remote hardware-breakpoint-limit LIMIT'
Restrict GDB to using LIMIT remote hardware watchpoints or
breakpoints. The LIMIT can be set to 0 to disable hardware
watchpoints or breakpoints, and `unlimited' for unlimited
watchpoints or breakpoints.

`show remote hardware-watchpoint-limit'
`show remote hardware-breakpoint-limit'
Show the current limit for the number of hardware watchpoints or
breakpoints that GDB can use.

`set remote hardware-watchpoint-length-limit LIMIT'
Restrict GDB to using LIMIT bytes for the maximum length of a
remote hardware watchpoint. A LIMIT of 0 disables hardware
watchpoints and `unlimited' allows watchpoints of any length.

`show remote hardware-watchpoint-length-limit'
Show the current limit (in bytes) of the maximum length of a
remote hardware watchpoint.

`set remote exec-file FILENAME'
`show remote exec-file'
Select the file used for `run' with `target extended-remote'.
This should be set to a filename valid on the target system. If
it is not set, the target will use a default filename (e.g. the
last program run).

`set remote interrupt-sequence'
Allow the user to select one of `Ctrl-C', a `BREAK' or `BREAK-g'
as the sequence to the remote target in order to interrupt the
execution. `Ctrl-C' is a default. Some system prefers `BREAK'
which is high level of serial line for some certain time. Linux
kernel prefers `BREAK-g', a.k.a Magic SysRq g. It is `BREAK'
signal followed by character `g'.

`show remote interrupt-sequence'
Show which of `Ctrl-C', `BREAK' or `BREAK-g' is sent by GDB to
interrupt the remote program. `BREAK-g' is BREAK signal followed
by `g' and also known as Magic SysRq g.

`set remote interrupt-on-connect'
Specify whether interrupt-sequence is sent to remote target when
GDB connects to it. This is mostly needed when you debug Linux
kernel. Linux kernel expects `BREAK' followed by `g' which is
known as Magic SysRq g in order to connect GDB.

`show remote interrupt-on-connect'
Show whether interrupt-sequence is sent to remote target when GDB
connects to it.

`set tcp auto-retry on'
Enable auto-retry for remote TCP connections. This is useful if
the remote debugging agent is launched in parallel with GDB; there
is a race condition because the agent may not become ready to
accept the connection before GDB attempts to connect. When
auto-retry is enabled, if the initial attempt to connect fails,
GDB reattempts to establish the connection using the timeout
specified by `set tcp connect-timeout'.

`set tcp auto-retry off'
Do not auto-retry failed TCP connections.

`show tcp auto-retry'
Show the current auto-retry setting.

`set tcp connect-timeout SECONDS'
`set tcp connect-timeout unlimited'
Set the timeout for establishing a TCP connection to the remote
target to SECONDS. The timeout affects both polling to retry
failed connections (enabled by `set tcp auto-retry on') and
waiting for connections that are merely slow to complete, and
represents an approximate cumulative value. If SECONDS is
`unlimited', there is no timeout and GDB will keep attempting to
establish a connection forever, unless interrupted with `Ctrl-c'.
The default is 15 seconds.

`show tcp connect-timeout'
Show the current connection timeout setting.

The GDB remote protocol autodetects the packets supported by your
debugging stub. If you need to override the autodetection, you can use
these commands to enable or disable individual packets. Each packet
can be set to `on' (the remote target supports this packet), `off' (the
remote target does not support this packet), or `auto' (detect remote
target support for this packet). They all default to `auto'. For more
information about each packet, see *Note Remote Protocol::.

During normal use, you should not have to use any of these commands.
If you do, that may be a bug in your remote debugging stub, or a bug in
GDB. You may want to report the problem to the GDB developers.

For each packet NAME, the command to enable or disable the packet is
`set remote NAME-packet'. If you configure a packet, the configuration
will apply for all future remote targets if no target is selected. In
case there is a target selected, only the configuration of the current
target is changed. All other existing remote targets' features are not
affected. The command to print the current configuration of a packet is
`show remote NAME-packet'. It displays the current remote target's
configuration. If no remote target is selected, the default
configuration for future connections is shown. The available settings
are:

Command Name Remote Packet Related Features
`fetch-register' `p' `info registers'
`set-register' `P' `set'
`binary-download' `X' `load', `set'
`read-aux-vector' `qXfer:auxv:read' `info auxv'
`symbol-lookup' `qSymbol' Detecting
multiple threads
`attach' `vAttach' `attach'
`verbose-resume' `vCont' Stepping or
resuming multiple
threads
`run' `vRun' `run'
`software-breakpoint'`Z0' `break'
`hardware-breakpoint'`Z1' `hbreak'
`write-watchpoint' `Z2' `watch'
`read-watchpoint' `Z3' `rwatch'
`access-watchpoint' `Z4' `awatch'
`pid-to-exec-file' `qXfer:exec-file:read' `attach', `run'
`target-features' `qXfer:features:read' `set architecture'
`library-info' `qXfer:libraries:read' `info
sharedlibrary'
`memory-map' `qXfer:memory-map:read' `info mem'
`read-sdata-object' `qXfer:sdata:read' `print $_sdata'
`read-siginfo-object'`qXfer:siginfo:read' `print $_siginfo'
`write-siginfo-object'`qXfer:siginfo:write' `set $_siginfo'
`threads' `qXfer:threads:read' `info threads'
`get-thread-local- `qGetTLSAddr' Displaying
storage-address' `__thread'
variables
`get-thread-information-block-address'`qGetTIBAddr' Display
MS-Windows Thread
Information Block.
`search-memory' `qSearch:memory' `find'
`supported-packets' `qSupported' Remote
communications
parameters
`catch-syscalls' `QCatchSyscalls' `catch syscall'
`pass-signals' `QPassSignals' `handle SIGNAL'
`program-signals' `QProgramSignals' `handle SIGNAL'
`hostio-close-packet'`vFile:close' `remote get',
`remote put'
`hostio-open-packet' `vFile:open' `remote get',
`remote put'
`hostio-pread-packet'`vFile:pread' `remote get',
`remote put'
`hostio-pwrite-packet'`vFile:pwrite' `remote get',
`remote put'
`hostio-unlink-packet'`vFile:unlink' `remote delete'
`hostio-readlink-packet'`vFile:readlink' Host I/O
`hostio-fstat-packet'`vFile:fstat' Host I/O
`hostio-setfs-packet'`vFile:setfs' Host I/O
`noack-packet' `QStartNoAckMode' Packet
acknowledgment
`osdata' `qXfer:osdata:read' `info os'
`query-attached' `qAttached' Querying remote
process attach
state.
`trace-buffer-size' `QTBuffer:size' `set
trace-buffer-size'
`trace-status' `qTStatus' `tstatus'
`traceframe-info' `qXfer:traceframe-info:read'Traceframe info
`install-in-trace' `InstallInTrace' Install
tracepoint in
tracing
`disable-randomization'`QDisableRandomization' `set
disable-randomization'
`startup-with-shell' `QStartupWithShell' `set
startup-with-shell'
`environment-hex-encoded'`QEnvironmentHexEncoded'`set environment'
`environment-unset' `QEnvironmentUnset' `unset
environment'
`environment-reset' `QEnvironmentReset' `Reset the
inferior
environment
(i.e., unset
user-set
variables)'
`set-working-dir' `QSetWorkingDir' `set cwd'
`conditional-breakpoints-packet'`Z0 and Z1' `Support for
target-side
breakpoint
condition
evaluation'
`multiprocess-extensions'`multiprocess Debug multiple
extensions' processes and
remote process
PID awareness
`swbreak-feature' `swbreak stop reason' `break'
`hwbreak-feature' `hwbreak stop reason' `hbreak'
`fork-event-feature' `fork stop reason' `fork'
`vfork-event-feature'`vfork stop reason' `vfork'
`exec-event-feature' `exec stop reason' `exec'
`thread-events' `QThreadEvents' Tracking thread
lifetime.
`thread-options' `QThreadOptions' Set thread event
reporting options.
`no-resumed-stop-reply'`no resumed thread Tracking thread
left stop reply' lifetime.

The number of bytes per memory-read or memory-write packet for a
remote target can be configured using the commands
`set remote memory-read-packet-size' and
`set remote memory-write-packet-size'. If set to `0' (zero) the
default packet size will be used. The actual limit is further reduced
depending on the target. Specify `fixed' to disable the
target-dependent restriction and `limit' to enable it. Similar to the
enabling and disabling of remote packets, the command applies to the
currently selected target (if available). If no remote target is
selected, it applies to all future remote connections. The
configuration of the selected target can be displayed using the commands
`show remote memory-read-packet-size' and
`show remote memory-write-packet-size'. If no remote target is
selected, the default configuration for future connections is shown.

File: gdb.info, Node: Remote Stub, Prev: Remote Configuration, Up: Remote Debugging

20.5 Implementing a Remote Stub
===============================

The stub files provided with GDB implement the target side of the
communication protocol, and the GDB side is implemented in the GDB
source file `remote.c'. Normally, you can simply allow these
subroutines to communicate, and ignore the details. (If you're
implementing your own stub file, you can still ignore the details: start
with one of the existing stub files. `sparc-stub.c' is the best
organized, and therefore the easiest to read.)

To debug a program running on another machine (the debugging
"target" machine), you must first arrange for all the usual
prerequisites for the program to run by itself. For example, for a C
program, you need:

1. A startup routine to set up the C runtime environment; these
usually have a name like `crt0'. The startup routine may be
supplied by your hardware supplier, or you may have to write your
own.

2. A C subroutine library to support your program's subroutine calls,
notably managing input and output.

3. A way of getting your program to the other machine--for example, a
download program. These are often supplied by the hardware
manufacturer, but you may have to write your own from hardware
documentation.

The next step is to arrange for your program to use a serial port to
communicate with the machine where GDB is running (the "host" machine).
In general terms, the scheme looks like this:

_On the host,_
GDB already understands how to use this protocol; when everything
else is set up, you can simply use the `target remote' command
(*note Specifying a Debugging Target: Targets.).

_On the target,_
you must link with your program a few special-purpose subroutines
that implement the GDB remote serial protocol. The file
containing these subroutines is called a "debugging stub".

On certain remote targets, you can use an auxiliary program
`gdbserver' instead of linking a stub into your program. *Note
Using the `gdbserver' Program: Server, for details.

The debugging stub is specific to the architecture of the remote
machine; for example, use `sparc-stub.c' to debug programs on SPARC
boards.

These working remote stubs are distributed with GDB:

`i386-stub.c'
For Intel 386 and compatible architectures.

`m68k-stub.c'
For Motorola 680x0 architectures.

`sh-stub.c'
For Renesas SH architectures.

`sparc-stub.c'
For SPARC architectures.

`sparcl-stub.c'
For Fujitsu SPARCLITE architectures.

The `README' file in the GDB distribution may list other recently
added stubs.

* Menu:

* Stub Contents:: What the stub can do for you
* Bootstrapping:: What you must do for the stub
* Debug Session:: Putting it all together

File: gdb.info, Node: Stub Contents, Next: Bootstrapping, Up: Remote Stub

20.5.1 What the Stub Can Do for You
-----------------------------------

The debugging stub for your architecture supplies these three
subroutines:

`set_debug_traps'
This routine arranges for `handle_exception' to run when your
program stops. You must call this subroutine explicitly in your
program's startup code.

`handle_exception'
This is the central workhorse, but your program never calls it
explicitly--the setup code arranges for `handle_exception' to run
when a trap is triggered.

`handle_exception' takes control when your program stops during
execution (for example, on a breakpoint), and mediates
communications with GDB on the host machine. This is where the
communications protocol is implemented; `handle_exception' acts as
the GDB representative on the target machine. It begins by
sending summary information on the state of your program, then
continues to execute, retrieving and transmitting any information
GDB needs, until you execute a GDB command that makes your program
resume; at that point, `handle_exception' returns control to your
own code on the target machine.

`breakpoint'
Use this auxiliary subroutine to make your program contain a
breakpoint. Depending on the particular situation, this may be
the only way for GDB to get control. For instance, if your target
machine has some sort of interrupt button, you won't need to call
this; pressing the interrupt button transfers control to
`handle_exception'--in effect, to GDB. On some machines, simply
receiving characters on the serial port may also trigger a trap;
again, in that situation, you don't need to call `breakpoint' from
your own program--simply running `target remote' from the host GDB
session gets control.

Call `breakpoint' if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.

File: gdb.info, Node: Bootstrapping, Next: Debug Session, Prev: Stub Contents, Up: Remote Stub

20.5.2 What You Must Do for the Stub
------------------------------------

The debugging stubs that come with GDB are set up for a particular chip
architecture, but they have no information about the rest of your
debugging target machine.

First of all you need to tell the stub how to communicate with the
serial port.

`int getDebugChar()'
Write this subroutine to read a single character from the serial
port. It may be identical to `getchar' for your target system; a
different name is used to allow you to distinguish the two if you
wish.

`void putDebugChar(int)'
Write this subroutine to write a single character to the serial
port. It may be identical to `putchar' for your target system; a
different name is used to allow you to distinguish the two if you
wish.

If you want GDB to be able to stop your program while it is running,
you need to use an interrupt-driven serial driver, and arrange for it
to stop when it receives a `^C' (`\003', the control-C character).
That is the character which GDB uses to tell the remote system to stop.

Getting the debugging target to return the proper status to GDB
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the "dirty" part is that
GDB reports a `SIGTRAP' instead of a `SIGINT').

Other routines you need to supply are:

`void exceptionHandler (int EXCEPTION_NUMBER, void *EXCEPTION_ADDRESS)'
Write this function to install EXCEPTION_ADDRESS in the exception
handling tables. You need to do this because the stub does not
have any way of knowing what the exception handling tables on your
target system are like (for example, the processor's table might
be in ROM, containing entries which point to a table in RAM). The
EXCEPTION_NUMBER specifies the exception which should be changed;
its meaning is architecture-dependent (for example, different
numbers might represent divide by zero, misaligned access, etc).
When this exception occurs, control should be transferred directly
to EXCEPTION_ADDRESS, and the processor state (stack, registers,
and so on) should be just as it is when a processor exception
occurs. So if you want to use a jump instruction to reach
EXCEPTION_ADDRESS, it should be a simple jump, not a jump to
subroutine.

For the 386, EXCEPTION_ADDRESS should be installed as an interrupt
gate so that interrupts are masked while the handler runs. The
gate should be at privilege level 0 (the most privileged level).
The SPARC and 68k stubs are able to mask interrupts themselves
without help from `exceptionHandler'.

`void flush_i_cache()'
On SPARC and SPARCLITE only, write this subroutine to flush the
instruction cache, if any, on your target machine. If there is no
instruction cache, this subroutine may be a no-op.

On target machines that have instruction caches, GDB requires this
function to make certain that the state of your program is stable.

You must also make sure this library routine is available:

`void *memset(void *, int, int)'
This is the standard library function `memset' that sets an area of
memory to a known value. If you have one of the free versions of
`libc.a', `memset' can be found there; otherwise, you must either
obtain it from your hardware manufacturer, or write your own.

If you do not use the GNU C compiler, you may need other standard
library subroutines as well; this varies from one stub to another, but
in general the stubs are likely to use any of the common library
subroutines which `GCC' generates as inline code.

File: gdb.info, Node: Debug Session, Prev: Bootstrapping, Up: Remote Stub

20.5.3 Putting it All Together
------------------------------

In summary, when your program is ready to debug, you must follow these
steps.

1. Make sure you have defined the supporting low-level routines
(*note What You Must Do for the Stub: Bootstrapping.):
`getDebugChar', `putDebugChar',
`flush_i_cache', `memset', `exceptionHandler'.

2. Insert these lines in your program's startup code, before the main
procedure is called:

set_debug_traps();
breakpoint();

On some machines, when a breakpoint trap is raised, the hardware
automatically makes the PC point to the instruction after the
breakpoint. If your machine doesn't do that, you may need to
adjust `handle_exception' to arrange for it to return to the
instruction after the breakpoint on this first invocation, so that
your program doesn't keep hitting the initial breakpoint instead
of making progress.

3. For the 680x0 stub only, you need to provide a variable called
`exceptionHook'. Normally you just use:

void (*exceptionHook)() = 0;

but if before calling `set_debug_traps', you set it to point to a
function in your program, that function is called when `GDB'
continues after stopping on a trap (for example, bus error). The
function indicated by `exceptionHook' is called with one
parameter: an `int' which is the exception number.

4. Compile and link together: your program, the GDB debugging stub for
your target architecture, and the supporting subroutines.

5. Make sure you have a serial connection between your target machine
and the GDB host, and identify the serial port on the host.

6. Download your program to your target machine (or get it there by
whatever means the manufacturer provides), and start it.

7. Start GDB on the host, and connect to the target (*note Connecting
to a Remote Target: Connecting.).

File: gdb.info, Node: Configurations, Next: Controlling GDB, Prev: Remote Debugging, Up: Top

21 Configuration-Specific Information
*************************************

While nearly all GDB commands are available for all native and cross
versions of the debugger, there are some exceptions. This chapter
describes things that are only available in certain configurations.

There are three major categories of configurations: native
configurations, where the host and target are the same, embedded
operating system configurations, which are usually the same for several
different processor architectures, and bare embedded processors, which
are quite different from each other.

* Menu:

* Native::
* Embedded OS::
* Embedded Processors::
* Architectures::

File: gdb.info, Node: Native, Next: Embedded OS, Up: Configurations

21.1 Native
===========

This section describes details specific to particular native
configurations.

* Menu:

* BSD libkvm Interface:: Debugging BSD kernel memory images
* Process Information:: Process information
* DJGPP Native:: Features specific to the DJGPP port
* Cygwin Native:: Features specific to the Cygwin port
* Hurd Native:: Features specific to GNU Hurd
* Darwin:: Features specific to Darwin
* FreeBSD:: Features specific to FreeBSD

File: gdb.info, Node: BSD libkvm Interface, Next: Process Information, Up: Native

21.1.1 BSD libkvm Interface
---------------------------

BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
interface that provides a uniform interface for accessing kernel virtual
memory images, including live systems and crash dumps. GDB uses this
interface to allow you to debug live kernels and kernel crash dumps on
many native BSD configurations. This is implemented as a special `kvm'
debugging target. For debugging a live system, load the currently
running kernel into GDB and connect to the `kvm' target:

(gdb) target kvm

For debugging crash dumps, provide the file name of the crash dump
as an argument:

(gdb) target kvm /var/crash/bsd.0

Once connected to the `kvm' target, the following commands are
available:

`kvm pcb'
Set current context from the "Process Control Block" (PCB) address.

`kvm proc'
Set current context from proc address. This command isn't
available on modern FreeBSD systems.

File: gdb.info, Node: Process Information, Next: DJGPP Native, Prev: BSD libkvm Interface, Up: Native

21.1.2 Process Information
--------------------------

Some operating systems provide interfaces to fetch additional
information about running processes beyond memory and per-thread
register state. If GDB is configured for an operating system with a
supported interface, the command `info proc' is available to report
information about the process running your program, or about any
process running on your system.

One supported interface is a facility called `/proc' that can be
used to examine the image of a running process using file-system
subroutines. This facility is supported on GNU/Linux and Solaris
systems.

On FreeBSD and NetBSD systems, system control nodes are used to query
process information.

In addition, some systems may provide additional process information
in core files. Note that a core file may include a subset of the
information available from a live process. Process information is
currently available from cores created on GNU/Linux and FreeBSD systems.

`info proc'
`info proc PROCESS-ID'
Summarize available information about a process. If a process ID
is specified by PROCESS-ID, display information about that
process; otherwise display information about the program being
debugged. The summary includes the debugged process ID, the
command line used to invoke it, its current working directory, and
its executable file's absolute file name.

On some systems, PROCESS-ID can be of the form `[PID]/TID' which
specifies a certain thread ID within a process. If the optional
PID part is missing, it means a thread from the process being
debugged (the leading `/' still needs to be present, or else GDB
will interpret the number as a process ID rather than a thread ID).

`info proc cmdline'
Show the original command line of the process. This command is
supported on GNU/Linux, FreeBSD and NetBSD.

`info proc cwd'
Show the current working directory of the process. This command is
supported on GNU/Linux, FreeBSD and NetBSD.

`info proc exe'
Show the name of executable of the process. This command is
supported on GNU/Linux, FreeBSD and NetBSD.

`info proc files'
Show the file descriptors open by the process. For each open file
descriptor, GDB shows its number, type (file, directory, character
device, socket), file pointer offset, and the name of the resource
open on the descriptor. The resource name can be a file name (for
files, directories, and devices) or a protocol followed by socket
address (for network connections). This command is supported on
FreeBSD.

This example shows the open file descriptors for a process using a
tty for standard input and output as well as two network sockets:

(gdb) info proc files 22136
process 22136
Open files:

FD Type Offset Flags Name
text file - r-------- /usr/bin/ssh
ctty chr - rw------- /dev/pts/20
cwd dir - r-------- /usr/home/john
root dir - r-------- /
0 chr 0x32933a4 rw------- /dev/pts/20
1 chr 0x32933a4 rw------- /dev/pts/20
2 chr 0x32933a4 rw------- /dev/pts/20
3 socket 0x0 rw----n-- tcp4 10.0.1.2:53014 -> 10.0.1.10:22
4 socket 0x0 rw------- unix stream:/tmp/ssh-FIt89oAzOn5f/agent.2456

`info proc mappings'
Report the memory address space ranges accessible in a process. On
Solaris, FreeBSD and NetBSD systems, each memory range includes
information on whether the process has read, write, or execute
access rights to each range. On GNU/Linux, FreeBSD and NetBSD
systems, each memory range includes the object file which is
mapped to that range.

`info proc stat'
`info proc status'
Show additional process-related information, including the user ID
and group ID; virtual memory usage; the signals that are pending,
blocked, and ignored; its TTY; its consumption of system and user
time; its stack size; its `nice' value; etc. These commands are
supported on GNU/Linux, FreeBSD and NetBSD.

For GNU/Linux systems, see the `proc' man page for more
information (type `man 5 proc' from your shell prompt).

For FreeBSD and NetBSD systems, `info proc stat' is an alias for
`info proc status'.

`info proc all'
Show all the information about the process described under all of
the above `info proc' subcommands.

`set procfs-trace'
This command enables and disables tracing of `procfs' API calls.

`show procfs-trace'
Show the current state of `procfs' API call tracing.

`set procfs-file FILE'
Tell GDB to write `procfs' API trace to the named FILE. GDB
appends the trace info to the previous contents of the file. The
default is to display the trace on the standard output.

`show procfs-file'
Show the file to which `procfs' API trace is written.

`proc-trace-entry'
`proc-trace-exit'
`proc-untrace-entry'
`proc-untrace-exit'
These commands enable and disable tracing of entries into and exits
from the `syscall' interface.

`info pidlist'
For QNX Neutrino only, this command displays the list of all the
processes and all the threads within each process.

`info meminfo'
For QNX Neutrino only, this command displays the list of all
mapinfos.

File: gdb.info, Node: DJGPP Native, Next: Cygwin Native, Prev: Process Information, Up: Native

21.1.3 Features for Debugging DJGPP Programs
--------------------------------------------

DJGPP is a port of the GNU development tools to MS-DOS and MS-Windows.
DJGPP programs are 32-bit protected-mode programs that use the "DPMI"
(DOS Protected-Mode Interface) API to run on top of real-mode DOS
systems and their emulations.

GDB supports native debugging of DJGPP programs, and defines a few
commands specific to the DJGPP port. This subsection describes those
commands.

`info dos'
This is a prefix of DJGPP-specific commands which print
information about the target system and important OS structures.

`info dos sysinfo'
This command displays assorted information about the underlying
platform: the CPU type and features, the OS version and flavor, the
DPMI version, and the available conventional and DPMI memory.

`info dos gdt'
`info dos ldt'
`info dos idt'
These 3 commands display entries from, respectively, Global, Local,
and Interrupt Descriptor Tables (GDT, LDT, and IDT). The
descriptor tables are data structures which store a descriptor for
each segment that is currently in use. The segment's selector is
an index into a descriptor table; the table entry for that index
holds the descriptor's base address and limit, and its attributes
and access rights.

A typical DJGPP program uses 3 segments: a code segment, a data
segment (used for both data and the stack), and a DOS segment
(which allows access to DOS/BIOS data structures and absolute
addresses in conventional memory). However, the DPMI host will
usually define additional segments in order to support the DPMI
environment.

These commands allow to display entries from the descriptor tables.
Without an argument, all entries from the specified table are
displayed. An argument, which should be an integer expression,
means display a single entry whose index is given by the argument.
For example, here's a convenient way to display information about
the debugged program's data segment:

`(gdb) info dos ldt $ds'
`0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)'

This comes in handy when you want to see whether a pointer is
outside the data segment's limit (i.e. "garbled").

`info dos pde'
`info dos pte'
These two commands display entries from, respectively, the Page
Directory and the Page Tables. Page Directories and Page Tables
are data structures which control how virtual memory addresses are
mapped into physical addresses. A Page Table includes an entry
for every page of memory that is mapped into the program's address
space; there may be several Page Tables, each one holding up to
4096 entries. A Page Directory has up to 4096 entries, one each
for every Page Table that is currently in use.

Without an argument, `info dos pde' displays the entire Page
Directory, and `info dos pte' displays all the entries in all of
the Page Tables. An argument, an integer expression, given to the
`info dos pde' command means display only that entry from the Page
Directory table. An argument given to the `info dos pte' command
means display entries from a single Page Table, the one pointed to
by the specified entry in the Page Directory.

These commands are useful when your program uses "DMA" (Direct
Memory Access), which needs physical addresses to program the DMA
controller.

These commands are supported only with some DPMI servers.

`info dos address-pte ADDR'
This command displays the Page Table entry for a specified linear
address. The argument ADDR is a linear address which should
already have the appropriate segment's base address added to it,
because this command accepts addresses which may belong to _any_
segment. For example, here's how to display the Page Table entry
for the page where a variable `i' is stored:

`(gdb) info dos address-pte __djgpp_base_address + (char *)&i'
`Page Table entry for address 0x11a00d30:'
`Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30'

This says that `i' is stored at offset `0xd30' from the page whose
physical base address is `0x02698000', and shows all the
attributes of that page.

Note that you must cast the addresses of variables to a `char *',
since otherwise the value of `__djgpp_base_address', the base
address of all variables and functions in a DJGPP program, will be
added using the rules of C pointer arithmetic: if `i' is declared
an `int', GDB will add 4 times the value of `__djgpp_base_address'
to the address of `i'.

Here's another example, it displays the Page Table entry for the
transfer buffer:

`(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)'
`Page Table entry for address 0x29110:'
`Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110'

(The `+ 3' offset is because the transfer buffer's address is the
3rd member of the `_go32_info_block' structure.) The output
clearly shows that this DPMI server maps the addresses in
conventional memory 1:1, i.e. the physical (`0x00029000' +
`0x110') and linear (`0x29110') addresses are identical.

This command is supported only with some DPMI servers.

In addition to native debugging, the DJGPP port supports remote
debugging via a serial data link. The following commands are specific
to remote serial debugging in the DJGPP port of GDB.

`set com1base ADDR'
This command sets the base I/O port address of the `COM1' serial
port.

`set com1irq IRQ'
This command sets the "Interrupt Request" (`IRQ') line to use for
the `COM1' serial port.

There are similar commands `set com2base', `set com3irq', etc. for
setting the port address and the `IRQ' lines for the other 3 COM
ports.

The related commands `show com1base', `show com1irq' etc. display
the current settings of the base address and the `IRQ' lines used
by the COM ports.

`info serial'
This command prints the status of the 4 DOS serial ports. For each
port, it prints whether it's active or not, its I/O base address
and IRQ number, whether it uses a 16550-style FIFO, its baudrate,
and the counts of various errors encountered so far.

File: gdb.info, Node: Cygwin Native, Next: Hurd Native, Prev: DJGPP Native, Up: Native

21.1.4 Features for Debugging MS Windows PE Executables
-------------------------------------------------------

GDB supports native debugging of MS Windows programs, including DLLs
with and without symbolic debugging information.

MS-Windows programs that call `SetConsoleMode' to switch off the
special meaning of the `Ctrl-C' keystroke cannot be interrupted by
typing `C-c'. For this reason, GDB on MS-Windows supports `C-<BREAK>'
as an alternative interrupt key sequence, which can be used to
interrupt the debuggee even if it ignores `C-c'.

There are various additional Cygwin-specific commands, described in
this section. Working with DLLs that have no debugging symbols is
described in *Note Non-debug DLL Symbols::.

`info w32'
This is a prefix of MS Windows-specific commands which print
information about the target system and important OS structures.

`info w32 selector'
This command displays information returned by the Win32 API
`GetThreadSelectorEntry' function. It takes an optional argument
that is evaluated to a long value to give the information about
this given selector. Without argument, this command displays
information about the six segment registers.

`info w32 thread-information-block'
This command displays thread specific information stored in the
Thread Information Block (readable on the X86 CPU family using
`$fs' selector for 32-bit programs and `$gs' for 64-bit programs).

`signal-event ID'
This command signals an event with user-provided ID. Used to
resume crashing process when attached to it using MS-Windows JIT
debugging (AeDebug).

To use it, create or edit the following keys in
`HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug' and/or
`HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows
NT\CurrentVersion\AeDebug' (for x86_64 versions):

- `Debugger' (REG_SZ) -- a command to launch the debugger.
Suggested command is: `FULLY-QUALIFIED-PATH-TO-GDB.EXE -ex
"attach %ld" -ex "signal-event %ld" -ex "continue"'.

The first `%ld' will be replaced by the process ID of the
crashing process, the second `%ld' will be replaced by the ID
of the event that blocks the crashing process, waiting for
GDB to attach.

- `Auto' (REG_SZ) -- either `1' or `0'. `1' will make the
system run debugger specified by the Debugger key
automatically, `0' will cause a dialog box with "OK" and
"Cancel" buttons to appear, which allows the user to either
terminate the crashing process (OK) or debug it (Cancel).

`set cygwin-exceptions MODE'
If MODE is `on', GDB will break on exceptions that happen inside
the Cygwin DLL. If MODE is `off', GDB will delay recognition of
exceptions, and may ignore some exceptions which seem to be caused
by internal Cygwin DLL "bookkeeping". This option is meant
primarily for debugging the Cygwin DLL itself; the default value
is `off' to avoid annoying GDB users with false `SIGSEGV' signals.

`show cygwin-exceptions'
Displays whether GDB will break on exceptions that happen inside
the Cygwin DLL itself.

`set new-console MODE'
If MODE is `on' the debuggee will be started in a new console on
next start. If MODE is `off', the debuggee will be started in the
same console as the debugger.

`show new-console'
Displays whether a new console is used when the debuggee is
started.

`set new-group MODE'
This boolean value controls whether the debuggee should start a
new group or stay in the same group as the debugger. This affects
the way the Windows OS handles `Ctrl-C'.

`show new-group'
Displays current value of new-group boolean.

`set debugevents'
This boolean value adds debug output concerning kernel events
related to the debuggee seen by the debugger. This includes
events that signal thread and process creation and exit, DLL
loading and unloading, console interrupts, and debugging messages
produced by the Windows `OutputDebugString' API call.

`set debugexec'
This boolean value adds debug output concerning execute events
(such as resume thread) seen by the debugger.

`set debugexceptions'
This boolean value adds debug output concerning exceptions in the
debuggee seen by the debugger.

`set debugmemory'
This boolean value adds debug output concerning debuggee memory
reads and writes by the debugger.

`set shell'
This boolean values specifies whether the debuggee is called via a
shell or directly (default value is on).

`show shell'
Displays if the debuggee will be started with a shell.

* Menu:

* Non-debug DLL Symbols:: Support for DLLs without debugging symbols

File: gdb.info, Node: Non-debug DLL Symbols, Up: Cygwin Native

21.1.4.1 Support for DLLs without Debugging Symbols
..................................................

Very often on windows, some of the DLLs that your program relies on do
not include symbolic debugging information (for example,
`kernel32.dll'). When GDB doesn't recognize any debugging symbols in a
DLL, it relies on the minimal amount of symbolic information contained
in the DLL's export table. This section describes working with such
symbols, known internally to GDB as "minimal symbols".

Note that before the debugged program has started execution, no DLLs
will have been loaded. The easiest way around this problem is simply to
start the program -- either by setting a breakpoint or letting the
program run once to completion.

21.1.4.2 DLL Name Prefixes
.........................

In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance `KERNEL32!CreateFileA'. The plain name is also
entered into the symbol table, so `CreateFileA' is often sufficient.
In some cases there will be name clashes within a program (particularly
if the executable itself includes full debugging symbols) necessitating
the use of the fully qualified name when referring to the contents of
the DLL. Use single-quotes around the name to avoid the exclamation
mark ("!") being interpreted as a language operator.

Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa. Since
symbols within GDB are _case-sensitive_ this may cause some confusion.
If in doubt, try the `info functions' and `info variables' commands or
even `maint print msymbols' (*note Symbols::). Here's an example:

(gdb) info function CreateFileA
All functions matching regular expression "CreateFileA":

Non-debugging symbols:
0x77e885f4 CreateFileA
0x77e885f4 KERNEL32!CreateFileA

(gdb) info function !
All functions matching regular expression "!":

Non-debugging symbols:
0x6100114c cygwin1!__assert
0x61004034 cygwin1!_dll_crt0@0
0x61004240 cygwin1!dll_crt0(per_process *)
[etc...]

21.1.4.3 Working with Minimal Symbols
....................................

Symbols extracted from a DLL's export table do not contain very much
type information. All that GDB can do is guess whether a symbol refers
to a function or variable depending on the linker section that contains
the symbol. Also note that the actual contents of the memory contained
in a DLL are not available unless the program is running. This means
that you cannot examine the contents of a variable or disassemble a
function within a DLL without a running program.

Variables are generally treated as pointers and dereferenced
automatically. For this reason, it is often necessary to prefix a
variable name with the address-of operator ("&") and provide explicit
type information in the command. Here's an example of the type of
problem:

(gdb) print 'cygwin1!__argv'
'cygwin1!__argv' has unknown type; cast it to its declared type

(gdb) x 'cygwin1!__argv'
'cygwin1!__argv' has unknown type; cast it to its declared type

And two possible solutions:

(gdb) print ((char **)'cygwin1!__argv')[0]
$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"

(gdb) x/2x &'cygwin1!__argv'
0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
(gdb) x/x 0x10021608
0x10021608: 0x0022fd98
(gdb) x/s 0x0022fd98
0x22fd98: "/cygdrive/c/mydirectory/myprogram"

Setting a break point within a DLL is possible even before the
program starts execution. However, under these circumstances, GDB can't
examine the initial instructions of the function in order to skip the
function's frame set-up code. You can work around this by using "*&" to
set the breakpoint at a raw memory address:

(gdb) break *&'python22!PyOS_Readline'
Breakpoint 1 at 0x1e04eff0

The author of these extensions is not entirely convinced that
setting a break point within a shared DLL like `kernel32.dll' is
completely safe.

File: gdb.info, Node: Hurd Native, Next: Darwin, Prev: Cygwin Native, Up: Native

21.1.5 Commands Specific to GNU Hurd Systems
--------------------------------------------

This subsection describes GDB commands specific to the GNU Hurd native
debugging.

`set signals'
`set sigs'
This command toggles the state of inferior signal interception by
GDB. Mach exceptions, such as breakpoint traps, are not affected
by this command. `sigs' is a shorthand alias for `signals'.

`show signals'
`show sigs'
Show the current state of intercepting inferior's signals.

`set signal-thread'
`set sigthread'
This command tells GDB which thread is the `libc' signal thread.
That thread is run when a signal is delivered to a running
process. `set sigthread' is the shorthand alias of `set
signal-thread'.

`show signal-thread'
`show sigthread'
These two commands show which thread will run when the inferior is
delivered a signal.

`set stopped'
This commands tells GDB that the inferior process is stopped, as
with the `SIGSTOP' signal. The stopped process can be continued
by delivering a signal to it.

`show stopped'
This command shows whether GDB thinks the debuggee is stopped.

`set exceptions'
Use this command to turn off trapping of exceptions in the
inferior. When exception trapping is off, neither breakpoints nor
single-stepping will work. To restore the default, set exception
trapping on.

`show exceptions'
Show the current state of trapping exceptions in the inferior.

`set task pause'
This command toggles task suspension when GDB has control.
Setting it to on takes effect immediately, and the task is
suspended whenever GDB gets control. Setting it to off will take
effect the next time the inferior is continued. If this option is
set to off, you can use `set thread default pause on' or `set
thread pause on' (see below) to pause individual threads.

`show task pause'
Show the current state of task suspension.

`set task detach-suspend-count'
This command sets the suspend count the task will be left with when
GDB detaches from it.

`show task detach-suspend-count'
Show the suspend count the task will be left with when detaching.

`set task exception-port'
`set task excp'
This command sets the task exception port to which GDB will
forward exceptions. The argument should be the value of the "send
rights" of the task. `set task excp' is a shorthand alias.

`set noninvasive'
This command switches GDB to a mode that is the least invasive as
far as interfering with the inferior is concerned. This is the
same as using `set task pause', `set exceptions', and `set
signals' to values opposite to the defaults.

`info send-rights'
`info receive-rights'
`info port-rights'
`info port-sets'
`info dead-names'
`info ports'
`info psets'
These commands display information about, respectively, send
rights, receive rights, port rights, port sets, and dead names of
a task. There are also shorthand aliases: `info ports' for `info
port-rights' and `info psets' for `info port-sets'.

`set thread pause'
This command toggles current thread suspension when GDB has
control. Setting it to on takes effect immediately, and the
current thread is suspended whenever GDB gets control. Setting it
to off will take effect the next time the inferior is continued.
Normally, this command has no effect, since when GDB has control,
the whole task is suspended. However, if you used `set task pause
off' (see above), this command comes in handy to suspend only the
current thread.

`show thread pause'
This command shows the state of current thread suspension.

`set thread run'
This command sets whether the current thread is allowed to run.

`show thread run'
Show whether the current thread is allowed to run.

`set thread detach-suspend-count'
This command sets the suspend count GDB will leave on a thread
when detaching. This number is relative to the suspend count
found by GDB when it notices the thread; use `set thread
takeover-suspend-count' to force it to an absolute value.

`show thread detach-suspend-count'
Show the suspend count GDB will leave on the thread when detaching.

`set thread exception-port'
`set thread excp'
Set the thread exception port to which to forward exceptions. This
overrides the port set by `set task exception-port' (see above).
`set thread excp' is the shorthand alias.

`set thread takeover-suspend-count'
Normally, GDB's thread suspend counts are relative to the value
GDB finds when it notices each thread. This command changes the
suspend counts to be absolute instead.

`set thread default'
`show thread default'
Each of the above `set thread' commands has a `set thread default'
counterpart (e.g., `set thread default pause', `set thread default
exception-port', etc.). The `thread default' variety of commands
sets the default thread properties for all threads; you can then
change the properties of individual threads with the non-default
commands.

File: gdb.info, Node: Darwin, Next: FreeBSD, Prev: Hurd Native, Up: Native

21.1.6 Darwin
-------------

GDB provides the following commands specific to the Darwin target:

`set debug darwin NUM'
When set to a non zero value, enables debugging messages specific
to the Darwin support. Higher values produce more verbose output.

`show debug darwin'
Show the current state of Darwin messages.

`set debug mach-o NUM'
When set to a non zero value, enables debugging messages while GDB
is reading Darwin object files. ("Mach-O" is the file format used
on Darwin for object and executable files.) Higher values produce
more verbose output. This is a command to diagnose problems
internal to GDB and should not be needed in normal usage.

`show debug mach-o'
Show the current state of Mach-O file messages.

`set mach-exceptions on'
`set mach-exceptions off'
On Darwin, faults are first reported as a Mach exception and are
then mapped to a Posix signal. Use this command to turn on
trapping of Mach exceptions in the inferior. This might be
sometimes useful to better understand the cause of a fault. The
default is off.

`show mach-exceptions'
Show the current state of exceptions trapping.

File: gdb.info, Node: FreeBSD, Prev: Darwin, Up: Native

21.1.7 FreeBSD
--------------

When the ABI of a system call is changed in the FreeBSD kernel, this is
implemented by leaving a compatibility system call using the old ABI at
the existing number and allocating a new system call number for the
version using the new ABI. As a convenience, when a system call is
caught by name (*note catch syscall::), compatibility system calls are
also caught.

For example, FreeBSD 12 introduced a new variant of the `kevent'
system call and catching the `kevent' system call by name catches both
variants:

(gdb) catch syscall kevent
Catchpoint 1 (syscalls 'freebsd11_kevent' [363] 'kevent' [560])
(gdb)

File: gdb.info, Node: Embedded OS, Next: Embedded Processors, Prev: Native, Up: Configurations

21.2 Embedded Operating Systems
===============================

This section describes configurations involving the debugging of
embedded operating systems that are available for several different
architectures.

GDB includes the ability to debug programs running on various
real-time operating systems.

File: gdb.info, Node: Embedded Processors, Next: Architectures, Prev: Embedded OS, Up: Configurations

21.3 Embedded Processors
========================

This section goes into details specific to particular embedded
configurations.

Whenever a specific embedded processor has a simulator, GDB allows
to send an arbitrary command to the simulator.

`sim COMMAND'
Send an arbitrary COMMAND string to the simulator. Consult the
documentation for the specific simulator in use for information
about acceptable commands.

* Menu:

* ARC:: Synopsys ARC
* ARM:: ARM
* BPF:: eBPF
* M68K:: Motorola M68K
* MicroBlaze:: Xilinx MicroBlaze
* MIPS Embedded:: MIPS Embedded
* OpenRISC 1000:: OpenRISC 1000 (or1k)
* PowerPC Embedded:: PowerPC Embedded
* AVR:: Atmel AVR
* CRIS:: CRIS
* Super-H:: Renesas Super-H

File: gdb.info, Node: ARC, Next: ARM, Up: Embedded Processors

21.3.1 Synopsys ARC
-------------------

GDB provides the following ARC-specific commands:

`set debug arc'
Control the level of ARC specific debug messages. Use 0 for no
messages (the default), 1 for debug messages, and 2 for even more
debug messages.

`show debug arc'
Show the level of ARC specific debugging in operation.

`maint print arc arc-instruction ADDRESS'
Print internal disassembler information about instruction at a
given address.

File: gdb.info, Node: ARM, Next: BPF, Prev: ARC, Up: Embedded Processors

21.3.2 ARM
----------

GDB provides the following ARM-specific commands:

`set arm disassembler'
This commands selects from a list of disassembly styles. The
`"std"' style is the standard style.

`show arm disassembler'
Show the current disassembly style.

`set arm apcs32'
This command toggles ARM operation mode between 32-bit and 26-bit.

`show arm apcs32'
Display the current usage of the ARM 32-bit mode.

`set arm fpu FPUTYPE'
This command sets the ARM floating-point unit (FPU) type. The
argument FPUTYPE can be one of these:

`auto'
Determine the FPU type by querying the OS ABI.

`softfpa'
Software FPU, with mixed-endian doubles on little-endian ARM
processors.

`fpa'
GCC-compiled FPA co-processor.

`softvfp'
Software FPU with pure-endian doubles.

`vfp'
VFP co-processor.

`show arm fpu'
Show the current type of the FPU.

`set arm abi'
This command forces GDB to use the specified ABI.

`show arm abi'
Show the currently used ABI.

`set arm fallback-mode (arm|thumb|auto)'
GDB uses the symbol table, when available, to determine whether
instructions are ARM or Thumb. This command controls GDB's
default behavior when the symbol table is not available. The
default is `auto', which causes GDB to use the current execution
mode (from the `T' bit in the `CPSR' register).

`show arm fallback-mode'
Show the current fallback instruction mode.

`set arm force-mode (arm|thumb|auto)'
This command overrides use of the symbol table to determine whether
instructions are ARM or Thumb. The default is `auto', which
causes GDB to use the symbol table and then the setting of `set
arm fallback-mode'.

`show arm force-mode'
Show the current forced instruction mode.

`set arm unwind-secure-frames'
This command enables unwinding from Non-secure to Secure mode on
Cortex-M with Security extension. This can trigger security
exceptions when unwinding the exception stack. It is enabled by
default.

`show arm unwind-secure-frames'
Show whether unwinding from Non-secure to Secure mode is enabled.

`set debug arm'
Toggle whether to display ARM-specific debugging messages from the
ARM target support subsystem.

`show debug arm'
Show whether ARM-specific debugging messages are enabled.

`target sim [SIMARGS] ...'
The GDB ARM simulator accepts the following optional arguments.

`--swi-support=TYPE'
Tell the simulator which SWI interfaces to support. The
argument TYPE may be a comma separated list of the following
values. The default value is `all'.

`none'

`demon'

`angel'

`redboot'

`all'

File: gdb.info, Node: BPF, Next: M68K, Prev: ARM, Up: Embedded Processors

21.3.3 BPF
----------

`target sim [SIMARGS] ...'
The GDB BPF simulator accepts the following optional arguments.

`--skb-data-offset=OFFSET'
Tell the simulator the offset, measured in bytes, of the
`skb_data' field in the kernel `struct sk_buff' structure.
This offset is used by some BPF specific-purpose load/store
instructions. Defaults to 0.

File: gdb.info, Node: M68K, Next: MicroBlaze, Prev: BPF, Up: Embedded Processors

21.3.4 M68k
-----------

The Motorola m68k configuration includes ColdFire support.

File: gdb.info, Node: MicroBlaze, Next: MIPS Embedded, Prev: M68K, Up: Embedded Processors

21.3.5 MicroBlaze
-----------------

The MicroBlaze is a soft-core processor supported on various Xilinx
FPGAs, such as Spartan or Virtex series. Boards with these processors
usually have JTAG ports which connect to a host system running the
Xilinx Embedded Development Kit (EDK) or Software Development Kit (SDK).
This host system is used to download the configuration bitstream to the
target FPGA. The Xilinx Microprocessor Debugger (XMD) program
communicates with the target board using the JTAG interface and
presents a `gdbserver' interface to the board. By default `xmd' uses
port `1234'. (While it is possible to change this default port, it
requires the use of undocumented `xmd' commands. Contact Xilinx
support if you need to do this.)

Use these GDB commands to connect to the MicroBlaze target processor.

`target remote :1234'
Use this command to connect to the target if you are running GDB
on the same system as `xmd'.

`target remote XMD-HOST:1234'
Use this command to connect to the target if it is connected to
`xmd' running on a different system named XMD-HOST.

`load'
Use this command to download a program to the MicroBlaze target.

`set debug microblaze N'
Enable MicroBlaze-specific debugging messages if non-zero.

`show debug microblaze N'
Show MicroBlaze-specific debugging level.

File: gdb.info, Node: MIPS Embedded, Next: OpenRISC 1000, Prev: MicroBlaze, Up: Embedded Processors

21.3.6 MIPS Embedded
--------------------

GDB supports these special commands for MIPS targets:

`set mipsfpu double'
`set mipsfpu single'
`set mipsfpu none'
`set mipsfpu auto'
`show mipsfpu'
If your target board does not support the MIPS floating point
coprocessor, you should use the command `set mipsfpu none' (if you
need this, you may wish to put the command in your GDB init file).
This tells GDB how to find the return value of functions which
return floating point values. It also allows GDB to avoid saving
the floating point registers when calling functions on the board.
If you are using a floating point coprocessor with only single
precision floating point support, as on the R4650 processor, use
the command `set mipsfpu single'. The default double precision
floating point coprocessor may be selected using `set mipsfpu
double'.

In previous versions the only choices were double precision or no
floating point, so `set mipsfpu on' will select double precision
and `set mipsfpu off' will select no floating point.

As usual, you can inquire about the `mipsfpu' variable with `show
mipsfpu'.

File: gdb.info, Node: OpenRISC 1000, Next: PowerPC Embedded, Prev: MIPS Embedded, Up: Embedded Processors

21.3.7 OpenRISC 1000
--------------------

The OpenRISC 1000 provides a free RISC instruction set architecture.
It is mainly provided as a soft-core which can run on Xilinx, Altera
and other FPGA's.

GDB for OpenRISC supports the below commands when connecting to a
target:

`target sim'
Runs the builtin CPU simulator which can run very basic programs
but does not support most hardware functions like MMU. For more
complex use cases the user is advised to run an external target,
and connect using `target remote'.

Example: `target sim'

`set debug or1k'
Toggle whether to display OpenRISC-specific debugging messages
from the OpenRISC target support subsystem.

`show debug or1k'
Show whether OpenRISC-specific debugging messages are enabled.

File: gdb.info, Node: PowerPC Embedded, Next: AVR, Prev: OpenRISC 1000, Up: Embedded Processors

21.3.8 PowerPC Embedded
-----------------------

GDB supports using the DVC (Data Value Compare) register to implement
in hardware simple hardware watchpoint conditions of the form:

(gdb) watch ADDRESS|VARIABLE \
if ADDRESS|VARIABLE == CONSTANT EXPRESSION

The DVC register will be automatically used when GDB detects such
pattern in a condition expression, and the created watchpoint uses one
debug register (either the `exact-watchpoints' option is on and the
variable is scalar, or the variable has a length of one byte). This
feature is available in native GDB running on a Linux kernel version
2.6.34 or newer.

When running on PowerPC embedded processors, GDB automatically uses
ranged hardware watchpoints, unless the `exact-watchpoints' option is
on, in which case watchpoints using only one debug register are created
when watching variables of scalar types.

You can create an artificial array to watch an arbitrary memory
region using one of the following commands (*note Expressions::):

(gdb) watch *((char *) ADDRESS)@LENGTH
(gdb) watch {char[LENGTH]} ADDRESS

PowerPC embedded processors support masked watchpoints. See the
discussion about the `mask' argument in *Note Set Watchpoints::.

PowerPC embedded processors support hardware accelerated "ranged
breakpoints". A ranged breakpoint stops execution of the inferior
whenever it executes an instruction at any address within the range it
was set at. To set a ranged breakpoint in GDB, use the `break-range'
command.

GDB provides the following PowerPC-specific commands:

`break-range START-LOCSPEC, END-LOCSPEC'
Set a breakpoint for an address range given by START-LOCSPEC and
END-LOCSPEC, which are location specs. *Note Location
Specifications::, for a list of all the possible forms of location
specs. GDB resolves both START-LOCSPEC and END-LOCSPEC, and uses
the addresses of the resolved code locations as start and end
addresses of the range to break at. The breakpoint will stop
execution of the inferior whenever it executes an instruction at
any address between the start and end addresses, inclusive. If
either START-LOCSPEC or END-LOCSPEC resolve to multiple code
locations in the program, then the command aborts with an error
without creating a breakpoint.

`set powerpc soft-float'
`show powerpc soft-float'
Force GDB to use (or not use) a software floating point calling
convention. By default, GDB selects the calling convention based
on the selected architecture and the provided executable file.

`set powerpc vector-abi'
`show powerpc vector-abi'
Force GDB to use the specified calling convention for vector
arguments and return values. The valid options are `auto';
`generic', to avoid vector registers even if they are present;
`altivec', to use AltiVec registers; and `spe' to use SPE
registers. By default, GDB selects the calling convention based
on the selected architecture and the provided executable file.

`set powerpc exact-watchpoints'
`show powerpc exact-watchpoints'
Allow GDB to use only one debug register when watching a variable
of scalar type, thus assuming that the variable is accessed
through the address of its first byte.

File: gdb.info, Node: AVR, Next: CRIS, Prev: PowerPC Embedded, Up: Embedded Processors

21.3.9 Atmel AVR
----------------

When configured for debugging the Atmel AVR, GDB supports the following
AVR-specific commands:

`info io_registers'
This command displays information about the AVR I/O registers. For
each register, GDB prints its number and value.

File: gdb.info, Node: CRIS, Next: Super-H, Prev: AVR, Up: Embedded Processors

21.3.10 CRIS
------------

When configured for debugging CRIS, GDB provides the following
CRIS-specific commands:

`set cris-version VER'
Set the current CRIS version to VER, either `10' or `32'. The
CRIS version affects register names and sizes. This command is
useful in case autodetection of the CRIS version fails.

`show cris-version'
Show the current CRIS version.

`set cris-dwarf2-cfi'
Set the usage of DWARF-2 CFI for CRIS debugging. The default is
`on'. Change to `off' when using `gcc-cris' whose version is below
`R59'.

`show cris-dwarf2-cfi'
Show the current state of using DWARF-2 CFI.

`set cris-mode MODE'
Set the current CRIS mode to MODE. It should only be changed when
debugging in guru mode, in which case it should be set to `guru'
(the default is `normal').

`show cris-mode'
Show the current CRIS mode.

File: gdb.info, Node: Super-H, Prev: CRIS, Up: Embedded Processors

21.3.11 Renesas Super-H
-----------------------

For the Renesas Super-H processor, GDB provides these commands:

`set sh calling-convention CONVENTION'
Set the calling-convention used when calling functions from GDB.
Allowed values are `gcc', which is the default setting, and
`renesas'. With the `gcc' setting, functions are called using the
GCC calling convention. If the DWARF-2 information of the called
function specifies that the function follows the Renesas calling
convention, the function is called using the Renesas calling
convention. If the calling convention is set to `renesas', the
Renesas calling convention is always used, regardless of the
DWARF-2 information. This can be used to override the default of
`gcc' if debug information is missing, or the compiler does not
emit the DWARF-2 calling convention entry for a function.

`show sh calling-convention'
Show the current calling convention setting.

File: gdb.info, Node: Architectures, Prev: Embedded Processors, Up: Configurations

21.4 Architectures
==================

This section describes characteristics of architectures that affect all
uses of GDB with the architecture, both native and cross.

* Menu:

* AArch64::
* x86::
* Alpha::
* MIPS::
* HPPA:: HP PA architecture
* PowerPC::
* Nios II::
* Sparc64::
* S12Z::
* AMD GPU:: AMD GPU architectures

File: gdb.info, Node: AArch64, Next: x86, Up: Architectures

21.4.1 AArch64
--------------

When GDB is debugging the AArch64 architecture, it provides the
following special commands:

`set debug aarch64'
This command determines whether AArch64 architecture-specific
debugging messages are to be displayed.

`show debug aarch64'
Show whether AArch64 debugging messages are displayed.

21.4.1.1 AArch64 SVE.
....................

When GDB is debugging the AArch64 architecture, if the Scalable Vector
Extension (SVE) is present, then GDB will provide the vector registers
`$z0' through `$z31', vector predicate registers `$p0' through `$p15',
and the `$ffr' register. In addition, the pseudo register `$vg' will
be provided. This is the vector granule for the current thread and
represents the number of 64-bit chunks in an SVE `z' register.

If the vector length changes, then the `$vg' register will be
updated, but the lengths of the `z' and `p' registers will not change.
This is a known limitation of GDB and does not affect the execution of
the target process.

For SVE, the following definitions are used throughout GDB's source
code and in this document:

* VL: The vector length, in bytes. It defines the size of each `Z'
register.

* VQ: The number of 128 bit units in VL. This is mostly used
internally by GDB and the Linux Kernel.

* VG: The number of 64 bit units in VL. This is mostly used
internally by GDB and the Linux Kernel.

21.4.1.2 AArch64 SME.
....................

The Scalable Matrix Extension (SME
(https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/scalable-matrix-extension-armv9-a-architecture))
is an AArch64 architecture extension that expands on the concept of the
Scalable Vector Extension (SVE
(https://developer.arm.com/documentation/101726/4-0/Learn-about-the-Scalable-Vector-Extension--SVE-/What-is-the-Scalable-Vector-Extension-))
by providing a 2-dimensional register `ZA', which is a square matrix of
variable size, just like SVE provides a group of vector registers of
variable size.

Similarly to SVE, where the size of each `Z' register is directly
related to the vector length (VL for short), the SME `ZA' matrix
register's size is directly related to the streaming vector length (SVL
for short). *Note vl::. *Note svl::.

The `ZA' register state can be either active or inactive, if it is
not in use.

SME also introduces a new execution mode called streaming SVE mode
(streaming mode for short). When streaming mode is enabled, the
program supports execution of SVE2 instructions and the SVE registers
will have vector length SVL. When streaming mode is disabled, the SVE
registers have vector length VL.

For more information about SME and SVE, please refer to official
architecture documentation
(https://developer.arm.com/documentation/ddi0487/latest).

The following definitions are used throughout GDB's source code and
in this document:

* SVL: The streaming vector length, in bytes. It defines the size
of each dimension of the 2-dimensional square `ZA' matrix. The
total size of `ZA' is therefore SVL by SVL.

When streaming mode is enabled, it defines the size of the SVE
registers as well.

* SVQ: The number of 128 bit units in SVL, also known as streaming
vector granule. This is mostly used internally by GDB and the
Linux Kernel.

* SVG: The number of 64 bit units in SVL. This is mostly used
internally by GDB and the Linux Kernel.

When GDB is debugging the AArch64 architecture, if the Scalable
Matrix Extension (SME) is present, then GDB will make the `ZA' register
available. GDB will also make the `SVG' register and `SVCR'
pseudo-register available.

The `ZA' register is a 2-dimensional square SVL by SVL matrix of
bytes. To simplify the representation and access to the `ZA' register
in GDB, it is defined as a vector of SVLxSVL bytes.

If the user wants to index the `ZA' register as a matrix, it is
possible to reference `ZA' as `ZA[I][J]', where I is the row number and
J is the column number.

The `SVG' register always contains the streaming vector granule
(SVG) for the current thread. From the value of register `SVG' we can
easily derive the SVL value.

The `SVCR' pseudo-register (streaming vector control register) is a
status register that holds two state bits: SM in bit 0 and ZA in bit 1.

If the SM bit is 1, it means the current thread is in streaming
mode, and the SVE registers will use SVL for their sizes. If the SM
bit is 0, the current thread is not in streaming mode, and the SVE
registers will use VL for their sizes. *Note vl::.

If the ZA bit is 1, it means the `ZA' register is being used and has
meaningful contents. If the ZA bit is 0, the `ZA' register is
unavailable and its contents are undefined.

For convenience and simplicity, if the ZA bit is 0, the `ZA'
register and all of its pseudo-registers will read as zero.

If SVL changes during the execution of a program, then the `ZA'
register size and the bits in the `SVCR' pseudo-register will be updated
to reflect it.

It is possible for users to change SVL during the execution of a
program by modifying the `SVG' register value.

Whenever the `SVG' register is modified with a new value, the
following will be observed:

* The ZA and SM bits will be cleared in the `SVCR' pseudo-register.

* The `ZA' register will have a new size and its state will be
cleared, forcing its contents and the contents of all of its
pseudo-registers back to zero.

* If the SM bit was 1, the SVE registers will be reset to having
their sizes based on VL as opposed to SVL. If the SM bit was 0
prior to modifying the `SVG' register, there will be no observable
effect on the SVE registers.

The possible values for the `SVG' register are 2, 4, 8, 16, 32.
These numbers correspond to streaming vector length (SVL) values of 16
bytes, 32 bytes, 64 bytes, 128 bytes and 256 bytes respectively.

The minimum size of the `ZA' register is 16 x 16 (256) bytes, and the
maximum size is 256 x 256 (65536) bytes. In streaming mode, with bit SM
set, the size of the `ZA' register is the size of all the SVE `Z'
registers combined.

The `ZA' register can also be accessed using tiles and tile slices.

Tile pseudo-registers are square, 2-dimensional sub-arrays of
elements within the `ZA' register.

The tile pseudo-registers have the following naming pattern:
`ZA<TILE NUMBER><QUALIFIER>'.

There is a total of 31 `ZA' tile pseudo-registers. They are `ZA0B',
`ZA0H' through `ZA1H', `ZA0S' through `ZA3S', `ZA0D' through `ZA7D' and
`ZA0Q' through `ZA15Q'.

Tile slice pseudo-registers are vectors of horizontally or vertically
contiguous elements within the `ZA' register.

The tile slice pseudo-registers have the following naming pattern:
`ZA<TILE NUMBER><DIRECTION><QUALIFIER> <SLICE NUMBER>'.

There are up to 16 tiles (0 ~ 15), the direction can be either `v'
(vertical) or `h' (horizontal), the qualifiers can be `b' (byte), `h'
(halfword), `s' (word), `d' (doubleword) and `q' (quadword) and there
are up to 256 slices (0 ~ 255) depending on the value of SVL. The
number of slices is the same as the value of SVL.

The number of available tile slice pseudo-registers can be large.
For a minimum SVL of 16 bytes, there are 5 (number of qualifiers) x 2
(number of directions) x 16 (SVL) pseudo-registers. For the maximum
SVL of 256 bytes, there are 5 x 2 x 256 pseudo-registers.

When listing all the available registers, users will see the
currently-available `ZA' pseudo-registers. Pseudo-registers that don't
exist for a given SVL value will not be displayed.

For more information on SME and its terminology, please refer to the
Arm Architecture Reference Manual Supplement
(https://developer.arm.com/documentation/ddi0616/aa/), The Scalable
Matrix Extension (SME), for Armv9-A.

Some features are still under development and rely on ACLE
(https://github.com/ARM-software/acle/releases/latest) and ABI
(https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst)
definitions, so there are known limitations to the current SME support
in GDB.

One such example is calling functions in the program being debugged
by GDB. Such calls are not SME-aware and thus don't take into account
the `SVCR' pseudo-register bits nor the `ZA' register contents. *Note
Calling::.

The lazy saving scheme
(https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#the-za-lazy-saving-scheme)
involving the `TPIDR2' register is not yet supported by GDB, though the
`TPIDR2' register is known and supported by GDB.

Lastly, an important limitation for `gdbserver' is its inability to
communicate SVL changes to GDB. This means `gdbserver', even though it
is capable of adjusting its internal caches to reflect a change in the
value of SVL mid-execution, will operate with a potentially different
SVL value compared to GDB. This can lead to GDB showing incorrect
values for the `ZA' register and incorrect values for SVE registers
(when in streaming mode).

This is the same limitation we have for the SVE registers, and there
are plans to address this limitation going forward.

21.4.1.3 AArch64 SME2.
.....................

The Scalable Matrix Extension 2 is an AArch64 architecture extension
that further expands the SME extension with the following:

* The ability to address the `ZA' array through groups of
one-dimensional `ZA' array vectors, as opposed to `ZA' tiles with
2 dimensions.

* Instructions to operate on groups of SVE `Z' registers and `ZA'
array vectors.

* A new 512 bit `ZT0' lookup table register, for data decompression.

When GDB is debugging the AArch64 architecture, if the Scalable
Matrix Extension 2 (SME2) is present, then GDB will make the `ZT0'
register available.

The `ZT0' register is only considered active when the `ZA' register
state is active, therefore when the ZA bit of the `SVCR' is 1.

When the ZA bit of `SVCR' is 0, that means the `ZA' register state
is not active, which means the `ZT0' register state is also not active.

When `ZT0' is not active, it is comprised of zeroes, just like `ZA'.

Similarly to the `ZA' register, if the `ZT0' state is not active and
the user attempts to modify its value such that any of its bytes is
non-zero, then GDB will initialize the `ZA' register state as well,
which means the `SVCR' ZA bit gets set to 1.

For more information about SME2, please refer to the official
architecture documentation
(https://developer.arm.com/documentation/ddi0487/latest).

21.4.1.4 AArch64 Pointer Authentication.
.......................................

When GDB is debugging the AArch64 architecture, and the program is
using the v8.3-A feature Pointer Authentication (PAC), then whenever
the link register `$lr' is pointing to an PAC function its value will
be masked. When GDB prints a backtrace, any addresses that required
unmasking will be postfixed with the marker [PAC]. When using the MI,
this is printed as part of the `addr_flags' field.

21.4.1.5 AArch64 Memory Tagging Extension.
.........................................

When GDB is debugging the AArch64 architecture, the program is using
the v8.5-A feature Memory Tagging Extension (MTE) and there is support
in the kernel for MTE, GDB will make memory tagging functionality
available for inspection and editing of logical and allocation tags.
*Note Memory Tagging::.

To aid debugging, GDB will output additional information when SIGSEGV
signals are generated as a result of memory tag failures.

If the tag violation is synchronous, the following will be shown:

Program received signal SIGSEGV, Segmentation fault
Memory tag violation while accessing address 0x0500fffff7ff8000
Allocation tag 0x1
Logical tag 0x5.

If the tag violation is asynchronous, the fault address is not
available. In this case GDB will show the following:

Program received signal SIGSEGV, Segmentation fault
Memory tag violation
Fault address unavailable.

A special register, `tag_ctl', is made available through the
`org.gnu.gdb.aarch64.mte' feature. This register exposes some options
that can be controlled at runtime and emulates the `prctl' option
`PR_SET_TAGGED_ADDR_CTRL'. For further information, see the
documentation in the Linux kernel.

GDB supports dumping memory tag data to core files through the
`gcore' command and reading memory tag data from core files generated
by the `gcore' command or the Linux kernel.

When a process uses memory-mapped pages protected by memory tags (for
example, AArch64 MTE), this additional information will be recorded in
the core file in the event of a crash or if GDB generates a core file
from the current process state.

The memory tag data will be used so developers can display the memory
tags from a particular memory region (using the `m' modifier to the `x'
command, using the `print' command or using the various `memory-tag'
subcommands.

In the case of a crash, GDB will attempt to retrieve the memory tag
information automatically from the core file, and will show one of the
above messages depending on whether the synchronous or asynchronous
mode is selected. *Note Memory Tagging::. *Note Memory::.

File: gdb.info, Node: x86, Next: Alpha, Prev: AArch64, Up: Architectures

21.4.2 x86
----------

`set struct-convention MODE'
Set the convention used by the inferior to return `struct's and
`union's from functions to MODE. Possible values of MODE are
`"pcc"', `"reg"', and `"default"' (the default). `"default"' or
`"pcc"' means that `struct's are returned on the stack, while
`"reg"' means that a `struct' or a `union' whose size is 1, 2, 4,
or 8 bytes will be returned in a register.

`show struct-convention'
Show the current setting of the convention to return `struct's
from functions.

21.4.2.1 Intel "Memory Protection Extensions" (MPX).
...................................................

Memory Protection Extension (MPX) adds the bound registers `BND0' (1)
through `BND3'. Bound registers store a pair of 64-bit values which
are the lower bound and upper bound. Bounds are effective addresses or
memory locations. The upper bounds are architecturally represented in
1's complement form. A bound having lower bound = 0, and upper bound =
0 (1's complement of all bits set) will allow access to the entire
address space.

`BND0' through `BND3' are represented in GDB as `bnd0raw' through
`bnd3raw'. Pseudo registers `bnd0' through `bnd3' display the upper
bound performing the complement of one operation on the upper bound
value, i.e. when upper bound in `bnd0raw' is 0 in the GDB `bnd0' it
will be `0xfff...'. In this sense it can also be noted that the upper
bounds are inclusive.

As an example, assume that the register BND0 holds bounds for a
pointer having access allowed for the range between 0x32 and 0x71. The
values present on bnd0raw and bnd registers are presented as follows:

bnd0raw = {0x32, 0xffffffff8e}
bnd0 = {lbound = 0x32, ubound = 0x71} : size 64

This way the raw value can be accessed via bnd0raw...bnd3raw. Any
change on bnd0...bnd3 or bnd0raw...bnd3raw is reflect on its
counterpart. When the bnd0...bnd3 registers are displayed via Python,
the display includes the memory size, in bits, accessible to the
pointer.

Bounds can also be stored in bounds tables, which are stored in
application memory. These tables store bounds for pointers by
specifying the bounds pointer's value along with its bounds.
Evaluating and changing bounds located in bound tables is therefore
interesting while investigating bugs on MPX context. GDB provides
commands for this purpose:

`show mpx bound POINTER'
Display bounds of the given POINTER.

`set mpx bound POINTER, LBOUND, UBOUND'
Set the bounds of a pointer in the bound table. This command
takes three parameters: POINTER is the pointers whose bounds are
to be changed, LBOUND and UBOUND are new values for lower and
upper bounds respectively.

Both commands are deprecated and will be removed in future versions
of GDB. MPX itself was listed as removed by Intel in 2019.

When you call an inferior function on an Intel MPX enabled program,
GDB sets the inferior's bound registers to the init (disabled) state
before calling the function. As a consequence, bounds checks for the
pointer arguments passed to the function will always pass.

This is necessary because when you call an inferior function, the
program is usually in the middle of the execution of other function.
Since at that point bound registers are in an arbitrary state, not
clearing them would lead to random bound violations in the called
function.

You can still examine the influence of the bound registers on the
execution of the called function by stopping the execution of the
called function at its prologue, setting bound registers, and
continuing the execution. For example:

$ break *upper
Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47.
$ print upper (a, b, c, d, 1)
Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48)....
$ print $bnd0
{lbound = 0x0, ubound = ffffffff} : size -1

At this last step the value of bnd0 can be changed for investigation
of bound violations caused along the execution of the call. In order
to know how to set the bound registers or bound table for the call
consult the ABI.

21.4.2.2 x87 registers
.....................

GDB provides access to the x87 state through the following registers:

* `$st0' to `st7': `ST(0)' to `ST(7)' floating-point registers

* `$fctrl': control word register (`FCW')

* `$fstat': status word register (`FSW')

* `$ftag': tag word (`FTW')

* `$fiseg': last instruction pointer segment

* `$fioff': last instruction pointer

* `$foseg': last data pointer segment

* `$fooff': last data pointer

* `$fop': last opcode

---------- Footnotes ----------

(1) The register named with capital letters represent the
architecture registers.

File: gdb.info, Node: Alpha, Next: MIPS, Prev: x86, Up: Architectures

21.4.3 Alpha
------------

See the following section.

File: gdb.info, Node: MIPS, Next: HPPA, Prev: Alpha, Up: Architectures

21.4.4 MIPS
-----------

Alpha- and MIPS-based computers use an unusual stack frame, which
sometimes requires GDB to search backward in the object code to find
the beginning of a function.

To improve response time (especially for embedded applications, where
GDB may be restricted to a slow serial line for this search) you may
want to limit the size of this search, using one of these commands:

`set heuristic-fence-post LIMIT'
Restrict GDB to examining at most LIMIT bytes in its search for
the beginning of a function. A value of 0 (the default) means
there is no limit. However, except for 0, the larger the limit
the more bytes `heuristic-fence-post' must search and therefore
the longer it takes to run. You should only need to use this
command when debugging a stripped executable.

`show heuristic-fence-post'
Display the current limit.

These commands are available _only_ when GDB is configured for
debugging programs on Alpha or MIPS processors.

Several MIPS-specific commands are available when debugging MIPS
programs:

`set mips abi ARG'
Tell GDB which MIPS ABI is used by the inferior. Possible values
of ARG are:

`auto'
The default ABI associated with the current binary (this is
the default).

`o32'

`o64'

`n32'

`n64'

`eabi32'

`eabi64'

`show mips abi'
Show the MIPS ABI used by GDB to debug the inferior.

`set mips compression ARG'
Tell GDB which MIPS compressed ISA (Instruction Set Architecture)
encoding is used by the inferior. GDB uses this for code
disassembly and other internal interpretation purposes. This
setting is only referred to when no executable has been associated
with the debugging session or the executable does not provide
information about the encoding it uses. Otherwise this setting is
automatically updated from information provided by the executable.

Possible values of ARG are `mips16' and `micromips'. The default
compressed ISA encoding is `mips16', as executables containing
MIPS16 code frequently are not identified as such.

This setting is "sticky"; that is, it retains its value across
debugging sessions until reset either explicitly with this command
or implicitly from an executable.

The compiler and/or assembler typically add symbol table
annotations to identify functions compiled for the MIPS16 or
microMIPS ISAs. If these function-scope annotations are present,
GDB uses them in preference to the global compressed ISA encoding
setting.

`show mips compression'
Show the MIPS compressed ISA encoding used by GDB to debug the
inferior.

`set mipsfpu'
`show mipsfpu'
*Note set mipsfpu: MIPS Embedded.

`set mips mask-address ARG'
This command determines whether the most-significant 32 bits of
64-bit MIPS addresses are masked off. The argument ARG can be
`on', `off', or `auto'. The latter is the default setting, which
lets GDB determine the correct value.

`show mips mask-address'
Show whether the upper 32 bits of MIPS addresses are masked off or
not.

`set remote-mips64-transfers-32bit-regs'
This command controls compatibility with 64-bit MIPS targets that
transfer data in 32-bit quantities. If you have an old MIPS 64
target that transfers 32 bits for some registers, like SR and FSR,
and 64 bits for other registers, set this option to `on'.

`show remote-mips64-transfers-32bit-regs'
Show the current setting of compatibility with older MIPS 64
targets.

`set debug mips'
This command turns on and off debugging messages for the
MIPS-specific target code in GDB.

`show debug mips'
Show the current setting of MIPS debugging messages.

File: gdb.info, Node: HPPA, Next: PowerPC, Prev: MIPS, Up: Architectures

21.4.5 HPPA
-----------

When GDB is debugging the HP PA architecture, it provides the following
special commands:

`set debug hppa'
This command determines whether HPPA architecture-specific
debugging messages are to be displayed.

`show debug hppa'
Show whether HPPA debugging messages are displayed.

`maint print unwind ADDRESS'
This command displays the contents of the unwind table entry at the
given ADDRESS.

File: gdb.info, Node: PowerPC, Next: Nios II, Prev: HPPA, Up: Architectures

21.4.6 PowerPC
--------------

When GDB is debugging the PowerPC architecture, it provides a set of
pseudo-registers to enable inspection of 128-bit wide Decimal Floating
Point numbers stored in the floating point registers. These values must
be stored in two consecutive registers, always starting at an even
register like `f0' or `f2'.

The pseudo-registers go from `$dl0' through `$dl15', and are formed
by joining the even/odd register pairs `f0' and `f1' for `$dl0', `f2'
and `f3' for `$dl1' and so on.

For POWER7 processors, GDB provides a set of pseudo-registers, the
64-bit wide Extended Floating Point Registers (`f32' through `f63').

File: gdb.info, Node: Nios II, Next: Sparc64, Prev: PowerPC, Up: Architectures

21.4.7 Nios II
--------------

When GDB is debugging the Nios II architecture, it provides the
following special commands:

`set debug nios2'
This command turns on and off debugging messages for the Nios II
target code in GDB.

`show debug nios2'
Show the current setting of Nios II debugging messages.

File: gdb.info, Node: Sparc64, Next: S12Z, Prev: Nios II, Up: Architectures

21.4.8 Sparc64
--------------

21.4.8.1 ADI Support
...................

The M7 processor supports an Application Data Integrity (ADI) feature
that detects invalid data accesses. When software allocates memory and
enables ADI on the allocated memory, it chooses a 4-bit version number,
sets the version in the upper 4 bits of the 64-bit pointer to that
data, and stores the 4-bit version in every cacheline of that data.
Hardware saves the latter in spare bits in the cache and memory
hierarchy. On each load and store, the processor compares the upper 4
VA (virtual address) bits to the cacheline's version. If there is a
mismatch, the processor generates a version mismatch trap which can be
either precise or disrupting. The trap is an error condition which the
kernel delivers to the process as a SIGSEGV signal.

Note that only 64-bit applications can use ADI and need to be built
with ADI-enabled.

Values of the ADI version tags, which are in granularity of a
cacheline (64 bytes), can be viewed or modified.

`adi (examine | x) [ / N ] ADDR'
The `adi examine' command displays the value of one ADI version
tag per cacheline.

N is a decimal integer specifying the number in bytes; the default
is 1. It specifies how much ADI version information, at the ratio
of 1:ADI block size, to display.

ADDR is the address in user address space where you want GDB to
begin displaying the ADI version tags.

Below is an example of displaying ADI versions of variable
"shmaddr".

(gdb) adi x/100 shmaddr
0xfff800010002c000: 0 0

`adi (assign | a) [ / N ] ADDR = TAG'
The `adi assign' command is used to assign new ADI version tag to
an address.

N is a decimal integer specifying the number in bytes; the default
is 1. It specifies how much ADI version information, at the ratio
of 1:ADI block size, to modify.

ADDR is the address in user address space where you want GDB to
begin modifying the ADI version tags.

TAG is the new ADI version tag.

For example, do the following to modify then verify ADI versions of
variable "shmaddr":

(gdb) adi a/100 shmaddr = 7
(gdb) adi x/100 shmaddr
0xfff800010002c000: 7 7

File: gdb.info, Node: S12Z, Next: AMD GPU, Prev: Sparc64, Up: Architectures

21.4.9 S12Z
-----------

When GDB is debugging the S12Z architecture, it provides the following
special command:

`maint info bdccsr'
This command displays the current value of the microprocessor's
BDCCSR register.

File: gdb.info, Node: AMD GPU, Prev: S12Z, Up: Architectures

21.4.10 AMD GPU
---------------

GDB supports debugging programs offloaded to AMD GPU devices using the
AMD ROCm (https://docs.amd.com/) platform. GDB presents host threads
alongside GPU wavefronts, allowing debugging both the host and device
parts of the program simultaneously.

21.4.10.1 AMD GPU Architectures
..............................

The list of AMD GPU architectures supported by GDB depends on the
version of the AMD Debugger API library used. See its documentation
(https://docs.amd.com/bundle/ROCDebugger_User_and_API) for more details.

21.4.10.2 AMD GPU Device Driver and AMD ROCm Runtime
...................................................

GDB requires a compatible AMD GPU device driver to be installed. A
warning message is displayed if either the device driver version or the
version of the debug support it implements is unsupported. GDB will
continue to function except no AMD GPU debugging will be possible.

GDB requires each agent to have compatible firmware installed by the
device driver. A warning message is displayed if unsupported firmware
is detected. GDB will continue to function except no AMD GPU debugging
will be possible on the agent.

GDB requires a compatible AMD ROCm runtime to be loaded in order to
detect AMD GPU code objects and wavefronts. A warning message is
displayed if an unsupported AMD ROCm runtime is detected, or there is
an error or restriction that prevents debugging. GDB will continue to
function except no AMD GPU debugging will be possible.

21.4.10.3 AMD GPU Wavefronts
...........................

An AMD GPU wavefront is represented in GDB as a thread.

Note that some AMD GPU architectures may have restrictions on
providing information about AMD GPU wavefronts created when GDB is not
attached (*note AMD GPU Attaching Restrictions: AMD GPU Attaching
Restrictions.).

When scheduler-locking is in effect (*note set scheduler-locking::),
new wavefronts created by the resumed thread (either CPU thread or GPU
wavefront) are held in the halt state.

21.4.10.4 AMD GPU Code Objects
.............................

The `info sharedlibrary' command will show the AMD GPU code objects as
file or memory URIs, together with the host's shared libraries. For
example:

(gdb) info sharedlibrary
From To Syms Read Shared Object Library
0x1111 0x2222 Yes (*) /lib64/ld-linux-x86-64.so.2
...
0x3333 0x4444 Yes (*) /opt/rocm-4.5.0/.../libamd_comgr.so
0x5555 0x6666 Yes (*) /lib/x86_64-linux-gnu/libtinfo.so.5
0x7777 0x8888 Yes file:///tmp/a.out#offset=6477&size=10832
0x9999 0xaaaa Yes (*) memory://95557/mem#offset=0x1234&size=100
(*): Shared library is missing debugging information.
(gdb)

For a `file' URI, the path portion is the file on disk containing
the code object. The OFFSET parameter is a 0-based offset in this
file, to the start of the code object. If omitted, it defaults to 0.
The SIZE parameter is the size of the code object in bytes. If
omitted, it defaults to the size of the file.

For a `memory' URI, the path portion is the process id of the
process owning the memory containing the code object. The OFFSET
parameter is the memory address where the code object is found, and the
SIZE parameter is its size in bytes.

AMD GPU code objects are loaded into each AMD GPU device separately.
The `info sharedlibrary' command may therefore show the same code
object loaded multiple times. As a consequence, setting a breakpoint
in AMD GPU code will result in multiple breakpoint locations if there
are multiple AMD GPU devices.

21.4.10.5 AMD GPU Entity Target Identifiers and Convenience Variables
....................................................................

The AMD GPU entities have the following target identifier formats:

Thread Target ID
The AMD GPU thread target identifier (SYSTAG) string has the
following format:

AMDGPU Wave AGENT-ID:QUEUE-ID:DISPATCH-ID:WAVE-ID (WORK-GROUP-X,WORK-GROUP-Y,WORK-GROUP-Z)/WORK-GROUP-THREAD-INDEX

21.4.10.6 AMD GPU Signals
........................

For AMD GPU wavefronts, GDB maps target conditions to stop signals in
the following way:

`SIGILL'
Execution of an illegal instruction.

`SIGTRAP'
Execution of a `S_TRAP' instruction other than:

* `S_TRAP 1' which is used by GDB to insert breakpoints.

* `S_TRAP 2' which raises `SIGABRT'.

`SIGABRT'
Execution of a `S_TRAP 2' instruction.

`SIGFPE'
Execution of a floating point or integer instruction detects a
condition that is enabled to raise a signal. The conditions
include:

* Floating point operation is invalid.

* Floating point operation had subnormal input that was rounded
to zero.

* Floating point operation performed a division by zero.

* Floating point operation produced an overflow result. The
result was rounded to infinity.

* Floating point operation produced an underflow result. A
subnormal result was rounded to zero.

* Floating point operation produced an inexact result.

* Integer operation performed a division by zero.

By default, these conditions are not enabled to raise signals. The
`set $mode' command can be used to change the AMD GPU wavefront's
register that has bits controlling which conditions are enabled to
raise signals. The `print $trapsts' command can be used to
inspect which conditions have been detected even if they are not
enabled to raise a signal.

`SIGBUS'
Execution of an instruction that accessed global memory using an
address that is outside the virtual address range.

`SIGSEGV'
Execution of an instruction that accessed a global memory page
that is either not mapped or accessed with incompatible
permissions.

If a single instruction raises more than one signal, they will be
reported one at a time each time the wavefront is continued.

21.4.10.7 AMD GPU Memory Violation Reporting
...........................................

A wavefront can report memory violation events. However, the program
location at which they are reported may be after the machine instruction
that caused them. This can result in the reported source statement
being incorrect. The following commands can be used to control this
behavior:

`set amdgpu precise-memory MODE'
Controls how AMD GPU devices detect memory violations, where MODE
can be:

`off'
The program location may not be immediately after the
instruction that caused the memory violation. This is the
default.

`on'
Requests that the program location will be immediately after
the instruction that caused a memory violation. Enabling
this mode may make the AMD GPU device execution significantly
slower as it has to wait for each memory operation to
complete before executing the next instruction.

The `amdgpu precise-memory' parameter is per-inferior. When an
inferior forks or execs, or the user uses the `clone-inferior'
command, and an inferior is created as a result, the newly created
inferior inherits the parameter value of the original inferior.

`show amdgpu precise-memory'
Displays the currently requested AMD GPU precise memory setting.

21.4.10.8 AMD GPU Logging
........................

The `set debug amd-dbgapi' command can be used to enable diagnostic
messages in the `amd-dbgapi' target. The `show debug amd-dbgapi'
command displays the current setting. *Note set debug amd-dbgapi::.

The `set debug amd-dbgapi-lib log-level LEVEL' command can be used
to enable diagnostic messages from the `amd-dbgapi' library (which GDB
uses under the hood). The `show debug amd-dbgapi-lib log-level'
command displays the current `amd-dbgapi' library log level. *Note set
debug amd-dbgapi-lib::.

21.4.10.9 AMD GPU Restrictions
.............................

1. When in non-stop mode, wavefronts may not hit breakpoints inserted
while not stopped, nor see memory updates made while not stopped,
until the wavefront is next stopped. Memory updated by non-stopped
wavefronts may not be visible until the wavefront is next stopped.

2. The HIP runtime performs deferred code object loading by default.
AMD GPU code objects are not loaded until the first kernel is
launched. Before then, all breakpoints have to be set as pending
breakpoints.

If source line positions are used that only correspond to source
lines in unloaded code objects, then GDB may not set pending
breakpoints, and instead set breakpoints on the next following
source line that maps to host code. This can result in unexpected
breakpoint hits being reported. When the code object containing
the source lines is loaded, the incorrect breakpoints will be
removed and replaced by the correct ones. This problem can be
avoided by only setting breakpoints in unloaded code objects using
symbol or function names.

Setting the `HIP_ENABLE_DEFERRED_LOADING' environment variable to
`0' can be used to disable deferred code object loading by the HIP
runtime. This ensures all code objects will be loaded when the
inferior reaches the beginning of the `main' function.

3. If no CPU thread is running, then `Ctrl-C' is not able to stop AMD
GPU threads. This can happen for example if you enable
`scheduler-locking' after the whole program stopped, and then
resume an AMD GPU thread. The only way to unblock the situation
is to kill the GDB process.

4. By default, for some architectures, the AMD GPU device driver
causes all AMD GPU wavefronts created when GDB is not attached to
be unable to report the dispatch associated with the wavefront, or
the wavefront's work-group position. The `info threads' command
will display this missing information with a `?'.

This does not affect wavefronts created while GDB is attached which
are always capable of reporting this information.

If the `HSA_ENABLE_DEBUG' environment variable is set to `1' when
the AMD ROCm runtime is initialized, then this information will be
available for all architectures even for wavefronts created when
GDB was not attached.

File: gdb.info, Node: Controlling GDB, Next: Extending GDB, Prev: Configurations, Up: Top

22 Controlling GDB
******************

You can alter the way GDB interacts with you by using the `set'
command. For commands controlling how GDB displays data, see *Note
Print Settings: Print Settings. Other settings are described here.

* Menu:

* Prompt:: Prompt
* Editing:: Command editing
* Command History:: Command history
* Screen Size:: Screen size
* Output Styling:: Output styling
* Numbers:: Numbers
* ABI:: Configuring the current ABI
* Auto-loading:: Automatically loading associated files
* Messages/Warnings:: Optional warnings and messages
* Debugging Output:: Optional messages about internal happenings
* Other Misc Settings:: Other Miscellaneous Settings

File: gdb.info, Node: Prompt, Next: Editing, Up: Controlling GDB

22.1 Prompt
===========

GDB indicates its readiness to read a command by printing a string
called the "prompt". This string is normally `(gdb)'. You can change
the prompt string with the `set prompt' command. For instance, when
debugging GDB with GDB, it is useful to change the prompt in one of the
GDB sessions so that you can always tell which one you are talking to.

_Note:_ `set prompt' does not add a space for you after the prompt
you set. This allows you to set a prompt which ends in a space or a
prompt that does not.

`set prompt NEWPROMPT'
Directs GDB to use NEWPROMPT as its prompt string henceforth.

`show prompt'
Prints a line of the form: `Gdb's prompt is: YOUR-PROMPT'

Versions of GDB that ship with Python scripting enabled have prompt
extensions. The commands for interacting with these extensions are:

`set extended-prompt PROMPT'
Set an extended prompt that allows for substitutions. *Note
gdb.prompt::, for a list of escape sequences that can be used for
substitution. Any escape sequences specified as part of the prompt
string are replaced with the corresponding strings each time the
prompt is displayed.

For example:

set extended-prompt Current working directory: \w (gdb)

Note that when an extended-prompt is set, it takes control of the
PROMPT_HOOK hook. *Note prompt_hook::, for further information.

`show extended-prompt'
Prints the extended prompt. Any escape sequences specified as
part of the prompt string with `set extended-prompt', are replaced
with the corresponding strings each time the prompt is displayed.

File: gdb.info, Node: Editing, Next: Command History, Prev: Prompt, Up: Controlling GDB

22.2 Command Editing
====================

GDB reads its input commands via the "Readline" interface. This GNU
library provides consistent behavior for programs which provide a
command line interface to the user. Advantages are GNU Emacs-style or
"vi"-style inline editing of commands, `csh'-like history substitution,
and a storage and recall of command history across debugging sessions.

You may control the behavior of command line editing in GDB with the
command `set'.

`set editing'
`set editing on'
Enable command line editing (enabled by default).

`set editing off'
Disable command line editing.

`show editing'
Show whether command line editing is enabled.

*Note Command Line Editing::, for more details about the Readline
interface. Users unfamiliar with GNU Emacs or `vi' are encouraged to
read that chapter.

GDB sets the Readline application name to `gdb'. This is useful for
conditions in `.inputrc'.

GDB defines a bindable Readline command, `operate-and-get-next'.
This is bound to `C-o' by default. This command accepts the current
line for execution and fetches the next line relative to the current
line from the history for editing. Any argument is ignored.

File: gdb.info, Node: Command History, Next: Screen Size, Prev: Editing, Up: Controlling GDB

22.3 Command History
====================

GDB can keep track of the commands you type during your debugging
sessions, so that you can be certain of precisely what happened. Use
these commands to manage the GDB command history facility.

GDB uses the GNU History library, a part of the Readline package, to
provide the history facility. *Note Using History Interactively::, for
the detailed description of the History library.

To issue a command to GDB without affecting certain aspects of the
state which is seen by users, prefix it with `server ' (*note Server
Prefix::). This means that this command will not affect the command
history, nor will it affect GDB's notion of which command to repeat if
<RET> is pressed on a line by itself.

The server prefix does not affect the recording of values into the
value history; to print a value without recording it into the value
history, use the `output' command instead of the `print' command.

Here is the description of GDB commands related to command history.

`set history filename [FNAME]'
Set the name of the GDB command history file to FNAME. This is
the file where GDB reads an initial command history list, and
where it writes the command history from this session when it
exits. You can access this list through history expansion or
through the history command editing characters listed below. This
file defaults to the value of the environment variable
`GDBHISTFILE', or to `./.gdb_history' (`./_gdb_history' on MS-DOS)
if this variable is not set.

The `GDBHISTFILE' environment variable is read after processing
any GDB initialization files (*note Startup::) and after
processing any commands passed using command line options (for
example, `-ex').

If the FNAME argument is not given, or if the `GDBHISTFILE' is the
empty string then GDB will neither try to load an existing history
file, nor will it try to save the history on exit.

`set history save'
`set history save on'
Record command history in a file, whose name may be specified with
the `set history filename' command. By default, this option is
disabled. The command history will be recorded when GDB exits.
If `set history filename' is set to the empty string then history
saving is disabled, even when `set history save' is `on'.

`set history save off'
Don't record the command history into the file specified by `set
history filename' when GDB exits.

`set history size SIZE'
`set history size unlimited'
Set the number of commands which GDB keeps in its history list.
This defaults to the value of the environment variable
`GDBHISTSIZE', or to 256 if this variable is not set. Non-numeric
values of `GDBHISTSIZE' are ignored. If SIZE is `unlimited' or if
`GDBHISTSIZE' is either a negative number or the empty string,
then the number of commands GDB keeps in the history list is
unlimited.

The `GDBHISTSIZE' environment variable is read after processing
any GDB initialization files (*note Startup::) and after
processing any commands passed using command line options (for
example, `-ex').

`set history remove-duplicates COUNT'
`set history remove-duplicates unlimited'
Control the removal of duplicate history entries in the command
history list. If COUNT is non-zero, GDB will look back at the
last COUNT history entries and remove the first entry that is a
duplicate of the current entry being added to the command history
list. If COUNT is `unlimited' then this lookbehind is unbounded.
If COUNT is 0, then removal of duplicate history entries is
disabled.

Only history entries added during the current session are
considered for removal. This option is set to 0 by default.

History expansion assigns special meaning to the character `!'.
*Note Event Designators::, for more details.

Since `!' is also the logical not operator in C, history expansion
is off by default. If you decide to enable history expansion with the
`set history expansion on' command, you may sometimes need to follow
`!' (when it is used as logical not, in an expression) with a space or
a tab to prevent it from being expanded. The readline history
facilities do not attempt substitution on the strings `!=' and `!(',
even when history expansion is enabled.

The commands to control history expansion are:

`set history expansion on'
`set history expansion'
Enable history expansion. History expansion is off by default.

`set history expansion off'
Disable history expansion.

`show history'
`show history filename'
`show history save'
`show history size'
`show history expansion'
These commands display the state of the GDB history parameters.
`show history' by itself displays all four states.

`show commands'
Display the last ten commands in the command history.

`show commands N'
Print ten commands centered on command number N.

`show commands +'
Print ten commands just after the commands last printed.

File: gdb.info, Node: Screen Size, Next: Output Styling, Prev: Command History, Up: Controlling GDB

22.4 Screen Size
================

Certain commands to GDB may produce large amounts of information output
to the screen. To help you read all of it, GDB pauses and asks you for
input at the end of each page of output. Type <RET> when you want to
see one more page of output, `q' to discard the remaining output, or
`c' to continue without paging for the rest of the current command.
Also, the screen width setting determines when to wrap lines of output.
Depending on what is being printed, GDB tries to break the line at a
readable place, rather than simply letting it overflow onto the
following line.

Normally GDB knows the size of the screen from the terminal driver
software. For example, on Unix GDB uses the termcap data base together
with the value of the `TERM' environment variable and the `stty rows'
and `stty cols' settings. If this is not correct, you can override it
with the `set height' and `set width' commands:

`set height LPP'
`set height unlimited'
`show height'
`set width CPL'
`set width unlimited'
`show width'
These `set' commands specify a screen height of LPP lines and a
screen width of CPL characters. The associated `show' commands
display the current settings.

If you specify a height of either `unlimited' or zero lines, GDB
does not pause during output no matter how long the output is.
This is useful if output is to a file or to an editor buffer.

Likewise, you can specify `set width unlimited' or `set width 0'
to prevent GDB from wrapping its output.

`set pagination on'
`set pagination off'
Turn the output pagination on or off; the default is on. Turning
pagination off is the alternative to `set height unlimited'. Note
that running GDB with the `--batch' option (*note -batch: Mode
Options.) also automatically disables pagination.

`show pagination'
Show the current pagination mode.

File: gdb.info, Node: Output Styling, Next: Numbers, Prev: Screen Size, Up: Controlling GDB

22.5 Output Styling
===================

GDB can style its output on a capable terminal. This is enabled by
default on most systems, but disabled by default when in batch mode
(*note Mode Options::). Various style settings are available; and
styles can also be disabled entirely.

`set style enabled `on|off''
Enable or disable all styling. The default is host-dependent, with
most hosts defaulting to `on'.

If the `NO_COLOR' environment variable is set to a non-empty
value, then GDB will change this to `off' at startup.

`show style enabled'
Show the current state of styling.

`set style sources `on|off''
Enable or disable source code styling. This affects whether source
code, such as the output of the `list' command, is styled. The
default is `on'. Note that source styling only works if styling
in general is enabled, and if a source highlighting library is
available to GDB.

There are two ways that highlighting can be done. First, if GDB
was linked with the GNU Source Highlight library, then it is used.
Otherwise, if GDB was configured with Python scripting support,
and if the Python Pygments package is available, then it will be
used.

`show style sources'
Show the current state of source code styling.

`set style tui-current-position `on|off''
Enable or disable styling of the source and assembly code
highlighted by the TUI's current position indicator. The default
is `off'. *Note GDB Text User Interface: TUI.

`show style tui-current-position'
Show whether the source and assembly code highlighted by the TUI's
current position indicator is styled.

`set style disassembler enabled `on|off''
Enable or disable disassembler styling. This affects whether
disassembler output, such as the output of the `disassemble'
command, is styled. Disassembler styling only works if styling in
general is enabled (with `set style enabled on'), and if a source
highlighting library is available to GDB.

The two source highlighting libraries that GDB could use to style
disassembler output are; GDB's builtin disassembler, or the Python
Pygments package.

GDB's first choice will be to use the builtin disassembler for
styling, this usually provides better results, being able to style
different types of instruction operands differently. However, the
builtin disassembler is not able to style all architectures.

For architectures that the builtin disassembler is unable to style,
GDB will fall back to use the Python Pygments package where
possible. In order to use the Python Pygments package, GDB must
be built with Python support, and the Pygments package must be
installed.

If neither of these options are available then GDB will produce
unstyled disassembler output, even when this setting is `on'.

To discover if the current architecture supports styling using the
builtin disassembler library see *Note `maint show
libopcodes-styling enabled': maint_libopcodes_styling.

`show style disassembler enabled'
Show the current state of disassembler styling.

Subcommands of `set style' control specific forms of styling. These
subcommands all follow the same pattern: each style-able object can be
styled with a foreground color, a background color, and an intensity.

For example, the style of file names can be controlled using the
`set style filename' group of commands:

`set style filename background COLOR'
Set the background to COLOR. Valid colors are `none' (meaning the
terminal's default color), `black', `red', `green', `yellow',
`blue', `magenta', `cyan', and`white'.

`set style filename foreground COLOR'
Set the foreground to COLOR. Valid colors are `none' (meaning the
terminal's default color), `black', `red', `green', `yellow',
`blue', `magenta', `cyan', and`white'.

`set style filename intensity VALUE'
Set the intensity to VALUE. Valid intensities are `normal' (the
default), `bold', and `dim'.

The `show style' command and its subcommands are styling a style
name in their output using its own style. So, use `show style' to see
the complete list of styles, their characteristics and the visual
aspect of each style.

The style-able objects are:
`filename'
Control the styling of file names and URLs. By default, this
style's foreground color is green.

`function'
Control the styling of function names. These are managed with the
`set style function' family of commands. By default, this style's
foreground color is yellow.

This style is also used for symbol names in styled disassembler
output if GDB is using its builtin disassembler library for styling
(*note `set style disassembler enabled':
style_disassembler_enabled.).

`variable'
Control the styling of variable names. These are managed with the
`set style variable' family of commands. By default, this style's
foreground color is cyan.

`address'
Control the styling of addresses. These are managed with the `set
style address' family of commands. By default, this style's
foreground color is blue.

This style is also used for addresses in styled disassembler output
if GDB is using its builtin disassembler library for styling
(*note `set style disassembler enabled':
style_disassembler_enabled.).

`version'
Control the styling of GDB's version number text. By default,
this style's foreground color is magenta and it has bold
intensity. The version number is displayed in two places, the
output of `show version', and when GDB starts up.

In order to control how GDB styles the version number at startup,
add the `set style version' family of commands to the early
initialization command file (*note Initialization Files::).

`title'
Control the styling of titles. These are managed with the `set
style title' family of commands. By default, this style's
intensity is bold. Commands are using the title style to improve
the readability of large output. For example, the commands
`apropos' and `help' are using the title style for the command
names.

`highlight'
Control the styling of highlightings. These are managed with the
`set style highlight' family of commands. By default, this style's
foreground color is red. Commands are using the highlight style
to draw the user attention to some specific parts of their output.
For example, the command `apropos -v REGEXP' uses the highlight
style to mark the documentation parts matching REGEXP.

`metadata'
Control the styling of data annotations added by GDB to data it
displays. By default, this style's intensity is dim. Metadata
annotations include the `repeats N times' annotation for
suppressed display of repeated array elements (*note Print
Settings::), `<unavailable>' and `<error DESCR>' annotations for
errors and `<optimized-out>' annotations for optimized-out values
in displaying stack frame information in backtraces (*note
Backtrace::), etc.

`tui-border'
Control the styling of the TUI border. Note that, unlike other
styling options, only the color of the border can be controlled via
`set style'. This was done for compatibility reasons, as TUI
controls to set the border's intensity predated the addition of
general styling to GDB. *Note TUI Configuration::.

`tui-active-border'
Control the styling of the active TUI border; that is, the TUI
window that has the focus.

`disassembler comment'
Control the styling of comments in the disassembler output. These
are managed with the `set style disassembler comment' family of
commands. This style is only used when GDB is styling using its
builtin disassembler library (*note `set style disassembler
enabled': style_disassembler_enabled.). By default, this style's
intensity is dim, and its foreground color is white.

`disassembler immediate'
Control the styling of numeric operands in the disassembler output.
These are managed with the `set style disassembler immediate'
family of commands. This style is not used for instruction
operands that represent addresses, in that case the `disassembler
address' style is used. This style is only used when GDB is
styling using its builtin disassembler library. By default, this
style's foreground color is blue.

`disassembler address'
Control the styling of address operands in the disassembler output.
This is an alias for the `address' style.

`disassembler symbol'
Control the styling of symbol names in the disassembler output.
This is an alias for the `function' style.

`disassembler mnemonic'
Control the styling of instruction mnemonics in the disassembler
output. These are managed with the `set style disassembler
mnemonic' family of commands. This style is also used for
assembler directives, e.g. `.byte', `.word', etc. This style is
only used when GDB is styling using its builtin disassembler
library. By default, this style's foreground color is green.

`disassembler register'
Control the styling of register operands in the disassembler
output. These are managed with the `set style disassembler
register' family of commands. This style is only used when GDB is
styling using its builtin disassembler library. By default, this
style's foreground color is red.

File: gdb.info, Node: Numbers, Next: ABI, Prev: Output Styling, Up: Controlling GDB

22.6 Numbers
============

You can always enter numbers in octal, decimal, or hexadecimal in GDB
by the usual conventions: octal numbers begin with `0', decimal numbers
end with `.', and hexadecimal numbers begin with `0x'. Numbers that
neither begin with `0' or `0x', nor end with a `.' are, by default,
entered in base 10; likewise, the default display for numbers--when no
particular format is specified--is base 10. You can change the default
base for both input and output with the commands described below.

`set input-radix BASE'
Set the default base for numeric input. Supported choices for
BASE are decimal 8, 10, or 16. The base must itself be specified
either unambiguously or using the current input radix; for
example, any of

set input-radix 012
set input-radix 10.
set input-radix 0xa

sets the input base to decimal. On the other hand, `set
input-radix 10' leaves the input radix unchanged, no matter what
it was, since `10', being without any leading or trailing signs of
its base, is interpreted in the current radix. Thus, if the
current radix is 16, `10' is interpreted in hex, i.e. as 16
decimal, which doesn't change the radix.

`set output-radix BASE'
Set the default base for numeric display. Supported choices for
BASE are decimal 8, 10, or 16. The base must itself be specified
either unambiguously or using the current input radix.

`show input-radix'
Display the current default base for numeric input.

`show output-radix'
Display the current default base for numeric display.

`set radix [BASE]'
`show radix'
These commands set and show the default base for both input and
output of numbers. `set radix' sets the radix of input and output
to the same base; without an argument, it resets the radix back to
its default value of 10.

File: gdb.info, Node: ABI, Next: Auto-loading, Prev: Numbers, Up: Controlling GDB

22.7 Configuring the Current ABI
================================

GDB can determine the "ABI" (Application Binary Interface) of your
application automatically. However, sometimes you need to override its
conclusions. Use these commands to manage GDB's view of the current
ABI.

One GDB configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation. GDB
will autodetect the "OS ABI" (Operating System ABI) in use, but you can
override its conclusion using the `set osabi' command. One example
where this is useful is in debugging of binaries which use an alternate
C library (e.g. UCLIBC for GNU/Linux) which does not have the same
identifying marks that the standard C library for your platform
provides.

When GDB is debugging the AArch64 architecture, it provides a
"Newlib" OS ABI. This is useful for handling `setjmp' and `longjmp'
when debugging binaries that use the NEWLIB C library. The "Newlib" OS
ABI can be selected by `set osabi Newlib'.

`show osabi'
Show the OS ABI currently in use.

`set osabi'
With no argument, show the list of registered available OS ABI's.

`set osabi ABI'
Set the current OS ABI to ABI.

Generally, the way that an argument of type `float' is passed to a
function depends on whether the function is prototyped. For a
prototyped (i.e. ANSI/ISO style) function, `float' arguments are passed
unchanged, according to the architecture's convention for `float'. For
unprototyped (i.e. K&R style) functions, `float' arguments are first
promoted to type `double' and then passed.

Unfortunately, some forms of debug information do not reliably
indicate whether a function is prototyped. If GDB calls a function
that is not marked as prototyped, it consults `set
coerce-float-to-double'.

`set coerce-float-to-double'
`set coerce-float-to-double on'
Arguments of type `float' will be promoted to `double' when passed
to an unprototyped function. This is the default setting.

`set coerce-float-to-double off'
Arguments of type `float' will be passed directly to unprototyped
functions.

`show coerce-float-to-double'
Show the current setting of promoting `float' to `double'.

GDB needs to know the ABI used for your program's C++ objects. The
correct C++ ABI depends on which C++ compiler was used to build your
application. GDB only fully supports programs with a single C++ ABI;
if your program contains code using multiple C++ ABI's or if GDB can
not identify your program's ABI correctly, you can tell GDB which ABI
to use. Currently supported ABI's include "gnu-v2", for `g++' versions
before 3.0, "gnu-v3", for `g++' versions 3.0 and later, and "hpaCC" for
the HP ANSI C++ compiler. Other C++ compilers may use the "gnu-v2" or
"gnu-v3" ABI's as well. The default setting is "auto".

`show cp-abi'
Show the C++ ABI currently in use.

`set cp-abi'
With no argument, show the list of supported C++ ABI's.

`set cp-abi ABI'
`set cp-abi auto'
Set the current C++ ABI to ABI, or return to automatic detection.

File: gdb.info, Node: Auto-loading, Next: Messages/Warnings, Prev: ABI, Up: Controlling GDB

22.8 Automatically loading associated files
===========================================

GDB sometimes reads files with commands and settings automatically,
without being explicitly told so by the user. We call this feature
"auto-loading". While auto-loading is useful for automatically adapting
GDB to the needs of your project, it can sometimes produce unexpected
results or introduce security risks (e.g., if the file comes from
untrusted sources).

There are various kinds of files GDB can automatically load. In
addition to these files, GDB supports auto-loading code written in
various extension languages. *Note Auto-loading extensions::.

Note that loading of these associated files (including the local
`.gdbinit' file) requires accordingly configured `auto-load safe-path'
(*note Auto-loading safe path::).

For these reasons, GDB includes commands and options to let you
control when to auto-load files and which files should be auto-loaded.

`set auto-load off'
Globally disable loading of all auto-loaded files. You may want
to use this command with the `-iex' option (*note Option
-init-eval-command::) such as:
$ gdb -iex "set auto-load off" untrusted-executable corefile

Be aware that system init file (*note System-wide configuration::)
and init files from your home directory (*note Home Directory Init
File::) still get read (as they come from generally trusted
directories). To prevent GDB from auto-loading even those init
files, use the `-nx' option (*note Mode Options::), in addition to
`set auto-load no'.

`show auto-load'
Show whether auto-loading of each specific `auto-load' file(s) is
enabled or disabled.

(gdb) show auto-load
gdb-scripts: Auto-loading of canned sequences of commands scripts is on.
libthread-db: Auto-loading of inferior specific libthread_db is on.
local-gdbinit: Auto-loading of .gdbinit script from current directory
is on.
python-scripts: Auto-loading of Python scripts is on.
safe-path: List of directories from which it is safe to auto-load files
is $debugdir:$datadir/auto-load.
scripts-directory: List of directories from which to load auto-loaded scripts
is $debugdir:$datadir/auto-load.

`info auto-load'
Print whether each specific `auto-load' file(s) have been
auto-loaded or not.

(gdb) info auto-load
gdb-scripts:
Loaded Script
Yes /home/user/gdb/gdb-gdb.gdb
libthread-db: No auto-loaded libthread-db.
local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been
loaded.
python-scripts:
Loaded Script
Yes /home/user/gdb/gdb-gdb.py

These are GDB control commands for the auto-loading:

*Note set auto-load off::. Disable auto-loading globally.
*Note show auto-load::. Show setting of all kinds of files.
*Note info auto-load::. Show state of all kinds of files.
*Note set auto-load gdb-scripts::. Control for GDB command scripts.
*Note show auto-load gdb-scripts::. Show setting of GDB command scripts.
*Note info auto-load gdb-scripts::. Show state of GDB command scripts.
*Note set auto-load Control for GDB Python scripts.
python-scripts::.
*Note show auto-load Show setting of GDB Python scripts.
python-scripts::.
*Note info auto-load Show state of GDB Python scripts.
python-scripts::.
*Note set auto-load guile-scripts::. Control for GDB Guile scripts.
*Note show auto-load Show setting of GDB Guile scripts.
guile-scripts::.
*Note info auto-load Show state of GDB Guile scripts.
guile-scripts::.
*Note set auto-load Control for GDB auto-loaded scripts
scripts-directory::. location.
*Note show auto-load Show GDB auto-loaded scripts
scripts-directory::. location.
*Note Add directory for auto-loaded
add-auto-load-scripts-directory::. scripts location list.
*Note set auto-load local-gdbinit::. Control for init file in the
current directory.
*Note show auto-load Show setting of init file in the
local-gdbinit::. current directory.
*Note info auto-load Show state of init file in the
local-gdbinit::. current directory.
*Note set auto-load libthread-db::. Control for thread debugging
library.
*Note show auto-load libthread-db::. Show setting of thread debugging
library.
*Note info auto-load libthread-db::. Show state of thread debugging
library.
*Note set auto-load safe-path::. Control directories trusted for
automatic loading.
*Note show auto-load safe-path::. Show directories trusted for
automatic loading.
*Note add-auto-load-safe-path::. Add directory trusted for automatic
loading.

* Menu:

* Init File in the Current Directory:: `set/show/info auto-load local-gdbinit'
* libthread_db.so.1 file:: `set/show/info auto-load libthread-db'

* Auto-loading safe path:: `set/show/info auto-load safe-path'
* Auto-loading verbose mode:: `set/show debug auto-load'

File: gdb.info, Node: Init File in the Current Directory, Next: libthread_db.so.1 file, Up: Auto-loading

22.8.1 Automatically loading init file in the current directory
---------------------------------------------------------------

By default, GDB reads and executes the canned sequences of commands
from init file (if any) in the current working directory, see *Note
Init File in the Current Directory during Startup::.

Note that loading of this local `.gdbinit' file also requires
accordingly configured `auto-load safe-path' (*note Auto-loading safe
path::).

`set auto-load local-gdbinit [on|off]'
Enable or disable the auto-loading of canned sequences of commands
(*note Sequences::) found in init file in the current directory.

`show auto-load local-gdbinit'
Show whether auto-loading of canned sequences of commands from
init file in the current directory is enabled or disabled.

`info auto-load local-gdbinit'
Print whether canned sequences of commands from init file in the
current directory have been auto-loaded.

File: gdb.info, Node: libthread_db.so.1 file, Next: Auto-loading safe path, Prev: Init File in the Current Directory, Up: Auto-loading

22.8.2 Automatically loading thread debugging library
-----------------------------------------------------

This feature is currently present only on GNU/Linux native hosts.

GDB reads in some cases thread debugging library from places specific
to the inferior (*note set libthread-db-search-path::).

The special `libthread-db-search-path' entry `$sdir' is processed
without checking this `set auto-load libthread-db' switch as system
libraries have to be trusted in general. In all other cases of
`libthread-db-search-path' entries GDB checks first if `set auto-load
libthread-db' is enabled before trying to open such thread debugging
library.

Note that loading of this debugging library also requires
accordingly configured `auto-load safe-path' (*note Auto-loading safe
path::).

`set auto-load libthread-db [on|off]'
Enable or disable the auto-loading of inferior specific thread
debugging library.

`show auto-load libthread-db'
Show whether auto-loading of inferior specific thread debugging
library is enabled or disabled.

`info auto-load libthread-db'
Print the list of all loaded inferior specific thread debugging
libraries and for each such library print list of inferior PIDs
using it.

File: gdb.info, Node: Auto-loading safe path, Next: Auto-loading verbose mode, Prev: libthread_db.so.1 file, Up: Auto-loading

22.8.3 Security restriction for auto-loading
--------------------------------------------

As the files of inferior can come from untrusted source (such as
submitted by an application user) GDB does not always load any files
automatically. GDB provides the `set auto-load safe-path' setting to
list directories trusted for loading files not explicitly requested by
user. Each directory can also be a shell wildcard pattern.

If the path is not set properly you will see a warning and the file
will not get loaded:

$ ./gdb -q ./gdb
Reading symbols from /home/user/gdb/gdb...
warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been
declined by your `auto-load safe-path' set
to "$debugdir:$datadir/auto-load".
warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been
declined by your `auto-load safe-path' set
to "$debugdir:$datadir/auto-load".

To instruct GDB to go ahead and use the init files anyway, invoke GDB
like this:

$ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb

The list of trusted directories is controlled by the following
commands:

`set auto-load safe-path [DIRECTORIES]'
Set the list of directories (and their subdirectories) trusted for
automatic loading and execution of scripts. You can also enter a
specific trusted file. Each directory can also be a shell
wildcard pattern; wildcards do not match directory separator - see
`FNM_PATHNAME' for system function `fnmatch' (*note fnmatch:
(libc)Wildcard Matching.). If you omit DIRECTORIES, `auto-load
safe-path' will be reset to its default value as specified during
GDB compilation.

The list of directories uses path separator (`:' on GNU and Unix
systems, `;' on MS-Windows and MS-DOS) to separate directories,
similarly to the `PATH' environment variable.

`show auto-load safe-path'
Show the list of directories trusted for automatic loading and
execution of scripts.

`add-auto-load-safe-path'
Add an entry (or list of entries) to the list of directories
trusted for automatic loading and execution of scripts. Multiple
entries may be delimited by the host platform path separator in
use.

This variable defaults to what `--with-auto-load-dir' has been
configured to (*note with-auto-load-dir::). `$debugdir' and `$datadir'
substitution applies the same as for *Note set auto-load
scripts-directory::. The default `set auto-load safe-path' value can
be also overridden by GDB configuration option
`--with-auto-load-safe-path'.

Setting this variable to `/' disables this security protection,
corresponding GDB configuration option is
`--without-auto-load-safe-path'. This variable is supposed to be set
to the system directories writable by the system superuser only. Users
can add their source directories in init files in their home
directories (*note Home Directory Init File::). See also deprecated
init file in the current directory (*note Init File in the Current
Directory during Startup::).

To force GDB to load the files it declined to load in the previous
example, you could use one of the following ways:

`~/.gdbinit': `add-auto-load-safe-path ~/src/gdb'
Specify this trusted directory (or a file) as additional component
of the list. You have to specify also any existing directories
displayed by by `show auto-load safe-path' (such as `/usr:/bin' in
this example).

`gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" ...'
Specify this directory as in the previous case but just for a
single GDB session.

`gdb -iex "set auto-load safe-path /" ...'
Disable auto-loading safety for a single GDB session. This
assumes all the files you debug during this GDB session will come
from trusted sources.

`./configure --without-auto-load-safe-path'
During compilation of GDB you may disable any auto-loading safety.
This assumes all the files you will ever debug with this GDB come
from trusted sources.

On the other hand you can also explicitly forbid automatic files
loading which also suppresses any such warning messages:

`gdb -iex "set auto-load no" ...'
You can use GDB command-line option for a single GDB session.

`~/.gdbinit': `set auto-load no'
Disable auto-loading globally for the user (*note Home Directory
Init File::). While it is improbable, you could also use system
init file instead (*note System-wide configuration::).

This setting applies to the file names as entered by user. If no
entry matches GDB tries as a last resort to also resolve all the file
names into their canonical form (typically resolving symbolic links)
and compare the entries again. GDB already canonicalizes most of the
filenames on its own before starting the comparison so a canonical form
of directories is recommended to be entered.

File: gdb.info, Node: Auto-loading verbose mode, Prev: Auto-loading safe path, Up: Auto-loading

22.8.4 Displaying files tried for auto-load
-------------------------------------------

For better visibility of all the file locations where you can place
scripts to be auto-loaded with inferior -- or to protect yourself
against accidental execution of untrusted scripts -- GDB provides a
feature for printing all the files attempted to be loaded. Both
existing and non-existing files may be printed.

For example the list of directories from which it is safe to
auto-load files (*note Auto-loading safe path::) applies also to
canonicalized filenames which may not be too obvious while setting it
up.

(gdb) set debug auto-load on
(gdb) file ~/src/t/true
auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb"
for objfile "/tmp/true".
auto-load: Updating directories of "/usr:/opt".
auto-load: Using directory "/usr".
auto-load: Using directory "/opt".
warning: File "/tmp/true-gdb.gdb" auto-loading has been declined
by your `auto-load safe-path' set to "/usr:/opt".

`set debug auto-load [on|off]'
Set whether to print the filenames attempted to be auto-loaded.

`show debug auto-load'
Show whether printing of the filenames attempted to be auto-loaded
is turned on or off.

File: gdb.info, Node: Messages/Warnings, Next: Debugging Output, Prev: Auto-loading, Up: Controlling GDB

22.9 Optional Warnings and Messages
===================================

By default, GDB is silent about its inner workings. If you are running
on a slow machine, you may want to use the `set verbose' command. This
makes GDB tell you when it does a lengthy internal operation, so you
will not think it has crashed.

Currently, the messages controlled by `set verbose' are those which
announce that the symbol table for a source file is being read; see
`symbol-file' in *Note Commands to Specify Files: Files.

`set verbose on'
Enables GDB output of certain informational messages.

`set verbose off'
Disables GDB output of certain informational messages.

`show verbose'
Displays whether `set verbose' is on or off.

By default, if GDB encounters bugs in the symbol table of an object
file, it is silent; but if you are debugging a compiler, you may find
this information useful (*note Errors Reading Symbol Files: Symbol
Errors.).

`set complaints LIMIT'
Permits GDB to output LIMIT complaints about each type of unusual
symbols before becoming silent about the problem. Set LIMIT to
zero to suppress all complaints; set it to a large number to
prevent complaints from being suppressed.

`show complaints'
Displays how many symbol complaints GDB is permitted to produce.

By default, GDB is cautious, and asks what sometimes seems to be a
lot of stupid questions to confirm certain commands. For example, if
you try to run a program which is already running:

(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)

If you are willing to unflinchingly face the consequences of your own
commands, you can disable this "feature":

`set confirm off'
Disables confirmation requests. Note that running GDB with the
`--batch' option (*note -batch: Mode Options.) also automatically
disables confirmation requests.

`set confirm on'
Enables confirmation requests (the default).

`show confirm'
Displays state of confirmation requests.

If you need to debug user-defined commands or sourced files you may
find it useful to enable "command tracing". In this mode each command
will be printed as it is executed, prefixed with one or more `+'
symbols, the quantity denoting the call depth of each command.

`set trace-commands on'
Enable command tracing.

`set trace-commands off'
Disable command tracing.

`show trace-commands'
Display the current state of command tracing.

File: gdb.info, Node: Debugging Output, Next: Other Misc Settings, Prev: Messages/Warnings, Up: Controlling GDB

22.10 Optional Messages about Internal Happenings
=================================================

GDB has commands that enable optional debugging messages from various
GDB subsystems; normally these commands are of interest to GDB
maintainers, or when reporting a bug. This section documents those
commands.

`set exec-done-display'
Turns on or off the notification of asynchronous commands'
completion. When on, GDB will print a message when an
asynchronous command finishes its execution. The default is off.

`show exec-done-display'
Displays the current setting of asynchronous command completion
notification.

`set debug aarch64'
Turns on or off display of debugging messages related to ARM
AArch64. The default is off.

`show debug aarch64'
Displays the current state of displaying debugging messages
related to ARM AArch64.

`set debug arch'
Turns on or off display of gdbarch debugging info. The default is
off

`show debug arch'
Displays the current state of displaying gdbarch debugging info.

`set debug aix-thread'
Display debugging messages about inner workings of the AIX thread
module.

`show debug aix-thread'
Show the current state of AIX thread debugging info display.

`set debug amd-dbgapi-lib'
`show debug amd-dbgapi-lib'
The `set debug amd-dbgapi-lib log-level LEVEL' command can be used
to enable diagnostic messages from the `amd-dbgapi' library, where
LEVEL can be:

`off'
no logging is enabled

`error'
fatal errors are reported

`warning'
fatal errors and warnings are reported

`info'
fatal errors, warnings, and info messages are reported

`verbose'
all messages are reported

The `show debug amd-dbgapi-lib log-level' command displays the
current amd-dbgapi library log level.

`set debug amd-dbgapi'
`show debug amd-dbgapi'
The `set debug amd-dbgapi' command can be used to enable
diagnostic messages in the `amd-dbgapi' target. The `show debug
amd-dbgapi' command displays the current setting. *Note set debug
amd-dbgapi::.

`set debug check-physname'
Check the results of the "physname" computation. When reading
DWARF debugging information for C++, GDB attempts to compute each
entity's name. GDB can do this computation in two different ways,
depending on exactly what information is present. When enabled,
this setting causes GDB to compute the names both ways and display
any discrepancies.

`show debug check-physname'
Show the current state of "physname" checking.

`set debug coff-pe-read'
Control display of debugging messages related to reading of COFF/PE
exported symbols. The default is off.

`show debug coff-pe-read'
Displays the current state of displaying debugging messages
related to reading of COFF/PE exported symbols.

`set debug dwarf-die'
Dump DWARF DIEs after they are read in. The value is the number
of nesting levels to print. A value of zero turns off the display.

`show debug dwarf-die'
Show the current state of DWARF DIE debugging.

`set debug dwarf-line'
Turns on or off display of debugging messages related to reading
DWARF line tables. The default is 0 (off). A value of 1 provides
basic information. A value greater than 1 provides more verbose
information.

`show debug dwarf-line'
Show the current state of DWARF line table debugging.

`set debug dwarf-read'
Turns on or off display of debugging messages related to reading
DWARF debug info. The default is 0 (off). A value of 1 provides
basic information. A value greater than 1 provides more verbose
information.

`show debug dwarf-read'
Show the current state of DWARF reader debugging.

`set debug displaced'
Turns on or off display of GDB debugging info for the displaced
stepping support. The default is off.

`show debug displaced'
Displays the current state of displaying GDB debugging info
related to displaced stepping.

`set debug event'
Turns on or off display of GDB event debugging info. The default
is off.

`show debug event'
Displays the current state of displaying GDB event debugging info.

`set debug event-loop'
Controls output of debugging info about the event loop. The
possible values are `off', `all' (shows all debugging info) and
`all-except-ui' (shows all debugging info except those about
UI-related events).

`show debug event-loop'
Shows the current state of displaying debugging info about the
event loop.

`set debug expression'
Turns on or off display of debugging info about GDB expression
parsing. The default is off.

`show debug expression'
Displays the current state of displaying debugging info about GDB
expression parsing.

`set debug fbsd-lwp'
Turns on or off debugging messages from the FreeBSD LWP debug
support.

`show debug fbsd-lwp'
Show the current state of FreeBSD LWP debugging messages.

`set debug fbsd-nat'
Turns on or off debugging messages from the FreeBSD native target.

`show debug fbsd-nat'
Show the current state of FreeBSD native target debugging messages.

`set debug fortran-array-slicing'
Turns on or off display of GDB Fortran array slicing debugging
info. The default is off.

`show debug fortran-array-slicing'
Displays the current state of displaying GDB Fortran array slicing
debugging info.

`set debug frame'
Turns on or off display of GDB frame debugging info. The default
is off.

`show debug frame'
Displays the current state of displaying GDB frame debugging info.

`set debug gnu-nat'
Turn on or off debugging messages from the GNU/Hurd debug support.

`show debug gnu-nat'
Show the current state of GNU/Hurd debugging messages.

`set debug infrun'
Turns on or off display of GDB debugging info for running the
inferior. The default is off. `infrun.c' contains GDB's runtime
state machine used for implementing operations such as
single-stepping the inferior.

`show debug infrun'
Displays the current state of GDB inferior debugging.

`set debug infcall'
Turns on or off display of debugging info related to inferior
function calls made by GDB.

`show debug infcall'
Displays the current state of GDB inferior function call debugging.

`set debug jit'
Turn on or off debugging messages from JIT debug support.

`show debug jit'
Displays the current state of GDB JIT debugging.

`set debug linux-nat [on|off]'
Turn on or off debugging messages from the Linux native target
debug support.

`show debug linux-nat'
Show the current state of Linux native target debugging messages.

`set debug linux-namespaces'
Turn on or off debugging messages from the Linux namespaces debug
support.

`show debug linux-namespaces'
Show the current state of Linux namespaces debugging messages.

`set debug mach-o'
Control display of debugging messages related to Mach-O symbols
processing. The default is off.

`show debug mach-o'
Displays the current state of displaying debugging messages
related to reading of COFF/PE exported symbols.

`set debug notification'
Turn on or off debugging messages about remote async notification.
The default is off.

`show debug notification'
Displays the current state of remote async notification debugging
messages.

`set debug observer'
Turns on or off display of GDB observer debugging. This includes
info such as the notification of observable events.

`show debug observer'
Displays the current state of observer debugging.

`set debug overload'
Turns on or off display of GDB C++ overload debugging info. This
includes info such as ranking of functions, etc. The default is
off.

`show debug overload'
Displays the current state of displaying GDB C++ overload
debugging info.

`set debug parser'
Turns on or off the display of expression parser debugging output.
Internally, this sets the `yydebug' variable in the expression
parser. *Note Tracing Your Parser: (bison)Tracing, for details.
The default is off.

`show debug parser'
Show the current state of expression parser debugging.

`set debug remote'
Turns on or off display of reports on all packets sent back and
forth across the serial line to the remote machine. The info is
printed on the GDB standard output stream. The default is off.

`show debug remote'
Displays the state of display of remote packets.

`set debug remote-packet-max-chars'
Sets the maximum number of characters to display for each remote
packet when `set debug remote' is on. This is useful to prevent
GDB from displaying lengthy remote packets and polluting the
console.

The default value is `512', which means GDB will truncate each
remote packet after 512 bytes.

Setting this option to `unlimited' will disable truncation and
will output the full length of the remote packets.

`show debug remote-packet-max-chars'
Displays the number of bytes to output for remote packet debugging.

`set debug separate-debug-file'
Turns on or off display of debug output about separate debug file
search.

`show debug separate-debug-file'
Displays the state of separate debug file search debug output.

`set debug serial'
Turns on or off display of GDB serial debugging info. The default
is off.

`show debug serial'
Displays the current state of displaying GDB serial debugging info.

`set debug solib'
Turns on or off display of debugging messages related to shared
libraries. The default is off.

`show debug solib'
Show the current state of solib debugging messages.

`set debug symbol-lookup'
Turns on or off display of debugging messages related to symbol
lookup. The default is 0 (off). A value of 1 provides basic
information. A value greater than 1 provides more verbose
information.

`show debug symbol-lookup'
Show the current state of symbol lookup debugging messages.

`set debug symfile'
Turns on or off display of debugging messages related to symbol
file functions. The default is off. *Note Files::.

`show debug symfile'
Show the current state of symbol file debugging messages.

`set debug symtab-create'
Turns on or off display of debugging messages related to symbol
table creation. The default is 0 (off). A value of 1 provides
basic information. A value greater than 1 provides more verbose
information.

`show debug symtab-create'
Show the current state of symbol table creation debugging.

`set debug target'
Turns on or off display of GDB target debugging info. This info
includes what is going on at the target level of GDB, as it
happens. The default is 0. Set it to 1 to track events, and to 2
to also track the value of large memory transfers.

`show debug target'
Displays the current state of displaying GDB target debugging info.

`set debug timestamp'
Turns on or off display of timestamps with GDB debugging info.
When enabled, seconds and microseconds are displayed before each
debugging message.

`show debug timestamp'
Displays the current state of displaying timestamps with GDB
debugging info.

`set debug varobj'
Turns on or off display of GDB variable object debugging info. The
default is off.

`show debug varobj'
Displays the current state of displaying GDB variable object
debugging info.

`set debug xml'
Turn on or off debugging messages for built-in XML parsers.

`show debug xml'
Displays the current state of XML debugging messages.

`set debug breakpoints'
Turns on or off display of GDB debugging info for breakpoint
insertion and removal. The default is off.

`show debug breakpoints'
Displays the current state of displaying GDB debugging info for
breakpoint insertion and removal.

File: gdb.info, Node: Other Misc Settings, Prev: Debugging Output, Up: Controlling GDB

22.11 Other Miscellaneous Settings
==================================

`set interactive-mode'
If `on', forces GDB to assume that GDB was started in a terminal.
In practice, this means that GDB should wait for the user to
answer queries generated by commands entered at the command
prompt. If `off', forces GDB to operate in the opposite mode, and
it uses the default answers to all queries. If `auto' (the
default), GDB tries to determine whether its standard input is a
terminal, and works in interactive-mode if it is,
non-interactively otherwise.

In the vast majority of cases, the debugger should be able to guess
correctly which mode should be used. But this setting can be
useful in certain specific cases, such as running a MinGW GDB
inside a cygwin window.

`show interactive-mode'
Displays whether the debugger is operating in interactive mode or
not.

`set suppress-cli-notifications'
If `on', command-line-interface (CLI) notifications that are
printed by GDB are suppressed. If `off', the notifications are
printed as usual. The default value is `off'. CLI notifications
occur when you change the selected context or when the program
being debugged stops, as detailed below.

_User-selected context changes:_
When you change the selected context (i.e. the current
inferior, thread and/or the frame), GDB prints information
about the new context. For example, the default behavior is
below:

(gdb) inferior 1
[Switching to inferior 1 [process 634] (/tmp/test)]
[Switching to thread 1 (process 634)]
#0 main () at test.c:3
3 return 0;
(gdb)

When the notifications are suppressed, the new context is not
printed:

(gdb) set suppress-cli-notifications on
(gdb) inferior 1
(gdb)

_The program being debugged stops:_
When the program you are debugging stops (e.g. because of
hitting a breakpoint, completing source-stepping, an
interrupt, etc.), GDB prints information about the stop
event. For example, below is a breakpoint hit:

(gdb) break test.c:3
Breakpoint 2 at 0x555555555155: file test.c, line 3.
(gdb) continue
Continuing.

Breakpoint 2, main () at test.c:3
3 return 0;
(gdb)

When the notifications are suppressed, the output becomes:

(gdb) break test.c:3
Breakpoint 2 at 0x555555555155: file test.c, line 3.
(gdb) set suppress-cli-notifications on
(gdb) continue
Continuing.
(gdb)

Suppressing CLI notifications may be useful in scripts to
obtain a reduced output from a list of commands.

`show suppress-cli-notifications'
Displays whether printing CLI notifications is suppressed or not.

File: gdb.info, Node: Extending GDB, Next: Interpreters, Prev: Controlling GDB, Up: Top

23 Extending GDB
****************

GDB provides several mechanisms for extension. GDB also provides the
ability to automatically load extensions when it reads a file for
debugging. This allows the user to automatically customize GDB for the
program being debugged.

To facilitate the use of extension languages, GDB is capable of
evaluating the contents of a file. When doing so, GDB can recognize
which extension language is being used by looking at the filename
extension. Files with an unrecognized filename extension are always
treated as a GDB Command Files. *Note Command files: Command Files.

You can control how GDB evaluates these files with the following
setting:

`set script-extension off'
All scripts are always evaluated as GDB Command Files.

`set script-extension soft'
The debugger determines the scripting language based on filename
extension. If this scripting language is supported, GDB evaluates
the script using that language. Otherwise, it evaluates the file
as a GDB Command File.

`set script-extension strict'
The debugger determines the scripting language based on filename
extension, and evaluates the script using that language. If the
language is not supported, then the evaluation fails.

`show script-extension'
Display the current value of the `script-extension' option.

* Menu:

* Sequences:: Canned Sequences of GDB Commands
* Aliases:: Command Aliases
* Python:: Extending GDB using Python
* Guile:: Extending GDB using Guile
* Auto-loading extensions:: Automatically loading extensions
* Multiple Extension Languages:: Working with multiple extension languages

File: gdb.info, Node: Sequences, Next: Aliases, Up: Extending GDB

23.1 Canned Sequences of Commands
=================================

Aside from breakpoint commands (*note Breakpoint Command Lists: Break
Commands.), GDB provides two ways to store sequences of commands for
execution as a unit: user-defined commands and command files.

* Menu:

* Define:: How to define your own commands
* Hooks:: Hooks for user-defined commands
* Command Files:: How to write scripts of commands to be stored in a file
* Output:: Commands for controlled output
* Auto-loading sequences:: Controlling auto-loaded command files

File: gdb.info, Node: Define, Next: Hooks, Up: Sequences

23.1.1 User-defined Commands
----------------------------

A "user-defined command" is a sequence of GDB commands to which you
assign a new name as a command. This is done with the `define'
command. User commands may accept an unlimited number of arguments
separated by whitespace. Arguments are accessed within the user command
via `$arg0...$argN'. A trivial example:

define adder
print $arg0 + $arg1 + $arg2
end

To execute the command use:

adder 1 2 3

This defines the command `adder', which prints the sum of its three
arguments. Note the arguments are text substitutions, so they may
reference variables, use complex expressions, or even perform inferior
functions calls.

In addition, `$argc' may be used to find out how many arguments have
been passed.

define adder
if $argc == 2
print $arg0 + $arg1
end
if $argc == 3
print $arg0 + $arg1 + $arg2
end
end

Combining with the `eval' command (*note eval::) makes it easier to
process a variable number of arguments:

define adder
set $i = 0
set $sum = 0
while $i < $argc
eval "set $sum = $sum + $arg%d", $i
set $i = $i + 1
end
print $sum
end

`define COMMANDNAME'
Define a command named COMMANDNAME. If there is already a command
by that name, you are asked to confirm that you want to redefine
it. The argument COMMANDNAME may be a bare command name
consisting of letters, numbers, dashes, dots, and underscores. It
may also start with any predefined or user-defined prefix command.
For example, `define target my-target' creates a user-defined
`target my-target' command.

The definition of the command is made up of other GDB command
lines, which are given following the `define' command. The end of
these commands is marked by a line containing `end'.

`document COMMANDNAME'
Document the user-defined command COMMANDNAME, so that it can be
accessed by `help'. The command COMMANDNAME must already be
defined. This command reads lines of documentation just as
`define' reads the lines of the command definition, ending with
`end'. After the `document' command is finished, `help' on command
COMMANDNAME displays the documentation you have written.

You may use the `document' command again to change the
documentation of a command. Redefining the command with `define'
does not change the documentation.

It is also possible to document user-defined aliases. The alias
documentation will then be used by the `help' and `apropos'
commands instead of the documentation of the aliased command.
Documenting a user-defined alias is particularly useful when
defining an alias as a set of nested `with' commands (*note
Command aliases default args::).

`define-prefix COMMANDNAME'
Define or mark the command COMMANDNAME as a user-defined prefix
command. Once marked, COMMANDNAME can be used as prefix command
by the `define' command. Note that `define-prefix' can be used
with a not yet defined COMMANDNAME. In such a case, COMMANDNAME
is defined as an empty user-defined command. In case you redefine
a command that was marked as a user-defined prefix command, the
subcommands of the redefined command are kept (and GDB indicates
so to the user).

Example:
(gdb) define-prefix abc
(gdb) define-prefix abc def
(gdb) define abc def
Type commands for definition of "abc def".
End with a line saying just "end".
>echo command initial def\n
>end
(gdb) define abc def ghi
Type commands for definition of "abc def ghi".
End with a line saying just "end".
>echo command ghi\n
>end
(gdb) define abc def
Keeping subcommands of prefix command "def".
Redefine command "def"? (y or n) y
Type commands for definition of "abc def".
End with a line saying just "end".
>echo command def\n
>end
(gdb) abc def ghi
command ghi
(gdb) abc def
command def
(gdb)

`dont-repeat'
Used inside a user-defined command, this tells GDB that this
command should not be repeated when the user hits <RET> (*note
repeat last command: Command Syntax.).

`help user-defined'
List all user-defined commands and all python commands defined in
class COMMAND_USER. The first line of the documentation or
docstring is included (if any).

`show user'
`show user COMMANDNAME'
Display the GDB commands used to define COMMANDNAME (but not its
documentation). If no COMMANDNAME is given, display the
definitions for all user-defined commands. This does not work for
user-defined python commands.

`show max-user-call-depth'
`set max-user-call-depth'
The value of `max-user-call-depth' controls how many recursion
levels are allowed in user-defined commands before GDB suspects an
infinite recursion and aborts the command. This does not apply to
user-defined python commands.

In addition to the above commands, user-defined commands frequently
use control flow commands, described in *Note Command Files::.

When user-defined commands are executed, the commands of the
definition are not printed. An error in any command stops execution of
the user-defined command.

If used interactively, commands that would ask for confirmation
proceed without asking when used inside a user-defined command. Many
GDB commands that normally print messages to say what they are doing
omit the messages when used in a user-defined command.

File: gdb.info, Node: Hooks, Next: Command Files, Prev: Define, Up: Sequences

23.1.2 User-defined Command Hooks
---------------------------------

You may define "hooks", which are a special kind of user-defined
command. Whenever you run the command `foo', if the user-defined
command `hook-foo' exists, it is executed (with no arguments) before
that command.

A hook may also be defined which is run after the command you
executed. Whenever you run the command `foo', if the user-defined
command `hookpost-foo' exists, it is executed (with no arguments) after
that command. Post-execution hooks may exist simultaneously with
pre-execution hooks, for the same command.

It is valid for a hook to call the command which it hooks. If this
occurs, the hook is not re-executed, thereby avoiding infinite
recursion.

In addition, a pseudo-command, `stop' exists. Defining
(`hook-stop') makes the associated commands execute every time
execution stops in your program: before breakpoint commands are run,
displays are printed, or the stack frame is printed.

For example, to ignore `SIGALRM' signals while single-stepping, but
treat them normally during normal execution, you could define:

define hook-stop
handle SIGALRM nopass
end

define hook-run
handle SIGALRM pass
end

define hook-continue
handle SIGALRM pass
end

As a further example, to hook at the beginning and end of the `echo'
command, and to add extra text to the beginning and end of the message,
you could define:

define hook-echo
echo <<<---
end

define hookpost-echo
echo --->>>\n
end

(gdb) echo Hello World
<<<---Hello World--->>>
(gdb)

You can define a hook for any single-word command in GDB, but not
for command aliases; you should define a hook for the basic command
name, e.g. `backtrace' rather than `bt'. You can hook a multi-word
command by adding `hook-' or `hookpost-' to the last word of the
command, e.g. `define target hook-remote' to add a hook to `target
remote'.

If an error occurs during the execution of your hook, execution of
GDB commands stops and GDB issues a prompt (before the command that you
actually typed had a chance to run).

If you try to define a hook which does not match any known command,
you get a warning from the `define' command.

File: gdb.info, Node: Command Files, Next: Output, Prev: Hooks, Up: Sequences

23.1.3 Command Files
--------------------

A command file for GDB is a text file made of lines that are GDB
commands. Comments (lines starting with `#') may also be included. An
empty line in a command file does nothing; it does not mean to repeat
the last command, as it would from the terminal.

You can request the execution of a command file with the `source'
command. Note that the `source' command is also used to evaluate
scripts that are not Command Files. The exact behavior can be
configured using the `script-extension' setting. *Note Extending GDB:
Extending GDB.

`source [-s] [-v] FILENAME'
Execute the command file FILENAME.

The lines in a command file are generally executed sequentially,
unless the order of execution is changed by one of the _flow-control
commands_ described below. The commands are not printed as they are
executed. An error in any command terminates execution of the command
file and control is returned to the console.

GDB first searches for FILENAME in the current directory. If the
file is not found there, and FILENAME does not specify a directory,
then GDB also looks for the file on the source search path (specified
with the `directory' command); except that `$cdir' is not searched
because the compilation directory is not relevant to scripts.

If `-s' is specified, then GDB searches for FILENAME on the search
path even if FILENAME specifies a directory. The search is done by
appending FILENAME to each element of the search path. So, for
example, if FILENAME is `mylib/myscript' and the search path contains
`/home/user' then GDB will look for the script
`/home/user/mylib/myscript'. The search is also done if FILENAME is an
absolute path. For example, if FILENAME is `/tmp/myscript' and the
search path contains `/home/user' then GDB will look for the script
`/home/user/tmp/myscript'. For DOS-like systems, if FILENAME contains
a drive specification, it is stripped before concatenation. For
example, if FILENAME is `d:myscript' and the search path contains
`c:/tmp' then GDB will look for the script `c:/tmp/myscript'.

If `-v', for verbose mode, is given then GDB displays each command
as it is executed. The option must be given before FILENAME, and is
interpreted as part of the filename anywhere else.

Commands that would ask for confirmation if used interactively
proceed without asking when used in a command file. Many GDB commands
that normally print messages to say what they are doing omit the
messages when called from command files.

GDB also accepts command input from standard input. In this mode,
normal output goes to standard output and error output goes to standard
error. Errors in a command file supplied on standard input do not
terminate execution of the command file--execution continues with the
next command.

gdb < cmds > log 2>&1

(The syntax above will vary depending on the shell used.) This
example will execute commands from the file `cmds'. All output and
errors would be directed to `log'.

Since commands stored on command files tend to be more general than
commands typed interactively, they frequently need to deal with
complicated situations, such as different or unexpected values of
variables and symbols, changes in how the program being debugged is
built, etc. GDB provides a set of flow-control commands to deal with
these complexities. Using these commands, you can write complex
scripts that loop over data structures, execute commands conditionally,
etc.

`if'
`else'
This command allows to include in your script conditionally
executed commands. The `if' command takes a single argument, which
is an expression to evaluate. It is followed by a series of
commands that are executed only if the expression is true (its
value is nonzero). There can then optionally be an `else' line,
followed by a series of commands that are only executed if the
expression was false. The end of the list is marked by a line
containing `end'.

`while'
This command allows to write loops. Its syntax is similar to
`if': the command takes a single argument, which is an expression
to evaluate, and must be followed by the commands to execute, one
per line, terminated by an `end'. These commands are called the
"body" of the loop. The commands in the body of `while' are
executed repeatedly as long as the expression evaluates to true.

`loop_break'
This command exits the `while' loop in whose body it is included.
Execution of the script continues after that `while's `end' line.

`loop_continue'
This command skips the execution of the rest of the body of
commands in the `while' loop in whose body it is included.
Execution branches to the beginning of the `while' loop, where it
evaluates the controlling expression.

`end'
Terminate the block of commands that are the body of `if', `else',
or `while' flow-control commands.

File: gdb.info, Node: Output, Next: Auto-loading sequences, Prev: Command Files, Up: Sequences

23.1.4 Commands for Controlled Output
-------------------------------------

During the execution of a command file or a user-defined command, normal
GDB output is suppressed; the only output that appears is what is
explicitly printed by the commands in the definition. This section
describes three commands useful for generating exactly the output you
want.

`echo TEXT'
Print TEXT. Nonprinting characters can be included in TEXT using
C escape sequences, such as `\n' to print a newline. *No newline
is printed unless you specify one.* In addition to the standard C
escape sequences, a backslash followed by a space stands for a
space. This is useful for displaying a string with spaces at the
beginning or the end, since leading and trailing spaces are
otherwise trimmed from all arguments. To print ` and foo = ', use
the command `echo \ and foo = \ '.

A backslash at the end of TEXT can be used, as in C, to continue
the command onto subsequent lines. For example,

echo This is some text\n\
which is continued\n\
onto several lines.\n

produces the same output as

echo This is some text\n
echo which is continued\n
echo onto several lines.\n

`output EXPRESSION'
Print the value of EXPRESSION and nothing but that value: no
newlines, no `$NN = '. The value is not entered in the value
history either. *Note Expressions: Expressions, for more
information on expressions.

`output/FMT EXPRESSION'
Print the value of EXPRESSION in format FMT. You can use the same
formats as for `print'. *Note Output Formats: Output Formats, for
more information.

`printf TEMPLATE, EXPRESSIONS...'
Print the values of one or more EXPRESSIONS under the control of
the string TEMPLATE. To print several values, make EXPRESSIONS be
a comma-separated list of individual expressions, which may be
either numbers or pointers. Their values are printed as specified
by TEMPLATE, exactly as a C program would do by executing the code
below:

printf (TEMPLATE, EXPRESSIONS...);

As in `C' `printf', ordinary characters in TEMPLATE are printed
verbatim, while "conversion specification" introduced by the `%'
character cause subsequent EXPRESSIONS to be evaluated, their
values converted and formatted according to type and style
information encoded in the conversion specifications, and then
printed.

For example, you can print two values in hex like this:

printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo

`printf' supports all the standard `C' conversion specifications,
including the flags and modifiers between the `%' character and
the conversion letter, with the following exceptions:

* The argument-ordering modifiers, such as `2$', are not
supported.

* The modifier `*' is not supported for specifying precision or
width.

* The `'' flag (for separation of digits into groups according
to `LC_NUMERIC'') is not supported.

* The type modifiers `hh', `j', `t', and `z' are not supported.

* The conversion letter `n' (as in `%n') is not supported.

* The conversion letters `a' and `A' are not supported.

Note that the `ll' type modifier is supported only if the
underlying `C' implementation used to build GDB supports the `long
long int' type, and the `L' type modifier is supported only if
`long double' type is available.

As in `C', `printf' supports simple backslash-escape sequences,
such as `\n', `\t', `\\', `\"', `\a', and `\f', that consist of
backslash followed by a single character. Octal and hexadecimal
escape sequences are not supported.

Additionally, `printf' supports conversion specifications for DFP
("Decimal Floating Point") types using the following length
modifiers together with a floating point specifier. letters:

* `H' for printing `Decimal32' types.

* `D' for printing `Decimal64' types.

* `DD' for printing `Decimal128' types.

If the underlying `C' implementation used to build GDB has support
for the three length modifiers for DFP types, other modifiers such
as width and precision will also be available for GDB to use.

In case there is no such `C' support, no additional modifiers will
be available and the value will be printed in the standard way.

Here's an example of printing DFP types using the above conversion
letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl

Additionally, `printf' supports a special `%V' output format.
This format prints the string representation of an expression just
as GDB would produce with the standard `print' command (*note
Examining Data: Data.):

(gdb) print array
$1 = {0, 1, 2, 3, 4, 5}
(gdb) printf "Array is: %V\n", array
Array is: {0, 1, 2, 3, 4, 5}

It is possible to include print options with the `%V' format by
placing them in `[...]' immediately after the `%V', like this:

(gdb) printf "Array is: %V[-array-indexes on]\n", array
Array is: {[0] = 0, [1] = 1, [2] = 2, [3] = 3, [4] = 4, [5] = 5}

If you need to print a literal `[' directly after a `%V', then
just include an empty print options list:

(gdb) printf "Array is: %V[][Hello]\n", array
Array is: {0, 1, 2, 3, 4, 5}[Hello]

`eval TEMPLATE, EXPRESSIONS...'
Convert the values of one or more EXPRESSIONS under the control of
the string TEMPLATE to a command line, and call it.

File: gdb.info, Node: Auto-loading sequences, Prev: Output, Up: Sequences

23.1.5 Controlling auto-loading native GDB scripts
--------------------------------------------------

When a new object file is read (for example, due to the `file' command,
or because the inferior has loaded a shared library), GDB will look for
the command file `OBJFILE-gdb.gdb'. *Note Auto-loading extensions::.

Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.

`set auto-load gdb-scripts [on|off]'
Enable or disable the auto-loading of canned sequences of commands
scripts.

`show auto-load gdb-scripts'
Show whether auto-loading of canned sequences of commands scripts
is enabled or disabled.

`info auto-load gdb-scripts [REGEXP]'
Print the list of all canned sequences of commands scripts that
GDB auto-loaded.

If REGEXP is supplied only canned sequences of commands scripts with
matching names are printed.

File: gdb.info, Node: Aliases, Next: Python, Prev: Sequences, Up: Extending GDB

23.2 Command Aliases
====================

Aliases allow you to define alternate spellings for existing commands.
For example, if a new GDB command defined in Python (*note Python::)
has a long name, it is handy to have an abbreviated version of it that
involves less typing.

GDB itself uses aliases. For example `s' is an alias of the `step'
command even though it is otherwise an ambiguous abbreviation of other
commands like `set' and `show'.

Aliases are also used to provide shortened or more common versions
of multi-word commands. For example, GDB provides the `tty' alias of
the `set inferior-tty' command.

You can define a new alias with the `alias' command.

`alias [-a] [--] ALIAS = COMMAND [DEFAULT-ARGS]'

ALIAS specifies the name of the new alias. Each word of ALIAS must
consist of letters, numbers, dashes and underscores.

COMMAND specifies the name of an existing command that is being
aliased.

COMMAND can also be the name of an existing alias. In this case,
COMMAND cannot be an alias that has default arguments.

The `-a' option specifies that the new alias is an abbreviation of
the command. Abbreviations are not used in command completion.

The `--' option specifies the end of options, and is useful when
ALIAS begins with a dash.

You can specify DEFAULT-ARGS for your alias. These DEFAULT-ARGS
will be automatically added before the alias arguments typed explicitly
on the command line.

For example, the below defines an alias `btfullall' that shows all
local variables and all frame arguments:
(gdb) alias btfullall = backtrace -full -frame-arguments all

For more information about DEFAULT-ARGS, see *Note Default
Arguments: Command aliases default args.

Here is a simple example showing how to make an abbreviation of a
command so that there is less to type. Suppose you were tired of
typing `disas', the current shortest unambiguous abbreviation of the
`disassemble' command and you wanted an even shorter version named
`di'. The following will accomplish this.

(gdb) alias -a di = disas

Note that aliases are different from user-defined commands. With a
user-defined command, you also need to write documentation for it with
the `document' command. An alias automatically picks up the
documentation of the existing command.

Here is an example where we make `elms' an abbreviation of
`elements' in the `set print elements' command. This is to show that
you can make an abbreviation of any part of a command.

(gdb) alias -a set print elms = set print elements
(gdb) alias -a show print elms = show print elements
(gdb) set p elms 200
(gdb) show p elms
Limit on string chars or array elements to print is 200.

Note that if you are defining an alias of a `set' command, and you
want to have an alias for the corresponding `show' command, then you
need to define the latter separately.

Unambiguously abbreviated commands are allowed in COMMAND and ALIAS,
just as they are normally.

(gdb) alias -a set pr elms = set p ele

Finally, here is an example showing the creation of a one word alias
for a more complex command. This creates alias `spe' of the command
`set print elements'.

(gdb) alias spe = set print elements
(gdb) spe 20

* Menu:

* Command aliases default args:: Default arguments for aliases

File: gdb.info, Node: Command aliases default args, Up: Aliases

23.2.1 Default Arguments
------------------------

You can tell GDB to always prepend some default arguments to the list
of arguments provided explicitly by the user when using a user-defined
alias.

If you repeatedly use the same arguments or options for a command,
you can define an alias for this command and tell GDB to automatically
prepend these arguments or options to the list of arguments you type
explicitly when using the alias(1).

For example, if you often use the command `thread apply all'
specifying to work on the threads in ascending order and to continue in
case it encounters an error, you can tell GDB to automatically preprend
the `-ascending' and `-c' options by using:

(gdb) alias thread apply asc-all = thread apply all -ascending -c

Once you have defined this alias with its default args, any time you
type the `thread apply asc-all' followed by `some arguments', GDB will
execute `thread apply all -ascending -c some arguments'.

To have even less to type, you can also define a one word alias:
(gdb) alias t_a_c = thread apply all -ascending -c

As usual, unambiguous abbreviations can be used for ALIAS and
DEFAULT-ARGS.

The different aliases of a command do not share their default args.
For example, you define a new alias `bt_ALL' showing all possible
information and another alias `bt_SMALL' showing very limited
information using:
(gdb) alias bt_ALL = backtrace -entry-values both -frame-arg all \
-past-main -past-entry -full
(gdb) alias bt_SMALL = backtrace -entry-values no -frame-arg none \
-past-main off -past-entry off

(For more on using the `alias' command, see *Note Aliases::.)

Default args are not limited to the arguments and options of COMMAND,
but can specify nested commands if COMMAND accepts such a nested command
as argument. For example, the below defines `faalocalsoftype' that
lists the frames having locals of a certain type, together with the
matching local vars:
(gdb) alias faalocalsoftype = frame apply all info locals -q -t
(gdb) faalocalsoftype int
#1 0x55554f5e in sleeper_or_burner (v=0xdf50) at sleepers.c:86
i = 0
ret = 21845

This is also very useful to define an alias for a set of nested
`with' commands to have a particular combination of temporary settings.
For example, the below defines the alias `pp10' that pretty prints an
expression argument, with a maximum of 10 elements if the expression is
a string or an array:
(gdb) alias pp10 = with print pretty -- with print elements 10 -- print
This defines the alias `pp10' as being a sequence of 3 commands.
The first part `with print pretty --' temporarily activates the setting
`set print pretty', then launches the command that follows the separator
`--'. The command following the first part is also a `with' command
that temporarily changes the setting `set print elements' to 10, then
launches the command that follows the second separator `--'. The third
part `print' is the command the `pp10' alias will launch, using the
temporary values of the settings and the arguments explicitly given by
the user. For more information about the `with' command usage, see
*Note Command Settings::.

By default, asking the help for an alias shows the documentation of
the aliased command. When the alias is a set of nested commands, `help'
of an alias shows the documentation of the first command. This help is
not particularly useful for an alias such as `pp10'. For such an
alias, it is useful to give a specific documentation using the
`document' command (*note document: Define.).

---------- Footnotes ----------

(1) GDB could easily accept default arguments for pre-defined
commands and aliases, but it was deemed this would be confusing, and so
is not allowed.

File: gdb.info, Node: Python, Next: Guile, Prev: Aliases, Up: Extending GDB

23.3 Extending GDB using Python
===============================

You can extend GDB using the Python programming language
(http://www.python.org/). This feature is available only if GDB was
configured using `--with-python'.

Python scripts used by GDB should be installed in
`DATA-DIRECTORY/python', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::). This directory, known
as the "python directory", is automatically added to the Python Search
Path in order to allow the Python interpreter to locate all scripts
installed at this location.

Additionally, GDB commands and convenience functions which are
written in Python and are located in the
`DATA-DIRECTORY/python/gdb/command' or
`DATA-DIRECTORY/python/gdb/function' directories are automatically
imported when GDB starts.

* Menu:

* Python Commands:: Accessing Python from GDB.
* Python API:: Accessing GDB from Python.
* Python Auto-loading:: Automatically loading Python code.
* Python modules:: Python modules provided by GDB.

File: gdb.info, Node: Python Commands, Next: Python API, Up: Python

23.3.1 Python Commands
----------------------

GDB provides two commands for accessing the Python interpreter, and one
related setting:

`python-interactive [COMMAND]'
`pi [COMMAND]'
Without an argument, the `python-interactive' command can be used
to start an interactive Python prompt. To return to GDB, type the
`EOF' character (e.g., `Ctrl-D' on an empty prompt).

Alternatively, a single-line Python command can be given as an
argument and evaluated. If the command is an expression, the
result will be printed; otherwise, nothing will be printed. For
example:

(gdb) python-interactive 2 + 3
5

`python [COMMAND]'
`py [COMMAND]'
The `python' command can be used to evaluate Python code.

If given an argument, the `python' command will evaluate the
argument as a Python command. For example:

(gdb) python print 23
23

If you do not provide an argument to `python', it will act as a
multi-line command, like `define'. In this case, the Python
script is made up of subsequent command lines, given after the
`python' command. This command list is terminated using a line
containing `end'. For example:

(gdb) python
>print 23
>end
23

`set python print-stack'
By default, GDB will print only the message component of a Python
exception when an error occurs in a Python script. This can be
controlled using `set python print-stack': if `full', then full
Python stack printing is enabled; if `none', then Python stack and
message printing is disabled; if `message', the default, only the
message component of the error is printed.

`set python ignore-environment [on|off]'
By default this option is `off', and, when GDB initializes its
internal Python interpreter, the Python interpreter will check the
environment for variables that will effect how it behaves, for
example `PYTHONHOME', and `PYTHONPATH'(1).

If this option is set to `on' before Python is initialized then
Python will ignore all such environment variables. As Python is
initialized early during GDB's startup process, then this option
must be placed into the early initialization file (*note
Initialization Files::) to have the desired effect.

This option is equivalent to passing `-E' to the real `python'
executable.

`set python dont-write-bytecode [auto|on|off]'
When this option is `off', then, once GDB has initialized the
Python interpreter, the interpreter will byte-compile any Python
modules that it imports and write the byte code to disk in `.pyc'
files.

If this option is set to `on' before Python is initialized then
Python will no longer write the byte code to disk. As Python is
initialized early during GDB's startup process, then this option
must be placed into the early initialization file (*note
Initialization Files::) to have the desired effect.

By default this option is set to `auto'. In this mode, provided
the `python ignore-environment' setting is `off', the environment
variable `PYTHONDONTWRITEBYTECODE' is examined to see if it should
write out byte-code or not. `PYTHONDONTWRITEBYTECODE' is
considered to be off/disabled either when set to the empty string
or when the environment variable doesn't exist. All other
settings, including those which don't seem to make sense, indicate
that it's on/enabled.

This option is equivalent to passing `-B' to the real `python'
executable.

It is also possible to execute a Python script from the GDB
interpreter:

`source `script-name''
The script name must end with `.py' and GDB must be configured to
recognize the script language based on filename extension using
the `script-extension' setting. *Note Extending GDB: Extending
GDB.

The following commands are intended to help debug GDB itself:

`set debug py-breakpoint on|off'
`show debug py-breakpoint'
When `on', GDB prints debug messages related to the Python
breakpoint API. This is `off' by default.

`set debug py-unwind on|off'
`show debug py-unwind'
When `on', GDB prints debug messages related to the Python
unwinder API. This is `off' by default.

---------- Footnotes ----------

(1) See the ENVIRONMENT VARIABLES section of `man 1 python' for a
comprehensive list.

File: gdb.info, Node: Python API, Next: Python Auto-loading, Prev: Python Commands, Up: Python

23.3.2 Python API
-----------------

You can get quick online help for GDB's Python API by issuing the
command `python help (gdb)'.

Functions and methods which have two or more optional arguments allow
them to be specified using keyword syntax. This allows passing some
optional arguments while skipping others. Example:
`gdb.some_function ('foo', bar = 1, baz = 2)'.

* Menu:

* Basic Python:: Basic Python Functions.
* Threading in GDB:: Using Python threads in GDB.
* Exception Handling:: How Python exceptions are translated.
* Values From Inferior:: Python representation of values.
* Types In Python:: Python representation of types.
* Pretty Printing API:: Pretty-printing values.
* Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
* Writing a Pretty-Printer:: Writing a Pretty-Printer.
* Type Printing API:: Pretty-printing types.
* Frame Filter API:: Filtering Frames.
* Frame Decorator API:: Decorating Frames.
* Writing a Frame Filter:: Writing a Frame Filter.
* Unwinding Frames in Python:: Writing frame unwinder.
* Xmethods In Python:: Adding and replacing methods of C++ classes.
* Xmethod API:: Xmethod types.
* Writing an Xmethod:: Writing an xmethod.
* Inferiors In Python:: Python representation of inferiors (processes)
* Events In Python:: Listening for events from GDB.
* Threads In Python:: Accessing inferior threads from Python.
* Recordings In Python:: Accessing recordings from Python.
* CLI Commands In Python:: Implementing new CLI commands in Python.
* GDB/MI Commands In Python:: Implementing new GDB/MI commands in Python.
* GDB/MI Notifications In Python:: Implementing new GDB/MI notifications in Python.
* Parameters In Python:: Adding new GDB parameters.
* Functions In Python:: Writing new convenience functions.
* Progspaces In Python:: Program spaces.
* Objfiles In Python:: Object files.
* Frames In Python:: Accessing inferior stack frames from Python.
* Blocks In Python:: Accessing blocks from Python.
* Symbols In Python:: Python representation of symbols.
* Symbol Tables In Python:: Python representation of symbol tables.
* Line Tables In Python:: Python representation of line tables.
* Breakpoints In Python:: Manipulating breakpoints using Python.
* Finish Breakpoints in Python:: Setting Breakpoints on function return
using Python.
* Lazy Strings In Python:: Python representation of lazy strings.
* Architectures In Python:: Python representation of architectures.
* Registers In Python:: Python representation of registers.
* Connections In Python:: Python representation of connections.
* TUI Windows In Python:: Implementing new TUI windows.
* Disassembly In Python:: Instruction Disassembly In Python
* Missing Debug Info In Python:: Handle missing debug info from Python.

File: gdb.info, Node: Basic Python, Next: Threading in GDB, Up: Python API

23.3.2.1 Basic Python
....................

At startup, GDB overrides Python's `sys.stdout' and `sys.stderr' to
print using GDB's output-paging streams. A Python program which
outputs to one of these streams may have its output interrupted by the
user (*note Screen Size::). In this situation, a Python
`KeyboardInterrupt' exception is thrown.

Some care must be taken when writing Python code to run in GDB. Two
things worth noting in particular:

* GDB installs handlers for `SIGCHLD' and `SIGINT'. Python code
must not override these, or even change the options using
`sigaction'. If your program changes the handling of these
signals, GDB will most likely stop working correctly. Note that
it is unfortunately common for GUI toolkits to install a `SIGCHLD'
handler. When creating a new Python thread, you can use
`gdb.block_signals' or `gdb.Thread' to handle this correctly; see
*Note Threading in GDB::.

* GDB takes care to mark its internal file descriptors as
close-on-exec. However, this cannot be done in a thread-safe way
on all platforms. Your Python programs should be aware of this and
should both create new file descriptors with the close-on-exec flag
set and arrange to close unneeded file descriptors before starting
a child process.

GDB introduces a new Python module, named `gdb'. All methods and
classes added by GDB are placed in this module. GDB automatically
`import's the `gdb' module for use in all scripts evaluated by the
`python' command.

Some types of the `gdb' module come with a textual representation
(accessible through the `repr' or `str' functions). These are offered
for debugging purposes only, expect them to change over time.

-- Variable: gdb.PYTHONDIR
A string containing the python directory (*note Python::).

-- Function: gdb.execute (command [, from_tty [, to_string]])
Evaluate COMMAND, a string, as a GDB CLI command. If a GDB
exception happens while COMMAND runs, it is translated as
described in *Note Exception Handling: Exception Handling.

The FROM_TTY flag specifies whether GDB ought to consider this
command as having originated from the user invoking it
interactively. It must be a boolean value. If omitted, it
defaults to `False'.

By default, any output produced by COMMAND is sent to GDB's
standard output (and to the log output if logging is turned on).
If the TO_STRING parameter is `True', then output will be
collected by `gdb.execute' and returned as a string. The default
is `False', in which case the return value is `None'. If
TO_STRING is `True', the GDB virtual terminal will be temporarily
set to unlimited width and height, and its pagination will be
disabled; *note Screen Size::.

-- Function: gdb.breakpoints ()
Return a sequence holding all of GDB's breakpoints. *Note
Breakpoints In Python::, for more information. In GDB version
7.11 and earlier, this function returned `None' if there were no
breakpoints. This peculiarity was subsequently fixed, and now
`gdb.breakpoints' returns an empty sequence in this case.

-- Function: gdb.rbreak (regex [, minsyms [, throttle, [, symtabs ]]])
Return a Python list holding a collection of newly set
`gdb.Breakpoint' objects matching function names defined by the
REGEX pattern. If the MINSYMS keyword is `True', all system
functions (those not explicitly defined in the inferior) will also
be included in the match. The THROTTLE keyword takes an integer
that defines the maximum number of pattern matches for functions
matched by the REGEX pattern. If the number of matches exceeds
the integer value of THROTTLE, a `RuntimeError' will be raised and
no breakpoints will be created. If THROTTLE is not defined then
there is no imposed limit on the maximum number of matches and
breakpoints to be created. The SYMTABS keyword takes a Python
iterable that yields a collection of `gdb.Symtab' objects and will
restrict the search to those functions only contained within the
`gdb.Symtab' objects.

-- Function: gdb.parameter (parameter)
Return the value of a GDB PARAMETER given by its name, a string;
the parameter name string may contain spaces if the parameter has a
multi-part name. For example, `print object' is a valid parameter
name.

If the named parameter does not exist, this function throws a
`gdb.error' (*note Exception Handling::). Otherwise, the
parameter's value is converted to a Python value of the appropriate
type, and returned.

-- Function: gdb.set_parameter (name, value)
Sets the gdb parameter NAME to VALUE. As with `gdb.parameter',
the parameter name string may contain spaces if the parameter has
a multi-part name.

-- Function: gdb.with_parameter (name, value)
Create a Python context manager (for use with the Python `with'
statement) that temporarily sets the gdb parameter NAME to VALUE.
On exit from the context, the previous value will be restored.

This uses `gdb.parameter' in its implementation, so it can throw
the same exceptions as that function.

For example, it's sometimes useful to evaluate some Python code
with a particular gdb language:

with gdb.with_parameter('language', 'pascal'):
... language-specific operations

-- Function: gdb.history (number)
Return a value from GDB's value history (*note Value History::).
The NUMBER argument indicates which history element to return. If
NUMBER is negative, then GDB will take its absolute value and
count backward from the last element (i.e., the most recent
element) to find the value to return. If NUMBER is zero, then GDB
will return the most recent element. If the element specified by
NUMBER doesn't exist in the value history, a `gdb.error' exception
will be raised.

If no exception is raised, the return value is always an instance
of `gdb.Value' (*note Values From Inferior::).

-- Function: gdb.add_history (value)
Takes VALUE, an instance of `gdb.Value' (*note Values From
Inferior::), and appends the value this object represents to GDB's
value history (*note Value History::), and return an integer, its
history number. If VALUE is not a `gdb.Value', it is is converted
using the `gdb.Value' constructor. If VALUE can't be converted to
a `gdb.Value' then a `TypeError' is raised.

When a command implemented in Python prints a single `gdb.Value'
as its result, then placing the value into the history will allow
the user convenient access to those values via CLI history
facilities.

-- Function: gdb.history_count ()
Return an integer indicating the number of values in GDB's value
history (*note Value History::).

-- Function: gdb.convenience_variable (name)
Return the value of the convenience variable (*note Convenience
Vars::) named NAME. NAME must be a string. The name should not
include the `$' that is used to mark a convenience variable in an
expression. If the convenience variable does not exist, then
`None' is returned.

-- Function: gdb.set_convenience_variable (name, value)
Set the value of the convenience variable (*note Convenience
Vars::) named NAME. NAME must be a string. The name should not
include the `$' that is used to mark a convenience variable in an
expression. If VALUE is `None', then the convenience variable is
removed. Otherwise, if VALUE is not a `gdb.Value' (*note Values
From Inferior::), it is is converted using the `gdb.Value'
constructor.

-- Function: gdb.parse_and_eval (expression [, global_context])
Parse EXPRESSION, which must be a string, as an expression in the
current language, evaluate it, and return the result as a
`gdb.Value'.

GLOBAL_CONTEXT, if provided, is a boolean indicating whether the
parsing should be done in the global context. The default is
`False', meaning that the current frame or current static context
should be used.

This function can be useful when implementing a new command (*note
CLI Commands In Python::, *note GDB/MI Commands In Python::), as
it provides a way to parse the command's argument as an
expression. It is also useful simply to compute values.

-- Function: gdb.find_pc_line (pc)
Return the `gdb.Symtab_and_line' object corresponding to the PC
value. *Note Symbol Tables In Python::. If an invalid value of
PC is passed as an argument, then the `symtab' and `line'
attributes of the returned `gdb.Symtab_and_line' object will be
`None' and 0 respectively. This is identical to
`gdb.current_progspace().find_pc_line(pc)' and is included for
historical compatibility.

-- Function: gdb.write (string [, stream])
Print a string to GDB's paginated output stream. The optional
STREAM determines the stream to print to. The default stream is
GDB's standard output stream. Possible stream values are:

`gdb.STDOUT'
GDB's standard output stream.

`gdb.STDERR'
GDB's standard error stream.

`gdb.STDLOG'
GDB's log stream (*note Logging Output::).

Writing to `sys.stdout' or `sys.stderr' will automatically call
this function and will automatically direct the output to the
relevant stream.

-- Function: gdb.flush ([, stream])
Flush the buffer of a GDB paginated stream so that the contents
are displayed immediately. GDB will flush the contents of a
stream automatically when it encounters a newline in the buffer.
The optional STREAM determines the stream to flush. The default
stream is GDB's standard output stream. Possible stream values
are:

`gdb.STDOUT'
GDB's standard output stream.

`gdb.STDERR'
GDB's standard error stream.

`gdb.STDLOG'
GDB's log stream (*note Logging Output::).

Flushing `sys.stdout' or `sys.stderr' will automatically call this
function for the relevant stream.

-- Function: gdb.target_charset ()
Return the name of the current target character set (*note
Character Sets::). This differs from
`gdb.parameter('target-charset')' in that `auto' is never returned.

-- Function: gdb.target_wide_charset ()
Return the name of the current target wide character set (*note
Character Sets::). This differs from
`gdb.parameter('target-wide-charset')' in that `auto' is never
returned.

-- Function: gdb.host_charset ()
Return a string, the name of the current host character set (*note
Character Sets::). This differs from
`gdb.parameter('host-charset')' in that `auto' is never returned.

-- Function: gdb.solib_name (address)
Return the name of the shared library holding the given ADDRESS as
a string, or `None'. This is identical to
`gdb.current_progspace().solib_name(address)' and is included for
historical compatibility.

-- Function: gdb.decode_line ([expression])
Return locations of the line specified by EXPRESSION, or of the
current line if no argument was given. This function returns a
Python tuple containing two elements. The first element contains
a string holding any unparsed section of EXPRESSION (or `None' if
the expression has been fully parsed). The second element contains
either `None' or another tuple that contains all the locations
that match the expression represented as `gdb.Symtab_and_line'
objects (*note Symbol Tables In Python::). If EXPRESSION is
provided, it is decoded the way that GDB's inbuilt `break' or
`edit' commands do (*note Location Specifications::).

-- Function: gdb.prompt_hook (current_prompt)
If PROMPT_HOOK is callable, GDB will call the method assigned to
this operation before a prompt is displayed by GDB.

The parameter `current_prompt' contains the current GDB prompt.
This method must return a Python string, or `None'. If a string
is returned, the GDB prompt will be set to that string. If `None'
is returned, GDB will continue to use the current prompt.

Some prompts cannot be substituted in GDB. Secondary prompts such
as those used by readline for command input, and annotation
related prompts are prohibited from being changed.

-- Function: gdb.architecture_names ()
Return a list containing all of the architecture names that the
current build of GDB supports. Each architecture name is a
string. The names returned in this list are the same names as are
returned from `gdb.Architecture.name' (*note Architecture.name:
gdbpy_architecture_name.).

-- Function: gdb.connections
Return a list of `gdb.TargetConnection' objects, one for each
currently active connection (*note Connections In Python::). The
connection objects are in no particular order in the returned list.

-- Function: gdb.format_address (address [, progspace, architecture])
Return a string in the format `ADDR <SYMBOL+OFFSET>', where ADDR
is ADDRESS formatted in hexadecimal, SYMBOL is the symbol whose
address is the nearest to ADDRESS and below it in memory, and
OFFSET is the offset from SYMBOL to ADDRESS in decimal.

If no suitable SYMBOL was found, then the <SYMBOL+OFFSET> part is
not included in the returned string, instead the returned string
will just contain the ADDRESS formatted as hexadecimal. How far
GDB looks back for a suitable symbol can be controlled with `set
print max-symbolic-offset' (*note Print Settings::).

Additionally, the returned string can include file name and line
number information when `set print symbol-filename on' (*note
Print Settings::), in this case the format of the returned string
is `ADDR <SYMBOL+OFFSET> at FILENAME:LINE-NUMBER'.

The PROGSPACE is the gdb.Progspace in which SYMBOL is looked up,
and ARCHITECTURE is used when formatting ADDR, e.g. in order to
determine the size of an address in bytes.

If neither PROGSPACE or ARCHITECTURE are passed, then by default
GDB will use the program space and architecture of the currently
selected inferior, thus, the following two calls are equivalent:

gdb.format_address(address)
gdb.format_address(address,
gdb.selected_inferior().progspace,
gdb.selected_inferior().architecture())

It is not valid to only pass one of PROGSPACE or ARCHITECTURE,
either they must both be provided, or neither must be provided
(and the defaults will be used).

This method uses the same mechanism for formatting address, symbol,
and offset information as core GDB does in commands such as
`disassemble'.

Here are some examples of the possible string formats:

0x00001042
0x00001042 <symbol+16>
0x00001042 <symbol+16 at file.c:123>

-- Function: gdb.current_language ()
Return the name of the current language as a string. Unlike
`gdb.parameter('language')', this function will never return
`auto'. If a `gdb.Frame' object is available (*note Frames In
Python::), the `language' method might be preferable in some
cases, as that is not affected by the user's language setting.

File: gdb.info, Node: Threading in GDB, Next: Exception Handling, Prev: Basic Python, Up: Python API

23.3.2.2 Threading in GDB
........................

GDB is not thread-safe. If your Python program uses multiple threads,
you must be careful to only call GDB-specific functions in the GDB
thread. GDB provides some functions to help with this.

-- Function: gdb.block_signals ()
As mentioned earlier (*note Basic Python::), certain signals must
be delivered to the GDB main thread. The `block_signals' function
returns a context manager that will block these signals on entry.
This can be used when starting a new thread to ensure that the
signals are blocked there, like:

with gdb.block_signals():
start_new_thread()

-- class: gdb.Thread
This is a subclass of Python's `threading.Thread' class. It
overrides the `start' method to call `block_signals', making this
an easy-to-use drop-in replacement for creating threads that will
work well in GDB.

-- Function: gdb.interrupt ()
This causes GDB to react as if the user had typed a control-C
character at the terminal. That is, if the inferior is running,
it is interrupted; if a GDB command is executing, it is stopped;
and if a Python command is running, `KeyboardInterrupt' will be
raised.

Unlike most Python APIs in GDB, `interrupt' is thread-safe.

-- Function: gdb.post_event (event)
Put EVENT, a callable object taking no arguments, into GDB's
internal event queue. This callable will be invoked at some later
point, during GDB's event processing. Events posted using
`post_event' will be run in the order in which they were posted;
however, there is no way to know when they will be processed
relative to other events inside GDB.

Unlike most Python APIs in GDB, `post_event' is thread-safe. For
example:

(gdb) python
>import threading
>
>class Writer():
> def __init__(self, message):
> self.message = message;
> def __call__(self):
> gdb.write(self.message)
>
>class MyThread1 (threading.Thread):
> def run (self):
> gdb.post_event(Writer("Hello "))
>
>class MyThread2 (threading.Thread):
> def run (self):
> gdb.post_event(Writer("World\n"))
>
>MyThread1().start()
>MyThread2().start()
>end
(gdb) Hello World

File: gdb.info, Node: Exception Handling, Next: Values From Inferior, Prev: Threading in GDB, Up: Python API

23.3.2.3 Exception Handling
..........................

When executing the `python' command, Python exceptions uncaught within
the Python code are translated to calls to GDB error-reporting
mechanism. If the command that called `python' does not handle the
error, GDB will terminate it and print an error message. Exactly what
will be printed depends on `set python print-stack' (*note Python
Commands::). Example:

(gdb) python print foo
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name 'foo' is not defined

GDB errors that happen in GDB commands invoked by Python code are
converted to Python exceptions. The type of the Python exception
depends on the error.

`gdb.error'
This is the base class for most exceptions generated by GDB. It
is derived from `RuntimeError', for compatibility with earlier
versions of GDB.

If an error occurring in GDB does not fit into some more specific
category, then the generated exception will have this type.

`gdb.MemoryError'
This is a subclass of `gdb.error' which is thrown when an
operation tried to access invalid memory in the inferior.

`KeyboardInterrupt'
User interrupt (via `C-c' or by typing `q' at a pagination prompt)
is translated to a Python `KeyboardInterrupt' exception.

In all cases, your exception handler will see the GDB error message
as its value and the Python call stack backtrace at the Python
statement closest to where the GDB error occurred as the traceback.

When implementing GDB commands in Python via `gdb.Command', or
functions via `gdb.Function', it is useful to be able to throw an
exception that doesn't cause a traceback to be printed. For example,
the user may have invoked the command incorrectly. GDB provides a
special exception class that can be used for this purpose.

`gdb.GdbError'
When thrown from a command or function, this exception will cause
the command or function to fail, but the Python stack will not be
displayed. GDB does not throw this exception itself, but rather
recognizes it when thrown from user Python code. Example:

(gdb) python
>class HelloWorld (gdb.Command):
> """Greet the whole world."""
> def __init__ (self):
> super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)
> def invoke (self, args, from_tty):
> argv = gdb.string_to_argv (args)
> if len (argv) != 0:
> raise gdb.GdbError ("hello-world takes no arguments")
> print ("Hello, World!")
>HelloWorld ()
>end
(gdb) hello-world 42
hello-world takes no arguments

File: gdb.info, Node: Values From Inferior, Next: Types In Python, Prev: Exception Handling, Up: Python API

23.3.2.4 Values From Inferior
............................

GDB provides values it obtains from the inferior program in an object
of type `gdb.Value'. GDB uses this object for its internal bookkeeping
of the inferior's values, and for fetching values when necessary.

Inferior values that are simple scalars can be used directly in
Python expressions that are valid for the value's data type. Here's an
example for an integer or floating-point value `some_val':

bar = some_val + 2

As result of this, `bar' will also be a `gdb.Value' object whose values
are of the same type as those of `some_val'. Valid Python operations
can also be performed on `gdb.Value' objects representing a `struct' or
`class' object. For such cases, the overloaded operator (if present),
is used to perform the operation. For example, if `val1' and `val2'
are `gdb.Value' objects representing instances of a `class' which
overloads the `+' operator, then one can use the `+' operator in their
Python script as follows:

val3 = val1 + val2

The result of the operation `val3' is also a `gdb.Value' object
corresponding to the value returned by the overloaded `+' operator. In
general, overloaded operators are invoked for the following operations:
`+' (binary addition), `-' (binary subtraction), `*' (multiplication),
`/', `%', `<<', `>>', `|', `&', `^'.

Inferior values that are structures or instances of some class can
be accessed using the Python "dictionary syntax". For example, if
`some_val' is a `gdb.Value' instance holding a structure, you can
access its `foo' element with:

bar = some_val['foo']

Again, `bar' will also be a `gdb.Value' object. Structure elements
can also be accessed by using `gdb.Field' objects as subscripts (*note
Types In Python::, for more information on `gdb.Field' objects). For
example, if `foo_field' is a `gdb.Field' object corresponding to
element `foo' of the above structure, then `bar' can also be accessed
as follows:

bar = some_val[foo_field]

If a `gdb.Value' has array or pointer type, an integer index can be
used to access elements.

result = some_array[23]

A `gdb.Value' that represents a function can be executed via
inferior function call. Any arguments provided to the call must match
the function's prototype, and must be provided in the order specified
by that prototype.

For example, `some_val' is a `gdb.Value' instance representing a
function that takes two integers as arguments. To execute this
function, call it like so:

result = some_val (10,20)

Any values returned from a function call will be stored as a
`gdb.Value'.

The following attributes are provided:

-- Variable: Value.address
If this object is addressable, this read-only attribute holds a
`gdb.Value' object representing the address. Otherwise, this
attribute holds `None'.

-- Variable: Value.is_optimized_out
This read-only boolean attribute is true if the compiler optimized
out this value, thus it is not available for fetching from the
inferior.

-- Variable: Value.type
The type of this `gdb.Value'. The value of this attribute is a
`gdb.Type' object (*note Types In Python::).

-- Variable: Value.dynamic_type
The dynamic type of this `gdb.Value'. This uses the object's
virtual table and the C++ run-time type information (RTTI) to
determine the dynamic type of the value. If this value is of
class type, it will return the class in which the value is
embedded, if any. If this value is of pointer or reference to a
class type, it will compute the dynamic type of the referenced
object, and return a pointer or reference to that type,
respectively. In all other cases, it will return the value's
static type.

Note that this feature will only work when debugging a C++ program
that includes RTTI for the object in question. Otherwise, it will
just return the static type of the value as in `ptype foo' (*note
ptype: Symbols.).

-- Variable: Value.is_lazy
The value of this read-only boolean attribute is `True' if this
`gdb.Value' has not yet been fetched from the inferior. GDB does
not fetch values until necessary, for efficiency. For example:

myval = gdb.parse_and_eval ('somevar')

The value of `somevar' is not fetched at this time. It will be
fetched when the value is needed, or when the `fetch_lazy' method
is invoked.

-- Variable: Value.bytes
The value of this attribute is a `bytes' object containing the
bytes that make up this `Value''s complete value in little endian
order. If the complete contents of this value are not available
then accessing this attribute will raise an exception.

This attribute can also be assigned to. The new value should be a
buffer object (e.g. a `bytes' object), the length of the new
buffer must exactly match the length of this `Value''s type. The
bytes values in the new buffer should be in little endian order.

As with `Value.assign' (*note Value.assign::), if this value
cannot be assigned to, then an exception will be thrown.

The following methods are provided:

-- Function: Value.__init__ (val)
Many Python values can be converted directly to a `gdb.Value' via
this object initializer. Specifically:

Python boolean
A Python boolean is converted to the boolean type from the
current language.

Python integer
A Python integer is converted to the C `long' type for the
current architecture.

Python long
A Python long is converted to the C `long long' type for the
current architecture.

Python float
A Python float is converted to the C `double' type for the
current architecture.

Python string
A Python string is converted to a target string in the
current target language using the current target encoding.
If a character cannot be represented in the current target
encoding, then an exception is thrown.

`gdb.Value'
If `val' is a `gdb.Value', then a copy of the value is made.

`gdb.LazyString'
If `val' is a `gdb.LazyString' (*note Lazy Strings In
Python::), then the lazy string's `value' method is called,
and its result is used.

-- Function: Value.__init__ (val, type)
This second form of the `gdb.Value' constructor returns a
`gdb.Value' of type TYPE where the value contents are taken from
the Python buffer object specified by VAL. The number of bytes in
the Python buffer object must be greater than or equal to the size
of TYPE.

If TYPE is `None' then this version of `__init__' behaves as
though TYPE was not passed at all.

-- Function: Value.assign (rhs)
Assign RHS to this value, and return `None'. If this value cannot
be assigned to, or if the assignment is invalid for some reason
(for example a type-checking failure), an exception will be thrown.

-- Function: Value.cast (type)
Return a new instance of `gdb.Value' that is the result of casting
this instance to the type described by TYPE, which must be a
`gdb.Type' object. If the cast cannot be performed for some
reason, this method throws an exception.

-- Function: Value.dereference ()
For pointer data types, this method returns a new `gdb.Value'
object whose contents is the object pointed to by the pointer.
For example, if `foo' is a C pointer to an `int', declared in your
C program as

int *foo;

then you can use the corresponding `gdb.Value' to access what
`foo' points to like this:

bar = foo.dereference ()

The result `bar' will be a `gdb.Value' object holding the value
pointed to by `foo'.

A similar function `Value.referenced_value' exists which also
returns `gdb.Value' objects corresponding to the values pointed to
by pointer values (and additionally, values referenced by reference
values). However, the behavior of `Value.dereference' differs
from `Value.referenced_value' by the fact that the behavior of
`Value.dereference' is identical to applying the C unary operator
`*' on a given value. For example, consider a reference to a
pointer `ptrref', declared in your C++ program as

typedef int *intptr;
...
int val = 10;
intptr ptr = &val;
intptr &ptrref = ptr;

Though `ptrref' is a reference value, one can apply the method
`Value.dereference' to the `gdb.Value' object corresponding to it
and obtain a `gdb.Value' which is identical to that corresponding
to `val'. However, if you apply the method
`Value.referenced_value', the result would be a `gdb.Value' object
identical to that corresponding to `ptr'.

py_ptrref = gdb.parse_and_eval ("ptrref")
py_val = py_ptrref.dereference ()
py_ptr = py_ptrref.referenced_value ()

The `gdb.Value' object `py_val' is identical to that corresponding
to `val', and `py_ptr' is identical to that corresponding to
`ptr'. In general, `Value.dereference' can be applied whenever
the C unary operator `*' can be applied to the corresponding C
value. For those cases where applying both `Value.dereference'
and `Value.referenced_value' is allowed, the results obtained need
not be identical (as we have seen in the above example). The
results are however identical when applied on `gdb.Value' objects
corresponding to pointers (`gdb.Value' objects with type code
`TYPE_CODE_PTR') in a C/C++ program.

-- Function: Value.referenced_value ()
For pointer or reference data types, this method returns a new
`gdb.Value' object corresponding to the value referenced by the
pointer/reference value. For pointer data types,
`Value.dereference' and `Value.referenced_value' produce identical
results. The difference between these methods is that
`Value.dereference' cannot get the values referenced by reference
values. For example, consider a reference to an `int', declared
in your C++ program as

int val = 10;
int &ref = val;

then applying `Value.dereference' to the `gdb.Value' object
corresponding to `ref' will result in an error, while applying
`Value.referenced_value' will result in a `gdb.Value' object
identical to that corresponding to `val'.

py_ref = gdb.parse_and_eval ("ref")
er_ref = py_ref.dereference () # Results in error
py_val = py_ref.referenced_value () # Returns the referenced value

The `gdb.Value' object `py_val' is identical to that corresponding
to `val'.

-- Function: Value.reference_value ()
Return a `gdb.Value' object which is a reference to the value
encapsulated by this instance.

-- Function: Value.const_value ()
Return a `gdb.Value' object which is a `const' version of the
value encapsulated by this instance.

-- Function: Value.dynamic_cast (type)
Like `Value.cast', but works as if the C++ `dynamic_cast' operator
were used. Consult a C++ reference for details.

-- Function: Value.reinterpret_cast (type)
Like `Value.cast', but works as if the C++ `reinterpret_cast'
operator were used. Consult a C++ reference for details.

-- Function: Value.format_string (...)
Convert a `gdb.Value' to a string, similarly to what the `print'
command does. Invoked with no arguments, this is equivalent to
calling the `str' function on the `gdb.Value'. The representation
of the same value may change across different versions of GDB, so
you shouldn't, for instance, parse the strings returned by this
method.

All the arguments are keyword only. If an argument is not
specified, the current global default setting is used.

`raw'
`True' if pretty-printers (*note Pretty Printing::) should
not be used to format the value. `False' if enabled
pretty-printers matching the type represented by the
`gdb.Value' should be used to format it.

`pretty_arrays'
`True' if arrays should be pretty printed to be more
convenient to read, `False' if they shouldn't (see `set print
array' in *Note Print Settings::).

`pretty_structs'
`True' if structs should be pretty printed to be more
convenient to read, `False' if they shouldn't (see `set print
pretty' in *Note Print Settings::).

`array_indexes'
`True' if array indexes should be included in the string
representation of arrays, `False' if they shouldn't (see `set
print array-indexes' in *Note Print Settings::).

`symbols'
`True' if the string representation of a pointer should
include the corresponding symbol name (if one exists),
`False' if it shouldn't (see `set print symbol' in *Note
Print Settings::).

`unions'
`True' if unions which are contained in other structures or
unions should be expanded, `False' if they shouldn't (see
`set print union' in *Note Print Settings::).

`address'
`True' if the string representation of a pointer should
include the address, `False' if it shouldn't (see `set print
address' in *Note Print Settings::).

`nibbles'
`True' if binary values should be displayed in groups of four
bits, known as nibbles. `False' if it shouldn't (*note set
print nibbles: Print Settings.).

`deref_refs'
`True' if C++ references should be resolved to the value they
refer to, `False' (the default) if they shouldn't. Note
that, unlike for the `print' command, references are not
automatically expanded when using the `format_string' method
or the `str' function. There is no global `print' setting to
change the default behaviour.

`actual_objects'
`True' if the representation of a pointer to an object should
identify the _actual_ (derived) type of the object rather
than the _declared_ type, using the virtual function table.
`False' if the _declared_ type should be used. (See `set
print object' in *Note Print Settings::).

`static_members'
`True' if static members should be included in the string
representation of a C++ object, `False' if they shouldn't (see
`set print static-members' in *Note Print Settings::).

`max_characters'
Number of string characters to print, `0' to follow
`max_elements', or `UINT_MAX' to print an unlimited number of
characters (see `set print characters' in *Note Print
Settings::).

`max_elements'
Number of array elements to print, or `0' to print an
unlimited number of elements (see `set print elements' in
*Note Print Settings::).

`max_depth'
The maximum depth to print for nested structs and unions, or
`-1' to print an unlimited number of elements (see `set print
max-depth' in *Note Print Settings::).

`repeat_threshold'
Set the threshold for suppressing display of repeated array
elements, or `0' to represent all elements, even if repeated.
(See `set print repeats' in *Note Print Settings::).

`format'
A string containing a single character representing the
format to use for the returned string. For instance, `'x''
is equivalent to using the GDB command `print' with the `/x'
option and formats the value as a hexadecimal number.

`styling'
`True' if GDB should apply styling to the returned string.
When styling is applied, the returned string might contain
ANSI terminal escape sequences. Escape sequences will only be
included if styling is turned on, see *Note Output Styling::.
Additionally, GDB only styles some value contents, so not
every output string will contain escape sequences.

When `False', which is the default, no output styling is
applied.

`summary'
`True' when just a summary should be printed. In this mode,
scalar values are printed in their entirety, but aggregates
such as structures or unions are omitted. This mode is used
by `set print frame-arguments scalars' (*note Print
Settings::).

-- Function: Value.to_array ()
If this value is array-like (*note Type.is_array_like::), then this
method converts it to an array, which is returned. If this value
is already an array, it is simply returned. Otherwise, an
exception is throw.

-- Function: Value.string ([encoding[, errors[, length]]])
If this `gdb.Value' represents a string, then this method converts
the contents to a Python string. Otherwise, this method will
throw an exception.

Values are interpreted as strings according to the rules of the
current language. If the optional length argument is given, the
string will be converted to that length, and will include any
embedded zeroes that the string may contain. Otherwise, for
languages where the string is zero-terminated, the entire string
will be converted.

For example, in C-like languages, a value is a string if it is a
pointer to or an array of characters or ints of type `wchar_t',
`char16_t', or `char32_t'.

If the optional ENCODING argument is given, it must be a string
naming the encoding of the string in the `gdb.Value', such as
`"ascii"', `"iso-8859-6"' or `"utf-8"'. It accepts the same
encodings as the corresponding argument to Python's
`string.decode' method, and the Python codec machinery will be used
to convert the string. If ENCODING is not given, or if ENCODING
is the empty string, then either the `target-charset' (*note
Character Sets::) will be used, or a language-specific encoding
will be used, if the current language is able to supply one.

The optional ERRORS argument is the same as the corresponding
argument to Python's `string.decode' method.

If the optional LENGTH argument is given, the string will be
fetched and converted to the given length.

-- Function: Value.lazy_string ([encoding [, length]])
If this `gdb.Value' represents a string, then this method converts
the contents to a `gdb.LazyString' (*note Lazy Strings In
Python::). Otherwise, this method will throw an exception.

If the optional ENCODING argument is given, it must be a string
naming the encoding of the `gdb.LazyString'. Some examples are:
`ascii', `iso-8859-6' or `utf-8'. If the ENCODING argument is an
encoding that GDB does recognize, GDB will raise an error.

When a lazy string is printed, the GDB encoding machinery is used
to convert the string during printing. If the optional ENCODING
argument is not provided, or is an empty string, GDB will
automatically select the encoding most suitable for the string
type. For further information on encoding in GDB please see *Note
Character Sets::.

If the optional LENGTH argument is given, the string will be
fetched and encoded to the length of characters specified. If the
LENGTH argument is not provided, the string will be fetched and
encoded until a null of appropriate width is found.

-- Function: Value.fetch_lazy ()
If the `gdb.Value' object is currently a lazy value
(`gdb.Value.is_lazy' is `True'), then the value is fetched from
the inferior. Any errors that occur in the process will produce a
Python exception.

If the `gdb.Value' object is not a lazy value, this method has no
effect.

This method does not return a value.

File: gdb.info, Node: Types In Python, Next: Pretty Printing API, Prev: Values From Inferior, Up: Python API

23.3.2.5 Types In Python
.......................

GDB represents types from the inferior using the class `gdb.Type'.

The following type-related functions are available in the `gdb'
module:

-- Function: gdb.lookup_type (name [, block])
This function looks up a type by its NAME, which must be a string.

If BLOCK is given, then NAME is looked up in that scope.
Otherwise, it is searched for globally.

Ordinarily, this function will return an instance of `gdb.Type'.
If the named type cannot be found, it will throw an exception.

Integer types can be found without looking them up by name. *Note
Architectures In Python::, for the `integer_type' method.

If the type is a structure or class type, or an enum type, the fields
of that type can be accessed using the Python "dictionary syntax". For
example, if `some_type' is a `gdb.Type' instance holding a structure
type, you can access its `foo' field with:

bar = some_type['foo']

`bar' will be a `gdb.Field' object; see below under the description
of the `Type.fields' method for a description of the `gdb.Field' class.

An instance of `Type' has the following attributes:

-- Variable: Type.alignof
The alignment of this type, in bytes. Type alignment comes from
the debugging information; if it was not specified, then GDB will
use the relevant ABI to try to determine the alignment. In some
cases, even this is not possible, and zero will be returned.

-- Variable: Type.code
The type code for this type. The type code will be one of the
`TYPE_CODE_' constants defined below.

-- Variable: Type.dynamic
A boolean indicating whether this type is dynamic. In some
situations, such as Rust `enum' types or Ada variant records, the
concrete type of a value may vary depending on its contents. That
is, the declared type of a variable, or the type returned by
`gdb.lookup_type' may be dynamic; while the type of the variable's
value will be a concrete instance of that dynamic type.

For example, consider this code:
int n;
int array[n];

Here, at least conceptually (whether your compiler actually does
this is a separate issue), examining
`gdb.lookup_symbol("array", ...).type' could yield a `gdb.Type'
which reports a size of `None'. This is the dynamic type.

However, examining `gdb.parse_and_eval("array").type' would yield
a concrete type, whose length would be known.

-- Variable: Type.name
The name of this type. If this type has no name, then `None' is
returned.

-- Variable: Type.sizeof
The size of this type, in target `char' units. Usually, a
target's `char' type will be an 8-bit byte. However, on some
unusual platforms, this type may have a different size. A dynamic
type may not have a fixed size; in this case, this attribute's
value will be `None'.

-- Variable: Type.tag
The tag name for this type. The tag name is the name after
`struct', `union', or `enum' in C and C++; not all languages have
this concept. If this type has no tag name, then `None' is
returned.

-- Variable: Type.objfile
The `gdb.Objfile' that this type was defined in, or `None' if
there is no associated objfile.

-- Variable: Type.is_scalar
This property is `True' if the type is a scalar type, otherwise,
this property is `False'. Examples of non-scalar types include
structures, unions, and classes.

-- Variable: Type.is_signed
For scalar types (those for which `Type.is_scalar' is `True'),
this property is `True' if the type is signed, otherwise this
property is `False'.

Attempting to read this property for a non-scalar type (a type for
which `Type.is_scalar' is `False'), will raise a `ValueError'.

-- Variable: Type.is_array_like
A boolean indicating whether this type is array-like.

Some languages have array-like objects that are represented
internally as structures. For example, this is true for a Rust
slice type, or for an Ada unconstrained array. GDB may know about
these types. This determination is done based on the language
from which the type originated.

-- Variable: Type.is_string_like
A boolean indicating whether this type is string-like. Like
`Type.is_array_like', this is determined based on the originating
language of the type.

The following methods are provided:

-- Function: Type.fields ()
Return the fields of this type. The behavior depends on the type
code:

* For structure and union types, this method returns the fields.

* Enum types have one field per enum constant.

* Function and method types have one field per parameter. The
base types of C++ classes are also represented as fields.

* Array types have one field representing the array's range.

* If the type does not fit into one of these categories, a
`TypeError' is raised.

Each field is a `gdb.Field' object, with some pre-defined
attributes:
`bitpos'
This attribute is not available for `enum' or `static' (as in
C++) fields. The value is the position, counting in bits,
from the start of the containing type. Note that, in a
dynamic type, the position of a field may not be constant.
In this case, the value will be `None'. Also, a dynamic type
may have fields that do not appear in a corresponding
concrete type.

`enumval'
This attribute is only available for `enum' fields, and its
value is the enumeration member's integer representation.

`name'
The name of the field, or `None' for anonymous fields.

`artificial'
This is `True' if the field is artificial, usually meaning
that it was provided by the compiler and not the user. This
attribute is always provided, and is `False' if the field is
not artificial.

`is_base_class'
This is `True' if the field represents a base class of a C++
structure. This attribute is always provided, and is `False'
if the field is not a base class of the type that is the
argument of `fields', or if that type was not a C++ class.

`bitsize'
If the field is packed, or is a bitfield, then this will have
a non-zero value, which is the size of the field in bits.
Otherwise, this will be zero; in this case the field's size
is given by its type.

`type'
The type of the field. This is usually an instance of `Type',
but it can be `None' in some situations.

`parent_type'
The type which contains this field. This is an instance of
`gdb.Type'.

-- Function: Type.array (n1 [, n2])
Return a new `gdb.Type' object which represents an array of this
type. If one argument is given, it is the inclusive upper bound of
the array; in this case the lower bound is zero. If two arguments
are given, the first argument is the lower bound of the array, and
the second argument is the upper bound of the array. An array's
length must not be negative, but the bounds can be.

-- Function: Type.vector (n1 [, n2])
Return a new `gdb.Type' object which represents a vector of this
type. If one argument is given, it is the inclusive upper bound of
the vector; in this case the lower bound is zero. If two
arguments are given, the first argument is the lower bound of the
vector, and the second argument is the upper bound of the vector.
A vector's length must not be negative, but the bounds can be.

The difference between an `array' and a `vector' is that arrays
behave like in C: when used in expressions they decay to a pointer
to the first element whereas vectors are treated as first class
values.

-- Function: Type.const ()
Return a new `gdb.Type' object which represents a
`const'-qualified variant of this type.

-- Function: Type.volatile ()
Return a new `gdb.Type' object which represents a
`volatile'-qualified variant of this type.

-- Function: Type.unqualified ()
Return a new `gdb.Type' object which represents an unqualified
variant of this type. That is, the result is neither `const' nor
`volatile'.

-- Function: Type.range ()
Return a Python `Tuple' object that contains two elements: the low
bound of the argument type and the high bound of that type. If
the type does not have a range, GDB will raise a `gdb.error'
exception (*note Exception Handling::).

-- Function: Type.reference ()
Return a new `gdb.Type' object which represents a reference to this
type.

-- Function: Type.pointer ()
Return a new `gdb.Type' object which represents a pointer to this
type.

-- Function: Type.strip_typedefs ()
Return a new `gdb.Type' that represents the real type, after
removing all layers of typedefs.

-- Function: Type.target ()
Return a new `gdb.Type' object which represents the target type of
this type.

For a pointer type, the target type is the type of the pointed-to
object. For an array type (meaning C-like arrays), the target
type is the type of the elements of the array. For a function or
method type, the target type is the type of the return value. For
a complex type, the target type is the type of the elements. For
a typedef, the target type is the aliased type.

If the type does not have a target, this method will throw an
exception.

-- Function: Type.template_argument (n [, block])
If this `gdb.Type' is an instantiation of a template, this will
return a new `gdb.Value' or `gdb.Type' which represents the value
of the Nth template argument (indexed starting at 0).

If this `gdb.Type' is not a template type, or if the type has fewer
than N template arguments, this will throw an exception.
Ordinarily, only C++ code will have template types.

If BLOCK is given, then NAME is looked up in that scope.
Otherwise, it is searched for globally.

-- Function: Type.optimized_out ()
Return `gdb.Value' instance of this type whose value is optimized
out. This allows a frame decorator to indicate that the value of
an argument or a local variable is not known.

Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the `gdb' module:

`gdb.TYPE_CODE_PTR'
The type is a pointer.

`gdb.TYPE_CODE_ARRAY'
The type is an array.

`gdb.TYPE_CODE_STRUCT'
The type is a structure.

`gdb.TYPE_CODE_UNION'
The type is a union.

`gdb.TYPE_CODE_ENUM'
The type is an enum.

`gdb.TYPE_CODE_FLAGS'
A bit flags type, used for things such as status registers.

`gdb.TYPE_CODE_FUNC'
The type is a function.

`gdb.TYPE_CODE_INT'
The type is an integer type.

`gdb.TYPE_CODE_FLT'
A floating point type.

`gdb.TYPE_CODE_VOID'
The special type `void'.

`gdb.TYPE_CODE_SET'
A Pascal set type.

`gdb.TYPE_CODE_RANGE'
A range type, that is, an integer type with bounds.

`gdb.TYPE_CODE_STRING'
A string type. Note that this is only used for certain languages
with language-defined string types; C strings are not represented
this way.

`gdb.TYPE_CODE_BITSTRING'
A string of bits. It is deprecated.

`gdb.TYPE_CODE_ERROR'
An unknown or erroneous type.

`gdb.TYPE_CODE_METHOD'
A method type, as found in C++.

`gdb.TYPE_CODE_METHODPTR'
A pointer-to-member-function.

`gdb.TYPE_CODE_MEMBERPTR'
A pointer-to-member.

`gdb.TYPE_CODE_REF'
A reference type.

`gdb.TYPE_CODE_RVALUE_REF'
A C++11 rvalue reference type.

`gdb.TYPE_CODE_CHAR'
A character type.

`gdb.TYPE_CODE_BOOL'
A boolean type.

`gdb.TYPE_CODE_COMPLEX'
A complex float type.

`gdb.TYPE_CODE_TYPEDEF'
A typedef to some other type.

`gdb.TYPE_CODE_NAMESPACE'
A C++ namespace.

`gdb.TYPE_CODE_DECFLOAT'
A decimal floating point type.

`gdb.TYPE_CODE_INTERNAL_FUNCTION'
A function internal to GDB. This is the type used to represent
convenience functions.

`gdb.TYPE_CODE_XMETHOD'
A method internal to GDB. This is the type used to represent
xmethods (*note Writing an Xmethod::).

`gdb.TYPE_CODE_FIXED_POINT'
A fixed-point number.

`gdb.TYPE_CODE_NAMESPACE'
A Fortran namelist.

Further support for types is provided in the `gdb.types' Python
module (*note gdb.types::).

File: gdb.info, Node: Pretty Printing API, Next: Selecting Pretty-Printers, Prev: Types In Python, Up: Python API

23.3.2.6 Pretty Printing API
...........................

A pretty-printer is just an object that holds a value and implements a
specific interface, defined here. An example output is provided (*note
Pretty Printing::).

Because GDB did not document extensibility for pretty-printers, by
default GDB will assume that only the basic pretty-printer methods may
be available. The basic methods are marked as such, below.

To allow extensibility, GDB provides the `gdb.ValuePrinter' base
class. This class does not provide any attributes or behavior, but
instead serves as a tag that can be recognized by GDB. For such
printers, GDB reserves all attributes starting with a lower-case
letter. That is, in the future, GDB may add a new method or attribute
to the pretty-printer protocol, and `gdb.ValuePrinter'-based printers
are expected to handle this gracefully. A simple way to do this would
be to use a leading underscore (or two, following the Python
name-mangling scheme) to any attributes local to the implementation.

-- Function: pretty_printer.children (self)
GDB will call this method on a pretty-printer to compute the
children of the pretty-printer's value.

This method must return an object conforming to the Python iterator
protocol. Each item returned by the iterator must be a tuple
holding two elements. The first element is the "name" of the
child; the second element is the child's value. The value can be
any Python object which is convertible to a GDB value.

This is a basic method, and is optional. If it does not exist,
GDB will act as though the value has no children.

For efficiency, the `children' method should lazily compute its
results. This will let GDB read as few elements as necessary, for
example when various print settings (*note Print Settings::) or
`-var-list-children' (*note GDB/MI Variable Objects::) limit the
number of elements to be displayed.

Children may be hidden from display based on the value of `set
print max-depth' (*note Print Settings::).

-- Function: pretty_printer.display_hint (self)
The CLI may call this method and use its result to change the
formatting of a value. The result will also be supplied to an MI
consumer as a `displayhint' attribute of the variable being
printed.

This is a basic method, and is optional. If it does exist, this
method must return a string or the special value `None'.

Some display hints are predefined by GDB:

`array'
Indicate that the object being printed is "array-like". The
CLI uses this to respect parameters such as `set print
elements' and `set print array'.

`map'
Indicate that the object being printed is "map-like", and
that the children of this value can be assumed to alternate
between keys and values.

`string'
Indicate that the object being printed is "string-like". If
the printer's `to_string' method returns a Python string of
some kind, then GDB will call its internal language-specific
string-printing function to format the string. For the CLI
this means adding quotation marks, possibly escaping some
characters, respecting `set print elements', and the like.

The special value `None' causes GDB to apply the default display
rules.

-- Function: pretty_printer.to_string (self)
GDB will call this method to display the string representation of
the value passed to the object's constructor.

This is a basic method, and is optional.

When printing from the CLI, if the `to_string' method exists, then
GDB will prepend its result to the values returned by `children'.
Exactly how this formatting is done is dependent on the display
hint, and may change as more hints are added. Also, depending on
the print settings (*note Print Settings::), the CLI may print
just the result of `to_string' in a stack trace, omitting the
result of `children'.

If this method returns a string, it is printed verbatim.

Otherwise, if this method returns an instance of `gdb.Value', then
GDB prints this value. This may result in a call to another
pretty-printer.

If instead the method returns a Python value which is convertible
to a `gdb.Value', then GDB performs the conversion and prints the
resulting value. Again, this may result in a call to another
pretty-printer. Python scalars (integers, floats, and booleans)
and strings are convertible to `gdb.Value'; other types are not.

Finally, if this method returns `None' then no further operations
are performed in this method and nothing is printed.

If the result is not one of these types, an exception is raised.

-- Function: pretty_printer.num_children ()
This is not a basic method, so GDB will only ever call it for
objects derived from `gdb.ValuePrinter'.

If available, this method should return the number of children.
`None' may be returned if the number can't readily be computed.

-- Function: pretty_printer.child (n)
This is not a basic method, so GDB will only ever call it for
objects derived from `gdb.ValuePrinter'.

If available, this method should return the child item (that is, a
tuple holding the name and value of this child) indicated by N.
Indices start at zero.

GDB provides a function which can be used to look up the default
pretty-printer for a `gdb.Value':

-- Function: gdb.default_visualizer (value)
This function takes a `gdb.Value' object as an argument. If a
pretty-printer for this value exists, then it is returned. If no
such printer exists, then this returns `None'.

Normally, a pretty-printer can respect the user's print settings
(including temporarily applied settings, such as `/x') simply by
calling `Value.format_string' (*note Values From Inferior::). However,
these settings can also be queried directly:

-- Function: gdb.print_options ()
Return a dictionary whose keys are the valid keywords that can be
given to `Value.format_string', and whose values are the user's
settings. During a `print' or other operation, the values will
reflect any flags that are temporarily in effect.

(gdb) python print (gdb.print_options ()['max_elements'])
200

File: gdb.info, Node: Selecting Pretty-Printers, Next: Writing a Pretty-Printer, Prev: Pretty Printing API, Up: Python API

23.3.2.7 Selecting Pretty-Printers
.................................

GDB provides several ways to register a pretty-printer: globally, per
program space, and per objfile. When choosing how to register your
pretty-printer, a good rule is to register it with the smallest scope
possible: that is prefer a specific objfile first, then a program
space, and only register a printer globally as a last resort.

-- Variable: gdb.pretty_printers
The Python list `gdb.pretty_printers' contains an array of
functions or callable objects that have been registered via
addition as a pretty-printer. Printers in this list are called
`global' printers, they're available when debugging all inferiors.

Each `gdb.Progspace' contains a `pretty_printers' attribute. Each
`gdb.Objfile' also contains a `pretty_printers' attribute.

Each function on these lists is passed a single `gdb.Value' argument
and should return a pretty-printer object conforming to the interface
definition above (*note Pretty Printing API::). If a function cannot
create a pretty-printer for the value, it should return `None'.

GDB first checks the `pretty_printers' attribute of each
`gdb.Objfile' in the current program space and iteratively calls each
enabled lookup routine in the list for that `gdb.Objfile' until it
receives a pretty-printer object. If no pretty-printer is found in the
objfile lists, GDB then searches the pretty-printer list of the current
program space, calling each enabled function until an object is
returned. After these lists have been exhausted, it tries the global
`gdb.pretty_printers' list, again calling each enabled function until an
object is returned.

The order in which the objfiles are searched is not specified. For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a printer
object is returned.

For various reasons a pretty-printer may not work. For example, the
underlying data structure may have changed and the pretty-printer is
out of date.

The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if `print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.

Pretty-printers are enabled and disabled by attaching an `enabled'
attribute to the registered function or callable object. If this
attribute is present and its value is `False', the printer is disabled,
otherwise the printer is enabled.

File: gdb.info, Node: Writing a Pretty-Printer, Next: Type Printing API, Prev: Selecting Pretty-Printers, Up: Python API

23.3.2.8 Writing a Pretty-Printer
................................

A pretty-printer consists of two parts: a lookup function to detect if
the type is supported, and the printer itself.

Here is an example showing how a `std::string' printer might be
written. *Note Pretty Printing API::, for details on the API this class
must provide. Note that this example uses the `gdb.ValuePrinter' base
class, and is careful to use a leading underscore for its local state.

class StdStringPrinter(gdb.ValuePrinter):
"Print a std::string"

def __init__(self, val):
self.__val = val

def to_string(self):
return self.__val['_M_dataplus']['_M_p']

def display_hint(self):
return 'string'

And here is an example showing how a lookup function for the printer
example above might be written.

def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag is None:
return None
regex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)
return None

The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a printer object. If not, it
returns `None'.

We recommend that you put your core pretty-printers into a Python
package. If your pretty-printers are for use with a library, we
further recommend embedding a version number into the package name.
This practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.

You should write auto-loaded code (*note Python Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of `import's of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.

Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Python package name will ensure that
GDB is able to load both sets of printers simultaneously. Then,
because the search for pretty-printers is done by objfile, and because
your auto-loaded code took care to register your library's printers
with a specific objfile, GDB will find the correct printers for the
specific version of the library used by each inferior.

To continue the `std::string' example (*note Pretty Printing API::),
this code might appear in `gdb.libstdcxx.v6':

def register_printers(objfile):
objfile.pretty_printers.append(str_lookup_function)

And then the corresponding contents of the auto-load file would be:

import gdb.libstdcxx.v6
gdb.libstdcxx.v6.register_printers(gdb.current_objfile())

The previous example illustrates a basic pretty-printer. There are
a few things that can be improved on. The printer doesn't have a name,
making it hard to identify in a list of installed printers. The lookup
function has a name, but lookup functions can have arbitrary, even
identical, names.

Second, the printer only handles one type, whereas a library
typically has several types. One could install a lookup function for
each desired type in the library, but one could also have a single
lookup function recognize several types. The latter is the
conventional way this is handled. If a pretty-printer can handle
multiple data types, then its "subprinters" are the printers for the
individual data types.

The `gdb.printing' module provides a formal way of solving these
problems (*note gdb.printing::). Here is another example that handles
multiple types.

These are the types we are going to pretty-print:

struct foo { int a, b; };
struct bar { struct foo x, y; };

Here are the printers:

class fooPrinter(gdb.ValuePrinter):
"""Print a foo object."""

def __init__(self, val):
self.__val = val

def to_string(self):
return ("a=<" + str(self.__val["a"]) +
"> b=<" + str(self.__val["b"]) + ">")

class barPrinter(gdb.ValuePrinter):
"""Print a bar object."""

def __init__(self, val):
self.__val = val

def to_string(self):
return ("x=<" + str(self.__val["x"]) +
"> y=<" + str(self.__val["y"]) + ">")

This example doesn't need a lookup function, that is handled by the
`gdb.printing' module. Instead a function is provided to build up the
object that handles the lookup.

import gdb.printing

def build_pretty_printer():
pp = gdb.printing.RegexpCollectionPrettyPrinter(
"my_library")
pp.add_printer('foo', '^foo$', fooPrinter)
pp.add_printer('bar', '^bar$', barPrinter)
return pp

And here is the autoload support:

import gdb.printing
import my_library
gdb.printing.register_pretty_printer(
gdb.current_objfile(),
my_library.build_pretty_printer())

Finally, when this printer is loaded into GDB, here is the
corresponding output of `info pretty-printer':

(gdb) info pretty-printer
my_library.so:
my_library
foo
bar

File: gdb.info, Node: Type Printing API, Next: Frame Filter API, Prev: Writing a Pretty-Printer, Up: Python API

23.3.2.9 Type Printing API
.........................

GDB provides a way for Python code to customize type display. This is
mainly useful for substituting canonical typedef names for types.

A "type printer" is just a Python object conforming to a certain
protocol. A simple base class implementing the protocol is provided;
see *Note gdb.types::. A type printer must supply at least:

-- Instance Variable of type_printer: enabled
A boolean which is True if the printer is enabled, and False
otherwise. This is manipulated by the `enable type-printer' and
`disable type-printer' commands.

-- Instance Variable of type_printer: name
The name of the type printer. This must be a string. This is
used by the `enable type-printer' and `disable type-printer'
commands.

-- Method on type_printer: instantiate (self)
This is called by GDB at the start of type-printing. It is only
called if the type printer is enabled. This method must return a
new object that supplies a `recognize' method, as described below.

When displaying a type, say via the `ptype' command, GDB will
compute a list of type recognizers. This is done by iterating first
over the per-objfile type printers (*note Objfiles In Python::),
followed by the per-progspace type printers (*note Progspaces In
Python::), and finally the global type printers.

GDB will call the `instantiate' method of each enabled type printer.
If this method returns `None', then the result is ignored; otherwise,
it is appended to the list of recognizers.

Then, when GDB is going to display a type name, it iterates over the
list of recognizers. For each one, it calls the recognition function,
stopping if the function returns a non-`None' value. The recognition
function is defined as:

-- Method on type_recognizer: recognize (self, type)
If TYPE is not recognized, return `None'. Otherwise, return a
string which is to be printed as the name of TYPE. The TYPE
argument will be an instance of `gdb.Type' (*note Types In
Python::).

GDB uses this two-pass approach so that type printers can
efficiently cache information without holding on to it too long. For
example, it can be convenient to look up type information in a type
printer and hold it for a recognizer's lifetime; if a single pass were
done then type printers would have to make use of the event system in
order to avoid holding information that could become stale as the
inferior changed.

File: gdb.info, Node: Frame Filter API, Next: Frame Decorator API, Prev: Type Printing API, Up: Python API

23.3.2.10 Filtering Frames
.........................

Frame filters are Python objects that manipulate the visibility of a
frame or frames when a backtrace (*note Backtrace::) is printed by GDB.

Only commands that print a backtrace, or, in the case of GDB/MI
commands (*note GDB/MI::), those that return a collection of frames are
affected. The commands that work with frame filters are:

`backtrace' (*note The backtrace command: backtrace-command.),
`-stack-list-frames' (*note The -stack-list-frames command:
-stack-list-frames.), `-stack-list-variables' (*note The
-stack-list-variables command: -stack-list-variables.),
`-stack-list-arguments' *note The -stack-list-arguments command:
-stack-list-arguments.) and `-stack-list-locals' (*note The
-stack-list-locals command: -stack-list-locals.).

A frame filter works by taking an iterator as an argument, applying
actions to the contents of that iterator, and returning another
iterator (or, possibly, the same iterator it was provided in the case
where the filter does not perform any operations). Typically, frame
filters utilize tools such as the Python's `itertools' module to work
with and create new iterators from the source iterator. Regardless of
how a filter chooses to apply actions, it must not alter the underlying
GDB frame or frames, or attempt to alter the call-stack within GDB.
This preserves data integrity within GDB. Frame filters are executed
on a priority basis and care should be taken that some frame filters
may have been executed before, and that some frame filters will be
executed after.

An important consideration when designing frame filters, and well
worth reflecting upon, is that frame filters should avoid unwinding the
call stack if possible. Some stacks can run very deep, into the tens
of thousands in some cases. To search every frame when a frame filter
executes may be too expensive at that step. The frame filter cannot
know how many frames it has to iterate over, and it may have to iterate
through them all. This ends up duplicating effort as GDB performs this
iteration when it prints the frames. If the filter can defer unwinding
frames until frame decorators are executed, after the last filter has
executed, it should. *Note Frame Decorator API::, for more information
on decorators. Also, there are examples for both frame decorators and
filters in later chapters. *Note Writing a Frame Filter::, for more
information.

The Python dictionary `gdb.frame_filters' contains key/object
pairings that comprise a frame filter. Frame filters in this
dictionary are called `global' frame filters, and they are available
when debugging all inferiors. These frame filters must register with
the dictionary directly. In addition to the `global' dictionary, there
are other dictionaries that are loaded with different inferiors via
auto-loading (*note Python Auto-loading::). The two other areas where
frame filter dictionaries can be found are: `gdb.Progspace' which
contains a `frame_filters' dictionary attribute, and each `gdb.Objfile'
object which also contains a `frame_filters' dictionary attribute.

When a command is executed from GDB that is compatible with frame
filters, GDB combines the `global', `gdb.Progspace' and all
`gdb.Objfile' dictionaries currently loaded. All of the `gdb.Objfile'
dictionaries are combined, as several frames, and thus several object
files, might be in use. GDB then prunes any frame filter whose
`enabled' attribute is `False'. This pruned list is then sorted
according to the `priority' attribute in each filter.

Once the dictionaries are combined, pruned and sorted, GDB creates
an iterator which wraps each frame in the call stack in a
`FrameDecorator' object, and calls each filter in order. The output
from the previous filter will always be the input to the next filter,
and so on.

Frame filters have a mandatory interface which each frame filter must
implement, defined here:

-- Function: FrameFilter.filter (iterator)
GDB will call this method on a frame filter when it has reached
the order in the priority list for that filter.

For example, if there are four frame filters:

Name Priority

Filter1 5
Filter2 10
Filter3 100
Filter4 1

The order that the frame filters will be called is:

Filter3 -> Filter2 -> Filter1 -> Filter4

Note that the output from `Filter3' is passed to the input of
`Filter2', and so on.

This `filter' method is passed a Python iterator. This iterator
contains a sequence of frame decorators that wrap each
`gdb.Frame', or a frame decorator that wraps another frame
decorator. The first filter that is executed in the sequence of
frame filters will receive an iterator entirely comprised of
default `FrameDecorator' objects. However, after each frame
filter is executed, the previous frame filter may have wrapped
some or all of the frame decorators with their own frame
decorator. As frame decorators must also conform to a mandatory
interface, these decorators can be assumed to act in a uniform
manner (*note Frame Decorator API::).

This method must return an object conforming to the Python iterator
protocol. Each item in the iterator must be an object conforming
to the frame decorator interface. If a frame filter does not wish
to perform any operations on this iterator, it should return that
iterator untouched.

This method is not optional. If it does not exist, GDB will raise
and print an error.

-- Variable: FrameFilter.name
The `name' attribute must be Python string which contains the name
of the filter displayed by GDB (*note Frame Filter Management::).
This attribute may contain any combination of letters or numbers.
Care should be taken to ensure that it is unique. This attribute
is mandatory.

-- Variable: FrameFilter.enabled
The `enabled' attribute must be Python boolean. This attribute
indicates to GDB whether the frame filter is enabled, and should
be considered when frame filters are executed. If `enabled' is
`True', then the frame filter will be executed when any of the
backtrace commands detailed earlier in this chapter are executed.
If `enabled' is `False', then the frame filter will not be
executed. This attribute is mandatory.

-- Variable: FrameFilter.priority
The `priority' attribute must be Python integer. This attribute
controls the order of execution in relation to other frame filters.
There are no imposed limits on the range of `priority' other than
it must be a valid integer. The higher the `priority' attribute,
the sooner the frame filter will be executed in relation to other
frame filters. Although `priority' can be negative, it is
recommended practice to assume zero is the lowest priority that a
frame filter can be assigned. Frame filters that have the same
priority are executed in unsorted order in that priority slot.
This attribute is mandatory. 100 is a good default priority.

File: gdb.info, Node: Frame Decorator API, Next: Writing a Frame Filter, Prev: Frame Filter API, Up: Python API

23.3.2.11 Decorating Frames
..........................

Frame decorators are sister objects to frame filters (*note Frame
Filter API::). Frame decorators are applied by a frame filter and can
only be used in conjunction with frame filters.

The purpose of a frame decorator is to customize the printed content
of each `gdb.Frame' in commands where frame filters are executed. This
concept is called decorating a frame. Frame decorators decorate a
`gdb.Frame' with Python code contained within each API call. This
separates the actual data contained in a `gdb.Frame' from the decorated
data produced by a frame decorator. This abstraction is necessary to
maintain integrity of the data contained in each `gdb.Frame'.

Frame decorators have a mandatory interface, defined below.

GDB already contains a frame decorator called `FrameDecorator'.
This contains substantial amounts of boilerplate code to decorate the
content of a `gdb.Frame'. It is recommended that other frame
decorators inherit and extend this object, and only to override the
methods needed.

`FrameDecorator' is defined in the Python module
`gdb.FrameDecorator', so your code can import it like:
from gdb.FrameDecorator import FrameDecorator

-- Function: FrameDecorator.elided (self)
The `elided' method groups frames together in a hierarchical
system. An example would be an interpreter, where multiple
low-level frames make up a single call in the interpreted
language. In this example, the frame filter would elide the
low-level frames and present a single high-level frame,
representing the call in the interpreted language, to the user.

The `elided' function must return an iterable and this iterable
must contain the frames that are being elided wrapped in a suitable
frame decorator. If no frames are being elided this function may
return an empty iterable, or `None'. Elided frames are indented
from normal frames in a `CLI' backtrace, or in the case of GDB/MI,
are placed in the `children' field of the eliding frame.

It is the frame filter's task to also filter out the elided frames
from the source iterator. This will avoid printing the frame
twice.

-- Function: FrameDecorator.function (self)
This method returns the name of the function in the frame that is
to be printed.

This method must return a Python string describing the function, or
`None'.

If this function returns `None', GDB will not print any data for
this field.

-- Function: FrameDecorator.address (self)
This method returns the address of the frame that is to be printed.

This method must return a Python numeric integer type of sufficient
size to describe the address of the frame, or `None'.

If this function returns a `None', GDB will not print any data for
this field.

-- Function: FrameDecorator.filename (self)
This method returns the filename and path associated with this
frame.

This method must return a Python string containing the filename and
the path to the object file backing the frame, or `None'.

If this function returns a `None', GDB will not print any data for
this field.

-- Function: FrameDecorator.line (self):
This method returns the line number associated with the current
position within the function addressed by this frame.

This method must return a Python integer type, or `None'.

If this function returns a `None', GDB will not print any data for
this field.

-- Function: FrameDecorator.frame_args (self)
This method must return an iterable, or `None'. Returning an
empty iterable, or `None' means frame arguments will not be
printed for this frame. This iterable must contain objects that
implement two methods, described here.

This object must implement a `symbol' method which takes a single
`self' parameter and must return a `gdb.Symbol' (*note Symbols In
Python::), or a Python string. The object must also implement a
`value' method which takes a single `self' parameter and must
return a `gdb.Value' (*note Values From Inferior::), a Python
value, or `None'. If the `value' method returns `None', and the
`argument' method returns a `gdb.Symbol', GDB will look-up and
print the value of the `gdb.Symbol' automatically.

A brief example:

class SymValueWrapper():

def __init__(self, symbol, value):
self.sym = symbol
self.val = value

def value(self):
return self.val

def symbol(self):
return self.sym

class SomeFrameDecorator()
...
...
def frame_args(self):
args = []
try:
block = self.inferior_frame.block()
except:
return None

# Iterate over all symbols in a block. Only add
# symbols that are arguments.
for sym in block:
if not sym.is_argument:
continue
args.append(SymValueWrapper(sym,None))

# Add example synthetic argument.
args.append(SymValueWrapper(``foo'', 42))

return args

-- Function: FrameDecorator.frame_locals (self)
This method must return an iterable or `None'. Returning an empty
iterable, or `None' means frame local arguments will not be
printed for this frame.

The object interface, the description of the various strategies for
reading frame locals, and the example are largely similar to those
described in the `frame_args' function, (*note The frame filter
frame_args function: frame_args.). Below is a modified example:

class SomeFrameDecorator()
...
...
def frame_locals(self):
vars = []
try:
block = self.inferior_frame.block()
except:
return None

# Iterate over all symbols in a block. Add all
# symbols, except arguments.
for sym in block:
if sym.is_argument:
continue
vars.append(SymValueWrapper(sym,None))

# Add an example of a synthetic local variable.
vars.append(SymValueWrapper(``bar'', 99))

return vars

-- Function: FrameDecorator.inferior_frame (self):
This method must return the underlying `gdb.Frame' that this frame
decorator is decorating. GDB requires the underlying frame for
internal frame information to determine how to print certain
values when printing a frame.

File: gdb.info, Node: Writing a Frame Filter, Next: Unwinding Frames in Python, Prev: Frame Decorator API, Up: Python API

23.3.2.12 Writing a Frame Filter
...............................

There are three basic elements that a frame filter must implement: it
must correctly implement the documented interface (*note Frame Filter
API::), it must register itself with GDB, and finally, it must decide
if it is to work on the data provided by GDB. In all cases, whether it
works on the iterator or not, each frame filter must return an
iterator. A bare-bones frame filter follows the pattern in the
following example.

import gdb

class FrameFilter():

def __init__(self):
# Frame filter attribute creation.
#
# 'name' is the name of the filter that GDB will display.
#
# 'priority' is the priority of the filter relative to other
# filters.
#
# 'enabled' is a boolean that indicates whether this filter is
# enabled and should be executed.

self.name = "Foo"
self.priority = 100
self.enabled = True

# Register this frame filter with the global frame_filters
# dictionary.
gdb.frame_filters[self.name] = self

def filter(self, frame_iter):
# Just return the iterator.
return frame_iter

The frame filter in the example above implements the three
requirements for all frame filters. It implements the API, self
registers, and makes a decision on the iterator (in this case, it just
returns the iterator untouched).

The first step is attribute creation and assignment, and as shown in
the comments the filter assigns the following attributes: `name',
`priority' and whether the filter should be enabled with the `enabled'
attribute.

The second step is registering the frame filter with the dictionary
or dictionaries that the frame filter has interest in. As shown in the
comments, this filter just registers itself with the global dictionary
`gdb.frame_filters'. As noted earlier, `gdb.frame_filters' is a
dictionary that is initialized in the `gdb' module when GDB starts.
What dictionary a filter registers with is an important consideration.
Generally, if a filter is specific to a set of code, it should be
registered either in the `objfile' or `progspace' dictionaries as they
are specific to the program currently loaded in GDB. The global
dictionary is always present in GDB and is never unloaded. Any filters
registered with the global dictionary will exist until GDB exits. To
avoid filters that may conflict, it is generally better to register
frame filters against the dictionaries that more closely align with the
usage of the filter currently in question. *Note Python
Auto-loading::, for further information on auto-loading Python scripts.

GDB takes a hands-off approach to frame filter registration,
therefore it is the frame filter's responsibility to ensure
registration has occurred, and that any exceptions are handled
appropriately. In particular, you may wish to handle exceptions
relating to Python dictionary key uniqueness. It is mandatory that the
dictionary key is the same as frame filter's `name' attribute. When a
user manages frame filters (*note Frame Filter Management::), the names
GDB will display are those contained in the `name' attribute.

The final step of this example is the implementation of the `filter'
method. As shown in the example comments, we define the `filter'
method and note that the method must take an iterator, and also must
return an iterator. In this bare-bones example, the frame filter is
not very useful as it just returns the iterator untouched. However
this is a valid operation for frame filters that have the `enabled'
attribute set, but decide not to operate on any frames.

In the next example, the frame filter operates on all frames and
utilizes a frame decorator to perform some work on the frames. *Note
Frame Decorator API::, for further information on the frame decorator
interface.

This example works on inlined frames. It highlights frames which are
inlined by tagging them with an "[inlined]" tag. By applying a frame
decorator to all frames with the Python `itertools imap' method, the
example defers actions to the frame decorator. Frame decorators are
only processed when GDB prints the backtrace.

This introduces a new decision making topic: whether to perform
decision making operations at the filtering step, or at the printing
step. In this example's approach, it does not perform any filtering
decisions at the filtering step beyond mapping a frame decorator to
each frame. This allows the actual decision making to be performed
when each frame is printed. This is an important consideration, and
well worth reflecting upon when designing a frame filter. An issue
that frame filters should avoid is unwinding the stack if possible.
Some stacks can run very deep, into the tens of thousands in some
cases. To search every frame to determine if it is inlined ahead of
time may be too expensive at the filtering step. The frame filter
cannot know how many frames it has to iterate over, and it would have
to iterate through them all. This ends up duplicating effort as GDB
performs this iteration when it prints the frames.

In this example decision making can be deferred to the printing step.
As each frame is printed, the frame decorator can examine each frame in
turn when GDB iterates. From a performance viewpoint, this is the most
appropriate decision to make as it avoids duplicating the effort that
the printing step would undertake anyway. Also, if there are many
frame filters unwinding the stack during filtering, it can
substantially delay the printing of the backtrace which will result in
large memory usage, and a poor user experience.

class InlineFilter():

def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self

def filter(self, frame_iter):
frame_iter = itertools.imap(InlinedFrameDecorator,
frame_iter)
return frame_iter

This frame filter is somewhat similar to the earlier example, except
that the `filter' method applies a frame decorator object called
`InlinedFrameDecorator' to each element in the iterator. The `imap'
Python method is light-weight. It does not proactively iterate over
the iterator, but rather creates a new iterator which wraps the
existing one.

Below is the frame decorator for this example.

class InlinedFrameDecorator(FrameDecorator):

def __init__(self, fobj):
super(InlinedFrameDecorator, self).__init__(fobj)

def function(self):
frame = self.inferior_frame()
name = str(frame.name())

if frame.type() == gdb.INLINE_FRAME:
name = name + " [inlined]"

return name

This frame decorator only defines and overrides the `function'
method. It lets the supplied `FrameDecorator', which is shipped with
GDB, perform the other work associated with printing this frame.

The combination of these two objects create this output from a
backtrace:

#0 0x004004e0 in bar () at inline.c:11
#1 0x00400566 in max [inlined] (b=6, a=12) at inline.c:21
#2 0x00400566 in main () at inline.c:31

So in the case of this example, a frame decorator is applied to all
frames, regardless of whether they may be inlined or not. As GDB
iterates over the iterator produced by the frame filters, GDB executes
each frame decorator which then makes a decision on what to print in
the `function' callback. Using a strategy like this is a way to defer
decisions on the frame content to printing time.

Eliding Frames
--------------

It might be that the above example is not desirable for representing
inlined frames, and a hierarchical approach may be preferred. If we
want to hierarchically represent frames, the `elided' frame decorator
interface might be preferable.

This example approaches the issue with the `elided' method. This
example is quite long, but very simplistic. It is out-of-scope for
this section to write a complete example that comprehensively covers
all approaches of finding and printing inlined frames. However, this
example illustrates the approach an author might use.

This example comprises of three sections.

class InlineFrameFilter():

def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self

def filter(self, frame_iter):
return ElidingInlineIterator(frame_iter)

This frame filter is very similar to the other examples. The only
difference is this frame filter is wrapping the iterator provided to it
(`frame_iter') with a custom iterator called `ElidingInlineIterator'.
This again defers actions to when GDB prints the backtrace, as the
iterator is not traversed until printing.

The iterator for this example is as follows. It is in this section
of the example where decisions are made on the content of the backtrace.

class ElidingInlineIterator:
def __init__(self, ii):
self.input_iterator = ii

def __iter__(self):
return self

def next(self):
frame = next(self.input_iterator)

if frame.inferior_frame().type() != gdb.INLINE_FRAME:
return frame

try:
eliding_frame = next(self.input_iterator)
except StopIteration:
return frame
return ElidingFrameDecorator(eliding_frame, [frame])

This iterator implements the Python iterator protocol. When the
`next' function is called (when GDB prints each frame), the iterator
checks if this frame decorator, `frame', is wrapping an inlined frame.
If it is not, it returns the existing frame decorator untouched. If it
is wrapping an inlined frame, it assumes that the inlined frame was
contained within the next oldest frame, `eliding_frame', which it
fetches. It then creates and returns a frame decorator,
`ElidingFrameDecorator', which contains both the elided frame, and the
eliding frame.

class ElidingInlineDecorator(FrameDecorator):

def __init__(self, frame, elided_frames):
super(ElidingInlineDecorator, self).__init__(frame)
self.frame = frame
self.elided_frames = elided_frames

def elided(self):
return iter(self.elided_frames)

This frame decorator overrides one function and returns the inlined
frame in the `elided' method. As before it lets `FrameDecorator' do
the rest of the work involved in printing this frame. This produces
the following output.

#0 0x004004e0 in bar () at inline.c:11
#2 0x00400529 in main () at inline.c:25
#1 0x00400529 in max (b=6, a=12) at inline.c:15

In that output, `max' which has been inlined into `main' is printed
hierarchically. Another approach would be to combine the `function'
method, and the `elided' method to both print a marker in the inlined
frame, and also show the hierarchical relationship.

File: gdb.info, Node: Unwinding Frames in Python, Next: Xmethods In Python, Prev: Writing a Frame Filter, Up: Python API

23.3.2.13 Unwinding Frames in Python
...................................

In GDB terminology "unwinding" is the process of finding the previous
frame (that is, caller's) from the current one. An unwinder has three
methods. The first one checks if it can handle given frame ("sniff"
it). For the frames it can sniff an unwinder provides two additional
methods: it can return frame's ID, and it can fetch registers from the
previous frame. A running GDB maintains a list of the unwinders and
calls each unwinder's sniffer in turn until it finds the one that
recognizes the current frame. There is an API to register an unwinder.

The unwinders that come with GDB handle standard frames. However,
mixed language applications (for example, an application running Java
Virtual Machine) sometimes use frame layouts that cannot be handled by
the GDB unwinders. You can write Python code that can handle such
custom frames.

You implement a frame unwinder in Python as a class with which has
two attributes, `name' and `enabled', with obvious meanings, and a
single method `__call__', which examines a given frame and returns an
object (an instance of `gdb.UnwindInfo class)' describing it. If an
unwinder does not recognize a frame, it should return `None'. The code
in GDB that enables writing unwinders in Python uses this object to
return frame's ID and previous frame registers when GDB core asks for
them.

An unwinder should do as little work as possible. Some otherwise
innocuous operations can cause problems (even crashes, as this code is
not well-hardened yet). For example, making an inferior call from an
unwinder is unadvisable, as an inferior call will reset GDB's stack
unwinding process, potentially causing re-entrant unwinding.

Unwinder Input
--------------

An object passed to an unwinder (a `gdb.PendingFrame' instance)
provides a method to read frame's registers:

-- Function: PendingFrame.read_register (register)
This method returns the contents of REGISTER in the frame as a
`gdb.Value' object. For a description of the acceptable values of
REGISTER see *Note Frame.read_register: gdbpy_frame_read_register.
If REGISTER does not name a register for the current
architecture, this method will throw an exception.

Note that this method will always return a `gdb.Value' for a valid
register name. This does not mean that the value will be valid.
For example, you may request a register that an earlier unwinder
could not unwind--the value will be unavailable. Instead, the
`gdb.Value' returned from this method will be lazy; that is, its
underlying bits will not be fetched until it is first used. So,
attempting to use such a value will cause an exception at the
point of use.

The type of the returned `gdb.Value' depends on the register and
the architecture. It is common for registers to have a scalar
type, like `long long'; but many other types are possible, such as
pointer, pointer-to-function, floating point or vector types.

It also provides a factory method to create a `gdb.UnwindInfo'
instance to be returned to GDB:

-- Function: PendingFrame.create_unwind_info (frame_id)
Returns a new `gdb.UnwindInfo' instance identified by given
FRAME_ID. The FRAME_ID is used internally by GDB to identify the
frames within the current thread's stack. The attributes of
FRAME_ID determine what type of frame is created within GDB:

`sp, pc'
The frame is identified by the given stack address and PC.
The stack address must be chosen so that it is constant
throughout the lifetime of the frame, so a typical choice is
the value of the stack pointer at the start of the
function--in the DWARF standard, this would be the "Call
Frame Address".

This is the most common case by far. The other cases are
documented for completeness but are only useful in
specialized situations.

`sp, pc, special'
The frame is identified by the stack address, the PC, and a
"special" address. The special address is used on
architectures that can have frames that do not change the
stack, but which are still distinct, for example the IA-64,
which has a second stack for registers. Both SP and SPECIAL
must be constant throughout the lifetime of the frame.

`sp'
The frame is identified by the stack address only. Any other
stack frame with a matching SP will be considered to match
this frame. Inside gdb, this is called a "wild frame". You
will never need this.

Each attribute value should either be an instance of `gdb.Value'
or an integer.

A helper class is provided in the `gdb.unwinder' module that can
be used to represent a frame-id (*note gdb.unwinder.FrameId::).

-- Function: PendingFrame.architecture ()
Return the `gdb.Architecture' (*note Architectures In Python::)
for this `gdb.PendingFrame'. This represents the architecture of
the particular frame being unwound.

-- Function: PendingFrame.level ()
Return an integer, the stack frame level for this frame. *Note
Stack Frames: Frames.

-- Function: PendingFrame.name ()
Returns the function name of this pending frame, or `None' if it
can't be obtained.

-- Function: PendingFrame.is_valid ()
Returns true if the `gdb.PendingFrame' object is valid, false if
not. A pending frame object becomes invalid when the call to the
unwinder, for which the pending frame was created, returns.

All `gdb.PendingFrame' methods, except this one, will raise an
exception if the pending frame object is invalid at the time the
method is called.

-- Function: PendingFrame.pc ()
Returns the pending frame's resume address.

-- Function: PendingFrame.block ()
Return the pending frame's code block (*note Blocks In Python::).
If the frame does not have a block - for example, if there is no
debugging information for the code in question - then this will
raise a `RuntimeError' exception.

-- Function: PendingFrame.function ()
Return the symbol for the function corresponding to this pending
frame. *Note Symbols In Python::.

-- Function: PendingFrame.find_sal ()
Return the pending frame's symtab and line object (*note Symbol
Tables In Python::).

-- Function: PendingFrame.language ()
Return the language of this frame, as a string, or None.

Unwinder Output: UnwindInfo
---------------------------

Use `PendingFrame.create_unwind_info' method described above to create
a `gdb.UnwindInfo' instance. Use the following method to specify
caller registers that have been saved in this frame:

-- Function: gdb.UnwindInfo.add_saved_register (register, value)
REGISTER identifies the register, for a description of the
acceptable values see *Note Frame.read_register:
gdbpy_frame_read_register. VALUE is a register value (a
`gdb.Value' object).

The `gdb.unwinder' Module
-------------------------

GDB comes with a `gdb.unwinder' module which contains the following
classes:

-- class: gdb.unwinder.Unwinder
The `Unwinder' class is a base class from which user created
unwinders can derive, though it is not required that unwinders
derive from this class, so long as any user created unwinder has
the required `name' and `enabled' attributes.

-- Function: gdb.unwinder.Unwinder.__init__(name)
The NAME is a string used to reference this unwinder within
some GDB commands (*note Managing Registered Unwinders::).

-- Variable: gdb.unwinder.name
A read-only attribute which is a string, the name of this
unwinder.

-- Variable: gdb.unwinder.enabled
A modifiable attribute containing a boolean; when `True', the
unwinder is enabled, and will be used by GDB. When `False',
the unwinder has been disabled, and will not be used.

-- class: gdb.unwinder.FrameId
This is a class suitable for being used as the frame-id when
calling `gdb.PendingFrame.create_unwind_info'. It is not required
to use this class, any class with the required attribute (*note
gdb.PendingFrame.create_unwind_info::) will be accepted, but in
most cases this class will be sufficient.

`gdb.unwinder.FrameId' has the following method:

-- Function: gdb.unwinder.FrameId.__init__(sp, pc, special =
`None')
The SP and PC arguments are required and should be either a
`gdb.Value' object, or an integer.

The SPECIAL argument is optional; if specified, it should be a
`gdb.Value' object, or an integer.

`gdb.unwinder.FrameId' has the following read-only attributes:

-- Variable: gdb.unwinder.sp
The SP value passed to the constructor.

-- Variable: gdb.unwinder.pc
The PC value passed to the constructor.

-- Variable: gdb.unwinder.special
The SPECIAL value passed to the constructor, or `None' if no
such value was passed.

Registering an Unwinder
-----------------------

Object files and program spaces can have unwinders registered with
them. In addition, you can register unwinders globally.

The `gdb.unwinders' module provides the function to register an
unwinder:

-- Function: gdb.unwinder.register_unwinder (locus, unwinder,
replace=False)
LOCUS specifies to which unwinder list to prepend the UNWINDER.
It can be either an object file (*note Objfiles In Python::), a
program space (*note Progspaces In Python::), or `None', in which
case the unwinder is registered globally. The newly added
UNWINDER will be called before any other unwinder from the same
locus. Two unwinders in the same locus cannot have the same name.
An attempt to add an unwinder with an already existing name
raises an exception unless REPLACE is `True', in which case the
old unwinder is deleted and the new unwinder is registered in its
place.

GDB first calls the unwinders from all the object files in no
particular order, then the unwinders from the current program
space, then the globally registered unwinders, and finally the
unwinders builtin to GDB.

Unwinder Skeleton Code
----------------------

Here is an example of how to structure a user created unwinder:

from gdb.unwinder import Unwinder, FrameId

class MyUnwinder(Unwinder):
def __init__(self):
super().__init___("MyUnwinder_Name")

def __call__(self, pending_frame):
if not <we recognize frame>:
return None

# Create a FrameID. Usually the frame is identified by a
# stack pointer and the function address.
sp = ... compute a stack address ...
pc = ... compute function address ...
unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))

# Find the values of the registers in the caller's frame and
# save them in the result:
unwind_info.add_saved_register(<register-number>, <register-value>)
....

# Return the result:
return unwind_info

gdb.unwinder.register_unwinder(<locus>, MyUnwinder(), <replace>)

Managing Registered Unwinders
-----------------------------

GDB defines 3 commands to manage registered unwinders. These are:

`info unwinder [ LOCUS [ NAME-REGEXP ] ]'
Lists all registered unwinders. Arguments LOCUS and NAME-REGEXP
are both optional and can be used to filter which unwinders are
listed.

The LOCUS argument should be either `global', `progspace', or the
name of an object file. Only unwinders registered for the
specified locus will be listed.

The NAME-REGEXP is a regular expression used to match against
unwinder names. When trying to match against unwinder names that
include a string enclose NAME-REGEXP in quotes.

`disable unwinder [ LOCUS [ NAME-REGEXP ] ]'
The LOCUS and NAME-REGEXP are interpreted as in `info unwinder'
above, but instead of listing the matching unwinders, all of the
matching unwinders are disabled. The `enabled' field of each
matching unwinder is set to `False'.

`enable unwinder [ LOCUS [ NAME-REGEXP ] ]'
The LOCUS and NAME-REGEXP are interpreted as in `info unwinder'
above, but instead of listing the matching unwinders, all of the
matching unwinders are enabled. The `enabled' field of each
matching unwinder is set to `True'.

File: gdb.info, Node: Xmethods In Python, Next: Xmethod API, Prev: Unwinding Frames in Python, Up: Python API

23.3.2.14 Xmethods In Python
...........................

"Xmethods" are additional methods or replacements for existing methods
of a C++ class. This feature is useful for those cases where a method
defined in C++ source code could be inlined or optimized out by the
compiler, making it unavailable to GDB. For such cases, one can define
an xmethod to serve as a replacement for the method defined in the C++
source code. GDB will then invoke the xmethod, instead of the C++
method, to evaluate expressions. One can also use xmethods when
debugging with core files. Moreover, when debugging live programs,
invoking an xmethod need not involve running the inferior (which can
potentially perturb its state). Hence, even if the C++ method is
available, it is better to use its replacement xmethod if one is
defined.

The xmethods feature in Python is available via the concepts of an
"xmethod matcher" and an "xmethod worker". To implement an xmethod,
one has to implement a matcher and a corresponding worker for it (more
than one worker can be implemented, each catering to a different
overloaded instance of the method). Internally, GDB invokes the
`match' method of a matcher to match the class type and method name.
On a match, the `match' method returns a list of matching _worker_
objects. Each worker object typically corresponds to an overloaded
instance of the xmethod. They implement a `get_arg_types' method which
returns a sequence of types corresponding to the arguments the xmethod
requires. GDB uses this sequence of types to perform overload
resolution and picks a winning xmethod worker. A winner is also
selected from among the methods GDB finds in the C++ source code.
Next, the winning xmethod worker and the winning C++ method are
compared to select an overall winner. In case of a tie between a
xmethod worker and a C++ method, the xmethod worker is selected as the
winner. That is, if a winning xmethod worker is found to be equivalent
to the winning C++ method, then the xmethod worker is treated as a
replacement for the C++ method. GDB uses the overall winner to invoke
the method. If the winning xmethod worker is the overall winner, then
the corresponding xmethod is invoked via the `__call__' method of the
worker object.

If one wants to implement an xmethod as a replacement for an
existing C++ method, then they have to implement an equivalent xmethod
which has exactly the same name and takes arguments of exactly the same
type as the C++ method. If the user wants to invoke the C++ method
even though a replacement xmethod is available for that method, then
they can disable the xmethod.

*Note Xmethod API::, for API to implement xmethods in Python. *Note
Writing an Xmethod::, for implementing xmethods in Python.

File: gdb.info, Node: Xmethod API, Next: Writing an Xmethod, Prev: Xmethods In Python, Up: Python API

23.3.2.15 Xmethod API
....................

The GDB Python API provides classes, interfaces and functions to
implement, register and manipulate xmethods. *Note Xmethods In
Python::.

An xmethod matcher should be an instance of a class derived from
`XMethodMatcher' defined in the module `gdb.xmethod', or an object with
similar interface and attributes. An instance of `XMethodMatcher' has
the following attributes:

-- Variable: name
The name of the matcher.

-- Variable: enabled
A boolean value indicating whether the matcher is enabled or
disabled.

-- Variable: methods
A list of named methods managed by the matcher. Each object in
the list is an instance of the class `XMethod' defined in the
module `gdb.xmethod', or any object with the following attributes:

`name'
Name of the xmethod which should be unique for each xmethod
managed by the matcher.

`enabled'
A boolean value indicating whether the xmethod is enabled or
disabled.

The class `XMethod' is a convenience class with same attributes as
above along with the following constructor:

-- Function: XMethod.__init__ (self, name)
Constructs an enabled xmethod with name NAME.

The `XMethodMatcher' class has the following methods:

-- Function: XMethodMatcher.__init__ (self, name)
Constructs an enabled xmethod matcher with name NAME. The
`methods' attribute is initialized to `None'.

-- Function: XMethodMatcher.match (self, class_type, method_name)
Derived classes should override this method. It should return a
xmethod worker object (or a sequence of xmethod worker objects)
matching the CLASS_TYPE and METHOD_NAME. CLASS_TYPE is a
`gdb.Type' object, and METHOD_NAME is a string value. If the
matcher manages named methods as listed in its `methods'
attribute, then only those worker objects whose corresponding
entries in the `methods' list are enabled should be returned.

An xmethod worker should be an instance of a class derived from
`XMethodWorker' defined in the module `gdb.xmethod', or support the
following interface:

-- Function: XMethodWorker.get_arg_types (self)
This method returns a sequence of `gdb.Type' objects corresponding
to the arguments that the xmethod takes. It can return an empty
sequence or `None' if the xmethod does not take any arguments. If
the xmethod takes a single argument, then a single `gdb.Type'
object corresponding to it can be returned.

-- Function: XMethodWorker.get_result_type (self, *args)
This method returns a `gdb.Type' object representing the type of
the result of invoking this xmethod. The ARGS argument is the
same tuple of arguments that would be passed to the `__call__'
method of this worker.

-- Function: XMethodWorker.__call__ (self, *args)
This is the method which does the _work_ of the xmethod. The ARGS
arguments is the tuple of arguments to the xmethod. Each element
in this tuple is a gdb.Value object. The first element is always
the `this' pointer value.

For GDB to lookup xmethods, the xmethod matchers should be
registered using the following function defined in the module
`gdb.xmethod':

-- Function: register_xmethod_matcher (locus, matcher, replace=False)
The `matcher' is registered with `locus', replacing an existing
matcher with the same name as `matcher' if `replace' is `True'.
`locus' can be a `gdb.Objfile' object (*note Objfiles In
Python::), or a `gdb.Progspace' object (*note Progspaces In
Python::), or `None'. If it is `None', then `matcher' is
registered globally.

File: gdb.info, Node: Writing an Xmethod, Next: Inferiors In Python, Prev: Xmethod API, Up: Python API

23.3.2.16 Writing an Xmethod
...........................

Implementing xmethods in Python will require implementing xmethod
matchers and xmethod workers (*note Xmethods In Python::). Consider
the following C++ class:

class MyClass
{
public:
MyClass (int a) : a_(a) { }

int geta (void) { return a_; }
int operator+ (int b);

private:
int a_;
};

int
MyClass::operator+ (int b)
{
return a_ + b;
}

Let us define two xmethods for the class `MyClass', one replacing the
method `geta', and another adding an overloaded flavor of `operator+'
which takes a `MyClass' argument (the C++ code above already has an
overloaded `operator+' which takes an `int' argument). The xmethod
matcher can be defined as follows:

class MyClass_geta(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, 'geta')

def get_worker(self, method_name):
if method_name == 'geta':
return MyClassWorker_geta()

class MyClass_sum(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, 'sum')

def get_worker(self, method_name):
if method_name == 'operator+':
return MyClassWorker_plus()

class MyClassMatcher(gdb.xmethod.XMethodMatcher):
def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, 'MyClassMatcher')
# List of methods 'managed' by this matcher
self.methods = [MyClass_geta(), MyClass_sum()]

def match(self, class_type, method_name):
if class_type.tag != 'MyClass':
return None
workers = []
for method in self.methods:
if method.enabled:
worker = method.get_worker(method_name)
if worker:
workers.append(worker)

return workers

Notice that the `match' method of `MyClassMatcher' returns a worker
object of type `MyClassWorker_geta' for the `geta' method, and a worker
object of type `MyClassWorker_plus' for the `operator+' method. This
is done indirectly via helper classes derived from
`gdb.xmethod.XMethod'. One does not need to use the `methods'
attribute in a matcher as it is optional. However, if a matcher
manages more than one xmethod, it is a good practice to list the
xmethods in the `methods' attribute of the matcher. This will then
facilitate enabling and disabling individual xmethods via the
`enable/disable' commands. Notice also that a worker object is
returned only if the corresponding entry in the `methods' attribute of
the matcher is enabled.

The implementation of the worker classes returned by the matcher
setup above is as follows:

class MyClassWorker_geta(gdb.xmethod.XMethodWorker):
def get_arg_types(self):
return None

def get_result_type(self, obj):
return gdb.lookup_type('int')

def __call__(self, obj):
return obj['a_']

class MyClassWorker_plus(gdb.xmethod.XMethodWorker):
def get_arg_types(self):
return gdb.lookup_type('MyClass')

def get_result_type(self, obj):
return gdb.lookup_type('int')

def __call__(self, obj, other):
return obj['a_'] + other['a_']

For GDB to actually lookup a xmethod, it has to be registered with
it. The matcher defined above is registered with GDB globally as
follows:

gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())

If an object `obj' of type `MyClass' is initialized in C++ code as
follows:

MyClass obj(5);

then, after loading the Python script defining the xmethod matchers and
workers into GDB, invoking the method `geta' or using the operator `+'
on `obj' will invoke the xmethods defined above:

(gdb) p obj.geta()
$1 = 5

(gdb) p obj + obj
$2 = 10

Consider another example with a C++ template class:

template <class T>
class MyTemplate
{
public:
MyTemplate () : dsize_(10), data_ (new T [10]) { }
~MyTemplate () { delete [] data_; }

int footprint (void)
{
return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);
}

private:
int dsize_;
T *data_;
};

Let us implement an xmethod for the above class which serves as a
replacement for the `footprint' method. The full code listing of the
xmethod workers and xmethod matchers is as follows:

class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):
def __init__(self, class_type):
self.class_type = class_type

def get_arg_types(self):
return None

def get_result_type(self):
return gdb.lookup_type('int')

def __call__(self, obj):
return (self.class_type.sizeof +
obj['dsize_'] *
self.class_type.template_argument(0).sizeof)

class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):
def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, 'MyTemplateMatcher')

def match(self, class_type, method_name):
if (re.match('MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>',
class_type.tag) and
method_name == 'footprint'):
return MyTemplateWorker_footprint(class_type)

Notice that, in this example, we have not used the `methods'
attribute of the matcher as the matcher manages only one xmethod. The
user can enable/disable this xmethod by enabling/disabling the matcher
itself.

File: gdb.info, Node: Inferiors In Python, Next: Events In Python, Prev: Writing an Xmethod, Up: Python API

23.3.2.17 Inferiors In Python
............................

Programs which are being run under GDB are called inferiors (*note
Inferiors Connections and Programs::). Python scripts can access
information about and manipulate inferiors controlled by GDB via
objects of the `gdb.Inferior' class.

The following inferior-related functions are available in the `gdb'
module:

-- Function: gdb.inferiors ()
Return a tuple containing all inferior objects.

-- Function: gdb.selected_inferior ()
Return an object representing the current inferior.

A `gdb.Inferior' object has the following attributes:

-- Variable: Inferior.num
ID of inferior, as assigned by GDB. You can use this to make
Python breakpoints inferior-specific, for example (*note The
Breakpoint.inferior attribute: python_breakpoint_inferior.).

-- Variable: Inferior.connection
The `gdb.TargetConnection' for this inferior (*note Connections In
Python::), or `None' if this inferior has no connection.

-- Variable: Inferior.connection_num
ID of inferior's connection as assigned by GDB, or None if the
inferior is not connected to a target. *Note Inferiors
Connections and Programs::. This is equivalent to
`gdb.Inferior.connection.num' in the case where
`gdb.Inferior.connection' is not `None'.

-- Variable: Inferior.pid
Process ID of the inferior, as assigned by the underlying operating
system.

-- Variable: Inferior.was_attached
Boolean signaling whether the inferior was created using `attach',
or started by GDB itself.

-- Variable: Inferior.main_name
A string holding the name of this inferior's "main" function, if it
can be determined. If the name of main is not known, this is
`None'.

-- Variable: Inferior.progspace
The inferior's program space. *Note Progspaces In Python::.

-- Variable: Inferior.arguments
The inferior's command line arguments, if known. This corresponds
to the `set args' and `show args' commands. *Note Arguments::.

When accessed, the value is a string holding all the arguments.
The contents are quoted as they would be when passed to the shell.
If there are no arguments, the value is `None'.

Either a string or a sequence of strings can be assigned to this
attribute. When a string is assigned, it is assumed to have any
necessary quoting for the shell; when a sequence is assigned, the
quoting is applied by GDB.

A `gdb.Inferior' object has the following methods:

-- Function: Inferior.is_valid ()
Returns `True' if the `gdb.Inferior' object is valid, `False' if
not. A `gdb.Inferior' object will become invalid if the inferior
no longer exists within GDB. All other `gdb.Inferior' methods
will throw an exception if it is invalid at the time the method is
called.

-- Function: Inferior.threads ()
This method returns a tuple holding all the threads which are valid
when it is called. If there are no valid threads, the method will
return an empty tuple.

-- Function: Inferior.architecture ()
Return the `gdb.Architecture' (*note Architectures In Python::)
for this inferior. This represents the architecture of the
inferior as a whole. Some platforms can have multiple
architectures in a single address space, so this may not match the
architecture of a particular frame (*note Frames In Python::).

-- Function: Inferior.read_memory (address, length)
Read LENGTH addressable memory units from the inferior, starting
at ADDRESS. Returns a `memoryview' object, which behaves much
like an array or a string. It can be modified and given to the
`Inferior.write_memory' function.

-- Function: Inferior.write_memory (address, buffer [, length])
Write the contents of BUFFER to the inferior, starting at ADDRESS.
The BUFFER parameter must be a Python object which supports the
buffer protocol, i.e., a string, an array or the object returned
from `Inferior.read_memory'. If given, LENGTH determines the
number of addressable memory units from BUFFER to be written.

-- Function: Inferior.search_memory (address, length, pattern)
Search a region of the inferior memory starting at ADDRESS with
the given LENGTH using the search pattern supplied in PATTERN.
The PATTERN parameter must be a Python object which supports the
buffer protocol, i.e., a string, an array or the object returned
from `gdb.read_memory'. Returns a Python `Long' containing the
address where the pattern was found, or `None' if the pattern
could not be found.

-- Function: Inferior.thread_from_handle (handle)
Return the thread object corresponding to HANDLE, a thread library
specific data structure such as `pthread_t' for pthreads library
implementations.

The function `Inferior.thread_from_thread_handle' provides the
same functionality, but use of `Inferior.thread_from_thread_handle'
is deprecated.

The environment that will be passed to the inferior can be changed
from Python by using the following methods. These methods only take
effect when the inferior is started - they will not affect an inferior
that is already executing.

-- Function: Inferior.clear_env ()
Clear the current environment variables that will be passed to this
inferior.

-- Function: Inferior.set_env (name, value)
Set the environment variable NAME to have the indicated value.
Both parameters must be strings.

-- Function: Inferior.unset_env (name)
Unset the environment variable NAME. NAME must be a string.

One may add arbitrary attributes to `gdb.Inferior' objects in the
usual Python way. This is useful if, for example, one needs to do some
extra record keeping associated with the inferior.

When selecting a name for a new attribute, avoid starting the new
attribute name with a lower case letter; future attributes added by GDB
will start with a lower case letter. Additionally, avoid starting
attribute names with two underscore characters, as these could clash
with Python builtin attribute names.

In this contrived example we record the time when an inferior last
stopped:

(gdb) python
import datetime

def thread_stopped(event):
if event.inferior_thread is not None:
thread = event.inferior_thread
else:
thread = gdb.selected_thread()
inferior = thread.inferior
inferior._last_stop_time = datetime.datetime.today()

gdb.events.stop.connect(thread_stopped)
(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
(gdb) start
Temporary breakpoint 1 at 0x401198: file /tmp/hello.c, line 18.
Starting program: /tmp/hello

Temporary breakpoint 1, main () at /tmp/hello.c:18
18 printf ("Hello World\n");
(gdb) python print(gdb.selected_inferior()._last_stop_time)
2024-01-04 14:48:41.347036

File: gdb.info, Node: Events In Python, Next: Threads In Python, Prev: Inferiors In Python, Up: Python API

23.3.2.18 Events In Python
.........................

GDB provides a general event facility so that Python code can be
notified of various state changes, particularly changes that occur in
the inferior.

An "event" is just an object that describes some state change. The
type of the object and its attributes will vary depending on the details
of the change. All the existing events are described below.

In order to be notified of an event, you must register an event
handler with an "event registry". An event registry is an object in the
`gdb.events' module which dispatches particular events. A registry
provides methods to register and unregister event handlers:

-- Function: EventRegistry.connect (object)
Add the given callable OBJECT to the registry. This object will be
called when an event corresponding to this registry occurs.

-- Function: EventRegistry.disconnect (object)
Remove the given OBJECT from the registry. Once removed, the
object will no longer receive notifications of events.

Here is an example:

def exit_handler (event):
print ("event type: exit")
if hasattr (event, 'exit_code'):
print ("exit code: %d" % (event.exit_code))
else:
print ("exit code not available")

gdb.events.exited.connect (exit_handler)

In the above example we connect our handler `exit_handler' to the
registry `events.exited'. Once connected, `exit_handler' gets called
when the inferior exits. The argument "event" in this example is of
type `gdb.ExitedEvent'. As you can see in the example the
`ExitedEvent' object has an attribute which indicates the exit code of
the inferior.

Some events can be thread specific when GDB is running in non-stop
mode. When represented in Python, these events all extend
`gdb.ThreadEvent'. This event is a base class and is never emitted
directly; instead, events which are emitted by this or other modules
might extend this event. Examples of these events are
`gdb.BreakpointEvent' and `gdb.ContinueEvent'. `gdb.ThreadEvent' holds
the following attributes:

-- Variable: ThreadEvent.inferior_thread
In non-stop mode this attribute will be set to the specific thread
which was involved in the emitted event. Otherwise, it will be set
to `None'.

The following is a listing of the event registries that are
available and details of the events they emit:

`events.cont'
Emits `gdb.ContinueEvent', which extends `gdb.ThreadEvent'. This
event indicates that the inferior has been continued after a stop.
For inherited attribute refer to `gdb.ThreadEvent' above.

`events.exited'
Emits `events.ExitedEvent', which indicates that the inferior has
exited. `events.ExitedEvent' has two attributes:

-- Variable: ExitedEvent.exit_code
An integer representing the exit code, if available, which
the inferior has returned. (The exit code could be
unavailable if, for example, GDB detaches from the inferior.)
If the exit code is unavailable, the attribute does not exist.

-- Variable: ExitedEvent.inferior
A reference to the inferior which triggered the `exited'
event.

`events.stop'
Emits `gdb.StopEvent', which extends `gdb.ThreadEvent'.

Indicates that the inferior has stopped. All events emitted by
this registry extend `gdb.StopEvent'. As a child of
`gdb.ThreadEvent', `gdb.StopEvent' will indicate the stopped
thread when GDB is running in non-stop mode. Refer to
`gdb.ThreadEvent' above for more details.

`gdb.StopEvent' has the following additional attributes:

-- Variable: StopEvent.details
A dictionary holding any details relevant to the stop. The
exact keys and values depend on the type of stop, but are
identical to the corresponding MI output (*note GDB/MI Async
Records::).

A dictionary was used for this (rather than adding attributes
directly to the event object) so that the MI keys could be
used unchanged.

When a `StopEvent' results from a `finish' command, it will
also hold the return value from the function, if that is
available. This will be an entry named `return-value' in the
`details' dictionary. The value of this entry will be a
`gdb.Value' object.

Emits `gdb.SignalEvent', which extends `gdb.StopEvent'.

This event indicates that the inferior or one of its threads has
received a signal. `gdb.SignalEvent' has the following attributes:

-- Variable: SignalEvent.stop_signal
A string representing the signal received by the inferior. A
list of possible signal values can be obtained by running the
command `info signals' in the GDB command prompt.

Also emits `gdb.BreakpointEvent', which extends `gdb.StopEvent'.

`gdb.BreakpointEvent' event indicates that one or more breakpoints
have been hit, and has the following attributes:

-- Variable: BreakpointEvent.breakpoints
A sequence containing references to all the breakpoints (type
`gdb.Breakpoint') that were hit. *Note Breakpoints In
Python::, for details of the `gdb.Breakpoint' object.

-- Variable: BreakpointEvent.breakpoint
A reference to the first breakpoint that was hit. This
attribute is maintained for backward compatibility and is now
deprecated in favor of the `gdb.BreakpointEvent.breakpoints'
attribute.

`events.new_objfile'
Emits `gdb.NewObjFileEvent' which indicates that a new object file
has been loaded by GDB. `gdb.NewObjFileEvent' has one attribute:

-- Variable: NewObjFileEvent.new_objfile
A reference to the object file (`gdb.Objfile') which has been
loaded. *Note Objfiles In Python::, for details of the
`gdb.Objfile' object.

`events.free_objfile'
Emits `gdb.FreeObjFileEvent' which indicates that an object file
is about to be removed from GDB. One reason this can happen is
when the inferior calls `dlclose'. `gdb.FreeObjFileEvent' has one
attribute:

-- Variable: FreeObjFileEvent.objfile
A reference to the object file (`gdb.Objfile') which will be
unloaded. *Note Objfiles In Python::, for details of the
`gdb.Objfile' object.

`events.clear_objfiles'
Emits `gdb.ClearObjFilesEvent' which indicates that the list of
object files for a program space has been reset.
`gdb.ClearObjFilesEvent' has one attribute:

-- Variable: ClearObjFilesEvent.progspace
A reference to the program space (`gdb.Progspace') whose
objfile list has been cleared. *Note Progspaces In Python::.

`events.inferior_call'
Emits events just before and after a function in the inferior is
called by GDB. Before an inferior call, this emits an event of
type `gdb.InferiorCallPreEvent', and after an inferior call, this
emits an event of type `gdb.InferiorCallPostEvent'.

``gdb.InferiorCallPreEvent''
Indicates that a function in the inferior is about to be
called.

-- Variable: InferiorCallPreEvent.ptid
The thread in which the call will be run.

-- Variable: InferiorCallPreEvent.address
The location of the function to be called.

``gdb.InferiorCallPostEvent''
Indicates that a function in the inferior has just been
called.

-- Variable: InferiorCallPostEvent.ptid
The thread in which the call was run.

-- Variable: InferiorCallPostEvent.address
The location of the function that was called.

`events.memory_changed'
Emits `gdb.MemoryChangedEvent' which indicates that the memory of
the inferior has been modified by the GDB user, for instance via a
command like `set *addr = value'. The event has the following
attributes:

-- Variable: MemoryChangedEvent.address
The start address of the changed region.

-- Variable: MemoryChangedEvent.length
Length in bytes of the changed region.

`events.register_changed'
Emits `gdb.RegisterChangedEvent' which indicates that a register
in the inferior has been modified by the GDB user.

-- Variable: RegisterChangedEvent.frame
A gdb.Frame object representing the frame in which the
register was modified.

-- Variable: RegisterChangedEvent.regnum
Denotes which register was modified.

`events.breakpoint_created'
This is emitted when a new breakpoint has been created. The
argument that is passed is the new `gdb.Breakpoint' object.

`events.breakpoint_modified'
This is emitted when a breakpoint has been modified in some way.
The argument that is passed is the new `gdb.Breakpoint' object.

`events.breakpoint_deleted'
This is emitted when a breakpoint has been deleted. The argument
that is passed is the `gdb.Breakpoint' object. When this event is
emitted, the `gdb.Breakpoint' object will already be in its
invalid state; that is, the `is_valid' method will return `False'.

`events.before_prompt'
This event carries no payload. It is emitted each time GDB
presents a prompt to the user.

`events.new_inferior'
This is emitted when a new inferior is created. Note that the
inferior is not necessarily running; in fact, it may not even have
an associated executable.

The event is of type `gdb.NewInferiorEvent'. This has a single
attribute:

-- Variable: NewInferiorEvent.inferior
The new inferior, a `gdb.Inferior' object.

`events.inferior_deleted'
This is emitted when an inferior has been deleted. Note that this
is not the same as process exit; it is notified when the inferior
itself is removed, say via `remove-inferiors'.

The event is of type `gdb.InferiorDeletedEvent'. This has a single
attribute:

-- Variable: InferiorDeletedEvent.inferior
The inferior that is being removed, a `gdb.Inferior' object.

`events.new_thread'
This is emitted when GDB notices a new thread. The event is of
type `gdb.NewThreadEvent', which extends `gdb.ThreadEvent'. This
has a single attribute:

-- Variable: NewThreadEvent.inferior_thread
The new thread.

`events.thread_exited'
This is emitted when GDB notices a thread has exited. The event
is of type `gdb.ThreadExitedEvent' which extends `gdb.ThreadEvent'.
This has a single attribute:

-- Variable: ThreadExitedEvent.inferior_thread
The exiting thread.

`events.gdb_exiting'
This is emitted when GDB exits. This event is not emitted if GDB
exits as a result of an internal error, or after an unexpected
signal. The event is of type `gdb.GdbExitingEvent', which has a
single attribute:

-- Variable: GdbExitingEvent.exit_code
An integer, the value of the exit code GDB will return.

`events.connection_removed'
This is emitted when GDB removes a connection (*note Connections
In Python::). The event is of type `gdb.ConnectionEvent'. This
has a single read-only attribute:

-- Variable: ConnectionEvent.connection
The `gdb.TargetConnection' that is being removed.

`events.executable_changed'
Emits `gdb.ExecutableChangedEvent' which indicates that the
`gdb.Progspace.executable_filename' has changed.

This event is emitted when either the value of
`gdb.Progspace.executable_filename ' has changed to name a
different file, or the executable file named by
`gdb.Progspace.executable_filename' has changed on disk, and GDB
has therefore reloaded it.

-- Variable: ExecutableChangedEvent.progspace
The `gdb.Progspace' in which the current executable has
changed. The file name of the updated executable will be
visible in `gdb.Progspace.executable_filename' (*note
Progspaces In Python::).

-- Variable: ExecutableChangedEvent.reload
This attribute will be `True' if the value of
`gdb.Progspace.executable_filename' didn't change, but the
file it names changed on disk instead, and GDB reloaded it.

When this attribute is `False', the value in
`gdb.Progspace.executable_filename' was changed to name a
different file.

Remember that GDB tracks the executable file and the symbol file
separately, these are visible as
`gdb.Progspace.executable_filename' and `gdb.Progspace.filename'
respectively. When using the `file' command, GDB updates both of
these fields, but the executable file is updated first, so when
this event is emitted, the executable filename will have changed,
but the symbol filename might still hold its previous value.

`events.new_progspace'
This is emitted when GDB adds a new program space (*note Program
Spaces In Python: Progspaces In Python.). The event is of type
`gdb.NewProgspaceEvent', and has a single read-only attribute:

-- Variable: NewProgspaceEvent.progspace
The `gdb.Progspace' that was added to GDB.

No `NewProgspaceEvent' is emitted for the very first program
space, which is assigned to the first inferior. This first program
space is created within GDB before any Python scripts are sourced.

`events.free_progspace'
This is emitted when GDB removes a program space (*note Program
Spaces In Python: Progspaces In Python.), for example as a result
of the `remove-inferiors' command (*note `remove-inferiors':
remove_inferiors_cli.). The event is of type
`gdb.FreeProgspaceEvent', and has a single read-only attribute:

-- Variable: FreeProgspaceEvent.progspace
The `gdb.Progspace' that is about to be removed from GDB.

File: gdb.info, Node: Threads In Python, Next: Recordings In Python, Prev: Events In Python, Up: Python API

23.3.2.19 Threads In Python
..........................

Python scripts can access information about, and manipulate inferior
threads controlled by GDB, via objects of the `gdb.InferiorThread'
class.

The following thread-related functions are available in the `gdb'
module:

-- Function: gdb.selected_thread ()
This function returns the thread object for the selected thread.
If there is no selected thread, this will return `None'.

To get the list of threads for an inferior, use the
`Inferior.threads()' method. *Note Inferiors In Python::.

A `gdb.InferiorThread' object has the following attributes:

-- Variable: InferiorThread.name
The name of the thread. If the user specified a name using
`thread name', then this returns that name. Otherwise, if an
OS-supplied name is available, then it is returned. Otherwise,
this returns `None'.

This attribute can be assigned to. The new value must be a string
object, which sets the new name, or `None', which removes any
user-specified thread name.

-- Variable: InferiorThread.num
The per-inferior number of the thread, as assigned by GDB.

-- Variable: InferiorThread.global_num
The global ID of the thread, as assigned by GDB. You can use this
to make Python breakpoints thread-specific, for example (*note The
Breakpoint.thread attribute: python_breakpoint_thread.).

-- Variable: InferiorThread.ptid
ID of the thread, as assigned by the operating system. This
attribute is a tuple containing three integers. The first is the
Process ID (PID); the second is the Lightweight Process ID
(LWPID), and the third is the Thread ID (TID). Either the LWPID
or TID may be 0, which indicates that the operating system does
not use that identifier.

-- Variable: InferiorThread.ptid_string
This read-only attribute contains a string representing
`InferiorThread.ptid'. This is the string that GDB uses in the
`Target Id' column in the `info threads' output (*note `info
threads': info_threads.).

-- Variable: InferiorThread.inferior
The inferior this thread belongs to. This attribute is
represented as a `gdb.Inferior' object. This attribute is not
writable.

-- Variable: InferiorThread.details
A string containing target specific thread state information. The
format of this string varies by target. If there is no additional
state information for this thread, then this attribute contains
`None'.

For example, on a GNU/Linux system, a thread that is in the
process of exiting will return the string `Exiting'. For remote
targets the `details' string will be obtained with the
`qThreadExtraInfo' remote packet, if the target supports it (*note
`qThreadExtraInfo': qThreadExtraInfo.).

GDB displays the `details' string as part of the `Target Id'
column, in the `info threads' output (*note `info threads':
info_threads.).

A `gdb.InferiorThread' object has the following methods:

-- Function: InferiorThread.is_valid ()
Returns `True' if the `gdb.InferiorThread' object is valid,
`False' if not. A `gdb.InferiorThread' object will become invalid
if the thread exits, or the inferior that the thread belongs is
deleted. All other `gdb.InferiorThread' methods will throw an
exception if it is invalid at the time the method is called.

-- Function: InferiorThread.switch ()
This changes GDB's currently selected thread to the one represented
by this object.

-- Function: InferiorThread.is_stopped ()
Return a Boolean indicating whether the thread is stopped.

-- Function: InferiorThread.is_running ()
Return a Boolean indicating whether the thread is running.

-- Function: InferiorThread.is_exited ()
Return a Boolean indicating whether the thread is exited.

-- Function: InferiorThread.handle ()
Return the thread object's handle, represented as a Python `bytes'
object. A `gdb.Value' representation of the handle may be
constructed via `gdb.Value(bufobj, type)' where BUFOBJ is the
Python `bytes' representation of the handle and TYPE is a
`gdb.Type' for the handle type.

One may add arbitrary attributes to `gdb.InferiorThread' objects in
the usual Python way. This is useful if, for example, one needs to do
some extra record keeping associated with the thread.

*Note choosing attribute names::, for guidance on selecting a
suitable name for new attributes.

In this contrived example we record the time when a thread last
stopped:

(gdb) python
import datetime

def thread_stopped(event):
if event.inferior_thread is not None:
thread = event.inferior_thread
else:
thread = gdb.selected_thread()
thread._last_stop_time = datetime.datetime.today()

gdb.events.stop.connect(thread_stopped)
(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
(gdb) start
Temporary breakpoint 1 at 0x401198: file /tmp/hello.c, line 18.
Starting program: /tmp/hello

Temporary breakpoint 1, main () at /tmp/hello.c:18
18 printf ("Hello World\n");
(gdb) python print(gdb.selected_thread()._last_stop_time)
2024-01-04 14:48:41.347036

File: gdb.info, Node: Recordings In Python, Next: CLI Commands In Python, Prev: Threads In Python, Up: Python API

23.3.2.20 Recordings In Python
.............................

The following recordings-related functions (*note Process Record and
Replay::) are available in the `gdb' module:

-- Function: gdb.start_recording ([method], [format])
Start a recording using the given METHOD and FORMAT. If no FORMAT
is given, the default format for the recording method is used. If
no METHOD is given, the default method will be used. Returns a
`gdb.Record' object on success. Throw an exception on failure.

The following strings can be passed as METHOD:

* `"full"'

* `"btrace"': Possible values for FORMAT: `"pt"', `"bts"' or
leave out for default format.

-- Function: gdb.current_recording ()
Access a currently running recording. Return a `gdb.Record'
object on success. Return `None' if no recording is currently
active.

-- Function: gdb.stop_recording ()
Stop the current recording. Throw an exception if no recording is
currently active. All record objects become invalid after this
call.

A `gdb.Record' object has the following attributes:

-- Variable: Record.method
A string with the current recording method, e.g. `full' or
`btrace'.

-- Variable: Record.format
A string with the current recording format, e.g. `bt', `pts' or
`None'.

-- Variable: Record.begin
A method specific instruction object representing the first
instruction in this recording.

-- Variable: Record.end
A method specific instruction object representing the current
instruction, that is not actually part of the recording.

-- Variable: Record.replay_position
The instruction representing the current replay position. If
there is no replay active, this will be `None'.

-- Variable: Record.instruction_history
A list with all recorded instructions.

-- Variable: Record.function_call_history
A list with all recorded function call segments.

A `gdb.Record' object has the following methods:

-- Function: Record.goto (instruction)
Move the replay position to the given INSTRUCTION.

The common `gdb.Instruction' class that recording method specific
instruction objects inherit from, has the following attributes:

-- Variable: Instruction.pc
An integer representing this instruction's address.

-- Variable: Instruction.data
A `memoryview' object holding the raw instruction data.

-- Variable: Instruction.decoded
A human readable string with the disassembled instruction.

-- Variable: Instruction.size
The size of the instruction in bytes.

Additionally `gdb.RecordInstruction' has the following attributes:

-- Variable: RecordInstruction.number
An integer identifying this instruction. `number' corresponds to
the numbers seen in `record instruction-history' (*note Process
Record and Replay::).

-- Variable: RecordInstruction.sal
A `gdb.Symtab_and_line' object representing the associated symtab
and line of this instruction. May be `None' if no debug
information is available.

-- Variable: RecordInstruction.is_speculative
A boolean indicating whether the instruction was executed
speculatively.

If an error occurred during recording or decoding a recording, this
error is represented by a `gdb.RecordGap' object in the instruction
list. It has the following attributes:

-- Variable: RecordGap.number
An integer identifying this gap. `number' corresponds to the
numbers seen in `record instruction-history' (*note Process Record
and Replay::).

-- Variable: RecordGap.error_code
A numerical representation of the reason for the gap. The value
is specific to the current recording method.

-- Variable: RecordGap.error_string
A human readable string with the reason for the gap.

A `gdb.RecordFunctionSegment' object has the following attributes:

-- Variable: RecordFunctionSegment.number
An integer identifying this function segment. `number'
corresponds to the numbers seen in `record function-call-history'
(*note Process Record and Replay::).

-- Variable: RecordFunctionSegment.symbol
A `gdb.Symbol' object representing the associated symbol. May be
`None' if no debug information is available.

-- Variable: RecordFunctionSegment.level
An integer representing the function call's stack level. May be
`None' if the function call is a gap.

-- Variable: RecordFunctionSegment.instructions
A list of `gdb.RecordInstruction' or `gdb.RecordGap' objects
associated with this function call.

-- Variable: RecordFunctionSegment.up
A `gdb.RecordFunctionSegment' object representing the caller's
function segment. If the call has not been recorded, this will be
the function segment to which control returns. If neither the
call nor the return have been recorded, this will be `None'.

-- Variable: RecordFunctionSegment.prev
A `gdb.RecordFunctionSegment' object representing the previous
segment of this function call. May be `None'.

-- Variable: RecordFunctionSegment.next
A `gdb.RecordFunctionSegment' object representing the next segment
of this function call. May be `None'.

The following example demonstrates the usage of these objects and
functions to create a function that will rewind a record to the last
time a function in a different file was executed. This would typically
be used to track the execution of user provided callback functions in a
library which typically are not visible in a back trace.

def bringback ():
rec = gdb.current_recording ()
if not rec:
return

insn = rec.instruction_history
if len (insn) == 0:
return

try:
position = insn.index (rec.replay_position)
except:
position = -1
try:
filename = insn[position].sal.symtab.fullname ()
except:
filename = None

for i in reversed (insn[:position]):
try:
current = i.sal.symtab.fullname ()
except:
current = None

if filename == current:
continue

rec.goto (i)
return

Another possible application is to write a function that counts the
number of code executions in a given line range. This line range can
contain parts of functions or span across several functions and is not
limited to be contiguous.

def countrange (filename, linerange):
count = 0

def filter_only (file_name):
for call in gdb.current_recording ().function_call_history:
try:
if file_name in call.symbol.symtab.fullname ():
yield call
except:
pass

for c in filter_only (filename):
for i in c.instructions:
try:
if i.sal.line in linerange:
count += 1
break;
except:
pass

return count

File: gdb.info, Node: CLI Commands In Python, Next: GDB/MI Commands In Python, Prev: Recordings In Python, Up: Python API

23.3.2.21 CLI Commands In Python
...............................

You can implement new GDB CLI commands in Python. A CLI command is
implemented using an instance of the `gdb.Command' class, most commonly
using a subclass.

-- Function: Command.__init__ (name, command_class [, completer_class
[, prefix]])
The object initializer for `Command' registers the new command
with GDB. This initializer is normally invoked from the subclass'
own `__init__' method.

NAME is the name of the command. If NAME consists of multiple
words, then the initial words are looked for as prefix commands.
In this case, if one of the prefix commands does not exist, an
exception is raised.

There is no support for multi-line commands.

COMMAND_CLASS should be one of the `COMMAND_' constants defined
below. This argument tells GDB how to categorize the new command
in the help system.

COMPLETER_CLASS is an optional argument. If given, it should be
one of the `COMPLETE_' constants defined below. This argument
tells GDB how to perform completion for this command. If not
given, GDB will attempt to complete using the object's `complete'
method (see below); if no such method is found, an error will
occur when completion is attempted.

PREFIX is an optional argument. If `True', then the new command
is a prefix command; sub-commands of this command may be
registered.

The help text for the new command is taken from the Python
documentation string for the command's class, if there is one. If
no documentation string is provided, the default value "This
command is not documented." is used.

-- Function: Command.dont_repeat ()
By default, a GDB command is repeated when the user enters a blank
line at the command prompt. A command can suppress this behavior
by invoking the `dont_repeat' method at some point in its `invoke'
method (normally this is done early in case of exception). This
is similar to the user command `dont-repeat', see *Note
dont-repeat: Define.

-- Function: Command.invoke (argument, from_tty)
This method is called by GDB when this command is invoked.

ARGUMENT is a string. It is the argument to the command, after
leading and trailing whitespace has been stripped.

FROM_TTY is a boolean argument. When true, this means that the
command was entered by the user at the terminal; when false it
means that the command came from elsewhere.

If this method throws an exception, it is turned into a GDB
`error' call. Otherwise, the return value is ignored.

To break ARGUMENT up into an argv-like string use
`gdb.string_to_argv'. This function behaves identically to GDB's
internal argument lexer `buildargv'. It is recommended to use
this for consistency. Arguments are separated by spaces and may
be quoted. Example:

print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"")
['1', '2 "3', '4 "5', "6 '7"]

-- Function: Command.complete (text, word)
This method is called by GDB when the user attempts completion on
this command. All forms of completion are handled by this method,
that is, the <TAB> and <M-?> key bindings (*note Completion::),
and the `complete' command (*note complete: Help.).

The arguments TEXT and WORD are both strings; TEXT holds the
complete command line up to the cursor's location, while WORD
holds the last word of the command line; this is computed using a
word-breaking heuristic.

The `complete' method can return several values:
* If the return value is a sequence, the contents of the
sequence are used as the completions. It is up to `complete'
to ensure that the contents actually do complete the word. A
zero-length sequence is allowed, it means that there were no
completions available. Only string elements of the sequence
are used; other elements in the sequence are ignored.

* If the return value is one of the `COMPLETE_' constants
defined below, then the corresponding GDB-internal completion
function is invoked, and its result is used.

* All other results are treated as though there were no
available completions.

When a new command is registered, it must be declared as a member of
some general class of commands. This is used to classify top-level
commands in the on-line help system; note that prefix commands are not
listed under their own category but rather that of their top-level
command. The available classifications are represented by constants
defined in the `gdb' module:

`gdb.COMMAND_NONE'
The command does not belong to any particular class. A command in
this category will not be displayed in any of the help categories.

`gdb.COMMAND_RUNNING'
The command is related to running the inferior. For example,
`start', `step', and `continue' are in this category. Type `help
running' at the GDB prompt to see a list of commands in this
category.

`gdb.COMMAND_DATA'
The command is related to data or variables. For example, `call',
`find', and `print' are in this category. Type `help data' at the
GDB prompt to see a list of commands in this category.

`gdb.COMMAND_STACK'
The command has to do with manipulation of the stack. For example,
`backtrace', `frame', and `return' are in this category. Type
`help stack' at the GDB prompt to see a list of commands in this
category.

`gdb.COMMAND_FILES'
This class is used for file-related commands. For example,
`file', `list' and `section' are in this category. Type `help
files' at the GDB prompt to see a list of commands in this
category.

`gdb.COMMAND_SUPPORT'
This should be used for "support facilities", generally meaning
things that are useful to the user when interacting with GDB, but
not related to the state of the inferior. For example, `help',
`make', and `shell' are in this category. Type `help support' at
the GDB prompt to see a list of commands in this category.

`gdb.COMMAND_STATUS'
The command is an `info'-related command, that is, related to the
state of GDB itself. For example, `info', `macro', and `show' are
in this category. Type `help status' at the GDB prompt to see a
list of commands in this category.

`gdb.COMMAND_BREAKPOINTS'
The command has to do with breakpoints. For example, `break',
`clear', and `delete' are in this category. Type `help
breakpoints' at the GDB prompt to see a list of commands in this
category.

`gdb.COMMAND_TRACEPOINTS'
The command has to do with tracepoints. For example, `trace',
`actions', and `tfind' are in this category. Type `help
tracepoints' at the GDB prompt to see a list of commands in this
category.

`gdb.COMMAND_TUI'
The command has to do with the text user interface (*note TUI::).
Type `help tui' at the GDB prompt to see a list of commands in
this category.

`gdb.COMMAND_USER'
The command is a general purpose command for the user, and
typically does not fit in one of the other categories. Type `help
user-defined' at the GDB prompt to see a list of commands in this
category, as well as the list of gdb macros (*note Sequences::).

`gdb.COMMAND_OBSCURE'
The command is only used in unusual circumstances, or is not of
general interest to users. For example, `checkpoint', `fork', and
`stop' are in this category. Type `help obscure' at the GDB
prompt to see a list of commands in this category.

`gdb.COMMAND_MAINTENANCE'
The command is only useful to GDB maintainers. The `maintenance'
and `flushregs' commands are in this category. Type `help
internals' at the GDB prompt to see a list of commands in this
category.

A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the `complete' method. These predefined completion constants are
all defined in the `gdb' module:

`gdb.COMPLETE_NONE'
This constant means that no completion should be done.

`gdb.COMPLETE_FILENAME'
This constant means that filename completion should be performed.

`gdb.COMPLETE_LOCATION'
This constant means that location completion should be done.
*Note Location Specifications::.

`gdb.COMPLETE_COMMAND'
This constant means that completion should examine GDB command
names.

`gdb.COMPLETE_SYMBOL'
This constant means that completion should be done using symbol
names as the source.

`gdb.COMPLETE_EXPRESSION'
This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.

The following code snippet shows how a trivial CLI command can be
implemented in Python:

class HelloWorld (gdb.Command):
"""Greet the whole world."""

def __init__ (self):
super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)

def invoke (self, arg, from_tty):
print ("Hello, World!")

HelloWorld ()

The last line instantiates the class, and is necessary to trigger the
registration of the command with GDB. Depending on how the Python code
is read into GDB, you may need to import the `gdb' module explicitly.

File: gdb.info, Node: GDB/MI Commands In Python, Next: GDB/MI Notifications In Python, Prev: CLI Commands In Python, Up: Python API

23.3.2.22 GDB/MI Commands In Python
..................................

It is possible to add GDB/MI (*note GDB/MI::) commands implemented in
Python. A GDB/MI command is implemented using an instance of the
`gdb.MICommand' class, most commonly using a subclass.

-- Function: MICommand.__init__ (name)
The object initializer for `MICommand' registers the new command
with GDB. This initializer is normally invoked from the subclass'
own `__init__' method.

NAME is the name of the command. It must be a valid name of a
GDB/MI command, and in particular must start with a hyphen (`-').
Reusing the name of a built-in GDB/MI is not allowed, and a
`RuntimeError' will be raised. Using the name of an GDB/MI
command previously defined in Python is allowed, the previous
command will be replaced with the new command.

-- Function: MICommand.invoke (arguments)
This method is called by GDB when the new MI command is invoked.

ARGUMENTS is a list of strings. Note, that `--thread' and
`--frame' arguments are handled by GDB itself therefore they do
not show up in `arguments'.

If this method raises an exception, then it is turned into a
GDB/MI `^error' response. Only `gdb.GdbError' exceptions (or its
sub-classes) should be used for reporting errors to users, any
other exception type is treated as a failure of the `invoke'
method, and the exception will be printed to the error stream
according to the `set python print-stack' setting (*note `set
python print-stack': set_python_print_stack.).

If this method returns `None', then the GDB/MI command will return
a `^done' response with no additional values.

Otherwise, the return value must be a dictionary, which is
converted to a GDB/MI RESULT-RECORD (*note GDB/MI Output Syntax::).
The keys of this dictionary must be strings, and are used as
VARIABLE names in the RESULT-RECORD, these strings must comply
with the naming rules detailed below. The values of this
dictionary are recursively handled as follows:

* If the value is Python sequence or iterator, it is converted
to GDB/MI LIST with elements converted recursively.

* If the value is Python dictionary, it is converted to GDB/MI
TUPLE. Keys in that dictionary must be strings, which comply
with the VARIABLE naming rules detailed below. Values are
converted recursively.

* Otherwise, value is first converted to a Python string using
`str ()' and then converted to GDB/MI CONST.

The strings used for VARIABLE names in the GDB/MI output must
follow the following rules; the string must be at least one
character long, the first character must be in the set `[a-zA-Z]',
while every subsequent character must be in the set
`[-_a-zA-Z0-9]'.

An instance of `MICommand' has the following attributes:

-- Variable: MICommand.name
A string, the name of this GDB/MI command, as was passed to the
`__init__' method. This attribute is read-only.

-- Variable: MICommand.installed
A boolean value indicating if this command is installed ready for a
user to call from the command line. Commands are automatically
installed when they are instantiated, after which this attribute
will be `True'.

If later, a new command is created with the same name, then the
original command will become uninstalled, and this attribute will
be `False'.

This attribute is read-write, setting this attribute to `False'
will uninstall the command, removing it from the set of available
commands. Setting this attribute to `True' will install the
command for use. If there is already a Python command with this
name installed, the currently installed command will be
uninstalled, and this command installed in its stead.

The following code snippet shows how some trivial MI commands can be
implemented in Python:

class MIEcho(gdb.MICommand):
"""Echo arguments passed to the command."""

def __init__(self, name, mode):
self._mode = mode
super(MIEcho, self).__init__(name)

def invoke(self, argv):
if self._mode == 'dict':
return { 'dict': { 'argv' : argv } }
elif self._mode == 'list':
return { 'list': argv }
else:
return { 'string': ", ".join(argv) }

MIEcho("-echo-dict", "dict")
MIEcho("-echo-list", "list")
MIEcho("-echo-string", "string")

The last three lines instantiate the class three times, creating
three new GDB/MI commands `-echo-dict', `-echo-list', and
`-echo-string'. Each time a subclass of `gdb.MICommand' is
instantiated, the new command is automatically registered with GDB.

Depending on how the Python code is read into GDB, you may need to
import the `gdb' module explicitly.

The following example shows a GDB session in which the above
commands have been added:

(gdb)
-echo-dict abc def ghi
^done,dict={argv=["abc","def","ghi"]}
(gdb)
-echo-list abc def ghi
^done,list=["abc","def","ghi"]
(gdb)
-echo-string abc def ghi
^done,string="abc, def, ghi"
(gdb)

Conversely, it is possible to execute GDB/MI commands from Python,
with the results being a Python object and not a specially-formatted
string. This is done with the `gdb.execute_mi' function.

-- Function: gdb.execute_mi (command [, arg ]...)
Invoke a GDB/MI command. COMMAND is the name of the command, a
string. The arguments, ARG, are passed to the command. Each
argument must also be a string.

This function returns a Python dictionary whose contents reflect
the corresponding GDB/MI command's output. Refer to the
documentation for these commands for details. Lists are
represented as Python lists, and tuples are represented as Python
dictionaries.

If the command fails, it will raise a Python exception.

Here is how this works using the commands from the example above:

(gdb) python print(gdb.execute_mi("-echo-dict", "abc", "def", "ghi"))
{'dict': {'argv': ['abc', 'def', 'ghi']}}
(gdb) python print(gdb.execute_mi("-echo-list", "abc", "def", "ghi"))
{'list': ['abc', 'def', 'ghi']}
(gdb) python print(gdb.execute_mi("-echo-string", "abc", "def", "ghi"))
{'string': 'abc, def, ghi'}

File: gdb.info, Node: GDB/MI Notifications In Python, Next: Parameters In Python, Prev: GDB/MI Commands In Python, Up: Python API

23.3.2.23 GDB/MI Notifications In Python
.......................................

It is possible to emit GDB/MI notifications from Python. Use the
`gdb.notify_mi' function to do that.

-- Function: gdb.notify_mi (name [, data])
Emit a GDB/MI asynchronous notification. NAME is the name of the
notification, consisting of alphanumeric characters and a hyphen
(`-'). DATA is any additional data to be emitted with the
notification, passed as a Python dictionary. This argument is
optional. The dictionary is converted to a GDB/MI RESULT records
(*note GDB/MI Output Syntax::) the same way as result of Python MI
command (*note GDB/MI Commands In Python::).

If DATA is `None' then no additional values are emitted.

While using existing notification names (*note GDB/MI Async
Records::) with `gdb.notify_mi' is allowed, users are encouraged to
prefix user-defined notification with a hyphen (`-') to avoid possible
conflict. GDB will never introduce notification starting with hyphen.

Here is how to emit `=-connection-removed' whenever a connection to
remote GDB server is closed (*note Connections In Python::):

def notify_connection_removed(event):
data = {"id": event.connection.num, "type": event.connection.type}
gdb.notify_mi("-connection-removed", data)

gdb.events.connection_removed.connect(notify_connection_removed)

Then, each time a connection is closed, there will be a notification
on MI channel:

=-connection-removed,id="1",type="remote"

File: gdb.info, Node: Parameters In Python, Next: Functions In Python, Prev: GDB/MI Notifications In Python, Up: Python API

23.3.2.24 Parameters In Python
.............................

You can implement new GDB parameters using Python. A new parameter is
implemented as an instance of the `gdb.Parameter' class.

Parameters are exposed to the user via the `set' and `show'
commands. *Note Help::.

There are many parameters that already exist and can be set in GDB.
Two examples are: `set follow fork' and `set charset'. Setting these
parameters influences certain behavior in GDB. Similarly, you can
define parameters that can be used to influence behavior in custom
Python scripts and commands.

-- Function: Parameter.__init__ (name, command_class, parameter_class
[, enum_sequence])
The object initializer for `Parameter' registers the new parameter
with GDB. This initializer is normally invoked from the subclass'
own `__init__' method.

NAME is the name of the new parameter. If NAME consists of
multiple words, then the initial words are looked for as prefix
parameters. An example of this can be illustrated with the `set
print' set of parameters. If NAME is `print foo', then `print'
will be searched as the prefix parameter. In this case the
parameter can subsequently be accessed in GDB as `set print foo'.

If NAME consists of multiple words, and no prefix parameter group
can be found, an exception is raised.

COMMAND_CLASS should be one of the `COMMAND_' constants (*note CLI
Commands In Python::). This argument tells GDB how to categorize
the new parameter in the help system.

PARAMETER_CLASS should be one of the `PARAM_' constants defined
below. This argument tells GDB the type of the new parameter;
this information is used for input validation and completion.

If PARAMETER_CLASS is `PARAM_ENUM', then ENUM_SEQUENCE must be a
sequence of strings. These strings represent the possible values
for the parameter.

If PARAMETER_CLASS is not `PARAM_ENUM', then the presence of a
fourth argument will cause an exception to be thrown.

The help text for the new parameter includes the Python
documentation string from the parameter's class, if there is one.
If there is no documentation string, a default value is used. The
documentation string is included in the output of the parameters
`help set' and `help show' commands, and should be written taking
this into account.

-- Variable: Parameter.set_doc
If this attribute exists, and is a string, then its value is used
as the first part of the help text for this parameter's `set'
command. The second part of the help text is taken from the
documentation string for the parameter's class, if there is one.

The value of `set_doc' should give a brief summary specific to the
set action, this text is only displayed when the user runs the
`help set' command for this parameter. The class documentation
should be used to give a fuller description of what the parameter
does, this text is displayed for both the `help set' and `help
show' commands.

The `set_doc' value is examined when `Parameter.__init__' is
invoked; subsequent changes have no effect.

-- Variable: Parameter.show_doc
If this attribute exists, and is a string, then its value is used
as the first part of the help text for this parameter's `show'
command. The second part of the help text is taken from the
documentation string for the parameter's class, if there is one.

The value of `show_doc' should give a brief summary specific to
the show action, this text is only displayed when the user runs the
`help show' command for this parameter. The class documentation
should be used to give a fuller description of what the parameter
does, this text is displayed for both the `help set' and `help
show' commands.

The `show_doc' value is examined when `Parameter.__init__' is
invoked; subsequent changes have no effect.

-- Variable: Parameter.value
The `value' attribute holds the underlying value of the parameter.
It can be read and assigned to just as any other attribute. GDB
does validation when assignments are made.

There are two methods that may be implemented in any `Parameter'
class. These are:

-- Function: Parameter.get_set_string (self)
If this method exists, GDB will call it when a PARAMETER's value
has been changed via the `set' API (for example, `set foo off').
The `value' attribute has already been populated with the new
value and may be used in output. This method must return a
string. If the returned string is not empty, GDB will present it
to the user.

If this method raises the `gdb.GdbError' exception (*note
Exception Handling::), then GDB will print the exception's string
and the `set' command will fail. Note, however, that the `value'
attribute will not be reset in this case. So, if your parameter
must validate values, it should store the old value internally and
reset the exposed value, like so:

class ExampleParam (gdb.Parameter):
def __init__ (self, name):
super (ExampleParam, self).__init__ (name,
gdb.COMMAND_DATA,
gdb.PARAM_BOOLEAN)
self.value = True
self.saved_value = True
def validate(self):
return False
def get_set_string (self):
if not self.validate():
self.value = self.saved_value
raise gdb.GdbError('Failed to validate')
self.saved_value = self.value
return ""

-- Function: Parameter.get_show_string (self, svalue)
GDB will call this method when a PARAMETER's `show' API has been
invoked (for example, `show foo'). The argument `svalue' receives
the string representation of the current value. This method must
return a string.

When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the `gdb'
module:

`gdb.PARAM_BOOLEAN'
The value is a plain boolean. The Python boolean values, `True'
and `False' are the only valid values.

`gdb.PARAM_AUTO_BOOLEAN'
The value has three possible states: true, false, and `auto'. In
Python, true and false are represented using boolean constants, and
`auto' is represented using `None'.

`gdb.PARAM_UINTEGER'
The value is an unsigned integer. The value of `None' should be
interpreted to mean "unlimited" (literal `'unlimited'' can also be
used to set that value), and the value of 0 is reserved and should
not be used.

`gdb.PARAM_INTEGER'
The value is a signed integer. The value of `None' should be
interpreted to mean "unlimited" (literal `'unlimited'' can also be
used to set that value), and the value of 0 is reserved and should
not be used.

`gdb.PARAM_STRING'
The value is a string. When the user modifies the string, any
escape sequences, such as `\t', `\f', and octal escapes, are
translated into corresponding characters and encoded into the
current host charset.

`gdb.PARAM_STRING_NOESCAPE'
The value is a string. When the user modifies the string, escapes
are passed through untranslated.

`gdb.PARAM_OPTIONAL_FILENAME'
The value is a either a filename (a string), or `None'.

`gdb.PARAM_FILENAME'
The value is a filename. This is just like
`PARAM_STRING_NOESCAPE', but uses file names for completion.

`gdb.PARAM_ZINTEGER'
The value is a signed integer. This is like `PARAM_INTEGER',
except that 0 is allowed and the value of `None' is not supported.

`gdb.PARAM_ZUINTEGER'
The value is an unsigned integer. This is like `PARAM_UINTEGER',
except that 0 is allowed and the value of `None' is not supported.

`gdb.PARAM_ZUINTEGER_UNLIMITED'
The value is a signed integer. This is like `PARAM_INTEGER'
including that the value of `None' should be interpreted to mean
"unlimited" (literal `'unlimited'' can also be used to set that
value), except that 0 is allowed, and the value cannot be negative,
except the special value -1 is returned for the setting of
"unlimited".

`gdb.PARAM_ENUM'
The value is a string, which must be one of a collection string
constants provided when the parameter is created.

File: gdb.info, Node: Functions In Python, Next: Progspaces In Python, Prev: Parameters In Python, Up: Python API

23.3.2.25 Writing new convenience functions
..........................................

You can implement new convenience functions (*note Convenience Vars::)
in Python. A convenience function is an instance of a subclass of the
class `gdb.Function'.

-- Function: Function.__init__ (name)
The initializer for `Function' registers the new function with
GDB. The argument NAME is the name of the function, a string.
The function will be visible to the user as a convenience variable
of type `internal function', whose name is the same as the given
NAME.

The documentation for the new function is taken from the
documentation string for the new class.

-- Function: Function.invoke (*args)
When a convenience function is evaluated, its arguments are
converted to instances of `gdb.Value', and then the function's
`invoke' method is called. Note that GDB does not predetermine
the arity of convenience functions. Instead, all available
arguments are passed to `invoke', following the standard Python
calling convention. In particular, a convenience function can
have default values for parameters without ill effect.

The return value of this method is used as its value in the
enclosing expression. If an ordinary Python value is returned, it
is converted to a `gdb.Value' following the usual rules.

The following code snippet shows how a trivial convenience function
can be implemented in Python:

class Greet (gdb.Function):
"""Return string to greet someone.
Takes a name as argument."""

def __init__ (self):
super (Greet, self).__init__ ("greet")

def invoke (self, name):
return "Hello, %s!" % name.string ()

Greet ()

The last line instantiates the class, and is necessary to trigger the
registration of the function with GDB. Depending on how the Python
code is read into GDB, you may need to import the `gdb' module
explicitly.

Now you can use the function in an expression:

(gdb) print $greet("Bob")
$1 = "Hello, Bob!"

File: gdb.info, Node: Progspaces In Python, Next: Objfiles In Python, Prev: Functions In Python, Up: Python API

23.3.2.26 Program Spaces In Python
.................................

A program space, or "progspace", represents a symbolic view of an
address space. It consists of all of the objfiles of the program.
*Note Objfiles In Python::. *Note program spaces: Inferiors
Connections and Programs, for more details about program spaces.

The following progspace-related functions are available in the `gdb'
module:

-- Function: gdb.current_progspace ()
This function returns the program space of the currently selected
inferior. *Note Inferiors Connections and Programs::. This is
identical to `gdb.selected_inferior().progspace' (*note Inferiors
In Python::) and is included for historical compatibility.

-- Function: gdb.progspaces ()
Return a sequence of all the progspaces currently known to GDB.

Each progspace is represented by an instance of the `gdb.Progspace'
class.

-- Variable: Progspace.filename
The file name, as a string, of the main symbol file (from which
debug symbols have been loaded) for the progspace, e.g. the
argument to the `symbol-file' or `file' commands.

If there is no main symbol table currently loaded, then this
attribute will be `None'.

-- Variable: Progspace.symbol_file
The `gdb.Objfile' representing the main symbol file (from which
debug symbols have been loaded) for the `gdb.Progspace'. This is
the symbol file set by the `symbol-file' or `file' commands.

This will be the `gdb.Objfile' representing `Progspace.filename'
when `Progspace.filename' is not `None'.

If there is no main symbol table currently loaded, then this
attribute will be `None'.

If the `Progspace' is invalid, i.e., when `Progspace.is_valid()'
returns `False', then attempting to access this attribute will
raise a `RuntimeError' exception.

-- Variable: Progspace.executable_filename
The file name, as a string, of the executable file in use by this
program space. The executable file is the file that GDB will
invoke in order to start an inferior when using a native target.
The file name within this attribute is updated by the `exec-file'
and `file' commands.

If no executable is currently set within this `Progspace' then
this attribute contains `None'.

If the `Progspace' is invalid, i.e., when `Progspace.is_valid()'
returns `False', then attempting to access this attribute will
raise a `RuntimeError' exception.

-- Variable: Progspace.pretty_printers
The `pretty_printers' attribute is a list of functions. It is
used to look up pretty-printers. A `Value' is passed to each
function in order; if the function returns `None', then the search
continues. Otherwise, the return value should be an object which
is used to format the value. *Note Pretty Printing API::, for more
information.

-- Variable: Progspace.type_printers
The `type_printers' attribute is a list of type printer objects.
*Note Type Printing API::, for more information.

-- Variable: Progspace.frame_filters
The `frame_filters' attribute is a dictionary of frame filter
objects. *Note Frame Filter API::, for more information.

-- Variable: Progspace.missing_debug_handlers
The `missing_debug_handlers' attribute is a list of the missing
debug handler objects for this program space. *Note Missing Debug
Info In Python::, for more information.

A program space has the following methods:

-- Function: Progspace.block_for_pc (pc)
Return the innermost `gdb.Block' containing the given PC value.
If the block cannot be found for the PC value specified, the
function will return `None'.

-- Function: Progspace.find_pc_line (pc)
Return the `gdb.Symtab_and_line' object corresponding to the PC
value. *Note Symbol Tables In Python::. If an invalid value of
PC is passed as an argument, then the `symtab' and `line'
attributes of the returned `gdb.Symtab_and_line' object will be
`None' and 0 respectively.

-- Function: Progspace.is_valid ()
Returns `True' if the `gdb.Progspace' object is valid, `False' if
not. A `gdb.Progspace' object can become invalid if the program
space file it refers to is not referenced by any inferior. All
other `gdb.Progspace' methods will throw an exception if it is
invalid at the time the method is called.

-- Function: Progspace.objfiles ()
Return a sequence of all the objfiles referenced by this program
space. *Note Objfiles In Python::.

-- Function: Progspace.solib_name (address)
Return the name of the shared library holding the given ADDRESS as
a string, or `None'.

-- Function: Progspace.objfile_for_address (address)
Return the `gdb.Objfile' holding the given address, or `None' if
no objfile covers it.

One may add arbitrary attributes to `gdb.Progspace' objects in the
usual Python way. This is useful if, for example, one needs to do some
extra record keeping associated with the program space.

*Note choosing attribute names::, for guidance on selecting a
suitable name for new attributes.

In this contrived example, we want to perform some processing when
an objfile with a certain symbol is loaded, but we only want to do this
once because it is expensive. To achieve this we record the results
with the program space because we can't predict when the desired objfile
will be loaded.

(gdb) python
def clear_objfiles_handler(event):
event.progspace.expensive_computation = None
def expensive(symbol):
"""A mock routine to perform an "expensive" computation on symbol."""
print ("Computing the answer to the ultimate question ...")
return 42
def new_objfile_handler(event):
objfile = event.new_objfile
progspace = objfile.progspace
if not hasattr(progspace, 'expensive_computation') or \
progspace.expensive_computation is None:
# We use 'main' for the symbol to keep the example simple.
# Note: There's no current way to constrain the lookup
# to one objfile.
symbol = gdb.lookup_global_symbol('main')
if symbol is not None:
progspace.expensive_computation = expensive(symbol)
gdb.events.clear_objfiles.connect(clear_objfiles_handler)
gdb.events.new_objfile.connect(new_objfile_handler)
end
(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
Computing the answer to the ultimate question ...
(gdb) python print(gdb.current_progspace().expensive_computation)
42
(gdb) run
Starting program: /tmp/hello
Hello.
[Inferior 1 (process 4242) exited normally]

File: gdb.info, Node: Objfiles In Python, Next: Frames In Python, Prev: Progspaces In Python, Up: Python API

23.3.2.27 Objfiles In Python
...........................

GDB loads symbols for an inferior from various symbol-containing files
(*note Files::). These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files
(*note Separate Debug Files::). GDB calls these symbol-containing
files "objfiles".

The following objfile-related functions are available in the `gdb'
module:

-- Function: gdb.current_objfile ()
When auto-loading a Python script (*note Python Auto-loading::),
GDB sets the "current objfile" to the corresponding objfile. This
function returns the current objfile. If there is no current
objfile, this function returns `None'.

-- Function: gdb.objfiles ()
Return a sequence of objfiles referenced by the current program
space. *Note Objfiles In Python::, and *Note Progspaces In
Python::. This is identical to
`gdb.selected_inferior().progspace.objfiles()' and is included for
historical compatibility.

-- Function: gdb.lookup_objfile (name [, by_build_id])
Look up NAME, a file name or build ID, in the list of objfiles for
the current program space (*note Progspaces In Python::). If the
objfile is not found throw the Python `ValueError' exception.

If NAME is a relative file name, then it will match any source
file name with the same trailing components. For example, if NAME
is `gcc/expr.c', then it will match source file name of
`/build/trunk/gcc/expr.c', but not `/build/trunk/libcpp/expr.c' or
`/build/trunk/gcc/x-expr.c'.

If BY_BUILD_ID is provided and is `True' then NAME is the build ID
of the objfile. Otherwise, NAME is a file name. This is
supported only on some operating systems, notably those which use
the ELF format for binary files and the GNU Binutils. For more
details about this feature, see the description of the `--build-id'
command-line option in *Note Command Line Options: (ld)Options.

Each objfile is represented by an instance of the `gdb.Objfile'
class.

-- Variable: Objfile.filename
The file name of the objfile as a string, with symbolic links
resolved.

The value is `None' if the objfile is no longer valid. See the
`gdb.Objfile.is_valid' method, described below.

-- Variable: Objfile.username
The file name of the objfile as specified by the user as a string.

The value is `None' if the objfile is no longer valid. See the
`gdb.Objfile.is_valid' method, described below.

-- Variable: Objfile.is_file
An objfile often comes from an ordinary file, but in some cases it
may be constructed from the contents of memory. This attribute is
`True' for file-backed objfiles, and `False' for other kinds.

-- Variable: Objfile.owner
For separate debug info objfiles this is the corresponding
`gdb.Objfile' object that debug info is being provided for.
Otherwise this is `None'. Separate debug info objfiles are added
with the `gdb.Objfile.add_separate_debug_file' method, described
below.

-- Variable: Objfile.build_id
The build ID of the objfile as a string. If the objfile does not
have a build ID then the value is `None'.

This is supported only on some operating systems, notably those
which use the ELF format for binary files and the GNU Binutils.
For more details about this feature, see the description of the
`--build-id' command-line option in *Note Command Line Options:
(ld)Options.

-- Variable: Objfile.progspace
The containing program space of the objfile as a `gdb.Progspace'
object. *Note Progspaces In Python::.

-- Variable: Objfile.pretty_printers
The `pretty_printers' attribute is a list of functions. It is
used to look up pretty-printers. A `Value' is passed to each
function in order; if the function returns `None', then the search
continues. Otherwise, the return value should be an object which
is used to format the value. *Note Pretty Printing API::, for more
information.

-- Variable: Objfile.type_printers
The `type_printers' attribute is a list of type printer objects.
*Note Type Printing API::, for more information.

-- Variable: Objfile.frame_filters
The `frame_filters' attribute is a dictionary of frame filter
objects. *Note Frame Filter API::, for more information.

One may add arbitrary attributes to `gdb.Objfile' objects in the
usual Python way. This is useful if, for example, one needs to do some
extra record keeping associated with the objfile.

*Note choosing attribute names::, for guidance on selecting a
suitable name for new attributes.

In this contrived example we record the time when GDB loaded the
objfile.

(gdb) python
import datetime
def new_objfile_handler(event):
# Set the time_loaded attribute of the new objfile.
event.new_objfile.time_loaded = datetime.datetime.today()
gdb.events.new_objfile.connect(new_objfile_handler)
end
(gdb) file ./hello
Reading symbols from ./hello...
(gdb) python print(gdb.objfiles()[0].time_loaded)
2014-10-09 11:41:36.770345

A `gdb.Objfile' object has the following methods:

-- Function: Objfile.is_valid ()
Returns `True' if the `gdb.Objfile' object is valid, `False' if
not. A `gdb.Objfile' object can become invalid if the object file
it refers to is not loaded in GDB any longer. All other
`gdb.Objfile' methods will throw an exception if it is invalid at
the time the method is called.

-- Function: Objfile.add_separate_debug_file (file)
Add FILE to the list of files that GDB will search for debug
information for the objfile. This is useful when the debug info
has been removed from the program and stored in a separate file.
GDB has built-in support for finding separate debug info files
(*note Separate Debug Files::), but if the file doesn't live in
one of the standard places that GDB searches then this function
can be used to add a debug info file from a different place.

-- Function: Objfile.lookup_global_symbol (name [, domain])
Search for a global symbol named NAME in this objfile.
Optionally, the search scope can be restricted with the DOMAIN
argument. The DOMAIN argument must be a domain constant defined
in the `gdb' module and described in *Note Symbols In Python::.
This function is similar to `gdb.lookup_global_symbol', except
that the search is limited to this objfile.

The result is a `gdb.Symbol' object or `None' if the symbol is not
found.

-- Function: Objfile.lookup_static_symbol (name [, domain])
Like `Objfile.lookup_global_symbol', but searches for a global
symbol with static linkage named NAME in this objfile.

File: gdb.info, Node: Frames In Python, Next: Blocks In Python, Prev: Objfiles In Python, Up: Python API

23.3.2.28 Accessing inferior stack frames from Python
....................................................

When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.). The `gdb.Frame' class represents a
frame in the stack. A `gdb.Frame' object is only valid while its
corresponding frame exists in the inferior's stack. If you try to use
an invalid frame object, GDB will throw a `gdb.error' exception (*note
Exception Handling::).

Two `gdb.Frame' objects can be compared for equality with the `=='
operator, like:

(gdb) python print gdb.newest_frame() == gdb.selected_frame ()
True

The following frame-related functions are available in the `gdb'
module:

-- Function: gdb.selected_frame ()
Return the selected frame object. (*note Selecting a Frame:
Selection.).

-- Function: gdb.newest_frame ()
Return the newest frame object for the selected thread.

-- Function: gdb.frame_stop_reason_string (reason)
Return a string explaining the reason why GDB stopped unwinding
frames, as expressed by the given REASON code (an integer, see the
`unwind_stop_reason' method further down in this section).

-- Function: gdb.invalidate_cached_frames
GDB internally keeps a cache of the frames that have been unwound.
This function invalidates this cache.

This function should not generally be called by ordinary Python
code. It is documented for the sake of completeness.

A `gdb.Frame' object has the following methods:

-- Function: Frame.is_valid ()
Returns true if the `gdb.Frame' object is valid, false if not. A
frame object can become invalid if the frame it refers to doesn't
exist anymore in the inferior. All `gdb.Frame' methods will throw
an exception if it is invalid at the time the method is called.

-- Function: Frame.name ()
Returns the function name of the frame, or `None' if it can't be
obtained.

-- Function: Frame.architecture ()
Returns the `gdb.Architecture' object corresponding to the frame's
architecture. *Note Architectures In Python::.

-- Function: Frame.type ()
Returns the type of the frame. The value can be one of:
`gdb.NORMAL_FRAME'
An ordinary stack frame.

`gdb.DUMMY_FRAME'
A fake stack frame that was created by GDB when performing an
inferior function call.

`gdb.INLINE_FRAME'
A frame representing an inlined function. The function was
inlined into a `gdb.NORMAL_FRAME' that is older than this one.

`gdb.TAILCALL_FRAME'
A frame representing a tail call. *Note Tail Call Frames::.

`gdb.SIGTRAMP_FRAME'
A signal trampoline frame. This is the frame created by the
OS when it calls into a signal handler.

`gdb.ARCH_FRAME'
A fake stack frame representing a cross-architecture call.

`gdb.SENTINEL_FRAME'
This is like `gdb.NORMAL_FRAME', but it is only used for the
newest frame.

-- Function: Frame.unwind_stop_reason ()
Return an integer representing the reason why it's not possible to
find more frames toward the outermost frame. Use
`gdb.frame_stop_reason_string' to convert the value returned by
this function to a string. The value can be one of:

`gdb.FRAME_UNWIND_NO_REASON'
No particular reason (older frames should be available).

`gdb.FRAME_UNWIND_NULL_ID'
The previous frame's analyzer returns an invalid result.
This is no longer used by GDB, and is kept only for backward
compatibility.

`gdb.FRAME_UNWIND_OUTERMOST'
This frame is the outermost.

`gdb.FRAME_UNWIND_UNAVAILABLE'
Cannot unwind further, because that would require knowing the
values of registers or memory that have not been collected.

`gdb.FRAME_UNWIND_INNER_ID'
This frame ID looks like it ought to belong to a NEXT frame,
but we got it for a PREV frame. Normally, this is a sign of
unwinder failure. It could also indicate stack corruption.

`gdb.FRAME_UNWIND_SAME_ID'
This frame has the same ID as the previous one. That means
that unwinding further would almost certainly give us another
frame with exactly the same ID, so break the chain. Normally,
this is a sign of unwinder failure. It could also indicate
stack corruption.

`gdb.FRAME_UNWIND_NO_SAVED_PC'
The frame unwinder did not find any saved PC, but we needed
one to unwind further.

`gdb.FRAME_UNWIND_MEMORY_ERROR'
The frame unwinder caused an error while trying to access
memory.

`gdb.FRAME_UNWIND_FIRST_ERROR'
Any stop reason greater or equal to this value indicates some
kind of error. This special value facilitates writing code
that tests for errors in unwinding in a way that will work
correctly even if the list of the other values is modified in
future GDB versions. Using it, you could write:
reason = gdb.selected_frame().unwind_stop_reason ()
reason_str = gdb.frame_stop_reason_string (reason)
if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
print ("An error occurred: %s" % reason_str)

-- Function: Frame.pc ()
Returns the frame's resume address.

-- Function: Frame.block ()
Return the frame's code block. *Note Blocks In Python::. If the
frame does not have a block - for example, if there is no debugging
information for the code in question - then this will throw an
exception.

-- Function: Frame.function ()
Return the symbol for the function corresponding to this frame.
*Note Symbols In Python::.

-- Function: Frame.older ()
Return the frame that called this frame. If this is the oldest
frame, return `None'.

-- Function: Frame.newer ()
Return the frame called by this frame. If this is the newest
frame, return `None'.

-- Function: Frame.find_sal ()
Return the frame's symtab and line object. *Note Symbol Tables In
Python::.

-- Function: Frame.read_register (register)
Return the value of REGISTER in this frame. Returns a `Gdb.Value'
object. Throws an exception if REGISTER does not exist. The
REGISTER argument must be one of the following:
1. A string that is the name of a valid register (e.g., `'sp'' or
`'rax'').

2. A `gdb.RegisterDescriptor' object (*note Registers In
Python::).

3. A GDB internal, platform specific number. Using these
numbers is supported for historic reasons, but is not
recommended as future changes to GDB could change the mapping
between numbers and the registers they represent, breaking
any Python code that uses the platform-specific numbers. The
numbers are usually found in the corresponding
`PLATFORM-tdep.h' file in the GDB source tree.
Using a string to access registers will be slightly slower
than the other two methods as GDB must look up the mapping between
name and internal register number. If performance is critical
consider looking up and caching a `gdb.RegisterDescriptor' object.

-- Function: Frame.read_var (variable [, block])
Return the value of VARIABLE in this frame. If the optional
argument BLOCK is provided, search for the variable from that
block; otherwise start at the frame's current block (which is
determined by the frame's current program counter). The VARIABLE
argument must be a string or a `gdb.Symbol' object; BLOCK must be a
`gdb.Block' object.

-- Function: Frame.select ()
Set this frame to be the selected frame. *Note Examining the
Stack: Stack.

-- Function: Frame.static_link ()
In some languages (e.g., Ada, but also a GNU C extension), a nested
function can access the variables in the outer scope. This is done
via a "static link", which is a reference from the nested frame to
the appropriate outer frame.

This method returns this frame's static link frame, if one exists.
If there is no static link, this method returns `None'.

-- Function: Frame.level ()
Return an integer, the stack frame level for this frame. *Note
Stack Frames: Frames.

-- Function: Frame.language ()
Return a string, the source language for this frame.

File: gdb.info, Node: Blocks In Python, Next: Symbols In Python, Prev: Frames In Python, Up: Python API

23.3.2.29 Accessing blocks from Python
.....................................

In GDB, symbols are stored in blocks. A block corresponds roughly to a
scope in the source code. Blocks are organized hierarchically, and are
represented individually in Python as a `gdb.Block'. Blocks rely on
debugging information being available.

A frame has a block. Please see *Note Frames In Python::, for a more
in-depth discussion of frames.

The outermost block is known as the "global block". The global
block typically holds public global variables and functions.

The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.

GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Python::).

Here is a short example that should help explain blocks:

/* This is in the global block. */
int global;

/* This is in the static block. */
static int file_scope;

/* 'function' is in the global block, and 'argument' is
in a block nested inside of 'function'. */
int function (int argument)
{
/* 'local' is in a block inside 'function'. It may or may
not be in the same block as 'argument'. */
int local;

{
/* 'inner' is in a block whose superblock is the one holding
'local'. */
int inner;

/* If this call is expanded by the compiler, you may see
a nested block here whose function is 'inline_function'
and whose superblock is the one holding 'inner'. */
inline_function ();
}
}

A `gdb.Block' is iterable. The iterator returns the symbols (*note
Symbols In Python::) local to the block. Python programs should not
assume that a specific block object will always contain a given symbol,
since changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table. You can also use Python's "dictionary
syntax" to access variables in this block, e.g.:

symbol = some_block['variable'] # symbol is of type gdb.Symbol

The following block-related functions are available in the `gdb'
module:

-- Function: gdb.block_for_pc (pc)
Return the innermost `gdb.Block' containing the given PC value.
If the block cannot be found for the PC value specified, the
function will return `None'. This is identical to
`gdb.current_progspace().block_for_pc(pc)' and is included for
historical compatibility.

A `gdb.Block' object has the following methods:

-- Function: Block.is_valid ()
Returns `True' if the `gdb.Block' object is valid, `False' if not.
A block object can become invalid if the block it refers to
doesn't exist anymore in the inferior. All other `gdb.Block'
methods will throw an exception if it is invalid at the time the
method is called. The block's validity is also checked during
iteration over symbols of the block.

A `gdb.Block' object has the following attributes:

-- Variable: Block.start
The start address of the block. This attribute is not writable.

-- Variable: Block.end
One past the last address that appears in the block. This
attribute is not writable.

-- Variable: Block.function
The name of the block represented as a `gdb.Symbol'. If the block
is not named, then this attribute holds `None'. This attribute is
not writable.

For ordinary function blocks, the superblock is the static block.
However, you should note that it is possible for a function block
to have a superblock that is not the static block - for instance
this happens for an inlined function.

-- Variable: Block.superblock
The block containing this block. If this parent block does not
exist, this attribute holds `None'. This attribute is not
writable.

-- Variable: Block.global_block
The global block associated with this block. This attribute is not
writable.

-- Variable: Block.static_block
The static block associated with this block. This attribute is not
writable.

-- Variable: Block.is_global
`True' if the `gdb.Block' object is a global block, `False' if
not. This attribute is not writable.

-- Variable: Block.is_static
`True' if the `gdb.Block' object is a static block, `False' if
not. This attribute is not writable.

File: gdb.info, Node: Symbols In Python, Next: Symbol Tables In Python, Prev: Blocks In Python, Up: Python API

23.3.2.30 Python representation of Symbols
.........................................

GDB represents every variable, function and type as an entry in a
symbol table. *Note Examining the Symbol Table: Symbols. Similarly,
Python represents these symbols in GDB with the `gdb.Symbol' object.

The following symbol-related functions are available in the `gdb'
module:

-- Function: gdb.lookup_symbol (name [, block [, domain]])
This function searches for a symbol by name. The search scope can
be restricted to the parameters defined in the optional domain and
block arguments.

NAME is the name of the symbol. It must be a string. The
optional BLOCK argument restricts the search to symbols visible in
that BLOCK. The BLOCK argument must be a `gdb.Block' object. If
omitted, the block for the current frame is used. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the `gdb'
module and described later in this chapter.

The result is a tuple of two elements. The first element is a
`gdb.Symbol' object or `None' if the symbol is not found. If the
symbol is found, the second element is `True' if the symbol is a
field of a method's object (e.g., `this' in C++), otherwise it is
`False'. If the symbol is not found, the second element is
`False'.

-- Function: gdb.lookup_global_symbol (name [, domain])
This function searches for a global symbol by name. The search
scope can be restricted to by the domain argument.

NAME is the name of the symbol. It must be a string. The
optional DOMAIN argument restricts the search to the domain type.
The DOMAIN argument must be a domain constant defined in the `gdb'
module and described later in this chapter.

The result is a `gdb.Symbol' object or `None' if the symbol is not
found.

-- Function: gdb.lookup_static_symbol (name [, domain])
This function searches for a global symbol with static linkage by
name. The search scope can be restricted to by the domain
argument.

NAME is the name of the symbol. It must be a string. The
optional DOMAIN argument restricts the search to the domain type.
The DOMAIN argument must be a domain constant defined in the `gdb'
module and described later in this chapter.

The result is a `gdb.Symbol' object or `None' if the symbol is not
found.

Note that this function will not find function-scoped static
variables. To look up such variables, iterate over the variables
of the function's `gdb.Block' and check that `block.addr_class' is
`gdb.SYMBOL_LOC_STATIC'.

There can be multiple global symbols with static linkage with the
same name. This function will only return the first matching
symbol that it finds. Which symbol is found depends on where GDB
is currently stopped, as GDB will first search for matching
symbols in the current object file, and then search all other
object files. If the application is not yet running then GDB will
search all object files in the order they appear in the debug
information.

-- Function: gdb.lookup_static_symbols (name [, domain])
Similar to `gdb.lookup_static_symbol', this function searches for
global symbols with static linkage by name, and optionally
restricted by the domain argument. However, this function returns
a list of all matching symbols found, not just the first one.

NAME is the name of the symbol. It must be a string. The
optional DOMAIN argument restricts the search to the domain type.
The DOMAIN argument must be a domain constant defined in the `gdb'
module and described later in this chapter.

The result is a list of `gdb.Symbol' objects which could be empty
if no matching symbols were found.

Note that this function will not find function-scoped static
variables. To look up such variables, iterate over the variables
of the function's `gdb.Block' and check that `block.addr_class' is
`gdb.SYMBOL_LOC_STATIC'.

A `gdb.Symbol' object has the following attributes:

-- Variable: Symbol.type
The type of the symbol or `None' if no type is recorded. This
attribute is represented as a `gdb.Type' object. *Note Types In
Python::. This attribute is not writable.

-- Variable: Symbol.symtab
The symbol table in which the symbol appears. This attribute is
represented as a `gdb.Symtab' object. *Note Symbol Tables In
Python::. This attribute is not writable.

-- Variable: Symbol.line
The line number in the source code at which the symbol was defined.
This is an integer.

-- Variable: Symbol.name
The name of the symbol as a string. This attribute is not
writable.

-- Variable: Symbol.linkage_name
The name of the symbol, as used by the linker (i.e., may be
mangled). This attribute is not writable.

-- Variable: Symbol.print_name
The name of the symbol in a form suitable for output. This is
either `name' or `linkage_name', depending on whether the user
asked GDB to display demangled or mangled names.

-- Variable: Symbol.addr_class
The address class of the symbol. This classifies how to find the
value of a symbol. Each address class is a constant defined in the
`gdb' module and described later in this chapter.

-- Variable: Symbol.needs_frame
This is `True' if evaluating this symbol's value requires a frame
(*note Frames In Python::) and `False' otherwise. Typically,
local variables will require a frame, but other symbols will not.

-- Variable: Symbol.is_argument
`True' if the symbol is an argument of a function.

-- Variable: Symbol.is_constant
`True' if the symbol is a constant.

-- Variable: Symbol.is_function
`True' if the symbol is a function or a method.

-- Variable: Symbol.is_variable
`True' if the symbol is a variable, as opposed to something like a
function or type. Note that this also returns `False' for
arguments.

A `gdb.Symbol' object has the following methods:

-- Function: Symbol.is_valid ()
Returns `True' if the `gdb.Symbol' object is valid, `False' if
not. A `gdb.Symbol' object can become invalid if the symbol it
refers to does not exist in GDB any longer. All other
`gdb.Symbol' methods will throw an exception if it is invalid at
the time the method is called.

-- Function: Symbol.value ([frame])
Compute the value of the symbol, as a `gdb.Value'. For functions,
this computes the address of the function, cast to the appropriate
type. If the symbol requires a frame in order to compute its
value, then FRAME must be given. If FRAME is not given, or if
FRAME is invalid, then this method will throw an exception.

The available domain categories in `gdb.Symbol' are represented as
constants in the `gdb' module:

`gdb.SYMBOL_UNDEF_DOMAIN'
This is used when a domain has not been discovered or none of the
following domains apply. This usually indicates an error either
in the symbol information or in GDB's handling of symbols.

`gdb.SYMBOL_VAR_DOMAIN'
This domain contains variables.

`gdb.SYMBOL_FUNCTION_DOMAIN'
This domain contains functions.

`gdb.SYMBOL_TYPE_DOMAIN'
This domain contains types. In a C-like language, types using a
tag (the name appearing after a `struct', `union', or `enum'
keyword) will not appear here; in other languages, all types are
in this domain.

`gdb.SYMBOL_STRUCT_DOMAIN'
This domain holds struct, union and enum tag names. This domain is
only used for C-like languages. For example, in this code:
struct type_one { int x; };
typedef struct type_one type_two;
Here `type_one' will be in `SYMBOL_STRUCT_DOMAIN', but `type_two'
will be in `SYMBOL_TYPE_DOMAIN'.

`gdb.SYMBOL_LABEL_DOMAIN'
This domain contains names of labels (for gotos).

`gdb.SYMBOL_MODULE_DOMAIN'
This domain contains names of Fortran module types.

`gdb.SYMBOL_COMMON_BLOCK_DOMAIN'
This domain contains names of Fortran common blocks.

When searching for a symbol, the desired domain constant can be
passed verbatim to the lookup function. For example:
symbol = gdb.lookup_symbol ("name", domain=gdb.SYMBOL_VAR_DOMAIN)

For more complex searches, there is a corresponding set of constants,
each named after one of the preceding constants, but with the `SEARCH'
prefix replacing the `SYMBOL' prefix; for example,
`SEARCH_LABEL_DOMAIN'. These may be or'd together to form a search
constant, e.g.:
symbol = gdb.lookup_symbol ("name",
domain=gdb.SEARCH_VAR_DOMAIN | gdb.SEARCH_TYPE_DOMAIN)

The available address class categories in `gdb.Symbol' are
represented as constants in the `gdb' module:

`gdb.SYMBOL_LOC_UNDEF'
If this is returned by address class, it indicates an error either
in the symbol information or in GDB's handling of symbols.

`gdb.SYMBOL_LOC_CONST'
Value is constant int.

`gdb.SYMBOL_LOC_STATIC'
Value is at a fixed address.

`gdb.SYMBOL_LOC_REGISTER'
Value is in a register.

`gdb.SYMBOL_LOC_ARG'
Value is an argument. This value is at the offset stored within
the symbol inside the frame's argument list.

`gdb.SYMBOL_LOC_REF_ARG'
Value address is stored in the frame's argument list. Just like
`LOC_ARG' except that the value's address is stored at the offset,
not the value itself.

`gdb.SYMBOL_LOC_REGPARM_ADDR'
Value is a specified register. Just like `LOC_REGISTER' except
the register holds the address of the argument instead of the
argument itself.

`gdb.SYMBOL_LOC_LOCAL'
Value is a local variable.

`gdb.SYMBOL_LOC_TYPEDEF'
Value not used. Symbols in the domain `SYMBOL_STRUCT_DOMAIN' all
have this class.

`gdb.SYMBOL_LOC_LABEL'
Value is a label.

`gdb.SYMBOL_LOC_BLOCK'
Value is a block.

`gdb.SYMBOL_LOC_CONST_BYTES'
Value is a byte-sequence.

`gdb.SYMBOL_LOC_UNRESOLVED'
Value is at a fixed address, but the address of the variable has
to be determined from the minimal symbol table whenever the
variable is referenced.

`gdb.SYMBOL_LOC_OPTIMIZED_OUT'
The value does not actually exist in the program.

`gdb.SYMBOL_LOC_COMPUTED'
The value's address is a computed location.

`gdb.SYMBOL_LOC_COMMON_BLOCK'
The value's address is a symbol. This is only used for Fortran
common blocks.

File: gdb.info, Node: Symbol Tables In Python, Next: Line Tables In Python, Prev: Symbols In Python, Up: Python API

23.3.2.31 Symbol table representation in Python
..............................................

Access to symbol table data maintained by GDB on the inferior is
exposed to Python via two objects: `gdb.Symtab_and_line' and
`gdb.Symtab'. Symbol table and line data for a frame is returned from
the `find_sal' method in `gdb.Frame' object. *Note Frames In Python::.

For more information on GDB's symbol table management, see *Note
Examining the Symbol Table: Symbols, for more information.

A `gdb.Symtab_and_line' object has the following attributes:

-- Variable: Symtab_and_line.symtab
The symbol table object (`gdb.Symtab') for this frame. This
attribute is not writable.

-- Variable: Symtab_and_line.pc
Indicates the start of the address range occupied by code for the
current source line. This attribute is not writable.

-- Variable: Symtab_and_line.last
Indicates the end of the address range occupied by code for the
current source line. This attribute is not writable.

-- Variable: Symtab_and_line.line
Indicates the current line number for this object. This attribute
is not writable.

A `gdb.Symtab_and_line' object has the following methods:

-- Function: Symtab_and_line.is_valid ()
Returns `True' if the `gdb.Symtab_and_line' object is valid,
`False' if not. A `gdb.Symtab_and_line' object can become invalid
if the Symbol table and line object it refers to does not exist in
GDB any longer. All other `gdb.Symtab_and_line' methods will
throw an exception if it is invalid at the time the method is
called.

A `gdb.Symtab' object has the following attributes:

-- Variable: Symtab.filename
The symbol table's source filename. This attribute is not
writable.

-- Variable: Symtab.objfile
The symbol table's backing object file. *Note Objfiles In
Python::. This attribute is not writable.

-- Variable: Symtab.producer
The name and possibly version number of the program that compiled
the code in the symbol table. The contents of this string is up
to the compiler. If no producer information is available then
`None' is returned. This attribute is not writable.

A `gdb.Symtab' object has the following methods:

-- Function: Symtab.is_valid ()
Returns `True' if the `gdb.Symtab' object is valid, `False' if
not. A `gdb.Symtab' object can become invalid if the symbol table
it refers to does not exist in GDB any longer. All other
`gdb.Symtab' methods will throw an exception if it is invalid at
the time the method is called.

-- Function: Symtab.fullname ()
Return the symbol table's source absolute file name.

-- Function: Symtab.global_block ()
Return the global block of the underlying symbol table. *Note
Blocks In Python::.

-- Function: Symtab.static_block ()
Return the static block of the underlying symbol table. *Note
Blocks In Python::.

-- Function: Symtab.linetable ()
Return the line table associated with the symbol table. *Note
Line Tables In Python::.

File: gdb.info, Node: Line Tables In Python, Next: Breakpoints In Python, Prev: Symbol Tables In Python, Up: Python API

23.3.2.32 Manipulating line tables using Python
..............................................

Python code can request and inspect line table information from a
symbol table that is loaded in GDB. A line table is a mapping of
source lines to their executable locations in memory. To acquire the
line table information for a particular symbol table, use the
`linetable' function (*note Symbol Tables In Python::).

A `gdb.LineTable' is iterable. The iterator returns
`LineTableEntry' objects that correspond to the source line and address
for each line table entry. `LineTableEntry' objects have the following
attributes:

-- Variable: LineTableEntry.line
The source line number for this line table entry. This number
corresponds to the actual line of source. This attribute is not
writable.

-- Variable: LineTableEntry.pc
The address that is associated with the line table entry where the
executable code for that source line resides in memory. This
attribute is not writable.

As there can be multiple addresses for a single source line, you may
receive multiple `LineTableEntry' objects with matching `line'
attributes, but with different `pc' attributes. The iterator is sorted
in ascending `pc' order. Here is a small example illustrating
iterating over a line table.

symtab = gdb.selected_frame().find_sal().symtab
linetable = symtab.linetable()
for line in linetable:
print ("Line: "+str(line.line)+" Address: "+hex(line.pc))

This will have the following output:

Line: 33 Address: 0x4005c8L
Line: 37 Address: 0x4005caL
Line: 39 Address: 0x4005d2L
Line: 40 Address: 0x4005f8L
Line: 42 Address: 0x4005ffL
Line: 44 Address: 0x400608L
Line: 42 Address: 0x40060cL
Line: 45 Address: 0x400615L

In addition to being able to iterate over a `LineTable', it also has
the following direct access methods:

-- Function: LineTable.line (line)
Return a Python `Tuple' of `LineTableEntry' objects for any
entries in the line table for the given LINE, which specifies the
source code line. If there are no entries for that source code
LINE, the Python `None' is returned.

-- Function: LineTable.has_line (line)
Return a Python `Boolean' indicating whether there is an entry in
the line table for this source line. Return `True' if an entry is
found, or `False' if not.

-- Function: LineTable.source_lines ()
Return a Python `List' of the source line numbers in the symbol
table. Only lines with executable code locations are returned.
The contents of the `List' will just be the source line entries
represented as Python `Long' values.

File: gdb.info, Node: Breakpoints In Python, Next: Finish Breakpoints in Python, Prev: Line Tables In Python, Up: Python API

23.3.2.33 Manipulating breakpoints using Python
..............................................

Python code can manipulate breakpoints via the `gdb.Breakpoint' class.

A breakpoint can be created using one of the two forms of the
`gdb.Breakpoint' constructor. The first one accepts a string like one
would pass to the `break' (*note Setting Breakpoints: Set Breaks.) and
`watch' (*note Setting Watchpoints: Set Watchpoints.) commands, and can
be used to create both breakpoints and watchpoints. The second accepts
separate Python arguments similar to *Note Explicit Locations::, and
can only be used to create breakpoints.

-- Function: Breakpoint.__init__ (spec [, type ][, wp_class ][,
internal ][, temporary ][, qualified ])
Create a new breakpoint according to SPEC, which is a string
naming the location of a breakpoint, or an expression that defines
a watchpoint. The string should describe a location in a format
recognized by the `break' command (*note Setting Breakpoints: Set
Breaks.) or, in the case of a watchpoint, by the `watch' command
(*note Setting Watchpoints: Set Watchpoints.).

The optional TYPE argument specifies the type of the breakpoint to
create, as defined below.

The optional WP_CLASS argument defines the class of watchpoint to
create, if TYPE is `gdb.BP_WATCHPOINT'. If WP_CLASS is omitted, it
defaults to `gdb.WP_WRITE'.

The optional INTERNAL argument allows the breakpoint to become
invisible to the user. The breakpoint will neither be reported
when created, nor will it be listed in the output from `info
breakpoints' (but will be listed with the `maint info breakpoints'
command).

The optional TEMPORARY argument makes the breakpoint a temporary
breakpoint. Temporary breakpoints are deleted after they have
been hit. Any further access to the Python breakpoint after it
has been hit will result in a runtime error (as that breakpoint
has now been automatically deleted).

The optional QUALIFIED argument is a boolean that allows
interpreting the function passed in `spec' as a fully-qualified
name. It is equivalent to `break''s `-qualified' flag (*note
Linespec Locations:: and *Note Explicit Locations::).

-- Function: Breakpoint.__init__ ([ source ][, function ][, label ][,
line ], ][ internal ][, temporary ][, qualified ])
This second form of creating a new breakpoint specifies the
explicit location (*note Explicit Locations::) using keywords.
The new breakpoint will be created in the specified source file
SOURCE, at the specified FUNCTION, LABEL and LINE.

INTERNAL, TEMPORARY and QUALIFIED have the same usage as explained
previously.

The available types are represented by constants defined in the `gdb'
module:

`gdb.BP_BREAKPOINT'
Normal code breakpoint.

`gdb.BP_HARDWARE_BREAKPOINT'
Hardware assisted code breakpoint.

`gdb.BP_WATCHPOINT'
Watchpoint breakpoint.

`gdb.BP_HARDWARE_WATCHPOINT'
Hardware assisted watchpoint.

`gdb.BP_READ_WATCHPOINT'
Hardware assisted read watchpoint.

`gdb.BP_ACCESS_WATCHPOINT'
Hardware assisted access watchpoint.

`gdb.BP_CATCHPOINT'
Catchpoint. Currently, this type can't be used when creating
`gdb.Breakpoint' objects, but will be present in `gdb.Breakpoint'
objects reported from `gdb.BreakpointEvent's (*note Events In
Python::).

The available watchpoint types are represented by constants defined
in the `gdb' module:

`gdb.WP_READ'
Read only watchpoint.

`gdb.WP_WRITE'
Write only watchpoint.

`gdb.WP_ACCESS'
Read/Write watchpoint.

-- Function: Breakpoint.stop (self)
The `gdb.Breakpoint' class can be sub-classed and, in particular,
you may choose to implement the `stop' method. If this method is
defined in a sub-class of `gdb.Breakpoint', it will be called when
the inferior reaches any location of a breakpoint which
instantiates that sub-class. If the method returns `True', the
inferior will be stopped at the location of the breakpoint,
otherwise the inferior will continue.

If there are multiple breakpoints at the same location with a
`stop' method, each one will be called regardless of the return
status of the previous. This ensures that all `stop' methods have
a chance to execute at that location. In this scenario if one of
the methods returns `True' but the others return `False', the
inferior will still be stopped.

You should not alter the execution state of the inferior (i.e.,
step, next, etc.), alter the current frame context (i.e., change
the current active frame), or alter, add or delete any breakpoint.
As a general rule, you should not alter any data within GDB or
the inferior at this time.

Example `stop' implementation:

class MyBreakpoint (gdb.Breakpoint):
def stop (self):
inf_val = gdb.parse_and_eval("foo")
if inf_val == 3:
return True
return False

-- Function: Breakpoint.is_valid ()
Return `True' if this `Breakpoint' object is valid, `False'
otherwise. A `Breakpoint' object can become invalid if the user
deletes the breakpoint. In this case, the object still exists,
but the underlying breakpoint does not. In the cases of
watchpoint scope, the watchpoint remains valid even if execution
of the inferior leaves the scope of that watchpoint.

-- Function: Breakpoint.delete ()
Permanently deletes the GDB breakpoint. This also invalidates the
Python `Breakpoint' object. Any further access to this object's
attributes or methods will raise an error.

-- Variable: Breakpoint.enabled
This attribute is `True' if the breakpoint is enabled, and `False'
otherwise. This attribute is writable. You can use it to enable
or disable the breakpoint.

-- Variable: Breakpoint.silent
This attribute is `True' if the breakpoint is silent, and `False'
otherwise. This attribute is writable.

Note that a breakpoint can also be silent if it has commands and
the first command is `silent'. This is not reported by the
`silent' attribute.

-- Variable: Breakpoint.pending
This attribute is `True' if the breakpoint is pending, and `False'
otherwise. *Note Set Breaks::. This attribute is read-only.

-- Variable: Breakpoint.thread
If the breakpoint is thread-specific (*note Thread-Specific
Breakpoints::), this attribute holds the thread's global id. If
the breakpoint is not thread-specific, this attribute is `None'.
This attribute is writable.

Only one of `Breakpoint.thread' or `Breakpoint.inferior' can be
set to a valid id at any time, that is, a breakpoint can be thread
specific, or inferior specific, but not both.

-- Variable: Breakpoint.inferior
If the breakpoint is inferior-specific (*note Inferior-Specific
Breakpoints::), this attribute holds the inferior's id. If the
breakpoint is not inferior-specific, this attribute is `None'.

This attribute can be written for breakpoints of type
`gdb.BP_BREAKPOINT' and `gdb.BP_HARDWARE_BREAKPOINT'.

-- Variable: Breakpoint.task
If the breakpoint is Ada task-specific, this attribute holds the
Ada task id. If the breakpoint is not task-specific (or the
underlying language is not Ada), this attribute is `None'. This
attribute is writable.

-- Variable: Breakpoint.ignore_count
This attribute holds the ignore count for the breakpoint, an
integer. This attribute is writable.

-- Variable: Breakpoint.number
This attribute holds the breakpoint's number -- the identifier
used by the user to manipulate the breakpoint. This attribute is
not writable.

-- Variable: Breakpoint.type
This attribute holds the breakpoint's type -- the identifier used
to determine the actual breakpoint type or use-case. This
attribute is not writable.

-- Variable: Breakpoint.visible
This attribute tells whether the breakpoint is visible to the user
when set, or when the `info breakpoints' command is run. This
attribute is not writable.

-- Variable: Breakpoint.temporary
This attribute indicates whether the breakpoint was created as a
temporary breakpoint. Temporary breakpoints are automatically
deleted after that breakpoint has been hit. Access to this
attribute, and all other attributes and functions other than the
`is_valid' function, will result in an error after the breakpoint
has been hit (as it has been automatically deleted). This
attribute is not writable.

-- Variable: Breakpoint.hit_count
This attribute holds the hit count for the breakpoint, an integer.
This attribute is writable, but currently it can only be set to
zero.

-- Variable: Breakpoint.location
This attribute holds the location of the breakpoint, as specified
by the user. It is a string. If the breakpoint does not have a
location (that is, it is a watchpoint) the attribute's value is
`None'. This attribute is not writable.

-- Variable: Breakpoint.locations
Get the most current list of breakpoint locations that are
inserted for this breakpoint, with elements of type
`gdb.BreakpointLocation' (described below). This functionality
matches that of the `info breakpoint' command (*note Set
Breaks::), in that it only retrieves the most current list of
locations, thus the list itself when returned is not updated
behind the scenes. This attribute is not writable.

-- Variable: Breakpoint.expression
This attribute holds a breakpoint expression, as specified by the
user. It is a string. If the breakpoint does not have an
expression (the breakpoint is not a watchpoint) the attribute's
value is `None'. This attribute is not writable.

-- Variable: Breakpoint.condition
This attribute holds the condition of the breakpoint, as specified
by the user. It is a string. If there is no condition, this
attribute's value is `None'. This attribute is writable.

-- Variable: Breakpoint.commands
This attribute holds the commands attached to the breakpoint. If
there are commands, this attribute's value is a string holding all
the commands, separated by newlines. If there are no commands,
this attribute is `None'. This attribute is writable.

Breakpoint Locations
--------------------

A breakpoint location is one of the actual places where a breakpoint
has been set, represented in the Python API by the
`gdb.BreakpointLocation' type. This type is never instantiated by the
user directly, but is retrieved from `Breakpoint.locations' which
returns a list of breakpoint locations where it is currently set.
Breakpoint locations can become invalid if new symbol files are loaded
or dynamically loaded libraries are closed. Accessing the attributes
of an invalidated breakpoint location will throw a `RuntimeError'
exception. Access the `Breakpoint.locations' attribute again to
retrieve the new and valid breakpoints location list.

-- Variable: BreakpointLocation.source
This attribute returns the source file path and line number where
this location was set. The type of the attribute is a tuple of
STRING and LONG. If the breakpoint location doesn't have a source
location, it returns None, which is the case for watchpoints and
catchpoints. This will throw a `RuntimeError' exception if the
location has been invalidated. This attribute is not writable.

-- Variable: BreakpointLocation.address
This attribute returns the address where this location was set.
This attribute is of type long. This will throw a `RuntimeError'
exception if the location has been invalidated. This attribute is
not writable.

-- Variable: BreakpointLocation.enabled
This attribute holds the value for whether or not this location is
enabled. This attribute is writable (boolean). This will throw a
`RuntimeError' exception if the location has been invalidated.

-- Variable: BreakpointLocation.owner
This attribute holds a reference to the `gdb.Breakpoint' owner
object, from which this `gdb.BreakpointLocation' was retrieved
from. This will throw a `RuntimeError' exception if the location
has been invalidated. This attribute is not writable.

-- Variable: BreakpointLocation.function
This attribute gets the name of the function where this location
was set. If no function could be found this attribute returns
`None'. This will throw a `RuntimeError' exception if the
location has been invalidated. This attribute is not writable.

-- Variable: BreakpointLocation.fullname
This attribute gets the full name of where this location was set.
If no full name could be found, this attribute returns `None'.
This will throw a `RuntimeError' exception if the location has
been invalidated. This attribute is not writable.

-- Variable: BreakpointLocation.thread_groups
This attribute gets the thread groups it was set in. It returns a
`List' of the thread group ID's. This will throw a `RuntimeError'
exception if the location has been invalidated. This attribute is
not writable.

File: gdb.info, Node: Finish Breakpoints in Python, Next: Lazy Strings In Python, Prev: Breakpoints In Python, Up: Python API

23.3.2.34 Finish Breakpoints
...........................

A finish breakpoint is a temporary breakpoint set at the return address
of a frame, based on the `finish' command. `gdb.FinishBreakpoint'
extends `gdb.Breakpoint'. The underlying breakpoint will be disabled
and deleted when the execution will run out of the breakpoint scope
(i.e. `Breakpoint.stop' or `FinishBreakpoint.out_of_scope' triggered).
Finish breakpoints are thread specific and must be create with the right
thread selected.

-- Function: FinishBreakpoint.__init__ ([frame] [, internal])
Create a finish breakpoint at the return address of the `gdb.Frame'
object FRAME. If FRAME is not provided, this defaults to the
newest frame. The optional INTERNAL argument allows the
breakpoint to become invisible to the user. *Note Breakpoints In
Python::, for further details about this argument.

-- Function: FinishBreakpoint.out_of_scope (self)
In some circumstances (e.g. `longjmp', C++ exceptions, GDB
`return' command, ...), a function may not properly terminate, and
thus never hit the finish breakpoint. When GDB notices such a
situation, the `out_of_scope' callback will be triggered.

You may want to sub-class `gdb.FinishBreakpoint' and override this
method:

class MyFinishBreakpoint (gdb.FinishBreakpoint)
def stop (self):
print ("normal finish")
return True

def out_of_scope ():
print ("abnormal finish")

-- Variable: FinishBreakpoint.return_value
When GDB is stopped at a finish breakpoint and the frame used to
build the `gdb.FinishBreakpoint' object had debug symbols, this
attribute will contain a `gdb.Value' object corresponding to the
return value of the function. The value will be `None' if the
function return type is `void' or if the return value was not
computable. This attribute is not writable.

File: gdb.info, Node: Lazy Strings In Python, Next: Architectures In Python, Prev: Finish Breakpoints in Python, Up: Python API

23.3.2.35 Python representation of lazy strings
..............................................

A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.

A `gdb.LazyString' is represented in GDB as an `address' that points
to a region of memory, an `encoding' that will be used to encode that
region of memory, and a `length' to delimit the region of memory that
represents the string. The difference between a `gdb.LazyString' and a
string wrapped within a `gdb.Value' is that a `gdb.LazyString' will be
treated differently by GDB when printing. A `gdb.LazyString' is
retrieved and encoded during printing, while a `gdb.Value' wrapping a
string is immediately retrieved and encoded on creation.

A `gdb.LazyString' object has the following functions:

-- Function: LazyString.value ()
Convert the `gdb.LazyString' to a `gdb.Value'. This value will
point to the string in memory, but will lose all the delayed
retrieval, encoding and handling that GDB applies to a
`gdb.LazyString'.

-- Variable: LazyString.address
This attribute holds the address of the string. This attribute is
not writable.

-- Variable: LazyString.length
This attribute holds the length of the string in characters. If
the length is -1, then the string will be fetched and encoded up
to the first null of appropriate width. This attribute is not
writable.

-- Variable: LazyString.encoding
This attribute holds the encoding that will be applied to the
string when the string is printed by GDB. If the encoding is not
set, or contains an empty string, then GDB will select the most
appropriate encoding when the string is printed. This attribute
is not writable.

-- Variable: LazyString.type
This attribute holds the type that is represented by the lazy
string's type. For a lazy string this is a pointer or array type.
To resolve this to the lazy string's character type, use the
type's `target' method. *Note Types In Python::. This attribute
is not writable.

File: gdb.info, Node: Architectures In Python, Next: Registers In Python, Prev: Lazy Strings In Python, Up: Python API

23.3.2.36 Python representation of architectures
...............................................

GDB uses architecture specific parameters and artifacts in a number of
its various computations. An architecture is represented by an
instance of the `gdb.Architecture' class.

A `gdb.Architecture' class has the following methods:

-- Function: Architecture.name ()
Return the name (string value) of the architecture.

-- Function: Architecture.disassemble (start_pc [, end_pc [, count]])
Return a list of disassembled instructions starting from the memory
address START_PC. The optional arguments END_PC and COUNT
determine the number of instructions in the returned list. If
both the optional arguments END_PC and COUNT are specified, then a
list of at most COUNT disassembled instructions whose start
address falls in the closed memory address interval from START_PC
to END_PC are returned. If END_PC is not specified, but COUNT is
specified, then COUNT number of instructions starting from the
address START_PC are returned. If COUNT is not specified but
END_PC is specified, then all instructions whose start address
falls in the closed memory address interval from START_PC to
END_PC are returned. If neither END_PC nor COUNT are specified,
then a single instruction at START_PC is returned. For all of
these cases, each element of the returned list is a Python `dict'
with the following string keys:

`addr'
The value corresponding to this key is a Python long integer
capturing the memory address of the instruction.

`asm'
The value corresponding to this key is a string value which
represents the instruction with assembly language mnemonics.
The assembly language flavor used is the same as that
specified by the current CLI variable `disassembly-flavor'.
*Note Machine Code::.

`length'
The value corresponding to this key is the length (integer
value) of the instruction in bytes.

-- Function: Architecture.integer_type (size [, signed])
This function looks up an integer type by its SIZE, and optionally
whether or not it is signed.

SIZE is the size, in bits, of the desired integer type. Only
certain sizes are currently supported: 0, 8, 16, 24, 32, 64, and
128.

If SIGNED is not specified, it defaults to `True'. If SIGNED is
`False', the returned type will be unsigned.

If the indicated type cannot be found, this function will throw a
`ValueError' exception.

-- Function: Architecture.registers ([ reggroup ])
Return a `gdb.RegisterDescriptorIterator' (*note Registers In
Python::) for all of the registers in REGGROUP, a string that is
the name of a register group. If REGGROUP is omitted, or is the
empty string, then the register group `all' is assumed.

-- Function: Architecture.register_groups ()
Return a `gdb.RegisterGroupsIterator' (*note Registers In
Python::) for all of the register groups available for the
`gdb.Architecture'.

File: gdb.info, Node: Registers In Python, Next: Connections In Python, Prev: Architectures In Python, Up: Python API

23.3.2.37 Registers In Python
............................

Python code can request from a `gdb.Architecture' information about the
set of registers available (*note `Architecture.registers':
gdbpy_architecture_registers.). The register information is returned
as a `gdb.RegisterDescriptorIterator', which is an iterator that in
turn returns `gdb.RegisterDescriptor' objects.

A `gdb.RegisterDescriptor' does not provide the value of a register
(*note `Frame.read_register': gdbpy_frame_read_register. for reading a
register's value), instead the `RegisterDescriptor' is a way to
discover which registers are available for a particular architecture.

A `gdb.RegisterDescriptor' has the following read-only properties:

-- Variable: RegisterDescriptor.name
The name of this register.

It is also possible to lookup a register descriptor based on its name
using the following `gdb.RegisterDescriptorIterator' function:

-- Function: RegisterDescriptorIterator.find (name)
Takes NAME as an argument, which must be a string, and returns a
`gdb.RegisterDescriptor' for the register with that name, or
`None' if there is no register with that name.

Python code can also request from a `gdb.Architecture' information
about the set of register groups available on a given architecture
(*note `Architecture.register_groups': gdbpy_architecture_reggroups.).

Every register can be a member of zero or more register groups. Some
register groups are used internally within GDB to control things like
which registers must be saved when calling into the program being
debugged (*note Calling Program Functions: Calling.). Other register
groups exist to allow users to easily see related sets of registers in
commands like `info registers' (*note `info registers REGGROUP':
info_registers_reggroup.).

The register groups information is returned as a
`gdb.RegisterGroupsIterator', which is an iterator that in turn returns
`gdb.RegisterGroup' objects.

A `gdb.RegisterGroup' object has the following read-only properties:

-- Variable: RegisterGroup.name
A string that is the name of this register group.

File: gdb.info, Node: Connections In Python, Next: TUI Windows In Python, Prev: Registers In Python, Up: Python API

23.3.2.38 Connections In Python
..............................

GDB lets you run and debug multiple programs in a single session. Each
program being debugged has a connection, the connection describes how
GDB controls the program being debugged. Examples of different
connection types are `native' and `remote'. *Note Inferiors
Connections and Programs::.

Connections in GDB are represented as instances of
`gdb.TargetConnection', or as one of its sub-classes. To get a list of
all connections use `gdb.connections' (*note gdb.connections:
gdbpy_connections.).

To get the connection for a single `gdb.Inferior' read its
`gdb.Inferior.connection' attribute (*note gdb.Inferior.connection:
gdbpy_inferior_connection.).

Currently there is only a single sub-class of
`gdb.TargetConnection', `gdb.RemoteTargetConnection', however,
additional sub-classes may be added in future releases of GDB. As a
result you should avoid writing code like:

conn = gdb.selected_inferior().connection
if type(conn) is gdb.RemoteTargetConnection:
print("This is a remote target connection")

as this may fail when more connection types are added. Instead, you
should write:

conn = gdb.selected_inferior().connection
if isinstance(conn, gdb.RemoteTargetConnection):
print("This is a remote target connection")

A `gdb.TargetConnection' has the following method:

-- Function: TargetConnection.is_valid ()
Return `True' if the `gdb.TargetConnection' object is valid,
`False' if not. A `gdb.TargetConnection' will become invalid if
the connection no longer exists within GDB, this might happen when
no inferiors are using the connection, but could be delayed until
the user replaces the current target.

Reading any of the `gdb.TargetConnection' properties will throw an
exception if the connection is invalid.

A `gdb.TargetConnection' has the following read-only properties:

-- Variable: TargetConnection.num
An integer assigned by GDB to uniquely identify this connection.
This is the same value as displayed in the `Num' column of the
`info connections' command output (*note info connections:
Inferiors Connections and Programs.).

-- Variable: TargetConnection.type
A string that describes what type of connection this is. This
string will be one of the valid names that can be passed to the
`target' command (*note target command: Target Commands.).

-- Variable: TargetConnection.description
A string that gives a short description of this target type. This
is the same string that is displayed in the `Description' column of
the `info connection' command output (*note info connections:
Inferiors Connections and Programs.).

-- Variable: TargetConnection.details
An optional string that gives additional information about this
connection. This attribute can be `None' if there are no
additional details for this connection.

An example of a connection type that might have additional details
is the `remote' connection, in this case the details string can
contain the `HOSTNAME:PORT' that was used to connect to the remote
target.

The `gdb.RemoteTargetConnection' class is a sub-class of
`gdb.TargetConnection', and is used to represent `remote' and
`extended-remote' connections. In addition to the attributes and
methods available from the `gdb.TargetConnection' base class, a
`gdb.RemoteTargetConnection' has the following method:

-- Function: RemoteTargetConnection.send_packet (packet)
This method sends PACKET to the remote target and returns the
response. The PACKET should either be a `bytes' object, or a
`Unicode' string.

If PACKET is a `Unicode' string, then the string is encoded to a
`bytes' object using the ASCII codec. If the string can't be
encoded then an `UnicodeError' is raised.

If PACKET is not a `bytes' object, or a `Unicode' string, then a
`TypeError' is raised. If PACKET is empty then a `ValueError' is
raised.

The response is returned as a `bytes' object. If it is known that
the response can be represented as a string then this can be
decoded from the buffer. For example, if it is known that the
response is an ASCII string:

remote_connection.send_packet("some_packet").decode("ascii")

The prefix, suffix, and checksum (as required by the remote serial
protocol) are automatically added to the outgoing packet, and
removed from the incoming packet before the contents of the reply
are returned.

This is equivalent to the `maintenance packet' command (*note
maint packet::).

File: gdb.info, Node: TUI Windows In Python, Next: Disassembly In Python, Prev: Connections In Python, Up: Python API

23.3.2.39 Implementing new TUI windows
.....................................

New TUI (*note TUI::) windows can be implemented in Python.

-- Function: gdb.register_window_type (name, factory)
Because TUI windows are created and destroyed depending on the
layout the user chooses, new window types are implemented by
registering a factory function with GDB.

NAME is the name of the new window. It's an error to try to
replace one of the built-in windows, but other window types can be
replaced. The NAME should match the regular expression
`[a-zA-Z][-_.a-zA-Z0-9]*', it is an error to try and create a
window with an invalid name.

FUNCTION is a factory function that is called to create the TUI
window. This is called with a single argument of type
`gdb.TuiWindow', described below. It should return an object that
implements the TUI window protocol, also described below.

As mentioned above, when a factory function is called, it is passed
an object of type `gdb.TuiWindow'. This object has these methods and
attributes:

-- Function: TuiWindow.is_valid ()
This method returns `True' when this window is valid. When the
user changes the TUI layout, windows no longer visible in the new
layout will be destroyed. At this point, the `gdb.TuiWindow' will
no longer be valid, and methods (and attributes) other than
`is_valid' will throw an exception.

When the TUI is disabled using `tui disable' (*note tui disable:
TUI Commands.) the window is hidden rather than destroyed, but
`is_valid' will still return `False' and other methods (and
attributes) will still throw an exception.

-- Variable: TuiWindow.width
This attribute holds the width of the window. It is not writable.

-- Variable: TuiWindow.height
This attribute holds the height of the window. It is not writable.

-- Variable: TuiWindow.title
This attribute holds the window's title, a string. This is
normally displayed above the window. This attribute can be
modified.

-- Function: TuiWindow.erase ()
Remove all the contents of the window.

-- Function: TuiWindow.write (string [, full_window])
Write STRING to the window. STRING can contain ANSI terminal
escape styling sequences; GDB will translate these as appropriate
for the terminal.

If the FULL_WINDOW parameter is `True', then STRING contains the
full contents of the window. This is similar to calling `erase'
before `write', but avoids the flickering.

The factory function that you supply should return an object
conforming to the TUI window protocol. These are the method that can
be called on this object, which is referred to below as the "window
object". The methods documented below are optional; if the object does
not implement one of these methods, GDB will not attempt to call it.
Additional new methods may be added to the window protocol in the
future. GDB guarantees that they will begin with a lower-case letter,
so you can start implementation methods with upper-case letters or
underscore to avoid any future conflicts.

-- Function: Window.close ()
When the TUI window is closed, the `gdb.TuiWindow' object will be
put into an invalid state. At this time, GDB will call `close'
method on the window object.

After this method is called, GDB will discard any references it
holds on this window object, and will no longer call methods on
this object.

-- Function: Window.render ()
In some situations, a TUI window can change size. For example,
this can happen if the user resizes the terminal, or changes the
layout. When this happens, GDB will call the `render' method on
the window object.

If your window is intended to update in response to changes in the
inferior, you will probably also want to register event listeners
and send output to the `gdb.TuiWindow'.

-- Function: Window.hscroll (num)
This is a request to scroll the window horizontally. NUM is the
amount by which to scroll, with negative numbers meaning to scroll
right. In the TUI model, it is the viewport that moves, not the
contents. A positive argument should cause the viewport to move
right, and so the content should appear to move to the left.

-- Function: Window.vscroll (num)
This is a request to scroll the window vertically. NUM is the
amount by which to scroll, with negative numbers meaning to scroll
backward. In the TUI model, it is the viewport that moves, not the
contents. A positive argument should cause the viewport to move
down, and so the content should appear to move up.

-- Function: Window.click (x, y, button)
This is called on a mouse click in this window. X and Y are the
mouse coordinates inside the window (0-based, from the top left
corner), and BUTTON specifies which mouse button was used, whose
values can be 1 (left), 2 (middle), or 3 (right).

When TUI mouse events are disabled by turning off the `tui
mouse-events' setting (*note set tui mouse-events:
tui-mouse-events.), then `click' will not be called.

File: gdb.info, Node: Disassembly In Python, Next: Missing Debug Info In Python, Prev: TUI Windows In Python, Up: Python API

23.3.2.40 Instruction Disassembly In Python
..........................................

GDB's builtin disassembler can be extended, or even replaced, using the
Python API. The disassembler related features are contained within the
`gdb.disassembler' module:

-- class: gdb.disassembler.DisassembleInfo
Disassembly is driven by instances of this class. Each time GDB
needs to disassemble an instruction, an instance of this class is
created and passed to a registered disassembler. The disassembler
is then responsible for disassembling an instruction and returning
a result.

Instances of this type are usually created within GDB, however, it
is possible to create a copy of an instance of this type, see the
description of `__init__' for more details.

This class has the following properties and methods:

-- Variable: DisassembleInfo.address
A read-only integer containing the address at which GDB
wishes to disassemble a single instruction.

-- Variable: DisassembleInfo.architecture
The `gdb.Architecture' (*note Architectures In Python::) for
which GDB is currently disassembling, this property is
read-only.

-- Variable: DisassembleInfo.progspace
The `gdb.Progspace' (*note Program Spaces In Python:
Progspaces In Python.) for which GDB is currently
disassembling, this property is read-only.

-- Function: DisassembleInfo.is_valid ()
Returns `True' if the `DisassembleInfo' object is valid,
`False' if not. A `DisassembleInfo' object will become
invalid once the disassembly call for which the
`DisassembleInfo' was created, has returned. Calling other
`DisassembleInfo' methods, or accessing `DisassembleInfo'
properties, will raise a `RuntimeError' exception if it is
invalid.

-- Function: DisassembleInfo.__init__ (info)
This can be used to create a new `DisassembleInfo' object
that is a copy of INFO. The copy will have the same
`address', `architecture', and `progspace' values as INFO, and
will become invalid at the same time as INFO.

This method exists so that sub-classes of `DisassembleInfo'
can be created, these sub-classes must be initialized as
copies of an existing `DisassembleInfo' object, but
sub-classes might choose to override the `read_memory'
method, and so control what GDB sees when reading from memory
(*note builtin_disassemble::).

-- Function: DisassembleInfo.read_memory (length, offset)
This method allows the disassembler to read the bytes of the
instruction to be disassembled. The method reads LENGTH
bytes, starting at OFFSET from `DisassembleInfo.address'.

It is important that the disassembler read the instruction
bytes using this method, rather than reading inferior memory
directly, as in some cases GDB disassembles from an internal
buffer rather than directly from inferior memory, calling
this method handles this detail.

Returns a buffer object, which behaves much like an array or
a string, just as `Inferior.read_memory' does (*note
Inferior.read_memory: gdbpy_inferior_read_memory.). The
length of the returned buffer will always be exactly LENGTH.

If GDB is unable to read the required memory then a
`gdb.MemoryError' exception is raised (*note Exception
Handling::).

This method can be overridden by a sub-class in order to
control what GDB sees when reading from memory (*note
builtin_disassemble::). When overriding this method it is
important to understand how `builtin_disassemble' makes use of
this method.

While disassembling a single instruction there could be
multiple calls to this method, and the same bytes might be
read multiple times. Any single call might only read a
subset of the total instruction bytes.

If an implementation of `read_memory' is unable to read the
requested memory contents, for example, if there's a request
to read from an invalid memory address, then a
`gdb.MemoryError' should be raised.

Raising a `MemoryError' inside `read_memory' does not
automatically mean a `MemoryError' will be raised by
`builtin_disassemble'. It is possible the GDB's builtin
disassembler is probing to see how many bytes are available.
When `read_memory' raises the `MemoryError' the builtin
disassembler might be able to perform a complete disassembly
with the bytes it has available, in this case
`builtin_disassemble' will not itself raise a `MemoryError'.

Any other exception type raised in `read_memory' will
propagate back and be re-raised by `builtin_disassemble'.

-- Function: DisassembleInfo.text_part (style, string)
Create a new `DisassemblerTextPart' representing a piece of a
disassembled instruction. STRING should be a non-empty
string, and STYLE should be an appropriate style constant
(*note Disassembler Style Constants::).

Disassembler parts are used when creating a
`DisassemblerResult' in order to represent the styling within
an instruction (*note DisassemblerResult Class::).

-- Function: DisassembleInfo.address_part (address)
Create a new `DisassemblerAddressPart'. ADDRESS is the value
of the absolute address this part represents. A
`DisassemblerAddressPart' is displayed as an absolute address
and an associated symbol, the address and symbol are styled
appropriately.

-- class: gdb.disassembler.Disassembler
This is a base class from which all user implemented disassemblers
must inherit.

-- Function: Disassembler.__init__ (name)
The constructor takes NAME, a string, which should be a short
name for this disassembler.

-- Function: Disassembler.__call__ (info)
The `__call__' method must be overridden by sub-classes to
perform disassembly. Calling `__call__' on this base class
will raise a `NotImplementedError' exception.

The INFO argument is an instance of `DisassembleInfo', and
describes the instruction that GDB wants disassembling.

If this function returns `None', this indicates to GDB that
this sub-class doesn't wish to disassemble the requested
instruction. GDB will then use its builtin disassembler to
perform the disassembly.

Alternatively, this function can return a `DisassemblerResult'
that represents the disassembled instruction, this type is
described in more detail below.

The `__call__' method can raise a `gdb.MemoryError' exception
(*note Exception Handling::) to indicate to GDB that there
was a problem accessing the required memory, this will then
be displayed by GDB within the disassembler output.

Ideally, the only three outcomes from invoking `__call__'
would be a return of `None', a successful disassembly
returned in a `DisassemblerResult', or a `MemoryError'
indicating that there was a problem reading memory.

However, as an implementation of `__call__' could fail due to
other reasons, e.g. some external resource required to perform
disassembly is temporarily unavailable, then, if `__call__'
raises a `GdbError', the exception will be converted to a
string and printed at the end of the disassembly output, the
disassembly request will then stop.

Any other exception type raised by the `__call__' method is
considered an error in the user code, the exception will be
printed to the error stream according to the `set python
print-stack' setting (*note `set python print-stack':
set_python_print_stack.).

-- class: gdb.disassembler.DisassemblerResult
This class represents the result of disassembling a single
instruction. An instance of this class will be returned from
`builtin_disassemble' (*note builtin_disassemble::), and an
instance of this class should be returned from
`Disassembler.__call__' (*note Disassembler Class::) if an
instruction was successfully disassembled.

It is not possible to sub-class the `DisassemblerResult' class.

The `DisassemblerResult' class has the following properties and
methods:

-- Function: DisassemblerResult.__init__ (length, string, parts)
Initialize an instance of this class, LENGTH is the length of
the disassembled instruction in bytes, which must be greater
than zero.

Only one of STRING or PARTS should be used to initialize a
new `DisassemblerResult'; the other one should be passed the
value `None'. Alternatively, the arguments can be passed by
name, and the unused argument can be ignored.

The STRING argument, if not `None', is a non-empty string
that represents the entire disassembled instruction.
Building a result object using the STRING argument does not
allow for any styling information to be included in the
result. GDB will style the result as a single
`DisassemblerTextPart' with `STYLE_TEXT' style (*note
Disassembler Styling Parts::).

The PARTS argument, if not `None', is a non-empty sequence of
`DisassemblerPart' objects. Each part represents a small part
of the disassembled instruction along with associated styling
information. A result object built using PARTS can be
displayed by GDB with full styling information (*note `set
style disassembler enabled': style_disassembler_enabled.).

-- Variable: DisassemblerResult.length
A read-only property containing the length of the disassembled
instruction in bytes, this will always be greater than zero.

-- Variable: DisassemblerResult.string
A read-only property containing a non-empty string
representing the disassembled instruction. The STRING is a
representation of the disassembled instruction without any
styling information. To see how the instruction will be
styled use the PARTS property.

If this instance was initialized using separate
`DisassemblerPart' objects, the STRING property will still be
valid. The STRING value is created by concatenating the
`DisassemblerPart.string' values of each component part
(*note Disassembler Styling Parts::).

-- Variable: DisassemblerResult.parts
A read-only property containing a non-empty sequence of
`DisassemblerPart' objects. Each `DisassemblerPart' object
contains a small part of the instruction along with
information about how that part should be styled. GDB uses
this information to create styled disassembler output (*note
`set style disassembler enabled':
style_disassembler_enabled.).

If this instance was initialized using a single string rather
than with a sequence of `DisassemblerPart' objects, the PARTS
property will still be valid. In this case the PARTS property
will hold a sequence containing a single
`DisassemblerTextPart' object, the string of which will
represent the entire instruction, and the style of which will
be `STYLE_TEXT'.

-- class: gdb.disassembler.DisassemblerPart
This is a parent class from which the different part sub-classes
inherit. Only instances of the sub-classes detailed below will be
returned by the Python API.

It is not possible to directly create instances of either this
parent class, or any of the sub-classes listed below. Instances
of the sub-classes listed below are created by calling
`builtin_disassemble' (*note builtin_disassemble::) and are
returned within the `DisassemblerResult' object, or can be created
by calling the `text_part' and `address_part' methods on the
`DisassembleInfo' class (*note DisassembleInfo Class::).

The `DisassemblerPart' class has a single property:

-- Variable: DisassemblerPart.string
A read-only property that contains a non-empty string
representing this part of the disassembled instruction. The
string within this property doesn't include any styling
information.

-- class: gdb.disassembler.DisassemblerTextPart
The `DisassemblerTextPart' class represents a piece of the
disassembled instruction and the associated style for that piece.
Instances of this class can't be created directly, instead call
`DisassembleInfo.text_part' to create a new instance of this class
(*note DisassembleInfo Class::).

As well as the properties of its parent class, the
`DisassemblerTextPart' has the following additional property:

-- Variable: DisassemblerTextPart.style
A read-only property that contains one of the defined style
constants. GDB will use this style when styling this part of
the disassembled instruction (*note Disassembler Style
Constants::).

-- class: gdb.disassembler.DisassemblerAddressPart
The `DisassemblerAddressPart' class represents an absolute address
within a disassembled instruction. Using a
`DisassemblerAddressPart' instead of a `DisassemblerTextPart' with
`STYLE_ADDRESS' is preferred, GDB will display the address as both
an absolute address, and will look up a suitable symbol to display
next to the address. Using `DisassemblerAddressPart' also ensures
that user settings such as `set print max-symbolic-offset' are
respected.

Here is an example of an x86-64 instruction:

call 0x401136 <foo>

In this instruction the `0x401136 <foo>' was generated from a
single `DisassemblerAddressPart'. The `0x401136' will be styled
with `STYLE_ADDRESS', and `foo' will be styled with
`STYLE_SYMBOL'. The `<' and `>' will be styled as `STYLE_TEXT'.

If the inclusion of the symbol name is not required then a
`DisassemblerTextPart' with style `STYLE_ADDRESS' can be used
instead.

Instances of this class can't be created directly, instead call
`DisassembleInfo.address_part' to create a new instance of this
class (*note DisassembleInfo Class::).

As well as the properties of its parent class, the
`DisassemblerAddressPart' has the following additional property:

-- Variable: DisassemblerAddressPart.address
A read-only property that contains the ADDRESS passed to this
object's `__init__' method.

The following table lists all of the disassembler styles that are
available. GDB maps these style constants onto its style settings
(*note Output Styling::). In some cases, several style constants
produce the same style settings, and thus will produce the same visual
effect on the screen. This could change in future releases of GDB, so
care should be taken to select the correct style constant to ensure
correct output styling in future releases of GDB.

`gdb.disassembler.STYLE_TEXT'
This is the default style used by GDB when styling disassembler
output. This style should be used for any parts of the
instruction that don't fit any of the other styles listed below.
GDB styles text with this style using its default style.

`gdb.disassembler.STYLE_MNEMONIC'
This style is used for styling the primary instruction mnemonic,
which usually appears at, or near, the start of the disassembled
instruction string.

GDB styles text with this style using the `disassembler mnemonic'
style setting.

`gdb.disassembler.STYLE_SUB_MNEMONIC'
This style is used for styling any sub-mnemonics within a
disassembled instruction. A sub-mnemonic is any text within the
instruction that controls the function of the instruction, but
which is disjoint from the primary mnemonic (which will have
styled `STYLE_MNEMONIC').

As an example, consider this AArch64 instruction:

add w16, w7, w1, lsl #1

The `add' is the primary instruction mnemonic, and would be given
style `STYLE_MNEMONIC', while `lsl' is the sub-mnemonic, and would
be given the style `STYLE_SUB_MNEMONIC'.

GDB styles text with this style using the `disassembler mnemonic'
style setting.

`gdb.disassembler.STYLE_ASSEMBLER_DIRECTIVE'
Sometimes a series of bytes doesn't decode to a valid instruction.
In this case the disassembler may choose to represent the result
of disassembling using an assembler directive, for example:

.word 0x1234

In this case, the `.word' would be give the
`STYLE_ASSEMBLER_DIRECTIVE' style. An assembler directive is
similar to a mnemonic in many ways but is something that is not
part of the architecture's instruction set.

GDB styles text with this style using the `disassembler mnemonic'
style setting.

`gdb.disassembler.STYLE_REGISTER'
This style is used for styling any text that represents a register
name, or register number, within a disassembled instruction.

GDB styles text with this style using the `disassembler register'
style setting.

`gdb.disassembler.STYLE_ADDRESS'
This style is used for styling numerical values that represent
absolute addresses within the disassembled instruction.

When creating a `DisassemblerTextPart' with this style, you should
consider if a `DisassemblerAddressPart' would be more appropriate.
See *Note Disassembler Styling Parts:: for a description of what
each part offers.

GDB styles text with this style using the `disassembler address'
style setting.

`gdb.disassembler.STYLE_ADDRESS_OFFSET'
This style is used for styling numerical values that represent
offsets to addresses within the disassembled instruction. A value
is considered an address offset when the instruction itself is
going to access memory, and the value is being used to offset
which address is accessed.

For example, an architecture might have an instruction that loads
from memory using an address within a register. If that
instruction also allowed for an immediate offset to be encoded
into the instruction, this would be an address offset. Similarly,
a branch instruction might jump to an address in a register plus
an address offset that is encoded into the instruction.

GDB styles text with this style using the `disassembler immediate'
style setting.

`gdb.disassembler.STYLE_IMMEDIATE'
Use `STYLE_IMMEDIATE' for any numerical values within a
disassembled instruction when those values are not addresses,
address offsets, or register numbers (The styles `STYLE_ADDRESS',
`STYLE_ADDRESS_OFFSET', or `STYLE_REGISTER' can be used in those
cases).

GDB styles text with this style using the `disassembler immediate'
style setting.

`gdb.disassembler.STYLE_SYMBOL'
This style is used for styling the textual name of a symbol that is
included within a disassembled instruction. A symbol name is often
included next to an absolute address within a disassembled
instruction to make it easier for the user to understand what the
address is referring too. For example:

call 0x401136 <foo>

Here `foo' is the name of a symbol, and should be given the
`STYLE_SYMBOL' style.

Adding symbols next to absolute addresses like this is handled
automatically by the `DisassemblerAddressPart' class (*note
Disassembler Styling Parts::).

GDB styles text with this style using the `disassembler symbol'
style setting.

`gdb.disassembler.STYLE_COMMENT_START'
This style is used to start a line comment in the disassembly
output. Unlike other styles, which only apply to the single
`DisassemblerTextPiece' to which they are applied, the comment
style is sticky, and overrides the style of any further pieces
within this instruction.

This means that, after a `STYLE_COMMENT_START' piece has been
seen, GDB will apply the comment style until the end of the line,
ignoring the specific style within a piece.

GDB styles text with this style using the `disassembler comment'
style setting.

The following functions are also contained in the `gdb.disassembler'
module:

-- Function: register_disassembler (disassembler, architecture)
The DISASSEMBLER must be a sub-class of
`gdb.disassembler.Disassembler' or `None'.

The optional ARCHITECTURE is either a string, or the value `None'.
If it is a string, then it should be the name of an architecture
known to GDB, as returned either from `gdb.Architecture.name'
(*note gdb.Architecture.name: gdbpy_architecture_name.), or from
`gdb.architecture_names' (*note gdb.architecture_names:
gdb_architecture_names.).

The DISASSEMBLER will be installed for the architecture named by
ARCHITECTURE, or if ARCHITECTURE is `None', then DISASSEMBLER will
be installed as a global disassembler for use by all architectures.

GDB only records a single disassembler for each architecture, and
a single global disassembler. Calling `register_disassembler' for
an architecture, or for the global disassembler, will replace any
existing disassembler registered for that ARCHITECTURE value. The
previous disassembler is returned.

If DISASSEMBLER is `None' then any disassembler currently
registered for ARCHITECTURE is deregistered and returned.

When GDB is looking for a disassembler to use, GDB first looks for
an architecture specific disassembler. If none has been
registered then GDB looks for a global disassembler (one
registered with ARCHITECTURE set to `None'). Only one
disassembler is called to perform disassembly, so, if there is
both an architecture specific disassembler, and a global
disassembler registered, it is the architecture specific
disassembler that will be used.

GDB tracks the architecture specific, and global disassemblers
separately, so it doesn't matter in which order disassemblers are
created or registered; an architecture specific disassembler, if
present, will always be used in preference to a global
disassembler.

You can use the `maint info python-disassemblers' command (*note
maint info python-disassemblers::) to see which disassemblers have
been registered.

-- Function: builtin_disassemble (info)
This function calls back into GDB's builtin disassembler to
disassemble the instruction identified by INFO, an instance, or
sub-class, of `DisassembleInfo'.

When the builtin disassembler needs to read memory the
`read_memory' method on INFO will be called. By sub-classing
`DisassembleInfo' and overriding the `read_memory' method, it is
possible to intercept calls to `read_memory' from the builtin
disassembler, and to modify the values returned.

It is important to understand that, even when
`DisassembleInfo.read_memory' raises a `gdb.MemoryError', it is
the internal disassembler itself that reports the memory error to
GDB. The reason for this is that the disassembler might probe
memory to see if a byte is readable or not; if the byte can't be
read then the disassembler may choose not to report an error, but
instead to disassemble the bytes that it does have available.

If the builtin disassembler is successful then an instance of
`DisassemblerResult' is returned from `builtin_disassemble',
alternatively, if something goes wrong, an exception will be
raised.

A `MemoryError' will be raised if `builtin_disassemble' is unable
to read some memory that is required in order to perform
disassembly correctly.

Any exception that is not a `MemoryError', that is raised in a
call to `read_memory', will pass through `builtin_disassemble',
and be visible to the caller.

Finally, there are a few cases where GDB's builtin disassembler
can fail for reasons that are not covered by `MemoryError'. In
these cases, a `GdbError' will be raised. The contents of the
exception will be a string describing the problem the disassembler
encountered.

Here is an example that registers a global disassembler. The new
disassembler invokes the builtin disassembler, and then adds a comment,
`## Comment', to each line of disassembly output:

class ExampleDisassembler(gdb.disassembler.Disassembler):
def __init__(self):
super().__init__("ExampleDisassembler")

def __call__(self, info):
result = gdb.disassembler.builtin_disassemble(info)
length = result.length
text = result.string + "\t## Comment"
return gdb.disassembler.DisassemblerResult(length, text)

gdb.disassembler.register_disassembler(ExampleDisassembler())

The following example creates a sub-class of `DisassembleInfo' in
order to intercept the `read_memory' calls, within `read_memory' any
bytes read from memory have the two 4-bit nibbles swapped around. This
isn't a very useful adjustment, but serves as an example.

class MyInfo(gdb.disassembler.DisassembleInfo):
def __init__(self, info):
super().__init__(info)

def read_memory(self, length, offset):
buffer = super().read_memory(length, offset)
result = bytearray()
for b in buffer:
v = int.from_bytes(b, 'little')
v = (v << 4) & 0xf0 | (v >> 4)
result.append(v)
return memoryview(result)

class NibbleSwapDisassembler(gdb.disassembler.Disassembler):
def __init__(self):
super().__init__("NibbleSwapDisassembler")

def __call__(self, info):
info = MyInfo(info)
return gdb.disassembler.builtin_disassemble(info)

gdb.disassembler.register_disassembler(NibbleSwapDisassembler())

File: gdb.info, Node: Missing Debug Info In Python, Prev: Disassembly In Python, Up: Python API

23.3.2.41 Missing Debug Info In Python
.....................................

When GDB encounters a new objfile (*note Objfiles In Python::), e.g.
the primary executable, or any shared libraries used by the inferior,
GDB will attempt to load the corresponding debug information for that
objfile. The debug information might be found within the objfile
itself, or within a separate objfile which GDB will automatically
locate and load.

Sometimes though, GDB might not find any debug information for an
objfile, in this case the debugging experience will be restricted.

If GDB fails to locate any debug information for a particular
objfile, there is an opportunity for a Python extension to step in. A
Python extension can potentially locate the missing debug information
using some platform- or project-specific steps, and inform GDB of its
location. Or a Python extension might provide some platform- or
project-specific advice to the user about how to obtain the missing
debug information.

A missing debug information Python extension consists of a handler
object which has the `name' and `enabled' attributes, and implements
the `__call__' method. When GDB encounters an objfile for which it is
unable to find any debug information, it invokes the `__call__' method.
Full details of how handlers are written can be found below.

The `gdb.missing_debug' Module
------------------------------

GDB comes with a `gdb.missing_debug' module which contains the
following class and global function:

-- class: gdb.missing_debug.MissingDebugHandler
`MissingDebugHandler' is a base class from which user-created
handlers can derive, though it is not required that handlers derive
from this class, so long as any user created handler has the
`name' and `enabled' attributes, and implements the `__call__'
method.

-- Function: MissingDebugHandler.__init__ (name)
The NAME is a string used to reference this missing debug
handler within some GDB commands. Valid names consist of the
characters `[-_a-zA-Z0-9]', creating a handler with an invalid
name raises a `ValueError' exception.

-- Function: MissingDebugHandler.__call__ (objfile)
Sub-classes must override the `__call__' method. The OBJFILE
argument will be a `gdb.Objfile', this is the objfile for
which GDB was unable to find any debug information.

The return value from the `__call__' method indicates what
GDB should do next. The possible return values are:

* `None'

This indicates that this handler could not help with
OBJFILE, GDB should call any other registered handlers.

* `True'

This indicates that this handler has installed the debug
information into a location where GDB would normally
expect to find it when looking for separate debug
information files (*note Separate Debug Files::). GDB
will repeat the normal lookup process, which should now
find the separate debug file.

If GDB still doesn't find the separate debug information
file after this second attempt, then the Python missing
debug information handlers are not invoked a second
time, this prevents a badly behaved handler causing GDB
to get stuck in a loop. GDB will continue without any
debug information for OBJFILE.

* `False'

This indicates that this handler has done everything
that it intends to do with OBJFILE, but no separate
debug information can be found. GDB will not call any
other registered handlers for OBJFILE. GDB will
continue without debugging information for OBJFILE.

* A string

The returned string should contain a filename. GDB will
not call any further registered handlers, and will
instead load the debug information from the file
identified by the returned filename.

Invoking the `__call__' method from this base class will
raise a `NotImplementedError' exception.

-- Variable: MissingDebugHandler.name
A read-only attribute which is a string, the name of this
handler passed to the `__init__' method.

-- Variable: MissingDebugHandler.enabled
A modifiable attribute containing a boolean; when `True', the
handler is enabled, and will be used by GDB. When `False',
the handler has been disabled, and will not be used.

-- Function: gdb.missing_debug.register_handler (locus, handler,
replace=`False')
Register a new missing debug handler with GDB.

HANDLER is an instance of a sub-class of `MissingDebugHandler', or
at least an instance of an object that has the same attributes and
methods as `MissingDebugHandler'.

LOCUS specifies to which handler list to prepend HANDLER. It can
be either a `gdb.Progspace' (*note Progspaces In Python::) or
`None', in which case the handler is registered globally. The
newly registered HANDLER will be called before any other handler
from the same locus. Two handlers in the same locus cannot have
the same name, an attempt to add a handler with an already
existing name raises an exception unless REPLACE is `True', in
which case the old handler is deleted and the new handler is
prepended to the selected handler list.

GDB first calls the handlers for the current program space, and
then the globally registered handlers. As soon as a handler
returns a value other than `None', no further handlers are called
for this objfile.

File: gdb.info, Node: Python Auto-loading, Next: Python modules, Prev: Python API, Up: Python

23.3.3 Python Auto-loading
--------------------------

When a new object file is read (for example, due to the `file' command,
or because the inferior has loaded a shared library), GDB will look for
Python support scripts in several ways: `OBJFILE-gdb.py' and
`.debug_gdb_scripts' section. *Note Auto-loading extensions::.

The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.

Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.

`set auto-load python-scripts [on|off]'
Enable or disable the auto-loading of Python scripts.

`show auto-load python-scripts'
Show whether auto-loading of Python scripts is enabled or disabled.

`info auto-load python-scripts [REGEXP]'
Print the list of all Python scripts that GDB auto-loaded.

Also printed is the list of Python scripts that were mentioned in
the `.debug_gdb_scripts' section and were either not found (*note
dotdebug_gdb_scripts section::) or were not auto-loaded due to
`auto-load safe-path' rejection (*note Auto-loading::). This is
useful because their names are not printed when GDB tries to load
them and fails. There may be many of them, and printing an error
message for each one is problematic.

If REGEXP is supplied only Python scripts with matching names are
printed.

Example:

(gdb) info auto-load python-scripts
Loaded Script
Yes py-section-script.py
full name: /tmp/py-section-script.py
No my-foo-pretty-printers.py

When reading an auto-loaded file or script, GDB sets the "current
objfile". This is available via the `gdb.current_objfile' function
(*note Objfiles In Python::). This can be useful for registering
objfile-specific pretty-printers and frame-filters.

File: gdb.info, Node: Python modules, Prev: Python Auto-loading, Up: Python

23.3.4 Python modules
---------------------

GDB comes with several modules to assist writing Python code.

* Menu:

* gdb.printing:: Building and registering pretty-printers.
* gdb.types:: Utilities for working with types.
* gdb.prompt:: Utilities for prompt value substitution.

File: gdb.info, Node: gdb.printing, Next: gdb.types, Up: Python modules

23.3.4.1 gdb.printing
....................

This module provides a collection of utilities for working with
pretty-printers.

`PrettyPrinter (NAME, SUBPRINTERS=None)'
This class specifies the API that makes `info pretty-printer',
`enable pretty-printer' and `disable pretty-printer' work.
Pretty-printers should generally inherit from this class.

`SubPrettyPrinter (NAME)'
For printers that handle multiple types, this class specifies the
corresponding API for the subprinters.

`RegexpCollectionPrettyPrinter (NAME)'
Utility class for handling multiple printers, all recognized via
regular expressions. *Note Writing a Pretty-Printer::, for an
example.

`FlagEnumerationPrinter (NAME)'
A pretty-printer which handles printing of `enum' values. Unlike
GDB's built-in `enum' printing, this printer attempts to work
properly when there is some overlap between the enumeration
constants. The argument NAME is the name of the printer and also
the name of the `enum' type to look up.

`register_pretty_printer (OBJ, PRINTER, REPLACE=False)'
Register PRINTER with the pretty-printer list of OBJ. If REPLACE
is `True' then any existing copy of the printer is replaced.
Otherwise a `RuntimeError' exception is raised if a printer with
the same name already exists.

File: gdb.info, Node: gdb.types, Next: gdb.prompt, Prev: gdb.printing, Up: Python modules

23.3.4.2 gdb.types
.................

This module provides a collection of utilities for working with
`gdb.Type' objects.

`get_basic_type (TYPE)'
Return TYPE with const and volatile qualifiers stripped, and with
typedefs and C++ references converted to the underlying type.

C++ example:

typedef const int const_int;
const_int foo (3);
const_int& foo_ref (foo);
int main () { return 0; }

Then in gdb:

(gdb) start
(gdb) python import gdb.types
(gdb) python foo_ref = gdb.parse_and_eval("foo_ref")
(gdb) python print gdb.types.get_basic_type(foo_ref.type)
int

`has_field (TYPE, FIELD)'
Return `True' if TYPE, assumed to be a type with fields (e.g., a
structure or union), has field FIELD.

`make_enum_dict (ENUM_TYPE)'
Return a Python `dictionary' type produced from ENUM_TYPE.

`deep_items (TYPE)'
Returns a Python iterator similar to the standard
`gdb.Type.iteritems' method, except that the iterator returned by
`deep_items' will recursively traverse anonymous struct or union
fields. For example:

struct A
{
int a;
union {
int b0;
int b1;
};
};

Then in GDB:
(gdb) python import gdb.types
(gdb) python struct_a = gdb.lookup_type("struct A")
(gdb) python print struct_a.keys ()
{['a', '']}
(gdb) python print [k for k,v in gdb.types.deep_items(struct_a)]
{['a', 'b0', 'b1']}

`get_type_recognizers ()'
Return a list of the enabled type recognizers for the current
context. This is called by GDB during the type-printing process
(*note Type Printing API::).

`apply_type_recognizers (recognizers, type_obj)'
Apply the type recognizers, RECOGNIZERS, to the type object
TYPE_OBJ. If any recognizer returns a string, return that string.
Otherwise, return `None'. This is called by GDB during the
type-printing process (*note Type Printing API::).

`register_type_printer (locus, printer)'
This is a convenience function to register a type printer PRINTER.
The printer must implement the type printer protocol. The LOCUS
argument is either a `gdb.Objfile', in which case the printer is
registered with that objfile; a `gdb.Progspace', in which case the
printer is registered with that progspace; or `None', in which
case the printer is registered globally.

`TypePrinter'
This is a base class that implements the type printer protocol.
Type printers are encouraged, but not required, to derive from
this class. It defines a constructor:

-- Method on TypePrinter: __init__ (self, name)
Initialize the type printer with the given name. The new
printer starts in the enabled state.

File: gdb.info, Node: gdb.prompt, Prev: gdb.types, Up: Python modules

23.3.4.3 gdb.prompt
..................

This module provides a method for prompt value-substitution.

`substitute_prompt (STRING)'
Return STRING with escape sequences substituted by values. Some
escape sequences take arguments. You can specify arguments inside
"{}" immediately following the escape sequence.

The escape sequences you can pass to this function are:

`\\'
Substitute a backslash.

`\e'
Substitute an ESC character.

`\f'
Substitute the selected frame; an argument names a frame
parameter.

`\n'
Substitute a newline.

`\p'
Substitute a parameter's value; the argument names the
parameter.

`\r'
Substitute a carriage return.

`\t'
Substitute the selected thread; an argument names a thread
parameter.

`\v'
Substitute the version of GDB.

`\w'
Substitute the current working directory.

`\['
Begin a sequence of non-printing characters. These sequences
are typically used with the ESC character, and are not
counted in the string length. Example:
"\[\e[0;34m\](gdb)\[\e[0m\]" will return a blue-colored
"(gdb)" prompt where the length is five.

`\]'
End a sequence of non-printing characters.

For example:

substitute_prompt ("frame: \f, args: \p{print frame-arguments}")

will return the string:

"frame: main, args: scalars"

File: gdb.info, Node: Guile, Next: Auto-loading extensions, Prev: Python, Up: Extending GDB

23.4 Extending GDB using Guile
==============================

You can extend GDB using the Guile implementation of the Scheme
programming language (http://www.gnu.org/software/guile/). This
feature is available only if GDB was configured using `--with-guile'.

* Menu:

* Guile Introduction:: Introduction to Guile scripting in GDB
* Guile Commands:: Accessing Guile from GDB
* Guile API:: Accessing GDB from Guile
* Guile Auto-loading:: Automatically loading Guile code
* Guile Modules:: Guile modules provided by GDB

File: gdb.info, Node: Guile Introduction, Next: Guile Commands, Up: Guile

23.4.1 Guile Introduction
-------------------------

Guile is an implementation of the Scheme programming language and is
the GNU project's official extension language.

Guile support in GDB follows the Python support in GDB reasonably
closely, so concepts there should carry over. However, some things are
done differently where it makes sense.

GDB requires Guile version 3.0, 2.2, or 2.0.

Guile scripts used by GDB should be installed in
`DATA-DIRECTORY/guile', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::). This directory, known
as the "guile directory", is automatically added to the Guile Search
Path in order to allow the Guile interpreter to locate all scripts
installed at this location.

File: gdb.info, Node: Guile Commands, Next: Guile API, Prev: Guile Introduction, Up: Guile

23.4.2 Guile Commands
---------------------

GDB provides two commands for accessing the Guile interpreter:

`guile-repl'
`gr'
The `guile-repl' command can be used to start an interactive Guile
prompt or "repl". To return to GDB, type `,q' or the `EOF'
character (e.g., `Ctrl-D' on an empty prompt). These commands do
not take any arguments.

`guile [SCHEME-EXPRESSION]'
`gu [SCHEME-EXPRESSION]'
The `guile' command can be used to evaluate a Scheme expression.

If given an argument, GDB will pass the argument to the Guile
interpreter for evaluation.

(gdb) guile (display (+ 20 3)) (newline)
23

The result of the Scheme expression is displayed using normal
Guile rules.

(gdb) guile (+ 20 3)
23

If you do not provide an argument to `guile', it will act as a
multi-line command, like `define'. In this case, the Guile script
is made up of subsequent command lines, given after the `guile'
command. This command list is terminated using a line containing
`end'. For example:

(gdb) guile
>(display 23)
>(newline)
>end
23

It is also possible to execute a Guile script from the GDB
interpreter:

`source `script-name''
The script name must end with `.scm' and GDB must be configured to
recognize the script language based on filename extension using
the `script-extension' setting. *Note Extending GDB: Extending
GDB.

`guile (load "script-name")'
This method uses the `load' Guile function. It takes a string
argument that is the name of the script to load. See the Guile
documentation for a description of this function. (*note Loading:
(guile)Loading.).

File: gdb.info, Node: Guile API, Next: Guile Auto-loading, Prev: Guile Commands, Up: Guile

23.4.3 Guile API
----------------

You can get quick online help for GDB's Guile API by issuing the
command `help guile', or by issuing the command `,help' from an
interactive Guile session. Furthermore, most Guile procedures provided
by GDB have doc strings which can be obtained with `,describe
PROCEDURE-NAME' or `,d PROCEDURE-NAME' from the Guile interactive
prompt.

* Menu:

* Basic Guile:: Basic Guile Functions
* Guile Configuration:: Guile configuration variables
* GDB Scheme Data Types:: Scheme representations of GDB objects
* Guile Exception Handling:: How Guile exceptions are translated
* Values From Inferior In Guile:: Guile representation of values
* Arithmetic In Guile:: Arithmetic in Guile
* Types In Guile:: Guile representation of types
* Guile Pretty Printing API:: Pretty-printing values with Guile
* Selecting Guile Pretty-Printers:: How GDB chooses a pretty-printer
* Writing a Guile Pretty-Printer:: Writing a pretty-printer
* Commands In Guile:: Implementing new commands in Guile
* Parameters In Guile:: Adding new GDB parameters
* Progspaces In Guile:: Program spaces
* Objfiles In Guile:: Object files in Guile
* Frames In Guile:: Accessing inferior stack frames from Guile
* Blocks In Guile:: Accessing blocks from Guile
* Symbols In Guile:: Guile representation of symbols
* Symbol Tables In Guile:: Guile representation of symbol tables
* Breakpoints In Guile:: Manipulating breakpoints using Guile
* Lazy Strings In Guile:: Guile representation of lazy strings
* Architectures In Guile:: Guile representation of architectures
* Disassembly In Guile:: Disassembling instructions from Guile
* I/O Ports in Guile:: GDB I/O ports
* Memory Ports in Guile:: Accessing memory through ports and bytevectors
* Iterators In Guile:: Basic iterator support

File: gdb.info, Node: Basic Guile, Next: Guile Configuration, Up: Guile API

23.4.3.1 Basic Guile
...................

At startup, GDB overrides Guile's `current-output-port' and
`current-error-port' to print using GDB's output-paging streams. A
Guile program which outputs to one of these streams may have its output
interrupted by the user (*note Screen Size::). In this situation, a
Guile `signal' exception is thrown with value `SIGINT'.

Guile's history mechanism uses the same naming as GDB's, namely the
user of dollar-variables (e.g., $1, $2, etc.). The results of
evaluations in Guile and in GDB are counted separately, `$1' in Guile
is not the same value as `$1' in GDB.

GDB is not thread-safe. If your Guile program uses multiple
threads, you must be careful to only call GDB-specific functions in the
GDB thread.

Some care must be taken when writing Guile code to run in GDB. Two
things are worth noting in particular:

* GDB installs handlers for `SIGCHLD' and `SIGINT'. Guile code must
not override these, or even change the options using `sigaction'.
If your program changes the handling of these signals, GDB will
most likely stop working correctly. Note that it is unfortunately
common for GUI toolkits to install a `SIGCHLD' handler.

* GDB takes care to mark its internal file descriptors as
close-on-exec. However, this cannot be done in a thread-safe way
on all platforms. Your Guile programs should be aware of this and
should both create new file descriptors with the close-on-exec flag
set and arrange to close unneeded file descriptors before starting
a child process.

GDB introduces a new Guile module, named `gdb'. All methods and
classes added by GDB are placed in this module. GDB does not
automatically `import' the `gdb' module, scripts must do this
themselves. There are various options for how to import a module, so
GDB leaves the choice of how the `gdb' module is imported to the user.
To simplify interactive use, it is recommended to add one of the
following to your ~/.gdbinit.

guile (use-modules (gdb))

guile (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:)))

Which one to choose depends on your preference. The second one adds
`gdb:' as a prefix to all module functions and variables.

The rest of this manual assumes the `gdb' module has been imported
without any prefix. See the Guile documentation for `use-modules' for
more information (*note Using Guile Modules: (guile)Using Guile
Modules.).

Example:

(gdb) guile (value-type (make-value 1))
ERROR: Unbound variable: value-type
Error while executing Scheme code.
(gdb) guile (use-modules (gdb))
(gdb) guile (value-type (make-value 1))
int
(gdb)

The `(gdb)' module provides these basic Guile functions.

-- Scheme Procedure: execute command [#:from-tty boolean]
[#:to-string boolean]
Evaluate COMMAND, a string, as a GDB CLI command. If a GDB
exception happens while COMMAND runs, it is translated as
described in *Note Guile Exception Handling: Guile Exception
Handling.

FROM-TTY specifies whether GDB ought to consider this command as
having originated from the user invoking it interactively. It
must be a boolean value. If omitted, it defaults to `#f'.

By default, any output produced by COMMAND is sent to GDB's
standard output (and to the log output if logging is turned on).
If the TO-STRING parameter is `#t', then output will be collected
by `execute' and returned as a string. The default is `#f', in
which case the return value is unspecified. If TO-STRING is `#t',
the GDB virtual terminal will be temporarily set to unlimited width
and height, and its pagination will be disabled; *note Screen
Size::.

-- Scheme Procedure: history-ref number
Return a value from GDB's value history (*note Value History::).
The NUMBER argument indicates which history element to return. If
NUMBER is negative, then GDB will take its absolute value and
count backward from the last element (i.e., the most recent
element) to find the value to return. If NUMBER is zero, then GDB
will return the most recent element. If the element specified by
NUMBER doesn't exist in the value history, a `gdb:error' exception
will be raised.

If no exception is raised, the return value is always an instance
of `<gdb:value>' (*note Values From Inferior In Guile::).

_Note:_ GDB's value history is independent of Guile's. `$1' in
GDB's value history contains the result of evaluating an
expression from GDB's command line and `$1' from Guile's history
contains the result of evaluating an expression from Guile's
command line.

-- Scheme Procedure: history-append! value
Append VALUE, an instance of `<gdb:value>', to GDB's value
history. Return its index in the history.

Putting into history values returned by Guile extensions will allow
the user convenient access to those values via CLI history
facilities.

-- Scheme Procedure: parse-and-eval expression
Parse EXPRESSION as an expression in the current language,
evaluate it, and return the result as a `<gdb:value>'. The
EXPRESSION must be a string.

This function can be useful when implementing a new command (*note
Commands In Guile::), as it provides a way to parse the command's
arguments as an expression. It is also is useful when computing
values. For example, it is the only way to get the value of a
convenience variable (*note Convenience Vars::) as a `<gdb:value>'.

File: gdb.info, Node: Guile Configuration, Next: GDB Scheme Data Types, Prev: Basic Guile, Up: Guile API

23.4.3.2 Guile Configuration
...........................

GDB provides these Scheme functions to access various configuration
parameters.

-- Scheme Procedure: data-directory
Return a string containing GDB's data directory. This directory
contains GDB's ancillary files.

-- Scheme Procedure: guile-data-directory
Return a string containing GDB's Guile data directory. This
directory contains the Guile modules provided by GDB.

-- Scheme Procedure: gdb-version
Return a string containing the GDB version.

-- Scheme Procedure: host-config
Return a string containing the host configuration. This is the
string passed to `--host' when GDB was configured.

-- Scheme Procedure: target-config
Return a string containing the target configuration. This is the
string passed to `--target' when GDB was configured.

File: gdb.info, Node: GDB Scheme Data Types, Next: Guile Exception Handling, Prev: Guile Configuration, Up: Guile API

23.4.3.3 GDB Scheme Data Types
.............................

The values exposed by GDB to Guile are known as "GDB objects". There
are several kinds of GDB object, and each is disjoint from all other
types known to Guile.

-- Scheme Procedure: gdb-object-kind object
Return the kind of the GDB object, e.g., `<gdb:breakpoint>', as a
symbol.

GDB defines the following object types:

`<gdb:arch>'
*Note Architectures In Guile::.

`<gdb:block>'
*Note Blocks In Guile::.

`<gdb:block-symbols-iterator>'
*Note Blocks In Guile::.

`<gdb:breakpoint>'
*Note Breakpoints In Guile::.

`<gdb:command>'
*Note Commands In Guile::.

`<gdb:exception>'
*Note Guile Exception Handling::.

`<gdb:frame>'
*Note Frames In Guile::.

`<gdb:iterator>'
*Note Iterators In Guile::.

`<gdb:lazy-string>'
*Note Lazy Strings In Guile::.

`<gdb:objfile>'
*Note Objfiles In Guile::.

`<gdb:parameter>'
*Note Parameters In Guile::.

`<gdb:pretty-printer>'
*Note Guile Pretty Printing API::.

`<gdb:pretty-printer-worker>'
*Note Guile Pretty Printing API::.

`<gdb:progspace>'
*Note Progspaces In Guile::.

`<gdb:symbol>'
*Note Symbols In Guile::.

`<gdb:symtab>'
*Note Symbol Tables In Guile::.

`<gdb:sal>'
*Note Symbol Tables In Guile::.

`<gdb:type>'
*Note Types In Guile::.

`<gdb:field>'
*Note Types In Guile::.

`<gdb:value>'
*Note Values From Inferior In Guile::.

The following GDB objects are managed internally so that the Scheme
function `eq?' may be applied to them.

`<gdb:arch>'

`<gdb:block>'

`<gdb:breakpoint>'

`<gdb:frame>'

`<gdb:objfile>'

`<gdb:progspace>'

`<gdb:symbol>'

`<gdb:symtab>'

`<gdb:type>'

File: gdb.info, Node: Guile Exception Handling, Next: Values From Inferior In Guile, Prev: GDB Scheme Data Types, Up: Guile API

23.4.3.4 Guile Exception Handling
................................

When executing the `guile' command, Guile exceptions uncaught within
the Guile code are translated to calls to the GDB error-reporting
mechanism. If the command that called `guile' does not handle the
error, GDB will terminate it and report the error according to the
setting of the `guile print-stack' parameter.

The `guile print-stack' parameter has three settings:

`none'
Nothing is printed.

`message'
An error message is printed containing the Guile exception name,
the associated value, and the Guile call stack backtrace at the
point where the exception was raised. Example:

(gdb) guile (display foo)
ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.

`full'
In addition to an error message a full backtrace is printed.

(gdb) set guile print-stack full
(gdb) guile (display foo)
Guile Backtrace:
In ice-9/boot-9.scm:
157: 10 [catch #t #<catch-closure 2c76e20> ...]
In unknown file:
?: 9 [apply-smob/1 #<catch-closure 2c76e20>]
In ice-9/boot-9.scm:
157: 8 [catch #t #<catch-closure 2c76d20> ...]
In unknown file:
?: 7 [apply-smob/1 #<catch-closure 2c76d20>]
?: 6 [call-with-input-string "(display foo)" ...]
In ice-9/boot-9.scm:
2320: 5 [save-module-excursion #<procedure 2c2dc30 ... ()>]
In ice-9/eval-string.scm:
44: 4 [read-and-eval #<input: string 27cb410> #:lang ...]
37: 3 [lp (display foo)]
In ice-9/eval.scm:
387: 2 [eval # ()]
393: 1 [eval #<memoized foo> ()]
In unknown file:
?: 0 [memoize-variable-access! #<memoized foo> ...]

ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.

GDB errors that happen in GDB commands invoked by Guile code are
converted to Guile exceptions. The type of the Guile exception depends
on the error.

Guile procedures provided by GDB can throw the standard Guile
exceptions like `wrong-type-arg' and `out-of-range'.

User interrupt (via `C-c' or by typing `q' at a pagination prompt)
is translated to a Guile `signal' exception with value `SIGINT'.

GDB Guile procedures can also throw these exceptions:

`gdb:error'
This exception is a catch-all for errors generated from within GDB.

`gdb:invalid-object'
This exception is thrown when accessing Guile objects that wrap
underlying GDB objects have become invalid. For example, a
`<gdb:breakpoint>' object becomes invalid if the user deletes it
from the command line. The object still exists in Guile, but the
object it represents is gone. Further operations on this
breakpoint will throw this exception.

`gdb:memory-error'
This exception is thrown when an operation tried to access invalid
memory in the inferior.

`gdb:pp-type-error'
This exception is thrown when a Guile pretty-printer passes a bad
object to GDB.

The following exception-related procedures are provided by the
`(gdb)' module.

-- Scheme Procedure: make-exception key args
Return a `<gdb:exception>' object given by its KEY and ARGS, which
are the standard Guile parameters of an exception. See the Guile
documentation for more information (*note Exceptions:
(guile)Exceptions.).

-- Scheme Procedure: exception? object
Return `#t' if OBJECT is a `<gdb:exception>' object. Otherwise
return `#f'.

-- Scheme Procedure: exception-key exception
Return the ARGS field of a `<gdb:exception>' object.

-- Scheme Procedure: exception-args exception
Return the ARGS field of a `<gdb:exception>' object.

File: gdb.info, Node: Values From Inferior In Guile, Next: Arithmetic In Guile, Prev: Guile Exception Handling, Up: Guile API

23.4.3.5 Values From Inferior In Guile
.....................................

GDB provides values it obtains from the inferior program in an object
of type `<gdb:value>'. GDB uses this object for its internal
bookkeeping of the inferior's values, and for fetching values when
necessary.

GDB does not memoize `<gdb:value>' objects. `make-value' always
returns a fresh object.

(gdb) guile (eq? (make-value 1) (make-value 1))
$1 = #f
(gdb) guile (equal? (make-value 1) (make-value 1))
$1 = #t

A `<gdb:value>' that represents a function can be executed via
inferior function call with `value-call'. Any arguments provided to
the call must match the function's prototype, and must be provided in
the order specified by that prototype.

For example, `some-val' is a `<gdb:value>' instance representing a
function that takes two integers as arguments. To execute this
function, call it like so:

(define result (value-call some-val 10 20))

Any values returned from a function call are `<gdb:value>' objects.

Note: Unlike Python scripting in GDB, inferior values that are
simple scalars cannot be used directly in Scheme expressions that are
valid for the value's data type. For example, `(+ (parse-and-eval
"int_variable") 2)' does not work. And inferior values that are
structures or instances of some class cannot be accessed using any
special syntax, instead `value-field' must be used.

The following value-related procedures are provided by the `(gdb)'
module.

-- Scheme Procedure: value? object
Return `#t' if OBJECT is a `<gdb:value>' object. Otherwise return
`#f'.

-- Scheme Procedure: make-value value [#:type type]
Many Scheme values can be converted directly to a `<gdb:value>'
with this procedure. If TYPE is specified, the result is a value
of this type, and if VALUE can't be represented with this type an
exception is thrown. Otherwise the type of the result is
determined from VALUE as described below.

*Note Architectures In Guile::, for a list of the builtin types
for an architecture.

Here's how Scheme values are converted when TYPE argument to
`make-value' is not specified:

Scheme boolean
A Scheme boolean is converted the boolean type for the
current language.

Scheme integer
A Scheme integer is converted to the first of a C `int',
`unsigned int', `long', `unsigned long', `long long' or
`unsigned long long' type for the current architecture that
can represent the value.

If the Scheme integer cannot be represented as a target
integer an `out-of-range' exception is thrown.

Scheme real
A Scheme real is converted to the C `double' type for the
current architecture.

Scheme string
A Scheme string is converted to a string in the current target
language using the current target encoding. Characters that
cannot be represented in the current target encoding are
replaced with the corresponding escape sequence. This is
Guile's `SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE' conversion
strategy (*note Strings: (guile)Strings.).

Passing TYPE is not supported in this case, if it is provided
a `wrong-type-arg' exception is thrown.

`<gdb:lazy-string>'
If VALUE is a `<gdb:lazy-string>' object (*note Lazy Strings
In Guile::), then the `lazy-string->value' procedure is
called, and its result is used.

Passing TYPE is not supported in this case, if it is provided
a `wrong-type-arg' exception is thrown.

Scheme bytevector
If VALUE is a Scheme bytevector and TYPE is provided, VALUE
must be the same size, in bytes, of values of type TYPE, and
the result is essentially created by using `memcpy'.

If VALUE is a Scheme bytevector and TYPE is not provided, the
result is an array of type `uint8' of the same length.

-- Scheme Procedure: value-optimized-out? value
Return `#t' if the compiler optimized out VALUE, thus it is not
available for fetching from the inferior. Otherwise return `#f'.

-- Scheme Procedure: value-address value
If VALUE is addressable, returns a `<gdb:value>' object
representing the address. Otherwise, `#f' is returned.

-- Scheme Procedure: value-type value
Return the type of VALUE as a `<gdb:type>' object (*note Types In
Guile::).

-- Scheme Procedure: value-dynamic-type value
Return the dynamic type of VALUE. This uses C++ run-time type
information (RTTI) to determine the dynamic type of the value. If
the value is of class type, it will return the class in which the
value is embedded, if any. If the value is of pointer or
reference to a class type, it will compute the dynamic type of the
referenced object, and return a pointer or reference to that type,
respectively. In all other cases, it will return the value's
static type.

Note that this feature will only work when debugging a C++ program
that includes RTTI for the object in question. Otherwise, it will
just return the static type of the value as in `ptype foo'. *Note
ptype: Symbols.

-- Scheme Procedure: value-cast value type
Return a new instance of `<gdb:value>' that is the result of
casting VALUE to the type described by TYPE, which must be a
`<gdb:type>' object. If the cast cannot be performed for some
reason, this method throws an exception.

-- Scheme Procedure: value-dynamic-cast value type
Like `value-cast', but works as if the C++ `dynamic_cast' operator
were used. Consult a C++ reference for details.

-- Scheme Procedure: value-reinterpret-cast value type
Like `value-cast', but works as if the C++ `reinterpret_cast'
operator were used. Consult a C++ reference for details.

-- Scheme Procedure: value-dereference value
For pointer data types, this method returns a new `<gdb:value>'
object whose contents is the object pointed to by VALUE. For
example, if `foo' is a C pointer to an `int', declared in your C
program as

int *foo;

then you can use the corresponding `<gdb:value>' to access what
`foo' points to like this:

(define bar (value-dereference foo))

The result `bar' will be a `<gdb:value>' object holding the value
pointed to by `foo'.

A similar function `value-referenced-value' exists which also
returns `<gdb:value>' objects corresponding to the values pointed
to by pointer values (and additionally, values referenced by
reference values). However, the behavior of `value-dereference'
differs from `value-referenced-value' by the fact that the
behavior of `value-dereference' is identical to applying the C
unary operator `*' on a given value. For example, consider a
reference to a pointer `ptrref', declared in your C++ program as

typedef int *intptr;
...
int val = 10;
intptr ptr = &val;
intptr &ptrref = ptr;

Though `ptrref' is a reference value, one can apply the method
`value-dereference' to the `<gdb:value>' object corresponding to
it and obtain a `<gdb:value>' which is identical to that
corresponding to `val'. However, if you apply the method
`value-referenced-value', the result would be a `<gdb:value>'
object identical to that corresponding to `ptr'.

(define scm-ptrref (parse-and-eval "ptrref"))
(define scm-val (value-dereference scm-ptrref))
(define scm-ptr (value-referenced-value scm-ptrref))

The `<gdb:value>' object `scm-val' is identical to that
corresponding to `val', and `scm-ptr' is identical to that
corresponding to `ptr'. In general, `value-dereference' can be
applied whenever the C unary operator `*' can be applied to the
corresponding C value. For those cases where applying both
`value-dereference' and `value-referenced-value' is allowed, the
results obtained need not be identical (as we have seen in the
above example). The results are however identical when applied on
`<gdb:value>' objects corresponding to pointers (`<gdb:value>'
objects with type code `TYPE_CODE_PTR') in a C/C++ program.

-- Scheme Procedure: value-referenced-value value
For pointer or reference data types, this method returns a new
`<gdb:value>' object corresponding to the value referenced by the
pointer/reference value. For pointer data types,
`value-dereference' and `value-referenced-value' produce identical
results. The difference between these methods is that
`value-dereference' cannot get the values referenced by reference
values. For example, consider a reference to an `int', declared
in your C++ program as

int val = 10;
int &ref = val;

then applying `value-dereference' to the `<gdb:value>' object
corresponding to `ref' will result in an error, while applying
`value-referenced-value' will result in a `<gdb:value>' object
identical to that corresponding to `val'.

(define scm-ref (parse-and-eval "ref"))
(define err-ref (value-dereference scm-ref)) ;; error
(define scm-val (value-referenced-value scm-ref)) ;; ok

The `<gdb:value>' object `scm-val' is identical to that
corresponding to `val'.

-- Scheme Procedure: value-reference-value value
Return a new `<gdb:value>' object which is a reference to the value
encapsulated by `<gdb:value>' object VALUE.

-- Scheme Procedure: value-rvalue-reference-value value
Return a new `<gdb:value>' object which is an rvalue reference to
the value encapsulated by `<gdb:value>' object VALUE.

-- Scheme Procedure: value-const-value value
Return a new `<gdb:value>' object which is a `const' version of
`<gdb:value>' object VALUE.

-- Scheme Procedure: value-field value field-name
Return field FIELD-NAME from `<gdb:value>' object VALUE.

-- Scheme Procedure: value-subscript value index
Return the value of array VALUE at index INDEX. The VALUE
argument must be a subscriptable `<gdb:value>' object.

-- Scheme Procedure: value-call value arg-list
Perform an inferior function call, taking VALUE as a pointer to
the function to call. Each element of list ARG-LIST must be a
<gdb:value> object or an object that can be converted to a value.
The result is the value returned by the function.

-- Scheme Procedure: value->bool value
Return the Scheme boolean representing `<gdb:value>' VALUE. The
value must be "integer like". Pointers are ok.

-- Scheme Procedure: value->integer
Return the Scheme integer representing `<gdb:value>' VALUE. The
value must be "integer like". Pointers are ok.

-- Scheme Procedure: value->real
Return the Scheme real number representing `<gdb:value>' VALUE.
The value must be a number.

-- Scheme Procedure: value->bytevector
Return a Scheme bytevector with the raw contents of `<gdb:value>'
VALUE. No transformation, endian or otherwise, is performed.

-- Scheme Procedure: value->string value [#:encoding encoding]
[#:errors errors] [#:length length]
If VALUE> represents a string, then this method converts the
contents to a Guile string. Otherwise, this method will throw an
exception.

Values are interpreted as strings according to the rules of the
current language. If the optional length argument is given, the
string will be converted to that length, and will include any
embedded zeroes that the string may contain. Otherwise, for
languages where the string is zero-terminated, the entire string
will be converted.

For example, in C-like languages, a value is a string if it is a
pointer to or an array of characters or ints of type `wchar_t',
`char16_t', or `char32_t'.

If the optional ENCODING argument is given, it must be a string
naming the encoding of the string in the `<gdb:value>', such as
`"ascii"', `"iso-8859-6"' or `"utf-8"'. It accepts the same
encodings as the corresponding argument to Guile's
`scm_from_stringn' function, and the Guile codec machinery will be
used to convert the string. If ENCODING is not given, or if
ENCODING is the empty string, then either the `target-charset'
(*note Character Sets::) will be used, or a language-specific
encoding will be used, if the current language is able to supply
one.

The optional ERRORS argument is one of `#f', `error' or
`substitute'. `error' and `substitute' must be symbols. If
ERRORS is not specified, or if its value is `#f', then the default
conversion strategy is used, which is set with the Scheme function
`set-port-conversion-strategy!'. If the value is `'error' then an
exception is thrown if there is any conversion error. If the
value is `'substitute' then any conversion error is replaced with
question marks. *Note Strings: (guile)Strings.

If the optional LENGTH argument is given, the string will be
fetched and converted to the given length. The length must be a
Scheme integer and not a `<gdb:value>' integer.

-- Scheme Procedure: value->lazy-string value [#:encoding encoding]
[#:length length]
If this `<gdb:value>' represents a string, then this method
converts VALUE to a `<gdb:lazy-string' (*note Lazy Strings In
Guile::). Otherwise, this method will throw an exception.

If the optional ENCODING argument is given, it must be a string
naming the encoding of the `<gdb:lazy-string'. Some examples are:
`"ascii"', `"iso-8859-6"' or `"utf-8"'. If the ENCODING argument
is an encoding that GDB does not recognize, GDB will raise an
error.

When a lazy string is printed, the GDB encoding machinery is used
to convert the string during printing. If the optional ENCODING
argument is not provided, or is an empty string, GDB will
automatically select the encoding most suitable for the string
type. For further information on encoding in GDB please see *Note
Character Sets::.

If the optional LENGTH argument is given, the string will be
fetched and encoded to the length of characters specified. If the
LENGTH argument is not provided, the string will be fetched and
encoded until a null of appropriate width is found. The length
must be a Scheme integer and not a `<gdb:value>' integer.

-- Scheme Procedure: value-lazy? value
Return `#t' if VALUE has not yet been fetched from the inferior.
Otherwise return `#f'. GDB does not fetch values until necessary,
for efficiency. For example:

(define myval (parse-and-eval "somevar"))

The value of `somevar' is not fetched at this time. It will be
fetched when the value is needed, or when the `fetch-lazy'
procedure is invoked.

-- Scheme Procedure: make-lazy-value type address
Return a `<gdb:value>' that will be lazily fetched from the
target. The object of type `<gdb:type>' whose value to fetch is
specified by its TYPE and its target memory ADDRESS, which is a
Scheme integer.

-- Scheme Procedure: value-fetch-lazy! value
If VALUE is a lazy value (`(value-lazy? value)' is `#t'), then the
value is fetched from the inferior. Any errors that occur in the
process will produce a Guile exception.

If VALUE is not a lazy value, this method has no effect.

The result of this function is unspecified.

-- Scheme Procedure: value-print value
Return the string representation (print form) of `<gdb:value>'
VALUE.

File: gdb.info, Node: Arithmetic In Guile, Next: Types In Guile, Prev: Values From Inferior In Guile, Up: Guile API

23.4.3.6 Arithmetic In Guile
...........................

The `(gdb)' module provides several functions for performing arithmetic
on `<gdb:value>' objects. The arithmetic is performed as if it were
done by the target, and therefore has target semantics which are not
necessarily those of Scheme. For example operations work with a fixed
precision, not the arbitrary precision of Scheme.

Wherever a function takes an integer or pointer as an operand, GDB
will convert appropriate Scheme values to perform the operation.

-- Scheme Procedure: value-add a b

-- Scheme Procedure: value-sub a b

-- Scheme Procedure: value-mul a b

-- Scheme Procedure: value-div a b

-- Scheme Procedure: value-rem a b

-- Scheme Procedure: value-mod a b

-- Scheme Procedure: value-pow a b

-- Scheme Procedure: value-not a

-- Scheme Procedure: value-neg a

-- Scheme Procedure: value-pos a

-- Scheme Procedure: value-abs a

-- Scheme Procedure: value-lsh a b

-- Scheme Procedure: value-rsh a b

-- Scheme Procedure: value-min a b

-- Scheme Procedure: value-max a b

-- Scheme Procedure: value-lognot a

-- Scheme Procedure: value-logand a b

-- Scheme Procedure: value-logior a b

-- Scheme Procedure: value-logxor a b

-- Scheme Procedure: value=? a b

-- Scheme Procedure: value<? a b

-- Scheme Procedure: value<=? a b

-- Scheme Procedure: value>? a b

-- Scheme Procedure: value>=? a b

Scheme does not provide a `not-equal' function, and thus Guile
support in GDB does not either.

File: gdb.info, Node: Types In Guile, Next: Guile Pretty Printing API, Prev: Arithmetic In Guile, Up: Guile API

23.4.3.7 Types In Guile
......................

GDB represents types from the inferior in objects of type `<gdb:type>'.

The following type-related procedures are provided by the `(gdb)'
module.

-- Scheme Procedure: type? object
Return `#t' if OBJECT is an object of type `<gdb:type>'.
Otherwise return `#f'.

-- Scheme Procedure: lookup-type name [#:block block]
This function looks up a type by its NAME, which must be a string.

If BLOCK is given, it is an object of type `<gdb:block>', and NAME
is looked up in that scope. Otherwise, it is searched for
globally.

Ordinarily, this function will return an instance of `<gdb:type>'.
If the named type cannot be found, it will throw an exception.

-- Scheme Procedure: type-code type
Return the type code of TYPE. The type code will be one of the
`TYPE_CODE_' constants defined below.

-- Scheme Procedure: type-tag type
Return the tag name of TYPE. The tag name is the name after
`struct', `union', or `enum' in C and C++; not all languages have
this concept. If this type has no tag name, then `#f' is returned.

-- Scheme Procedure: type-name type
Return the name of TYPE. If this type has no name, then `#f' is
returned.

-- Scheme Procedure: type-print-name type
Return the print name of TYPE. This returns something even for
anonymous types. For example, for an anonymous C struct `"struct
{...}"' is returned.

-- Scheme Procedure: type-sizeof type
Return the size of this type, in target `char' units. Usually, a
target's `char' type will be an 8-bit byte. However, on some
unusual platforms, this type may have a different size.

-- Scheme Procedure: type-strip-typedefs type
Return a new `<gdb:type>' that represents the real type of TYPE,
after removing all layers of typedefs.

-- Scheme Procedure: type-array type n1 [n2]
Return a new `<gdb:type>' object which represents an array of this
type. If one argument is given, it is the inclusive upper bound of
the array; in this case the lower bound is zero. If two arguments
are given, the first argument is the lower bound of the array, and
the second argument is the upper bound of the array. An array's
length must not be negative, but the bounds can be.

-- Scheme Procedure: type-vector type n1 [n2]
Return a new `<gdb:type>' object which represents a vector of this
type. If one argument is given, it is the inclusive upper bound of
the vector; in this case the lower bound is zero. If two
arguments are given, the first argument is the lower bound of the
vector, and the second argument is the upper bound of the vector.
A vector's length must not be negative, but the bounds can be.

The difference between an `array' and a `vector' is that arrays
behave like in C: when used in expressions they decay to a pointer
to the first element whereas vectors are treated as first class
values.

-- Scheme Procedure: type-pointer type
Return a new `<gdb:type>' object which represents a pointer to
TYPE.

-- Scheme Procedure: type-range type
Return a list of two elements: the low bound and high bound of
TYPE. If TYPE does not have a range, an exception is thrown.

-- Scheme Procedure: type-reference type
Return a new `<gdb:type>' object which represents a reference to
TYPE.

-- Scheme Procedure: type-target type
Return a new `<gdb:type>' object which represents the target type
of TYPE.

For a pointer type, the target type is the type of the pointed-to
object. For an array type (meaning C-like arrays), the target
type is the type of the elements of the array. For a function or
method type, the target type is the type of the return value. For
a complex type, the target type is the type of the elements. For
a typedef, the target type is the aliased type.

If the type does not have a target, this method will throw an
exception.

-- Scheme Procedure: type-const type
Return a new `<gdb:type>' object which represents a
`const'-qualified variant of TYPE.

-- Scheme Procedure: type-volatile type
Return a new `<gdb:type>' object which represents a
`volatile'-qualified variant of TYPE.

-- Scheme Procedure: type-unqualified type
Return a new `<gdb:type>' object which represents an unqualified
variant of TYPE. That is, the result is neither `const' nor
`volatile'.

-- Scheme Procedure: type-num-fields
Return the number of fields of `<gdb:type>' TYPE.

-- Scheme Procedure: type-fields type
Return the fields of TYPE as a list. For structure and union
types, `fields' has the usual meaning. Range types have two
fields, the minimum and maximum values. Enum types have one field
per enum constant. Function and method types have one field per
parameter. The base types of C++ classes are also represented as
fields. If the type has no fields, or does not fit into one of
these categories, an empty list will be returned. *Note Fields of
a type in Guile::.

-- Scheme Procedure: make-field-iterator type
Return the fields of TYPE as a <gdb:iterator> object. *Note
Iterators In Guile::.

-- Scheme Procedure: type-field type field-name
Return field named FIELD-NAME in TYPE. The result is an object of
type `<gdb:field>'. *Note Fields of a type in Guile::. If the
type does not have fields, or FIELD-NAME is not a field of TYPE,
an exception is thrown.

For example, if `some-type' is a `<gdb:type>' instance holding a
structure type, you can access its `foo' field with:

(define bar (type-field some-type "foo"))

`bar' will be a `<gdb:field>' object.

-- Scheme Procedure: type-has-field? type name
Return `#t' if `<gdb:type>' TYPE has field named NAME. Otherwise
return `#f'.

Each type has a code, which indicates what category this type falls
into. The available type categories are represented by constants
defined in the `(gdb)' module:

`TYPE_CODE_PTR'
The type is a pointer.

`TYPE_CODE_ARRAY'
The type is an array.

`TYPE_CODE_STRUCT'
The type is a structure.

`TYPE_CODE_UNION'
The type is a union.

`TYPE_CODE_ENUM'
The type is an enum.

`TYPE_CODE_FLAGS'
A bit flags type, used for things such as status registers.

`TYPE_CODE_FUNC'
The type is a function.

`TYPE_CODE_INT'
The type is an integer type.

`TYPE_CODE_FLT'
A floating point type.

`TYPE_CODE_VOID'
The special type `void'.

`TYPE_CODE_SET'
A Pascal set type.

`TYPE_CODE_RANGE'
A range type, that is, an integer type with bounds.

`TYPE_CODE_STRING'
A string type. Note that this is only used for certain languages
with language-defined string types; C strings are not represented
this way.

`TYPE_CODE_BITSTRING'
A string of bits. It is deprecated.

`TYPE_CODE_ERROR'
An unknown or erroneous type.

`TYPE_CODE_METHOD'
A method type, as found in C++.

`TYPE_CODE_METHODPTR'
A pointer-to-member-function.

`TYPE_CODE_MEMBERPTR'
A pointer-to-member.

`TYPE_CODE_REF'
A reference type.

`TYPE_CODE_RVALUE_REF'
A C++11 rvalue reference type.

`TYPE_CODE_CHAR'
A character type.

`TYPE_CODE_BOOL'
A boolean type.

`TYPE_CODE_COMPLEX'
A complex float type.

`TYPE_CODE_TYPEDEF'
A typedef to some other type.

`TYPE_CODE_NAMESPACE'
A C++ namespace.

`TYPE_CODE_DECFLOAT'
A decimal floating point type.

`TYPE_CODE_INTERNAL_FUNCTION'
A function internal to GDB. This is the type used to represent
convenience functions (*note Convenience Funs::).

`gdb.TYPE_CODE_XMETHOD'
A method internal to GDB. This is the type used to represent
xmethods (*note Writing an Xmethod::).

`gdb.TYPE_CODE_FIXED_POINT'
A fixed-point number.

`gdb.TYPE_CODE_NAMESPACE'
A Fortran namelist.

Further support for types is provided in the `(gdb types)' Guile
module (*note Guile Types Module::).

Each field is represented as an object of type `<gdb:field>'.

The following field-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: field? object
Return `#t' if OBJECT is an object of type `<gdb:field>'.
Otherwise return `#f'.

-- Scheme Procedure: field-name field
Return the name of the field, or `#f' for anonymous fields.

-- Scheme Procedure: field-type field
Return the type of the field. This is usually an instance of
`<gdb:type>', but it can be `#f' in some situations.

-- Scheme Procedure: field-enumval field
Return the enum value represented by `<gdb:field>' FIELD.

-- Scheme Procedure: field-bitpos field
Return the bit position of `<gdb:field>' FIELD. This attribute is
not available for `static' fields (as in C++).

-- Scheme Procedure: field-bitsize field
If the field is packed, or is a bitfield, return the size of
`<gdb:field>' FIELD in bits. Otherwise, zero is returned; in
which case the field's size is given by its type.

-- Scheme Procedure: field-artificial? field
Return `#t' if the field is artificial, usually meaning that it
was provided by the compiler and not the user. Otherwise return
`#f'.

-- Scheme Procedure: field-base-class? field
Return `#t' if the field represents a base class of a C++
structure. Otherwise return `#f'.

File: gdb.info, Node: Guile Pretty Printing API, Next: Selecting Guile Pretty-Printers, Prev: Types In Guile, Up: Guile API

23.4.3.8 Guile Pretty Printing API
.................................

An example output is provided (*note Pretty Printing::).

A pretty-printer is represented by an object of type
<gdb:pretty-printer>. Pretty-printer objects are created with
`make-pretty-printer'.

The following pretty-printer-related procedures are provided by the
`(gdb)' module:

-- Scheme Procedure: make-pretty-printer name lookup-function
Return a `<gdb:pretty-printer>' object named NAME.

LOOKUP-FUNCTION is a function of one parameter: the value to be
printed. If the value is handled by this pretty-printer, then
LOOKUP-FUNCTION returns an object of type
<gdb:pretty-printer-worker> to perform the actual pretty-printing.
Otherwise LOOKUP-FUNCTION returns `#f'.

-- Scheme Procedure: pretty-printer? object
Return `#t' if OBJECT is a `<gdb:pretty-printer>' object.
Otherwise return `#f'.

-- Scheme Procedure: pretty-printer-enabled? pretty-printer
Return `#t' if PRETTY-PRINTER is enabled. Otherwise return `#f'.

-- Scheme Procedure: set-pretty-printer-enabled! pretty-printer flag
Set the enabled flag of PRETTY-PRINTER to FLAG. The value
returned is unspecified.

-- Scheme Procedure: pretty-printers
Return the list of global pretty-printers.

-- Scheme Procedure: set-pretty-printers! pretty-printers
Set the list of global pretty-printers to PRETTY-PRINTERS. The
value returned is unspecified.

-- Scheme Procedure: make-pretty-printer-worker display-hint to-string
children
Return an object of type `<gdb:pretty-printer-worker>'.

This function takes three parameters:

`display-hint'
DISPLAY-HINT provides a hint to GDB or GDB front end via MI
to change the formatting of the value being printed. The
value must be a string or `#f' (meaning there is no hint).
Several values for DISPLAY-HINT are predefined by GDB:

`array'
Indicate that the object being printed is "array-like".
The CLI uses this to respect parameters such as `set
print elements' and `set print array'.

`map'
Indicate that the object being printed is "map-like",
and that the children of this value can be assumed to
alternate between keys and values.

`string'
Indicate that the object being printed is "string-like".
If the printer's `to-string' function returns a Guile
string of some kind, then GDB will call its internal
language-specific string-printing function to format the
string. For the CLI this means adding quotation marks,
possibly escaping some characters, respecting `set print
elements', and the like.

`to-string'
TO-STRING is either a function of one parameter, the
`<gdb:pretty-printer-worker>' object, or `#f'.

When printing from the CLI, if the `to-string' method exists,
then GDB will prepend its result to the values returned by
`children'. Exactly how this formatting is done is dependent
on the display hint, and may change as more hints are added.
Also, depending on the print settings (*note Print
Settings::), the CLI may print just the result of `to-string'
in a stack trace, omitting the result of `children'.

If this method returns a string, it is printed verbatim.

Otherwise, if this method returns an instance of
`<gdb:value>', then GDB prints this value. This may result
in a call to another pretty-printer.

If instead the method returns a Guile value which is
convertible to a `<gdb:value>', then GDB performs the
conversion and prints the resulting value. Again, this may
result in a call to another pretty-printer. Guile scalars
(integers, floats, and booleans) and strings are convertible
to `<gdb:value>'; other types are not.

Finally, if this method returns `#f' then no further
operations are performed in this method and nothing is
printed.

If the result is not one of these types, an exception is
raised.

TO-STRING may also be `#f' in which case it is left to
CHILDREN to print the value.

`children'
CHILDREN is either a function of one parameter, the
`<gdb:pretty-printer-worker>' object, or `#f'.

GDB will call this function on a pretty-printer to compute the
children of the pretty-printer's value.

This function must return a <gdb:iterator> object. Each item
returned by the iterator must be a tuple holding two
elements. The first element is the "name" of the child; the
second element is the child's value. The value can be any
Guile object which is convertible to a GDB value.

If CHILDREN is `#f', GDB will act as though the value has no
children.

Children may be hidden from display based on the value of `set
print max-depth' (*note Print Settings::).

GDB provides a function which can be used to look up the default
pretty-printer for a `<gdb:value>':

-- Scheme Procedure: default-visualizer value
This function takes a `<gdb:value>' object as an argument. If a
pretty-printer for this value exists, then it is returned. If no
such printer exists, then this returns `#f'.

File: gdb.info, Node: Selecting Guile Pretty-Printers, Next: Writing a Guile Pretty-Printer, Prev: Guile Pretty Printing API, Up: Guile API

23.4.3.9 Selecting Guile Pretty-Printers
.......................................

There are three sets of pretty-printers that GDB searches:

* Per-objfile list of pretty-printers (*note Objfiles In Guile::).

* Per-progspace list of pretty-printers (*note Progspaces In
Guile::).

* The global list of pretty-printers (*note Guile Pretty Printing
API::). These printers are available when debugging any inferior.

Pretty-printer lookup is done by passing the value to be printed to
the lookup function of each enabled object in turn. Lookup stops when
a lookup function returns a non-`#f' value or when the list is
exhausted. Lookup functions must return either a
`<gdb:pretty-printer-worker>' object or `#f'. Otherwise an exception
is thrown.

GDB first checks the result of `objfile-pretty-printers' of each
`<gdb:objfile>' in the current program space and iteratively calls each
enabled lookup function in the list for that `<gdb:objfile>' until a
non-`#f' object is returned. If no pretty-printer is found in the
objfile lists, GDB then searches the result of
`progspace-pretty-printers' of the current program space, calling each
enabled function until a non-`#f' object is returned. After these
lists have been exhausted, it tries the global pretty-printers list,
obtained with `pretty-printers', again calling each enabled function
until a non-`#f' object is returned.

The order in which the objfiles are searched is not specified. For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a
`<gdb:pretty-printer-worker>' object is returned.

For various reasons a pretty-printer may not work. For example, the
underlying data structure may have changed and the pretty-printer is
out of date.

The consequences of a broken pretty-printer are severe enough that
GDB provides support for enabling and disabling individual printers.
For example, if `print frame-arguments' is on, a backtrace can become
highly illegible if any argument is printed with a broken printer.

Pretty-printers are enabled and disabled from Scheme by calling
`set-pretty-printer-enabled!'. *Note Guile Pretty Printing API::.

File: gdb.info, Node: Writing a Guile Pretty-Printer, Next: Commands In Guile, Prev: Selecting Guile Pretty-Printers, Up: Guile API

23.4.3.10 Writing a Guile Pretty-Printer
.......................................

A pretty-printer consists of two basic parts: a lookup function to
determine if the type is supported, and the printer itself.

Here is an example showing how a `std::string' printer might be
written. *Note Guile Pretty Printing API::, for details.

(define (make-my-string-printer value)
"Print a my::string string"
(make-pretty-printer-worker
"string"
(lambda (printer)
(value-field value "_data"))
#f))

And here is an example showing how a lookup function for the printer
example above might be written.

(define (str-lookup-function pretty-printer value)
(let ((tag (type-tag (value-type value))))
(and tag
(string-prefix? "std::string<" tag)
(make-my-string-printer value))))

Then to register this printer in the global printer list:

(append-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function))

The example lookup function extracts the value's type, and attempts
to match it to a type that it can pretty-print. If it is a type the
printer can pretty-print, it will return a <gdb:pretty-printer-worker>
object. If not, it returns `#f'.

We recommend that you put your core pretty-printers into a Guile
package. If your pretty-printers are for use with a library, we
further recommend embedding a version number into the package name.
This practice will enable GDB to load multiple versions of your
pretty-printers at the same time, because they will have different
names.

You should write auto-loaded code (*note Guile Auto-loading::) such
that it can be evaluated multiple times without changing its meaning.
An ideal auto-load file will consist solely of `import's of your
printer modules, followed by a call to a register pretty-printers with
the current objfile.

Taken as a whole, this approach will scale nicely to multiple
inferiors, each potentially using a different library version.
Embedding a version number in the Guile package name will ensure that
GDB is able to load both sets of printers simultaneously. Then,
because the search for pretty-printers is done by objfile, and because
your auto-loaded code took care to register your library's printers
with a specific objfile, GDB will find the correct printers for the
specific version of the library used by each inferior.

To continue the `my::string' example, this code might appear in
`(my-project my-library v1)':

(use-modules (gdb))
(define (register-printers objfile)
(append-objfile-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function)))

And then the corresponding contents of the auto-load file would be:

(use-modules (gdb) (my-project my-library v1))
(register-printers (current-objfile))

The previous example illustrates a basic pretty-printer. There are
a few things that can be improved on. The printer only handles one
type, whereas a library typically has several types. One could install
a lookup function for each desired type in the library, but one could
also have a single lookup function recognize several types. The latter
is the conventional way this is handled. If a pretty-printer can
handle multiple data types, then its "subprinters" are the printers for
the individual data types.

The `(gdb printing)' module provides a formal way of solving this
problem (*note Guile Printing Module::). Here is another example that
handles multiple types.

These are the types we are going to pretty-print:

struct foo { int a, b; };
struct bar { struct foo x, y; };

Here are the printers:

(define (make-foo-printer value)
"Print a foo object"
(make-pretty-printer-worker
"foo"
(lambda (printer)
(format #f "a=<~a> b=<~a>"
(value-field value "a") (value-field value "a")))
#f))

(define (make-bar-printer value)
"Print a bar object"
(make-pretty-printer-worker
"foo"
(lambda (printer)
(format #f "x=<~a> y=<~a>"
(value-field value "x") (value-field value "y")))
#f))

This example doesn't need a lookup function, that is handled by the
`(gdb printing)' module. Instead a function is provided to build up
the object that handles the lookup.

(use-modules (gdb printing))

(define (build-pretty-printer)
(let ((pp (make-pretty-printer-collection "my-library")))
(pp-collection-add-tag-printer "foo" make-foo-printer)
(pp-collection-add-tag-printer "bar" make-bar-printer)
pp))

And here is the autoload support:

(use-modules (gdb) (my-library))
(append-objfile-pretty-printer! (current-objfile) (build-pretty-printer))

Finally, when this printer is loaded into GDB, here is the
corresponding output of `info pretty-printer':

(gdb) info pretty-printer
my_library.so:
my-library
foo
bar

File: gdb.info, Node: Commands In Guile, Next: Parameters In Guile, Prev: Writing a Guile Pretty-Printer, Up: Guile API

23.4.3.11 Commands In Guile
..........................

You can implement new GDB CLI commands in Guile. A CLI command object
is created with the `make-command' Guile function, and added to GDB
with the `register-command!' Guile function. This two-step approach is
taken to separate out the side-effect of adding the command to GDB from
`make-command'.

There is no support for multi-line commands, that is commands that
consist of multiple lines and are terminated with `end'.

-- Scheme Procedure: make-command name [#:invoke invoke]
[#:command-class command-class] [#:completer-class completer]
[#:prefix? prefix] [#:doc doc-string]
The argument NAME is the name of the command. If NAME consists of
multiple words, then the initial words are looked for as prefix
commands. In this case, if one of the prefix commands does not
exist, an exception is raised.

The result is the `<gdb:command>' object representing the command.
The command is not usable until it has been registered with GDB
with `register-command!'.

The rest of the arguments are optional.

The argument INVOKE is a procedure of three arguments: SELF, ARGS
and FROM-TTY. The argument SELF is the `<gdb:command>' object
representing the command. The argument ARGS is a string
representing the arguments passed to the command, after leading
and trailing whitespace has been stripped. The argument FROM-TTY
is a boolean flag and specifies whether the command should
consider itself to have been originated from the user invoking it
interactively. If this function throws an exception, it is turned
into a GDB `error' call. Otherwise, the return value is ignored.

The argument COMMAND-CLASS is one of the `COMMAND_' constants
defined below. This argument tells GDB how to categorize the new
command in the help system. The default is `COMMAND_NONE'.

The argument COMPLETER is either `#f', one of the `COMPLETE_'
constants defined below, or a procedure, also defined below. This
argument tells GDB how to perform completion for this command. If
not provided or if the value is `#f', then no completion is
performed on the command.

The argument PREFIX is a boolean flag indicating whether the new
command is a prefix command; sub-commands of this command may be
registered.

The argument DOC-STRING is help text for the new command. If no
documentation string is provided, the default value "This command
is not documented." is used.

-- Scheme Procedure: register-command! command
Add COMMAND, a `<gdb:command>' object, to GDB's list of commands.
It is an error to register a command more than once. The result
is unspecified.

-- Scheme Procedure: command? object
Return `#t' if OBJECT is a `<gdb:command>' object. Otherwise
return `#f'.

-- Scheme Procedure: dont-repeat
By default, a GDB command is repeated when the user enters a blank
line at the command prompt. A command can suppress this behavior
by invoking the `dont-repeat' function. This is similar to the
user command `dont-repeat', see *Note dont-repeat: Define.

-- Scheme Procedure: string->argv string
Convert a string to a list of strings split up according to GDB's
argv parsing rules. It is recommended to use this for consistency.
Arguments are separated by spaces and may be quoted. Example:

scheme@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
$1 = ("1" "2 \"3" "4 \"5" "6 '7")

-- Scheme Procedure: throw-user-error message . args
Throw a `gdb:user-error' exception. The argument MESSAGE is the
error message as a format string, like the FMT argument to the
`format' Scheme function. *Note Formatted Output:
(guile)Formatted Output. The argument ARGS is a list of the
optional arguments of MESSAGE.

This is used when the command detects a user error of some kind,
say a bad command argument.

(gdb) guile (use-modules (gdb))
(gdb) guile
(register-command! (make-command "test-user-error"
#:command-class COMMAND_OBSCURE
#:invoke (lambda (self arg from-tty)
(throw-user-error "Bad argument ~a" arg))))
end
(gdb) test-user-error ugh
ERROR: Bad argument ugh

-- completer: self text word
If the COMPLETER option to `make-command' is a procedure, it takes
three arguments: SELF which is the `<gdb:command>' object, and
TEXT and WORD which are both strings. The argument TEXT holds the
complete command line up to the cursor's location. The argument
WORD holds the last word of the command line; this is computed
using a word-breaking heuristic.

All forms of completion are handled by this function, that is, the
<TAB> and <M-?> key bindings (*note Completion::), and the
`complete' command (*note complete: Help.).

This procedure can return several kinds of values:

* If the return value is a list, the contents of the list are
used as the completions. It is up to COMPLETER to ensure
that the contents actually do complete the word. An empty
list is allowed, it means that there were no completions
available. Only string elements of the list are used; other
elements in the list are ignored.

* If the return value is a `<gdb:iterator>' object, it is
iterated over to obtain the completions. It is up to
`completer-procedure' to ensure that the results actually do
complete the word. Only string elements of the result are
used; other elements in the sequence are ignored.

* All other results are treated as though there were no
available completions.

When a new command is registered, it will have been declared as a
member of some general class of commands. This is used to classify
top-level commands in the on-line help system; note that prefix
commands are not listed under their own category but rather that of
their top-level command. The available classifications are represented
by constants defined in the `gdb' module:

`COMMAND_NONE'
The command does not belong to any particular class. A command in
this category will not be displayed in any of the help categories.
This is the default.

`COMMAND_RUNNING'
The command is related to running the inferior. For example,
`start', `step', and `continue' are in this category. Type `help
running' at the GDB prompt to see a list of commands in this
category.

`COMMAND_DATA'
The command is related to data or variables. For example, `call',
`find', and `print' are in this category. Type `help data' at the
GDB prompt to see a list of commands in this category.

`COMMAND_STACK'
The command has to do with manipulation of the stack. For example,
`backtrace', `frame', and `return' are in this category. Type
`help stack' at the GDB prompt to see a list of commands in this
category.

`COMMAND_FILES'
This class is used for file-related commands. For example,
`file', `list' and `section' are in this category. Type `help
files' at the GDB prompt to see a list of commands in this
category.

`COMMAND_SUPPORT'
This should be used for "support facilities", generally meaning
things that are useful to the user when interacting with GDB, but
not related to the state of the inferior. For example, `help',
`make', and `shell' are in this category. Type `help support' at
the GDB prompt to see a list of commands in this category.

`COMMAND_STATUS'
The command is an `info'-related command, that is, related to the
state of GDB itself. For example, `info', `macro', and `show' are
in this category. Type `help status' at the GDB prompt to see a
list of commands in this category.

`COMMAND_BREAKPOINTS'
The command has to do with breakpoints. For example, `break',
`clear', and `delete' are in this category. Type `help
breakpoints' at the GDB prompt to see a list of commands in this
category.

`COMMAND_TRACEPOINTS'
The command has to do with tracepoints. For example, `trace',
`actions', and `tfind' are in this category. Type `help
tracepoints' at the GDB prompt to see a list of commands in this
category.

`COMMAND_USER'
The command is a general purpose command for the user, and
typically does not fit in one of the other categories. Type `help
user-defined' at the GDB prompt to see a list of commands in this
category, as well as the list of gdb macros (*note Sequences::).

`COMMAND_OBSCURE'
The command is only used in unusual circumstances, or is not of
general interest to users. For example, `checkpoint', `fork', and
`stop' are in this category. Type `help obscure' at the GDB
prompt to see a list of commands in this category.

`COMMAND_MAINTENANCE'
The command is only useful to GDB maintainers. The `maintenance'
and `flushregs' commands are in this category. Type `help
internals' at the GDB prompt to see a list of commands in this
category.

A new command can use a predefined completion function, either by
specifying it via an argument at initialization, or by returning it
from the `completer' procedure. These predefined completion constants
are all defined in the `gdb' module:

`COMPLETE_NONE'
This constant means that no completion should be done.

`COMPLETE_FILENAME'
This constant means that filename completion should be performed.

`COMPLETE_LOCATION'
This constant means that location completion should be done.
*Note Location Specifications::.

`COMPLETE_COMMAND'
This constant means that completion should examine GDB command
names.

`COMPLETE_SYMBOL'
This constant means that completion should be done using symbol
names as the source.

`COMPLETE_EXPRESSION'
This constant means that completion should be done on expressions.
Often this means completing on symbol names, but some language
parsers also have support for completing on field names.

The following code snippet shows how a trivial CLI command can be
implemented in Guile:

(gdb) guile
(register-command! (make-command "hello-world"
#:command-class COMMAND_USER
#:doc "Greet the whole world."
#:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
end
(gdb) hello-world
Hello, World!

File: gdb.info, Node: Parameters In Guile, Next: Progspaces In Guile, Prev: Commands In Guile, Up: Guile API

23.4.3.12 Parameters In Guile
............................

You can implement new GDB "parameters" using Guile (1).

There are many parameters that already exist and can be set in GDB.
Two examples are: `set follow-fork' and `set charset'. Setting these
parameters influences certain behavior in GDB. Similarly, you can
define parameters that can be used to influence behavior in custom
Guile scripts and commands.

A new parameter is defined with the `make-parameter' Guile function,
and added to GDB with the `register-parameter!' Guile function. This
two-step approach is taken to separate out the side-effect of adding
the parameter to GDB from `make-parameter'.

Parameters are exposed to the user via the `set' and `show'
commands. *Note Help::.

-- Scheme Procedure: make-parameter name
[#:command-class command-class]
[#:parameter-type parameter-type] [#:enum-list enum-list]
[#:set-func set-func] [#:show-func show-func] [#:doc doc]
[#:set-doc set-doc] [#:show-doc show-doc]
[#:initial-value initial-value]
The argument NAME is the name of the new parameter. If NAME
consists of multiple words, then the initial words are looked for
as prefix parameters. An example of this can be illustrated with
the `set print' set of parameters. If NAME is `print foo', then
`print' will be searched as the prefix parameter. In this case
the parameter can subsequently be accessed in GDB as `set print
foo'. If NAME consists of multiple words, and no prefix parameter
group can be found, an exception is raised.

The result is the `<gdb:parameter>' object representing the
parameter. The parameter is not usable until it has been
registered with GDB with `register-parameter!'.

The rest of the arguments are optional.

The argument COMMAND-CLASS should be one of the `COMMAND_'
constants (*note Commands In Guile::). This argument tells GDB
how to categorize the new parameter in the help system. The
default is `COMMAND_NONE'.

The argument PARAMETER-TYPE should be one of the `PARAM_' constants
defined below. This argument tells GDB the type of the new
parameter; this information is used for input validation and
completion. The default is `PARAM_BOOLEAN'.

If PARAMETER-TYPE is `PARAM_ENUM', then ENUM-LIST must be a list
of strings. These strings represent the possible values for the
parameter.

If PARAMETER-TYPE is not `PARAM_ENUM', then the presence of
ENUM-LIST will cause an exception to be thrown.

The argument SET-FUNC is a function of one argument: SELF which is
the `<gdb:parameter>' object representing the parameter. GDB will
call this function when a PARAMETER's value has been changed via
the `set' API (for example, `set foo off'). The value of the
parameter has already been set to the new value. This function
must return a string to be displayed to the user. GDB will add a
trailing newline if the string is non-empty. GDB generally
doesn't print anything when a parameter is set, thus typically
this function should return `""'. A non-empty string result
should typically be used for displaying warnings and errors.

The argument SHOW-FUNC is a function of two arguments: SELF which
is the `<gdb:parameter>' object representing the parameter, and
SVALUE which is the string representation of the current value.
GDB will call this function when a PARAMETER's `show' API has been
invoked (for example, `show foo'). This function must return a
string, and will be displayed to the user. GDB will add a
trailing newline.

The argument DOC is the help text for the new parameter. If there
is no documentation string, a default value is used.

The argument SET-DOC is the help text for this parameter's `set'
command.

The argument SHOW-DOC is the help text for this parameter's `show'
command.

The argument INITIAL-VALUE specifies the initial value of the
parameter. If it is a function, it takes one parameter, the
`<gdb:parameter>' object and its result is used as the initial
value of the parameter. The initial value must be valid for the
parameter type, otherwise an exception is thrown.

-- Scheme Procedure: register-parameter! parameter
Add PARAMETER, a `<gdb:parameter>' object, to GDB's list of
parameters. It is an error to register a parameter more than once.
The result is unspecified.

-- Scheme Procedure: parameter? object
Return `#t' if OBJECT is a `<gdb:parameter>' object. Otherwise
return `#f'.

-- Scheme Procedure: parameter-value parameter
Return the value of PARAMETER which may either be a
`<gdb:parameter>' object or a string naming the parameter.

-- Scheme Procedure: set-parameter-value! parameter new-value
Assign PARAMETER the value of NEW-VALUE. The argument PARAMETER
must be an object of type `<gdb:parameter>'. GDB does validation
when assignments are made.

When a new parameter is defined, its type must be specified. The
available types are represented by constants defined in the `gdb'
module:

`PARAM_BOOLEAN'
The value is a plain boolean. The Guile boolean values, `#t' and
`#f' are the only valid values.

`PARAM_AUTO_BOOLEAN'
The value has three possible states: true, false, and `auto'. In
Guile, true and false are represented using boolean constants, and
`auto' is represented using `#:auto'.

`PARAM_UINTEGER'
The value is an unsigned integer. The value of `#:unlimited'
should be interpreted to mean "unlimited", and the value of `0' is
reserved and should not be used.

`PARAM_ZINTEGER'
The value is an integer.

`PARAM_ZUINTEGER'
The value is an unsigned integer.

`PARAM_ZUINTEGER_UNLIMITED'
The value is an integer in the range `[0, INT_MAX]'. The value of
`#:unlimited' means "unlimited", the value of `-1' is reserved and
should not be used, and other negative numbers are not allowed.

`PARAM_STRING'
The value is a string. When the user modifies the string, any
escape sequences, such as `\t', `\f', and octal escapes, are
translated into corresponding characters and encoded into the
current host charset.

`PARAM_STRING_NOESCAPE'
The value is a string. When the user modifies the string, escapes
are passed through untranslated.

`PARAM_OPTIONAL_FILENAME'
The value is a either a filename (a string), or `#f'.

`PARAM_FILENAME'
The value is a filename. This is just like
`PARAM_STRING_NOESCAPE', but uses file names for completion.

`PARAM_ENUM'
The value is a string, which must be one of a collection of string
constants provided when the parameter is created.

---------- Footnotes ----------

(1) Note that GDB parameters must not be confused with Guile’s
parameter objects (*note Parameters: (guile)Parameters.).

File: gdb.info, Node: Progspaces In Guile, Next: Objfiles In Guile, Prev: Parameters In Guile, Up: Guile API

23.4.3.13 Program Spaces In Guile
................................

A program space, or "progspace", represents a symbolic view of an
address space. It consists of all of the objfiles of the program.
*Note Objfiles In Guile::. *Note program spaces: Inferiors Connections
and Programs, for more details about program spaces.

Each progspace is represented by an instance of the `<gdb:progspace>'
smob. *Note GDB Scheme Data Types::.

The following progspace-related functions are available in the
`(gdb)' module:

-- Scheme Procedure: progspace? object
Return `#t' if OBJECT is a `<gdb:progspace>' object. Otherwise
return `#f'.

-- Scheme Procedure: progspace-valid? progspace
Return `#t' if PROGSPACE is valid, `#f' if not. A
`<gdb:progspace>' object can become invalid if the program it
refers to is not loaded in GDB any longer.

-- Scheme Procedure: current-progspace
This function returns the program space of the currently selected
inferior. There is always a current progspace, this never returns
`#f'. *Note Inferiors Connections and Programs::.

-- Scheme Procedure: progspaces
Return a list of all the progspaces currently known to GDB.

-- Scheme Procedure: progspace-filename progspace
Return the absolute file name of PROGSPACE as a string. This is
the name of the file passed as the argument to the `file' or
`symbol-file' commands. If the program space does not have an
associated file name, then `#f' is returned. This occurs, for
example, when GDB is started without a program to debug.

A `gdb:invalid-object-error' exception is thrown if PROGSPACE is
invalid.

-- Scheme Procedure: progspace-objfiles progspace
Return the list of objfiles of PROGSPACE. The order of objfiles
in the result is arbitrary. Each element is an object of type
`<gdb:objfile>'. *Note Objfiles In Guile::.

A `gdb:invalid-object-error' exception is thrown if PROGSPACE is
invalid.

-- Scheme Procedure: progspace-pretty-printers progspace
Return the list of pretty-printers of PROGSPACE. Each element is
an object of type `<gdb:pretty-printer>'. *Note Guile Pretty
Printing API::, for more information.

-- Scheme Procedure: set-progspace-pretty-printers! progspace
printer-list
Set the list of registered `<gdb:pretty-printer>' objects for
PROGSPACE to PRINTER-LIST. *Note Guile Pretty Printing API::, for
more information.

File: gdb.info, Node: Objfiles In Guile, Next: Frames In Guile, Prev: Progspaces In Guile, Up: Guile API

23.4.3.14 Objfiles In Guile
..........................

GDB loads symbols for an inferior from various symbol-containing files
(*note Files::). These include the primary executable file, any shared
libraries used by the inferior, and any separate debug info files
(*note Separate Debug Files::). GDB calls these symbol-containing
files "objfiles".

Each objfile is represented as an object of type `<gdb:objfile>'.

The following objfile-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: objfile? object
Return `#t' if OBJECT is a `<gdb:objfile>' object. Otherwise
return `#f'.

-- Scheme Procedure: objfile-valid? objfile
Return `#t' if OBJFILE is valid, `#f' if not. A `<gdb:objfile>'
object can become invalid if the object file it refers to is not
loaded in GDB any longer. All other `<gdb:objfile>' procedures
will throw an exception if it is invalid at the time the procedure
is called.

-- Scheme Procedure: objfile-filename objfile
Return the file name of OBJFILE as a string, with symbolic links
resolved.

-- Scheme Procedure: objfile-progspace objfile
Return the `<gdb:progspace>' that this object file lives in.
*Note Progspaces In Guile::, for more on progspaces.

-- Scheme Procedure: objfile-pretty-printers objfile
Return the list of registered `<gdb:pretty-printer>' objects for
OBJFILE. *Note Guile Pretty Printing API::, for more information.

-- Scheme Procedure: set-objfile-pretty-printers! objfile printer-list
Set the list of registered `<gdb:pretty-printer>' objects for
OBJFILE to PRINTER-LIST. The PRINTER-LIST must be a list of
`<gdb:pretty-printer>' objects. *Note Guile Pretty Printing
API::, for more information.

-- Scheme Procedure: current-objfile
When auto-loading a Guile script (*note Guile Auto-loading::), GDB
sets the "current objfile" to the corresponding objfile. This
function returns the current objfile. If there is no current
objfile, this function returns `#f'.

-- Scheme Procedure: objfiles
Return a list of all the objfiles in the current program space.

File: gdb.info, Node: Frames In Guile, Next: Blocks In Guile, Prev: Objfiles In Guile, Up: Guile API

23.4.3.15 Accessing inferior stack frames from Guile.
....................................................

When the debugged program stops, GDB is able to analyze its call stack
(*note Stack frames: Frames.). The `<gdb:frame>' class represents a
frame in the stack. A `<gdb:frame>' object is only valid while its
corresponding frame exists in the inferior's stack. If you try to use
an invalid frame object, GDB will throw a `gdb:invalid-object'
exception (*note Guile Exception Handling::).

Two `<gdb:frame>' objects can be compared for equality with the
`equal?' function, like:

(gdb) guile (equal? (newest-frame) (selected-frame))
#t

The following frame-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: frame? object
Return `#t' if OBJECT is a `<gdb:frame>' object. Otherwise return
`#f'.

-- Scheme Procedure: frame-valid? frame
Returns `#t' if FRAME is valid, `#f' if not. A frame object can
become invalid if the frame it refers to doesn't exist anymore in
the inferior. All `<gdb:frame>' procedures will throw an
exception if the frame is invalid at the time the procedure is
called.

-- Scheme Procedure: frame-name frame
Return the function name of FRAME, or `#f' if it can't be obtained.

-- Scheme Procedure: frame-arch frame
Return the `<gdb:architecture>' object corresponding to FRAME's
architecture. *Note Architectures In Guile::.

-- Scheme Procedure: frame-type frame
Return the type of FRAME. The value can be one of:

`NORMAL_FRAME'
An ordinary stack frame.

`DUMMY_FRAME'
A fake stack frame that was created by GDB when performing an
inferior function call.

`INLINE_FRAME'
A frame representing an inlined function. The function was
inlined into a `NORMAL_FRAME' that is older than this one.

`TAILCALL_FRAME'
A frame representing a tail call. *Note Tail Call Frames::.

`SIGTRAMP_FRAME'
A signal trampoline frame. This is the frame created by the
OS when it calls into a signal handler.

`ARCH_FRAME'
A fake stack frame representing a cross-architecture call.

`SENTINEL_FRAME'
This is like `NORMAL_FRAME', but it is only used for the
newest frame.

-- Scheme Procedure: frame-unwind-stop-reason frame
Return an integer representing the reason why it's not possible to
find more frames toward the outermost frame. Use
`unwind-stop-reason-string' to convert the value returned by this
function to a string. The value can be one of:

`FRAME_UNWIND_NO_REASON'
No particular reason (older frames should be available).

`FRAME_UNWIND_NULL_ID'
The previous frame's analyzer returns an invalid result.

`FRAME_UNWIND_OUTERMOST'
This frame is the outermost.

`FRAME_UNWIND_UNAVAILABLE'
Cannot unwind further, because that would require knowing the
values of registers or memory that have not been collected.

`FRAME_UNWIND_INNER_ID'
This frame ID looks like it ought to belong to a NEXT frame,
but we got it for a PREV frame. Normally, this is a sign of
unwinder failure. It could also indicate stack corruption.

`FRAME_UNWIND_SAME_ID'
This frame has the same ID as the previous one. That means
that unwinding further would almost certainly give us another
frame with exactly the same ID, so break the chain. Normally,
this is a sign of unwinder failure. It could also indicate
stack corruption.

`FRAME_UNWIND_NO_SAVED_PC'
The frame unwinder did not find any saved PC, but we needed
one to unwind further.

`FRAME_UNWIND_MEMORY_ERROR'
The frame unwinder caused an error while trying to access
memory.

`FRAME_UNWIND_FIRST_ERROR'
Any stop reason greater or equal to this value indicates some
kind of error. This special value facilitates writing code
that tests for errors in unwinding in a way that will work
correctly even if the list of the other values is modified in
future GDB versions. Using it, you could write:

(define reason (frame-unwind-stop-readon (selected-frame)))
(define reason-str (unwind-stop-reason-string reason))
(if (>= reason FRAME_UNWIND_FIRST_ERROR)
(format #t "An error occurred: ~s\n" reason-str))

-- Scheme Procedure: frame-pc frame
Return the frame's resume address.

-- Scheme Procedure: frame-block frame
Return the frame's code block as a `<gdb:block>' object. *Note
Blocks In Guile::.

-- Scheme Procedure: frame-function frame
Return the symbol for the function corresponding to this frame as
a `<gdb:symbol>' object, or `#f' if there isn't one. *Note
Symbols In Guile::.

-- Scheme Procedure: frame-older frame
Return the frame that called FRAME.

-- Scheme Procedure: frame-newer frame
Return the frame called by FRAME.

-- Scheme Procedure: frame-sal frame
Return the frame's `<gdb:sal>' (symtab and line) object. *Note
Symbol Tables In Guile::.

-- Scheme Procedure: frame-read-register frame register
Return the value of REGISTER in FRAME. REGISTER should be a
string, like `pc'.

-- Scheme Procedure: frame-read-var frame variable [#:block block]
Return the value of VARIABLE in FRAME. If the optional argument
BLOCK is provided, search for the variable from that block;
otherwise start at the frame's current block (which is determined
by the frame's current program counter). The VARIABLE must be
given as a string or a `<gdb:symbol>' object, and BLOCK must be a
`<gdb:block>' object.

-- Scheme Procedure: frame-select frame
Set FRAME to be the selected frame. *Note Examining the Stack:
Stack.

-- Scheme Procedure: selected-frame
Return the selected frame object. *Note Selecting a Frame:
Selection.

-- Scheme Procedure: newest-frame
Return the newest frame object for the selected thread.

-- Scheme Procedure: unwind-stop-reason-string reason
Return a string explaining the reason why GDB stopped unwinding
frames, as expressed by the given REASON code (an integer, see the
`frame-unwind-stop-reason' procedure above in this section).

File: gdb.info, Node: Blocks In Guile, Next: Symbols In Guile, Prev: Frames In Guile, Up: Guile API

23.4.3.16 Accessing blocks from Guile.
.....................................

In GDB, symbols are stored in blocks. A block corresponds roughly to a
scope in the source code. Blocks are organized hierarchically, and are
represented individually in Guile as an object of type `<gdb:block>'.
Blocks rely on debugging information being available.

A frame has a block. Please see *Note Frames In Guile::, for a more
in-depth discussion of frames.

The outermost block is known as the "global block". The global
block typically holds public global variables and functions.

The block nested just inside the global block is the "static block".
The static block typically holds file-scoped variables and functions.

GDB provides a method to get a block's superblock, but there is
currently no way to examine the sub-blocks of a block, or to iterate
over all the blocks in a symbol table (*note Symbol Tables In Guile::).

Here is a short example that should help explain blocks:

/* This is in the global block. */
int global;

/* This is in the static block. */
static int file_scope;

/* 'function' is in the global block, and 'argument' is
in a block nested inside of 'function'. */
int function (int argument)
{
/* 'local' is in a block inside 'function'. It may or may
not be in the same block as 'argument'. */
int local;

{
/* 'inner' is in a block whose superblock is the one holding
'local'. */
int inner;

/* If this call is expanded by the compiler, you may see
a nested block here whose function is 'inline_function'
and whose superblock is the one holding 'inner'. */
inline_function ();
}
}

The following block-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: block? object
Return `#t' if OBJECT is a `<gdb:block>' object. Otherwise return
`#f'.

-- Scheme Procedure: block-valid? block
Returns `#t' if `<gdb:block>' BLOCK is valid, `#f' if not. A
block object can become invalid if the block it refers to doesn't
exist anymore in the inferior. All other `<gdb:block>' methods
will throw an exception if it is invalid at the time the procedure
is called. The block's validity is also checked during iteration
over symbols of the block.

-- Scheme Procedure: block-start block
Return the start address of `<gdb:block>' BLOCK.

-- Scheme Procedure: block-end block
Return the end address of `<gdb:block>' BLOCK.

-- Scheme Procedure: block-function block
Return the name of `<gdb:block>' BLOCK represented as a
`<gdb:symbol>' object. If the block is not named, then `#f' is
returned.

For ordinary function blocks, the superblock is the static block.
However, you should note that it is possible for a function block
to have a superblock that is not the static block - for instance
this happens for an inlined function.

-- Scheme Procedure: block-superblock block
Return the block containing `<gdb:block>' BLOCK. If the parent
block does not exist, then `#f' is returned.

-- Scheme Procedure: block-global-block block
Return the global block associated with `<gdb:block>' BLOCK.

-- Scheme Procedure: block-static-block block
Return the static block associated with `<gdb:block>' BLOCK.

-- Scheme Procedure: block-global? block
Return `#t' if `<gdb:block>' BLOCK is a global block. Otherwise
return `#f'.

-- Scheme Procedure: block-static? block
Return `#t' if `<gdb:block>' BLOCK is a static block. Otherwise
return `#f'.

-- Scheme Procedure: block-symbols
Return a list of all symbols (as <gdb:symbol> objects) in
`<gdb:block>' BLOCK.

-- Scheme Procedure: make-block-symbols-iterator block
Return an object of type `<gdb:iterator>' that will iterate over
all symbols of the block. Guile programs should not assume that a
specific block object will always contain a given symbol, since
changes in GDB features and infrastructure may cause symbols move
across blocks in a symbol table. *Note Iterators In Guile::.

-- Scheme Procedure: block-symbols-progress?
Return #t if the object is a <gdb:block-symbols-progress> object.
This object would be obtained from the `progress' element of the
`<gdb:iterator>' object returned by `make-block-symbols-iterator'.

-- Scheme Procedure: lookup-block pc
Return the innermost `<gdb:block>' containing the given PC value.
If the block cannot be found for the PC value specified, the
function will return `#f'.

File: gdb.info, Node: Symbols In Guile, Next: Symbol Tables In Guile, Prev: Blocks In Guile, Up: Guile API

23.4.3.17 Guile representation of Symbols.
.........................................

GDB represents every variable, function and type as an entry in a
symbol table. *Note Examining the Symbol Table: Symbols. Guile
represents these symbols in GDB with the `<gdb:symbol>' object.

The following symbol-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: symbol? object
Return `#t' if OBJECT is an object of type `<gdb:symbol>'.
Otherwise return `#f'.

-- Scheme Procedure: symbol-valid? symbol
Return `#t' if the `<gdb:symbol>' object is valid, `#f' if not. A
`<gdb:symbol>' object can become invalid if the symbol it refers
to does not exist in GDB any longer. All other `<gdb:symbol>'
procedures will throw an exception if it is invalid at the time
the procedure is called.

-- Scheme Procedure: symbol-type symbol
Return the type of SYMBOL or `#f' if no type is recorded. The
result is an object of type `<gdb:type>'. *Note Types In Guile::.

-- Scheme Procedure: symbol-symtab symbol
Return the symbol table in which SYMBOL appears. The result is an
object of type `<gdb:symtab>'. *Note Symbol Tables In Guile::.

-- Scheme Procedure: symbol-line symbol
Return the line number in the source code at which SYMBOL was
defined. This is an integer.

-- Scheme Procedure: symbol-name symbol
Return the name of SYMBOL as a string.

-- Scheme Procedure: symbol-linkage-name symbol
Return the name of SYMBOL, as used by the linker (i.e., may be
mangled).

-- Scheme Procedure: symbol-print-name symbol
Return the name of SYMBOL in a form suitable for output. This is
either `name' or `linkage_name', depending on whether the user
asked GDB to display demangled or mangled names.

-- Scheme Procedure: symbol-addr-class symbol
Return the address class of the symbol. This classifies how to
find the value of a symbol. Each address class is a constant
defined in the `(gdb)' module and described later in this chapter.

-- Scheme Procedure: symbol-needs-frame? symbol
Return `#t' if evaluating SYMBOL's value requires a frame (*note
Frames In Guile::) and `#f' otherwise. Typically, local variables
will require a frame, but other symbols will not.

-- Scheme Procedure: symbol-argument? symbol
Return `#t' if SYMBOL is an argument of a function. Otherwise
return `#f'.

-- Scheme Procedure: symbol-constant? symbol
Return `#t' if SYMBOL is a constant. Otherwise return `#f'.

-- Scheme Procedure: symbol-function? symbol
Return `#t' if SYMBOL is a function or a method. Otherwise return
`#f'.

-- Scheme Procedure: symbol-variable? symbol
Return `#t' if SYMBOL is a variable. Otherwise return `#f'.

-- Scheme Procedure: symbol-value symbol [#:frame frame]
Compute the value of SYMBOL, as a `<gdb:value>'. For functions,
this computes the address of the function, cast to the appropriate
type. If the symbol requires a frame in order to compute its
value, then FRAME must be given. If FRAME is not given, or if
FRAME is invalid, then an exception is thrown.

-- Scheme Procedure: lookup-symbol name [#:block block]
[#:domain domain]
This function searches for a symbol by name. The search scope can
be restricted to the parameters defined in the optional domain and
block arguments.

NAME is the name of the symbol. It must be a string. The
optional BLOCK argument restricts the search to symbols visible in
that BLOCK. The BLOCK argument must be a `<gdb:block>' object.
If omitted, the block for the current frame is used. The optional
DOMAIN argument restricts the search to the domain type. The
DOMAIN argument must be a domain constant defined in the `(gdb)'
module and described later in this chapter.

The result is a list of two elements. The first element is a
`<gdb:symbol>' object or `#f' if the symbol is not found. If the
symbol is found, the second element is `#t' if the symbol is a
field of a method's object (e.g., `this' in C++), otherwise it is
`#f'. If the symbol is not found, the second element is `#f'.

-- Scheme Procedure: lookup-global-symbol name [#:domain domain]
This function searches for a global symbol by name. The search
scope can be restricted by the domain argument.

NAME is the name of the symbol. It must be a string. The
optional DOMAIN argument restricts the search to the domain type.
The DOMAIN argument must be a domain constant defined in the
`(gdb)' module and described later in this chapter.

The result is a `<gdb:symbol>' object or `#f' if the symbol is not
found.

The available domain categories in `<gdb:symbol>' are represented as
constants in the `(gdb)' module:

`SYMBOL_UNDEF_DOMAIN'
This is used when a domain has not been discovered or none of the
following domains apply. This usually indicates an error either
in the symbol information or in GDB's handling of symbols.

`SYMBOL_VAR_DOMAIN'
This domain contains variables, function names, typedef names and
enum type values.

`SYMBOL_FUNCTION_DOMAIN'
This domain contains functions.

`SYMBOL_TYPE_DOMAIN'
This domain contains types. In a C-like language, types using a
tag (the name appearing after a `struct', `union', or `enum'
keyword) will not appear here; in other languages, all types are
in this domain.

`SYMBOL_STRUCT_DOMAIN'
This domain holds struct, union and enum tag names. This domain is
only used for C-like languages. For example, in this code:
struct type_one { int x; };
typedef struct type_one type_two;
Here `type_one' will be in `SYMBOL_STRUCT_DOMAIN', but `type_two'
will be in `SYMBOL_TYPE_DOMAIN'.

`SYMBOL_LABEL_DOMAIN'
This domain contains names of labels (for gotos).

`SYMBOL_VARIABLES_DOMAIN'
This domain holds a subset of the `SYMBOLS_VAR_DOMAIN'; it
contains everything minus functions and types.

`SYMBOL_FUNCTIONS_DOMAIN'
This domain contains all functions.

`SYMBOL_TYPES_DOMAIN'
This domain contains all types.

The available address class categories in `<gdb:symbol>' are
represented as constants in the `gdb' module:

When searching for a symbol, the desired domain constant can be
passed verbatim to the lookup function.

For more complex searches, there is a corresponding set of constants,
each named after one of the preceding constants, but with the `SEARCH'
prefix replacing the `SYMBOL' prefix; for example,
`SEARCH_LABEL_DOMAIN'. These may be or'd together to form a search
constant.

`SYMBOL_LOC_UNDEF'
If this is returned by address class, it indicates an error either
in the symbol information or in GDB's handling of symbols.

`SYMBOL_LOC_CONST'
Value is constant int.

`SYMBOL_LOC_STATIC'
Value is at a fixed address.

`SYMBOL_LOC_REGISTER'
Value is in a register.

`SYMBOL_LOC_ARG'
Value is an argument. This value is at the offset stored within
the symbol inside the frame's argument list.

`SYMBOL_LOC_REF_ARG'
Value address is stored in the frame's argument list. Just like
`LOC_ARG' except that the value's address is stored at the offset,
not the value itself.

`SYMBOL_LOC_REGPARM_ADDR'
Value is a specified register. Just like `LOC_REGISTER' except
the register holds the address of the argument instead of the
argument itself.

`SYMBOL_LOC_LOCAL'
Value is a local variable.

`SYMBOL_LOC_TYPEDEF'
Value not used. Symbols in the domain `SYMBOL_STRUCT_DOMAIN' all
have this class.

`SYMBOL_LOC_BLOCK'
Value is a block.

`SYMBOL_LOC_CONST_BYTES'
Value is a byte-sequence.

`SYMBOL_LOC_UNRESOLVED'
Value is at a fixed address, but the address of the variable has
to be determined from the minimal symbol table whenever the
variable is referenced.

`SYMBOL_LOC_OPTIMIZED_OUT'
The value does not actually exist in the program.

`SYMBOL_LOC_COMPUTED'
The value's address is a computed location.

File: gdb.info, Node: Symbol Tables In Guile, Next: Breakpoints In Guile, Prev: Symbols In Guile, Up: Guile API

23.4.3.18 Symbol table representation in Guile.
..............................................

Access to symbol table data maintained by GDB on the inferior is
exposed to Guile via two objects: `<gdb:sal>' (symtab-and-line) and
`<gdb:symtab>'. Symbol table and line data for a frame is returned
from the `frame-find-sal' `<gdb:frame>' procedure. *Note Frames In
Guile::.

For more information on GDB's symbol table management, see *Note
Examining the Symbol Table: Symbols.

The following symtab-related procedures are provided by the `(gdb)'
module:

-- Scheme Procedure: symtab? object
Return `#t' if OBJECT is an object of type `<gdb:symtab>'.
Otherwise return `#f'.

-- Scheme Procedure: symtab-valid? symtab
Return `#t' if the `<gdb:symtab>' object is valid, `#f' if not. A
`<gdb:symtab>' object becomes invalid when the symbol table it
refers to no longer exists in GDB. All other `<gdb:symtab>'
procedures will throw an exception if it is invalid at the time
the procedure is called.

-- Scheme Procedure: symtab-filename symtab
Return the symbol table's source filename.

-- Scheme Procedure: symtab-fullname symtab
Return the symbol table's source absolute file name.

-- Scheme Procedure: symtab-objfile symtab
Return the symbol table's backing object file. *Note Objfiles In
Guile::.

-- Scheme Procedure: symtab-global-block symtab
Return the global block of the underlying symbol table. *Note
Blocks In Guile::.

-- Scheme Procedure: symtab-static-block symtab
Return the static block of the underlying symbol table. *Note
Blocks In Guile::.

The following symtab-and-line-related procedures are provided by the
`(gdb)' module:

-- Scheme Procedure: sal? object
Return `#t' if OBJECT is an object of type `<gdb:sal>'. Otherwise
return `#f'.

-- Scheme Procedure: sal-valid? sal
Return `#t' if SAL is valid, `#f' if not. A `<gdb:sal>' object
becomes invalid when the Symbol table object it refers to no
longer exists in GDB. All other `<gdb:sal>' procedures will throw
an exception if it is invalid at the time the procedure is called.

-- Scheme Procedure: sal-symtab sal
Return the symbol table object (`<gdb:symtab>') for SAL.

-- Scheme Procedure: sal-line sal
Return the line number for SAL.

-- Scheme Procedure: sal-pc sal
Return the start of the address range occupied by code for SAL.

-- Scheme Procedure: sal-last sal
Return the end of the address range occupied by code for SAL.

-- Scheme Procedure: find-pc-line pc
Return the `<gdb:sal>' object corresponding to the PC value. If
an invalid value of PC is passed as an argument, then the `symtab'
and `line' attributes of the returned `<gdb:sal>' object will be
`#f' and 0 respectively.

File: gdb.info, Node: Breakpoints In Guile, Next: Lazy Strings In Guile, Prev: Symbol Tables In Guile, Up: Guile API

23.4.3.19 Manipulating breakpoints using Guile
.............................................

Breakpoints in Guile are represented by objects of type
`<gdb:breakpoint>'. New breakpoints can be created with the
`make-breakpoint' Guile function, and then added to GDB with the
`register-breakpoint!' Guile function. This two-step approach is taken
to separate out the side-effect of adding the breakpoint to GDB from
`make-breakpoint'.

Support is also provided to view and manipulate breakpoints created
outside of Guile.

The following breakpoint-related procedures are provided by the
`(gdb)' module:

-- Scheme Procedure: make-breakpoint location [#:type type]
[#:wp-class wp-class] [#:internal internal]
[#:temporary temporary]
Create a new breakpoint at LOCATION, a string naming the location
of the breakpoint, or an expression that defines a watchpoint.
The contents can be any location recognized by the `break' command,
or in the case of a watchpoint, by the `watch' command.

The breakpoint is initially marked as `invalid'. The breakpoint
is not usable until it has been registered with GDB with
`register-breakpoint!', at which point it becomes `valid'. The
result is the `<gdb:breakpoint>' object representing the
breakpoint.

The optional TYPE denotes the breakpoint to create. This argument
can be either `BP_BREAKPOINT' or `BP_WATCHPOINT', and defaults to
`BP_BREAKPOINT'.

The optional WP-CLASS argument defines the class of watchpoint to
create, if TYPE is `BP_WATCHPOINT'. If a watchpoint class is not
provided, it is assumed to be a `WP_WRITE' class.

The optional INTERNAL argument allows the breakpoint to become
invisible to the user. The breakpoint will neither be reported
when registered, nor will it be listed in the output from `info
breakpoints' (but will be listed with the `maint info breakpoints'
command). If an internal flag is not provided, the breakpoint is
visible (non-internal).

The optional TEMPORARY argument makes the breakpoint a temporary
breakpoint. Temporary breakpoints are deleted after they have
been hit, after which the Guile breakpoint is no longer usable
(although it may be re-registered with `register-breakpoint!').

When a watchpoint is created, GDB will try to create a hardware
assisted watchpoint. If successful, the type of the watchpoint is
changed from `BP_WATCHPOINT' to `BP_HARDWARE_WATCHPOINT' for
`WP_WRITE', `BP_READ_WATCHPOINT' for `WP_READ', and
`BP_ACCESS_WATCHPOINT' for `WP_ACCESS'. If not successful, the
type of the watchpoint is left as `WP_WATCHPOINT'.

The available types are represented by constants defined in the
`gdb' module:

`BP_BREAKPOINT'
Normal code breakpoint.

`BP_WATCHPOINT'
Watchpoint breakpoint.

`BP_HARDWARE_WATCHPOINT'
Hardware assisted watchpoint. This value cannot be specified
when creating the breakpoint.

`BP_READ_WATCHPOINT'
Hardware assisted read watchpoint. This value cannot be
specified when creating the breakpoint.

`BP_ACCESS_WATCHPOINT'
Hardware assisted access watchpoint. This value cannot be
specified when creating the breakpoint.

`BP_CATCHPOINT'
Catchpoint. This value cannot be specified when creating the
breakpoint.

The available watchpoint types are represented by constants
defined in the `(gdb)' module:

`WP_READ'
Read only watchpoint.

`WP_WRITE'
Write only watchpoint.

`WP_ACCESS'
Read/Write watchpoint.

-- Scheme Procedure: register-breakpoint! breakpoint
Add BREAKPOINT, a `<gdb:breakpoint>' object, to GDB's list of
breakpoints. The breakpoint must have been created with
`make-breakpoint'. One cannot register breakpoints that have been
created outside of Guile. Once a breakpoint is registered it
becomes `valid'. It is an error to register an already registered
breakpoint. The result is unspecified.

-- Scheme Procedure: delete-breakpoint! breakpoint
Remove BREAKPOINT from GDB's list of breakpoints. This also
invalidates the Guile BREAKPOINT object. Any further attempt to
access the object will throw an exception.

If BREAKPOINT was created from Guile with `make-breakpoint' it may
be re-registered with GDB, in which case the breakpoint becomes
valid again.

-- Scheme Procedure: breakpoints
Return a list of all breakpoints. Each element of the list is a
`<gdb:breakpoint>' object.

-- Scheme Procedure: breakpoint? object
Return `#t' if OBJECT is a `<gdb:breakpoint>' object, and `#f'
otherwise.

-- Scheme Procedure: breakpoint-valid? breakpoint
Return `#t' if BREAKPOINT is valid, `#f' otherwise. Breakpoints
created with `make-breakpoint' are marked as invalid until they
are registered with GDB with `register-breakpoint!'. A
`<gdb:breakpoint>' object can become invalid if the user deletes
the breakpoint. In this case, the object still exists, but the
underlying breakpoint does not. In the cases of watchpoint scope,
the watchpoint remains valid even if execution of the inferior
leaves the scope of that watchpoint.

-- Scheme Procedure: breakpoint-number breakpoint
Return the breakpoint's number -- the identifier used by the user
to manipulate the breakpoint.

-- Scheme Procedure: breakpoint-temporary? breakpoint
Return `#t' if the breakpoint was created as a temporary
breakpoint. Temporary breakpoints are automatically deleted after
they've been hit. Calling this procedure, and all other procedures
other than `breakpoint-valid?' and `register-breakpoint!', will
result in an error after the breakpoint has been hit (since it has
been automatically deleted).

-- Scheme Procedure: breakpoint-type breakpoint
Return the breakpoint's type -- the identifier used to determine
the actual breakpoint type or use-case.

-- Scheme Procedure: breakpoint-visible? breakpoint
Return `#t' if the breakpoint is visible to the user when hit, or
when the `info breakpoints' command is run. Otherwise return `#f'.

-- Scheme Procedure: breakpoint-location breakpoint
Return the location of the breakpoint, as specified by the user.
It is a string. If the breakpoint does not have a location (that
is, it is a watchpoint) return `#f'.

-- Scheme Procedure: breakpoint-expression breakpoint
Return the breakpoint expression, as specified by the user. It is
a string. If the breakpoint does not have an expression (the
breakpoint is not a watchpoint) return `#f'.

-- Scheme Procedure: breakpoint-enabled? breakpoint
Return `#t' if the breakpoint is enabled, and `#f' otherwise.

-- Scheme Procedure: set-breakpoint-enabled! breakpoint flag
Set the enabled state of BREAKPOINT to FLAG. If flag is `#f' it
is disabled, otherwise it is enabled.

-- Scheme Procedure: breakpoint-silent? breakpoint
Return `#t' if the breakpoint is silent, and `#f' otherwise.

Note that a breakpoint can also be silent if it has commands and
the first command is `silent'. This is not reported by the
`silent' attribute.

-- Scheme Procedure: set-breakpoint-silent! breakpoint flag
Set the silent state of BREAKPOINT to FLAG. If flag is `#f' the
breakpoint is made silent, otherwise it is made non-silent (or
noisy).

-- Scheme Procedure: breakpoint-ignore-count breakpoint
Return the ignore count for BREAKPOINT.

-- Scheme Procedure: set-breakpoint-ignore-count! breakpoint count
Set the ignore count for BREAKPOINT to COUNT.

-- Scheme Procedure: breakpoint-hit-count breakpoint
Return hit count of BREAKPOINT.

-- Scheme Procedure: set-breakpoint-hit-count! breakpoint count
Set the hit count of BREAKPOINT to COUNT. At present, COUNT must
be zero.

-- Scheme Procedure: breakpoint-thread breakpoint
Return the global-thread-id for thread-specific breakpoint
BREAKPOINT. Return #f if BREAKPOINT is not thread-specific.

-- Scheme Procedure: set-breakpoint-thread! breakpoint
global-thread-id|#f
Set the thread-id for BREAKPOINT to GLOBAL-THREAD-ID If set to
`#f', the breakpoint is no longer thread-specific.

-- Scheme Procedure: breakpoint-task breakpoint
If the breakpoint is Ada task-specific, return the Ada task id.
If the breakpoint is not task-specific (or the underlying language
is not Ada), return `#f'.

-- Scheme Procedure: set-breakpoint-task! breakpoint task
Set the Ada task of BREAKPOINT to TASK. If set to `#f', the
breakpoint is no longer task-specific.

-- Scheme Procedure: breakpoint-condition breakpoint
Return the condition of BREAKPOINT, as specified by the user. It
is a string. If there is no condition, return `#f'.

-- Scheme Procedure: set-breakpoint-condition! breakpoint condition
Set the condition of BREAKPOINT to CONDITION, which must be a
string. If set to `#f' then the breakpoint becomes unconditional.

-- Scheme Procedure: breakpoint-stop breakpoint
Return the stop predicate of BREAKPOINT. See
`set-breakpoint-stop!' below in this section.

-- Scheme Procedure: set-breakpoint-stop! breakpoint procedure|#f
Set the stop predicate of BREAKPOINT. The predicate PROCEDURE
takes one argument: the <gdb:breakpoint> object. If this
predicate is set to a procedure then it is invoked whenever the
inferior reaches this breakpoint. If it returns `#t', or any
non-`#f' value, then the inferior is stopped, otherwise the
inferior will continue.

If there are multiple breakpoints at the same location with a
`stop' predicate, each one will be called regardless of the return
status of the previous. This ensures that all `stop' predicates
have a chance to execute at that location. In this scenario if
one of the methods returns `#t' but the others return `#f', the
inferior will still be stopped.

You should not alter the execution state of the inferior (i.e.,
step, next, etc.), alter the current frame context (i.e., change
the current active frame), or alter, add or delete any breakpoint.
As a general rule, you should not alter any data within GDB or
the inferior at this time.

Example `stop' implementation:

(define (my-stop? bkpt)
(let ((int-val (parse-and-eval "foo")))
(value=? int-val 3)))
(define bkpt (make-breakpoint "main.c:42"))
(register-breakpoint! bkpt)
(set-breakpoint-stop! bkpt my-stop?)

-- Scheme Procedure: breakpoint-commands breakpoint
Return the commands attached to BREAKPOINT as a string, or `#f' if
there are none.

File: gdb.info, Node: Lazy Strings In Guile, Next: Architectures In Guile, Prev: Breakpoints In Guile, Up: Guile API

23.4.3.20 Guile representation of lazy strings.
..............................................

A "lazy string" is a string whose contents is not retrieved or encoded
until it is needed.

A `<gdb:lazy-string>' is represented in GDB as an `address' that
points to a region of memory, an `encoding' that will be used to encode
that region of memory, and a `length' to delimit the region of memory
that represents the string. The difference between a
`<gdb:lazy-string>' and a string wrapped within a `<gdb:value>' is that
a `<gdb:lazy-string>' will be treated differently by GDB when printing.
A `<gdb:lazy-string>' is retrieved and encoded during printing, while
a `<gdb:value>' wrapping a string is immediately retrieved and encoded
on creation.

The following lazy-string-related procedures are provided by the
`(gdb)' module:

-- Scheme Procedure: lazy-string? object
Return `#t' if OBJECT is an object of type `<gdb:lazy-string>'.
Otherwise return `#f'.

-- Scheme Procedure: lazy-string-address lazy-sring
Return the address of LAZY-STRING.

-- Scheme Procedure: lazy-string-length lazy-string
Return the length of LAZY-STRING in characters. If the length is
-1, then the string will be fetched and encoded up to the first
null of appropriate width.

-- Scheme Procedure: lazy-string-encoding lazy-string
Return the encoding that will be applied to LAZY-STRING when the
string is printed by GDB. If the encoding is not set, or contains
an empty string, then GDB will select the most appropriate
encoding when the string is printed.

-- Scheme Procedure: lazy-string-type lazy-string
Return the type that is represented by LAZY-STRING's type. For a
lazy string this is a pointer or array type. To resolve this to
the lazy string's character type, use `type-target-type'. *Note
Types In Guile::.

-- Scheme Procedure: lazy-string->value lazy-string
Convert the `<gdb:lazy-string>' to a `<gdb:value>'. This value
will point to the string in memory, but will lose all the delayed
retrieval, encoding and handling that GDB applies to a
`<gdb:lazy-string>'.

File: gdb.info, Node: Architectures In Guile, Next: Disassembly In Guile, Prev: Lazy Strings In Guile, Up: Guile API

23.4.3.21 Guile representation of architectures
..............................................

GDB uses architecture specific parameters and artifacts in a number of
its various computations. An architecture is represented by an
instance of the `<gdb:arch>' class.

The following architecture-related procedures are provided by the
`(gdb)' module:

-- Scheme Procedure: arch? object
Return `#t' if OBJECT is an object of type `<gdb:arch>'.
Otherwise return `#f'.

-- Scheme Procedure: current-arch
Return the current architecture as a `<gdb:arch>' object.

-- Scheme Procedure: arch-name arch
Return the name (string value) of `<gdb:arch>' ARCH.

-- Scheme Procedure: arch-charset arch
Return name of target character set of `<gdb:arch>' ARCH.

-- Scheme Procedure: arch-wide-charset
Return name of target wide character set of `<gdb:arch>' ARCH.

Each architecture provides a set of predefined types, obtained by
the following functions.

-- Scheme Procedure: arch-void-type arch
Return the `<gdb:type>' object for a `void' type of architecture
ARCH.

-- Scheme Procedure: arch-char-type arch
Return the `<gdb:type>' object for a `char' type of architecture
ARCH.

-- Scheme Procedure: arch-short-type arch
Return the `<gdb:type>' object for a `short' type of architecture
ARCH.

-- Scheme Procedure: arch-int-type arch
Return the `<gdb:type>' object for an `int' type of architecture
ARCH.

-- Scheme Procedure: arch-long-type arch
Return the `<gdb:type>' object for a `long' type of architecture
ARCH.

-- Scheme Procedure: arch-schar-type arch
Return the `<gdb:type>' object for a `signed char' type of
architecture ARCH.

-- Scheme Procedure: arch-uchar-type arch
Return the `<gdb:type>' object for an `unsigned char' type of
architecture ARCH.

-- Scheme Procedure: arch-ushort-type arch
Return the `<gdb:type>' object for an `unsigned short' type of
architecture ARCH.

-- Scheme Procedure: arch-uint-type arch
Return the `<gdb:type>' object for an `unsigned int' type of
architecture ARCH.

-- Scheme Procedure: arch-ulong-type arch
Return the `<gdb:type>' object for an `unsigned long' type of
architecture ARCH.

-- Scheme Procedure: arch-float-type arch
Return the `<gdb:type>' object for a `float' type of architecture
ARCH.

-- Scheme Procedure: arch-double-type arch
Return the `<gdb:type>' object for a `double' type of architecture
ARCH.

-- Scheme Procedure: arch-longdouble-type arch
Return the `<gdb:type>' object for a `long double' type of
architecture ARCH.

-- Scheme Procedure: arch-bool-type arch
Return the `<gdb:type>' object for a `bool' type of architecture
ARCH.

-- Scheme Procedure: arch-longlong-type arch
Return the `<gdb:type>' object for a `long long' type of
architecture ARCH.

-- Scheme Procedure: arch-ulonglong-type arch
Return the `<gdb:type>' object for an `unsigned long long' type of
architecture ARCH.

-- Scheme Procedure: arch-int8-type arch
Return the `<gdb:type>' object for an `int8' type of architecture
ARCH.

-- Scheme Procedure: arch-uint8-type arch
Return the `<gdb:type>' object for a `uint8' type of architecture
ARCH.

-- Scheme Procedure: arch-int16-type arch
Return the `<gdb:type>' object for an `int16' type of architecture
ARCH.

-- Scheme Procedure: arch-uint16-type arch
Return the `<gdb:type>' object for a `uint16' type of architecture
ARCH.

-- Scheme Procedure: arch-int32-type arch
Return the `<gdb:type>' object for an `int32' type of architecture
ARCH.

-- Scheme Procedure: arch-uint32-type arch
Return the `<gdb:type>' object for a `uint32' type of architecture
ARCH.

-- Scheme Procedure: arch-int64-type arch
Return the `<gdb:type>' object for an `int64' type of architecture
ARCH.

-- Scheme Procedure: arch-uint64-type arch
Return the `<gdb:type>' object for a `uint64' type of architecture
ARCH.

Example:

(gdb) guile (type-name (arch-uchar-type (current-arch)))
"unsigned char"

File: gdb.info, Node: Disassembly In Guile, Next: I/O Ports in Guile, Prev: Architectures In Guile, Up: Guile API

23.4.3.22 Disassembly In Guile
.............................

The disassembler can be invoked from Scheme code. Furthermore, the
disassembler can take a Guile port as input, allowing one to
disassemble from any source, and not just target memory.

-- Scheme Procedure: arch-disassemble arch start-pc [#:port port]
[#:offset offset] [#:size size] [#:count count]
Return a list of disassembled instructions starting from the memory
address START-PC.

The optional argument PORT specifies the input port to read bytes
from. If PORT is `#f' then bytes are read from target memory.

The optional argument OFFSET specifies the address offset of the
first byte in PORT. This is useful, for example, when PORT
specifies a `bytevector' and you want the bytevector to be
disassembled as if it came from that address. The START-PC passed
to the reader for PORT is offset by the same amount.

Example:
(gdb) guile (use-modules (rnrs io ports))
(gdb) guile (define pc (value->integer (parse-and-eval "$pc")))
(gdb) guile (define mem (open-memory #:start pc))
(gdb) guile (define bv (get-bytevector-n mem 10))
(gdb) guile (define bv-port (open-bytevector-input-port bv))
(gdb) guile (define arch (current-arch))
(gdb) guile (arch-disassemble arch pc #:port bv-port #:offset pc)
(((address . 4195516) (asm . "mov $0x4005c8,%edi") (length . 5)))

The optional arguments SIZE and COUNT determine the number of
instructions in the returned list. If either SIZE or COUNT is
specified as zero, then no instructions are disassembled and an
empty list is returned. If both the optional arguments SIZE and
COUNT are specified, then a list of at most COUNT disassembled
instructions whose start address falls in the closed memory
address interval from START-PC to (START-PC + SIZE - 1) are
returned. If SIZE is not specified, but COUNT is specified, then
COUNT number of instructions starting from the address START-PC
are returned. If COUNT is not specified but SIZE is specified,
then all instructions whose start address falls in the closed
memory address interval from START-PC to (START-PC + SIZE - 1) are
returned. If neither SIZE nor COUNT are specified, then a single
instruction at START-PC is returned.

Each element of the returned list is an alist (associative list)
with the following keys:

`address'
The value corresponding to this key is a Guile integer of the
memory address of the instruction.

`asm'
The value corresponding to this key is a string value which
represents the instruction with assembly language mnemonics.
The assembly language flavor used is the same as that
specified by the current CLI variable `disassembly-flavor'.
*Note Machine Code::.

`length'
The value corresponding to this key is the length of the
instruction in bytes.

File: gdb.info, Node: I/O Ports in Guile, Next: Memory Ports in Guile, Prev: Disassembly In Guile, Up: Guile API

23.4.3.23 I/O Ports in Guile
...........................

-- Scheme Procedure: input-port
Return GDB's input port as a Guile port object.

-- Scheme Procedure: output-port
Return GDB's output port as a Guile port object.

-- Scheme Procedure: error-port
Return GDB's error port as a Guile port object.

-- Scheme Procedure: stdio-port? object
Return `#t' if OBJECT is a GDB stdio port. Otherwise return `#f'.

File: gdb.info, Node: Memory Ports in Guile, Next: Iterators In Guile, Prev: I/O Ports in Guile, Up: Guile API

23.4.3.24 Memory Ports in Guile
..............................

GDB provides a `port' interface to target memory. This allows Guile
code to read/write target memory using Guile's port and bytevector
functionality. The main routine is `open-memory' which returns a port
object. One can then read/write memory using that object.

-- Scheme Procedure: open-memory [#:mode mode] [#:start address]
[#:size size]
Return a port object that can be used for reading and writing
memory. The port will be open according to MODE, which is the
standard mode argument to Guile port open routines, except that
the `"a"' and `"l"' modes are not supported. *Note File Ports:
(guile)File Ports. The `"b"' (binary) character may be present,
but is ignored: memory ports are binary only. If `"0"' is
appended then the port is marked as unbuffered. The default is
`"r"', read-only and buffered.

The chunk of memory that can be accessed can be bounded. If both
START and SIZE are unspecified, all of memory can be accessed. If
only START is specified, all of memory from that point on can be
accessed. If only SIZE if specified, all memory in the range
[0,SIZE) can be accessed. If both are specified, all memory in
the rane [START,START+SIZE) can be accessed.

-- Scheme Procedure: memory-port?
Return `#t' if OBJECT is an object of type `<gdb:memory-port>'.
Otherwise return `#f'.

-- Scheme Procedure: memory-port-range memory-port
Return the range of `<gdb:memory-port>' MEMORY-PORT as a list of
two elements: `(start end)'. The range is START to END inclusive.

-- Scheme Procedure: memory-port-read-buffer-size memory-port
Return the size of the read buffer of `<gdb:memory-port>'
MEMORY-PORT.

This procedure is deprecated and will be removed in GDB 11. It
returns 0 when using Guile 2.2 or later.

-- Scheme Procedure: set-memory-port-read-buffer-size! memory-port size
Set the size of the read buffer of `<gdb:memory-port>' MEMORY-PORT
to SIZE. The result is unspecified.

This procedure is deprecated and will be removed in GDB 11. When
GDB is built with Guile 2.2 or later, you can call `setvbuf'
instead (*note `setvbuf': (guile)Buffering.).

-- Scheme Procedure: memory-port-write-buffer-size memory-port
Return the size of the write buffer of `<gdb:memory-port>'
MEMORY-PORT.

This procedure is deprecated and will be removed in GDB 11. It
returns 0 when GDB is built with Guile 2.2 or later.

-- Scheme Procedure: set-memory-port-write-buffer-size! memory-port
size
Set the size of the write buffer of `<gdb:memory-port>'
MEMORY-PORT to SIZE. The result is unspecified.

This procedure is deprecated and will be removed in GDB 11. When
GDB is built with Guile 2.2 or later, you can call `setvbuf'
instead.

A memory port is closed like any other port, with `close-port'.

Combined with Guile's `bytevectors', memory ports provide a lot of
utility. For example, to fill a buffer of 10 integers in memory, one
can do something like the following.

;; In the program: int buffer[10];
(use-modules (rnrs bytevectors))
(use-modules (rnrs io ports))
(define addr (parse-and-eval "buffer"))
(define n 10)
(define byte-size (* n 4))
(define mem-port (open-memory #:mode "r+" #:start
(value->integer addr) #:size byte-size))
(define byte-vec (make-bytevector byte-size))
(do ((i 0 (+ i 1)))
((>= i n))
(bytevector-s32-native-set! byte-vec (* i 4) (* i 42)))
(put-bytevector mem-port byte-vec)
(close-port mem-port)

File: gdb.info, Node: Iterators In Guile, Prev: Memory Ports in Guile, Up: Guile API

23.4.3.25 Iterators In Guile
...........................

A simple iterator facility is provided to allow, for example, iterating
over the set of program symbols without having to first construct a
list of all of them. A useful contribution would be to add support for
SRFI 41 and SRFI 45.

-- Scheme Procedure: make-iterator object progress next!
A `<gdb:iterator>' object is constructed with the `make-iterator'
procedure. It takes three arguments: the object to be iterated
over, an object to record the progress of the iteration, and a
procedure to return the next element in the iteration, or an
implementation chosen value to denote the end of iteration.

By convention, end of iteration is marked with
`(end-of-iteration)', and may be tested with the
`end-of-iteration?' predicate. The result of `(end-of-iteration)'
is chosen so that it is not otherwise used by the `(gdb)' module.
If you are using `<gdb:iterator>' in your own code it is your
responsibility to maintain this invariant.

A trivial example for illustration's sake:

(use-modules (gdb iterator))
(define my-list (list 1 2 3))
(define iter
(make-iterator my-list my-list
(lambda (iter)
(let ((l (iterator-progress iter)))
(if (eq? l '())
(end-of-iteration)
(begin
(set-iterator-progress! iter (cdr l))
(car l)))))))

Here is a slightly more realistic example, which computes a list
of all the functions in `my-global-block'.

(use-modules (gdb iterator))
(define this-sal (find-pc-line (frame-pc (selected-frame))))
(define this-symtab (sal-symtab this-sal))
(define this-global-block (symtab-global-block this-symtab))
(define syms-iter (make-block-symbols-iterator this-global-block))
(define functions (iterator-filter symbol-function? syms-iter))

-- Scheme Procedure: iterator? object
Return `#t' if OBJECT is a `<gdb:iterator>' object. Otherwise
return `#f'.

-- Scheme Procedure: iterator-object iterator
Return the first argument that was passed to `make-iterator'.
This is the object being iterated over.

-- Scheme Procedure: iterator-progress iterator
Return the object tracking iteration progress.

-- Scheme Procedure: set-iterator-progress! iterator new-value
Set the object tracking iteration progress.

-- Scheme Procedure: iterator-next! iterator
Invoke the procedure that was the third argument to
`make-iterator', passing it one argument, the `<gdb:iterator>'
object. The result is either the next element in the iteration,
or an end marker as implemented by the `next!' procedure. By
convention the end marker is the result of `(end-of-iteration)'.

-- Scheme Procedure: end-of-iteration
Return the Scheme object that denotes end of iteration.

-- Scheme Procedure: end-of-iteration? object
Return `#t' if OBJECT is the end of iteration marker. Otherwise
return `#f'.

These functions are provided by the `(gdb iterator)' module to
assist in using iterators.

-- Scheme Procedure: make-list-iterator list
Return a `<gdb:iterator>' object that will iterate over LIST.

-- Scheme Procedure: iterator->list iterator
Return the elements pointed to by ITERATOR as a list.

-- Scheme Procedure: iterator-map proc iterator
Return the list of objects obtained by applying PROC to the object
pointed to by ITERATOR and to each subsequent object.

-- Scheme Procedure: iterator-for-each proc iterator
Apply PROC to each element pointed to by ITERATOR. The result is
unspecified.

-- Scheme Procedure: iterator-filter pred iterator
Return the list of elements pointed to by ITERATOR that satisfy
PRED.

-- Scheme Procedure: iterator-until pred iterator
Run ITERATOR until the result of `(pred element)' is true and
return that as the result. Otherwise return `#f'.

File: gdb.info, Node: Guile Auto-loading, Next: Guile Modules, Prev: Guile API, Up: Guile

23.4.4 Guile Auto-loading
-------------------------

When a new object file is read (for example, due to the `file' command,
or because the inferior has loaded a shared library), GDB will look for
Guile support scripts in two ways: `OBJFILE-gdb.scm' and the
`.debug_gdb_scripts' section. *Note Auto-loading extensions::.

The auto-loading feature is useful for supplying application-specific
debugging commands and scripts.

Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed.

`set auto-load guile-scripts [on|off]'
Enable or disable the auto-loading of Guile scripts.

`show auto-load guile-scripts'
Show whether auto-loading of Guile scripts is enabled or disabled.

`info auto-load guile-scripts [REGEXP]'
Print the list of all Guile scripts that GDB auto-loaded.

Also printed is the list of Guile scripts that were mentioned in
the `.debug_gdb_scripts' section and were not found. This is
useful because their names are not printed when GDB tries to load
them and fails. There may be many of them, and printing an error
message for each one is problematic.

If REGEXP is supplied only Guile scripts with matching names are
printed.

Example:

(gdb) info auto-load guile-scripts
Loaded Script
Yes scm-section-script.scm
full name: /tmp/scm-section-script.scm
No my-foo-pretty-printers.scm

When reading an auto-loaded file, GDB sets the "current objfile".
This is available via the `current-objfile' procedure (*note Objfiles
In Guile::). This can be useful for registering objfile-specific
pretty-printers.

File: gdb.info, Node: Guile Modules, Prev: Guile Auto-loading, Up: Guile

23.4.5 Guile Modules
--------------------

GDB comes with several modules to assist writing Guile code.

* Menu:

* Guile Printing Module:: Building and registering pretty-printers
* Guile Types Module:: Utilities for working with types

File: gdb.info, Node: Guile Printing Module, Next: Guile Types Module, Up: Guile Modules

23.4.5.1 Guile Printing Module
.............................

This module provides a collection of utilities for working with
pretty-printers.

Usage:

(use-modules (gdb printing))

-- Scheme Procedure: prepend-pretty-printer! object printer
Add PRINTER to the front of the list of pretty-printers for
OBJECT. The OBJECT must either be a `<gdb:objfile>' object, or
`#f' in which case PRINTER is added to the global list of printers.

-- Scheme Procedure: append-pretty-printer! object printer
Add PRINTER to the end of the list of pretty-printers for OBJECT.
The OBJECT must either be a `<gdb:objfile>' object, or `#f' in
which case PRINTER is added to the global list of printers.

File: gdb.info, Node: Guile Types Module, Prev: Guile Printing Module, Up: Guile Modules

23.4.5.2 Guile Types Module
..........................

This module provides a collection of utilities for working with
`<gdb:type>' objects.

Usage:

(use-modules (gdb types))

-- Scheme Procedure: get-basic-type type
Return TYPE with const and volatile qualifiers stripped, and with
typedefs and C++ references converted to the underlying type.

C++ example:

typedef const int const_int;
const_int foo (3);
const_int& foo_ref (foo);
int main () { return 0; }

Then in gdb:

(gdb) start
(gdb) guile (use-modules (gdb) (gdb types))
(gdb) guile (define foo-ref (parse-and-eval "foo_ref"))
(gdb) guile (get-basic-type (value-type foo-ref))
int

-- Scheme Procedure: type-has-field-deep? type field
Return `#t' if TYPE, assumed to be a type with fields (e.g., a
structure or union), has field FIELD. Otherwise return `#f'.
This searches baseclasses, whereas `type-has-field?' does not.

-- Scheme Procedure: make-enum-hashtable enum-type
Return a Guile hash table produced from ENUM-TYPE. Elements in
the hash table are referenced with `hashq-ref'.

File: gdb.info, Node: Auto-loading extensions, Next: Multiple Extension Languages, Prev: Guile, Up: Extending GDB

23.5 Auto-loading extensions
============================

GDB provides two mechanisms for automatically loading extensions when a
new object file is read (for example, due to the `file' command, or
because the inferior has loaded a shared library): `OBJFILE-gdb.EXT'
(*note The `OBJFILE-gdb.EXT' file: objfile-gdbdotext file.) and the
`.debug_gdb_scripts' section of modern file formats like ELF (*note The
`.debug_gdb_scripts' section: dotdebug_gdb_scripts section.). For a
discussion of the differences between these two approaches see *Note
Which flavor to choose?::.

The auto-loading feature is useful for supplying application-specific
debugging commands and features.

Auto-loading can be enabled or disabled, and the list of auto-loaded
scripts can be printed. See the `auto-loading' section of each
extension language for more information. For GDB command files see
*Note Auto-loading sequences::. For Python files see *Note Python
Auto-loading::.

Note that loading of this script file also requires accordingly
configured `auto-load safe-path' (*note Auto-loading safe path::).

* Menu:

* objfile-gdbdotext file:: The `OBJFILE-gdb.EXT' file
* dotdebug_gdb_scripts section:: The `.debug_gdb_scripts' section
* Which flavor to choose?:: Choosing between these approaches

File: gdb.info, Node: objfile-gdbdotext file, Next: dotdebug_gdb_scripts section, Up: Auto-loading extensions

23.5.1 The `OBJFILE-gdb.EXT' file
---------------------------------

When a new object file is read, GDB looks for a file named
`OBJFILE-gdb.EXT' (we call it SCRIPT-NAME below), where OBJFILE is the
object file's name and where EXT is the file extension for the
extension language:

``OBJFILE-gdb.gdb''
GDB's own command language

``OBJFILE-gdb.py''
Python

``OBJFILE-gdb.scm''
Guile

SCRIPT-NAME is formed by ensuring that the file name of OBJFILE is
absolute, following all symlinks, and resolving `.' and `..'
components, and appending the `-gdb.EXT' suffix. If this file exists
and is readable, GDB will evaluate it as a script in the specified
extension language.

If this file does not exist, then GDB will look for SCRIPT-NAME file
in all of the directories as specified below. (On MS-Windows/MS-DOS,
the drive letter of the executable's leading directories is converted
to a one-letter subdirectory, i.e. `d:/usr/bin/' is converted to
`/d/usr/bin/', because Windows filesystems disallow colons in file
names.)

Note that loading of these files requires an accordingly configured
`auto-load safe-path' (*note Auto-loading safe path::).

For object files using `.exe' suffix GDB tries to load first the
scripts normally according to its `.exe' filename. But if no scripts
are found GDB also tries script filenames matching the object file
without its `.exe' suffix. This `.exe' stripping is case insensitive
and it is attempted on any platform. This makes the script filenames
compatible between Unix and MS-Windows hosts.

`set auto-load scripts-directory [DIRECTORIES]'
Control GDB auto-loaded scripts location. Multiple directory
entries may be delimited by the host platform path separator in use
(`:' on Unix, `;' on MS-Windows and MS-DOS).

Each entry here needs to be covered also by the security setting
`set auto-load safe-path' (*note set auto-load safe-path::).

This variable defaults to `$debugdir:$datadir/auto-load'. The
default `set auto-load safe-path' value can be also overridden by
GDB configuration option `--with-auto-load-dir'.

Any reference to `$debugdir' will get replaced by
DEBUG-FILE-DIRECTORY value (*note Separate Debug Files::) and any
reference to `$datadir' will get replaced by DATA-DIRECTORY which
is determined at GDB startup (*note Data Files::). `$debugdir' and
`$datadir' must be placed as a directory component -- either alone
or delimited by `/' or `\' directory separators, depending on the
host platform.

The list of directories uses path separator (`:' on GNU and Unix
systems, `;' on MS-Windows and MS-DOS) to separate directories,
similarly to the `PATH' environment variable.

`show auto-load scripts-directory'
Show GDB auto-loaded scripts location.

`add-auto-load-scripts-directory [DIRECTORIES...]'
Add an entry (or list of entries) to the list of auto-loaded
scripts locations. Multiple entries may be delimited by the host
platform path separator in use.

GDB does not track which files it has already auto-loaded this way.
GDB will load the associated script every time the corresponding
OBJFILE is opened. So your `-gdb.EXT' file should be careful to avoid
errors if it is evaluated more than once.

File: gdb.info, Node: dotdebug_gdb_scripts section, Next: Which flavor to choose?, Prev: objfile-gdbdotext file, Up: Auto-loading extensions

23.5.2 The `.debug_gdb_scripts' section
---------------------------------------

For systems using file formats like ELF and COFF, when GDB loads a new
object file it will look for a special section named
`.debug_gdb_scripts'. If this section exists, its contents is a list
of null-terminated entries specifying scripts to load. Each entry
begins with a non-null prefix byte that specifies the kind of entry,
typically the extension language and whether the script is in a file or
inlined in `.debug_gdb_scripts'.

The following entries are supported:

`SECTION_SCRIPT_ID_PYTHON_FILE = 1'

`SECTION_SCRIPT_ID_SCHEME_FILE = 3'

`SECTION_SCRIPT_ID_PYTHON_TEXT = 4'

`SECTION_SCRIPT_ID_SCHEME_TEXT = 6'

23.5.2.1 Script File Entries
...........................

If the entry specifies a file, GDB will look for the file first in the
current directory and then along the source search path (*note
Specifying Source Directories: Source Path.), except that `$cdir' is
not searched, since the compilation directory is not relevant to
scripts.

File entries can be placed in section `.debug_gdb_scripts' with, for
example, this GCC macro for Python scripts.

/* Note: The "MS" section flags are to remove duplicates. */
#define DEFINE_GDB_PY_SCRIPT(script_name) \
asm("\
.pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\
.byte 1 /* Python */\n\
.asciz \"" script_name "\"\n\
.popsection \n\
");

For Guile scripts, replace `.byte 1' with `.byte 3'. Then one can
reference the macro in a header or source file like this:

DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")

The script name may include directories if desired.

Note that loading of this script file also requires accordingly
configured `auto-load safe-path' (*note Auto-loading safe path::).

If the macro invocation is put in a header, any application or
library using this header will get a reference to the specified script,
and with the use of `"MS"' attributes on the section, the linker will
remove duplicates.

23.5.2.2 Script Text Entries
...........................

Script text entries allow to put the executable script in the entry
itself instead of loading it from a file. The first line of the entry,
everything after the prefix byte and up to the first newline (`0xa')
character, is the script name, and must not contain any kind of space
character, e.g., spaces or tabs. The rest of the entry, up to the
trailing null byte, is the script to execute in the specified language.
The name needs to be unique among all script names, as GDB executes
each script only once based on its name.

Here is an example from file `py-section-script.c' in the GDB
testsuite.

#include "symcat.h"
#include "gdb/section-scripts.h"
asm(
".pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n"
".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n"
".ascii \"gdb.inlined-script\\n\"\n"
".ascii \"class test_cmd (gdb.Command):\\n\"\n"
".ascii \" def __init__ (self):\\n\"\n"
".ascii \" super (test_cmd, self).__init__ ("
"\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n"
".ascii \" def invoke (self, arg, from_tty):\\n\"\n"
".ascii \" print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n"
".ascii \"test_cmd ()\\n\"\n"
".byte 0\n"
".popsection\n"
);

Loading of inlined scripts requires a properly configured `auto-load
safe-path' (*note Auto-loading safe path::). The path to specify in
`auto-load safe-path' is the path of the file containing the
`.debug_gdb_scripts' section.

File: gdb.info, Node: Which flavor to choose?, Prev: dotdebug_gdb_scripts section, Up: Auto-loading extensions

23.5.3 Which flavor to choose?
------------------------------

Given the multiple ways of auto-loading extensions, it might not always
be clear which one to choose. This section provides some guidance.

Benefits of the `-gdb.EXT' way:

* Can be used with file formats that don't support multiple sections.

* Ease of finding scripts for public libraries.

Scripts specified in the `.debug_gdb_scripts' section are searched
for in the source search path. For publicly installed libraries,
e.g., `libstdc++', there typically isn't a source directory in
which to find the script.

* Doesn't require source code additions.

Benefits of the `.debug_gdb_scripts' way:

* Works with static linking.

Scripts for libraries done the `-gdb.EXT' way require an objfile to
trigger their loading. When an application is statically linked
the only objfile available is the executable, and it is cumbersome
to attach all the scripts from all the input libraries to the
executable's `-gdb.EXT' script.

* Works with classes that are entirely inlined.

Some classes can be entirely inlined, and thus there may not be an
associated shared library to attach a `-gdb.EXT' script to.

* Scripts needn't be copied out of the source tree.

In some circumstances, apps can be built out of large collections
of internal libraries, and the build infrastructure necessary to
install the `-gdb.EXT' scripts in a place where GDB can find them
is cumbersome. It may be easier to specify the scripts in the
`.debug_gdb_scripts' section as relative paths, and add a path to
the top of the source tree to the source search path.

File: gdb.info, Node: Multiple Extension Languages, Prev: Auto-loading extensions, Up: Extending GDB

23.6 Multiple Extension Languages
=================================

The Guile and Python extension languages do not share any state, and
generally do not interfere with each other. There are some things to
be aware of, however.

23.6.1 Python comes first
-------------------------

Python was GDB's first extension language, and to avoid breaking
existing behaviour Python comes first. This is generally solved by the
"first one wins" principle. GDB maintains a list of enabled extension
languages, and when it makes a call to an extension language, (say to
pretty-print a value), it tries each in turn until an extension
language indicates it has performed the request (e.g., has returned the
pretty-printed form of a value). This extends to errors while
performing such requests: If an error happens while, for example,
trying to pretty-print an object then the error is reported and any
following extension languages are not tried.

File: gdb.info, Node: Interpreters, Next: TUI, Prev: Extending GDB, Up: Top

24 Command Interpreters
***********************

GDB supports multiple command interpreters, and some command
infrastructure to allow users or user interface writers to switch
between interpreters or run commands in other interpreters.

GDB currently supports two command interpreters, the console
interpreter (sometimes called the command-line interpreter or CLI) and
the machine interface interpreter (or GDB/MI). This manual describes
both of these interfaces in great detail.

By default, GDB will start with the console interpreter. However,
the user may choose to start GDB with another interpreter by specifying
the `-i' or `--interpreter' startup options. Defined interpreters
include:

`console'
The traditional console or command-line interpreter. This is the
most often used interpreter with GDB. With no interpreter
specified at runtime, GDB will use this interpreter.

`dap'
When GDB has been built with Python support, it also supports the
Debugger Adapter Protocol. This protocol can be used by a
debugger GUI or an IDE to communicate with GDB. This protocol is
documented at
`https://microsoft.github.io/debug-adapter-protocol/'. *Note
Debugger Adapter Protocol::, for information about GDB extensions
to the protocol.

`mi'
The newest GDB/MI interface (currently `mi3'). Used primarily by
programs wishing to use GDB as a backend for a debugger GUI or an
IDE. For more information, see *Note The GDB/MI Interface: GDB/MI.

`mi3'
The GDB/MI interface introduced in GDB 9.1.

`mi2'
The GDB/MI interface introduced in GDB 6.0.

You may execute commands in any interpreter from the current
interpreter using the appropriate command. If you are running the
console interpreter, simply use the `interpreter-exec' command:

interpreter-exec mi "-data-list-register-names"

GDB/MI has a similar command, although it is only available in
versions of GDB which support GDB/MI version 2 (or greater).

Note that `interpreter-exec' only changes the interpreter for the
duration of the specified command. It does not change the interpreter
permanently.

Although you may only choose a single interpreter at startup, it is
possible to run an independent interpreter on a specified input/output
device (usually a tty).

For example, consider a debugger GUI or IDE that wants to provide a
GDB console view. It may do so by embedding a terminal emulator widget
in its GUI, starting GDB in the traditional command-line mode with
stdin/stdout/stderr redirected to that terminal, and then creating an
MI interpreter running on a specified input/output device. The console
interpreter created by GDB at startup handles commands the user types
in the terminal widget, while the GUI controls and synchronizes state
with GDB using the separate MI interpreter.

To start a new secondary "user interface" running MI, use the
`new-ui' command:

new-ui INTERPRETER TTY

The INTERPRETER parameter specifies the interpreter to run. This
accepts the same values as the `interpreter-exec' command. For
example, `console', `mi', `mi2', etc. The TTY parameter specifies the
name of the bidirectional file the interpreter uses for input/output,
usually the name of a pseudoterminal slave on Unix systems. For
example:

(gdb) new-ui mi /dev/pts/9

runs an MI interpreter on `/dev/pts/9'.

File: gdb.info, Node: TUI, Next: Emacs, Prev: Interpreters, Up: Top

25 GDB Text User Interface
**************************

The GDB Text User Interface (TUI) is a terminal interface which uses
the `curses' library to show the source file, the assembly output, the
program registers and GDB commands in separate text windows. The TUI
mode is supported only on platforms where a suitable version of the
`curses' library is available.

The TUI mode is enabled by default when you invoke GDB as `gdb -tui'.
You can also switch in and out of TUI mode while GDB runs by using
various TUI commands and key bindings, such as `tui enable' or `C-x
C-a'. *Note TUI Commands: TUI Commands, and *Note TUI Key Bindings:
TUI Keys.

* Menu:

* TUI Overview:: TUI overview
* TUI Keys:: TUI key bindings
* TUI Single Key Mode:: TUI single key mode
* TUI Mouse Support:: TUI mouse support
* TUI Commands:: TUI-specific commands
* TUI Configuration:: TUI configuration variables

File: gdb.info, Node: TUI Overview, Next: TUI Keys, Up: TUI

25.1 TUI Overview
=================

In TUI mode, GDB can display several text windows:

_command_
This window is the GDB command window with the GDB prompt and the
GDB output. The GDB input is still managed using readline.

_source_
The source window shows the source file of the program. The
current line and active breakpoints are displayed in this window.

_assembly_
The assembly window shows the disassembly output of the program.

_register_
This window shows the processor registers. Registers are
highlighted when their values change.

The source and assembly windows show the current program position by
highlighting the current line and marking it with a `>' marker. By
default, source and assembly code styling is disabled for the
highlighted text, but you can enable it with the `set style
tui-current-position on' command. *Note Output Styling::.

Breakpoints are indicated with two markers. The first marker
indicates the breakpoint type:

`B'
Breakpoint which was hit at least once.

`b'
Breakpoint which was never hit.

`H'
Hardware breakpoint which was hit at least once.

`h'
Hardware breakpoint which was never hit.

The second marker indicates whether the breakpoint is enabled or not:

`+'
Breakpoint is enabled.

`-'
Breakpoint is disabled.

The source, assembly and register windows are updated when the
current thread changes, when the frame changes, or when the program
counter changes.

These windows are not all visible at the same time. The command
window is always visible. The others can be arranged in several
layouts:

* source only,

* assembly only,

* source and assembly,

* source and registers, or

* assembly and registers.

These are the standard layouts, but other layouts can be defined.

A status line above the command window shows the following
information:

_target_
Indicates the current GDB target. (*note Specifying a Debugging
Target: Targets.).

_process_
Gives the current process or thread number. When no process is
being debugged, this field is set to `No process'.

_focus_
Shows the name of the TUI window that has the focus.

_function_
Gives the current function name for the selected frame. The name
is demangled if demangling is turned on (*note Print Settings::).
When there is no symbol corresponding to the current program
counter, the string `??' is displayed.

_line_
Indicates the current line number for the selected frame. When
the current line number is not known, the string `??' is displayed.

_pc_
Indicates the current program counter address.

File: gdb.info, Node: TUI Keys, Next: TUI Single Key Mode, Prev: TUI Overview, Up: TUI

25.2 TUI Key Bindings
=====================

The TUI installs several key bindings in the readline keymaps (*note
Command Line Editing::). The following key bindings are installed for
both TUI mode and the GDB standard mode.

`C-x C-a'
`C-x a'
`C-x A'
Enter or leave the TUI mode. When leaving the TUI mode, the
curses window management stops and GDB operates using its standard
mode, writing on the terminal directly. When reentering the TUI
mode, control is given back to the curses windows. The screen is
then refreshed.

This key binding uses the bindable Readline function
`tui-switch-mode'.

`C-x 1'
Use a TUI layout with only one window. The layout will either be
`source' or `assembly'. When the TUI mode is not active, it will
switch to the TUI mode.

Think of this key binding as the Emacs `C-x 1' binding.

This key binding uses the bindable Readline function
`tui-delete-other-windows'.

`C-x 2'
Use a TUI layout with at least two windows. When the current
layout already has two windows, the next layout with two windows
is used. When a new layout is chosen, one window will always be
common to the previous layout and the new one.

Think of it as the Emacs `C-x 2' binding.

This key binding uses the bindable Readline function
`tui-change-windows'.

`C-x o'
Change the active window. The TUI associates several key bindings
(like scrolling and arrow keys) with the active window. This
command gives the focus to the next TUI window.

Think of it as the Emacs `C-x o' binding.

This key binding uses the bindable Readline function
`tui-other-window'.

`C-x s'
Switch in and out of the TUI SingleKey mode that binds single keys
to GDB commands (*note TUI Single Key Mode::).

This key binding uses the bindable Readline function `next-keymap'.

The following key bindings only work in the TUI mode:

<PgUp>
Scroll the active window one page up.

<PgDn>
Scroll the active window one page down.

<Up>
Scroll the active window one line up.

<Down>
Scroll the active window one line down.

<Left>
Scroll the active window one column left.

<Right>
Scroll the active window one column right.

`C-L'
Refresh the screen.

Because the arrow keys scroll the active window in the TUI mode, they
are not available for their normal use by readline unless the command
window has the focus. When another window is active, you must use
other readline key bindings such as `C-p', `C-n', `C-b' and `C-f' to
control the command window.

File: gdb.info, Node: TUI Single Key Mode, Next: TUI Mouse Support, Prev: TUI Keys, Up: TUI

25.3 TUI Single Key Mode
========================

The TUI also provides a "SingleKey" mode, which binds several
frequently used GDB commands to single keys. Type `C-x s' to switch
into this mode, where the following key bindings are used:

`c'
continue

`C'
reverse-continue

`d'
down

`f'
finish

`F'
reverse-finish

`n'
next

`N'
reverse-next

`o'
nexti. The shortcut letter `o' stands for "step Over".

`O'
reverse-nexti

`q'
exit the SingleKey mode.

`r'
run

`s'
step

`S'
reverse-step

`i'
stepi. The shortcut letter `i' stands for "step Into".

`I'
reverse-stepi

`u'
up

`v'
info locals

`w'
where

Other keys temporarily switch to the GDB command prompt. The key
that was pressed is inserted in the editing buffer so that it is
possible to type most GDB commands without interaction with the TUI
SingleKey mode. Once the command is entered the TUI SingleKey mode is
restored. The only way to permanently leave this mode is by typing `q'
or `C-x s'.

If GDB was built with Readline 8.0 or later, the TUI SingleKey
keymap will be named `SingleKey'. This can be used in `.inputrc' to
add additional bindings to this keymap.

File: gdb.info, Node: TUI Mouse Support, Next: TUI Commands, Prev: TUI Single Key Mode, Up: TUI

25.4 TUI Mouse Support
======================

If the curses library supports the mouse, the TUI supports mouse
actions.

The mouse wheel scrolls the appropriate window under the mouse
cursor.

The TUI itself does not directly support copying/pasting with the
mouse. However, on Unix terminals, you can typically press and hold
the <SHIFT> key on your keyboard to temporarily bypass GDB's TUI and
access the terminal's native mouse copy/paste functionality (commonly,
click-drag-release or double-click to select text, middle-click to
paste). This copy/paste works with the terminal's selection buffer, as
opposed to the TUI's buffer. Alternatively, to disable mouse support
in the TUI entirely and give the terminal control over mouse clicks,
turn off the `tui mouse-events' setting (*note set tui mouse-events:
tui-mouse-events.).

Python extensions can react to mouse clicks (*note Window.click:
python-window-click.).

File: gdb.info, Node: TUI Commands, Next: TUI Configuration, Prev: TUI Mouse Support, Up: TUI

25.5 TUI-specific Commands
==========================

The TUI has specific commands to control the text windows. These
commands are always available, even when GDB is not in the TUI mode.
When GDB is in the standard mode, most of these commands will
automatically switch to the TUI mode.

Note that if GDB's `stdout' is not connected to a terminal, or GDB
has been started with the machine interface interpreter (*note The
GDB/MI Interface: GDB/MI.), most of these commands will fail with an
error, because it would not be possible or desirable to enable curses
window management.

`tui enable'
Activate TUI mode. The last active TUI window layout will be used
if TUI mode has previously been used in the current debugging
session, otherwise a default layout is used.

`tui disable'
Disable TUI mode, returning to the console interpreter.

`info win'
List the names and sizes of all currently displayed windows.

`tui new-layout NAME WINDOW WEIGHT [WINDOW WEIGHT...]'
Create a new TUI layout. The new layout will be named NAME, and
can be accessed using the `layout' command (see below).

Each WINDOW parameter is either the name of a window to display,
or a window description. The windows will be displayed from top to
bottom in the order listed.

The names of the windows are the same as the ones given to the
`focus' command (see below); additionally, the `status' window can
be specified. Note that, because it is of fixed height, the
weight assigned to the status window is of no importance. It is
conventional to use `0' here.

A window description looks a bit like an invocation of `tui
new-layout', and is of the form {[`-horizontal']WINDOW WEIGHT
[WINDOW WEIGHT...]}.

This specifies a sub-layout. If `-horizontal' is given, the
windows in this description will be arranged side-by-side, rather
than top-to-bottom.

Each WEIGHT is an integer. It is the weight of this window
relative to all the other windows in the layout. These numbers are
used to calculate how much of the screen is given to each window.

For example:

(gdb) tui new-layout example src 1 regs 1 status 0 cmd 1

Here, the new layout is called `example'. It shows the source and
register windows, followed by the status window, and then finally
the command window. The non-status windows all have the same
weight, so the terminal will be split into three roughly equal
sections.

Here is a more complex example, showing a horizontal layout:

(gdb) tui new-layout example {-horizontal src 1 asm 1} 2 status 0 cmd 1

This will result in side-by-side source and assembly windows; with
the status and command window being beneath these, filling the
entire width of the terminal. Because they have weight 2, the
source and assembly windows will be twice the height of the
command window.

`tui layout NAME'
`layout NAME'
Changes which TUI windows are displayed. The NAME parameter
controls which layout is shown. It can be either one of the
built-in layout names, or the name of a layout defined by the user
using `tui new-layout'.

The built-in layouts are as follows:

`next'
Display the next layout.

`prev'
Display the previous layout.

`src'
Display the source and command windows.

`asm'
Display the assembly and command windows.

`split'
Display the source, assembly, and command windows.

`regs'
When in `src' layout display the register, source, and command
windows. When in `asm' or `split' layout display the
register, assembler, and command windows.

`tui focus NAME'
`focus NAME'
Changes which TUI window is currently active for scrolling. The
NAME parameter can be any of the following:

`next'
Make the next window active for scrolling.

`prev'
Make the previous window active for scrolling.

`src'
Make the source window active for scrolling.

`asm'
Make the assembly window active for scrolling.

`regs'
Make the register window active for scrolling.

`cmd'
Make the command window active for scrolling.

`tui refresh'
`refresh'
Refresh the screen. This is similar to typing `C-L'.

`tui reg GROUP'
Changes the register group displayed in the tui register window to
GROUP. If the register window is not currently displayed this
command will cause the register window to be displayed. The list
of register groups, as well as their order is target specific. The
following groups are available on most targets:
`next'
Repeatedly selecting this group will cause the display to
cycle through all of the available register groups.

`prev'
Repeatedly selecting this group will cause the display to
cycle through all of the available register groups in the
reverse order to NEXT.

`general'
Display the general registers.

`float'
Display the floating point registers.

`system'
Display the system registers.

`vector'
Display the vector registers.

`all'
Display all registers.

`update'
Update the source window and the current execution point.

`tui window height NAME +COUNT'
`tui window height NAME -COUNT'
`winheight NAME +COUNT'
`winheight NAME -COUNT'
Change the height of the window NAME by COUNT lines. Positive
counts increase the height, while negative counts decrease it.
The NAME parameter can be the name of any currently visible
window. The names of the currently visible windows can be
discovered using `info win' (*note info win: info_win_command.).

The set of currently visible windows must always fill the terminal,
and so, it is only possible to resize on window if there are other
visible windows that can either give or receive the extra terminal
space.

`tui window width NAME +COUNT'
`tui window width NAME -COUNT'
`winwidth NAME +COUNT'
`winwidth NAME -COUNT'
Change the width of the window NAME by COUNT columns. Positive
counts increase the width, while negative counts decrease it. The
NAME parameter can be the name of any currently visible window.
The names of the currently visible windows can be discovered using
`info win' (*note info win: info_win_command.).

The set of currently visible windows must always fill the terminal,
and so, it is only possible to resize on window if there are other
visible windows that can either give or receive the extra terminal
space.

File: gdb.info, Node: TUI Configuration, Prev: TUI Commands, Up: TUI

25.6 TUI Configuration Variables
================================

Several configuration variables control the appearance of TUI windows.

`set tui border-kind KIND'
Select the border appearance for the source, assembly and register
windows. The possible values are the following:
`space'
Use a space character to draw the border.

`ascii'
Use ASCII characters `+', `-' and `|' to draw the border.

`acs'
Use the Alternate Character Set to draw the border. The
border is drawn using character line graphics if the terminal
supports them.

`set tui border-mode MODE'
`set tui active-border-mode MODE'
Select the display attributes for the borders of the inactive
windows or the active window. The MODE can be one of the
following:
`normal'
Use normal attributes to display the border.

`standout'
Use standout mode.

`reverse'
Use reverse video mode.

`half'
Use half bright mode.

`half-standout'
Use half bright and standout mode.

`bold'
Use extra bright or bold mode.

`bold-standout'
Use extra bright or bold and standout mode.

`set tui tab-width NCHARS'
Set the width of tab stops to be NCHARS characters. This setting
affects the display of TAB characters in the source and assembly
windows.

`set tui compact-source [on|off]'
Set whether the TUI source window is displayed in "compact" form.
The default display uses more space for line numbers; the compact
display uses only as much space as is needed for the line numbers
in the current file.

`set tui mouse-events [on|off]'
When on (default), mouse clicks control the TUI (*note TUI Mouse
Support::). When off, mouse clicks are handled by the terminal,
enabling terminal-native text selection.

`set debug tui [on|off]'
Turn on or off display of GDB internal debug messages relating to
the TUI.

`show debug tui'
Show the current status of displaying GDB internal debug messages
relating to the TUI.

Note that the colors of the TUI borders can be controlled using the
appropriate `set style' commands. *Note Output Styling::.

File: gdb.info, Node: Emacs, Next: GDB/MI, Prev: TUI, Up: Top

26 Using GDB under GNU Emacs
****************************

A special interface allows you to use GNU Emacs to view (and edit) the
source files for the program you are debugging with GDB.

To use this interface, use the command `M-x gdb' in Emacs. Give the
executable file you want to debug as an argument. This command starts
GDB as a subprocess of Emacs, with input and output through a newly
created Emacs buffer.

Running GDB under Emacs can be just like running GDB normally except
for two things:

* All "terminal" input and output goes through an Emacs buffer,
called the GUD buffer.

This applies both to GDB commands and their output, and to the
input and output done by the program you are debugging.

This is useful because it means that you can copy the text of
previous commands and input them again; you can even use parts of
the output in this way.

All the facilities of Emacs' Shell mode are available for
interacting with your program. In particular, you can send
signals the usual way--for example, `C-c C-c' for an interrupt,
`C-c C-z' for a stop.

* GDB displays source code through Emacs.

Each time GDB displays a stack frame, Emacs automatically finds the
source file for that frame and puts an arrow (`=>') at the left
margin of the current line. Emacs uses a separate buffer for
source display, and splits the screen to show both your GDB session
and the source.

Explicit GDB `list' or search commands still produce output as
usual, but you probably have no reason to use them from Emacs.

We call this "text command mode". Emacs 22.1, and later, also uses
a graphical mode, enabled by default, which provides further buffers
that can control the execution and describe the state of your program.
*Note GDB Graphical Interface: (Emacs)GDB Graphical Interface.

If you specify an absolute file name when prompted for the `M-x gdb'
argument, then Emacs sets your current working directory to where your
program resides. If you only specify the file name, then Emacs sets
your current working directory to the directory associated with the
previous buffer. In this case, GDB may find your program by searching
your environment's `PATH' variable, but on some operating systems it
might not find the source. So, although the GDB input and output
session proceeds normally, the auxiliary buffer does not display the
current source and line of execution.

The initial working directory of GDB is printed on the top line of
the GUD buffer and this serves as a default for the commands that
specify files for GDB to operate on. *Note Commands to Specify Files:
Files.

By default, `M-x gdb' calls the program called `gdb'. If you need
to call GDB by a different name (for example, if you keep several
configurations around, with different names) you can customize the
Emacs variable `gud-gdb-command-name' to run the one you want.

In the GUD buffer, you can use these special Emacs commands in
addition to the standard Shell mode commands:

`C-h m'
Describe the features of Emacs' GUD Mode.

`C-c C-s'
Execute to another source line, like the GDB `step' command; also
update the display window to show the current file and location.

`C-c C-n'
Execute to next source line in this function, skipping all function
calls, like the GDB `next' command. Then update the display window
to show the current file and location.

`C-c C-i'
Execute one instruction, like the GDB `stepi' command; update
display window accordingly.

`C-c C-f'
Execute until exit from the selected stack frame, like the GDB
`finish' command.

`C-c C-r'
Continue execution of your program, like the GDB `continue'
command.

`C-c <'
Go up the number of frames indicated by the numeric argument
(*note Numeric Arguments: (Emacs)Arguments.), like the GDB `up'
command.

`C-c >'
Go down the number of frames indicated by the numeric argument,
like the GDB `down' command.

In any source file, the Emacs command `C-x <SPC>' (`gud-break')
tells GDB to set a breakpoint on the source line point is on.

In text command mode, if you type `M-x speedbar', Emacs displays a
separate frame which shows a backtrace when the GUD buffer is current.
Move point to any frame in the stack and type <RET> to make it become
the current frame and display the associated source in the source
buffer. Alternatively, click `Mouse-2' to make the selected frame
become the current one. In graphical mode, the speedbar displays watch
expressions.

If you accidentally delete the source-display buffer, an easy way to
get it back is to type the command `f' in the GDB buffer, to request a
frame display; when you run under Emacs, this recreates the source
buffer if necessary to show you the context of the current frame.

The source files displayed in Emacs are in ordinary Emacs buffers
which are visiting the source files in the usual way. You can edit the
files with these buffers if you wish; but keep in mind that GDB
communicates with Emacs in terms of line numbers. If you add or delete
lines from the text, the line numbers that GDB knows cease to
correspond properly with the code.

A more detailed description of Emacs' interaction with GDB is given
in the Emacs manual (*note Debuggers: (Emacs)Debuggers.).

File: gdb.info, Node: GDB/MI, Next: Annotations, Prev: Emacs, Up: Top

27 The GDB/MI Interface
***********************

Function and Purpose
====================

GDB/MI is a line based machine oriented text interface to GDB and is
activated by specifying using the `--interpreter' command line option
(*note Mode Options::). It is specifically intended to support the
development of systems which use the debugger as just one small
component of a larger system.

This chapter is a specification of the GDB/MI interface. It is
written in the form of a reference manual.

Note that GDB/MI is still under construction, so some of the
features described below are incomplete and subject to change (*note
GDB/MI Development and Front Ends: GDB/MI Development and Front Ends.).

Notation and Terminology
========================

This chapter uses the following notation:

* `|' separates two alternatives.

* `[ SOMETHING ]' indicates that SOMETHING is optional: it may or
may not be given.

* `( GROUP )*' means that GROUP inside the parentheses may repeat
zero or more times.

* `( GROUP )+' means that GROUP inside the parentheses may repeat
one or more times.

* `( GROUP )' means that GROUP inside the parentheses occurs exactly
once.

* `"STRING"' means a literal STRING.

* Menu:

* GDB/MI General Design::
* GDB/MI Command Syntax::
* GDB/MI Compatibility with CLI::
* GDB/MI Development and Front Ends::
* GDB/MI Output Records::
* GDB/MI Simple Examples::
* GDB/MI Command Description Format::
* GDB/MI Breakpoint Commands::
* GDB/MI Catchpoint Commands::
* GDB/MI Program Context::
* GDB/MI Thread Commands::
* GDB/MI Ada Tasking Commands::
* GDB/MI Program Execution::
* GDB/MI Stack Manipulation::
* GDB/MI Variable Objects::
* GDB/MI Data Manipulation::
* GDB/MI Tracepoint Commands::
* GDB/MI Symbol Query::
* GDB/MI File Commands::
* GDB/MI Target Manipulation::
* GDB/MI File Transfer Commands::
* GDB/MI Ada Exceptions Commands::
* GDB/MI Support Commands::
* GDB/MI Miscellaneous Commands::

File: gdb.info, Node: GDB/MI General Design, Next: GDB/MI Command Syntax, Up: GDB/MI

27.1 GDB/MI General Design
==========================

Interaction of a GDB/MI frontend with GDB involves three
parts--commands sent to GDB, responses to those commands and
notifications. Each command results in exactly one response,
indicating either successful completion of the command, or an error.
For the commands that do not resume the target, the response contains
the requested information. For the commands that resume the target, the
response only indicates whether the target was successfully resumed.
Notifications is the mechanism for reporting changes in the state of the
target, or in GDB state, that cannot conveniently be associated with a
command and reported as part of that command response.

The important examples of notifications are:
* Exec notifications. These are used to report changes in target
state--when a target is resumed, or stopped. It would not be
feasible to include this information in response of resuming
commands, because one resume commands can result in multiple
events in different threads. Also, quite some time may pass
before any event happens in the target, while a frontend needs to
know whether the resuming command itself was successfully executed.

* Console output, and status notifications. Console output
notifications are used to report output of CLI commands, as well as
diagnostics for other commands. Status notifications are used to
report the progress of a long-running operation. Naturally,
including this information in command response would mean no
output is produced until the command is finished, which is
undesirable.

* General notifications. Commands may have various side effects on
the GDB or target state beyond their official purpose. For
example, a command may change the selected thread. Although such
changes can be included in command response, using notification
allows for more orthogonal frontend design.

There's no guarantee that whenever an MI command reports an error,
GDB or the target are in any specific state, and especially, the state
is not reverted to the state before the MI command was processed.
Therefore, whenever an MI command results in an error, we recommend
that the frontend refreshes all the information shown in the user
interface.

* Menu:

* Context management::
* Asynchronous and non-stop modes::
* Thread groups::

File: gdb.info, Node: Context management, Next: Asynchronous and non-stop modes, Up: GDB/MI General Design

27.1.1 Context management
-------------------------

27.1.1.1 Threads and Frames
..........................

In most cases when GDB accesses the target, this access is done in
context of a specific thread and frame (*note Frames::). Often, even
when accessing global data, the target requires that a thread be
specified. The CLI interface maintains the selected thread and frame,
and supplies them to target on each command. This is convenient,
because a command line user would not want to specify that information
explicitly on each command, and because user interacts with GDB via a
single terminal, so no confusion is possible as to what thread and
frame are the current ones.

In the case of MI, the concept of selected thread and frame is less
useful. First, a frontend can easily remember this information itself.
Second, a graphical frontend can have more than one window, each one
used for debugging a different thread, and the frontend might want to
access additional threads for internal purposes. This increases the
risk that by relying on implicitly selected thread, the frontend may be
operating on a wrong one. Therefore, each MI command should explicitly
specify which thread and frame to operate on. To make it possible,
each MI command accepts the `--thread' and `--frame' options, the value
to each is GDB global identifier for thread and frame to operate on.

Usually, each top-level window in a frontend allows the user to
select a thread and a frame, and remembers the user selection for
further operations. However, in some cases GDB may suggest that the
current thread or frame be changed. For example, when stopping on a
breakpoint it is reasonable to switch to the thread where breakpoint is
hit. For another example, if the user issues the CLI `thread' or
`frame' commands via the frontend, it is desirable to change the
frontend's selection to the one specified by user. GDB communicates
the suggestion to change current thread and frame using the
`=thread-selected' notification.

Note that historically, MI shares the selected thread with CLI, so
frontends used the `-thread-select' to execute commands in the right
context. However, getting this to work right is cumbersome. The
simplest way is for frontend to emit `-thread-select' command before
every command. This doubles the number of commands that need to be
sent. The alternative approach is to suppress `-thread-select' if the
selected thread in GDB is supposed to be identical to the thread the
frontend wants to operate on. However, getting this optimization right
can be tricky. In particular, if the frontend sends several commands
to GDB, and one of the commands changes the selected thread, then the
behaviour of subsequent commands will change. So, a frontend should
either wait for response from such problematic commands, or explicitly
add `-thread-select' for all subsequent commands. No frontend is known
to do this exactly right, so it is suggested to just always pass the
`--thread' and `--frame' options.

27.1.1.2 Language
................

The execution of several commands depends on which language is selected.
By default, the current language (*note show language::) is used. But
for commands known to be language-sensitive, it is recommended to use
the `--language' option. This option takes one argument, which is the
name of the language to use while executing the command. For instance:

-data-evaluate-expression --language c "sizeof (void*)"
^done,value="4"
(gdb)

The valid language names are the same names accepted by the `set
language' command (*note Manually::), excluding `auto', `local' or
`unknown'.

File: gdb.info, Node: Asynchronous and non-stop modes, Next: Thread groups, Prev: Context management, Up: GDB/MI General Design

27.1.2 Asynchronous command execution and non-stop mode
-------------------------------------------------------

On some targets, GDB is capable of processing MI commands even while
the target is running. This is called "asynchronous command execution"
(*note Background Execution::). The frontend may specify a preference
for asynchronous execution using the `-gdb-set mi-async 1' command,
which should be emitted before either running the executable or
attaching to the target. After the frontend has started the executable
or attached to the target, it can find if asynchronous execution is
enabled using the `-list-target-features' command.

`-gdb-set mi-async [on|off]'
Set whether MI is in asynchronous mode.

When `off', which is the default, MI execution commands (e.g.,
`-exec-continue') are foreground commands, and GDB waits for the
program to stop before processing further commands.

When `on', MI execution commands are background execution commands
(e.g., `-exec-continue' becomes the equivalent of the `c&' CLI
command), and so GDB is capable of processing MI commands even
while the target is running.

`-gdb-show mi-async'
Show whether MI asynchronous mode is enabled.

Note: In GDB version 7.7 and earlier, this option was called
`target-async' instead of `mi-async', and it had the effect of both
putting MI in asynchronous mode and making CLI background commands
possible. CLI background commands are now always possible "out of the
box" if the target supports them. The old spelling is kept as a
deprecated alias for backwards compatibility.

Even if GDB can accept a command while target is running, many
commands that access the target do not work when the target is running.
Therefore, asynchronous command execution is most useful when combined
with non-stop mode (*note Non-Stop Mode::). Then, it is possible to
examine the state of one thread, while other threads are running.

When a given thread is running, MI commands that try to access the
target in the context of that thread may not work, or may work only on
some targets. In particular, commands that try to operate on thread's
stack will not work, on any target. Commands that read memory, or
modify breakpoints, may work or not work, depending on the target. Note
that even commands that operate on global state, such as `print',
`set', and breakpoint commands, still access the target in the context
of a specific thread, so frontend should try to find a stopped thread
and perform the operation on that thread (using the `--thread' option).

Which commands will work in the context of a running thread is
highly target dependent. However, the two commands `-exec-interrupt',
to stop a thread, and `-thread-info', to find the state of a thread,
will always work.

File: gdb.info, Node: Thread groups, Prev: Asynchronous and non-stop modes, Up: GDB/MI General Design

27.1.3 Thread groups
--------------------

GDB may be used to debug several processes at the same time. On some
platforms, GDB may support debugging of several hardware systems, each
one having several cores with several different processes running on
each core. This section describes the MI mechanism to support such
debugging scenarios.

The key observation is that regardless of the structure of the
target, MI can have a global list of threads, because most commands that
accept the `--thread' option do not need to know what process that
thread belongs to. Therefore, it is not necessary to introduce neither
additional `--process' option, nor an notion of the current process in
the MI interface. The only strictly new feature that is required is
the ability to find how the threads are grouped into processes.

To allow the user to discover such grouping, and to support arbitrary
hierarchy of machines/cores/processes, MI introduces the concept of a
"thread group". Thread group is a collection of threads and other
thread groups. A thread group always has a string identifier, a type,
and may have additional attributes specific to the type. A new
command, `-list-thread-groups', returns the list of top-level thread
groups, which correspond to processes that GDB is debugging at the
moment. By passing an identifier of a thread group to the
`-list-thread-groups' command, it is possible to obtain the members of
specific thread group.

To allow the user to easily discover processes, and other objects, he
wishes to debug, a concept of "available thread group" is introduced.
Available thread group is an thread group that GDB is not debugging,
but that can be attached to, using the `-target-attach' command. The
list of available top-level thread groups can be obtained using
`-list-thread-groups --available'. In general, the content of a thread
group may be only retrieved only after attaching to that thread group.

Thread groups are related to inferiors (*note Inferiors Connections
and Programs::). Each inferior corresponds to a thread group of a
special type `process', and some additional operations are permitted on
such thread groups.

File: gdb.info, Node: GDB/MI Command Syntax, Next: GDB/MI Compatibility with CLI, Prev: GDB/MI General Design, Up: GDB/MI

27.2 GDB/MI Command Syntax
==========================

* Menu:

* GDB/MI Input Syntax::
* GDB/MI Output Syntax::

File: gdb.info, Node: GDB/MI Input Syntax, Next: GDB/MI Output Syntax, Up: GDB/MI Command Syntax

27.2.1 GDB/MI Input Syntax
--------------------------

`COMMAND ==>'
`CLI-COMMAND | MI-COMMAND'

`CLI-COMMAND ==>'
`[ TOKEN ] CLI-COMMAND NL', where CLI-COMMAND is any existing GDB
CLI command.

`MI-COMMAND ==>'
`[ TOKEN ] "-" OPERATION ( " " OPTION )* `[' " --" `]' ( " "
PARAMETER )* NL'

`TOKEN ==>'
"any sequence of digits"

`OPTION ==>'
`"-" PARAMETER [ " " PARAMETER ]'

`PARAMETER ==>'
`NON-BLANK-SEQUENCE | C-STRING'

`OPERATION ==>'
_any of the operations described in this chapter_

`NON-BLANK-SEQUENCE ==>'
_anything, provided it doesn't contain special characters such as
"-", NL, """ and of course " "_

`C-STRING ==>'
`""" SEVEN-BIT-ISO-C-STRING-CONTENT """'

`NL ==>'
`CR | CR-LF'

Notes:

* The CLI commands are still handled by the MI interpreter; their
output is described below.

* The `TOKEN', when present, is passed back when the command
finishes.

* Some MI commands accept optional arguments as part of the parameter
list. Each option is identified by a leading `-' (dash) and may be
followed by an optional argument parameter. Options occur first
in the parameter list and can be delimited from normal parameters
using `--' (this is useful when some parameters begin with a dash).

Pragmatics:

* We want easy access to the existing CLI syntax (for debugging).

* We want it to be easy to spot a MI operation.

File: gdb.info, Node: GDB/MI Output Syntax, Prev: GDB/MI Input Syntax, Up: GDB/MI Command Syntax

27.2.2 GDB/MI Output Syntax
---------------------------

The output from GDB/MI consists of zero or more out-of-band records
followed, optionally, by a single result record. This result record is
for the most recent command. The sequence of output records is
terminated by `(gdb)'.

If an input command was prefixed with a `TOKEN' then the
corresponding output for that command will also be prefixed by that same
TOKEN.

`OUTPUT ==>'
`( OUT-OF-BAND-RECORD )* [ RESULT-RECORD ] "(gdb)" NL'

`RESULT-RECORD ==>'
` [ TOKEN ] "^" RESULT-CLASS ( "," RESULT )* NL'

`OUT-OF-BAND-RECORD ==>'
`ASYNC-RECORD | STREAM-RECORD'

`ASYNC-RECORD ==>'
`EXEC-ASYNC-OUTPUT | STATUS-ASYNC-OUTPUT | NOTIFY-ASYNC-OUTPUT'

`EXEC-ASYNC-OUTPUT ==>'
`[ TOKEN ] "*" ASYNC-OUTPUT NL'

`STATUS-ASYNC-OUTPUT ==>'
`[ TOKEN ] "+" ASYNC-OUTPUT NL'

`NOTIFY-ASYNC-OUTPUT ==>'
`[ TOKEN ] "=" ASYNC-OUTPUT NL'

`ASYNC-OUTPUT ==>'
`ASYNC-CLASS ( "," RESULT )*'

`RESULT-CLASS ==>'
`"done" | "running" | "connected" | "error" | "exit"'

`ASYNC-CLASS ==>'
`"stopped" | OTHERS' (where OTHERS will be added depending on the
needs--this is still in development).

`RESULT ==>'
` VARIABLE "=" VALUE'

`VARIABLE ==>'
` STRING '

`VALUE ==>'
` CONST | TUPLE | LIST '

`CONST ==>'
`C-STRING'

`TUPLE ==>'
` "{}" | "{" RESULT ( "," RESULT )* "}" '

`LIST ==>'
` "[]" | "[" VALUE ( "," VALUE )* "]" | "[" RESULT ( "," RESULT )*
"]" '

`STREAM-RECORD ==>'
`CONSOLE-STREAM-OUTPUT | TARGET-STREAM-OUTPUT | LOG-STREAM-OUTPUT'

`CONSOLE-STREAM-OUTPUT ==>'
`"~" C-STRING NL'

`TARGET-STREAM-OUTPUT ==>'
`"@" C-STRING NL'

`LOG-STREAM-OUTPUT ==>'
`"&" C-STRING NL'

`NL ==>'
`CR | CR-LF'

`TOKEN ==>'
_any sequence of digits_.

Notes:

* All output sequences end in a single line containing a period.

* The `TOKEN' is from the corresponding request. Note that for all
async output, while the token is allowed by the grammar and may be
output by future versions of GDB for select async output messages,
it is generally omitted. Frontends should treat all async output
as reporting general changes in the state of the target and there
should be no need to associate async output to any prior command.

* STATUS-ASYNC-OUTPUT contains on-going status information about the
progress of a slow operation. It can be discarded. All status
output is prefixed by `+'.

* EXEC-ASYNC-OUTPUT contains asynchronous state change on the target
(stopped, started, disappeared). All async output is prefixed by
`*'.

* NOTIFY-ASYNC-OUTPUT contains supplementary information that the
client should handle (e.g., a new breakpoint information). All
notify output is prefixed by `='.

* CONSOLE-STREAM-OUTPUT is output that should be displayed as is in
the console. It is the textual response to a CLI command. All
the console output is prefixed by `~'.

* TARGET-STREAM-OUTPUT is the output produced by the target program.
All the target output is prefixed by `@'.

* LOG-STREAM-OUTPUT is output text coming from GDB's internals, for
instance messages that should be displayed as part of an error
log. All the log output is prefixed by `&'.

* New GDB/MI commands should only output LISTS containing VALUES.

*Note GDB/MI Stream Records: GDB/MI Stream Records, for more details
about the various output records.

File: gdb.info, Node: GDB/MI Compatibility with CLI, Next: GDB/MI Development and Front Ends, Prev: GDB/MI Command Syntax, Up: GDB/MI

27.3 GDB/MI Compatibility with CLI
==================================

For the developers convenience CLI commands can be entered directly,
but there may be some unexpected behaviour. For example, commands that
query the user will behave as if the user replied yes, breakpoint
command lists are not executed and some CLI commands, such as `if',
`when' and `define', prompt for further input with `>', which is not
valid MI output.

This feature may be removed at some stage in the future and it is
recommended that front ends use the `-interpreter-exec' command (*note
-interpreter-exec::).

File: gdb.info, Node: GDB/MI Development and Front Ends, Next: GDB/MI Output Records, Prev: GDB/MI Compatibility with CLI, Up: GDB/MI

27.4 GDB/MI Development and Front Ends
======================================

The application which takes the MI output and presents the state of the
program being debugged to the user is called a "front end".

Since GDB/MI is used by a variety of front ends to GDB, changes to
the MI interface may break existing usage. This section describes how
the protocol changes and how to request previous version of the
protocol when it does.

Some changes in MI need not break a carefully designed front end, and
for these the MI version will remain unchanged. The following is a
list of changes that may occur within one level, so front ends should
parse MI output in a way that can handle them:

* New MI commands may be added.

* New fields may be added to the output of any MI command.

* The range of values for fields with specified values, e.g.,
`in_scope' (*note -var-update::) may be extended.

If the changes are likely to break front ends, the MI version level
will be increased by one. The new versions of the MI protocol are not
compatible with the old versions. Old versions of MI remain available,
allowing front ends to keep using them until they are modified to use
the latest MI version.

Since `--interpreter=mi' always points to the latest MI version, it
is recommended that front ends request a specific version of MI when
launching GDB (e.g. `--interpreter=mi2') to make sure they get an
interpreter with the MI version they expect.

The following table gives a summary of the released versions of the
MI interface: the version number, the version of GDB in which it first
appeared and the breaking changes compared to the previous version.

MI GDB Breaking changes
version version
---------------------------------------------------------------------------
1 5.1 None
2 6.0 * The `-environment-pwd', `-environment-directory' and
`-environment-path' commands now returns values
using the MI output syntax, rather than CLI output
syntax.

* `-var-list-children''s `children' result field is
now a list, rather than a tuple.

* `-var-update''s `changelist' result field is now a
list, rather than a tuple.
3 9.1 * The output of information about multi-location
breakpoints has changed in the responses to the
`-break-insert' and `-break-info' commands, as well
as in the `=breakpoint-created' and
`=breakpoint-modified' events. The multiple
locations are now placed in a `locations' field,
whose value is a list.
4 13.1 * The syntax of the "script" field in breakpoint
output has changed in the responses to the
`-break-insert' and `-break-info' commands, as well
as the `=breakpoint-created' and
`=breakpoint-modified' events. The previous output
was syntactically invalid. The new output is a list.

If your front end cannot yet migrate to a more recent version of the
MI protocol, you can nevertheless selectively enable specific features
available in those recent MI versions, using the following commands:

`-fix-multi-location-breakpoint-output'
Use the output for multi-location breakpoints which was introduced
by MI 3, even when using MI versions below 3. This command has no
effect when using MI version 3 or later.

`-fix-breakpoint-script-output'
Use the output for the breakpoint "script" field which was
introduced by MI 4, even when using MI versions below 4. This
command has no effect when using MI version 4 or later.

The best way to avoid unexpected changes in MI that might break your
front end is to make your project known to GDB developers and follow
development on <[email protected]> and <[email protected]>.

File: gdb.info, Node: GDB/MI Output Records, Next: GDB/MI Simple Examples, Prev: GDB/MI Development and Front Ends, Up: GDB/MI

27.5 GDB/MI Output Records
==========================

* Menu:

* GDB/MI Result Records::
* GDB/MI Stream Records::
* GDB/MI Async Records::
* GDB/MI Breakpoint Information::
* GDB/MI Frame Information::
* GDB/MI Thread Information::
* GDB/MI Ada Exception Information::

File: gdb.info, Node: GDB/MI Result Records, Next: GDB/MI Stream Records, Up: GDB/MI Output Records

27.5.1 GDB/MI Result Records
----------------------------

In addition to a number of out-of-band notifications, the response to a
GDB/MI command includes one of the following result indications:

`"^done" [ "," RESULTS ]'
The synchronous operation was successful, `RESULTS' are the return
values.

`"^running"'
This result record is equivalent to `^done'. Historically, it was
output instead of `^done' if the command has resumed the target.
This behaviour is maintained for backward compatibility, but all
frontends should treat `^done' and `^running' identically and rely
on the `*running' output record to determine which threads are
resumed.

`"^connected"'
GDB has connected to a remote target.

`"^error" "," "msg=" C-STRING [ "," "code=" C-STRING ]'
The operation failed. The `msg=C-STRING' variable contains the
corresponding error message.

If present, the `code=C-STRING' variable provides an error code on
which consumers can rely on to detect the corresponding error
condition. At present, only one error code is defined:

`"undefined-command"'
Indicates that the command causing the error does not exist.

`"^exit"'
GDB has terminated.

File: gdb.info, Node: GDB/MI Stream Records, Next: GDB/MI Async Records, Prev: GDB/MI Result Records, Up: GDB/MI Output Records

27.5.2 GDB/MI Stream Records
----------------------------

GDB internally maintains a number of output streams: the console, the
target, and the log. The output intended for each of these streams is
funneled through the GDB/MI interface using "stream records".

Each stream record begins with a unique "prefix character" which
identifies its stream (*note GDB/MI Output Syntax: GDB/MI Output
Syntax.). In addition to the prefix, each stream record contains a
`STRING-OUTPUT'. This is either raw text (with an implicit new line)
or a quoted C string (which does not contain an implicit newline).

`"~" STRING-OUTPUT'
The console output stream contains text that should be displayed
in the CLI console window. It contains the textual responses to
CLI commands.

`"@" STRING-OUTPUT'
The target output stream contains any textual output from the
running target. This is only present when GDB's event loop is
truly asynchronous, which is currently only the case for remote
targets.

`"&" STRING-OUTPUT'
The log stream contains debugging messages being produced by GDB's
internals.

File: gdb.info, Node: GDB/MI Async Records, Next: GDB/MI Breakpoint Information, Prev: GDB/MI Stream Records, Up: GDB/MI Output Records

27.5.3 GDB/MI Async Records
---------------------------

"Async" records are used to notify the GDB/MI client of additional
changes that have occurred. Those changes can either be a consequence
of GDB/MI commands (e.g., a breakpoint modified) or a result of target
activity (e.g., target stopped).

The following is the list of possible async records:

`*running,thread-id="THREAD"'
The target is now running. The THREAD field can be the global
thread ID of the thread that is now running, and it can be `all'
if all threads are running. The frontend should assume that no
interaction with a running thread is possible after this
notification is produced. The frontend should not assume that this
notification is output only once for any command. GDB may emit
this notification several times, either for different threads,
because it cannot resume all threads together, or even for a single
thread, if the thread must be stepped though some code before
letting it run freely.

`*stopped,reason="REASON",thread-id="ID",stopped-threads="STOPPED",core="CORE"'
The target has stopped. The REASON field can have one of the
following values:

`breakpoint-hit'
A breakpoint was reached.

`watchpoint-trigger'
A watchpoint was triggered.

`read-watchpoint-trigger'
A read watchpoint was triggered.

`access-watchpoint-trigger'
An access watchpoint was triggered.

`function-finished'
An -exec-finish or similar CLI command was accomplished.

`location-reached'
An -exec-until or similar CLI command was accomplished.

`watchpoint-scope'
A watchpoint has gone out of scope.

`end-stepping-range'
An -exec-next, -exec-next-instruction, -exec-step,
-exec-step-instruction or similar CLI command was
accomplished.

`exited-signalled'
The inferior exited because of a signal.

`exited'
The inferior exited.

`exited-normally'
The inferior exited normally.

`signal-received'
A signal was received by the inferior.

`solib-event'
The inferior has stopped due to a library being loaded or
unloaded. This can happen when `stop-on-solib-events' (*note
Files::) is set or when a `catch load' or `catch unload'
catchpoint is in use (*note Set Catchpoints::).

`fork'
The inferior has forked. This is reported when `catch fork'
(*note Set Catchpoints::) has been used.

`vfork'
The inferior has vforked. This is reported in when `catch
vfork' (*note Set Catchpoints::) has been used.

`syscall-entry'
The inferior entered a system call. This is reported when
`catch syscall' (*note Set Catchpoints::) has been used.

`syscall-return'
The inferior returned from a system call. This is reported
when `catch syscall' (*note Set Catchpoints::) has been used.

`exec'
The inferior called `exec'. This is reported when `catch
exec' (*note Set Catchpoints::) has been used.

`no-history'
There isn't enough history recorded to continue reverse
execution.

The ID field identifies the global thread ID of the thread that
directly caused the stop - for example by hitting a breakpoint.
Depending on whether all-stop mode is in effect (*note All-Stop
Mode::), GDB may either stop all threads, or only the thread that
directly triggered the stop. If all threads are stopped, the
STOPPED field will have the value of `"all"'. Otherwise, the
value of the STOPPED field will be a list of thread identifiers.
Presently, this list will always include a single thread, but
frontend should be prepared to see several threads in the list.
The CORE field reports the processor core on which the stop event
has happened. This field may be absent if such information is not
available.

`=thread-group-added,id="ID"'
`=thread-group-removed,id="ID"'
A thread group was either added or removed. The ID field contains
the GDB identifier of the thread group. When a thread group is
added, it generally might not be associated with a running
process. When a thread group is removed, its id becomes invalid
and cannot be used in any way.

`=thread-group-started,id="ID",pid="PID"'
A thread group became associated with a running program, either
because the program was just started or the thread group was
attached to a program. The ID field contains the GDB identifier
of the thread group. The PID field contains process identifier,
specific to the operating system.

`=thread-group-exited,id="ID"[,exit-code="CODE"]'
A thread group is no longer associated with a running program,
either because the program has exited, or because it was detached
from. The ID field contains the GDB identifier of the thread
group. The CODE field is the exit code of the inferior; it exists
only when the inferior exited with some code.

`=thread-created,id="ID",group-id="GID"'
`=thread-exited,id="ID",group-id="GID"'
A thread either was created, or has exited. The ID field contains
the global GDB identifier of the thread. The GID field identifies
the thread group this thread belongs to.

`=thread-selected,id="ID"[,frame="FRAME"]'
Informs that the selected thread or frame were changed. This
notification is not emitted as result of the `-thread-select' or
`-stack-select-frame' commands, but is emitted whenever an MI
command that is not documented to change the selected thread and
frame actually changes them. In particular, invoking, directly or
indirectly (via user-defined command), the CLI `thread' or `frame'
commands, will generate this notification. Changing the thread or
frame from another user interface (see *Note Interpreters::) will
also generate this notification.

The FRAME field is only present if the newly selected thread is
stopped. See *Note GDB/MI Frame Information:: for the format of
its value.

We suggest that in response to this notification, front ends
highlight the selected thread and cause subsequent commands to
apply to that thread.

`=library-loaded,...'
Reports that a new library file was loaded by the program. This
notification has 5 fields--ID, TARGET-NAME, HOST-NAME,
SYMBOLS-LOADED and RANGES. The ID field is an opaque identifier
of the library. For remote debugging case, TARGET-NAME and
HOST-NAME fields give the name of the library file on the target,
and on the host respectively. For native debugging, both those
fields have the same value. The SYMBOLS-LOADED field is emitted
only for backward compatibility and should not be relied on to
convey any useful information. The THREAD-GROUP field, if
present, specifies the id of the thread group in whose context the
library was loaded. If the field is absent, it means the library
was loaded in the context of all present thread groups. The
RANGES field specifies the ranges of addresses belonging to this
library.

`=library-unloaded,...'
Reports that a library was unloaded by the program. This
notification has 3 fields--ID, TARGET-NAME and HOST-NAME with the
same meaning as for the `=library-loaded' notification. The
THREAD-GROUP field, if present, specifies the id of the thread
group in whose context the library was unloaded. If the field is
absent, it means the library was unloaded in the context of all
present thread groups.

`=traceframe-changed,num=TFNUM,tracepoint=TPNUM'
`=traceframe-changed,end'
Reports that the trace frame was changed and its new number is
TFNUM. The number of the tracepoint associated with this trace
frame is TPNUM.

`=tsv-created,name=NAME,initial=INITIAL'
Reports that the new trace state variable NAME is created with
initial value INITIAL.

`=tsv-deleted,name=NAME'
`=tsv-deleted'
Reports that the trace state variable NAME is deleted or all trace
state variables are deleted.

`=tsv-modified,name=NAME,initial=INITIAL[,current=CURRENT]'
Reports that the trace state variable NAME is modified with the
initial value INITIAL. The current value CURRENT of trace state
variable is optional and is reported if the current value of trace
state variable is known.

`=breakpoint-created,bkpt={...}'
`=breakpoint-modified,bkpt={...}'
`=breakpoint-deleted,id=NUMBER'
Reports that a breakpoint was created, modified, or deleted,
respectively. Only user-visible breakpoints are reported to the MI
user.

The BKPT argument is of the same form as returned by the various
breakpoint commands; *Note GDB/MI Breakpoint Commands::. The
NUMBER is the ordinal number of the breakpoint.

Note that if a breakpoint is emitted in the result record of a
command, then it will not also be emitted in an async record.

`=record-started,thread-group="ID",method="METHOD"[,format="FORMAT"]'
`=record-stopped,thread-group="ID"'
Execution log recording was either started or stopped on an
inferior. The ID is the GDB identifier of the thread group
corresponding to the affected inferior.

The METHOD field indicates the method used to record execution.
If the method in use supports multiple recording formats, FORMAT
will be present and contain the currently used format. *Note
Process Record and Replay::, for existing method and format values.

`=cmd-param-changed,param=PARAM,value=VALUE'
Reports that a parameter of the command `set PARAM' is changed to
VALUE. In the multi-word `set' command, the PARAM is the whole
parameter list to `set' command. For example, In command `set
check type on', PARAM is `check type' and VALUE is `on'.

`=memory-changed,thread-group=ID,addr=ADDR,len=LEN[,type="code"]'
Reports that bytes from ADDR to DATA + LEN were written in an
inferior. The ID is the identifier of the thread group
corresponding to the affected inferior. The optional
`type="code"' part is reported if the memory written to holds
executable code.

File: gdb.info, Node: GDB/MI Breakpoint Information, Next: GDB/MI Frame Information, Prev: GDB/MI Async Records, Up: GDB/MI Output Records

27.5.4 GDB/MI Breakpoint Information
------------------------------------

When GDB reports information about a breakpoint, a tracepoint, a
watchpoint, or a catchpoint, it uses a tuple with the following fields:

`number'
The breakpoint number.

`type'
The type of the breakpoint. For ordinary breakpoints this will be
`breakpoint', but many values are possible.

`catch-type'
If the type of the breakpoint is `catchpoint', then this indicates
the exact type of catchpoint.

`disp'
This is the breakpoint disposition--either `del', meaning that the
breakpoint will be deleted at the next stop, or `keep', meaning
that the breakpoint will not be deleted.

`enabled'
This indicates whether the breakpoint is enabled, in which case the
value is `y', or disabled, in which case the value is `n'. Note
that this is not the same as the field `enable'.

`addr'
The address of the breakpoint. This may be a hexadecimal number,
giving the address; or the string `<PENDING>', for a pending
breakpoint; or the string `<MULTIPLE>', for a breakpoint with
multiple locations. This field will not be present if no address
can be determined. For example, a watchpoint does not have an
address.

`addr_flags'
Optional field containing any flags related to the address. These
flags are architecture-dependent; see *Note Architectures:: for
their meaning for a particular CPU.

`func'
If known, the function in which the breakpoint appears. If not
known, this field is not present.

`filename'
The name of the source file which contains this function, if known.
If not known, this field is not present.

`fullname'
The full file name of the source file which contains this
function, if known. If not known, this field is not present.

`line'
The line number at which this breakpoint appears, if known. If
not known, this field is not present.

`at'
If the source file is not known, this field may be provided. If
provided, this holds the address of the breakpoint, possibly
followed by a symbol name.

`pending'
If this breakpoint is pending, this field is present and holds the
text used to set the breakpoint, as entered by the user.

`evaluated-by'
Where this breakpoint's condition is evaluated, either `host' or
`target'.

`thread'
If this is a thread-specific breakpoint, then this identifies the
thread in which the breakpoint can trigger.

`inferior'
If this is an inferior-specific breakpoint, this this identifies
the inferior in which the breakpoint can trigger.

`task'
If this breakpoint is restricted to a particular Ada task, then
this field will hold the task identifier.

`cond'
If the breakpoint is conditional, this is the condition expression.

`ignore'
The ignore count of the breakpoint.

`enable'
The enable count of the breakpoint.

`traceframe-usage'
FIXME.

`static-tracepoint-marker-string-id'
For a static tracepoint, the name of the static tracepoint marker.

`mask'
For a masked watchpoint, this is the mask.

`pass'
A tracepoint's pass count.

`original-location'
The location of the breakpoint as originally specified by the user.
This field is optional.

`times'
The number of times the breakpoint has been hit.

`installed'
This field is only given for tracepoints. This is either `y',
meaning that the tracepoint is installed, or `n', meaning that it
is not.

`what'
Some extra data, the exact contents of which are type-dependent.

`locations'
This field is present if the breakpoint has multiple locations.
It is also exceptionally present if the breakpoint is enabled and
has a single, disabled location.

The value is a list of locations. The format of a location is
described below.

A location in a multi-location breakpoint is represented as a tuple
with the following fields:

`number'
The location number as a dotted pair, like `1.2'. The first digit
is the number of the parent breakpoint. The second digit is the
number of the location within that breakpoint.

`enabled'
There are three possible values, with the following meanings:
`y'
The location is enabled.

`n'
The location is disabled by the user.

`N'
The location is disabled because the breakpoint condition is
invalid at this location.

`addr'
The address of this location as an hexadecimal number.

`addr_flags'
Optional field containing any flags related to the address. These
flags are architecture-dependent; see *Note Architectures:: for
their meaning for a particular CPU.

`func'
If known, the function in which the location appears. If not
known, this field is not present.

`file'
The name of the source file which contains this location, if known.
If not known, this field is not present.

`fullname'
The full file name of the source file which contains this
location, if known. If not known, this field is not present.

`line'
The line number at which this location appears, if known. If not
known, this field is not present.

`thread-groups'
The thread groups this location is in.

For example, here is what the output of `-break-insert' (*note
GDB/MI Breakpoint Commands::) might be:

-> -break-insert main
<- ^done,bkpt={number="1",type="breakpoint",disp="keep",
enabled="y",addr="0x08048564",func="main",file="myprog.c",
fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
times="0"}
<- (gdb)

File: gdb.info, Node: GDB/MI Frame Information, Next: GDB/MI Thread Information, Prev: GDB/MI Breakpoint Information, Up: GDB/MI Output Records

27.5.5 GDB/MI Frame Information
-------------------------------

Response from many MI commands includes an information about stack
frame. This information is a tuple that may have the following fields:

`level'
The level of the stack frame. The innermost frame has the level of
zero. This field is always present.

`func'
The name of the function corresponding to the frame. This field
may be absent if GDB is unable to determine the function name.

`addr'
The code address for the frame. This field is always present.

`addr_flags'
Optional field containing any flags related to the address. These
flags are architecture-dependent; see *Note Architectures:: for
their meaning for a particular CPU.

`file'
The name of the source files that correspond to the frame's code
address. This field may be absent.

`line'
The source line corresponding to the frames' code address. This
field may be absent.

`from'
The name of the binary file (either executable or shared library)
the corresponds to the frame's code address. This field may be
absent.

File: gdb.info, Node: GDB/MI Thread Information, Next: GDB/MI Ada Exception Information, Prev: GDB/MI Frame Information, Up: GDB/MI Output Records

27.5.6 GDB/MI Thread Information
--------------------------------

Whenever GDB has to report an information about a thread, it uses a
tuple with the following fields. The fields are always present unless
stated otherwise.

`id'
The global numeric id assigned to the thread by GDB.

`target-id'
The target-specific string identifying the thread.

`details'
Additional information about the thread provided by the target.
It is supposed to be human-readable and not interpreted by the
frontend. This field is optional.

`name'
The name of the thread. If the user specified a name using the
`thread name' command, then this name is given. Otherwise, if GDB
can extract the thread name from the target, then that name is
given. If GDB cannot find the thread name, then this field is
omitted.

`state'
The execution state of the thread, either `stopped' or `running',
depending on whether the thread is presently running.

`frame'
The stack frame currently executing in the thread. This field is
only present if the thread is stopped. Its format is documented in
*Note GDB/MI Frame Information::.

`core'
The value of this field is an integer number of the processor core
the thread was last seen on. This field is optional.

File: gdb.info, Node: GDB/MI Ada Exception Information, Prev: GDB/MI Thread Information, Up: GDB/MI Output Records

27.5.7 GDB/MI Ada Exception Information
---------------------------------------

Whenever a `*stopped' record is emitted because the program stopped
after hitting an exception catchpoint (*note Set Catchpoints::), GDB
provides the name of the exception that was raised via the
`exception-name' field. Also, for exceptions that were raised with an
exception message, GDB provides that message via the
`exception-message' field.

File: gdb.info, Node: GDB/MI Simple Examples, Next: GDB/MI Command Description Format, Prev: GDB/MI Output Records, Up: GDB/MI

27.6 Simple Examples of GDB/MI Interaction
==========================================

This subsection presents several simple examples of interaction using
the GDB/MI interface. In these examples, `->' means that the following
line is passed to GDB/MI as input, while `<-' means the output received
from GDB/MI.

Note the line breaks shown in the examples are here only for
readability, they don't appear in the real output.

Setting a Breakpoint
--------------------

Setting a breakpoint generates synchronous output which contains
detailed information of the breakpoint.

-> -break-insert main
<- ^done,bkpt={number="1",type="breakpoint",disp="keep",
enabled="y",addr="0x08048564",func="main",file="myprog.c",
fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
times="0"}
<- (gdb)

Program Execution
-----------------

Program execution generates asynchronous records and MI gives the
reason that execution stopped.

-> -exec-run
<- ^running
<- (gdb)
<- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
frame={addr="0x08048564",func="main",
args=[{name="argc",value="1"},{name="argv",value="0xbfc4d4d4"}],
file="myprog.c",fullname="/home/nickrob/myprog.c",line="68",
arch="i386:x86_64"}
<- (gdb)
-> -exec-continue
<- ^running
<- (gdb)
<- *stopped,reason="exited-normally"
<- (gdb)

Quitting GDB
------------

Quitting GDB just prints the result class `^exit'.

-> (gdb)
<- -gdb-exit
<- ^exit

Please note that `^exit' is printed immediately, but it might take
some time for GDB to actually exit. During that time, GDB performs
necessary cleanups, including killing programs being debugged or
disconnecting from debug hardware, so the frontend should wait till GDB
exits and should only forcibly kill GDB if it fails to exit in
reasonable time.

A Bad Command
-------------

Here's what happens if you pass a non-existent command:

-> -rubbish
<- ^error,msg="Undefined MI command: rubbish"
<- (gdb)

File: gdb.info, Node: GDB/MI Command Description Format, Next: GDB/MI Breakpoint Commands, Prev: GDB/MI Simple Examples, Up: GDB/MI

27.7 GDB/MI Command Description Format
======================================

The remaining sections describe blocks of commands. Each block of
commands is laid out in a fashion similar to this section.

Motivation
----------

The motivation for this collection of commands.

Introduction
------------

A brief introduction to this collection of commands as a whole.

Commands
--------

For each command in the block, the following is described:

Synopsis
.......

-command ARGS...

Result
.....

GDB Command
..........

The corresponding GDB CLI command(s), if any.

Example
......

Example(s) formatted for readability. Some of the described commands
have not been implemented yet and these are labeled N.A. (not
available).

File: gdb.info, Node: GDB/MI Breakpoint Commands, Next: GDB/MI Catchpoint Commands, Prev: GDB/MI Command Description Format, Up: GDB/MI

27.8 GDB/MI Breakpoint Commands
===============================

This section documents GDB/MI commands for manipulating breakpoints.

The `-break-after' Command
--------------------------

Synopsis
.......

-break-after NUMBER COUNT

The breakpoint number NUMBER is not in effect until it has been hit
COUNT times. To see how this is reflected in the output of the
`-break-list' command, see the description of the `-break-list' command
below.

GDB Command
..........

The corresponding GDB command is `ignore'.

Example
......

(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",
enabled="y",addr="0x000100d0",func="main",file="hello.c",
fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
times="0"}
(gdb)
-break-after 1 3
~
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
line="5",thread-groups=["i1"],times="0",ignore="3"}]}
(gdb)

The `-break-commands' Command
-----------------------------

Synopsis
.......

-break-commands NUMBER [ COMMAND1 ... COMMANDN ]

Specifies the CLI commands that should be executed when breakpoint
NUMBER is hit. The parameters COMMAND1 to COMMANDN are the commands.
If no command is specified, any previously-set commands are cleared.
*Note Break Commands::. Typical use of this functionality is tracing a
program, that is, printing of values of some variables whenever
breakpoint is hit and then continuing.

GDB Command
..........

The corresponding GDB command is `commands'.

Example
......

(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",
enabled="y",addr="0x000100d0",func="main",file="hello.c",
fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
times="0"}
(gdb)
-break-commands 1 "print v" "continue"
^done
(gdb)

The `-break-condition' Command
------------------------------

Synopsis
.......

-break-condition [ --force ] NUMBER [ EXPR ]

Breakpoint NUMBER will stop the program only if the condition in
EXPR is true. The condition becomes part of the `-break-list' output
(see the description of the `-break-list' command below). If the
`--force' flag is passed, the condition is forcibly defined even when
it is invalid for all locations of breakpoint NUMBER. If the EXPR
argument is omitted, breakpoint NUMBER becomes unconditional.

GDB Command
..........

The corresponding GDB command is `condition'.

Example
......

(gdb)
-break-condition 1 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
line="5",cond="1",thread-groups=["i1"],times="0",ignore="3"}]}
(gdb)

The `-break-delete' Command
---------------------------

Synopsis
.......

-break-delete ( BREAKPOINT )+

Delete the breakpoint(s) whose number(s) are specified in the
argument list. This is obviously reflected in the breakpoint list.

GDB Command
..........

The corresponding GDB command is `delete'.

Example
......

(gdb)
-break-delete 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)

The `-break-disable' Command
----------------------------

Synopsis
.......

-break-disable ( BREAKPOINT )+

Disable the named BREAKPOINT(s). The field `enabled' in the break
list is now set to `n' for the named BREAKPOINT(s).

GDB Command
..........

The corresponding GDB command is `disable'.

Example
......

(gdb)
-break-disable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n",
addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
line="5",thread-groups=["i1"],times="0"}]}
(gdb)

The `-break-enable' Command
---------------------------

Synopsis
.......

-break-enable ( BREAKPOINT )+

Enable (previously disabled) BREAKPOINT(s).

GDB Command
..........

The corresponding GDB command is `enable'.

Example
......

(gdb)
-break-enable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
line="5",thread-groups=["i1"],times="0"}]}
(gdb)

The `-break-info' Command
-------------------------

Synopsis
.......

-break-info BREAKPOINT

Get information about a single breakpoint.

The result is a table of breakpoints. *Note GDB/MI Breakpoint
Information::, for details on the format of each breakpoint in the
table.

GDB Command
..........

The corresponding GDB command is `info break BREAKPOINT'.

Example
......

N.A.

The `-break-insert' Command
---------------------------

Synopsis
.......

-break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ] [ --qualified ]
[ -c CONDITION ] [ --force-condition ] [ -i IGNORE-COUNT ]
[ -p THREAD-ID ] [ -g THREAD-GROUP-ID ] [ LOCSPEC ]

If specified, LOCSPEC, can be one of:

LINESPEC LOCATION
A linespec location. *Note Linespec Locations::.

EXPLICIT LOCATION
An explicit location. GDB/MI explicit locations are analogous to
the CLI's explicit locations using the option names listed below.
*Note Explicit Locations::.

`--source FILENAME'
The source file name of the location. This option requires
the use of either `--function' or `--line'.

`--function FUNCTION'
The name of a function or method.

`--label LABEL'
The name of a label.

`--line LINEOFFSET'
An absolute or relative line offset from the start of the
location.

ADDRESS LOCATION
An address location, *ADDRESS. *Note Address Locations::.

The possible optional parameters of this command are:

`-t'
Insert a temporary breakpoint.

`-h'
Insert a hardware breakpoint.

`-f'
If LOCSPEC cannot be resolved (for example if it refers to unknown
files or functions), create a pending breakpoint. Without this
flag, GDB will report an error, and won't create a breakpoint, if
LOCSPEC cannot be parsed.

`-d'
Create a disabled breakpoint.

`-a'
Create a tracepoint. *Note Tracepoints::. When this parameter is
used together with `-h', a fast tracepoint is created.

`-c CONDITION'
Make the breakpoint conditional on CONDITION.

`--force-condition'
Forcibly define the breakpoint even if the condition is invalid at
all of the breakpoint locations.

`-i IGNORE-COUNT'
Initialize the IGNORE-COUNT.

`-p THREAD-ID'
Restrict the breakpoint to the thread with the specified global
THREAD-ID. THREAD-ID must be a valid thread-id at the time the
breakpoint is requested. Breakpoints created with a THREAD-ID
will automatically be deleted when the corresponding thread exits.

`-g THREAD-GROUP-ID'
Restrict the breakpoint to the thread group with the specified
THREAD-GROUP-ID.

`--qualified'
This option makes GDB interpret a function name specified as a
complete fully-qualified name.

Result
.....

*Note GDB/MI Breakpoint Information::, for details on the format of the
resulting breakpoint.

Note: this format is open to change.

GDB Command
..........

The corresponding GDB commands are `break', `tbreak', `hbreak', and
`thbreak'.

Example
......

(gdb)
-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",
fullname="/home/foo/recursive2.c,line="4",thread-groups=["i1"],
times="0"}
(gdb)
-break-insert -t foo
^done,bkpt={number="2",addr="0x00010774",file="recursive2.c",
fullname="/home/foo/recursive2.c,line="11",thread-groups=["i1"],
times="0"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x0001072c", func="main",file="recursive2.c",
fullname="/home/foo/recursive2.c,"line="4",thread-groups=["i1"],
times="0"},
bkpt={number="2",type="breakpoint",disp="del",enabled="y",
addr="0x00010774",func="foo",file="recursive2.c",
fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"],
times="0"}]}
(gdb)

The `-dprintf-insert' Command
-----------------------------

Synopsis
.......

-dprintf-insert [ -t ] [ -f ] [ -d ] [ --qualified ]
[ -c CONDITION ] [--force-condition] [ -i IGNORE-COUNT ]
[ -p THREAD-ID ] [ LOCSPEC ] FORMAT
[ ARGUMENT... ]

Insert a new dynamic print breakpoint at the given location. *Note
Dynamic Printf::. FORMAT is the format to use, and any remaining
arguments are passed as expressions to substitute.

If supplied, LOCSPEC and `--qualified' may be specified the same way as
for the `-break-insert' command. *Note -break-insert::.

The possible optional parameters of this command are:

`-t'
Insert a temporary breakpoint.

`-f'
If LOCSPEC cannot be parsed (for example, if it refers to unknown
files or functions), create a pending breakpoint. Without this
flag, GDB will report an error, and won't create a breakpoint, if
LOCSPEC cannot be parsed.

`-d'
Create a disabled breakpoint.

`-c CONDITION'
Make the breakpoint conditional on CONDITION.

`--force-condition'
Forcibly define the breakpoint even if the condition is invalid at
all of the breakpoint locations.

`-i IGNORE-COUNT'
Set the ignore count of the breakpoint (*note ignore count:
Conditions.) to IGNORE-COUNT.

`-p THREAD-ID'
Restrict the breakpoint to the thread with the specified global
THREAD-ID.

Result
.....

*Note GDB/MI Breakpoint Information::, for details on the format of the
resulting breakpoint.

GDB Command
..........

The corresponding GDB command is `dprintf'.

Example
......

(gdb)
4-dprintf-insert foo "At foo entry\n"
4^done,bkpt={number="1",type="dprintf",disp="keep",enabled="y",
addr="0x000000000040061b",func="foo",file="mi-dprintf.c",
fullname="mi-dprintf.c",line="25",thread-groups=["i1"],
times="0",script=["printf \"At foo entry\\n\"","continue"],
original-location="foo"}
(gdb)
5-dprintf-insert 26 "arg=%d, g=%d\n" arg g
5^done,bkpt={number="2",type="dprintf",disp="keep",enabled="y",
addr="0x000000000040062a",func="foo",file="mi-dprintf.c",
fullname="mi-dprintf.c",line="26",thread-groups=["i1"],
times="0",script=["printf \"arg=%d, g=%d\\n\", arg, g","continue"],
original-location="mi-dprintf.c:26"}
(gdb)

The `-break-list' Command
-------------------------

Synopsis
.......

-break-list

Displays the list of inserted breakpoints, showing the following
fields:

`Number'
number of the breakpoint

`Type'
type of the breakpoint: `breakpoint' or `watchpoint'

`Disposition'
should the breakpoint be deleted or disabled when it is hit: `keep'
or `nokeep'

`Enabled'
is the breakpoint enabled or no: `y' or `n'

`Address'
memory location at which the breakpoint is set

`What'
logical location of the breakpoint, expressed by function name,
file name, line number

`Thread-groups'
list of thread groups to which this breakpoint applies

`Times'
number of times the breakpoint has been hit

If there are no breakpoints, watchpoints, tracepoints, or
catchpoints, the `BreakpointTable' `body' field is an empty list.

GDB Command
..........

The corresponding GDB command is `info break'.

Example
......

(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x000100d0",func="main",file="hello.c",line="5",thread-groups=["i1"],
times="0"},
bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
line="13",thread-groups=["i1"],times="0"}]}
(gdb)

Here's an example of the result when there are no breakpoints:

(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)

The `-break-passcount' Command
------------------------------

Synopsis
.......

-break-passcount TRACEPOINT-NUMBER PASSCOUNT

Set the passcount for tracepoint TRACEPOINT-NUMBER to PASSCOUNT. If
the breakpoint referred to by TRACEPOINT-NUMBER is not a tracepoint,
error is emitted. This corresponds to CLI command `passcount'.

The `-break-watch' Command
--------------------------

Synopsis
.......

-break-watch [ -a | -r ]

Create a watchpoint. With the `-a' option it will create an
"access" watchpoint, i.e., a watchpoint that triggers either on a read
from or on a write to the memory location. With the `-r' option, the
watchpoint created is a "read" watchpoint, i.e., it will trigger only
when the memory location is accessed for reading. Without either of
the options, the watchpoint created is a regular watchpoint, i.e., it
will trigger when the memory location is accessed for writing. *Note
Setting Watchpoints: Set Watchpoints.

Note that `-break-list' will report a single list of watchpoints and
breakpoints inserted.

GDB Command
..........

The corresponding GDB commands are `watch', `awatch', and `rwatch'.

Example
......

Setting a watchpoint on a variable in the `main' function:

(gdb)
-break-watch x
^done,wpt={number="2",exp="x"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt={number="2",exp="x"},
value={old="-268439212",new="55"},
frame={func="main",args=[],file="recursive2.c",
fullname="/home/foo/bar/recursive2.c",line="5",arch="i386:x86_64"}
(gdb)

Setting a watchpoint on a variable local to a function. GDB will
stop the program execution twice: first for the variable changing
value, then for the watchpoint going out of scope.

(gdb)
-break-watch C
^done,wpt={number="5",exp="C"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",
wpt={number="5",exp="C"},value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13",
arch="i386:x86_64"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-scope",wpnum="5",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}
(gdb)

Listing breakpoints and watchpoints, at different points in the
program execution. Note that once the watchpoint goes out of scope, it
is deleted.

(gdb)
-break-watch C
^done,wpt={number="2",exp="C"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",thread-groups=["i1"],
times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
enabled="y",addr="",what="C",thread-groups=["i1"],times="0"}]}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt={number="2",exp="C"},
value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13",
arch="i386:x86_64"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"],
times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
enabled="y",addr="",what="C",thread-groups=["i1"],times="-5"}]}
(gdb)
-exec-continue
^running
^done,reason="watchpoint-scope",wpnum="2",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="10",alignment="-1",col_name="addr",colhdr="Address"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
thread-groups=["i1"],times="1"}]}
(gdb)

File: gdb.info, Node: GDB/MI Catchpoint Commands, Next: GDB/MI Program Context, Prev: GDB/MI Breakpoint Commands, Up: GDB/MI

27.9 GDB/MI Catchpoint Commands
===============================

This section documents GDB/MI commands for manipulating catchpoints.

* Menu:

* Shared Library GDB/MI Catchpoint Commands::
* Ada Exception GDB/MI Catchpoint Commands::
* C++ Exception GDB/MI Catchpoint Commands::

File: gdb.info, Node: Shared Library GDB/MI Catchpoint Commands, Next: Ada Exception GDB/MI Catchpoint Commands, Up: GDB/MI Catchpoint Commands

27.9.1 Shared Library GDB/MI Catchpoints
----------------------------------------

The `-catch-load' Command
-------------------------

Synopsis
.......

-catch-load [ -t ] [ -d ] REGEXP

Add a catchpoint for library load events. If the `-t' option is
used, the catchpoint is a temporary one (*note Setting Breakpoints: Set
Breaks.). If the `-d' option is used, the catchpoint is created in a
disabled state. The `regexp' argument is a regular expression used to
match the name of the loaded library.

GDB Command
..........

The corresponding GDB command is `catch load'.

Example
......

-catch-load -t foo.so
^done,bkpt={number="1",type="catchpoint",disp="del",enabled="y",
what="load of library matching foo.so",catch-type="load",times="0"}
(gdb)

The `-catch-unload' Command
---------------------------

Synopsis
.......

-catch-unload [ -t ] [ -d ] REGEXP

Add a catchpoint for library unload events. If the `-t' option is
used, the catchpoint is a temporary one (*note Setting Breakpoints: Set
Breaks.). If the `-d' option is used, the catchpoint is created in a
disabled state. The `regexp' argument is a regular expression used to
match the name of the unloaded library.

GDB Command
..........

The corresponding GDB command is `catch unload'.

Example
......

-catch-unload -d bar.so
^done,bkpt={number="2",type="catchpoint",disp="keep",enabled="n",
what="load of library matching bar.so",catch-type="unload",times="0"}
(gdb)

File: gdb.info, Node: Ada Exception GDB/MI Catchpoint Commands, Next: C++ Exception GDB/MI Catchpoint Commands, Prev: Shared Library GDB/MI Catchpoint Commands, Up: GDB/MI Catchpoint Commands

27.9.2 Ada Exception GDB/MI Catchpoints
---------------------------------------

The following GDB/MI commands can be used to create catchpoints that
stop the execution when Ada exceptions are being raised.

The `-catch-assert' Command
---------------------------

Synopsis
.......

-catch-assert [ -c CONDITION] [ -d ] [ -t ]

Add a catchpoint for failed Ada assertions.

The possible optional parameters for this command are:

`-c CONDITION'
Make the catchpoint conditional on CONDITION.

`-d'
Create a disabled catchpoint.

`-t'
Create a temporary catchpoint.

GDB Command
..........

The corresponding GDB command is `catch assert'.

Example
......

-catch-assert
^done,bkptno="5",bkpt={number="5",type="breakpoint",disp="keep",
enabled="y",addr="0x0000000000404888",what="failed Ada assertions",
thread-groups=["i1"],times="0",
original-location="__gnat_debug_raise_assert_failure"}
(gdb)

The `-catch-exception' Command
------------------------------

Synopsis
.......

-catch-exception [ -c CONDITION] [ -d ] [ -e EXCEPTION-NAME ]
[ -t ] [ -u ]

Add a catchpoint stopping when Ada exceptions are raised. By
default, the command stops the program when any Ada exception gets
raised. But it is also possible, by using some of the optional
parameters described below, to create more selective catchpoints.

The possible optional parameters for this command are:

`-c CONDITION'
Make the catchpoint conditional on CONDITION.

`-d'
Create a disabled catchpoint.

`-e EXCEPTION-NAME'
Only stop when EXCEPTION-NAME is raised. This option cannot be
used combined with `-u'.

`-t'
Create a temporary catchpoint.

`-u'
Stop only when an unhandled exception gets raised. This option
cannot be used combined with `-e'.

GDB Command
..........

The corresponding GDB commands are `catch exception' and `catch
exception unhandled'.

Example
......

-catch-exception -e Program_Error
^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep",
enabled="y",addr="0x0000000000404874",
what="`Program_Error' Ada exception", thread-groups=["i1"],
times="0",original-location="__gnat_debug_raise_exception"}
(gdb)

The `-catch-handlers' Command
-----------------------------

Synopsis
.......

-catch-handlers [ -c CONDITION] [ -d ] [ -e EXCEPTION-NAME ]
[ -t ]

Add a catchpoint stopping when Ada exceptions are handled. By
default, the command stops the program when any Ada exception gets
handled. But it is also possible, by using some of the optional
parameters described below, to create more selective catchpoints.

The possible optional parameters for this command are:

`-c CONDITION'
Make the catchpoint conditional on CONDITION.

`-d'
Create a disabled catchpoint.

`-e EXCEPTION-NAME'
Only stop when EXCEPTION-NAME is handled.

`-t'
Create a temporary catchpoint.

GDB Command
..........

The corresponding GDB command is `catch handlers'.

Example
......

-catch-handlers -e Constraint_Error
^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep",
enabled="y",addr="0x0000000000402f68",
what="`Constraint_Error' Ada exception handlers",thread-groups=["i1"],
times="0",original-location="__gnat_begin_handler"}
(gdb)

File: gdb.info, Node: C++ Exception GDB/MI Catchpoint Commands, Prev: Ada Exception GDB/MI Catchpoint Commands, Up: GDB/MI Catchpoint Commands

27.9.3 C++ Exception GDB/MI Catchpoints
---------------------------------------

The following GDB/MI commands can be used to create catchpoints that
stop the execution when C++ exceptions are being throw, rethrown, or
caught.

The `-catch-throw' Command
--------------------------

Synopsis
.......

-catch-throw [ -t ] [ -r REGEXP]

Stop when the debuggee throws a C++ exception. If REGEXP is given,
then only exceptions whose type matches the regular expression will be
caught.

If `-t' is given, then the catchpoint is enabled only for one stop,
the catchpoint is automatically deleted after stopping once for the
event.

GDB Command
..........

The corresponding GDB commands are `catch throw' and `tcatch throw'
(*note Set Catchpoints::).

Example
......

-catch-throw -r exception_type
^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",
what="exception throw",catch-type="throw",
thread-groups=["i1"],
regexp="exception_type",times="0"}
(gdb)
-exec-run
^running
(gdb)
~"\n"
~"Catchpoint 1 (exception thrown), 0x00007ffff7ae00ed
in __cxa_throw () from /lib64/libstdc++.so.6\n"
*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",
frame={addr="0x00007ffff7ae00ed",func="__cxa_throw",
args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"
(gdb)

The `-catch-rethrow' Command
----------------------------

Synopsis
.......

-catch-rethrow [ -t ] [ -r REGEXP]

Stop when a C++ exception is re-thrown. If REGEXP is given, then
only exceptions whose type matches the regular expression will be
caught.

If `-t' is given, then the catchpoint is enabled only for one stop,
the catchpoint is automatically deleted after the first event is caught.

GDB Command
..........

The corresponding GDB commands are `catch rethrow' and `tcatch rethrow'
(*note Set Catchpoints::).

Example
......

-catch-rethrow -r exception_type
^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",
what="exception rethrow",catch-type="rethrow",
thread-groups=["i1"],
regexp="exception_type",times="0"}
(gdb)
-exec-run
^running
(gdb)
~"\n"
~"Catchpoint 1 (exception rethrown), 0x00007ffff7ae00ed
in __cxa_rethrow () from /lib64/libstdc++.so.6\n"
*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",
frame={addr="0x00007ffff7ae00ed",func="__cxa_rethrow",
args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"
(gdb)

The `-catch-catch' Command
--------------------------

Synopsis
.......

-catch-catch [ -t ] [ -r REGEXP]

Stop when the debuggee catches a C++ exception. If REGEXP is given,
then only exceptions whose type matches the regular expression will be
caught.

If `-t' is given, then the catchpoint is enabled only for one stop,
the catchpoint is automatically deleted after the first event is caught.

GDB Command
..........

The corresponding GDB commands are `catch catch' and `tcatch catch'
(*note Set Catchpoints::).

Example
......

-catch-catch -r exception_type
^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",
what="exception catch",catch-type="catch",
thread-groups=["i1"],
regexp="exception_type",times="0"}
(gdb)
-exec-run
^running
(gdb)
~"\n"
~"Catchpoint 1 (exception caught), 0x00007ffff7ae00ed
in __cxa_begin_catch () from /lib64/libstdc++.so.6\n"
*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",
frame={addr="0x00007ffff7ae00ed",func="__cxa_begin_catch",
args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"
(gdb)

File: gdb.info, Node: GDB/MI Program Context, Next: GDB/MI Thread Commands, Prev: GDB/MI Catchpoint Commands, Up: GDB/MI

27.10 GDB/MI Program Context
=============================

The `-exec-arguments' Command
-----------------------------

Synopsis
.......

-exec-arguments ARGS

Set the inferior program arguments, to be used in the next
`-exec-run'.

GDB Command
..........

The corresponding GDB command is `set args'.

Example
......

(gdb)
-exec-arguments -v word
^done
(gdb)

The `-environment-cd' Command
-----------------------------

Synopsis
.......

-environment-cd PATHDIR

Set GDB's working directory.

GDB Command
..........

The corresponding GDB command is `cd'.

Example
......

(gdb)
-environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done
(gdb)

The `-environment-directory' Command
------------------------------------

Synopsis
.......

-environment-directory [ -r ] [ PATHDIR ]+

Add directories PATHDIR to beginning of search path for source files.
If the `-r' option is used, the search path is reset to the default
search path. If directories PATHDIR are supplied in addition to the
`-r' option, the search path is first reset and then addition occurs as
normal. Multiple directories may be specified, separated by blanks.
Specifying multiple directories in a single command results in the
directories added to the beginning of the search path in the same order
they were presented in the command. If blanks are needed as part of a
directory name, double-quotes should be used around the name. In the
command output, the path will show up separated by the system
directory-separator character. The directory-separator character must
not be used in any directory name. If no directories are specified,
the current search path is displayed.

GDB Command
..........

The corresponding GDB command is `dir'.

Example
......

(gdb)
-environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory ""
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory -r /home/jjohnstn/src/gdb /usr/src
^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
(gdb)
-environment-directory -r
^done,source-path="$cdir:$cwd"
(gdb)

The `-environment-path' Command
-------------------------------

Synopsis
.......

-environment-path [ -r ] [ PATHDIR ]+

Add directories PATHDIR to beginning of search path for object files.
If the `-r' option is used, the search path is reset to the original
search path that existed at gdb start-up. If directories PATHDIR are
supplied in addition to the `-r' option, the search path is first reset
and then addition occurs as normal. Multiple directories may be
specified, separated by blanks. Specifying multiple directories in a
single command results in the directories added to the beginning of the
search path in the same order they were presented in the command. If
blanks are needed as part of a directory name, double-quotes should be
used around the name. In the command output, the path will show up
separated by the system directory-separator character. The
directory-separator character must not be used in any directory name.
If no directories are specified, the current path is displayed.

GDB Command
..........

The corresponding GDB command is `path'.

Example
......

(gdb)
-environment-path
^done,path="/usr/bin"
(gdb)
-environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
(gdb)
-environment-path -r /usr/local/bin
^done,path="/usr/local/bin:/usr/bin"
(gdb)

The `-environment-pwd' Command
------------------------------

Synopsis
.......

-environment-pwd

Show the current working directory.

GDB Command
..........

The corresponding GDB command is `pwd'.

Example
......

(gdb)
-environment-pwd
^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
(gdb)

File: gdb.info, Node: GDB/MI Thread Commands, Next: GDB/MI Ada Tasking Commands, Prev: GDB/MI Program Context, Up: GDB/MI

27.11 GDB/MI Thread Commands
============================

The `-thread-info' Command
--------------------------

Synopsis
.......

-thread-info [ THREAD-ID ]

Reports information about either a specific thread, if the THREAD-ID
parameter is present, or about all threads. THREAD-ID is the thread's
global thread ID. When printing information about all threads, also
reports the global ID of the current thread.

GDB Command
..........

The `info thread' command prints the same information about all threads.

Result
.....

The result contains the following attributes:

`threads'
A list of threads. The format of the elements of the list is
described in *Note GDB/MI Thread Information::.

`current-thread-id'
The global id of the currently selected thread. This field is
omitted if there is no selected thread (for example, when the
selected inferior is not running, and therefore has no threads) or
if a THREAD-ID argument was passed to the command.

Example
......

-thread-info
^done,threads=[
{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",
args=[]},state="running"},
{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
frame={level="0",addr="0x0804891f",func="foo",
args=[{name="i",value="10"}],
file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"},
state="running"}],
current-thread-id="1"
(gdb)

The `-thread-list-ids' Command
------------------------------

Synopsis
.......

-thread-list-ids

Produces a list of the currently known global GDB thread ids. At
the end of the list it also prints the total number of such threads.

This command is retained for historical reasons, the `-thread-info'
command should be used instead.

GDB Command
..........

Part of `info threads' supplies the same information.

Example
......

(gdb)
-thread-list-ids
^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"},
current-thread-id="1",number-of-threads="3"
(gdb)

The `-thread-select' Command
----------------------------

Synopsis
.......

-thread-select THREAD-ID

Make thread with global thread number THREAD-ID the current thread.
It prints the number of the new current thread, and the topmost frame
for that thread.

This command is deprecated in favor of explicitly using the
`--thread' option to each command.

GDB Command
..........

The corresponding GDB command is `thread'.

Example
......

(gdb)
-exec-next
^running
(gdb)
*stopped,reason="end-stepping-range",thread-id="2",line="187",
file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
(gdb)
-thread-list-ids
^done,
thread-ids={thread-id="3",thread-id="2",thread-id="1"},
number-of-threads="3"
(gdb)
-thread-select 3
^done,new-thread-id="3",
frame={level="0",func="vprintf",
args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""},
{name="arg",value="0x2"}],file="vprintf.c",line="31",arch="i386:x86_64"}
(gdb)

File: gdb.info, Node: GDB/MI Ada Tasking Commands, Next: GDB/MI Program Execution, Prev: GDB/MI Thread Commands, Up: GDB/MI

27.12 GDB/MI Ada Tasking Commands
=================================

The `-ada-task-info' Command
----------------------------

Synopsis
.......

-ada-task-info [ TASK-ID ]

Reports information about either a specific Ada task, if the TASK-ID
parameter is present, or about all Ada tasks.

GDB Command
..........

The `info tasks' command prints the same information about all Ada
tasks (*note Ada Tasks::).

Result
.....

The result is a table of Ada tasks. The following columns are defined
for each Ada task:

`current'
This field exists only for the current thread. It has the value
`*'.

`id'
The identifier that GDB uses to refer to the Ada task.

`task-id'
The identifier that the target uses to refer to the Ada task.

`thread-id'
The global thread identifier of the thread corresponding to the Ada
task.

This field should always exist, as Ada tasks are always implemented
on top of a thread. But if GDB cannot find this corresponding
thread for any reason, the field is omitted.

`parent-id'
This field exists only when the task was created by another task.
In this case, it provides the ID of the parent task.

`priority'
The base priority of the task.

`state'
The current state of the task. For a detailed description of the
possible states, see *Note Ada Tasks::.

`name'
The name of the task.

Example
......

-ada-task-info
^done,tasks={nr_rows="3",nr_cols="8",
hdr=[{width="1",alignment="-1",col_name="current",colhdr=""},
{width="3",alignment="1",col_name="id",colhdr="ID"},
{width="9",alignment="1",col_name="task-id",colhdr="TID"},
{width="4",alignment="1",col_name="thread-id",colhdr=""},
{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"},
{width="3",alignment="1",col_name="priority",colhdr="Pri"},
{width="22",alignment="-1",col_name="state",colhdr="State"},
{width="1",alignment="2",col_name="name",colhdr="Name"}],
body=[{current="*",id="1",task-id=" 644010",thread-id="1",priority="48",
state="Child Termination Wait",name="main_task"}]}
(gdb)

File: gdb.info, Node: GDB/MI Program Execution, Next: GDB/MI Stack Manipulation, Prev: GDB/MI Ada Tasking Commands, Up: GDB/MI

27.13 GDB/MI Program Execution
==============================

These are the asynchronous commands which generate the out-of-band
record `*stopped'. Currently GDB only really executes asynchronously
with remote targets and this interaction is mimicked in other cases.

The `-exec-continue' Command
----------------------------

Synopsis
.......

-exec-continue [--reverse] [--all|--thread-group N]

Resumes the execution of the inferior program, which will continue
to execute until it reaches a debugger stop event. If the `--reverse'
option is specified, execution resumes in reverse until it reaches a
stop event. Stop events may include
* breakpoints, watchpoints, tracepoints, or catchpoints

* signals or exceptions

* the end of the process (or its beginning under `--reverse')

* the end or beginning of a replay log if one is being used.
In all-stop mode (*note All-Stop Mode::), may resume only one
thread, or all threads, depending on the value of the
`scheduler-locking' variable. If `--all' is specified, all threads (in
all inferiors) will be resumed. The `--all' option is ignored in
all-stop mode. If the `--thread-group' options is specified, then all
threads in that thread group are resumed.

GDB Command
..........

The corresponding GDB corresponding is `continue'.

Example
......

-exec-continue
^running
(gdb)
@Hello world
*stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame={
func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
line="13",arch="i386:x86_64"}
(gdb)

For a `breakpoint-hit' stopped reason, when the breakpoint
encountered has multiple locations, the field `bkptno' is followed by
the field `locno'.

-exec-continue
^running
(gdb)
@Hello world
*stopped,reason="breakpoint-hit",disp="keep",bkptno="2",locno="3",frame={
func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
line="13",arch="i386:x86_64"}
(gdb)

The `-exec-finish' Command
--------------------------

Synopsis
.......

-exec-finish [--reverse]

Resumes the execution of the inferior program until the current
function is exited. Displays the results returned by the function. If
the `--reverse' option is specified, resumes the reverse execution of
the inferior program until the point where current function was called.

GDB Command
..........

The corresponding GDB command is `finish'.

Example
......

Function returning `void'.

-exec-finish
^running
(gdb)
@hello from foo
*stopped,reason="function-finished",frame={func="main",args=[],
file="hello.c",fullname="/home/foo/bar/hello.c",line="7",arch="i386:x86_64"}
(gdb)

Function returning other than `void'. The name of the internal GDB
variable storing the result is printed, together with the value itself.

-exec-finish
^running
(gdb)
*stopped,reason="function-finished",frame={addr="0x000107b0",func="foo",
args=[{name="a",value="1"],{name="b",value="9"}},
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
gdb-result-var="$1",return-value="0"
(gdb)

The `-exec-interrupt' Command
-----------------------------

Synopsis
.......

-exec-interrupt [--all|--thread-group N]

Interrupts the background execution of the target. Note how the
token associated with the stop message is the one for the execution
command that has been interrupted. The token for the interrupt itself
only appears in the `^done' output. If the user is trying to interrupt
a non-running program, an error message will be printed.

Note that when asynchronous execution is enabled, this command is
asynchronous just like other execution commands. That is, first the
`^done' response will be printed, and the target stop will be reported
after that using the `*stopped' notification.

In non-stop mode, only the context thread is interrupted by default.
All threads (in all inferiors) will be interrupted if the `--all'
option is specified. If the `--thread-group' option is specified, all
threads in that group will be interrupted.

GDB Command
..........

The corresponding GDB command is `interrupt'.

Example
......

(gdb)
111-exec-continue
111^running

(gdb)
222-exec-interrupt
222^done
(gdb)
111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
frame={addr="0x00010140",func="foo",args=[],file="try.c",
fullname="/home/foo/bar/try.c",line="13",arch="i386:x86_64"}
(gdb)

(gdb)
-exec-interrupt
^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
(gdb)

The `-exec-jump' Command
------------------------

Synopsis
.......

-exec-jump LOCSPEC

Resumes execution of the inferior program at the address to which
LOCSPEC resolves. *Note Location Specifications::, for a description
of the different forms of LOCSPEC.

GDB Command
..........

The corresponding GDB command is `jump'.

Example
......

-exec-jump foo.c:10
*running,thread-id="all"
^running

The `-exec-next' Command
------------------------

Synopsis
.......

-exec-next [--reverse]

Resumes execution of the inferior program, stopping when the
beginning of the next source line is reached.

If the `--reverse' option is specified, resumes reverse execution of
the inferior program, stopping at the beginning of the previous source
line. If you issue this command on the first line of a function, it
will take you back to the caller of that function, to the source line
where the function was called.

GDB Command
..........

The corresponding GDB command is `next'.

Example
......

-exec-next
^running
(gdb)
*stopped,reason="end-stepping-range",line="8",file="hello.c"
(gdb)

The `-exec-next-instruction' Command
------------------------------------

Synopsis
.......

-exec-next-instruction [--reverse]

Executes one machine instruction. If the instruction is a function
call, continues until the function returns. If the program stops at an
instruction in the middle of a source line, the address will be printed
as well.

If the `--reverse' option is specified, resumes reverse execution of
the inferior program, stopping at the previous instruction. If the
previously executed instruction was a return from another function, it
will continue to execute in reverse until the call to that function
(from the current stack frame) is reached.

GDB Command
..........

The corresponding GDB command is `nexti'.

Example
......

(gdb)
-exec-next-instruction
^running

(gdb)
*stopped,reason="end-stepping-range",
addr="0x000100d4",line="5",file="hello.c"
(gdb)

The `-exec-return' Command
--------------------------

Synopsis
.......

-exec-return

Makes current function return immediately. Doesn't execute the
inferior. Displays the new current frame.

GDB Command
..........

The corresponding GDB command is `return'.

Example
......

(gdb)
200-break-insert callee4
200^done,bkpt={number="1",addr="0x00010734",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"}
(gdb)
000-exec-run
000^running
(gdb)
000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
arch="i386:x86_64"}
(gdb)
205-break-delete
205^done
(gdb)
111-exec-return
111^done,frame={level="0",func="callee3",
args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}
(gdb)

The `-exec-run' Command
-----------------------

Synopsis
.......

-exec-run [ --all | --thread-group N ] [ --start ]

Starts execution of the inferior from the beginning. The inferior
executes until either a breakpoint is encountered or the program exits.
In the latter case the output will include an exit code, if the
program has exited exceptionally.

When neither the `--all' nor the `--thread-group' option is
specified, the current inferior is started. If the `--thread-group'
option is specified, it should refer to a thread group of type
`process', and that thread group will be started. If the `--all'
option is specified, then all inferiors will be started.

Using the `--start' option instructs the debugger to stop the
execution at the start of the inferior's main subprogram, following the
same behavior as the `start' command (*note Starting::).

GDB Command
..........

The corresponding GDB command is `run'.

Examples
.......

(gdb)
-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"}
(gdb)
-exec-run
^running
(gdb)
*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
frame={func="main",args=[],file="recursive2.c",
fullname="/home/foo/bar/recursive2.c",line="4",arch="i386:x86_64"}
(gdb)

Program exited normally:

(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited-normally"
(gdb)

Program exited exceptionally:

(gdb)
-exec-run
^running
(gdb)
x = 55
*stopped,reason="exited",exit-code="01"
(gdb)

Another way the program can terminate is if it receives a signal
such as `SIGINT'. In this case, GDB/MI displays this:

(gdb)
*stopped,reason="exited-signalled",signal-name="SIGINT",
signal-meaning="Interrupt"

The `-exec-step' Command
------------------------

Synopsis
.......

-exec-step [--reverse]

Resumes execution of the inferior program, stopping when the
beginning of the next source line is reached, if the next source line
is not a function call. If it is, stop at the first instruction of the
called function. If the `--reverse' option is specified, resumes
reverse execution of the inferior program, stopping at the beginning of
the previously executed source line.

GDB Command
..........

The corresponding GDB command is `step'.

Example
......

Stepping into a function:

-exec-step
^running
(gdb)
*stopped,reason="end-stepping-range",
frame={func="foo",args=[{name="a",value="10"},
{name="b",value="0"}],file="recursive2.c",
fullname="/home/foo/bar/recursive2.c",line="11",arch="i386:x86_64"}
(gdb)

Regular stepping:

-exec-step
^running
(gdb)
*stopped,reason="end-stepping-range",line="14",file="recursive2.c"
(gdb)

The `-exec-step-instruction' Command
------------------------------------

Synopsis
.......

-exec-step-instruction [--reverse]

Resumes the inferior which executes one machine instruction. If the
`--reverse' option is specified, resumes reverse execution of the
inferior program, stopping at the previously executed instruction. The
output, once GDB has stopped, will vary depending on whether we have
stopped in the middle of a source line or not. In the former case, the
address at which the program stopped will be printed as well.

GDB Command
..........

The corresponding GDB command is `stepi'.

Example
......

(gdb)
-exec-step-instruction
^running

(gdb)
*stopped,reason="end-stepping-range",
frame={func="foo",args=[],file="try.c",
fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"}
(gdb)
-exec-step-instruction
^running

(gdb)
*stopped,reason="end-stepping-range",
frame={addr="0x000100f4",func="foo",args=[],file="try.c",
fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"}
(gdb)

The `-exec-until' Command
-------------------------

Synopsis
.......

-exec-until [ LOCSPEC ]

Executes the inferior until it reaches the address to which LOCSPEC
resolves. If there is no argument, the inferior executes until it
reaches a source line greater than the current one. The reason for
stopping in this case will be `location-reached'.

GDB Command
..........

The corresponding GDB command is `until'.

Example
......

(gdb)
-exec-until recursive2.c:6
^running
(gdb)
x = 55
*stopped,reason="location-reached",frame={func="main",args=[],
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6",
arch="i386:x86_64"}
(gdb)

File: gdb.info, Node: GDB/MI Stack Manipulation, Next: GDB/MI Variable Objects, Prev: GDB/MI Program Execution, Up: GDB/MI

27.14 GDB/MI Stack Manipulation Commands
========================================

The `-enable-frame-filters' Command
-----------------------------------

-enable-frame-filters

GDB allows Python-based frame filters to affect the output of the MI
commands relating to stack traces. As there is no way to implement
this in a fully backward-compatible way, a front end must request that
this functionality be enabled.

Once enabled, this feature cannot be disabled.

Note that if Python support has not been compiled into GDB, this
command will still succeed (and do nothing).

The `-stack-info-frame' Command
-------------------------------

Synopsis
.......

-stack-info-frame

Get info on the selected frame.

GDB Command
..........

The corresponding GDB command is `info frame' or `frame' (without
arguments).

Example
......

(gdb)
-stack-info-frame
^done,frame={level="1",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17",
arch="i386:x86_64"}
(gdb)

The `-stack-info-depth' Command
-------------------------------

Synopsis
.......

-stack-info-depth [ MAX-DEPTH ]

Return the depth of the stack. If the integer argument MAX-DEPTH is
specified, do not count beyond MAX-DEPTH frames.

GDB Command
..........

There's no equivalent GDB command.

Example
......

For a stack with frame levels 0 through 11:

(gdb)
-stack-info-depth
^done,depth="12"
(gdb)
-stack-info-depth 4
^done,depth="4"
(gdb)
-stack-info-depth 12
^done,depth="12"
(gdb)
-stack-info-depth 11
^done,depth="11"
(gdb)
-stack-info-depth 13
^done,depth="12"
(gdb)

The `-stack-list-arguments' Command
-----------------------------------

Synopsis
.......

-stack-list-arguments [ --no-frame-filters ] [ --skip-unavailable ] PRINT-VALUES
[ LOW-FRAME HIGH-FRAME ]

Display a list of the arguments for the frames between LOW-FRAME and
HIGH-FRAME (inclusive). If LOW-FRAME and HIGH-FRAME are not provided,
list the arguments for the whole call stack. If the two arguments are
equal, show the single frame at the corresponding level. It is an
error if LOW-FRAME is larger than the actual number of frames. On the
other hand, HIGH-FRAME may be larger than the actual number of frames,
in which case only existing frames will be returned.

If PRINT-VALUES is 0 or `--no-values', print only the names of the
variables; if it is 1 or `--all-values', print also their values; and
if it is 2 or `--simple-values', print the name, type and value for
simple data types, and the name and type for arrays, structures and
unions. If the option `--no-frame-filters' is supplied, then Python
frame filters will not be executed.

If the `--skip-unavailable' option is specified, arguments that are
not available are not listed. Partially available arguments are still
displayed, however.

Use of this command to obtain arguments in a single frame is
deprecated in favor of the `-stack-list-variables' command.

GDB Command
..........

GDB does not have an equivalent command. `gdbtk' has a `gdb_get_args'
command which partially overlaps with the functionality of
`-stack-list-arguments'.

Example
......

(gdb)
-stack-list-frames
^done,
stack=[
frame={level="0",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
arch="i386:x86_64"},
frame={level="1",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17",
arch="i386:x86_64"},
frame={level="2",addr="0x0001078c",func="callee2",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22",
arch="i386:x86_64"},
frame={level="3",addr="0x000107b4",func="callee1",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27",
arch="i386:x86_64"},
frame={level="4",addr="0x000107e0",func="main",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32",
arch="i386:x86_64"}]
(gdb)
-stack-list-arguments 0
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",args=[name="strarg"]},
frame={level="2",args=[name="intarg",name="strarg"]},
frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 1
^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",
args=[{name="strarg",value="0x11940 \"A string argument.\""}]},
frame={level="2",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]},
{frame={level="3",args=[
{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""},
{name="fltarg",value="3.5"}]},
frame={level="4",args=[]}]
(gdb)
-stack-list-arguments 0 2 2
^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}]
(gdb)
-stack-list-arguments 1 2 2
^done,stack-args=[frame={level="2",
args=[{name="intarg",value="2"},
{name="strarg",value="0x11940 \"A string argument.\""}]}]
(gdb)

The `-stack-list-frames' Command
--------------------------------

Synopsis
.......

-stack-list-frames [ --no-frame-filters LOW-FRAME HIGH-FRAME ]

List the frames currently on the stack. For each frame it displays
the following info:

`LEVEL'
The frame number, 0 being the topmost frame, i.e., the innermost
function.

`ADDR'
The `$pc' value for that frame.

`FUNC'
Function name.

`FILE'
File name of the source file where the function lives.

`FULLNAME'
The full file name of the source file where the function lives.

`LINE'
Line number corresponding to the `$pc'.

`FROM'
The shared library where this function is defined. This is only
given if the frame's function is not known.

`ARCH'
Frame's architecture.

If invoked without arguments, this command prints a backtrace for the
whole stack. If given two integer arguments, it shows the frames whose
levels are between the two arguments (inclusive). If the two arguments
are equal, it shows the single frame at the corresponding level. It is
an error if LOW-FRAME is larger than the actual number of frames. On
the other hand, HIGH-FRAME may be larger than the actual number of
frames, in which case only existing frames will be returned. If the
option `--no-frame-filters' is supplied, then Python frame filters will
not be executed.

GDB Command
..........

The corresponding GDB commands are `backtrace' and `where'.

Example
......

Full stack backtrace:

(gdb)
-stack-list-frames
^done,stack=
[frame={level="0",addr="0x0001076c",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11",
arch="i386:x86_64"},
frame={level="1",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="2",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="6",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="7",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="8",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="9",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="10",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="11",addr="0x00010738",func="main",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4",
arch="i386:x86_64"}]
(gdb)

Show frames between LOW_FRAME and HIGH_FRAME:

(gdb)
-stack-list-frames 3 5
^done,stack=
[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"}]
(gdb)

Show a single frame:

(gdb)
-stack-list-frames 3 3
^done,stack=
[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",
arch="i386:x86_64"}]
(gdb)

The `-stack-list-locals' Command
--------------------------------

Synopsis
.......

-stack-list-locals [ --no-frame-filters ] [ --skip-unavailable ] PRINT-VALUES

Display the local variable names for the selected frame. If
PRINT-VALUES is 0 or `--no-values', print only the names of the
variables; if it is 1 or `--all-values', print also their values; and
if it is 2 or `--simple-values', print the name, type and value for
simple data types, and the name and type for arrays, structures and
unions. In this last case, a frontend can immediately display the
value of simple data types and create variable objects for other data
types when the user wishes to explore their values in more detail. If
the option `--no-frame-filters' is supplied, then Python frame filters
will not be executed.

If the `--skip-unavailable' option is specified, local variables
that are not available are not listed. Partially available local
variables are still displayed, however.

This command is deprecated in favor of the `-stack-list-variables'
command.

GDB Command
..........

`info locals' in GDB, `gdb_get_locals' in `gdbtk'.

Example
......

(gdb)
-stack-list-locals 0
^done,locals=[name="A",name="B",name="C"]
(gdb)
-stack-list-locals --all-values
^done,locals=[{name="A",value="1"},{name="B",value="2"},
{name="C",value="{1, 2, 3}"}]
-stack-list-locals --simple-values
^done,locals=[{name="A",type="int",value="1"},
{name="B",type="int",value="2"},{name="C",type="int [3]"}]
(gdb)

The `-stack-list-variables' Command
-----------------------------------

Synopsis
.......

-stack-list-variables [ --no-frame-filters ] [ --skip-unavailable ] PRINT-VALUES

Display the names of local variables and function arguments for the
selected frame. If PRINT-VALUES is 0 or `--no-values', print only the
names of the variables; if it is 1 or `--all-values', print also their
values; and if it is 2 or `--simple-values', print the name, type and
value for simple data types, and the name and type for arrays,
structures and unions. If the option `--no-frame-filters' is supplied,
then Python frame filters will not be executed.

If the `--skip-unavailable' option is specified, local variables and
arguments that are not available are not listed. Partially available
arguments and local variables are still displayed, however.

Example
......

(gdb)
-stack-list-variables --thread 1 --frame 0 --all-values
^done,variables=[{name="x",value="11"},{name="s",value="{a = 1, b = 2}"}]
(gdb)

The `-stack-select-frame' Command
---------------------------------

Synopsis
.......

-stack-select-frame FRAMENUM

Change the selected frame. Select a different frame FRAMENUM on the
stack.

This command in deprecated in favor of passing the `--frame' option
to every command.

GDB Command
..........

The corresponding GDB commands are `frame', `up', `down',
`select-frame', `up-silent', and `down-silent'.

Example
......

(gdb)
-stack-select-frame 2
^done
(gdb)

File: gdb.info, Node: GDB/MI Variable Objects, Next: GDB/MI Data Manipulation, Prev: GDB/MI Stack Manipulation, Up: GDB/MI

27.15 GDB/MI Variable Objects
=============================

Introduction to Variable Objects
--------------------------------

Variable objects are "object-oriented" MI interface for examining and
changing values of expressions. Unlike some other MI interfaces that
work with expressions, variable objects are specifically designed for
simple and efficient presentation in the frontend. A variable object
is identified by string name. When a variable object is created, the
frontend specifies the expression for that variable object. The
expression can be a simple variable, or it can be an arbitrary complex
expression, and can even involve CPU registers. After creating a
variable object, the frontend can invoke other variable object
operations--for example to obtain or change the value of a variable
object, or to change display format.

Variable objects have hierarchical tree structure. Any variable
object that corresponds to a composite type, such as structure in C, has
a number of child variable objects, for example corresponding to each
element of a structure. A child variable object can itself have
children, recursively. Recursion ends when we reach leaf variable
objects, which always have built-in types. Child variable objects are
created only by explicit request, so if a frontend is not interested in
the children of a particular variable object, no child will be created.

For a leaf variable object it is possible to obtain its value as a
string, or set the value from a string. String value can be also
obtained for a non-leaf variable object, but it's generally a string
that only indicates the type of the object, and does not list its
contents. Assignment to a non-leaf variable object is not allowed.

A frontend does not need to read the values of all variable objects
each time the program stops. Instead, MI provides an update command
that lists all variable objects whose values has changed since the last
update operation. This considerably reduces the amount of data that
must be transferred to the frontend. As noted above, children variable
objects are created on demand, and only leaf variable objects have a
real value. As result, gdb will read target memory only for leaf
variables that frontend has created.

The automatic update is not always desirable. For example, a
frontend might want to keep a value of some expression for future
reference, and never update it. For another example, fetching memory
is relatively slow for embedded targets, so a frontend might want to
disable automatic update for the variables that are either not visible
on the screen, or "closed". This is possible using so called "frozen
variable objects". Such variable objects are never implicitly updated.

Variable objects can be either "fixed" or "floating". For the fixed
variable object, the expression is parsed when the variable object is
created, including associating identifiers to specific variables. The
meaning of expression never changes. For a floating variable object
the values of variables whose names appear in the expressions are
re-evaluated every time in the context of the current frame. Consider
this example:

void do_work(...)
{
struct work_state state;

if (...)
do_work(...);
}

If a fixed variable object for the `state' variable is created in
this function, and we enter the recursive call, the variable object
will report the value of `state' in the top-level `do_work' invocation.
On the other hand, a floating variable object will report the value of
`state' in the current frame.

If an expression specified when creating a fixed variable object
refers to a local variable, the variable object becomes bound to the
thread and frame in which the variable object is created. When such
variable object is updated, GDB makes sure that the thread/frame
combination the variable object is bound to still exists, and
re-evaluates the variable object in context of that thread/frame.

The following is the complete set of GDB/MI operations defined to
access this functionality:

*Operation* *Description*
`-enable-pretty-printing' enable Python-based pretty-printing
`-var-create' create a variable object
`-var-delete' delete the variable object and/or its
children
`-var-set-format' set the display format of this variable
`-var-show-format' show the display format of this variable
`-var-info-num-children' tells how many children this object has
`-var-list-children' return a list of the object's children
`-var-info-type' show the type of this variable object
`-var-info-expression' print parent-relative expression that this
variable object represents
`-var-info-path-expression' print full expression that this variable
object represents
`-var-show-attributes' is this variable editable? does it exist
here?
`-var-evaluate-expression' get the value of this variable
`-var-assign' set the value of this variable
`-var-update' update the variable and its children
`-var-set-frozen' set frozenness attribute
`-var-set-update-range' set range of children to display on update

In the next subsection we describe each operation in detail and
suggest how it can be used.

Description And Use of Operations on Variable Objects
-----------------------------------------------------

The `-enable-pretty-printing' Command
-------------------------------------

-enable-pretty-printing

GDB allows Python-based visualizers to affect the output of the MI
variable object commands. However, because there was no way to
implement this in a fully backward-compatible way, a front end must
request that this functionality be enabled.

Once enabled, this feature cannot be disabled.

Note that if Python support has not been compiled into GDB, this
command will still succeed (and do nothing).

The `-var-create' Command
-------------------------

Synopsis
.......

-var-create {NAME | "-"}
{FRAME-ADDR | "*" | "@"} EXPRESSION

This operation creates a variable object, which allows the
monitoring of a variable, the result of an expression, a memory cell or
a CPU register.

The NAME parameter is the string by which the object can be
referenced. It must be unique. If `-' is specified, the varobj system
will generate a string "varNNNNNN" automatically. It will be unique
provided that one does not specify NAME of that format. The command
fails if a duplicate name is found.

The frame under which the expression should be evaluated can be
specified by FRAME-ADDR. A `*' indicates that the current frame should
be used. A `@' indicates that a floating variable object must be
created.

EXPRESSION is any expression valid on the current language set (must
not begin with a `*'), or one of the following:

* `*ADDR', where ADDR is the address of a memory cell

* `*ADDR-ADDR' -- a memory address range (TBD)

* `$REGNAME' -- a CPU register name

A varobj's contents may be provided by a Python-based
pretty-printer. In this case the varobj is known as a "dynamic
varobj". Dynamic varobjs have slightly different semantics in some
cases. If the `-enable-pretty-printing' command is not sent, then GDB
will never create a dynamic varobj. This ensures backward
compatibility for existing clients.

Result
.....

This operation returns attributes of the newly-created varobj. These
are:

`name'
The name of the varobj.

`numchild'
The number of children of the varobj. This number is not
necessarily reliable for a dynamic varobj. Instead, you must
examine the `has_more' attribute.

`value'
The varobj's scalar value. For a varobj whose type is some sort of
aggregate (e.g., a `struct'), this value will not be interesting.
For a dynamic varobj, this value comes directly from the Python
pretty-printer object's `to_string' method.

`type'
The varobj's type. This is a string representation of the type, as
would be printed by the GDB CLI. If `print object' (*note set
print object: Print Settings.) is set to `on', the _actual_
(derived) type of the object is shown rather than the _declared_
one.

`thread-id'
If a variable object is bound to a specific thread, then this is
the thread's global identifier.

`has_more'
For a dynamic varobj, this indicates whether there appear to be any
children available. For a non-dynamic varobj, this will be 0.

`dynamic'
This attribute will be present and have the value `1' if the
varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
then this attribute will not be present.

`displayhint'
A dynamic varobj can supply a display hint to the front end. The
value comes directly from the Python pretty-printer object's
`display_hint' method. *Note Pretty Printing API::.

Typical output will look like this:

name="NAME",numchild="N",type="TYPE",thread-id="M",
has_more="HAS_MORE"

The `-var-delete' Command
-------------------------

Synopsis
.......

-var-delete [ -c ] NAME

Deletes a previously created variable object and all of its children.
With the `-c' option, just deletes the children.

Returns an error if the object NAME is not found.

The `-var-set-format' Command
-----------------------------

Synopsis
.......

-var-set-format NAME FORMAT-SPEC

Sets the output format for the value of the object NAME to be
FORMAT-SPEC.

The syntax for the FORMAT-SPEC is as follows:

FORMAT-SPEC ==>
{binary | decimal | hexadecimal | octal | natural | zero-hexadecimal}

The natural format is the default format chosen automatically based
on the variable type (like decimal for an `int', hex for pointers,
etc.).

The zero-hexadecimal format has a representation similar to
hexadecimal but with padding zeroes to the left of the value. For
example, a 32-bit hexadecimal value of 0x1234 would be represented as
0x00001234 in the zero-hexadecimal format.

For a variable with children, the format is set only on the variable
itself, and the children are not affected.

The `-var-show-format' Command
------------------------------

Synopsis
.......

-var-show-format NAME

Returns the format used to display the value of the object NAME.

FORMAT ==>
FORMAT-SPEC

The `-var-info-num-children' Command
------------------------------------

Synopsis
.......

-var-info-num-children NAME

Returns the number of children of a variable object NAME:

numchild=N

Note that this number is not completely reliable for a dynamic
varobj. It will return the current number of children, but more
children may be available.

The `-var-list-children' Command
--------------------------------

Synopsis
.......

-var-list-children [PRINT-VALUES] NAME [FROM TO]

Return a list of the children of the specified variable object and
create variable objects for them, if they do not already exist. With a
single argument or if PRINT-VALUES has a value of 0 or `--no-values',
print only the names of the variables; if PRINT-VALUES is 1 or
`--all-values', also print their values; and if it is 2 or
`--simple-values' print the name and value for simple data types and
just the name for arrays, structures and unions.

FROM and TO, if specified, indicate the range of children to report.
If FROM or TO is less than zero, the range is reset and all children
will be reported. Otherwise, children starting at FROM (zero-based)
and up to and excluding TO will be reported.

If a child range is requested, it will only affect the current call
to `-var-list-children', but not future calls to `-var-update'. For
this, you must instead use `-var-set-update-range'. The intent of this
approach is to enable a front end to implement any update approach it
likes; for example, scrolling a view may cause the front end to request
more children with `-var-list-children', and then the front end could
call `-var-set-update-range' with a different range to ensure that
future updates are restricted to just the visible items.

For each child the following results are returned:

NAME
Name of the variable object created for this child.

EXP
The expression to be shown to the user by the front end to
designate this child. For example this may be the name of a
structure member.

For a dynamic varobj, this value cannot be used to form an
expression. There is no way to do this at all with a dynamic
varobj.

For C/C++ structures there are several pseudo children returned to
designate access qualifiers. For these pseudo children EXP is
`public', `private', or `protected'. In this case the type and
value are not present.

A dynamic varobj will not report the access qualifying
pseudo-children, regardless of the language. This information is
not available at all with a dynamic varobj.

NUMCHILD
Number of children this child has. For a dynamic varobj, this
will be 0.

TYPE
The type of the child. If `print object' (*note set print object:
Print Settings.) is set to `on', the _actual_ (derived) type of
the object is shown rather than the _declared_ one.

VALUE
If values were requested, this is the value.

THREAD-ID
If this variable object is associated with a thread, this is the
thread's global thread id. Otherwise this result is not present.

FROZEN
If the variable object is frozen, this variable will be present
with a value of 1.

DISPLAYHINT
A dynamic varobj can supply a display hint to the front end. The
value comes directly from the Python pretty-printer object's
`display_hint' method. *Note Pretty Printing API::.

DYNAMIC
This attribute will be present and have the value `1' if the
varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
then this attribute will not be present.

The result may have its own attributes:

`displayhint'
A dynamic varobj can supply a display hint to the front end. The
value comes directly from the Python pretty-printer object's
`display_hint' method. *Note Pretty Printing API::.

`has_more'
This is an integer attribute which is nonzero if there are children
remaining after the end of the selected range.

Example
......

(gdb)
-var-list-children n
^done,numchild=N,children=[child={name=NAME,exp=EXP,
numchild=N,type=TYPE},(repeats N times)]
(gdb)
-var-list-children --all-values n
^done,numchild=N,children=[child={name=NAME,exp=EXP,
numchild=N,value=VALUE,type=TYPE},(repeats N times)]

The `-var-info-type' Command
----------------------------

Synopsis
.......

-var-info-type NAME

Returns the type of the specified variable NAME. The type is
returned as a string in the same format as it is output by the GDB CLI:

type=TYPENAME

The `-var-info-expression' Command
----------------------------------

Synopsis
.......

-var-info-expression NAME

Returns a string that is suitable for presenting this variable
object in user interface. The string is generally not valid expression
in the current language, and cannot be evaluated.

For example, if `a' is an array, and variable object `A' was created
for `a', then we'll get this output:

(gdb) -var-info-expression A.1
^done,lang="C",exp="1"

Here, the value of `lang' is the language name, which can be found in
*Note Supported Languages::.

Note that the output of the `-var-list-children' command also
includes those expressions, so the `-var-info-expression' command is of
limited use.

The `-var-info-path-expression' Command
---------------------------------------

Synopsis
.......

-var-info-path-expression NAME

Returns an expression that can be evaluated in the current context
and will yield the same value that a variable object has. Compare this
with the `-var-info-expression' command, which result can be used only
for UI presentation. Typical use of the `-var-info-path-expression'
command is creating a watchpoint from a variable object.

This command is currently not valid for children of a dynamic varobj,
and will give an error when invoked on one.

For example, suppose `C' is a C++ class, derived from class `Base',
and that the `Base' class has a member called `m_size'. Assume a
variable `c' is has the type of `C' and a variable object `C' was
created for variable `c'. Then, we'll get this output:
(gdb) -var-info-path-expression C.Base.public.m_size
^done,path_expr=((Base)c).m_size)

The `-var-show-attributes' Command
----------------------------------

Synopsis
.......

-var-show-attributes NAME

List attributes of the specified variable object NAME:

status=ATTR [ ( ,ATTR )* ]

where ATTR is `{ { editable | noneditable } | TBD }'.

The `-var-evaluate-expression' Command
--------------------------------------

Synopsis
.......

-var-evaluate-expression [-f FORMAT-SPEC] NAME

Evaluates the expression that is represented by the specified
variable object and returns its value as a string. The format of the
string can be specified with the `-f' option. The possible values of
this option are the same as for `-var-set-format' (*note
-var-set-format::). If the `-f' option is not specified, the current
display format will be used. The current display format can be changed
using the `-var-set-format' command.

value=VALUE

Note that one must invoke `-var-list-children' for a variable before
the value of a child variable can be evaluated.

The `-var-assign' Command
-------------------------

Synopsis
.......

-var-assign NAME EXPRESSION

Assigns the value of EXPRESSION to the variable object specified by
NAME. The object must be `editable'. If the variable's value is
altered by the assign, the variable will show up in any subsequent
`-var-update' list.

Example
......

(gdb)
-var-assign var1 3
^done,value="3"
(gdb)
-var-update *
^done,changelist=[{name="var1",in_scope="true",type_changed="false"}]
(gdb)

The `-var-update' Command
-------------------------

Synopsis
.......

-var-update [PRINT-VALUES] {NAME | "*"}

Reevaluate the expressions corresponding to the variable object NAME
and all its direct and indirect children, and return the list of
variable objects whose values have changed; NAME must be a root
variable object. Here, "changed" means that the result of
`-var-evaluate-expression' before and after the `-var-update' is
different. If `*' is used as the variable object names, all existing
variable objects are updated, except for frozen ones (*note
-var-set-frozen::). The option PRINT-VALUES determines whether both
names and values, or just names are printed. The possible values of
this option are the same as for `-var-list-children' (*note
-var-list-children::). It is recommended to use the `--all-values'
option, to reduce the number of MI commands needed on each program stop.

With the `*' parameter, if a variable object is bound to a currently
running thread, it will not be updated, without any diagnostic.

If `-var-set-update-range' was previously used on a varobj, then
only the selected range of children will be reported.

`-var-update' reports all the changed varobjs in a tuple named
`changelist'.

Each item in the change list is itself a tuple holding:

`name'
The name of the varobj.

`value'
If values were requested for this update, then this field will be
present and will hold the value of the varobj.

`in_scope'
This field is a string which may take one of three values:

`"true"'
The variable object's current value is valid.

`"false"'
The variable object does not currently hold a valid value but
it may hold one in the future if its associated expression
comes back into scope.

`"invalid"'
The variable object no longer holds a valid value. This can
occur when the executable file being debugged has changed,
either through recompilation or by using the GDB `file'
command. The front end should normally choose to delete
these variable objects.

In the future new values may be added to this list so the front
should be prepared for this possibility. *Note GDB/MI Development
and Front Ends: GDB/MI Development and Front Ends.

`type_changed'
This is only present if the varobj is still valid. If the type
changed, then this will be the string `true'; otherwise it will be
`false'.

When a varobj's type changes, its children are also likely to have
become incorrect. Therefore, the varobj's children are
automatically deleted when this attribute is `true'. Also, the
varobj's update range, when set using the `-var-set-update-range'
command, is unset.

`new_type'
If the varobj's type changed, then this field will be present and
will hold the new type.

`new_num_children'
For a dynamic varobj, if the number of children changed, or if the
type changed, this will be the new number of children.

The `numchild' field in other varobj responses is generally not
valid for a dynamic varobj - it will show the number of children
that GDB knows about, but because dynamic varobjs lazily
instantiate their children, this will not reflect the number of
children which may be available.

The `new_num_children' attribute only reports changes to the
number of children known by GDB. This is the only way to detect
whether an update has removed children (which necessarily can only
happen at the end of the update range).

`displayhint'
The display hint, if any.

`has_more'
This is an integer value, which will be 1 if there are more
children available outside the varobj's update range.

`dynamic'
This attribute will be present and have the value `1' if the
varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
then this attribute will not be present.

`new_children'
If new children were added to a dynamic varobj within the selected
update range (as set by `-var-set-update-range'), then they will
be listed in this attribute.

Example
......

(gdb)
-var-assign var1 3
^done,value="3"
(gdb)
-var-update --all-values var1
^done,changelist=[{name="var1",value="3",in_scope="true",
type_changed="false"}]
(gdb)

The `-var-set-frozen' Command
-----------------------------

Synopsis
.......

-var-set-frozen NAME FLAG

Set the frozenness flag on the variable object NAME. The FLAG
parameter should be either `1' to make the variable frozen or `0' to
make it unfrozen. If a variable object is frozen, then neither itself,
nor any of its children, are implicitly updated by `-var-update' of a
parent variable or by `-var-update *'. Only `-var-update' of the
variable itself will update its value and values of its children.
After a variable object is unfrozen, it is implicitly updated by all
subsequent `-var-update' operations. Unfreezing a variable does not
update it, only subsequent `-var-update' does.

Example
......

(gdb)
-var-set-frozen V 1
^done
(gdb)

The `-var-set-update-range' command
-----------------------------------

Synopsis
.......

-var-set-update-range NAME FROM TO

Set the range of children to be returned by future invocations of
`-var-update'.

FROM and TO indicate the range of children to report. If FROM or TO
is less than zero, the range is reset and all children will be
reported. Otherwise, children starting at FROM (zero-based) and up to
and excluding TO will be reported.

Example
......

(gdb)
-var-set-update-range V 1 2
^done

The `-var-set-visualizer' command
---------------------------------

Synopsis
.......

-var-set-visualizer NAME VISUALIZER

Set a visualizer for the variable object NAME.

VISUALIZER is the visualizer to use. The special value `None' means
to disable any visualizer in use.

If not `None', VISUALIZER must be a Python expression. This
expression must evaluate to a callable object which accepts a single
argument. GDB will call this object with the value of the varobj NAME
as an argument (this is done so that the same Python pretty-printing
code can be used for both the CLI and MI). When called, this object
must return an object which conforms to the pretty-printing interface
(*note Pretty Printing API::).

The pre-defined function `gdb.default_visualizer' may be used to
select a visualizer by following the built-in process (*note Selecting
Pretty-Printers::). This is done automatically when a varobj is
created, and so ordinarily is not needed.

This feature is only available if Python support is enabled. The MI
command `-list-features' (*note GDB/MI Support Commands::) can be used
to check this.

Example
......

Resetting the visualizer:

(gdb)
-var-set-visualizer V None
^done

Reselecting the default (type-based) visualizer:

(gdb)
-var-set-visualizer V gdb.default_visualizer
^done

Suppose `SomeClass' is a visualizer class. A lambda expression can
be used to instantiate this class for a varobj:

(gdb)
-var-set-visualizer V "lambda val: SomeClass()"
^done

File: gdb.info, Node: GDB/MI Data Manipulation, Next: GDB/MI Tracepoint Commands, Prev: GDB/MI Variable Objects, Up: GDB/MI

27.16 GDB/MI Data Manipulation
==============================

This section describes the GDB/MI commands that manipulate data:
examine memory and registers, evaluate expressions, etc.

For details about what an addressable memory unit is, *note
addressable memory unit::.

The `-data-disassemble' Command
-------------------------------

Synopsis
.......

-data-disassemble
( -s START-ADDR -e END-ADDR
| -a ADDR
| -f FILENAME -l LINENUM [ -n LINES ] )
[ --opcodes OPCODES-MODE ]
[ --source ]
[ -- MODE ]

Where:

`START-ADDR'
is the beginning address (or `$pc')

`END-ADDR'
is the end address

`ADDR'
is an address anywhere within (or the name of) the function to
disassemble. If an address is specified, the whole function
surrounding that address will be disassembled. If a name is
specified, the whole function with that name will be disassembled.

`FILENAME'
is the name of the file to disassemble

`LINENUM'
is the line number to disassemble around

`LINES'
is the number of disassembly lines to be produced. If it is -1,
the whole function will be disassembled, in case no END-ADDR is
specified. If END-ADDR is specified as a non-zero value, and
LINES is lower than the number of disassembly lines between
START-ADDR and END-ADDR, only LINES lines are displayed; if LINES
is higher than the number of lines between START-ADDR and
END-ADDR, only the lines up to END-ADDR are displayed.

`OPCODES-MODE'
can only be used with MODE 0, and should be one of the following:
`none'
no opcode information will be included in the result.

`bytes'
opcodes will be included in the result, the opcodes will be
formatted as for `disassemble /b'.

`display'
opcodes will be included in the result, the opcodes will be
formatted as for `disassemble /r'.

`MODE'
the use of MODE is deprecated in favour of using the `--opcodes'
and `--source' options. When no MODE is given, MODE 0 will be
assumed. However, the MODE is still available for backward
compatibility. The MODE should be one of:
`0'
_disassembly only_, this is the default mode if no mode is
specified.

`1'
_mixed source and disassembly (deprecated)_, it is not
possible to recreate this mode using `--opcodes' and
`--source' options.

`2'
_disassembly with raw opcodes_, this mode is equivalent to
using MODE 0 and passing `--opcodes bytes' to the command.

`3'
_mixed source and disassembly with raw opcodes (deprecated)_,
it is not possible to recreate this mode using `--opcodes' and
`--source' options.

`4'
_mixed source and disassembly_, this mode is equivalent to
using MODE 0 and passing `--source' to the command.

`5'
_mixed source and disassembly with raw opcodes_, this mode is
equivalent to using MODE 0 and passing `--opcodes bytes' and
`--source' to the command.
Modes 1 and 3 are deprecated. The output is "source centric"
which hasn't proved useful in practice. *Note Machine Code::, for
a discussion of the difference between `/m' and `/s' output of the
`disassemble' command.

The `--source' can only be used with MODE 0. Passing this option
will include the source code in the disassembly result as if MODE 4 or
5 had been used.

Result
.....

The result of the `-data-disassemble' command will be a list named
`asm_insns', the contents of this list depend on the options used with
the `-data-disassemble' command.

For modes 0 and 2, and when the `--source' option is not used, the
`asm_insns' list contains tuples with the following fields:

`address'
The address at which this instruction was disassembled.

`func-name'
The name of the function this instruction is within.

`offset'
The decimal offset in bytes from the start of `func-name'.

`inst'
The text disassembly for this `address'.

`opcodes'
This field is only present for modes 2, 3 and 5, or when the
`--opcodes' option `bytes' or `display' is used. This contains
the raw opcode bytes for the `inst' field.

When the `--opcodes' option is not passed to `-data-disassemble',
or the `bytes' value is passed to `--opcodes', then the bytes are
formatted as a series of single bytes, in hex, in ascending
address order, with a single space between each byte. This format
is equivalent to the `/b' option being used with the `disassemble'
command (*note `disassemble': disassemble.).

When `--opcodes' is passed the value `display' then the bytes are
formatted in the natural instruction display order. This means
multiple bytes can be grouped together, and the bytes might be
byte-swapped. This format is equivalent to the `/r' option being
used with the `disassemble' command.

For modes 1, 3, 4 and 5, or when the `--source' option is used, the
`asm_insns' list contains tuples named `src_and_asm_line', each of
which has the following fields:

`line'
The line number within `file'.

`file'
The file name from the compilation unit. This might be an absolute
file name or a relative file name depending on the compile command
used.

`fullname'
Absolute file name of `file'. It is converted to a canonical form
using the source file search path (*note Specifying Source
Directories: Source Path.) and after resolving all the symbolic
links.

If the source file is not found this field will contain the path as
present in the debug information.

`line_asm_insn'
This is a list of tuples containing the disassembly for `line' in
`file'. The fields of each tuple are the same as for
`-data-disassemble' in MODE 0 and 2, so `address', `func-name',
`offset', `inst', and optionally `opcodes'.

Note that whatever included in the `inst' field, is not manipulated
directly by GDB/MI, i.e., it is not possible to adjust its format.

GDB Command
..........

The corresponding GDB command is `disassemble'.

Example
......

Disassemble from the current value of `$pc' to `$pc + 20':

(gdb)
-data-disassemble -s $pc -e "$pc + 20" -- 0
^done,
asm_insns=[
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107c8",func-name="main",offset="12",
inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"},
{address="0x000107cc",func-name="main",offset="16",
inst="sethi %hi(0x11800), %o2"},
{address="0x000107d0",func-name="main",offset="20",
inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}]
(gdb)

Disassemble the whole `main' function. Line 32 is part of `main'.

-data-disassemble -f basics.c -l 32 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},
[...]
{address="0x0001081c",func-name="main",offset="96",inst="ret "},
{address="0x00010820",func-name="main",offset="100",inst="restore "}]
(gdb)

Disassemble 3 instructions from the start of `main':

(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 0
^done,asm_insns=[
{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},
{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]
(gdb)

Disassemble 3 instructions from the start of `main' in mixed mode:

(gdb)
-data-disassemble -f basics.c -l 32 -n 3 -- 1
^done,asm_insns=[
src_and_asm_line={line="31",
file="../../../src/gdb/testsuite/gdb.mi/basics.c",
fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",
line_asm_insn=[{address="0x000107bc",
func-name="main",offset="0",inst="save %sp, -112, %sp"}]},
src_and_asm_line={line="32",
file="../../../src/gdb/testsuite/gdb.mi/basics.c",
fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",
line_asm_insn=[{address="0x000107c0",
func-name="main",offset="4",inst="mov 2, %o0"},
{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]}]
(gdb)

The `-data-evaluate-expression' Command
---------------------------------------

Synopsis
.......

-data-evaluate-expression EXPR

Evaluate EXPR as an expression. The expression could contain an
inferior function call. The function call will execute synchronously.
If the expression contains spaces, it must be enclosed in double quotes.

GDB Command
..........

The corresponding GDB commands are `print', `output', and `call'. In
`gdbtk' only, there's a corresponding `gdb_eval' command.

Example
......

In the following example, the numbers that precede the commands are the
"tokens" described in *Note GDB/MI Command Syntax: GDB/MI Command
Syntax. Notice how GDB/MI returns the same tokens in its output.

211-data-evaluate-expression A
211^done,value="1"
(gdb)
311-data-evaluate-expression &A
311^done,value="0xefffeb7c"
(gdb)
411-data-evaluate-expression A+3
411^done,value="4"
(gdb)
511-data-evaluate-expression "A + 3"
511^done,value="4"
(gdb)

The `-data-list-changed-registers' Command
------------------------------------------

Synopsis
.......

-data-list-changed-registers

Display a list of the registers that have changed.

GDB Command
..........

GDB doesn't have a direct analog for this command; `gdbtk' has the
corresponding command `gdb_changed_register_list'.

Example
......

On a PPC MBX board:

(gdb)
-exec-continue
^running

(gdb)
*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={
func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
line="5",arch="powerpc"}
(gdb)
-data-list-changed-registers
^done,changed-registers=["0","1","2","4","5","6","7","8","9",
"10","11","13","14","15","16","17","18","19","20","21","22","23",
"24","25","26","27","28","30","31","64","65","66","67","69"]
(gdb)

The `-data-list-register-names' Command
---------------------------------------

Synopsis
.......

-data-list-register-names [ ( REGNO )+ ]

Show a list of register names for the current target. If no
arguments are given, it shows a list of the names of all the registers.
If integer numbers are given as arguments, it will print a list of the
names of the registers corresponding to the arguments. To ensure
consistency between a register name and its number, the output list may
include empty register names.

GDB Command
..........

GDB does not have a command which corresponds to
`-data-list-register-names'. In `gdbtk' there is a corresponding
command `gdb_regnames'.

Example
......

For the PPC MBX board:
(gdb)
-data-list-register-names
^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
"r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
"r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
"r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
"f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
"f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
"", "pc","ps","cr","lr","ctr","xer"]
(gdb)
-data-list-register-names 1 2 3
^done,register-names=["r1","r2","r3"]
(gdb)

The `-data-list-register-values' Command
----------------------------------------

Synopsis
.......

-data-list-register-values
[ `--skip-unavailable' ] FMT [ ( REGNO )*]

Display the registers' contents. The format according to which the
registers' contents are to be returned is given by FMT, followed by an
optional list of numbers specifying the registers to display. A
missing list of numbers indicates that the contents of all the
registers must be returned. The `--skip-unavailable' option indicates
that only the available registers are to be returned.

Allowed formats for FMT are:

`x'
Hexadecimal

`o'
Octal

`t'
Binary

`d'
Decimal

`r'
Raw

`N'
Natural

GDB Command
..........

The corresponding GDB commands are `info reg', `info all-reg', and (in
`gdbtk') `gdb_fetch_registers'.

Example
......

For a PPC MBX board (note: line breaks are for readability only, they
don't appear in the actual output):

(gdb)
-data-list-register-values r 64 65
^done,register-values=[{number="64",value="0xfe00a300"},
{number="65",value="0x00029002"}]
(gdb)
-data-list-register-values x
^done,register-values=[{number="0",value="0xfe0043c8"},
{number="1",value="0x3fff88"},{number="2",value="0xfffffffe"},
{number="3",value="0x0"},{number="4",value="0xa"},
{number="5",value="0x3fff68"},{number="6",value="0x3fff58"},
{number="7",value="0xfe011e98"},{number="8",value="0x2"},
{number="9",value="0xfa202820"},{number="10",value="0xfa202808"},
{number="11",value="0x1"},{number="12",value="0x0"},
{number="13",value="0x4544"},{number="14",value="0xffdfffff"},
{number="15",value="0xffffffff"},{number="16",value="0xfffffeff"},
{number="17",value="0xefffffed"},{number="18",value="0xfffffffe"},
{number="19",value="0xffffffff"},{number="20",value="0xffffffff"},
{number="21",value="0xffffffff"},{number="22",value="0xfffffff7"},
{number="23",value="0xffffffff"},{number="24",value="0xffffffff"},
{number="25",value="0xffffffff"},{number="26",value="0xfffffffb"},
{number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"},
{number="29",value="0x0"},{number="30",value="0xfe010000"},
{number="31",value="0x0"},{number="32",value="0x0"},
{number="33",value="0x0"},{number="34",value="0x0"},
{number="35",value="0x0"},{number="36",value="0x0"},
{number="37",value="0x0"},{number="38",value="0x0"},
{number="39",value="0x0"},{number="40",value="0x0"},
{number="41",value="0x0"},{number="42",value="0x0"},
{number="43",value="0x0"},{number="44",value="0x0"},
{number="45",value="0x0"},{number="46",value="0x0"},
{number="47",value="0x0"},{number="48",value="0x0"},
{number="49",value="0x0"},{number="50",value="0x0"},
{number="51",value="0x0"},{number="52",value="0x0"},
{number="53",value="0x0"},{number="54",value="0x0"},
{number="55",value="0x0"},{number="56",value="0x0"},
{number="57",value="0x0"},{number="58",value="0x0"},
{number="59",value="0x0"},{number="60",value="0x0"},
{number="61",value="0x0"},{number="62",value="0x0"},
{number="63",value="0x0"},{number="64",value="0xfe00a300"},
{number="65",value="0x29002"},{number="66",value="0x202f04b5"},
{number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"},
{number="69",value="0x20002b03"}]
(gdb)

The `-data-read-memory' Command
-------------------------------

This command is deprecated, use `-data-read-memory-bytes' instead.

Synopsis
.......

-data-read-memory [ -o BYTE-OFFSET ]
ADDRESS WORD-FORMAT WORD-SIZE
NR-ROWS NR-COLS [ ASCHAR ]

where:

`ADDRESS'
An expression specifying the address of the first memory word to be
read. Complex expressions containing embedded white space should
be quoted using the C convention.

`WORD-FORMAT'
The format to be used to print the memory words. The notation is
the same as for GDB's `print' command (*note Output Formats:
Output Formats.).

`WORD-SIZE'
The size of each memory word in bytes.

`NR-ROWS'
The number of rows in the output table.

`NR-COLS'
The number of columns in the output table.

`ASCHAR'
If present, indicates that each row should include an ASCII dump.
The value of ASCHAR is used as a padding character when a byte is
not a member of the printable ASCII character set (printable ASCII
characters are those whose code is between 32 and 126,
inclusively).

`BYTE-OFFSET'
An offset to add to the ADDRESS before fetching memory.

This command displays memory contents as a table of NR-ROWS by
NR-COLS words, each word being WORD-SIZE bytes. In total, `NR-ROWS *
NR-COLS * WORD-SIZE' bytes are read (returned as `total-bytes').
Should less than the requested number of bytes be returned by the
target, the missing words are identified using `N/A'. The number of
bytes read from the target is returned in `nr-bytes' and the starting
address used to read memory in `addr'.

The address of the next/previous row or page is available in
`next-row' and `prev-row', `next-page' and `prev-page'.

GDB Command
..........

The corresponding GDB command is `x'. `gdbtk' has `gdb_get_mem' memory
read command.

Example
......

Read six bytes of memory starting at `bytes+6' but then offset by `-6'
bytes. Format as three rows of two columns. One byte per word.
Display each word in hex.

(gdb)
9-data-read-memory -o -6 -- bytes+6 x 1 3 2
9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
prev-page="0x0000138a",memory=[
{addr="0x00001390",data=["0x00","0x01"]},
{addr="0x00001392",data=["0x02","0x03"]},
{addr="0x00001394",data=["0x04","0x05"]}]
(gdb)

Read two bytes of memory starting at address `shorts + 64' and
display as a single word formatted in decimal.

(gdb)
5-data-read-memory shorts+64 d 2 1 1
5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
next-row="0x00001512",prev-row="0x0000150e",
next-page="0x00001512",prev-page="0x0000150e",memory=[
{addr="0x00001510",data=["128"]}]
(gdb)

Read thirty two bytes of memory starting at `bytes+16' and format as
eight rows of four columns. Include a string encoding with `x' used as
the non-printable character.

(gdb)
4-data-read-memory bytes+16 x 1 8 4 x
4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
next-row="0x000013c0",prev-row="0x0000139c",
next-page="0x000013c0",prev-page="0x00001380",memory=[
{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"},
{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"},
{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"},
{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"},
{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"},
{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"},
{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"},
{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}]
(gdb)

The `-data-read-memory-bytes' Command
-------------------------------------

Synopsis
.......

-data-read-memory-bytes [ -o OFFSET ]
ADDRESS COUNT

where:

`ADDRESS'
An expression specifying the address of the first addressable
memory unit to be read. Complex expressions containing embedded
white space should be quoted using the C convention.

`COUNT'
The number of addressable memory units to read. This should be an
integer literal.

`OFFSET'
The offset relative to ADDRESS at which to start reading. This
should be an integer literal. This option is provided so that a
frontend is not required to first evaluate address and then
perform address arithmetic itself.

This command attempts to read all accessible memory regions in the
specified range. First, all regions marked as unreadable in the memory
map (if one is defined) will be skipped. *Note Memory Region
Attributes::. Second, GDB will attempt to read the remaining regions.
For each one, if reading full region results in an errors, GDB will try
to read a subset of the region.

In general, every single memory unit in the region may be readable
or not, and the only way to read every readable unit is to try a read at
every address, which is not practical. Therefore, GDB will attempt to
read all accessible memory units at either beginning or the end of the
region, using a binary division scheme. This heuristic works well for
reading across a memory map boundary. Note that if a region has a
readable range that is neither at the beginning or the end, GDB will
not read it.

The result record (*note GDB/MI Result Records::) that is output of
the command includes a field named `memory' whose content is a list of
tuples. Each tuple represent a successfully read memory block and has
the following fields:

`begin'
The start address of the memory block, as hexadecimal literal.

`end'
The end address of the memory block, as hexadecimal literal.

`offset'
The offset of the memory block, as hexadecimal literal, relative to
the start address passed to `-data-read-memory-bytes'.

`contents'
The contents of the memory block, in hex.

GDB Command
..........

The corresponding GDB command is `x'.

Example
......

(gdb)
-data-read-memory-bytes &a 10
^done,memory=[{begin="0xbffff154",offset="0x00000000",
end="0xbffff15e",
contents="01000000020000000300"}]
(gdb)

The `-data-write-memory-bytes' Command
--------------------------------------

Synopsis
.......

-data-write-memory-bytes ADDRESS CONTENTS
-data-write-memory-bytes ADDRESS CONTENTS [COUNT]

where:

`ADDRESS'
An expression specifying the address of the first addressable
memory unit to be written. Complex expressions containing
embedded white space should be quoted using the C convention.

`CONTENTS'
The hex-encoded data to write. It is an error if CONTENTS does
not represent an integral number of addressable memory units.

`COUNT'
Optional argument indicating the number of addressable memory
units to be written. If COUNT is greater than CONTENTS' length,
GDB will repeatedly write CONTENTS until it fills COUNT memory
units.

GDB Command
..........

There's no corresponding GDB command.

Example
......

(gdb)
-data-write-memory-bytes &a "aabbccdd"
^done
(gdb)

(gdb)
-data-write-memory-bytes &a "aabbccdd" 16e
^done
(gdb)

File: gdb.info, Node: GDB/MI Tracepoint Commands, Next: GDB/MI Symbol Query, Prev: GDB/MI Data Manipulation, Up: GDB/MI

27.17 GDB/MI Tracepoint Commands
================================

The commands defined in this section implement MI support for
tracepoints. For detailed introduction, see *Note Tracepoints::.

The `-trace-find' Command
-------------------------

Synopsis
.......

-trace-find MODE [PARAMETERS...]

Find a trace frame using criteria defined by MODE and PARAMETERS.
The following table lists permissible modes and their parameters. For
details of operation, see *Note tfind::.

`none'
No parameters are required. Stops examining trace frames.

`frame-number'
An integer is required as parameter. Selects tracepoint frame with
that index.

`tracepoint-number'
An integer is required as parameter. Finds next trace frame that
corresponds to tracepoint with the specified number.

`pc'
An address is required as parameter. Finds next trace frame that
corresponds to any tracepoint at the specified address.

`pc-inside-range'
Two addresses are required as parameters. Finds next trace frame
that corresponds to a tracepoint at an address inside the
specified range. Both bounds are considered to be inside the
range.

`pc-outside-range'
Two addresses are required as parameters. Finds next trace frame
that corresponds to a tracepoint at an address outside the
specified range. Both bounds are considered to be inside the
range.

`line'
Location specification is required as parameter. *Note Location
Specifications::. Finds next trace frame that corresponds to a
tracepoint at the specified location.

If `none' was passed as MODE, the response does not have fields.
Otherwise, the response may have the following fields:

`found'
This field has either `0' or `1' as the value, depending on
whether a matching tracepoint was found.

`traceframe'
The index of the found traceframe. This field is present iff the
`found' field has value of `1'.

`tracepoint'
The index of the found tracepoint. This field is present iff the
`found' field has value of `1'.

`frame'
The information about the frame corresponding to the found trace
frame. This field is present only if a trace frame was found.
*Note GDB/MI Frame Information::, for description of this field.

GDB Command
..........

The corresponding GDB command is `tfind'.

The `-trace-define-variable' Command
------------------------------------

Synopsis
.......

-trace-define-variable NAME [ VALUE ]

Create trace variable NAME if it does not exist. If VALUE is
specified, sets the initial value of the specified trace variable to
that value. Note that the NAME should start with the `$' character.

GDB Command
..........

The corresponding GDB command is `tvariable'.

The `-trace-frame-collected' Command
------------------------------------

Synopsis
.......

-trace-frame-collected
[--var-print-values VAR_PVAL]
[--comp-print-values COMP_PVAL]
[--registers-format REGFORMAT]
[--memory-contents]

This command returns the set of collected objects, register names,
trace state variable names, memory ranges and computed expressions that
have been collected at a particular trace frame. The optional
parameters to the command affect the output format in different ways.
See the output description table below for more details.

The reported names can be used in the normal manner to create
varobjs and inspect the objects themselves. The items returned by this
command are categorized so that it is clear which is a variable, which
is a register, which is a trace state variable, which is a memory range
and which is a computed expression.

For instance, if the actions were
collect myVar, myArray[myIndex], myObj.field, myPtr->field, myCount + 2
collect *(int*)0xaf02bef0@40

the object collected in its entirety would be `myVar'. The object
`myArray' would be partially collected, because only the element at
index `myIndex' would be collected. The remaining objects would be
computed expressions.

An example output would be:

(gdb)
-trace-frame-collected
^done,
explicit-variables=[{name="myVar",value="1"}],
computed-expressions=[{name="myArray[myIndex]",value="0"},
{name="myObj.field",value="0"},
{name="myPtr->field",value="1"},
{name="myCount + 2",value="3"},
{name="$tvar1 + 1",value="43970027"}],
registers=[{number="0",value="0x7fe2c6e79ec8"},
{number="1",value="0x0"},
{number="2",value="0x4"},
...
{number="125",value="0x0"}],
tvars=[{name="$tvar1",current="43970026"}],
memory=[{address="0x0000000000602264",length="4"},
{address="0x0000000000615bc0",length="4"}]
(gdb)

Where:

`explicit-variables'
The set of objects that have been collected in their entirety (as
opposed to collecting just a few elements of an array or a few
struct members). For each object, its name and value are printed.
The `--var-print-values' option affects how or whether the value
field is output. If VAR_PVAL is 0, then print only the names; if
it is 1, print also their values; and if it is 2, print the name,
type and value for simple data types, and the name and type for
arrays, structures and unions.

`computed-expressions'
The set of computed expressions that have been collected at the
current trace frame. The `--comp-print-values' option affects
this set like the `--var-print-values' option affects the
`explicit-variables' set. See above.

`registers'
The registers that have been collected at the current trace frame.
For each register collected, the name and current value are
returned. The value is formatted according to the
`--registers-format' option. See the `-data-list-register-values'
command for a list of the allowed formats. The default is `x'.

`tvars'
The trace state variables that have been collected at the current
trace frame. For each trace state variable collected, the name and
current value are returned.

`memory'
The set of memory ranges that have been collected at the current
trace frame. Its content is a list of tuples. Each tuple
represents a collected memory range and has the following fields:

`address'
The start address of the memory range, as hexadecimal literal.

`length'
The length of the memory range, as decimal literal.

`contents'
The contents of the memory block, in hex. This field is only
present if the `--memory-contents' option is specified.

GDB Command
..........

There is no corresponding GDB command.

Example
......

The `-trace-list-variables' Command
-----------------------------------

Synopsis
.......

-trace-list-variables

Return a table of all defined trace variables. Each element of the
table has the following fields:

`name'
The name of the trace variable. This field is always present.

`initial'
The initial value. This is a 64-bit signed integer. This field
is always present.

`current'
The value the trace variable has at the moment. This is a 64-bit
signed integer. This field is absent iff current value is not
defined, for example if the trace was never run, or is presently
running.

GDB Command
..........

The corresponding GDB command is `tvariables'.

Example
......

(gdb)
-trace-list-variables
^done,trace-variables={nr_rows="1",nr_cols="3",
hdr=[{width="15",alignment="-1",col_name="name",colhdr="Name"},
{width="11",alignment="-1",col_name="initial",colhdr="Initial"},
{width="11",alignment="-1",col_name="current",colhdr="Current"}],
body=[variable={name="$trace_timestamp",initial="0"}
variable={name="$foo",initial="10",current="15"}]}
(gdb)

The `-trace-save' Command
-------------------------

Synopsis
.......

-trace-save [ -r ] [ -ctf ] FILENAME

Saves the collected trace data to FILENAME. Without the `-r'
option, the data is downloaded from the target and saved in a local
file. With the `-r' option the target is asked to perform the save.

By default, this command will save the trace in the tfile format.
You can supply the optional `-ctf' argument to save it the CTF format.
See *Note Trace Files:: for more information about CTF.

GDB Command
..........

The corresponding GDB command is `tsave'.

The `-trace-start' Command
--------------------------

Synopsis
.......

-trace-start

Starts a tracing experiment. The result of this command does not
have any fields.

GDB Command
..........

The corresponding GDB command is `tstart'.

The `-trace-status' Command
---------------------------

Synopsis
.......

-trace-status

Obtains the status of a tracing experiment. The result may include
the following fields:

`supported'
May have a value of either `0', when no tracing operations are
supported, `1', when all tracing operations are supported, or
`file' when examining trace file. In the latter case, examining
of trace frame is possible but new tracing experiment cannot be
started. This field is always present.

`running'
May have a value of either `0' or `1' depending on whether tracing
experiment is in progress on target. This field is present if
`supported' field is not `0'.

`stop-reason'
Report the reason why the tracing was stopped last time. This
field may be absent iff tracing was never stopped on target yet.
The value of `request' means the tracing was stopped as result of
the `-trace-stop' command. The value of `overflow' means the
tracing buffer is full. The value of `disconnection' means
tracing was automatically stopped when GDB has disconnected. The
value of `passcount' means tracing was stopped when a tracepoint
was passed a maximal number of times for that tracepoint. This
field is present if `supported' field is not `0'.

`stopping-tracepoint'
The number of tracepoint whose passcount as exceeded. This field
is present iff the `stop-reason' field has the value of
`passcount'.

`frames'
`frames-created'
The `frames' field is a count of the total number of trace frames
in the trace buffer, while `frames-created' is the total created
during the run, including ones that were discarded, such as when a
circular trace buffer filled up. Both fields are optional.

`buffer-size'
`buffer-free'
These fields tell the current size of the tracing buffer and the
remaining space. These fields are optional.

`circular'
The value of the circular trace buffer flag. `1' means that the
trace buffer is circular and old trace frames will be discarded if
necessary to make room, `0' means that the trace buffer is linear
and may fill up.

`disconnected'
The value of the disconnected tracing flag. `1' means that
tracing will continue after GDB disconnects, `0' means that the
trace run will stop.

`trace-file'
The filename of the trace file being examined. This field is
optional, and only present when examining a trace file.

GDB Command
..........

The corresponding GDB command is `tstatus'.

The `-trace-stop' Command
-------------------------

Synopsis
.......

-trace-stop

Stops a tracing experiment. The result of this command has the same
fields as `-trace-status', except that the `supported' and `running'
fields are not output.

GDB Command
..........

The corresponding GDB command is `tstop'.

File: gdb.info, Node: GDB/MI Symbol Query, Next: GDB/MI File Commands, Prev: GDB/MI Tracepoint Commands, Up: GDB/MI

27.18 GDB/MI Symbol Query Commands
==================================

The `-symbol-info-functions' Command
------------------------------------

Synopsis
.......

-symbol-info-functions [--include-nondebug]
[--type TYPE_REGEXP]
[--name NAME_REGEXP]
[--max-results LIMIT]

Return a list containing the names and types for all global functions
taken from the debug information. The functions are grouped by source
file, and shown with the line number on which each function is defined.

The `--include-nondebug' option causes the output to include code
symbols from the symbol table.

The options `--type' and `--name' allow the symbols returned to be
filtered based on either the name of the function, or the type
signature of the function.

The option `--max-results' restricts the command to return no more
than LIMIT results. If exactly LIMIT results are returned then there
might be additional results available if a higher limit is used.

GDB Command
..........

The corresponding GDB command is `info functions'.

Example
......

(gdb)
-symbol-info-functions
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"},
{line="42", name="main", type="int ()",
description="int main();"},
{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="33", name="f2", type="float (another_float_t)",
description="float f2(another_float_t);"},
{line="39", name="f3", type="int (another_int_t)",
description="int f3(another_int_t);"},
{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}]}
(gdb)
-symbol-info-functions --name f1
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}]}
(gdb)
-symbol-info-functions --type void
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"}]}]}
(gdb)
-symbol-info-functions --include-nondebug
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"},
{line="42", name="main", type="int ()",
description="int main();"},
{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="33", name="f2", type="float (another_float_t)",
description="float f2(another_float_t);"},
{line="39", name="f3", type="int (another_int_t)",
description="int f3(another_int_t);"},
{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}],
nondebug=
[{address="0x0000000000400398",name="_init"},
{address="0x00000000004003b0",name="_start"},
...
]}

The `-symbol-info-module-functions' Command
-------------------------------------------

Synopsis
.......

-symbol-info-module-functions [--module MODULE_REGEXP]
[--name NAME_REGEXP]
[--type TYPE_REGEXP]

Return a list containing the names of all known functions within all
know Fortran modules. The functions are grouped by source file and
containing module, and shown with the line number on which each
function is defined.

The option `--module' only returns results for modules matching
MODULE_REGEXP. The option `--name' only returns functions whose name
matches NAME_REGEXP, and `--type' only returns functions whose type
matches TYPE_REGEXP.

GDB Command
..........

The corresponding GDB command is `info module functions'.

Example
......

(gdb)
-symbol-info-module-functions
^done,symbols=
[{module="mod1",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="21",name="mod1::check_all",type="void (void)",
description="void mod1::check_all(void);"}]}]},
{module="mod2",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="30",name="mod2::check_var_i",type="void (void)",
description="void mod2::check_var_i(void);"}]}]},
{module="mod3",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="21",name="mod3::check_all",type="void (void)",
description="void mod3::check_all(void);"},
{line="27",name="mod3::check_mod2",type="void (void)",
description="void mod3::check_mod2(void);"}]}]},
{module="modmany",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="35",name="modmany::check_some",type="void (void)",
description="void modmany::check_some(void);"}]}]},
{module="moduse",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="44",name="moduse::check_all",type="void (void)",
description="void moduse::check_all(void);"},
{line="49",name="moduse::check_var_x",type="void (void)",
description="void moduse::check_var_x(void);"}]}]}]

The `-symbol-info-module-variables' Command
-------------------------------------------

Synopsis
.......

-symbol-info-module-variables [--module MODULE_REGEXP]
[--name NAME_REGEXP]
[--type TYPE_REGEXP]

Return a list containing the names of all known variables within all
know Fortran modules. The variables are grouped by source file and
containing module, and shown with the line number on which each
variable is defined.

The option `--module' only returns results for modules matching
MODULE_REGEXP. The option `--name' only returns variables whose name
matches NAME_REGEXP, and `--type' only returns variables whose type
matches TYPE_REGEXP.

GDB Command
..........

The corresponding GDB command is `info module variables'.

Example
......

(gdb)
-symbol-info-module-variables
^done,symbols=
[{module="mod1",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="18",name="mod1::var_const",type="integer(kind=4)",
description="integer(kind=4) mod1::var_const;"},
{line="17",name="mod1::var_i",type="integer(kind=4)",
description="integer(kind=4) mod1::var_i;"}]}]},
{module="mod2",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="28",name="mod2::var_i",type="integer(kind=4)",
description="integer(kind=4) mod2::var_i;"}]}]},
{module="mod3",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="18",name="mod3::mod1",type="integer(kind=4)",
description="integer(kind=4) mod3::mod1;"},
{line="17",name="mod3::mod2",type="integer(kind=4)",
description="integer(kind=4) mod3::mod2;"},
{line="19",name="mod3::var_i",type="integer(kind=4)",
description="integer(kind=4) mod3::var_i;"}]}]},
{module="modmany",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="33",name="modmany::var_a",type="integer(kind=4)",
description="integer(kind=4) modmany::var_a;"},
{line="33",name="modmany::var_b",type="integer(kind=4)",
description="integer(kind=4) modmany::var_b;"},
{line="33",name="modmany::var_c",type="integer(kind=4)",
description="integer(kind=4) modmany::var_c;"},
{line="33",name="modmany::var_i",type="integer(kind=4)",
description="integer(kind=4) modmany::var_i;"}]}]},
{module="moduse",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="42",name="moduse::var_x",type="integer(kind=4)",
description="integer(kind=4) moduse::var_x;"},
{line="42",name="moduse::var_y",type="integer(kind=4)",
description="integer(kind=4) moduse::var_y;"}]}]}]

The `-symbol-info-modules' Command
----------------------------------

Synopsis
.......

-symbol-info-modules [--name NAME_REGEXP]
[--max-results LIMIT]

Return a list containing the names of all known Fortran modules. The
modules are grouped by source file, and shown with the line number on
which each modules is defined.

The option `--name' allows the modules returned to be filtered based
the name of the module.

The option `--max-results' restricts the command to return no more
than LIMIT results. If exactly LIMIT results are returned then there
might be additional results available if a higher limit is used.

GDB Command
..........

The corresponding GDB command is `info modules'.

Example
......

(gdb)
-symbol-info-modules
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="16",name="mod1"},
{line="22",name="mod2"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="16",name="mod3"},
{line="22",name="modmany"},
{line="26",name="moduse"}]}]}
(gdb)
-symbol-info-modules --name mod[123]
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="16",name="mod1"},
{line="22",name="mod2"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="16",name="mod3"}]}]}

The `-symbol-info-types' Command
--------------------------------

Synopsis
.......

-symbol-info-types [--name NAME_REGEXP]
[--max-results LIMIT]

Return a list of all defined types. The types are grouped by source
file, and shown with the line number on which each user defined type is
defined. Some base types are not defined in the source code but are
added to the debug information by the compiler, for example `int',
`float', etc.; these types do not have an associated line number.

The option `--name' allows the list of types returned to be filtered
by name.

The option `--max-results' restricts the command to return no more
than LIMIT results. If exactly LIMIT results are returned then there
might be additional results available if a higher limit is used.

GDB Command
..........

The corresponding GDB command is `info types'.

Example
......

(gdb)
-symbol-info-types
^done,symbols=
{debug=
[{filename="gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{name="float"},
{name="int"},
{line="27",name="typedef int my_int_t;"}]},
{filename="gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb.mi/mi-sym-info-2.c",
symbols=[{line="24",name="typedef float another_float_t;"},
{line="23",name="typedef int another_int_t;"},
{name="float"},
{name="int"}]}]}
(gdb)
-symbol-info-types --name _int_
^done,symbols=
{debug=
[{filename="gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="27",name="typedef int my_int_t;"}]},
{filename="gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb.mi/mi-sym-info-2.c",
symbols=[{line="23",name="typedef int another_int_t;"}]}]}

The `-symbol-info-variables' Command
------------------------------------

Synopsis
.......

-symbol-info-variables [--include-nondebug]
[--type TYPE_REGEXP]
[--name NAME_REGEXP]
[--max-results LIMIT]

Return a list containing the names and types for all global variables
taken from the debug information. The variables are grouped by source
file, and shown with the line number on which each variable is defined.

The `--include-nondebug' option causes the output to include data
symbols from the symbol table.

The options `--type' and `--name' allow the symbols returned to be
filtered based on either the name of the variable, or the type of the
variable.

The option `--max-results' restricts the command to return no more
than LIMIT results. If exactly LIMIT results are returned then there
might be additional results available if a higher limit is used.

GDB Command
..........

The corresponding GDB command is `info variables'.

Example
......

(gdb)
-symbol-info-variables
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"},
{line="24",name="global_i1",type="int",
description="static int global_i1;"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="21",name="global_f2",type="int",
description="int global_f2;"},
{line="20",name="global_i2",type="int",
description="int global_i2;"},
{line="19",name="global_f1",type="float",
description="static float global_f1;"},
{line="18",name="global_i1",type="int",
description="static int global_i1;"}]}]}
(gdb)
-symbol-info-variables --name f1
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="19",name="global_f1",type="float",
description="static float global_f1;"}]}]}
(gdb)
-symbol-info-variables --type float
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="19",name="global_f1",type="float",
description="static float global_f1;"}]}]}
(gdb)
-symbol-info-variables --include-nondebug
^done,symbols=
{debug=
[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",
symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"},
{line="24",name="global_i1",type="int",
description="static int global_i1;"}]},
{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",
symbols=[{line="21",name="global_f2",type="int",
description="int global_f2;"},
{line="20",name="global_i2",type="int",
description="int global_i2;"},
{line="19",name="global_f1",type="float",
description="static float global_f1;"},
{line="18",name="global_i1",type="int",
description="static int global_i1;"}]}],
nondebug=
[{address="0x00000000004005d0",name="_IO_stdin_used"},
{address="0x00000000004005d8",name="__dso_handle"}
...
]}

The `-symbol-list-lines' Command
--------------------------------

Synopsis
.......

-symbol-list-lines FILENAME

Print the list of lines that contain code and their associated
program addresses for the given source filename. The entries are
sorted in ascending PC order.

GDB Command
..........

There is no corresponding GDB command.

Example
......

(gdb)
-symbol-list-lines basics.c
^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}]
(gdb)

File: gdb.info, Node: GDB/MI File Commands, Next: GDB/MI Target Manipulation, Prev: GDB/MI Symbol Query, Up: GDB/MI

27.19 GDB/MI File Commands
==========================

This section describes the GDB/MI commands to specify executable file
names and to read in and obtain symbol table information.

The `-file-exec-and-symbols' Command
------------------------------------

Synopsis
.......

-file-exec-and-symbols FILE

Specify the executable file to be debugged. This file is the one
from which the symbol table is also read. If no file is specified, the
command clears the executable and symbol information. If breakpoints
are set when using this command with no arguments, GDB will produce
error messages. Otherwise, no output is produced, except a completion
notification.

GDB Command
..........

The corresponding GDB command is `file'.

Example
......

(gdb)
-file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

The `-file-exec-file' Command
-----------------------------

Synopsis
.......

-file-exec-file FILE

Specify the executable file to be debugged. Unlike
`-file-exec-and-symbols', the symbol table is _not_ read from this
file. If used without argument, GDB clears the information about the
executable file. No output is produced, except a completion
notification.

GDB Command
..........

The corresponding GDB command is `exec-file'.

Example
......

(gdb)
-file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

The `-file-list-exec-source-file' Command
-----------------------------------------

Synopsis
.......

-file-list-exec-source-file

List the line number, the current source file, and the absolute path
to the current source file for the current executable. The macro
information field has a value of `1' or `0' depending on whether or not
the file includes preprocessor macro information.

GDB Command
..........

The GDB equivalent is `info source'

Example
......

(gdb)
123-file-list-exec-source-file
123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
(gdb)

The `-file-list-exec-source-files' Command
------------------------------------------

Synopsis
.......

-file-list-exec-source-files [ -GROUP-BY-OBJFILE ]
[ -DIRNAME | -BASENAME ]
[ -- ]
[ REGEXP ]

This command returns information about the source files GDB knows
about, it will output both the filename and fullname (absolute file
name) of a source file, though the fullname can be elided if this
information is not known to GDB.

With no arguments this command returns a list of source files. Each
source file is represented by a tuple with the fields; FILE, FULLNAME,
and DEBUG-FULLY-READ. The FILE is the display name for the file, while
FULLNAME is the absolute name of the file. The FULLNAME field can be
elided if the absolute name of the source file can't be computed. The
field DEBUG-FULLY-READ will be a string, either `true' or `false'.
When `true', this indicates the full debug information for the
compilation unit describing this file has been read in. When `false',
the full debug information has not yet been read in. While reading in
the full debug information it is possible that GDB could become aware
of additional source files.

The optional REGEXP can be used to filter the list of source files
returned. The REGEXP will be matched against the full source file
name. The matching is case-sensitive, except on operating systems that
have case-insensitive filesystem (e.g., MS-Windows). `--' can be used
before REGEXP to prevent GDB interpreting REGEXP as a command option
(e.g. if REGEXP starts with `-').

If `--dirname' is provided, then REGEXP is matched only against the
directory name of each source file. If `--basename' is provided, then
REGEXP is matched against the basename of each source file. Only one
of `--dirname' or `--basename' may be given, and if either is given
then REGEXP is required.

If `--group-by-objfile' is used then the format of the results is
changed. The results will now be a list of tuples, with each tuple
representing an object file (executable or shared library) loaded into
GDB. The fields of these tuples are; FILENAME, DEBUG-INFO, and
SOURCES. The FILENAME is the absolute name of the object file,
DEBUG-INFO is a string with one of the following values:

`none'
This object file has no debug information.

`partially-read'
This object file has debug information, but it is not fully read in
yet. When it is read in later, GDB might become aware of
additional source files.

`fully-read'
This object file has debug information, and this information is
fully read into GDB. The list of source files is complete.

The SOURCES is a list or tuples, with each tuple describing a single
source file with the same fields as described previously. The SOURCES
list can be empty for object files that have no debug information.

GDB Command
..........

The GDB equivalent is `info sources'. `gdbtk' has an analogous command
`gdb_listfiles'.

Example
......

(gdb)
-file-list-exec-source-files
^done,files=[{file="foo.c",fullname="/home/foo.c",debug-fully-read="true"},
{file="/home/bar.c",fullname="/home/bar.c",debug-fully-read="true"},
{file="gdb_could_not_find_fullpath.c",debug-fully-read="true"}]
(gdb)
-file-list-exec-source-files
^done,files=[{file="test.c",
fullname="/tmp/info-sources/test.c",
debug-fully-read="true"},
{file="/usr/include/stdc-predef.h",
fullname="/usr/include/stdc-predef.h",
debug-fully-read="true"},
{file="header.h",
fullname="/tmp/info-sources/header.h",
debug-fully-read="true"},
{file="helper.c",
fullname="/tmp/info-sources/helper.c",
debug-fully-read="true"}]
(gdb)
-file-list-exec-source-files -- \\.c
^done,files=[{file="test.c",
fullname="/tmp/info-sources/test.c",
debug-fully-read="true"},
{file="helper.c",
fullname="/tmp/info-sources/helper.c",
debug-fully-read="true"}]
(gdb)
-file-list-exec-source-files --group-by-objfile
^done,files=[{filename="/tmp/info-sources/test.x",
debug-info="fully-read",
sources=[{file="test.c",
fullname="/tmp/info-sources/test.c",
debug-fully-read="true"},
{file="/usr/include/stdc-predef.h",
fullname="/usr/include/stdc-predef.h",
debug-fully-read="true"},
{file="header.h",
fullname="/tmp/info-sources/header.h",
debug-fully-read="true"}]},
{filename="/lib64/ld-linux-x86-64.so.2",
debug-info="none",
sources=[]},
{filename="system-supplied DSO at 0x7ffff7fcf000",
debug-info="none",
sources=[]},
{filename="/tmp/info-sources/libhelper.so",
debug-info="fully-read",
sources=[{file="helper.c",
fullname="/tmp/info-sources/helper.c",
debug-fully-read="true"},
{file="/usr/include/stdc-predef.h",
fullname="/usr/include/stdc-predef.h",
debug-fully-read="true"},
{file="header.h",
fullname="/tmp/info-sources/header.h",
debug-fully-read="true"}]},
{filename="/lib64/libc.so.6",
debug-info="none",
sources=[]}]

The `-file-list-shared-libraries' Command
-----------------------------------------

Synopsis
.......

-file-list-shared-libraries [ REGEXP ]

List the shared libraries in the program. With a regular expression
REGEXP, only those libraries whose names match REGEXP are listed.

GDB Command
..........

The corresponding GDB command is `info shared'. The fields have a
similar meaning to the `=library-loaded' notification. The `ranges'
field specifies the multiple segments belonging to this library. Each
range has the following fields:

`from'
The address defining the inclusive lower bound of the segment.

`to'
The address defining the exclusive upper bound of the segment.

Example
......

(gdb)
-file-list-exec-source-files
^done,shared-libraries=[
{id="/lib/libfoo.so",target-name="/lib/libfoo.so",host-name="/lib/libfoo.so",symbols-loaded="1",thread-group="i1",ranges=[{from="0x72815989",to="0x728162c0"}]},
{id="/lib/libbar.so",target-name="/lib/libbar.so",host-name="/lib/libbar.so",symbols-loaded="1",thread-group="i1",ranges=[{from="0x76ee48c0",to="0x76ee9160"}]}]
(gdb)

The `-file-symbol-file' Command
-------------------------------

Synopsis
.......

-file-symbol-file FILE

Read symbol table info from the specified FILE argument. When used
without arguments, clears GDB's symbol table info. No output is
produced, except for a completion notification.

GDB Command
..........

The corresponding GDB command is `symbol-file'.

Example
......

(gdb)
-file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

File: gdb.info, Node: GDB/MI Target Manipulation, Next: GDB/MI File Transfer Commands, Prev: GDB/MI File Commands, Up: GDB/MI

27.20 GDB/MI Target Manipulation Commands
=========================================

The `-target-attach' Command
----------------------------

Synopsis
.......

-target-attach PID | GID | FILE

Attach to a process PID or a file FILE outside of GDB, or a thread
group GID. If attaching to a thread group, the id previously returned
by `-list-thread-groups --available' must be used.

GDB Command
..........

The corresponding GDB command is `attach'.

Example
......

(gdb)
-target-attach 34
=thread-created,id="1"
*stopped,thread-id="1",frame={addr="0xb7f7e410",func="bar",args=[]}
^done
(gdb)

The `-target-detach' Command
----------------------------

Synopsis
.......

-target-detach [ PID | GID ]

Detach from the remote target which normally resumes its execution.
If either PID or GID is specified, detaches from either the specified
process, or specified thread group. There's no output.

GDB Command
..........

The corresponding GDB command is `detach'.

Example
......

(gdb)
-target-detach
^done
(gdb)

The `-target-disconnect' Command
--------------------------------

Synopsis
.......

-target-disconnect

Disconnect from the remote target. There's no output and the target
is generally not resumed.

GDB Command
..........

The corresponding GDB command is `disconnect'.

Example
......

(gdb)
-target-disconnect
^done
(gdb)

The `-target-download' Command
------------------------------

Synopsis
.......

-target-download

Loads the executable onto the remote target. It prints out an
update message every half second, which includes the fields:

`section'
The name of the section.

`section-sent'
The size of what has been sent so far for that section.

`section-size'
The size of the section.

`total-sent'
The total size of what was sent so far (the current and the
previous sections).

`total-size'
The size of the overall executable to download.

Each message is sent as status record (*note GDB/MI Output Syntax:
GDB/MI Output Syntax.).

In addition, it prints the name and size of the sections, as they are
downloaded. These messages include the following fields:

`section'
The name of the section.

`section-size'
The size of the section.

`total-size'
The size of the overall executable to download.

At the end, a summary is printed.

GDB Command
..........

The corresponding GDB command is `load'.

Example
......

Note: each status message appears on a single line. Here the messages
have been broken down so that they can fit onto a page.

(gdb)
-target-download
+download,{section=".text",section-size="6668",total-size="9880"}
+download,{section=".text",section-sent="512",section-size="6668",
total-sent="512",total-size="9880"}
+download,{section=".text",section-sent="1024",section-size="6668",
total-sent="1024",total-size="9880"}
+download,{section=".text",section-sent="1536",section-size="6668",
total-sent="1536",total-size="9880"}
+download,{section=".text",section-sent="2048",section-size="6668",
total-sent="2048",total-size="9880"}
+download,{section=".text",section-sent="2560",section-size="6668",
total-sent="2560",total-size="9880"}
+download,{section=".text",section-sent="3072",section-size="6668",
total-sent="3072",total-size="9880"}
+download,{section=".text",section-sent="3584",section-size="6668",
total-sent="3584",total-size="9880"}
+download,{section=".text",section-sent="4096",section-size="6668",
total-sent="4096",total-size="9880"}
+download,{section=".text",section-sent="4608",section-size="6668",
total-sent="4608",total-size="9880"}
+download,{section=".text",section-sent="5120",section-size="6668",
total-sent="5120",total-size="9880"}
+download,{section=".text",section-sent="5632",section-size="6668",
total-sent="5632",total-size="9880"}
+download,{section=".text",section-sent="6144",section-size="6668",
total-sent="6144",total-size="9880"}
+download,{section=".text",section-sent="6656",section-size="6668",
total-sent="6656",total-size="9880"}
+download,{section=".init",section-size="28",total-size="9880"}
+download,{section=".fini",section-size="28",total-size="9880"}
+download,{section=".data",section-size="3156",total-size="9880"}
+download,{section=".data",section-sent="512",section-size="3156",
total-sent="7236",total-size="9880"}
+download,{section=".data",section-sent="1024",section-size="3156",
total-sent="7748",total-size="9880"}
+download,{section=".data",section-sent="1536",section-size="3156",
total-sent="8260",total-size="9880"}
+download,{section=".data",section-sent="2048",section-size="3156",
total-sent="8772",total-size="9880"}
+download,{section=".data",section-sent="2560",section-size="3156",
total-sent="9284",total-size="9880"}
+download,{section=".data",section-sent="3072",section-size="3156",
total-sent="9796",total-size="9880"}
^done,address="0x10004",load-size="9880",transfer-rate="6586",
write-rate="429"
(gdb)

GDB Command
..........

No equivalent.

Example
......

N.A.

The `-target-flash-erase' Command
---------------------------------

Synopsis
.......

-target-flash-erase

Erases all known flash memory regions on the target.

The corresponding GDB command is `flash-erase'.

The output is a list of flash regions that have been erased, with
starting addresses and memory region sizes.

(gdb)
-target-flash-erase
^done,erased-regions={address="0x0",size="0x40000"}
(gdb)

The `-target-select' Command
----------------------------

Synopsis
.......

-target-select TYPE PARAMETERS ...

Connect GDB to the remote target. This command takes two args:

`TYPE'
The type of target, for instance `remote', etc.

`PARAMETERS'
Device names, host names and the like. *Note Commands for
Managing Targets: Target Commands, for more details.

The output is a connection notification, followed by the address at
which the target program is, in the following form:

^connected,addr="ADDRESS",func="FUNCTION NAME",
args=[ARG LIST]

GDB Command
..........

The corresponding GDB command is `target'.

Example
......

(gdb)
-target-select remote /dev/ttya
^connected,addr="0xfe00a300",func="??",args=[]
(gdb)

File: gdb.info, Node: GDB/MI File Transfer Commands, Next: GDB/MI Ada Exceptions Commands, Prev: GDB/MI Target Manipulation, Up: GDB/MI

27.21 GDB/MI File Transfer Commands
===================================

The `-target-file-put' Command
------------------------------

Synopsis
.......

-target-file-put HOSTFILE TARGETFILE

Copy file HOSTFILE from the host system (the machine running GDB) to
TARGETFILE on the target system.

GDB Command
..........

The corresponding GDB command is `remote put'.

Example
......

(gdb)
-target-file-put localfile remotefile
^done
(gdb)

The `-target-file-get' Command
------------------------------

Synopsis
.......

-target-file-get TARGETFILE HOSTFILE

Copy file TARGETFILE from the target system to HOSTFILE on the host
system.

GDB Command
..........

The corresponding GDB command is `remote get'.

Example
......

(gdb)
-target-file-get remotefile localfile
^done
(gdb)

The `-target-file-delete' Command
---------------------------------

Synopsis
.......

-target-file-delete TARGETFILE

Delete TARGETFILE from the target system.

GDB Command
..........

The corresponding GDB command is `remote delete'.

Example
......

(gdb)
-target-file-delete remotefile
^done
(gdb)

File: gdb.info, Node: GDB/MI Ada Exceptions Commands, Next: GDB/MI Support Commands, Prev: GDB/MI File Transfer Commands, Up: GDB/MI

27.22 Ada Exceptions GDB/MI Commands
====================================

The `-info-ada-exceptions' Command
----------------------------------

Synopsis
.......

-info-ada-exceptions [ REGEXP]

List all Ada exceptions defined within the program being debugged.
With a regular expression REGEXP, only those exceptions whose names
match REGEXP are listed.

GDB Command
..........

The corresponding GDB command is `info exceptions'.

Result
.....

The result is a table of Ada exceptions. The following columns are
defined for each exception:

`name'
The name of the exception.

`address'
The address of the exception.

Example
......

-info-ada-exceptions aint
^done,ada-exceptions={nr_rows="2",nr_cols="2",
hdr=[{width="1",alignment="-1",col_name="name",colhdr="Name"},
{width="1",alignment="-1",col_name="address",colhdr="Address"}],
body=[{name="constraint_error",address="0x0000000000613da0"},
{name="const.aint_global_e",address="0x0000000000613b00"}]}

Catching Ada Exceptions
-----------------------

The commands describing how to ask GDB to stop when a program raises an
exception are described at *Note Ada Exception GDB/MI Catchpoint
Commands::.

File: gdb.info, Node: GDB/MI Support Commands, Next: GDB/MI Miscellaneous Commands, Prev: GDB/MI Ada Exceptions Commands, Up: GDB/MI

27.23 GDB/MI Support Commands
=============================

Since new commands and features get regularly added to GDB/MI, some
commands are available to help front-ends query the debugger about
support for these capabilities. Similarly, it is also possible to
query GDB about target support of certain features.

The `-info-gdb-mi-command' Command
----------------------------------

Synopsis
.......

-info-gdb-mi-command CMD_NAME

Query support for the GDB/MI command named CMD_NAME.

Note that the dash (`-') starting all GDB/MI commands is technically
not part of the command name (*note GDB/MI Input Syntax::), and thus
should be omitted in CMD_NAME. However, for ease of use, this command
also accepts the form with the leading dash.

GDB Command
..........

There is no corresponding GDB command.

Result
.....

The result is a tuple. There is currently only one field:

`exists'
This field is equal to `"true"' if the GDB/MI command exists,
`"false"' otherwise.

Example
......

Here is an example where the GDB/MI command does not exist:

-info-gdb-mi-command unsupported-command
^done,command={exists="false"}

And here is an example where the GDB/MI command is known to the
debugger:

-info-gdb-mi-command symbol-list-lines
^done,command={exists="true"}

The `-list-features' Command
----------------------------

Returns a list of particular features of the MI protocol that this
version of gdb implements. A feature can be a command, or a new field
in an output of some command, or even an important bugfix. While a
frontend can sometimes detect presence of a feature at runtime, it is
easier to perform detection at debugger startup.

The command returns a list of strings, with each string naming an
available feature. Each returned string is just a name, it does not
have any internal structure. The list of possible feature names is
given below.

Example output:

(gdb) -list-features
^done,result=["feature1","feature2"]

The current list of features is:

`frozen-varobjs'
Indicates support for the `-var-set-frozen' command, as well as
possible presence of the `frozen' field in the output of
`-varobj-create'.

`pending-breakpoints'
Indicates support for the `-f' option to the `-break-insert'
command.

`python'
Indicates Python scripting support, Python-based pretty-printing
commands, and possible presence of the `display_hint' field in the
output of `-var-list-children'

`thread-info'
Indicates support for the `-thread-info' command.

`data-read-memory-bytes'
Indicates support for the `-data-read-memory-bytes' and the
`-data-write-memory-bytes' commands.

`breakpoint-notifications'
Indicates that changes to breakpoints and breakpoints created via
the CLI will be announced via async records.

`ada-task-info'
Indicates support for the `-ada-task-info' command.

`language-option'
Indicates that all GDB/MI commands accept the `--language' option
(*note Context management::).

`info-gdb-mi-command'
Indicates support for the `-info-gdb-mi-command' command.

`undefined-command-error-code'
Indicates support for the "undefined-command" error code in error
result records, produced when trying to execute an undefined
GDB/MI command (*note GDB/MI Result Records::).

`exec-run-start-option'
Indicates that the `-exec-run' command supports the `--start'
option (*note GDB/MI Program Execution::).

`data-disassemble-a-option'
Indicates that the `-data-disassemble' command supports the `-a'
option (*note GDB/MI Data Manipulation::).

`simple-values-ref-types'
Indicates that the `--simple-values' argument to the
`-stack-list-arguments', `-stack-list-locals',
`-stack-list-variables', and `-var-list-children' commands takes
reference types into account: that is, a value is considered
simple if it is neither an array, structure, or union, nor a
reference to an array, structure, or union.

The `-list-target-features' Command
-----------------------------------

Returns a list of particular features that are supported by the target.
Those features affect the permitted MI commands, but unlike the
features reported by the `-list-features' command, the features depend
on which target GDB is using at the moment. Whenever a target can
change, due to commands such as `-target-select', `-target-attach' or
`-exec-run', the list of target features may change, and the frontend
should obtain it again. Example output:

(gdb) -list-target-features
^done,result=["async"]

The current list of features is:

`async'
Indicates that the target is capable of asynchronous command
execution, which means that GDB will accept further commands while
the target is running.

`reverse'
Indicates that the target is capable of reverse execution. *Note
Reverse Execution::, for more information.

File: gdb.info, Node: GDB/MI Miscellaneous Commands, Prev: GDB/MI Support Commands, Up: GDB/MI

27.24 Miscellaneous GDB/MI Commands
===================================

The `-gdb-exit' Command
-----------------------

Synopsis
.......

-gdb-exit

Exit GDB immediately.

GDB Command
..........

Approximately corresponds to `quit'.

Example
......

(gdb)
-gdb-exit
^exit

The `-gdb-set' Command
----------------------

Synopsis
.......

-gdb-set

Set an internal GDB variable.

GDB Command
..........

The corresponding GDB command is `set'.

Example
......

(gdb)
-gdb-set $foo=3
^done
(gdb)

The `-gdb-show' Command
-----------------------

Synopsis
.......

-gdb-show

Show the current value of a GDB variable.

GDB Command
..........

The corresponding GDB command is `show'.

Example
......

(gdb)
-gdb-show annotate
^done,value="0"
(gdb)

The `-gdb-version' Command
--------------------------

Synopsis
.......

-gdb-version

Show version information for GDB. Used mostly in testing.

GDB Command
..........

The GDB equivalent is `show version'. GDB by default shows this
information when you start an interactive session.

Example
......

(gdb)
-gdb-version
~GNU gdb 5.2.1
~Copyright 2000 Free Software Foundation, Inc.
~GDB is free software, covered by the GNU General Public License, and
~you are welcome to change it and/or distribute copies of it under
~ certain conditions.
~Type "show copying" to see the conditions.
~There is absolutely no warranty for GDB. Type "show warranty" for
~ details.
~This GDB was configured as
"--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
^done
(gdb)

The `-list-thread-groups' Command
---------------------------------

Synopsis
.......

-list-thread-groups [ --available ] [ --recurse 1 ] [ GROUP ... ]

Lists thread groups (*note Thread groups::). When a single thread
group is passed as the argument, lists the children of that group.
When several thread group are passed, lists information about those
thread groups. Without any parameters, lists information about all
top-level thread groups.

Normally, thread groups that are being debugged are reported. With
the `--available' option, GDB reports thread groups available on the
target.

The output of this command may have either a `threads' result or a
`groups' result. The `thread' result has a list of tuples as value,
with each tuple describing a thread (*note GDB/MI Thread
Information::). The `groups' result has a list of tuples as value,
each tuple describing a thread group. If top-level groups are
requested (that is, no parameter is passed), or when several groups are
passed, the output always has a `groups' result. The format of the
`group' result is described below.

To reduce the number of roundtrips it's possible to list thread
groups together with their children, by passing the `--recurse' option
and the recursion depth. Presently, only recursion depth of 1 is
permitted. If this option is present, then every reported thread group
will also include its children, either as `group' or `threads' field.

In general, any combination of option and parameters is permitted,
with the following caveats:

* When a single thread group is passed, the output will typically be
the `threads' result. Because threads may not contain anything,
the `recurse' option will be ignored.

* When the `--available' option is passed, limited information may
be available. In particular, the list of threads of a process
might be inaccessible. Further, specifying specific thread groups
might not give any performance advantage over listing all thread
groups. The frontend should assume that `-list-thread-groups
--available' is always an expensive operation and cache the
results.

The `groups' result is a list of tuples, where each tuple may have
the following fields:

`id'
Identifier of the thread group. This field is always present.
The identifier is an opaque string; frontends should not try to
convert it to an integer, even though it might look like one.

`type'
The type of the thread group. At present, only `process' is a
valid type.

`pid'
The target-specific process identifier. This field is only present
for thread groups of type `process' and only if the process exists.

`exit-code'
The exit code of this group's last exited thread, formatted in
octal. This field is only present for thread groups of type
`process' and only if the process is not running.

`num_children'
The number of children this thread group has. This field may be
absent for an available thread group.

`threads'
This field has a list of tuples as value, each tuple describing a
thread. It may be present if the `--recurse' option is specified,
and it's actually possible to obtain the threads.

`cores'
This field is a list of integers, each identifying a core that one
thread of the group is running on. This field may be absent if
such information is not available.

`executable'
The name of the executable file that corresponds to this thread
group. The field is only present for thread groups of type
`process', and only if there is a corresponding executable file.

Example
......

(gdb)
-list-thread-groups
^done,groups=[{id="17",type="process",pid="yyy",num_children="2"}]
-list-thread-groups 17
^done,threads=[{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]},state="running"},
{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
frame={level="0",addr="0x0804891f",func="foo",args=[{name="i",value="10"}],
file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"},state="running"}]]
-list-thread-groups --available
^done,groups=[{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]}]
-list-thread-groups --available --recurse 1
^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]},
{id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},..]
-list-thread-groups --available --recurse 1 17 18
^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]},
{id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},...]

The `-info-os' Command
----------------------

Synopsis
.......

-info-os [ TYPE ]

If no argument is supplied, the command returns a table of available
operating-system-specific information types. If one of these types is
supplied as an argument TYPE, then the command returns a table of data
of that type.

The types of information available depend on the target operating
system.

GDB Command
..........

The corresponding GDB command is `info os'.

Example
......

When run on a GNU/Linux system, the output will look something like
this:

(gdb)
-info-os
^done,OSDataTable={nr_rows="10",nr_cols="3",
hdr=[{width="10",alignment="-1",col_name="col0",colhdr="Type"},
{width="10",alignment="-1",col_name="col1",colhdr="Description"},
{width="10",alignment="-1",col_name="col2",colhdr="Title"}],
body=[item={col0="cpus",col1="Listing of all cpus/cores on the system",
col2="CPUs"},
item={col0="files",col1="Listing of all file descriptors",
col2="File descriptors"},
item={col0="modules",col1="Listing of all loaded kernel modules",
col2="Kernel modules"},
item={col0="msg",col1="Listing of all message queues",
col2="Message queues"},
item={col0="processes",col1="Listing of all processes",
col2="Processes"},
item={col0="procgroups",col1="Listing of all process groups",
col2="Process groups"},
item={col0="semaphores",col1="Listing of all semaphores",
col2="Semaphores"},
item={col0="shm",col1="Listing of all shared-memory regions",
col2="Shared-memory regions"},
item={col0="sockets",col1="Listing of all internet-domain sockets",
col2="Sockets"},
item={col0="threads",col1="Listing of all threads",
col2="Threads"}]
(gdb)
-info-os processes
^done,OSDataTable={nr_rows="190",nr_cols="4",
hdr=[{width="10",alignment="-1",col_name="col0",colhdr="pid"},
{width="10",alignment="-1",col_name="col1",colhdr="user"},
{width="10",alignment="-1",col_name="col2",colhdr="command"},
{width="10",alignment="-1",col_name="col3",colhdr="cores"}],
body=[item={col0="1",col1="root",col2="/sbin/init",col3="0"},
item={col0="2",col1="root",col2="[kthreadd]",col3="1"},
item={col0="3",col1="root",col2="[ksoftirqd/0]",col3="0"},
...
item={col0="26446",col1="stan",col2="bash",col3="0"},
item={col0="28152",col1="stan",col2="bash",col3="1"}]}
(gdb)

(Note that the MI output here includes a `"Title"' column that does
not appear in command-line `info os'; this column is useful for MI
clients that want to enumerate the types of data, such as in a popup
menu, but is needless clutter on the command line, and `info os' omits
it.)

The `-add-inferior' Command
---------------------------

Synopsis
.......

-add-inferior [ --no-connection ]

Creates a new inferior (*note Inferiors Connections and Programs::).
The created inferior is not associated with any executable. Such
association may be established with the `-file-exec-and-symbols' command
(*note GDB/MI File Commands::).

By default, the new inferior begins connected to the same target
connection as the current inferior. For example, if the current
inferior was connected to `gdbserver' with `target remote', then the
new inferior will be connected to the same `gdbserver' instance. The
`--no-connection' option starts the new inferior with no connection
yet. You can then for example use the `-target-select remote' command
to connect to some other `gdbserver' instance, use `-exec-run' to spawn
a local program, etc.

The command response always has a field, INFERIOR, whose value is
the identifier of the thread group corresponding to the new inferior.

An additional section field, CONNECTION, is optional. This field
will only exist if the new inferior has a target connection. If this
field exists, then its value will be a tuple containing the following
fields:

`number'
The number of the connection used for the new inferior.

`name'
The name of the connection type used for the new inferior.

GDB Command
..........

The corresponding GDB command is `add-inferior' (*note `add-inferior':
add_inferior_cli.).

Example
......

(gdb)
-add-inferior
^done,inferior="i3"

The `-remove-inferior' Command
------------------------------

Synopsis
.......

-remove-inferior INFERIOR-ID

Removes an inferior (*note Inferiors Connections and Programs::).
Only inferiors that have exited can be removed. The INFERIOR-ID is the
inferior to be removed, and should be the same id string as returned by
the `-add-inferior' command.

When an inferior is successfully removed a `=thread-group-removed'
notification (*note GDB/MI Async Records::) is emitted, the ID field of
which contains the INFERIOR-ID for the removed inferior.

GDB Command
..........

The corresponding GDB command is `remove-inferiors' (*note
`remove-inferiors': remove_inferiors_cli.).

Example
......

(gdb)
-remove-inferior i3
=thread-group-removed,id="i3"
^done

The `-interpreter-exec' Command
-------------------------------

Synopsis
.......

-interpreter-exec INTERPRETER COMMAND

Execute the specified COMMAND in the given INTERPRETER.

GDB Command
..........

The corresponding GDB command is `interpreter-exec'.

Example
......

(gdb)
-interpreter-exec console "break main"
&"During symbol reading, couldn't parse type; debugger out of date?.\n"
&"During symbol reading, bad structure-type format.\n"
~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
^done
(gdb)

The `-inferior-tty-set' Command
-------------------------------

Synopsis
.......

-inferior-tty-set /dev/pts/1

Set terminal for future runs of the program being debugged.

GDB Command
..........

The corresponding GDB command is `set inferior-tty' /dev/pts/1.

Example
......

(gdb)
-inferior-tty-set /dev/pts/1
^done
(gdb)

The `-inferior-tty-show' Command
--------------------------------

Synopsis
.......

-inferior-tty-show

Show terminal for future runs of program being debugged.

GDB Command
..........

The corresponding GDB command is `show inferior-tty'.

Example
......

(gdb)
-inferior-tty-set /dev/pts/1
^done
(gdb)
-inferior-tty-show
^done,inferior_tty_terminal="/dev/pts/1"
(gdb)

The `-enable-timings' Command
-----------------------------

Synopsis
.......

-enable-timings [yes | no]

Toggle the printing of the wallclock, user and system times for an MI
command as a field in its output. This command is to help frontend
developers optimize the performance of their code. No argument is
equivalent to `yes'.

GDB Command
..........

No equivalent.

Example
......

(gdb)
-enable-timings
^done
(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
addr="0x080484ed",func="main",file="myprog.c",
fullname="/home/nickrob/myprog.c",line="73",thread-groups=["i1"],
times="0"},
time={wallclock="0.05185",user="0.00800",system="0.00000"}
(gdb)
-enable-timings no
^done
(gdb)
-exec-run
^running
(gdb)
*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
frame={addr="0x080484ed",func="main",args=[{name="argc",value="1"},
{name="argv",value="0xbfb60364"}],file="myprog.c",
fullname="/home/nickrob/myprog.c",line="73",arch="i386:x86_64"}
(gdb)

The `-complete' Command
-----------------------

Synopsis
.......

-complete COMMAND

Show a list of completions for partially typed CLI COMMAND.

This command is intended for GDB/MI frontends that cannot use two
separate CLI and MI channels -- for example: because of lack of PTYs
like on Windows or because GDB is used remotely via a SSH connection.

Result
.....

The result consists of two or three fields:

`completion'
This field contains the completed COMMAND. If COMMAND has no
known completions, this field is omitted.

`matches'
This field contains a (possibly empty) array of matches. It is
always present.

`max_completions_reached'
This field contains `1' if number of known completions is above
`max-completions' limit (*note Completion::), otherwise it contains
`0'. It is always present.

GDB Command
..........

The corresponding GDB command is `complete'.

Example
......

(gdb)
-complete br
^done,completion="break",
matches=["break","break-range"],
max_completions_reached="0"
(gdb)
-complete "b ma"
^done,completion="b ma",
matches=["b madvise","b main"],max_completions_reached="0"
(gdb)
-complete "b push_b"
^done,completion="b push_back(",
matches=[
"b A::push_back(void*)",
"b std::string::push_back(char)",
"b std::vector<int, std::allocator<int> >::push_back(int&&)"],
max_completions_reached="0"
(gdb)
-complete "nonexist"
^done,matches=[],max_completions_reached="0"
(gdb)

File: gdb.info, Node: Annotations, Next: Debugger Adapter Protocol, Prev: GDB/MI, Up: Top

28 GDB Annotations
******************

This chapter describes annotations in GDB. Annotations were designed
to interface GDB to graphical user interfaces or other similar programs
which want to interact with GDB at a relatively high level.

The annotation mechanism has largely been superseded by GDB/MI
(*note GDB/MI::).

* Menu:

* Annotations Overview:: What annotations are; the general syntax.
* Server Prefix:: Issuing a command without affecting user state.
* Prompting:: Annotations marking GDB's need for input.
* Errors:: Annotations for error messages.
* Invalidation:: Some annotations describe things now invalid.
* Annotations for Running::
Whether the program is running, how it stopped, etc.
* Source Annotations:: Annotations describing source code.

File: gdb.info, Node: Annotations Overview, Next: Server Prefix, Up: Annotations

28.1 What is an Annotation?
===========================

Annotations start with a newline character, two `control-z' characters,
and the name of the annotation. If there is no additional information
associated with this annotation, the name of the annotation is followed
immediately by a newline. If there is additional information, the name
of the annotation is followed by a space, the additional information,
and a newline. The additional information cannot contain newline
characters.

Any output not beginning with a newline and two `control-z'
characters denotes literal output from GDB. Currently there is no need
for GDB to output a newline followed by two `control-z' characters, but
if there was such a need, the annotations could be extended with an
`escape' annotation which means those three characters as output.

The annotation LEVEL, which is specified using the `--annotate'
command line option (*note Mode Options::), controls how much
information GDB prints together with its prompt, values of expressions,
source lines, and other types of output. Level 0 is for no
annotations, level 1 is for use when GDB is run as a subprocess of GNU
Emacs, level 3 is the maximum annotation suitable for programs that
control GDB, and level 2 annotations have been made obsolete (*note
Limitations of the Annotation Interface: (annotate)Limitations.).

`set annotate LEVEL'
The GDB command `set annotate' sets the level of annotations to
the specified LEVEL.

`show annotate'
Show the current annotation level.

This chapter describes level 3 annotations.

A simple example of starting up GDB with annotations is:

$ gdb --annotate=3
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it
under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty"
for details.
This GDB was configured as "i386-pc-linux-gnu"

^Z^Zpre-prompt
(gdb)
^Z^Zprompt
quit

^Z^Zpost-prompt
$

Here `quit' is input to GDB; the rest is output from GDB. The three
lines beginning `^Z^Z' (where `^Z' denotes a `control-z' character) are
annotations; the rest is output from GDB.

File: gdb.info, Node: Server Prefix, Next: Prompting, Prev: Annotations Overview, Up: Annotations

28.2 The Server Prefix
======================

If you prefix a command with `server ' then it will not affect the
command history, nor will it affect GDB's notion of which command to
repeat if <RET> is pressed on a line by itself. This means that
commands can be run behind a user's back by a front-end in a
transparent manner.

The `server ' prefix does not affect the recording of values into
the value history; to print a value without recording it into the value
history, use the `output' command instead of the `print' command.

Using this prefix also disables confirmation requests (*note
confirmation requests::).

File: gdb.info, Node: Prompting, Next: Errors, Prev: Server Prefix, Up: Annotations

28.3 Annotation for GDB Input
=============================

When GDB prompts for input, it annotates this fact so it is possible to
know when to send output, when the output from a given command is over,
etc.

Different kinds of input each have a different "input type". Each
input type has three annotations: a `pre-' annotation, which denotes
the beginning of any prompt which is being output, a plain annotation,
which denotes the end of the prompt, and then a `post-' annotation
which denotes the end of any echo which may (or may not) be associated
with the input. For example, the `prompt' input type features the
following annotations:

^Z^Zpre-prompt
^Z^Zprompt
^Z^Zpost-prompt

The input types are

`prompt'
When GDB is prompting for a command (the main GDB prompt).

`commands'
When GDB prompts for a set of commands, like in the `commands'
command. The annotations are repeated for each command which is
input.

`overload-choice'
When GDB wants the user to select between various overloaded
functions.

`query'
When GDB wants the user to confirm a potentially dangerous
operation.

`prompt-for-continue'
When GDB is asking the user to press return to continue. Note:
Don't expect this to work well; instead use `set height 0' to
disable prompting. This is because the counting of lines is buggy
in the presence of annotations.

File: gdb.info, Node: Errors, Next: Invalidation, Prev: Prompting, Up: Annotations

28.4 Errors
===========

^Z^Zquit

This annotation occurs right before GDB responds to an interrupt.

^Z^Zerror

This annotation occurs right before GDB responds to an error.

Quit and error annotations indicate that any annotations which GDB
was in the middle of may end abruptly. For example, if a
`value-history-begin' annotation is followed by a `error', one cannot
expect to receive the matching `value-history-end'. One cannot expect
not to receive it either, however; an error annotation does not
necessarily mean that GDB is immediately returning all the way to the
top level.

A quit or error annotation may be preceded by

^Z^Zerror-begin

Any output between that and the quit or error annotation is the error
message.

Warning messages are not yet annotated.

File: gdb.info, Node: Invalidation, Next: Annotations for Running, Prev: Errors, Up: Annotations

28.5 Invalidation Notices
=========================

The following annotations say that certain pieces of state may have
changed.

`^Z^Zframes-invalid'
The frames (for example, output from the `backtrace' command) may
have changed.

`^Z^Zbreakpoints-invalid'
The breakpoints may have changed. For example, the user just
added or deleted a breakpoint.

File: gdb.info, Node: Annotations for Running, Next: Source Annotations, Prev: Invalidation, Up: Annotations

28.6 Running the Program
========================

When the program starts executing due to a GDB command such as `step'
or `continue',

^Z^Zstarting

is output. When the program stops,

^Z^Zstopped

is output. Before the `stopped' annotation, a variety of
annotations describe how the program stopped.

`^Z^Zexited EXIT-STATUS'
The program exited, and EXIT-STATUS is the exit status (zero for
successful exit, otherwise nonzero).

`^Z^Zsignalled'
The program exited with a signal. After the `^Z^Zsignalled', the
annotation continues:

INTRO-TEXT
^Z^Zsignal-name
NAME
^Z^Zsignal-name-end
MIDDLE-TEXT
^Z^Zsignal-string
STRING
^Z^Zsignal-string-end
END-TEXT

where NAME is the name of the signal, such as `SIGILL' or
`SIGSEGV', and STRING is the explanation of the signal, such as
`Illegal Instruction' or `Segmentation fault'. The arguments
INTRO-TEXT, MIDDLE-TEXT, and END-TEXT are for the user's benefit
and have no particular format.

`^Z^Zsignal'
The syntax of this annotation is just like `signalled', but GDB is
just saying that the program received the signal, not that it was
terminated with it.

`^Z^Zbreakpoint NUMBER'
The program hit breakpoint number NUMBER.

`^Z^Zwatchpoint NUMBER'
The program hit watchpoint number NUMBER.

File: gdb.info, Node: Source Annotations, Prev: Annotations for Running, Up: Annotations

28.7 Displaying Source
======================

The following annotation is used instead of displaying source code:

^Z^Zsource FILENAME:LINE:CHARACTER:MIDDLE:ADDR

where FILENAME is an absolute file name indicating which source
file, LINE is the line number within that file (where 1 is the first
line in the file), CHARACTER is the character position within the file
(where 0 is the first character in the file) (for most debug formats
this will necessarily point to the beginning of a line), MIDDLE is
`middle' if ADDR is in the middle of the line, or `beg' if ADDR is at
the beginning of the line, and ADDR is the address in the target
program associated with the source which is being displayed. The ADDR
is in the form `0x' followed by one or more lowercase hex digits (note
that this does not depend on the language).

File: gdb.info, Node: Debugger Adapter Protocol, Next: JIT Interface, Prev: Annotations, Up: Top

29 Debugger Adapter Protocol
****************************

The Debugger Adapter Protocol is a generic API that is used by some
IDEs to communicate with debuggers. It is documented at
`https://microsoft.github.io/debug-adapter-protocol/'.

Generally, GDB implements the Debugger Adapter Protocol as written.
However, in some cases, extensions are either needed or even expected.

GDB defines some parameters that can be passed to the `launch'
request:

`args'
If provided, this should be an array of strings. These strings are
provided as command-line arguments to the inferior, as if by `set
args'. *Note Arguments::.

`cwd'
If provided, this should be a string. GDB will change its working
directory to this directory, as if by the `cd' command (*note
Working Directory::). The launched program will inherit this as
its working directory. Note that change of directory happens
before the `program' parameter is processed. This will affect the
result if `program' is a relative filename.

`env'
If provided, this should be an object. Each key of the object
will be used as the name of an environment variable; each value
must be a string and will be the value of that variable. The
environment of the inferior will be set to exactly as passed in.
*Note Environment::.

`program'
If provided, this is a string that specifies the program to use.
This corresponds to the `file' command. *Note Files::.

`stopAtBeginningOfMainSubprogram'
If provided, this must be a boolean. When `True', GDB will set a
temporary breakpoint at the program's main procedure, using the
same approach as the `start' command. *Note Starting::.

GDB defines some parameters that can be passed to the `attach'
request. Either `pid' or `target' must be specified, but if both are
specified then `target' will be ignored.

`pid'
The process ID to which GDB should attach. *Note Attach::.

`program'
If provided, this is a string that specifies the program to use.
This corresponds to the `file' command. *Note Files::. In some
cases, GDB can automatically determine which program is running.
However, for many remote targets, this is not the case, and so this
should be supplied.

`target'
The target to which GDB should connect. This is a string and is
passed to the `target remote' command. *Note Connecting::.

In response to the `disassemble' request, DAP allows the client to
return the bytes of each instruction in an implementation-defined
format. GDB implements this by sending a string with the bytes encoded
in hex, like `"55a2b900"'.

When the `repl' context is used for the `evaluate' request, GDB
evaluates the provided expression as a CLI command.

Evaluation in general can cause the inferior to continue execution.
For example, evaluating the `continue' command could do this, as could
evaluating an expression that involves an inferior function call.

`repl' evaluation can also cause GDB to appear to stop responding to
requests, for example if a CLI script does a lengthy computation.

Evaluations like this can be interrupted using the DAP `cancel'
request. (In fact, `cancel' should work for any request, but it is
unlikely to be useful for most of them.)

GDB provides a couple of logging settings that can be used in DAP
mode. These can be set on the command line using the `-iex' option
(*note File Options::).

`set debug dap-log-file [FILENAME]'
Enable DAP logging. Logs are written to FILENAME. If no FILENAME
is given, logging is stopped.

`set debug dap-log-level LEVEL'
Set the DAP logging level. The default is `1', which logs the DAP
protocol, whatever debug messages the developers thought were
useful, and unexpected exceptions. Level `2' can be used to log
all exceptions, including ones that are considered to be expected.
For example, a failure to parse an expression would be considered a
normal exception and not normally be logged.

File: gdb.info, Node: JIT Interface, Next: In-Process Agent, Prev: Debugger Adapter Protocol, Up: Top

30 JIT Compilation Interface
****************************

This chapter documents GDB's "just-in-time" (JIT) compilation
interface. A JIT compiler is a program or library that generates native
executable code at runtime and executes it, usually in order to achieve
good performance while maintaining platform independence.

Programs that use JIT compilation are normally difficult to debug
because portions of their code are generated at runtime, instead of
being loaded from object files, which is where GDB normally finds the
program's symbols and debug information. In order to debug programs
that use JIT compilation, GDB has an interface that allows the program
to register in-memory symbol files with GDB at runtime.

If you are using GDB to debug a program that uses this interface,
then it should work transparently so long as you have not stripped the
binary. If you are developing a JIT compiler, then the interface is
documented in the rest of this chapter. At this time, the only known
client of this interface is the LLVM JIT.

Broadly speaking, the JIT interface mirrors the dynamic loader
interface. The JIT compiler communicates with GDB by writing data into
a global variable and calling a function at a well-known symbol. When
GDB attaches, it reads a linked list of symbol files from the global
variable to find existing code, and puts a breakpoint in the function
so that it can find out about additional code.

* Menu:

* Declarations:: Relevant C struct declarations
* Registering Code:: Steps to register code
* Unregistering Code:: Steps to unregister code
* Custom Debug Info:: Emit debug information in a custom format

File: gdb.info, Node: Declarations, Next: Registering Code, Up: JIT Interface

30.1 JIT Declarations
=====================

These are the relevant struct declarations that a C program should
include to implement the interface:

typedef enum
{
JIT_NOACTION = 0,
JIT_REGISTER_FN,
JIT_UNREGISTER_FN
} jit_actions_t;

struct jit_code_entry
{
struct jit_code_entry *next_entry;
struct jit_code_entry *prev_entry;
const char *symfile_addr;
uint64_t symfile_size;
};

struct jit_descriptor
{
uint32_t version;
/* This type should be jit_actions_t, but we use uint32_t
to be explicit about the bitwidth. */
uint32_t action_flag;
struct jit_code_entry *relevant_entry;
struct jit_code_entry *first_entry;
};

/* GDB puts a breakpoint in this function. */
void __attribute__((noinline)) __jit_debug_register_code() { };

/* Make sure to specify the version statically, because the
debugger may check the version before we can set it. */
struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

If the JIT is multi-threaded, then it is important that the JIT
synchronize any modifications to this global data properly, which can
easily be done by putting a global mutex around modifications to these
structures.

File: gdb.info, Node: Registering Code, Next: Unregistering Code, Prev: Declarations, Up: JIT Interface

30.2 Registering Code
=====================

To register code with GDB, the JIT should follow this protocol:

* Generate an object file in memory with symbols and other desired
debug information. The file must include the virtual addresses of
the sections.

* Create a code entry for the file, which gives the start and size
of the symbol file.

* Add it to the linked list in the JIT descriptor.

* Point the relevant_entry field of the descriptor at the entry.

* Set `action_flag' to `JIT_REGISTER' and call
`__jit_debug_register_code'.

When GDB is attached and the breakpoint fires, GDB uses the
`relevant_entry' pointer so it doesn't have to walk the list looking for
new code. However, the linked list must still be maintained in order
to allow GDB to attach to a running process and still find the symbol
files.

File: gdb.info, Node: Unregistering Code, Next: Custom Debug Info, Prev: Registering Code, Up: JIT Interface

30.3 Unregistering Code
=======================

If code is freed, then the JIT should use the following protocol:

* Remove the code entry corresponding to the code from the linked
list.

* Point the `relevant_entry' field of the descriptor at the code
entry.

* Set `action_flag' to `JIT_UNREGISTER' and call
`__jit_debug_register_code'.

If the JIT frees or recompiles code without unregistering it, then
GDB and the JIT will leak the memory used for the associated symbol
files.

File: gdb.info, Node: Custom Debug Info, Prev: Unregistering Code, Up: JIT Interface

30.4 Custom Debug Info
======================

Generating debug information in platform-native file formats (like ELF
or COFF) may be an overkill for JIT compilers; especially if all the
debug info is used for is displaying a meaningful backtrace. The issue
can be resolved by having the JIT writers decide on a debug info format
and also provide a reader that parses the debug info generated by the
JIT compiler. This section gives a brief overview on writing such a
parser. More specific details can be found in the source file
`gdb/jit-reader.in', which is also installed as a header at
`INCLUDEDIR/gdb/jit-reader.h' for easy inclusion.

The reader is implemented as a shared object (so this functionality
is not available on platforms which don't allow loading shared objects
at runtime). Two GDB commands, `jit-reader-load' and
`jit-reader-unload' are provided, to be used to load and unload the
readers from a preconfigured directory. Once loaded, the shared object
is used the parse the debug information emitted by the JIT compiler.

* Menu:

* Using JIT Debug Info Readers:: How to use supplied readers correctly
* Writing JIT Debug Info Readers:: Creating a debug-info reader

File: gdb.info, Node: Using JIT Debug Info Readers, Next: Writing JIT Debug Info Readers, Up: Custom Debug Info

30.4.1 Using JIT Debug Info Readers
-----------------------------------

Readers can be loaded and unloaded using the `jit-reader-load' and
`jit-reader-unload' commands.

`jit-reader-load READER'
Load the JIT reader named READER, which is a shared object
specified as either an absolute or a relative file name. In the
latter case, GDB will try to load the reader from a pre-configured
directory, usually `LIBDIR/gdb/' on a UNIX system (here LIBDIR is
the system library directory, often `/usr/local/lib').

Only one reader can be active at a time; trying to load a second
reader when one is already loaded will result in GDB reporting an
error. A new JIT reader can be loaded by first unloading the
current one using `jit-reader-unload' and then invoking
`jit-reader-load'.

`jit-reader-unload'
Unload the currently loaded JIT reader.

File: gdb.info, Node: Writing JIT Debug Info Readers, Prev: Using JIT Debug Info Readers, Up: Custom Debug Info

30.4.2 Writing JIT Debug Info Readers
-------------------------------------

As mentioned, a reader is essentially a shared object conforming to a
certain ABI. This ABI is described in `jit-reader.h'.

`jit-reader.h' defines the structures, macros and functions required
to write a reader. It is installed (along with GDB), in
`INCLUDEDIR/gdb' where INCLUDEDIR is the system include directory.

Readers need to be released under a GPL compatible license. A reader
can be declared as released under such a license by placing the macro
`GDB_DECLARE_GPL_COMPATIBLE_READER' in a source file.

The entry point for readers is the symbol `gdb_init_reader', which
is expected to be a function with the prototype

extern struct gdb_reader_funcs *gdb_init_reader (void);

`struct gdb_reader_funcs' contains a set of pointers to callback
functions. These functions are executed to read the debug info
generated by the JIT compiler (`read'), to unwind stack frames
(`unwind') and to create canonical frame IDs (`get_frame_id'). It also
has a callback that is called when the reader is being unloaded
(`destroy'). The struct looks like this

struct gdb_reader_funcs
{
/* Must be set to GDB_READER_INTERFACE_VERSION. */
int reader_version;

/* For use by the reader. */
void *priv_data;

gdb_read_debug_info *read;
gdb_unwind_frame *unwind;
gdb_get_frame_id *get_frame_id;
gdb_destroy_reader *destroy;
};

The callbacks are provided with another set of callbacks by GDB to
do their job. For `read', these callbacks are passed in a `struct
gdb_symbol_callbacks' and for `unwind' and `get_frame_id', in a `struct
gdb_unwind_callbacks'. `struct gdb_symbol_callbacks' has callbacks to
create new object files and new symbol tables inside those object
files. `struct gdb_unwind_callbacks' has callbacks to read registers
off the current frame and to write out the values of the registers in
the previous frame. Both have a callback (`target_read') to read bytes
off the target's address space.

File: gdb.info, Node: In-Process Agent, Next: GDB Bugs, Prev: JIT Interface, Up: Top

31 In-Process Agent
*******************

The traditional debugging model is conceptually low-speed, but works
fine, because most bugs can be reproduced in debugging-mode execution.
However, as multi-core or many-core processors are becoming mainstream,
and multi-threaded programs become more and more popular, there should
be more and more bugs that only manifest themselves at normal-mode
execution, for example, thread races, because debugger's interference
with the program's timing may conceal the bugs. On the other hand, in
some applications, it is not feasible for the debugger to interrupt the
program's execution long enough for the developer to learn anything
helpful about its behavior. If the program's correctness depends on
its real-time behavior, delays introduced by a debugger might cause the
program to fail, even when the code itself is correct. It is useful to
be able to observe the program's behavior without interrupting it.

Therefore, traditional debugging model is too intrusive to reproduce
some bugs. In order to reduce the interference with the program, we can
reduce the number of operations performed by debugger. The "In-Process
Agent", a shared library, is running within the same process with
inferior, and is able to perform some debugging operations itself. As
a result, debugger is only involved when necessary, and performance of
debugging can be improved accordingly. Note that interference with
program can be reduced but can't be removed completely, because the
in-process agent will still stop or slow down the program.

The in-process agent can interpret and execute Agent Expressions
(*note Agent Expressions::) during performing debugging operations. The
agent expressions can be used for different purposes, such as collecting
data in tracepoints, and condition evaluation in breakpoints.

You can control whether the in-process agent is used as an aid for
debugging with the following commands:

`set agent on'
Causes the in-process agent to perform some operations on behalf
of the debugger. Just which operations requested by the user will
be done by the in-process agent depends on the its capabilities.
For example, if you request to evaluate breakpoint conditions in
the in-process agent, and the in-process agent has such capability
as well, then breakpoint conditions will be evaluated in the
in-process agent.

`set agent off'
Disables execution of debugging operations by the in-process
agent. All of the operations will be performed by GDB.

`show agent'
Display the current setting of execution of debugging operations by
the in-process agent.

* Menu:

* In-Process Agent Protocol::

File: gdb.info, Node: In-Process Agent Protocol, Up: In-Process Agent

31.1 In-Process Agent Protocol
==============================

The in-process agent is able to communicate with both GDB and GDBserver
(*note In-Process Agent::). This section documents the protocol used
for communications between GDB or GDBserver and the IPA. In general,
GDB or GDBserver sends commands (*note IPA Protocol Commands::) and
data to in-process agent, and then in-process agent replies back with
the return result of the command, or some other information. The data
sent to in-process agent is composed of primitive data types, such as
4-byte or 8-byte type, and composite types, which are called objects
(*note IPA Protocol Objects::).

* Menu:

* IPA Protocol Objects::
* IPA Protocol Commands::

File: gdb.info, Node: IPA Protocol Objects, Next: IPA Protocol Commands, Up: In-Process Agent Protocol

31.1.1 IPA Protocol Objects
---------------------------

The commands sent to and results received from agent may contain some
complex data types called "objects".

The in-process agent is running on the same machine with GDB or
GDBserver, so it doesn't have to handle as much differences between two
ends as remote protocol (*note Remote Protocol::) tries to handle.
However, there are still some differences of two ends in two processes:

1. word size. On some 64-bit machines, GDB or GDBserver can be
compiled as a 64-bit executable, while in-process agent is a
32-bit one.

2. ABI. Some machines may have multiple types of ABI, GDB or
GDBserver is compiled with one, and in-process agent is compiled
with the other one.

Here are the IPA Protocol Objects:

1. agent expression object. It represents an agent expression (*note
Agent Expressions::).

2. tracepoint action object. It represents a tracepoint action
(*note Tracepoint Action Lists: Tracepoint Actions.) to collect
registers, memory, static trace data and to evaluate expression.

3. tracepoint object. It represents a tracepoint (*note
Tracepoints::).

The following table describes important attributes of each IPA
protocol object:

Name Size Description
---------------------------------------------------------------------------
_agent expression
object_
length 4 length of bytes code
byte code LENGTH contents of byte code
_tracepoint action
for collecting
memory_
'M' 1 type of tracepoint action
addr 8 if BASEREG is `-1', ADDR is the
address of the lowest byte to
collect, otherwise ADDR is the
offset of BASEREG for memory
collecting.
len 8 length of memory for collecting
basereg 4 the register number containing the
starting memory address for
collecting.
_tracepoint action
for collecting
registers_
'R' 1 type of tracepoint action
_tracepoint action
for collecting static
trace data_
'L' 1 type of tracepoint action
_tracepoint action
for expression
evaluation_
'X' 1 type of tracepoint action
agent expression length of *Note agent expression object::
_tracepoint object_
number 4 number of tracepoint
address 8 address of tracepoint inserted on
type 4 type of tracepoint
enabled 1 enable or disable of tracepoint
step_count 8 step
pass_count 8 pass
numactions 4 number of tracepoint actions
hit count 8 hit count
trace frame usage 8 trace frame usage
compiled_cond 8 compiled condition
orig_size 8 orig size
condition 4 if zero if condition is NULL,
condition is otherwise is *Note agent expression
NULL object::
otherwise
length of
*Note agent
expression
object::
actions variable numactions number of *Note
tracepoint action object::

File: gdb.info, Node: IPA Protocol Commands, Prev: IPA Protocol Objects, Up: In-Process Agent Protocol

31.1.2 IPA Protocol Commands
----------------------------

The spaces in each command are delimiters to ease reading this commands
specification. They don't exist in real commands.

`FastTrace:TRACEPOINT_OBJECT GDB_JUMP_PAD_HEAD'
Installs a new fast tracepoint described by TRACEPOINT_OBJECT
(*note tracepoint object::). The GDB_JUMP_PAD_HEAD, 8-byte long,
is the head of "jumppad", which is used to jump to data collection
routine in IPA finally.

Replies:
`OK TARGET_ADDRESS GDB_JUMP_PAD_HEAD FJUMP_SIZE FJUMP'
TARGET_ADDRESS is address of tracepoint in the inferior. The
GDB_JUMP_PAD_HEAD is updated head of jumppad. Both of
TARGET_ADDRESS and GDB_JUMP_PAD_HEAD are 8-byte long. The
FJUMP contains a sequence of instructions jump to jumppad
entry. The FJUMP_SIZE, 4-byte long, is the size of FJUMP.

`close'
Closes the in-process agent. This command is sent when GDB or
GDBserver is about to kill inferiors.

`qTfSTM'
*Note qTfSTM::.

`qTsSTM'
*Note qTsSTM::.

`qTSTMat'
*Note qTSTMat::.

`probe_marker_at:ADDRESS'
Asks in-process agent to probe the marker at ADDRESS.

Replies:

`unprobe_marker_at:ADDRESS'
Asks in-process agent to unprobe the marker at ADDRESS.

File: gdb.info, Node: GDB Bugs, Next: Command Line Editing, Prev: In-Process Agent, Up: Top

32 Reporting Bugs in GDB
************************

Your bug reports play an essential role in making GDB reliable.

Reporting a bug may help you by bringing a solution to your problem,
or it may not. But in any case the principal function of a bug report
is to help the entire community by making the next version of GDB work
better. Bug reports are your contribution to the maintenance of GDB.

In order for a bug report to serve its purpose, you must include the
information that enables us to fix the bug.

* Menu:

* Bug Criteria:: Have you found a bug?
* Bug Reporting:: How to report bugs

File: gdb.info, Node: Bug Criteria, Next: Bug Reporting, Up: GDB Bugs

32.1 Have You Found a Bug?
==========================

If you are not sure whether you have found a bug, here are some
guidelines:

* If the debugger gets a fatal signal, for any input whatever, that
is a GDB bug. Reliable debuggers never crash.

* If GDB produces an error message for valid input, that is a bug.
(Note that if you're cross debugging, the problem may also be
somewhere in the connection to the target.)

* If GDB does not produce an error message for invalid input, that
is a bug. However, you should note that your idea of "invalid
input" might be our idea of "an extension" or "support for
traditional practice".

* If you are an experienced user of debugging tools, your suggestions
for improvement of GDB are welcome in any case.

File: gdb.info, Node: Bug Reporting, Prev: Bug Criteria, Up: GDB Bugs

32.2 How to Report Bugs
=======================

A number of companies and individuals offer support for GNU products.
If you obtained GDB from a support organization, we recommend you
contact that organization first.

You can find contact information for many support companies and
individuals in the file `etc/SERVICE' in the GNU Emacs distribution.

In any event, we also recommend that you submit bug reports for GDB
to `https://www.gnu.org/software/gdb/bugs/'.

The fundamental principle of reporting bugs usefully is this:
*report all the facts*. If you are not sure whether to state a fact or
leave it out, state it!

Often people omit facts because they think they know what causes the
problem and assume that some details do not matter. Thus, you might
assume that the name of the variable you use in an example does not
matter. Well, probably it does not, but one cannot be sure. Perhaps
the bug is a stray memory reference which happens to fetch from the
location where that name is stored in memory; perhaps, if the name were
different, the contents of that location would fool the debugger into
doing the right thing despite the bug. Play it safe and give a
specific, complete example. That is the easiest thing for you to do,
and the most helpful.

Keep in mind that the purpose of a bug report is to enable us to fix
the bug. It may be that the bug has been reported previously, but
neither you nor we can know that unless your bug report is complete and
self-contained.

Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?" Those bug reports are useless, and we urge everyone to _refuse
to respond to them_ except to chide the sender to report bugs properly.

To enable us to fix the bug, you should include all these things:

* The version of GDB. GDB announces it if you start with no
arguments; you can also print it at any time using `show version'.

Without this, we will not know whether there is any point in
looking for the bug in the current version of GDB.

* The type of machine you are using, and the operating system name
and version number.

* The details of the GDB build-time configuration. GDB shows these
details if you invoke it with the `--configuration' command-line
option, or if you type `show configuration' at GDB's prompt.

* What compiler (and its version) was used to compile GDB--e.g.
"gcc-2.8.1".

* What compiler (and its version) was used to compile the program
you are debugging--e.g. "gcc-2.8.1", or "HP92453-01 A.10.32.03 HP
C Compiler". For GCC, you can say `gcc --version' to get this
information; for other compilers, see the documentation for those
compilers.

* The command arguments you gave the compiler to compile your
example and observe the bug. For example, did you use `-O'? To
guarantee you will not omit something important, list them all. A
copy of the Makefile (or the output from make) is sufficient.

If we were to try to guess the arguments, we would probably guess
wrong and then we might not encounter the bug.

* A complete input script, and all necessary source files, that will
reproduce the bug.

* A description of what behavior you observe that you believe is
incorrect. For example, "It gets a fatal signal."

Of course, if the bug is that GDB gets a fatal signal, then we
will certainly notice it. But if the bug is incorrect output, we
might not notice unless it is glaringly wrong. You might as well
not give us a chance to make a mistake.

Even if the problem you experience is a fatal signal, you should
still say so explicitly. Suppose something strange is going on,
such as, your copy of GDB is out of synch, or you have encountered
a bug in the C library on your system. (This has happened!) Your
copy might crash and ours would not. If you told us to expect a
crash, then when ours fails to crash, we would know that the bug
was not happening for us. If you had not told us to expect a
crash, then we would not be able to draw any conclusion from our
observations.

To collect all this information, you can use a session recording
program such as `script', which is available on many Unix systems.
Just run your GDB session inside `script' and then include the
`typescript' file with your bug report.

Another way to record a GDB session is to run GDB inside Emacs and
then save the entire buffer to a file.

* If you wish to suggest changes to the GDB source, send us context
diffs. If you even discuss something in the GDB source, refer to
it by context, not by line number.

The line numbers in our development sources will not match those
in your sources. Your line numbers would convey no useful
information to us.

Here are some things that are not necessary:

* A description of the envelope of the bug.

Often people who encounter a bug spend a lot of time investigating
which changes to the input file will make the bug go away and which
changes will not affect it.

This is often time consuming and not very useful, because the way
we will find the bug is by running a single example under the
debugger with breakpoints, not by pure deduction from a series of
examples. We recommend that you save your time for something else.

Of course, if you can find a simpler example to report _instead_
of the original one, that is a convenience for us. Errors in the
output will be easier to spot, running under the debugger will take
less time, and so on.

However, simplification is not vital; if you do not want to do
this, report the bug anyway and send us the entire test case you
used.

* A patch for the bug.

A patch for the bug does help us if it is a good one. But do not
omit the necessary information, such as the test case, on the
assumption that a patch is all we need. We might see problems
with your patch and decide to fix the problem another way, or we
might not understand it at all.

Sometimes with a program as complicated as GDB it is very hard to
construct an example that will make the program follow a certain
path through the code. If you do not send us the example, we will
not be able to construct one, so we will not be able to verify
that the bug is fixed.

And if we cannot understand what bug you are trying to fix, or why
your patch should be an improvement, we will not install it. A
test case will help us to understand.

* A guess about what the bug is or what it depends on.

Such guesses are usually wrong. Even we cannot guess right about
such things without first using the debugger to find the facts.

File: gdb.info, Node: Command Line Editing, Next: Using History Interactively, Prev: GDB Bugs, Up: Top

33 Command Line Editing
***********************

This chapter describes the basic features of the GNU command line
editing interface.

* Menu:

* Introduction and Notation:: Notation used in this text.
* Readline Interaction:: The minimum set of commands for editing a line.
* Readline Init File:: Customizing Readline from a user's view.
* Bindable Readline Commands:: A description of most of the Readline commands
available for binding
* Readline vi Mode:: A short description of how to make Readline
behave like the vi editor.

File: gdb.info, Node: Introduction and Notation, Next: Readline Interaction, Up: Command Line Editing

33.1 Introduction to Line Editing
=================================

The following paragraphs describe the notation used to represent
keystrokes.

The text `C-k' is read as `Control-K' and describes the character
produced when the <k> key is pressed while the Control key is depressed.

The text `M-k' is read as `Meta-K' and describes the character
produced when the Meta key (if you have one) is depressed, and the <k>
key is pressed. The Meta key is labeled <ALT> on many keyboards. On
keyboards with two keys labeled <ALT> (usually to either side of the
space bar), the <ALT> on the left side is generally set to work as a
Meta key. The <ALT> key on the right may also be configured to work as
a Meta key or may be configured as some other modifier, such as a
Compose key for typing accented characters.

If you do not have a Meta or <ALT> key, or another key working as a
Meta key, the identical keystroke can be generated by typing <ESC>
_first_, and then typing <k>. Either process is known as "metafying"
the <k> key.

The text `M-C-k' is read as `Meta-Control-k' and describes the
character produced by "metafying" `C-k'.

In addition, several keys have their own names. Specifically,
<DEL>, <ESC>, <LFD>, <SPC>, <RET>, and <TAB> all stand for themselves
when seen in this text, or in an init file (*note Readline Init File::).
If your keyboard lacks a <LFD> key, typing <C-j> will produce the
desired character. The <RET> key may be labeled <Return> or <Enter> on
some keyboards.

File: gdb.info, Node: Readline Interaction, Next: Readline Init File, Prev: Introduction and Notation, Up: Command Line Editing

33.2 Readline Interaction
=========================

Often during an interactive session you type in a long line of text,
only to notice that the first word on the line is misspelled. The
Readline library gives you a set of commands for manipulating the text
as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line. Using these editing commands,
you move the cursor to the place that needs correction, and delete or
insert the text of the corrections. Then, when you are satisfied with
the line, you simply press <RET>. You do not have to be at the end of
the line to press <RET>; the entire line is accepted regardless of the
location of the cursor within the line.

* Menu:

* Readline Bare Essentials:: The least you need to know about Readline.
* Readline Movement Commands:: Moving about the input line.
* Readline Killing Commands:: How to delete text, and how to get it back!
* Readline Arguments:: Giving numeric arguments to commands.
* Searching:: Searching through previous lines.

File: gdb.info, Node: Readline Bare Essentials, Next: Readline Movement Commands, Up: Readline Interaction

33.2.1 Readline Bare Essentials
-------------------------------

In order to enter characters into the line, simply type them. The typed
character appears where the cursor was, and then the cursor moves one
space to the right. If you mistype a character, you can use your erase
character to back up and delete the mistyped character.

Sometimes you may mistype a character, and not notice the error
until you have typed several other characters. In that case, you can
type `C-b' to move the cursor to the left, and then correct your
mistake. Afterwards, you can move the cursor to the right with `C-f'.

When you add text in the middle of a line, you will notice that
characters to the right of the cursor are `pushed over' to make room
for the text that you have inserted. Likewise, when you delete text
behind the cursor, characters to the right of the cursor are `pulled
back' to fill in the blank space created by the removal of the text. A
list of the bare essentials for editing the text of an input line
follows.

`C-b'
Move back one character.

`C-f'
Move forward one character.

<DEL> or <Backspace>
Delete the character to the left of the cursor.

`C-d'
Delete the character underneath the cursor.

Printing characters
Insert the character into the line at the cursor.

`C-_' or `C-x C-u'
Undo the last editing command. You can undo all the way back to an
empty line.

(Depending on your configuration, the <Backspace> key be set to delete
the character to the left of the cursor and the <DEL> key set to delete
the character underneath the cursor, like `C-d', rather than the
character to the left of the cursor.)

File: gdb.info, Node: Readline Movement Commands, Next: Readline Killing Commands, Prev: Readline Bare Essentials, Up: Readline Interaction

33.2.2 Readline Movement Commands
---------------------------------

The above table describes the most basic keystrokes that you need in
order to do editing of the input line. For your convenience, many
other commands have been added in addition to `C-b', `C-f', `C-d', and
<DEL>. Here are some commands for moving more rapidly about the line.

`C-a'
Move to the start of the line.

`C-e'
Move to the end of the line.

`M-f'
Move forward a word, where a word is composed of letters and
digits.

`M-b'
Move backward a word.

`C-l'
Clear the screen, reprinting the current line at the top.

Notice how `C-f' moves forward a character, while `M-f' moves
forward a word. It is a loose convention that control keystrokes
operate on characters while meta keystrokes operate on words.

File: gdb.info, Node: Readline Killing Commands, Next: Readline Arguments, Prev: Readline Movement Commands, Up: Readline Interaction

33.2.3 Readline Killing Commands
--------------------------------

"Killing" text means to delete the text from the line, but to save it
away for later use, usually by "yanking" (re-inserting) it back into
the line. (`Cut' and `paste' are more recent jargon for `kill' and
`yank'.)

If the description for a command says that it `kills' text, then you
can be sure that you can get the text back in a different (or the same)
place later.

When you use a kill command, the text is saved in a "kill-ring".
Any number of consecutive kills save all of the killed text together, so
that when you yank it back, you get it all. The kill ring is not line
specific; the text that you killed on a previously typed line is
available to be yanked back later, when you are typing another line.

Here is the list of commands for killing text.

`C-k'
Kill the text from the current cursor position to the end of the
line.

`M-d'
Kill from the cursor to the end of the current word, or, if between
words, to the end of the next word. Word boundaries are the same
as those used by `M-f'.

`M-<DEL>'
Kill from the cursor the start of the current word, or, if between
words, to the start of the previous word. Word boundaries are the
same as those used by `M-b'.

`C-w'
Kill from the cursor to the previous whitespace. This is
different than `M-<DEL>' because the word boundaries differ.

Here is how to "yank" the text back into the line. Yanking means to
copy the most-recently-killed text from the kill buffer.

`C-y'
Yank the most recently killed text back into the buffer at the
cursor.

`M-y'
Rotate the kill-ring, and yank the new top. You can only do this
if the prior command is `C-y' or `M-y'.

File: gdb.info, Node: Readline Arguments, Next: Searching, Prev: Readline Killing Commands, Up: Readline Interaction

33.2.4 Readline Arguments
-------------------------

You can pass numeric arguments to Readline commands. Sometimes the
argument acts as a repeat count, other times it is the sign of the
argument that is significant. If you pass a negative argument to a
command which normally acts in a forward direction, that command will
act in a backward direction. For example, to kill text back to the
start of the line, you might type `M-- C-k'.

The general way to pass numeric arguments to a command is to type
meta digits before the command. If the first `digit' typed is a minus
sign (`-'), then the sign of the argument will be negative. Once you
have typed one meta digit to get the argument started, you can type the
remainder of the digits, and then the command. For example, to give
the `C-d' command an argument of 10, you could type `M-1 0 C-d', which
will delete the next ten characters on the input line.

File: gdb.info, Node: Searching, Prev: Readline Arguments, Up: Readline Interaction

33.2.5 Searching for Commands in the History
--------------------------------------------

Readline provides commands for searching through the command history
for lines containing a specified string. There are two search modes:
"incremental" and "non-incremental".

Incremental searches begin before the user has finished typing the
search string. As each character of the search string is typed,
Readline displays the next entry from the history matching the string
typed so far. An incremental search requires only as many characters
as needed to find the desired history entry. To search backward in the
history for a particular string, type `C-r'. Typing `C-s' searches
forward through the history. The characters present in the value of
the `isearch-terminators' variable are used to terminate an incremental
search. If that variable has not been assigned a value, the <ESC> and
`C-J' characters will terminate an incremental search. `C-g' will
abort an incremental search and restore the original line. When the
search is terminated, the history entry containing the search string
becomes the current line.

To find other matching entries in the history list, type `C-r' or
`C-s' as appropriate. This will search backward or forward in the
history for the next entry matching the search string typed so far.
Any other key sequence bound to a Readline command will terminate the
search and execute that command. For instance, a <RET> will terminate
the search and accept the line, thereby executing the command from the
history list. A movement command will terminate the search, make the
last line found the current line, and begin editing.

Readline remembers the last incremental search string. If two
`C-r's are typed without any intervening characters defining a new
search string, any remembered search string is used.

Non-incremental searches read the entire search string before
starting to search for matching history lines. The search string may be
typed by the user or be part of the contents of the current line.

File: gdb.info, Node: Readline Init File, Next: Bindable Readline Commands, Prev: Readline Interaction, Up: Command Line Editing

33.3 Readline Init File
=======================

Although the Readline library comes with a set of Emacs-like
keybindings installed by default, it is possible to use a different set
of keybindings. Any user can customize programs that use Readline by
putting commands in an "inputrc" file, conventionally in his home
directory. The name of this file is taken from the value of the
environment variable `INPUTRC'. If that variable is unset, the default
is `~/.inputrc'. If that file does not exist or cannot be read, the
ultimate default is `/etc/inputrc'.

When a program which uses the Readline library starts up, the init
file is read, and the key bindings are set.

In addition, the `C-x C-r' command re-reads this init file, thus
incorporating any changes that you might have made to it.

* Menu:

* Readline Init File Syntax:: Syntax for the commands in the inputrc file.

* Conditional Init Constructs:: Conditional key bindings in the inputrc file.

* Sample Init File:: An example inputrc file.

File: gdb.info, Node: Readline Init File Syntax, Next: Conditional Init Constructs, Up: Readline Init File

33.3.1 Readline Init File Syntax
--------------------------------

There are only a few basic constructs allowed in the Readline init
file. Blank lines are ignored. Lines beginning with a `#' are
comments. Lines beginning with a `$' indicate conditional constructs
(*note Conditional Init Constructs::). Other lines denote variable
settings and key bindings.

Variable Settings
You can modify the run-time behavior of Readline by altering the
values of variables in Readline using the `set' command within the
init file. The syntax is simple:

set VARIABLE VALUE

Here, for example, is how to change from the default Emacs-like
key binding to use `vi' line editing commands:

set editing-mode vi

Variable names and values, where appropriate, are recognized
without regard to case. Unrecognized variable names are ignored.

Boolean variables (those that can be set to on or off) are set to
on if the value is null or empty, ON (case-insensitive), or 1.
Any other value results in the variable being set to off.

A great deal of run-time behavior is changeable with the following
variables.

`bell-style'
Controls what happens when Readline wants to ring the
terminal bell. If set to `none', Readline never rings the
bell. If set to `visible', Readline uses a visible bell if
one is available. If set to `audible' (the default),
Readline attempts to ring the terminal's bell.

`bind-tty-special-chars'
If set to `on' (the default), Readline attempts to bind the
control characters treated specially by the kernel's
terminal driver to their Readline equivalents.

`blink-matching-paren'
If set to `on', Readline attempts to briefly move the cursor
to an opening parenthesis when a closing parenthesis is
inserted. The default is `off'.

`colored-completion-prefix'
If set to `on', when listing completions, Readline displays
the common prefix of the set of possible completions using a
different color. The color definitions are taken from the
value of the `LS_COLORS' environment variable. The default
is `off'.

`colored-stats'
If set to `on', Readline displays possible completions using
different colors to indicate their file type. The color
definitions are taken from the value of the `LS_COLORS'
environment variable. The default is `off'.

`comment-begin'
The string to insert at the beginning of the line when the
`insert-comment' command is executed. The default value is
`"#"'.

`completion-display-width'
The number of screen columns used to display possible matches
when performing completion. The value is ignored if it is
less than 0 or greater than the terminal screen width. A
value of 0 will cause matches to be displayed one per line.
The default value is -1.

`completion-ignore-case'
If set to `on', Readline performs filename matching and
completion in a case-insensitive fashion. The default value
is `off'.

`completion-map-case'
If set to `on', and COMPLETION-IGNORE-CASE is enabled,
Readline treats hyphens (`-') and underscores (`_') as
equivalent when performing case-insensitive filename matching
and completion. The default value is `off'.

`completion-prefix-display-length'
The length in characters of the common prefix of a list of
possible completions that is displayed without modification.
When set to a value greater than zero, common prefixes longer
than this value are replaced with an ellipsis when displaying
possible completions.

`completion-query-items'
The number of possible completions that determines when the
user is asked whether the list of possibilities should be
displayed. If the number of possible completions is greater
than or equal to this value, Readline will ask whether or not
the user wishes to view them; otherwise, they are simply
listed. This variable must be set to an integer value
greater than or equal to 0. A negative value means Readline
should never ask. The default limit is `100'.

`convert-meta'
If set to `on', Readline will convert characters with the
eighth bit set to an ASCII key sequence by stripping the
eighth bit and prefixing an <ESC> character, converting them
to a meta-prefixed key sequence. The default value is `on',
but will be set to `off' if the locale is one that contains
eight-bit characters.

`disable-completion'
If set to `On', Readline will inhibit word completion.
Completion characters will be inserted into the line as if
they had been mapped to `self-insert'. The default is `off'.

`echo-control-characters'
When set to `on', on operating systems that indicate they
support it, readline echoes a character corresponding to a
signal generated from the keyboard. The default is `on'.

`editing-mode'
The `editing-mode' variable controls which default set of key
bindings is used. By default, Readline starts up in Emacs
editing mode, where the keystrokes are most similar to Emacs.
This variable can be set to either `emacs' or `vi'.

`emacs-mode-string'
If the SHOW-MODE-IN-PROMPT variable is enabled, this string
is displayed immediately before the last line of the primary
prompt when emacs editing mode is active. The value is
expanded like a key binding, so the standard set of meta- and
control prefixes and backslash escape sequences is available.
Use the `\1' and `\2' escapes to begin and end sequences of
non-printing characters, which can be used to embed a
terminal control sequence into the mode string. The default
is `@'.

`enable-bracketed-paste'
When set to `On', Readline will configure the terminal in a
way that will enable it to insert each paste into the editing
buffer as a single string of characters, instead of treating
each character as if it had been read from the keyboard.
This can prevent pasted characters from being interpreted as
editing commands. The default is `On'.

`enable-keypad'
When set to `on', Readline will try to enable the application
keypad when it is called. Some systems need this to enable
the arrow keys. The default is `off'.

`enable-meta-key'
When set to `on', Readline will try to enable any meta
modifier key the terminal claims to support when it is
called. On many terminals, the meta key is used to send
eight-bit characters. The default is `on'.

`expand-tilde'
If set to `on', tilde expansion is performed when Readline
attempts word completion. The default is `off'.

`history-preserve-point'
If set to `on', the history code attempts to place the point
(the current cursor position) at the same location on each
history line retrieved with `previous-history' or
`next-history'. The default is `off'.

`history-size'
Set the maximum number of history entries saved in the
history list. If set to zero, any existing history entries
are deleted and no new entries are saved. If set to a value
less than zero, the number of history entries is not limited.
By default, the number of history entries is not limited. If
an attempt is made to set HISTORY-SIZE to a non-numeric value,
the maximum number of history entries will be set to 500.

`horizontal-scroll-mode'
This variable can be set to either `on' or `off'. Setting it
to `on' means that the text of the lines being edited will
scroll horizontally on a single screen line when they are
longer than the width of the screen, instead of wrapping onto
a new screen line. This variable is automatically set to
`on' for terminals of height 1. By default, this variable is
set to `off'.

`input-meta'
If set to `on', Readline will enable eight-bit input (it will
not clear the eighth bit in the characters it reads),
regardless of what the terminal claims it can support. The
default value is `off', but Readline will set it to `on' if
the locale contains eight-bit characters. The name
`meta-flag' is a synonym for this variable.

`isearch-terminators'
The string of characters that should terminate an incremental
search without subsequently executing the character as a
command (*note Searching::). If this variable has not been
given a value, the characters <ESC> and `C-J' will terminate
an incremental search.

`keymap'
Sets Readline's idea of the current keymap for key binding
commands. Built-in `keymap' names are `emacs',
`emacs-standard', `emacs-meta', `emacs-ctlx', `vi', `vi-move',
`vi-command', and `vi-insert'. `vi' is equivalent to
`vi-command' (`vi-move' is also a synonym); `emacs' is
equivalent to `emacs-standard'. Applications may add
additional names. The default value is `emacs'. The value
of the `editing-mode' variable also affects the default
keymap.

`keyseq-timeout'
Specifies the duration Readline will wait for a character
when reading an ambiguous key sequence (one that can form a
complete key sequence using the input read so far, or can
take additional input to complete a longer key sequence). If
no input is received within the timeout, Readline will use
the shorter but complete key sequence. Readline uses this
value to determine whether or not input is available on the
current input source (`rl_instream' by default). The value
is specified in milliseconds, so a value of 1000 means that
Readline will wait one second for additional input. If this
variable is set to a value less than or equal to zero, or to a
non-numeric value, Readline will wait until another key is
pressed to decide which key sequence to complete. The
default value is `500'.

`mark-directories'
If set to `on', completed directory names have a slash
appended. The default is `on'.

`mark-modified-lines'
This variable, when set to `on', causes Readline to display an
asterisk (`*') at the start of history lines which have been
modified. This variable is `off' by default.

`mark-symlinked-directories'
If set to `on', completed names which are symbolic links to
directories have a slash appended (subject to the value of
`mark-directories'). The default is `off'.

`match-hidden-files'
This variable, when set to `on', causes Readline to match
files whose names begin with a `.' (hidden files) when
performing filename completion. If set to `off', the leading
`.' must be supplied by the user in the filename to be
completed. This variable is `on' by default.

`menu-complete-display-prefix'
If set to `on', menu completion displays the common prefix of
the list of possible completions (which may be empty) before
cycling through the list. The default is `off'.

`output-meta'
If set to `on', Readline will display characters with the
eighth bit set directly rather than as a meta-prefixed escape
sequence. The default is `off', but Readline will set it to
`on' if the locale contains eight-bit characters.

`page-completions'
If set to `on', Readline uses an internal `more'-like pager
to display a screenful of possible completions at a time.
This variable is `on' by default.

`print-completions-horizontally'
If set to `on', Readline will display completions with matches
sorted horizontally in alphabetical order, rather than down
the screen. The default is `off'.

`revert-all-at-newline'
If set to `on', Readline will undo all changes to history
lines before returning when `accept-line' is executed. By
default, history lines may be modified and retain individual
undo lists across calls to `readline'. The default is `off'.

`show-all-if-ambiguous'
This alters the default behavior of the completion functions.
If set to `on', words which have more than one possible
completion cause the matches to be listed immediately instead
of ringing the bell. The default value is `off'.

`show-all-if-unmodified'
This alters the default behavior of the completion functions
in a fashion similar to SHOW-ALL-IF-AMBIGUOUS. If set to
`on', words which have more than one possible completion
without any possible partial completion (the possible
completions don't share a common prefix) cause the matches to
be listed immediately instead of ringing the bell. The
default value is `off'.

`show-mode-in-prompt'
If set to `on', add a string to the beginning of the prompt
indicating the editing mode: emacs, vi command, or vi
insertion. The mode strings are user-settable (e.g.,
EMACS-MODE-STRING). The default value is `off'.

`skip-completed-text'
If set to `on', this alters the default completion behavior
when inserting a single match into the line. It's only
active when performing completion in the middle of a word.
If enabled, readline does not insert characters from the
completion that match characters after point in the word
being completed, so portions of the word following the cursor
are not duplicated. For instance, if this is enabled,
attempting completion when the cursor is after the `e' in
`Makefile' will result in `Makefile' rather than
`Makefilefile', assuming there is a single possible
completion. The default value is `off'.

`vi-cmd-mode-string'
If the SHOW-MODE-IN-PROMPT variable is enabled, this string
is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in command mode.
The value is expanded like a key binding, so the standard set
of meta- and control prefixes and backslash escape sequences
is available. Use the `\1' and `\2' escapes to begin and end
sequences of non-printing characters, which can be used to
embed a terminal control sequence into the mode string. The
default is `(cmd)'.

`vi-ins-mode-string'
If the SHOW-MODE-IN-PROMPT variable is enabled, this string
is displayed immediately before the last line of the primary
prompt when vi editing mode is active and in insertion mode.
The value is expanded like a key binding, so the standard set
of meta- and control prefixes and backslash escape sequences
is available. Use the `\1' and `\2' escapes to begin and end
sequences of non-printing characters, which can be used to
embed a terminal control sequence into the mode string. The
default is `(ins)'.

`visible-stats'
If set to `on', a character denoting a file's type is
appended to the filename when listing possible completions.
The default is `off'.

Key Bindings
The syntax for controlling key bindings in the init file is
simple. First you need to find the name of the command that you
want to change. The following sections contain tables of the
command name, the default keybinding, if any, and a short
description of what the command does.

Once you know the name of the command, simply place on a line in
the init file the name of the key you wish to bind the command to,
a colon, and then the name of the command. There can be no space
between the key name and the colon - that will be interpreted as
part of the key name. The name of the key can be expressed in
different ways, depending on what you find most comfortable.

In addition to command names, readline allows keys to be bound to
a string that is inserted when the key is pressed (a MACRO).

KEYNAME: FUNCTION-NAME or MACRO
KEYNAME is the name of a key spelled out in English. For
example:
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"

In the example above, `C-u' is bound to the function
`universal-argument', `M-DEL' is bound to the function
`backward-kill-word', and `C-o' is bound to run the macro
expressed on the right hand side (that is, to insert the text
`> output' into the line).

A number of symbolic character names are recognized while
processing this key binding syntax: DEL, ESC, ESCAPE, LFD,
NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.

"KEYSEQ": FUNCTION-NAME or MACRO
KEYSEQ differs from KEYNAME above in that strings denoting an
entire key sequence can be specified, by placing the key
sequence in double quotes. Some GNU Emacs style key escapes
can be used, as in the following example, but the special
character names are not recognized.

"\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"

In the above example, `C-u' is again bound to the function
`universal-argument' (just as it was in the first example),
`C-x C-r' is bound to the function `re-read-init-file', and
`<ESC> <[> <1> <1> <~>' is bound to insert the text `Function
Key 1'.

The following GNU Emacs style escape sequences are available when
specifying key sequences:

`\C-'
control prefix

`\M-'
meta prefix

`\e'
an escape character

`\\'
backslash

`\"'
<">, a double quotation mark

`\''
<'>, a single quote or apostrophe

In addition to the GNU Emacs style escape sequences, a second set
of backslash escapes is available:

`\a'
alert (bell)

`\b'
backspace

`\d'
delete

`\f'
form feed

`\n'
newline

`\r'
carriage return

`\t'
horizontal tab

`\v'
vertical tab

`\NNN'
the eight-bit character whose value is the octal value NNN
(one to three digits)

`\xHH'
the eight-bit character whose value is the hexadecimal value
HH (one or two hex digits)

When entering the text of a macro, single or double quotes must be
used to indicate a macro definition. Unquoted text is assumed to
be a function name. In the macro body, the backslash escapes
described above are expanded. Backslash will quote any other
character in the macro text, including `"' and `''. For example,
the following binding will make `C-x \' insert a single `\' into
the line:
"\C-x\\": "\\"

File: gdb.info, Node: Conditional Init Constructs, Next: Sample Init File, Prev: Readline Init File Syntax, Up: Readline Init File

33.3.2 Conditional Init Constructs
----------------------------------

Readline implements a facility similar in spirit to the conditional
compilation features of the C preprocessor which allows key bindings
and variable settings to be performed as the result of tests. There
are four parser directives used.

`$if'
The `$if' construct allows bindings to be made based on the
editing mode, the terminal being used, or the application using
Readline. The text of the test, after any comparison operator,
extends to the end of the line; unless otherwise noted, no
characters are required to isolate it.

`mode'
The `mode=' form of the `$if' directive is used to test
whether Readline is in `emacs' or `vi' mode. This may be
used in conjunction with the `set keymap' command, for
instance, to set bindings in the `emacs-standard' and
`emacs-ctlx' keymaps only if Readline is starting out in
`emacs' mode.

`term'
The `term=' form may be used to include terminal-specific key
bindings, perhaps to bind the key sequences output by the
terminal's function keys. The word on the right side of the
`=' is tested against both the full name of the terminal and
the portion of the terminal name before the first `-'. This
allows `sun' to match both `sun' and `sun-cmd', for instance.

`version'
The `version' test may be used to perform comparisons against
specific Readline versions. The `version' expands to the
current Readline version. The set of comparison operators
includes `=' (and `=='), `!=', `<=', `>=', `<', and `>'. The
version number supplied on the right side of the operator
consists of a major version number, an optional decimal
point, and an optional minor version (e.g., `7.1'). If the
minor version is omitted, it is assumed to be `0'. The
operator may be separated from the string `version' and from
the version number argument by whitespace. The following
example sets a variable if the Readline version being used is
7.0 or newer:
$if version >= 7.0
set show-mode-in-prompt on
$endif

`application'
The APPLICATION construct is used to include
application-specific settings. Each program using the
Readline library sets the APPLICATION NAME, and you can test
for a particular value. This could be used to bind key
sequences to functions useful for a specific program. For
instance, the following command adds a key sequence that
quotes the current or previous word in Bash:
$if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif

`variable'
The VARIABLE construct provides simple equality tests for
Readline variables and values. The permitted comparison
operators are `=', `==', and `!='. The variable name must be
separated from the comparison operator by whitespace; the
operator may be separated from the value on the right hand
side by whitespace. Both string and boolean variables may be
tested. Boolean variables must be tested against the values
ON and OFF. The following example is equivalent to the
`mode=emacs' test described above:
$if editing-mode == emacs
set show-mode-in-prompt on
$endif

`$endif'
This command, as seen in the previous example, terminates an `$if'
command.

`$else'
Commands in this branch of the `$if' directive are executed if the
test fails.

`$include'
This directive takes a single filename as an argument and reads
commands and bindings from that file. For example, the following
directive reads from `/etc/inputrc':
$include /etc/inputrc

File: gdb.info, Node: Sample Init File, Prev: Conditional Init Constructs, Up: Readline Init File

33.3.3 Sample Init File
-----------------------

Here is an example of an INPUTRC file. This illustrates key binding,
variable assignment, and conditional syntax.

# This file controls the behaviour of line input editing for
# programs that use the GNU Readline library. Existing
# programs include FTP, Bash, and GDB.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any system-wide bindings and variable
# assignments from /etc/Inputrc
$include /etc/Inputrc

#
# Set various bindings for emacs mode.

set editing-mode emacs

$if mode=emacs

Meta-Control-h: backward-kill-word Text after the function name is ignored

#
# Arrow keys in keypad mode
#
#"\M-OD": backward-char
#"\M-OC": forward-char
#"\M-OA": previous-history
#"\M-OB": next-history
#
# Arrow keys in ANSI mode
#
"\M-[D": backward-char
"\M-[C": forward-char
"\M-[A": previous-history
"\M-[B": next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD": backward-char
#"\M-\C-OC": forward-char
#"\M-\C-OA": previous-history
#"\M-\C-OB": next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D": backward-char
#"\M-\C-[C": forward-char
#"\M-\C-[A": previous-history
#"\M-\C-[B": next-history

C-q: quoted-insert

$endif

# An old-style binding. This happens to be the default.
TAB: complete

# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word --
# insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes
# in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif

# use a visible bell if one is available
set bell-style visible

# don't strip characters to 7 bits when reading
set input-meta on

# allow iso-latin1 characters to be inserted rather
# than converted to prefix-meta sequences
set convert-meta off

# display characters with the eighth bit set directly
# rather than as meta-prefixed characters
set output-meta on

# if there are 150 or more possible completions for a word,
# ask whether or not the user wants to see all of them
set completion-query-items 150

# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif

File: gdb.info, Node: Bindable Readline Commands, Next: Readline vi Mode, Prev: Readline Init File, Up: Command Line Editing

33.4 Bindable Readline Commands
===============================

* Menu:

* Commands For Moving:: Moving about the line.
* Commands For History:: Getting at previous lines.
* Commands For Text:: Commands for changing text.
* Commands For Killing:: Commands for killing and yanking.
* Numeric Arguments:: Specifying numeric arguments, repeat counts.
* Commands For Completion:: Getting Readline to do the typing for you.
* Keyboard Macros:: Saving and re-executing typed characters
* Miscellaneous Commands:: Other miscellaneous commands.

This section describes Readline commands that may be bound to key
sequences. Command names without an accompanying key sequence are
unbound by default.

In the following descriptions, "point" refers to the current cursor
position, and "mark" refers to a cursor position saved by the
`set-mark' command. The text between the point and mark is referred to
as the "region".

File: gdb.info, Node: Commands For Moving, Next: Commands For History, Up: Bindable Readline Commands

33.4.1 Commands For Moving
--------------------------

`beginning-of-line (C-a)'
Move to the start of the current line.

`end-of-line (C-e)'
Move to the end of the line.

`forward-char (C-f)'
Move forward a character.

`backward-char (C-b)'
Move back a character.

`forward-word (M-f)'
Move forward to the end of the next word. Words are composed of
letters and digits.

`backward-word (M-b)'
Move back to the start of the current or previous word. Words are
composed of letters and digits.

`previous-screen-line ()'
Attempt to move point to the same physical screen column on the
previous physical screen line. This will not have the desired
effect if the current Readline line does not take up more than one
physical line or if point is not greater than the length of the
prompt plus the screen width.

`next-screen-line ()'
Attempt to move point to the same physical screen column on the
next physical screen line. This will not have the desired effect
if the current Readline line does not take up more than one
physical line or if the length of the current Readline line is not
greater than the length of the prompt plus the screen width.

`clear-display (M-C-l)'
Clear the screen and, if possible, the terminal's scrollback
buffer, then redraw the current line, leaving the current line at
the top of the screen.

`clear-screen (C-l)'
Clear the screen, then redraw the current line, leaving the
current line at the top of the screen.

`redraw-current-line ()'
Refresh the current line. By default, this is unbound.

File: gdb.info, Node: Commands For History, Next: Commands For Text, Prev: Commands For Moving, Up: Bindable Readline Commands

33.4.2 Commands For Manipulating The History
--------------------------------------------

`accept-line (Newline or Return)'
Accept the line regardless of where the cursor is. If this line is
non-empty, it may be added to the history list for future recall
with `add_history()'. If this line is a modified history line,
the history line is restored to its original state.

`previous-history (C-p)'
Move `back' through the history list, fetching the previous
command.

`next-history (C-n)'
Move `forward' through the history list, fetching the next command.

`beginning-of-history (M-<)'
Move to the first line in the history.

`end-of-history (M->)'
Move to the end of the input history, i.e., the line currently
being entered.

`reverse-search-history (C-r)'
Search backward starting at the current line and moving `up'
through the history as necessary. This is an incremental search.
This command sets the region to the matched text and activates the
mark.

`forward-search-history (C-s)'
Search forward starting at the current line and moving `down'
through the history as necessary. This is an incremental search.
This command sets the region to the matched text and activates the
mark.

`non-incremental-reverse-search-history (M-p)'
Search backward starting at the current line and moving `up'
through the history as necessary using a non-incremental search
for a string supplied by the user. The search string may match
anywhere in a history line.

`non-incremental-forward-search-history (M-n)'
Search forward starting at the current line and moving `down'
through the history as necessary using a non-incremental search
for a string supplied by the user. The search string may match
anywhere in a history line.

`history-search-forward ()'
Search forward through the history for the string of characters
between the start of the current line and the point. The search
string must match at the beginning of a history line. This is a
non-incremental search. By default, this command is unbound.

`history-search-backward ()'
Search backward through the history for the string of characters
between the start of the current line and the point. The search
string must match at the beginning of a history line. This is a
non-incremental search. By default, this command is unbound.

`history-substring-search-forward ()'
Search forward through the history for the string of characters
between the start of the current line and the point. The search
string may match anywhere in a history line. This is a
non-incremental search. By default, this command is unbound.

`history-substring-search-backward ()'
Search backward through the history for the string of characters
between the start of the current line and the point. The search
string may match anywhere in a history line. This is a
non-incremental search. By default, this command is unbound.

`yank-nth-arg (M-C-y)'
Insert the first argument to the previous command (usually the
second word on the previous line) at point. With an argument N,
insert the Nth word from the previous command (the words in the
previous command begin with word 0). A negative argument inserts
the Nth word from the end of the previous command. Once the
argument N is computed, the argument is extracted as if the `!N'
history expansion had been specified.

`yank-last-arg (M-. or M-_)'
Insert last argument to the previous command (the last word of the
previous history entry). With a numeric argument, behave exactly
like `yank-nth-arg'. Successive calls to `yank-last-arg' move
back through the history list, inserting the last word (or the
word specified by the argument to the first call) of each line in
turn. Any numeric argument supplied to these successive calls
determines the direction to move through the history. A negative
argument switches the direction through the history (back or
forward). The history expansion facilities are used to extract
the last argument, as if the `!$' history expansion had been
specified.

`operate-and-get-next (C-o)'
Accept the current line for return to the calling application as
if a newline had been entered, and fetch the next line relative to
the current line from the history for editing. A numeric
argument, if supplied, specifies the history entry to use instead
of the current line.

File: gdb.info, Node: Commands For Text, Next: Commands For Killing, Prev: Commands For History, Up: Bindable Readline Commands

33.4.3 Commands For Changing Text
---------------------------------

`end-of-file (usually C-d)'
The character indicating end-of-file as set, for example, by
`stty'. If this character is read when there are no characters on
the line, and point is at the beginning of the line, Readline
interprets it as the end of input and returns EOF.

`delete-char (C-d)'
Delete the character at point. If this function is bound to the
same character as the tty EOF character, as `C-d' commonly is, see
above for the effects.

`backward-delete-char (Rubout)'
Delete the character behind the cursor. A numeric argument means
to kill the characters instead of deleting them.

`forward-backward-delete-char ()'
Delete the character under the cursor, unless the cursor is at the
end of the line, in which case the character behind the cursor is
deleted. By default, this is not bound to a key.

`quoted-insert (C-q or C-v)'
Add the next character typed to the line verbatim. This is how to
insert key sequences like `C-q', for example.

`tab-insert (M-<TAB>)'
Insert a tab character.

`self-insert (a, b, A, 1, !, ...)'
Insert yourself.

`bracketed-paste-begin ()'
This function is intended to be bound to the "bracketed paste"
escape sequence sent by some terminals, and such a binding is
assigned by default. It allows Readline to insert the pasted text
as a single unit without treating each character as if it had been
read from the keyboard. The characters are inserted as if each
one was bound to `self-insert' instead of executing any editing
commands.

Bracketed paste sets the region (the characters between point and
the mark) to the inserted text. It uses the concept of an _active
mark_: when the mark is active, Readline redisplay uses the
terminal's standout mode to denote the region.

`transpose-chars (C-t)'
Drag the character before the cursor forward over the character at
the cursor, moving the cursor forward as well. If the insertion
point is at the end of the line, then this transposes the last two
characters of the line. Negative arguments have no effect.

`transpose-words (M-t)'
Drag the word before point past the word after point, moving point
past that word as well. If the insertion point is at the end of
the line, this transposes the last two words on the line.

`upcase-word (M-u)'
Uppercase the current (or following) word. With a negative
argument, uppercase the previous word, but do not move the cursor.

`downcase-word (M-l)'
Lowercase the current (or following) word. With a negative
argument, lowercase the previous word, but do not move the cursor.

`capitalize-word (M-c)'
Capitalize the current (or following) word. With a negative
argument, capitalize the previous word, but do not move the cursor.

`overwrite-mode ()'
Toggle overwrite mode. With an explicit positive numeric argument,
switches to overwrite mode. With an explicit non-positive numeric
argument, switches to insert mode. This command affects only
`emacs' mode; `vi' mode does overwrite differently. Each call to
`readline()' starts in insert mode.

In overwrite mode, characters bound to `self-insert' replace the
text at point rather than pushing the text to the right.
Characters bound to `backward-delete-char' replace the character
before point with a space.

By default, this command is unbound.

File: gdb.info, Node: Commands For Killing, Next: Numeric Arguments, Prev: Commands For Text, Up: Bindable Readline Commands

33.4.4 Killing And Yanking
--------------------------

`kill-line (C-k)'
Kill the text from point to the end of the line. With a negative
numeric argument, kill backward from the cursor to the beginning
of the current line.

`backward-kill-line (C-x Rubout)'
Kill backward from the cursor to the beginning of the current line.
With a negative numeric argument, kill forward from the cursor to
the end of the current line.

`unix-line-discard (C-u)'
Kill backward from the cursor to the beginning of the current line.

`kill-whole-line ()'
Kill all characters on the current line, no matter where point is.
By default, this is unbound.

`kill-word (M-d)'
Kill from point to the end of the current word, or if between
words, to the end of the next word. Word boundaries are the same
as `forward-word'.

`backward-kill-word (M-<DEL>)'
Kill the word behind point. Word boundaries are the same as
`backward-word'.

`shell-transpose-words (M-C-t)'
Drag the word before point past the word after point, moving point
past that word as well. If the insertion point is at the end of
the line, this transposes the last two words on the line. Word
boundaries are the same as `shell-forward-word' and
`shell-backward-word'.

`unix-word-rubout (C-w)'
Kill the word behind point, using white space as a word boundary.
The killed text is saved on the kill-ring.

`unix-filename-rubout ()'
Kill the word behind point, using white space and the slash
character as the word boundaries. The killed text is saved on the
kill-ring.

`delete-horizontal-space ()'
Delete all spaces and tabs around point. By default, this is
unbound.

`kill-region ()'
Kill the text in the current region. By default, this command is
unbound.

`copy-region-as-kill ()'
Copy the text in the region to the kill buffer, so it can be yanked
right away. By default, this command is unbound.

`copy-backward-word ()'
Copy the word before point to the kill buffer. The word
boundaries are the same as `backward-word'. By default, this
command is unbound.

`copy-forward-word ()'
Copy the word following point to the kill buffer. The word
boundaries are the same as `forward-word'. By default, this
command is unbound.

`yank (C-y)'
Yank the top of the kill ring into the buffer at point.

`yank-pop (M-y)'
Rotate the kill-ring, and yank the new top. You can only do this
if the prior command is `yank' or `yank-pop'.

File: gdb.info, Node: Numeric Arguments, Next: Commands For Completion, Prev: Commands For Killing, Up: Bindable Readline Commands

33.4.5 Specifying Numeric Arguments
-----------------------------------

`digit-argument (M-0, M-1, ... M--)'
Add this digit to the argument already accumulating, or start a new
argument. `M--' starts a negative argument.

`universal-argument ()'
This is another way to specify an argument. If this command is
followed by one or more digits, optionally with a leading minus
sign, those digits define the argument. If the command is
followed by digits, executing `universal-argument' again ends the
numeric argument, but is otherwise ignored. As a special case, if
this command is immediately followed by a character that is
neither a digit nor minus sign, the argument count for the next
command is multiplied by four. The argument count is initially
one, so executing this function the first time makes the argument
count four, a second time makes the argument count sixteen, and so
on. By default, this is not bound to a key.

File: gdb.info, Node: Commands For Completion, Next: Keyboard Macros, Prev: Numeric Arguments, Up: Bindable Readline Commands

33.4.6 Letting Readline Type For You
------------------------------------

`complete (<TAB>)'
Attempt to perform completion on the text before point. The
actual completion performed is application-specific. The default
is filename completion.

`possible-completions (M-?)'
List the possible completions of the text before point. When
displaying completions, Readline sets the number of columns used
for display to the value of `completion-display-width', the value
of the environment variable `COLUMNS', or the screen width, in
that order.

`insert-completions (M-*)'
Insert all completions of the text before point that would have
been generated by `possible-completions'.

`menu-complete ()'
Similar to `complete', but replaces the word to be completed with
a single match from the list of possible completions. Repeated
execution of `menu-complete' steps through the list of possible
completions, inserting each match in turn. At the end of the list
of completions, the bell is rung (subject to the setting of
`bell-style') and the original text is restored. An argument of N
moves N positions forward in the list of matches; a negative
argument may be used to move backward through the list. This
command is intended to be bound to <TAB>, but is unbound by
default.

`menu-complete-backward ()'
Identical to `menu-complete', but moves backward through the list
of possible completions, as if `menu-complete' had been given a
negative argument.

`delete-char-or-list ()'
Deletes the character under the cursor if not at the beginning or
end of the line (like `delete-char'). If at the end of the line,
behaves identically to `possible-completions'. This command is
unbound by default.

File: gdb.info, Node: Keyboard Macros, Next: Miscellaneous Commands, Prev: Commands For Completion, Up: Bindable Readline Commands

33.4.7 Keyboard Macros
----------------------

`start-kbd-macro (C-x ()'
Begin saving the characters typed into the current keyboard macro.

`end-kbd-macro (C-x ))'
Stop saving the characters typed into the current keyboard macro
and save the definition.

`call-last-kbd-macro (C-x e)'
Re-execute the last keyboard macro defined, by making the
characters in the macro appear as if typed at the keyboard.

`print-last-kbd-macro ()'
Print the last keboard macro defined in a format suitable for the
INPUTRC file.

File: gdb.info, Node: Miscellaneous Commands, Prev: Keyboard Macros, Up: Bindable Readline Commands

33.4.8 Some Miscellaneous Commands
----------------------------------

`re-read-init-file (C-x C-r)'
Read in the contents of the INPUTRC file, and incorporate any
bindings or variable assignments found there.

`abort (C-g)'
Abort the current editing command and ring the terminal's bell
(subject to the setting of `bell-style').

`do-lowercase-version (M-A, M-B, M-X, ...)'
If the metafied character X is upper case, run the command that is
bound to the corresponding metafied lower case character. The
behavior is undefined if X is already lower case.

`prefix-meta (<ESC>)'
Metafy the next character typed. This is for keyboards without a
meta key. Typing `<ESC> f' is equivalent to typing `M-f'.

`undo (C-_ or C-x C-u)'
Incremental undo, separately remembered for each line.

`revert-line (M-r)'
Undo all changes made to this line. This is like executing the
`undo' command enough times to get back to the beginning.

`tilde-expand (M-~)'
Perform tilde expansion on the current word.

`set-mark (C-@)'
Set the mark to the point. If a numeric argument is supplied, the
mark is set to that position.

`exchange-point-and-mark (C-x C-x)'
Swap the point with the mark. The current cursor position is set
to the saved position, and the old cursor position is saved as the
mark.

`character-search (C-])'
A character is read and point is moved to the next occurrence of
that character. A negative count searches for previous
occurrences.

`character-search-backward (M-C-])'
A character is read and point is moved to the previous occurrence
of that character. A negative count searches for subsequent
occurrences.

`skip-csi-sequence ()'
Read enough characters to consume a multi-key sequence such as
those defined for keys like Home and End. Such sequences begin
with a Control Sequence Indicator (CSI), usually ESC-[. If this
sequence is bound to "\e[", keys producing such sequences will
have no effect unless explicitly bound to a readline command,
instead of inserting stray characters into the editing buffer.
This is unbound by default, but usually bound to ESC-[.

`insert-comment (M-#)'
Without a numeric argument, the value of the `comment-begin'
variable is inserted at the beginning of the current line. If a
numeric argument is supplied, this command acts as a toggle: if
the characters at the beginning of the line do not match the value
of `comment-begin', the value is inserted, otherwise the
characters in `comment-begin' are deleted from the beginning of
the line. In either case, the line is accepted as if a newline
had been typed.

`dump-functions ()'
Print all of the functions and their key bindings to the Readline
output stream. If a numeric argument is supplied, the output is
formatted in such a way that it can be made part of an INPUTRC
file. This command is unbound by default.

`dump-variables ()'
Print all of the settable variables and their values to the
Readline output stream. If a numeric argument is supplied, the
output is formatted in such a way that it can be made part of an
INPUTRC file. This command is unbound by default.

`dump-macros ()'
Print all of the Readline key sequences bound to macros and the
strings they output. If a numeric argument is supplied, the
output is formatted in such a way that it can be made part of an
INPUTRC file. This command is unbound by default.

`emacs-editing-mode (C-e)'
When in `vi' command mode, this causes a switch to `emacs' editing
mode.

`vi-editing-mode (M-C-j)'
When in `emacs' editing mode, this causes a switch to `vi' editing
mode.

File: gdb.info, Node: Readline vi Mode, Prev: Bindable Readline Commands, Up: Command Line Editing

33.5 Readline vi Mode
=====================

While the Readline library does not have a full set of `vi' editing
functions, it does contain enough to allow simple editing of the line.
The Readline `vi' mode behaves as specified in the POSIX standard.

In order to switch interactively between `emacs' and `vi' editing
modes, use the command `M-C-j' (bound to emacs-editing-mode when in
`vi' mode and to vi-editing-mode in `emacs' mode). The Readline
default is `emacs' mode.

When you enter a line in `vi' mode, you are already placed in
`insertion' mode, as if you had typed an `i'. Pressing <ESC> switches
you into `command' mode, where you can edit the text of the line with
the standard `vi' movement keys, move to previous history lines with
`k' and subsequent lines with `j', and so forth.

File: gdb.info, Node: Using History Interactively, Next: In Memoriam, Prev: Command Line Editing, Up: Top

34 Using History Interactively
******************************

This chapter describes how to use the GNU History Library interactively,
from a user's standpoint. It should be considered a user's guide. For
information on using the GNU History Library in your own programs,
*note Programming with GNU History: (history)Programming with GNU
History.

* Menu:

* History Interaction:: What it feels like using History as a user.

File: gdb.info, Node: History Interaction, Up: Using History Interactively

34.1 History Expansion
======================

The History library provides a history expansion feature that is similar
to the history expansion provided by `csh'. This section describes the
syntax used to manipulate the history information.

History expansions introduce words from the history list into the
input stream, making it easy to repeat commands, insert the arguments
to a previous command into the current input line, or fix errors in
previous commands quickly.

History expansion takes place in two parts. The first is to
determine which line from the history list should be used during
substitution. The second is to select portions of that line for
inclusion into the current one. The line selected from the history is
called the "event", and the portions of that line that are acted upon
are called "words". Various "modifiers" are available to manipulate
the selected words. The line is broken into words in the same fashion
that Bash does, so that several words surrounded by quotes are
considered one word. History expansions are introduced by the
appearance of the history expansion character, which is `!' by default.

History expansion implements shell-like quoting conventions: a
backslash can be used to remove the special handling for the next
character; single quotes enclose verbatim sequences of characters, and
can be used to inhibit history expansion; and characters enclosed
within double quotes may be subject to history expansion, since
backslash can escape the history expansion character, but single quotes
may not, since they are not treated specially within double quotes.

* Menu:

* Event Designators:: How to specify which history line to use.
* Word Designators:: Specifying which words are of interest.
* Modifiers:: Modifying the results of substitution.

File: gdb.info, Node: Event Designators, Next: Word Designators, Up: History Interaction

34.1.1 Event Designators
------------------------

An event designator is a reference to a command line entry in the
history list. Unless the reference is absolute, events are relative to
the current position in the history list.

`!'
Start a history substitution, except when followed by a space, tab,
the end of the line, or `='.

`!N'
Refer to command line N.

`!-N'
Refer to the command N lines back.

`!!'
Refer to the previous command. This is a synonym for `!-1'.

`!STRING'
Refer to the most recent command preceding the current position in
the history list starting with STRING.

`!?STRING[?]'
Refer to the most recent command preceding the current position in
the history list containing STRING. The trailing `?' may be
omitted if the STRING is followed immediately by a newline. If
STRING is missing, the string from the most recent search is used;
it is an error if there is no previous search string.

`^STRING1^STRING2^'
Quick Substitution. Repeat the last command, replacing STRING1
with STRING2. Equivalent to `!!:s^STRING1^STRING2^'.

`!#'
The entire command line typed so far.

File: gdb.info, Node: Word Designators, Next: Modifiers, Prev: Event Designators, Up: History Interaction

34.1.2 Word Designators
-----------------------

Word designators are used to select desired words from the event. A
`:' separates the event specification from the word designator. It may
be omitted if the word designator begins with a `^', `$', `*', `-', or
`%'. Words are numbered from the beginning of the line, with the first
word being denoted by 0 (zero). Words are inserted into the current
line separated by single spaces.

For example,

`!!'
designates the preceding command. When you type this, the
preceding command is repeated in toto.

`!!:$'
designates the last argument of the preceding command. This may be
shortened to `!$'.

`!fi:2'
designates the second argument of the most recent command starting
with the letters `fi'.

Here are the word designators:

`0 (zero)'
The `0'th word. For many applications, this is the command word.

`N'
The Nth word.

`^'
The first argument; that is, word 1.

`$'
The last argument.

`%'
The first word matched by the most recent `?STRING?' search, if
the search string begins with a character that is part of a word.

`X-Y'
A range of words; `-Y' abbreviates `0-Y'.

`*'
All of the words, except the `0'th. This is a synonym for `1-$'.
It is not an error to use `*' if there is just one word in the
event; the empty string is returned in that case.

`X*'
Abbreviates `X-$'

`X-'
Abbreviates `X-$' like `X*', but omits the last word. If `x' is
missing, it defaults to 0.

If a word designator is supplied without an event specification, the
previous command is used as the event.

File: gdb.info, Node: Modifiers, Prev: Word Designators, Up: History Interaction

34.1.3 Modifiers
----------------

After the optional word designator, you can add a sequence of one or
more of the following modifiers, each preceded by a `:'. These modify,
or edit, the word or words selected from the history event.

`h'
Remove a trailing pathname component, leaving only the head.

`t'
Remove all leading pathname components, leaving the tail.

`r'
Remove a trailing suffix of the form `.SUFFIX', leaving the
basename.

`e'
Remove all but the trailing suffix.

`p'
Print the new command but do not execute it.

`s/OLD/NEW/'
Substitute NEW for the first occurrence of OLD in the event line.
Any character may be used as the delimiter in place of `/'. The
delimiter may be quoted in OLD and NEW with a single backslash.
If `&' appears in NEW, it is replaced by OLD. A single backslash
will quote the `&'. If OLD is null, it is set to the last OLD
substituted, or, if no previous history substitutions took place,
the last STRING in a !?STRING`[?]' search. If NEW is is null,
each matching OLD is deleted. The final delimiter is optional if
it is the last character on the input line.

`&'
Repeat the previous substitution.

`g'
`a'
Cause changes to be applied over the entire event line. Used in
conjunction with `s', as in `gs/OLD/NEW/', or with `&'.

`G'
Apply the following `s' or `&' modifier once to each word in the
event.

File: gdb.info, Node: In Memoriam, Next: Formatting Documentation, Prev: Using History Interactively, Up: Top

Appendix A In Memoriam
**********************

The GDB project mourns the loss of the following long-time contributors:

`Fred Fish'
Fred was a long-standing contributor to GDB (1991-2006), and to
Free Software in general. Outside of GDB, he was known in the
Amiga world for his series of Fish Disks, and the GeekGadget
project.

`Michael Snyder'
Michael was one of the Global Maintainers of the GDB project, with
contributions recorded as early as 1996, until 2011. In addition
to his day to day participation, he was a large driving force
behind adding Reverse Debugging to GDB.

Beyond their technical contributions to the project, they were also
enjoyable members of the Free Software Community. We will miss them.

File: gdb.info, Node: Formatting Documentation, Next: Installing GDB, Prev: In Memoriam, Up: Top

Appendix B Formatting Documentation
***********************************

The GDB 4 release includes an already-formatted reference card, ready
for printing with PostScript or Ghostscript, in the `gdb' subdirectory
of the main source directory(1). If you can use PostScript or
Ghostscript with your printer, you can print the reference card
immediately with `refcard.ps'.

The release also includes the source for the reference card. You
can format it, using TeX, by typing:

make refcard.dvi

The GDB reference card is designed to print in "landscape" mode on
US "letter" size paper; that is, on a sheet 11 inches wide by 8.5 inches
high. You will need to specify this form of printing as an option to
your DVI output program.

All the documentation for GDB comes as part of the machine-readable
distribution. The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual. You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or `texi2roff') to typeset the printed version.

GDB includes an already formatted copy of the on-line Info version
of this manual in the `gdb' subdirectory. The main Info file is
`gdb-15.1/gdb/gdb.info', and it refers to subordinate files matching
`gdb.info*' in the same directory. If necessary, you can print out
these files, or read them with any editor; but they are easier to read
using the `info' subsystem in GNU Emacs or the standalone `info'
program, available as part of the GNU Texinfo distribution.

If you want to format these Info files yourself, you need one of the
Info formatting programs, such as `texinfo-format-buffer' or `makeinfo'.

If you have `makeinfo' installed, and are in the top level GDB
source directory (`gdb-15.1', in the case of version 15.1), you can
make the Info file by typing:

cd gdb
make gdb.info

If you want to typeset and print copies of this manual, you need TeX,
a program to print its DVI output files, and `texinfo.tex', the Texinfo
definitions file.

TeX is a typesetting program; it does not print files directly, but
produces output files called DVI files. To print a typeset document,
you need a program to print DVI files. If your system has TeX
installed, chances are it has such a program. The precise command to
use depends on your system; `lpr -d' is common; another (for PostScript
devices) is `dvips'. The DVI print command may require a file name
without any extension or a `.dvi' extension.

TeX also requires a macro definitions file called `texinfo.tex'.
This file tells TeX how to typeset a document written in Texinfo
format. On its own, TeX cannot either read or typeset a Texinfo file.
`texinfo.tex' is distributed with GDB and is located in the
`gdb-VERSION-NUMBER/texinfo' directory.

If you have TeX and a DVI printer program installed, you can typeset
and print this manual. First switch to the `gdb' subdirectory of the
main source directory (for example, to `gdb-15.1/gdb') and type:

make gdb.dvi

Then give `gdb.dvi' to your DVI printing program.

---------- Footnotes ----------

(1) In `gdb-15.1/gdb/refcard.ps' of the version 15.1 release.

File: gdb.info, Node: Installing GDB, Next: Maintenance Commands, Prev: Formatting Documentation, Up: Top

Appendix C Installing GDB
*************************

* Menu:

* Requirements:: Requirements for building GDB
* Running Configure:: Invoking the GDB `configure' script
* Separate Objdir:: Compiling GDB in another directory
* Config Names:: Specifying names for hosts and targets
* Configure Options:: Summary of options for configure
* System-wide configuration:: Having a system-wide init file

File: gdb.info, Node: Requirements, Next: Running Configure, Up: Installing GDB

C.1 Requirements for Building GDB
=================================

Building GDB requires various tools and packages to be available.
Other packages will be used only if they are found.

Tools/Packages Necessary for Building GDB
=========================================

C++17 compiler
GDB is written in C++17. It should be buildable with any recent
C++17 compiler, e.g. GCC.

GNU make
GDB's build system relies on features only found in the GNU make
program. Other variants of `make' will not work.

Libraries
The following libraries are mandatory for building GDB. The
`configure' script searches for each of these libraries in several
standard locations; if some library is installed in an unusual
place, you can use either the `--with-LIB' `configure' option to
specify its installation directory, or the two separate options
`---with-LIBRARY-include' (to specify the location of its header
files) and `--with-LIBRARY-lib' (to specify the location of its
libraries). For example, for the GMP library, the 3 options are
`--with-gmp', `--with-gmp-include', and `--with-gmp-lib'. *Note
Configure Options::. We mention below the home site of each
library, so that you could download and install them if your
system doesn't already include them.

GMP (The GNU Multiple Precision arithmetic library)
GDB uses GMP to perform some of its extended-precision
arithmetic. The latest version of GMP is available from
`https://gmplib.org/'.

MPFR (The GNU Multiple-precision floating-point library)
GDB uses MPFR to emulate the target floating-point arithmetic
during expression evaluation, if the target uses different
floating-point formats than the host. The latest version of
MPFR is available from `http://www.mpfr.org'.

Tools/Packages Optional for Building GDB
========================================

The tools/packages and libraries listed below are optional; GDB can be
build without them, at the expense of some run-time functionality that
will be missing. As above, we list the home sites for each
package/library, and the command-line options supported by the
`configure' script to specify their installation directories if they
are non-standard. In addition, for each package you can use the option
`--with-PACKAGE' to force GDB to be compiled with the named PACKAGE, and
`--without-PACKAGE' to disable building with it even if it is
available. *Note Configure Options::, for detailed description of the
options to `configure'.

Python
GDB can be scripted using Python language. *Note Python::. The
latest version is available from
`https://www.python.org/downloads/'. Use the `--with-python=DIR'
to specify the non-standard directory where Python is installed.

Guile
GDB can also be scripted using GNU Guile. *Note Guile::. The
latest version can be found on
`https://www.gnu.org/software/guile/download/'. If you have more
than one version of Guile installed, use the
`--with-guile=GUILE-VERSION' to specify the Guile version to
include in the build.

Expat
If available, GDB uses the Expat library for parsing XML files.
GDB uses XML files for the following functionalities:

* Remote protocol memory maps (*note Memory Map Format::)

* Target descriptions (*note Target Descriptions::)

* Remote shared library lists (*Note Library List Format::, or
alternatively *note Library List Format for SVR4 Targets::)

* MS-Windows shared libraries (*note Shared Libraries::)

* Traceframe info (*note Traceframe Info Format::)

* Branch trace (*note Branch Trace Format::, *note Branch Trace
Configuration Format::)

The latest version of Expat is available from
`http://expat.sourceforge.net'. Use the `--with-libexpat-prefix'
to specify non-standard installation places for Expat.

iconv
GDB's features related to character sets (*note Character Sets::)
require a functioning `iconv' implementation. If you are on a GNU
system, then this is provided by the GNU C Library. Some other
systems also provide a working `iconv'. Use the option
`--with-iconv-bin' to specify where to find the `iconv' program.

On systems without `iconv', you can install the GNU Libiconv
library; its latest version can be found on
`https://ftp.gnu.org/pub/gnu/libiconv/' if your system doesn't
provide it. Use the `--with-libiconv-prefix' option to
`configure' to specify non-standard installation place for it.

Alternatively, GDB's top-level `configure' and `Makefile' will
arrange to build Libiconv if a directory named `libiconv' appears
in the top-most source directory. If Libiconv is built this way,
and if the operating system does not provide a suitable `iconv'
implementation, then the just-built library will automatically be
used by GDB. One easy way to set this up is to download GNU
Libiconv, unpack it inside the top-level directory of the GDB
source tree, and then rename the directory holding the Libiconv
source code to `libiconv'.

lzma
GDB can support debugging sections that are compressed with the
LZMA library. *Note MiniDebugInfo::. If this library is not
included with your operating system, you can find it in the xz
package at `http://tukaani.org/xz/'. Use the
`--with-liblzma-prefix' option to specify its non-standard
location.

zlib
GDB will use the `zlib' library, if available, to read compressed
debug sections. Some linkers, such as GNU `gold', are capable of
producing binaries with compressed debug sections. If GDB is
compiled with `zlib', it will be able to read the debug
information in such binaries.

The `zlib' library is likely included with your operating system
distribution; if it is not, you can get the latest version from
`http://zlib.net'.

File: gdb.info, Node: Running Configure, Next: Separate Objdir, Prev: Requirements, Up: Installing GDB

C.2 Invoking the GDB `configure' Script
=======================================

GDB comes with a `configure' script that automates the process of
preparing GDB for installation; you can then use `make' to build the
`gdb' program.

The GDB distribution includes all the source code you need for GDB
in a single directory, whose name is usually composed by appending the
version number to `gdb'.

For example, the GDB version 15.1 distribution is in the `gdb-15.1'
directory. That directory contains:

`gdb-15.1/configure (and supporting files)'
script for configuring GDB and all its supporting libraries

`gdb-15.1/gdb'
the source specific to GDB itself

`gdb-15.1/bfd'
source for the Binary File Descriptor library

`gdb-15.1/include'
GNU include files

`gdb-15.1/libiberty'
source for the `-liberty' free software library

`gdb-15.1/opcodes'
source for the library of opcode tables and disassemblers

`gdb-15.1/readline'
source for the GNU command-line interface

There may be other subdirectories as well.

The simplest way to configure and build GDB is to run `configure'
from the `gdb-VERSION-NUMBER' source directory, which in this example
is the `gdb-15.1' directory.

First switch to the `gdb-VERSION-NUMBER' source directory if you are
not already in it; then run `configure'. Pass the identifier for the
platform on which GDB will run as an argument.

For example:

cd gdb-15.1
./configure
make

Running `configure' and then running `make' builds the included
supporting libraries, then `gdb' itself. The configured source files,
and the binaries, are left in the corresponding source directories.

`configure' is a Bourne-shell (`/bin/sh') script; if your system
does not recognize this automatically when you run a different shell,
you may need to run `sh' on it explicitly:

sh configure

You should run the `configure' script from the top directory in the
source tree, the `gdb-VERSION-NUMBER' directory. If you run
`configure' from one of the subdirectories, you will configure only
that subdirectory. That is usually not what you want. In particular,
if you run the first `configure' from the `gdb' subdirectory of the
`gdb-VERSION-NUMBER' directory, you will omit the configuration of
`bfd', `readline', and other sibling directories of the `gdb'
subdirectory. This leads to build errors about missing include files
such as `bfd/bfd.h'.

You can install `GDB' anywhere. The best way to do this is to pass
the `--prefix' option to `configure', and then install it with `make
install'.

File: gdb.info, Node: Separate Objdir, Next: Config Names, Prev: Running Configure, Up: Installing GDB

C.3 Compiling GDB in Another Directory
======================================

If you want to run GDB versions for several host or target machines,
you need a different `gdb' compiled for each combination of host and
target. `configure' is designed to make this easy by allowing you to
generate each configuration in a separate subdirectory, rather than in
the source directory. If your `make' program handles the `VPATH'
feature (GNU `make' does), running `make' in each of these directories
builds the `gdb' program specified there.

To build `gdb' in a separate directory, run `configure' with the
`--srcdir' option to specify where to find the source. (You also need
to specify a path to find `configure' itself from your working
directory. If the path to `configure' would be the same as the
argument to `--srcdir', you can leave out the `--srcdir' option; it is
assumed.)

For example, with version 15.1, you can build GDB in a separate
directory for a Sun 4 like this:

cd gdb-15.1
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-15.1/configure
make

When `configure' builds a configuration using a remote source
directory, it creates a tree for the binaries with the same structure
(and using the same names) as the tree under the source directory. In
the example, you'd find the Sun 4 library `libiberty.a' in the
directory `gdb-sun4/libiberty', and GDB itself in `gdb-sun4/gdb'.

Make sure that your path to the `configure' script has just one
instance of `gdb' in it. If your path to `configure' looks like
`../gdb-15.1/gdb/configure', you are configuring only one subdirectory
of GDB, not the whole package. This leads to build errors about
missing include files such as `bfd/bfd.h'.

One popular reason to build several GDB configurations in separate
directories is to configure GDB for cross-compiling (where GDB runs on
one machine--the "host"--while debugging programs that run on another
machine--the "target"). You specify a cross-debugging target by giving
the `--target=TARGET' option to `configure'.

When you run `make' to build a program or library, you must run it
in a configured directory--whatever directory you were in when you
called `configure' (or one of its subdirectories).

The `Makefile' that `configure' generates in each source directory
also runs recursively. If you type `make' in a source directory such
as `gdb-15.1' (or in a separate configured directory configured with
`--srcdir=DIRNAME/gdb-15.1'), you will build all the required
libraries, and then build GDB.

When you have multiple hosts or targets configured in separate
directories, you can run `make' on them in parallel (for example, if
they are NFS-mounted on each of the hosts); they will not interfere
with each other.

File: gdb.info, Node: Config Names, Next: Configure Options, Prev: Separate Objdir, Up: Installing GDB

C.4 Specifying Names for Hosts and Targets
==========================================

The specifications used for hosts and targets in the `configure' script
are based on a three-part naming scheme, but some short predefined
aliases are also supported. The full naming scheme encodes three pieces
of information in the following pattern:

ARCHITECTURE-VENDOR-OS

For example, you can use the alias `sun4' as a HOST argument, or as
the value for TARGET in a `--target=TARGET' option. The equivalent
full name is `sparc-sun-sunos4'.

The `configure' script accompanying GDB does not provide any query
facility to list all supported host and target names or aliases.
`configure' calls the Bourne shell script `config.sub' to map
abbreviations to full names; you can read the script, if you wish, or
you can use it to test your guesses on abbreviations--for example:

% sh config.sub i386-linux
i386-pc-linux-gnu
% sh config.sub alpha-linux
alpha-unknown-linux-gnu
% sh config.sub hp9k700
hppa1.1-hp-hpux
% sh config.sub sun4
sparc-sun-sunos4.1.1
% sh config.sub sun3
m68k-sun-sunos4.1.1
% sh config.sub i986v
Invalid configuration `i986v': machine `i986v' not recognized

`config.sub' is also distributed in the GDB source directory
(`gdb-15.1', for version 15.1).

File: gdb.info, Node: Configure Options, Next: System-wide configuration, Prev: Config Names, Up: Installing GDB

C.5 `configure' Options
=======================

Here is a summary of the `configure' options and arguments that are
most often useful for building GDB. `configure' also has several other
options not listed here. *Note Running configure Scripts:
(autoconf)Running configure Scripts, for a full explanation of
`configure'.

configure [--help]
[--prefix=DIR]
[--exec-prefix=DIR]
[--srcdir=DIRNAME]
[--target=TARGET]

You may introduce options with a single `-' rather than `--' if you
prefer; but you may abbreviate option names if you use `--'.

`--help'
Display a quick summary of how to invoke `configure'.

`--prefix=DIR'
Configure the source to install programs and files under directory
`DIR'.

`--exec-prefix=DIR'
Configure the source to install programs under directory `DIR'.

`--srcdir=DIRNAME'
Use this option to make configurations in directories separate
from the GDB source directories. Among other things, you can use
this to build (or maintain) several configurations simultaneously,
in separate directories. `configure' writes
configuration-specific files in the current directory, but
arranges for them to use the source in the directory DIRNAME.
`configure' creates directories under the working directory in
parallel to the source directories below DIRNAME.

`--target=TARGET'
Configure GDB for cross-debugging programs running on the specified
TARGET. Without this option, GDB is configured to debug programs
that run on the same machine (HOST) as GDB itself.

There is no convenient way to generate a list of all available
targets. Also see the `--enable-targets' option, below.

There are many other options that are specific to GDB. This lists
just the most common ones; there are some very specialized options not
described here.

`--enable-targets=[TARGET]...'
`--enable-targets=all'
Configure GDB for cross-debugging programs running on the
specified list of targets. The special value `all' configures GDB
for debugging programs running on any target it supports.

`--with-gdb-datadir=PATH'
Set the GDB-specific data directory. GDB will look here for
certain supporting files or scripts. This defaults to the `gdb'
subdirectory of `datadir' (which can be set using `--datadir').

`--with-relocated-sources=DIR'
Sets up the default source path substitution rule so that directory
names recorded in debug information will be automatically adjusted
for any directory under DIR. DIR should be a subdirectory of
GDB's configured prefix, the one mentioned in the `--prefix' or
`--exec-prefix' options to configure. This option is useful if
GDB is supposed to be moved to a different place after it is built.

`--enable-64-bit-bfd'
Enable 64-bit support in BFD on 32-bit hosts.

`--disable-gdbmi'
Build GDB without the GDB/MI machine interface (*note GDB/MI::).

`--enable-tui'
Build GDB with the text-mode full-screen user interface (TUI).
Requires a curses library (ncurses and cursesX are also supported).

`--with-curses'
Use the curses library instead of the termcap library, for
text-mode terminal operations.

`--with-debuginfod'
Build GDB with `libdebuginfod', the `debuginfod' client library.
Used to automatically fetch ELF, DWARF and source files from
`debuginfod' servers using build IDs associated with any missing
files. Enabled by default if `libdebuginfod' is installed and
found at configure time. For more information regarding
`debuginfod' see *Note Debuginfod::.

`--with-libunwind-ia64'
Use the libunwind library for unwinding function call stack on ia64
target platforms. See
`http://www.nongnu.org/libunwind/index.html' for details.

`--with-system-readline'
Use the readline library installed on the host, rather than the
library supplied as part of GDB. Readline 7 or newer is required;
this is enforced by the build system.

`--with-system-zlib'
Use the zlib library installed on the host, rather than the library
supplied as part of GDB.

`--with-expat'
Build GDB with Expat, a library for XML parsing. (Done by default
if libexpat is installed and found at configure time.) This
library is used to read XML files supplied with GDB. If it is
unavailable, some features, such as remote protocol memory maps,
target descriptions, and shared library lists, that are based on
XML files, will not be available in GDB. If your host does not
have libexpat installed, you can get the latest version from
`http://expat.sourceforge.net'.

`--with-libiconv-prefix[=DIR]'
Build GDB with GNU libiconv, a character set encoding conversion
library. This is not done by default, as on GNU systems the
`iconv' that is built in to the C library is sufficient. If your
host does not have a working `iconv', you can get the latest
version of GNU iconv from `https://www.gnu.org/software/libiconv/'.

GDB's build system also supports building GNU libiconv as part of
the overall build. *Note Requirements::.

`--with-lzma'
Build GDB with LZMA, a compression library. (Done by default if
liblzma is installed and found at configure time.) LZMA is used by
GDB's "mini debuginfo" feature, which is only useful on platforms
using the ELF object file format. If your host does not have
liblzma installed, you can get the latest version from
`https://tukaani.org/xz/'.

`--with-python[=PYTHON]'
Build GDB with Python scripting support. (Done by default if
libpython is present and found at configure time.) Python makes
GDB scripting much more powerful than the restricted CLI scripting
language. If your host does not have Python installed, you can
find it on `http://www.python.org/download/'. The oldest version
of Python supported by GDB is 3.0.1. The optional argument PYTHON
is used to find the Python headers and libraries. It can be either
the name of a Python executable, or the name of the directory in
which Python is installed.

`--with-guile[=GUILE]'
Build GDB with GNU Guile scripting support. (Done by default if
libguile is present and found at configure time.) If your host
does not have Guile installed, you can find it at
`https://www.gnu.org/software/guile/'. The optional argument GUILE
can be a version number, which will cause `configure' to try to
use that version of Guile; or the file name of a `pkg-config'
executable, which will be queried to find the information needed to
compile and link against Guile.

`--without-included-regex'
Don't use the regex library included with GDB (as part of the
libiberty library). This is the default on hosts with version 2 of
the GNU C library.

`--with-sysroot=DIR'
Use DIR as the default system root directory for libraries whose
file names begin with `/lib'' or `/usr/lib''. (The value of DIR
can be modified at run time by using the `set sysroot' command.)
If DIR is under the GDB configured prefix (set with `--prefix' or
`--exec-prefix options', the default system root will be
automatically adjusted if and when GDB is moved to a different
location.

`--with-system-gdbinit=FILE'
Configure GDB to automatically load a system-wide init file. FILE
should be an absolute file name. If FILE is in a directory under
the configured prefix, and GDB is moved to another location after
being built, the location of the system-wide init file will be
adjusted accordingly.

`--with-system-gdbinit-dir=DIRECTORY'
Configure GDB to automatically load init files from a system-wide
directory. DIRECTORY should be an absolute directory name. If
DIRECTORY is in a directory under the configured prefix, and GDB
is moved to another location after being built, the location of
the system-wide init directory will be adjusted accordingly.

`--enable-build-warnings'
When building the GDB sources, ask the compiler to warn about any
code which looks even vaguely suspicious. It passes many
different warning flags, depending on the exact version of the
compiler you are using.

`--enable-werror'
Treat compiler warnings as errors. It adds the `-Werror' flag to
the compiler, which will fail the compilation if the compiler
outputs any warning messages.

`--enable-ubsan'
Enable the GCC undefined behavior sanitizer. This is disabled by
default, but passing `--enable-ubsan=yes' or `--enable-ubsan=auto'
to `configure' will enable it. The undefined behavior sanitizer
checks for C++ undefined behavior. It has a performance cost, so
if you are looking at GDB's performance, you should disable it.
The undefined behavior sanitizer was first introduced in GCC 4.9.

File: gdb.info, Node: System-wide configuration, Prev: Configure Options, Up: Installing GDB

C.6 System-wide configuration and settings
==========================================

GDB can be configured to have a system-wide init file and a system-wide
init file directory; this file and files in that directory (if they
have a recognized file extension) will be read and executed at startup
(*note What GDB does during startup: Startup.).

Here are the corresponding configure options:

`--with-system-gdbinit=FILE'
Specify that the default location of the system-wide init file is
FILE.

`--with-system-gdbinit-dir=DIRECTORY'
Specify that the default location of the system-wide init file
directory is DIRECTORY.

If GDB has been configured with the option `--prefix=$prefix', they
may be subject to relocation. Two possible cases:

* If the default location of this init file/directory contains
`$prefix', it will be subject to relocation. Suppose that the
configure options are `--prefix=$prefix
--with-system-gdbinit=$prefix/etc/gdbinit'; if GDB is moved from
`$prefix' to `$install', the system init file is looked for as
`$install/etc/gdbinit' instead of `$prefix/etc/gdbinit'.

* By contrast, if the default location does not contain the prefix,
it will not be relocated. E.g. if GDB has been configured with
`--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit',
then GDB will always look for `/usr/share/gdb/gdbinit', wherever
GDB is installed.

If the configured location of the system-wide init file (as given by
the `--with-system-gdbinit' option at configure time) is in the
data-directory (as specified by `--with-gdb-datadir' at configure time)
or in one of its subdirectories, then GDB will look for the system-wide
init file in the directory specified by the `--data-directory'
command-line option. Note that the system-wide init file is only read
once, during GDB initialization. If the data-directory is changed
after GDB has started with the `set data-directory' command, the file
will not be reread.

This applies similarly to the system-wide directory specified in
`--with-system-gdbinit-dir'.

Any supported scripting language can be used for these init files,
as long as the file extension matches the scripting language. To be
interpreted as regular GDB commands, the files needs to have a `.gdb'
extension.

* Menu:

* System-wide Configuration Scripts:: Installed System-wide Configuration Scripts

File: gdb.info, Node: System-wide Configuration Scripts, Up: System-wide configuration

C.6.1 Installed System-wide Configuration Scripts
-------------------------------------------------

The `system-gdbinit' directory, located inside the data-directory (as
specified by `--with-gdb-datadir' at configure time) contains a number
of scripts which can be used as system-wide init files. To
automatically source those scripts at startup, GDB should be configured
with `--with-system-gdbinit'. Otherwise, any user should be able to
source them by hand as needed.

The following scripts are currently available:
* `elinos.py' This script is useful when debugging a program on an
ELinOS target. It takes advantage of the environment variables
defined in a standard ELinOS environment in order to determine the
location of the system shared libraries, and then sets the
`solib-absolute-prefix' and `solib-search-path' variables
appropriately.

* `wrs-linux.py' This script is useful when debugging a program on a
target running Wind River Linux. It expects the `ENV_PREFIX' to
be set to the host-side sysroot used by the target system.

File: gdb.info, Node: Maintenance Commands, Next: Remote Protocol, Prev: Installing GDB, Up: Top

Appendix D Maintenance Commands
*******************************

In addition to commands intended for GDB users, GDB includes a number
of commands intended for GDB developers, that are not documented
elsewhere in this manual. These commands are provided here for
reference. (For commands that turn on debugging messages, see *Note
Debugging Output::.)

`maint agent [-at LINESPEC,] EXPRESSION'
`maint agent-eval [-at LINESPEC,] EXPRESSION'
Translate the given EXPRESSION into remote agent bytecodes. This
command is useful for debugging the Agent Expression mechanism
(*note Agent Expressions::). The `agent' version produces an
expression useful for data collection, such as by tracepoints,
while `maint agent-eval' produces an expression that evaluates
directly to a result. For instance, a collection expression for
`globa + globb' will include bytecodes to record four bytes of
memory at each of the addresses of `globa' and `globb', while
discarding the result of the addition, while an evaluation
expression will do the addition and return the sum. If `-at' is
given, generate remote agent bytecode for all the addresses to
which LINESPEC resolves (*note Linespec Locations::). If not,
generate remote agent bytecode for current frame PC address.

`maint agent-printf FORMAT,EXPR,...'
Translate the given format string and list of argument expressions
into remote agent bytecodes and display them as a disassembled
list. This command is useful for debugging the agent version of
dynamic printf (*note Dynamic Printf::).

`maint info breakpoints'
Using the same format as `info breakpoints', display both the
breakpoints you've set explicitly, and those GDB is using for
internal purposes. Internal breakpoints are shown with negative
breakpoint numbers. The type column identifies what kind of
breakpoint is shown:

`breakpoint'
Normal, explicitly set breakpoint.

`watchpoint'
Normal, explicitly set watchpoint.

`longjmp'
Internal breakpoint, used to handle correctly stepping through
`longjmp' calls.

`longjmp resume'
Internal breakpoint at the target of a `longjmp'.

`until'
Temporary internal breakpoint used by the GDB `until' command.

`finish'
Temporary internal breakpoint used by the GDB `finish'
command.

`shlib events'
Shared library events.

`maint info btrace'
Pint information about raw branch tracing data.

`maint btrace packet-history'
Print the raw branch trace packets that are used to compute the
execution history for the `record btrace' command. Both the
information and the format in which it is printed depend on the
btrace recording format.

`bts'
For the BTS recording format, print a list of blocks of
sequential code. For each block, the following information
is printed:

Block number
Newer blocks have higher numbers. The oldest block has
number zero.

Lowest `PC'

Highest `PC'

`pt'
For the Intel Processor Trace recording format, print a list
of Intel Processor Trace packets. For each packet, the
following information is printed:

Packet number
Newer packets have higher numbers. The oldest packet
has number zero.

Trace offset
The packet's offset in the trace stream.

Packet opcode and payload

`maint btrace clear-packet-history'
Discards the cached packet history printed by the `maint btrace
packet-history' command. The history will be computed again when
needed.

`maint btrace clear'
Discard the branch trace data. The data will be fetched anew and
the branch trace will be recomputed when needed.

This implicitly truncates the branch trace to a single branch trace
buffer. When updating branch trace incrementally, the branch trace
available to GDB may be bigger than a single branch trace buffer.

`maint set btrace pt skip-pad'

`maint show btrace pt skip-pad'
Control whether GDB will skip PAD packets when computing the
packet history.

`maint info jit'
Print information about JIT code objects loaded in the current
inferior.

`maint info python-disassemblers'
This command is defined within the `gdb.disassembler' Python
module (*note Disassembly In Python::), and will only be present
after that module has been imported. To force the module to be
imported do the following:

`maint info linux-lwps'
Print information about LWPs under control of the Linux native
target.

(gdb) python import gdb.disassembler

This command lists all the architectures for which a disassembler
is currently registered, and the name of the disassembler. If a
disassembler is registered for all architectures, then this is
listed last against the `GLOBAL' architecture.

If one of the disassemblers would be selected for the architecture
of the current inferior, then this disassembler will be marked.

The following example shows a situation in which two disassemblers
are registered, initially the `i386' disassembler matches the
current architecture, then the architecture is changed, now the
`GLOBAL' disassembler matches.

(gdb) show architecture
The target architecture is set to "auto" (currently "i386").
(gdb) maint info python-disassemblers
Architecture Disassember Name
i386 Disassembler_1 (Matches current architecture)
GLOBAL Disassembler_2
(gdb) set architecture arm
The target architecture is set to "arm".
(gdb) maint info python-disassemblers
quit
Architecture Disassember Name
i386 Disassembler_1
GLOBAL Disassembler_2 (Matches current architecture)

`set displaced-stepping'
`show displaced-stepping'
Control whether or not GDB will do "displaced stepping" if the
target supports it. Displaced stepping is a way to single-step
over breakpoints without removing them from the inferior, by
executing an out-of-line copy of the instruction that was
originally at the breakpoint location. It is also known as
out-of-line single-stepping.

`set displaced-stepping on'
If the target architecture supports it, GDB will use
displaced stepping to step over breakpoints.

`set displaced-stepping off'
GDB will not use displaced stepping to step over breakpoints,
even if such is supported by the target architecture.

`set displaced-stepping auto'
This is the default mode. GDB will use displaced stepping
only if non-stop mode is active (*note Non-Stop Mode::) and
the target architecture supports displaced stepping.

`maint check-psymtabs'
Check the consistency of currently expanded psymtabs versus
symtabs. Use this to check, for example, whether a symbol is in
one but not the other.

`maint check-symtabs'
Check the consistency of currently expanded symtabs.

`maint expand-symtabs [REGEXP]'
Expand symbol tables. If REGEXP is specified, only expand symbol
tables for file names matching REGEXP.

`maint set catch-demangler-crashes [on|off]'
`maint show catch-demangler-crashes'
Control whether GDB should attempt to catch crashes in the symbol
name demangler. The default is to attempt to catch crashes. If
enabled, the first time a crash is caught, a core file is created,
the offending symbol is displayed and the user is presented with
the option to terminate the current session.

`maint cplus first_component NAME'
Print the first C++ class/namespace component of NAME.

`maint cplus namespace'
Print the list of possible C++ namespaces.

`maint deprecate COMMAND [REPLACEMENT]'
`maint undeprecate COMMAND'
Deprecate or undeprecate the named COMMAND. Deprecated commands
cause GDB to issue a warning when you use them. The optional
argument REPLACEMENT says which newer command should be used in
favor of the deprecated one; if it is given, GDB will mention the
replacement as part of the warning.

`maint dump-me'
Cause a fatal signal in the debugger and force it to dump its core.
This is supported only on systems which support aborting a program
with the `SIGQUIT' signal.

`maint internal-error [MESSAGE-TEXT]'
`maint internal-warning [MESSAGE-TEXT]'
`maint demangler-warning [MESSAGE-TEXT]'
Cause GDB to call the internal function `internal_error',
`internal_warning' or `demangler_warning' and hence behave as
though an internal problem has been detected. In addition to
reporting the internal problem, these functions give the user the
opportunity to either quit GDB or (for `internal_error' and
`internal_warning') create a core file of the current GDB session.

These commands take an optional parameter MESSAGE-TEXT that is
used as the text of the error or warning message.

Here's an example of using `internal-error':

(gdb) maint internal-error testing, 1, 2
.../maint.c:121: internal-error: testing, 1, 2
A problem internal to GDB has been detected. Further
debugging may prove unreliable.
Quit this debugging session? (y or n) n
Create a core file? (y or n) n
(gdb)

`maint set debuginfod download-sections'
`maint set debuginfod download-sections [on|off]'
`maint show debuginfod download-sections'
Controls whether GDB will attempt to download individual ELF/DWARF
sections from `debuginfod'. If disabled, only whole debug info
files will be downloaded; this could result in GDB downloading
larger amounts of data.

`maint set internal-error ACTION [ask|yes|no]'
`maint show internal-error ACTION'
`maint set internal-warning ACTION [ask|yes|no]'
`maint show internal-warning ACTION'
`maint set demangler-warning ACTION [ask|yes|no]'
`maint show demangler-warning ACTION'
When GDB reports an internal problem (error or warning) it gives
the user the opportunity to both quit GDB and create a core file
of the current GDB session. These commands let you override the
default behaviour for each particular ACTION, described in the
table below.

`quit'
You can specify that GDB should always (yes) or never (no)
quit. The default is to ask the user what to do.

`corefile'
You can specify that GDB should always (yes) or never (no)
create a core file. The default is to ask the user what to
do. Note that there is no `corefile' option for
`demangler-warning': demangler warnings always create a core
file and this cannot be disabled.

`maint set internal-error backtrace [on|off]'
`maint show internal-error backtrace'
`maint set internal-warning backtrace [on|off]'
`maint show internal-warning backtrace'
When GDB reports an internal problem (error or warning) it is
possible to have a backtrace of GDB printed to the standard error
stream. This is `on' by default for `internal-error' and `off' by
default for `internal-warning'.

`maint packet TEXT'
If GDB is talking to an inferior via the serial protocol, then
this command sends the string TEXT to the inferior, and displays
the response packet. GDB supplies the initial `$' character, the
terminating `#' character, and the checksum.

Any non-printable characters in the reply are printed as escaped
hex, e.g. `\x00', `\x01', etc.

`maint print architecture [FILE]'
Print the entire architecture configuration. The optional argument
FILE names the file where the output goes.

`maint print c-tdesc [-single-feature] [FILE]'
Print the target description (*note Target Descriptions::) as a C
source file. By default, the target description is for the current
target, but if the optional argument FILE is provided, that file
is used to produce the description. The FILE should be an XML
document, of the form described in *Note Target Description
Format::. The created source file is built into GDB when GDB is
built again. This command is used by developers after they add or
modify XML target descriptions.

When the optional flag `-single-feature' is provided then the
target description being processed (either the default, or from
FILE) must only contain a single feature. The source file
produced is different in this case.

`maint print xml-tdesc [FILE]'
Print the target description (*note Target Descriptions::) as an
XML file. By default print the target description for the current
target, but if the optional argument FILE is provided, then that
file is read in by GDB and then used to produce the description.
The FILE should be an XML document, of the form described in *Note
Target Description Format::.

`maint check xml-descriptions DIR'
Check that the target descriptions dynamically created by GDB
equal the descriptions created from XML files found in DIR.

`maint check libthread-db'
Run integrity checks on the current inferior's thread debugging
library. This exercises all `libthread_db' functionality used by
GDB on GNU/Linux systems, and by extension also exercises the
`proc_service' functions provided by GDB that `libthread_db' uses.
Note that parts of the test may be skipped on some platforms when
debugging core files.

`maint print core-file-backed-mappings'
Print the file-backed mappings which were loaded from a core file
note. This output represents state internal to GDB and should be
similar to the mappings displayed by the `info proc mappings'
command.

`maint print dummy-frames'
Prints the contents of GDB's internal dummy-frame stack.

(gdb) b add
...
(gdb) print add(2,3)
Breakpoint 2, add (a=2, b=3) at ...
58 return (a + b);
The program being debugged stopped while in a function called from GDB.
...
(gdb) maint print dummy-frames
0xa8206d8: id={stack=0xbfffe734,code=0xbfffe73f,!special}, ptid=process 9353
(gdb)

Takes an optional file parameter.

`maint print frame-id'
`maint print frame-id LEVEL'
Print GDB's internal frame-id for the frame at relative LEVEL, or
for the currently selected frame when LEVEL is not given.

If used, LEVEL should be an integer, as displayed in the
`backtrace' output.

(gdb) maint print frame-id
frame-id for frame #0: {stack=0x7fffffffac70,code=0x0000000000401106,!special}
(gdb) maint print frame-id 2
frame-id for frame #2: {stack=0x7fffffffac90,code=0x000000000040111c,!special}

`maint print registers [FILE]'
`maint print raw-registers [FILE]'
`maint print cooked-registers [FILE]'
`maint print register-groups [FILE]'
`maint print remote-registers [FILE]'
Print GDB's internal register data structures.

The command `maint print raw-registers' includes the contents of
the raw register cache; the command `maint print cooked-registers'
includes the (cooked) value of all registers, including registers
which aren't available on the target nor visible to user; the
command `maint print register-groups' includes the groups that
each register is a member of; and the command `maint print
remote-registers' includes the remote target's register numbers
and offsets in the `G' packets.

These commands take an optional parameter, a file name to which to
write the information.

`maint print reggroups [FILE]'
Print GDB's internal register group data structures. The optional
argument FILE tells to what file to write the information.

The register groups info looks like this:

(gdb) maint print reggroups
Group Type
general user
float user
all user
vector user
system user
save internal
restore internal

`maint flush register-cache'
`flushregs'
Flush the contents of the register cache and as a consequence the
frame cache. This command is useful when debugging issues related
to register fetching, or frame unwinding. The command `flushregs'
is deprecated in favor of `maint flush register-cache'.

`maint flush source-cache'
Flush GDB's cache of source code file contents. After GDB reads a
source file, and optionally applies styling (*note Output
Styling::), the file contents are cached. This command clears
that cache. The next time GDB wants to show lines from a source
file, the content will be re-read.

This command is useful when debugging issues related to source code
styling. After flushing the cache any source code displayed by
GDB will be re-read and re-styled.

`maint print objfiles [REGEXP]'
Print a dump of all known object files. If REGEXP is specified,
only print object files whose names match REGEXP. For each object
file, this command prints its name, address in memory, and all of
its psymtabs and symtabs.

`maint print user-registers'
List all currently available "user registers". User registers
typically provide alternate names for actual hardware registers.
They include the four "standard" registers `$fp', `$pc', `$sp',
and `$ps'. *Note standard registers::. User registers can be
used in expressions in the same way as the canonical register
names, but only the latter are listed by the `info registers' and
`maint print registers' commands.

`maint print section-scripts [REGEXP]'
Print a dump of scripts specified in the `.debug_gdb_section'
section. If REGEXP is specified, only print scripts loaded by
object files matching REGEXP. For each script, this command
prints its name as specified in the objfile, and the full path if
known. *Note dotdebug_gdb_scripts section::.

`maint print statistics'
This command prints, for each object file in the program, various
data about that object file followed by the byte cache ("bcache")
statistics for the object file. The objfile data includes the
number of minimal, partial, full, and stabs symbols, the number of
types defined by the objfile, the number of as yet unexpanded psym
tables, the number of line tables and string tables, and the
amount of memory used by the various tables. The bcache
statistics include the counts, sizes, and counts of duplicates of
all and unique objects, max, average, and median entry size, total
memory used and its overhead and savings, and various measures of
the hash table size and chain lengths.

`maint print target-stack'
A "target" is an interface between the debugger and a particular
kind of file or process. Targets can be stacked in "strata", so
that more than one target can potentially respond to a request.
In particular, memory accesses will walk down the stack of targets
until they find a target that is interested in handling that
particular address.

This command prints a short description of each layer that was
pushed on the "target stack", starting from the top layer down to
the bottom one.

`maint print type EXPR'
Print the type chain for a type specified by EXPR. The argument
can be either a type name or a symbol. If it is a symbol, the
type of that symbol is described. The type chain produced by this
command is a recursive definition of the data type as stored in
GDB's data structures, including its flags and contained types.

`maint print record-instruction'
`maint print record-instruction N'
print how GDB recorded a given instruction. If N is not positive
number, it prints the values stored by the inferior before the
N-th previous instruction was executed. If N is positive, print
the values after the N-th following instruction is executed. If N
is not given, 0 is assumed.

`maint selftest [-verbose] [FILTER]'
Run any self tests that were compiled in to GDB. This will print
a message showing how many tests were run, and how many failed.
If a FILTER is passed, only the tests with FILTER in their name
will be ran. If `-verbose' is passed, the self tests can be more
verbose.

`maint set selftest verbose'

`maint show selftest verbose'
Control whether self tests are run verbosely or not.

`maint info selftests'
List the selftests compiled in to GDB.

`maint set dwarf always-disassemble'

`maint show dwarf always-disassemble'
Control the behavior of `info address' when using DWARF debugging
information.

The default is `off', which means that GDB should try to describe
a variable's location in an easily readable format. When `on',
GDB will instead display the DWARF location expression in an
assembly-like format. Note that some locations are too complex
for GDB to describe simply; in this case you will always see the
disassembly form.

Here is an example of the resulting disassembly:

(gdb) info addr argc
Symbol "argc" is a complex DWARF expression:
1: DW_OP_fbreg 0

For more information on these expressions, see the DWARF standard
(http://www.dwarfstd.org/).

`maint set dwarf max-cache-age'
`maint show dwarf max-cache-age'
Control the DWARF compilation unit cache.

In object files with inter-compilation-unit references, such as
those produced by the GCC option `-feliminate-dwarf2-dups', the
DWARF reader needs to frequently refer to previously read
compilation units. This setting controls how long a compilation
unit will remain in the cache if it is not referenced. A higher
limit means that cached compilation units will be stored in memory
longer, and more total memory will be used. Setting it to zero
disables caching, which will slow down GDB startup, but reduce
memory consumption.

`maint set dwarf synchronous'
`maint show dwarf synchronous'
Control whether DWARF is read asynchronously.

On hosts where threading is available, the DWARF reader is mostly
asynchronous with respect to the rest of GDB. That is, the bulk
of the reading is done in the background, and GDB will only pause
for completion of this task when absolutely necessary.

When this setting is enabled, GDB will instead wait for DWARF
processing to complete before continuing.

On hosts without threading, or where worker threads have been
disabled at runtime, this setting has no effect, as DWARF reading
is always done on the main thread, and is therefore always
synchronous.

`maint set dwarf unwinders'
`maint show dwarf unwinders'
Control use of the DWARF frame unwinders.

Many targets that support DWARF debugging use GDB's DWARF frame
unwinders to build the backtrace. Many of these targets will also
have a second mechanism for building the backtrace for use in
cases where DWARF information is not available, this second
mechanism is often an analysis of a function's prologue.

In order to extend testing coverage of the second level stack
unwinding mechanisms it is helpful to be able to disable the DWARF
stack unwinders, this can be done with this switch.

In normal use of GDB disabling the DWARF unwinders is not
advisable, there are cases that are better handled through DWARF
than prologue analysis, and the debug experience is likely to be
better with the DWARF frame unwinders enabled.

If DWARF frame unwinders are not supported for a particular target
architecture, then enabling this flag does not cause them to be
used.

`maint info frame-unwinders'
List the frame unwinders currently in effect, starting with the
highest priority.

`maint set worker-threads'

`maint show worker-threads'
Control the number of worker threads that may be used by GDB. On
capable hosts, GDB may use multiple threads to speed up certain
CPU-intensive operations, such as demangling symbol names. While
the number of threads used by GDB may vary, this command can be
used to set an upper bound on this number. The default is
`unlimited', which lets GDB choose a reasonable number. Note that
this only controls worker threads started by GDB itself; libraries
used by GDB may start threads of their own.

`maint set profile'
`maint show profile'
Control profiling of GDB.

Profiling will be disabled until you use the `maint set profile'
command to enable it. When you enable profiling, the system will
begin collecting timing and execution count data; when you disable
profiling or exit GDB, the results will be written to a log file.
Remember that if you use profiling, GDB will overwrite the
profiling log file (often called `gmon.out'). If you have a
record of important profiling data in a `gmon.out' file, be sure
to move it to a safe location.

Configuring with `--enable-profiling' arranges for GDB to be
compiled with the `-pg' compiler option.

`maint set show-debug-regs'
`maint show show-debug-regs'
Control whether to show variables that mirror the hardware debug
registers. Use `on' to enable, `off' to disable. If enabled, the
debug registers values are shown when GDB inserts or removes a
hardware breakpoint or watchpoint, and when the inferior triggers
a hardware-assisted breakpoint or watchpoint.

`maint set show-all-tib'
`maint show show-all-tib'
Control whether to show all non zero areas within a 1k block
starting at thread local base, when using the `info w32
thread-information-block' command.

`maint set target-async'
`maint show target-async'
This controls whether GDB targets operate in synchronous or
asynchronous mode (*note Background Execution::). Normally the
default is asynchronous, if it is available; but this can be
changed to more easily debug problems occurring only in
synchronous mode.

`maint set target-non-stop'
`maint show target-non-stop'
This controls whether GDB targets always operate in non-stop mode
even if `set non-stop' is `off' (*note Non-Stop Mode::). The
default is `auto', meaning non-stop mode is enabled if supported
by the target.

`maint set target-non-stop auto'
This is the default mode. GDB controls the target in
non-stop mode if the target supports it.

`maint set target-non-stop on'
GDB controls the target in non-stop mode even if the target
does not indicate support.

`maint set target-non-stop off'
GDB does not control the target in non-stop mode even if the
target supports it.

`maint set tui-resize-message'

`maint show tui-resize-message'
Control whether GDB displays a message each time the terminal is
resized when in TUI mode. The default is `off', which means that
GDB is silent during resizes. When `on', GDB will display a
message after a resize is completed; the message will include a
number indicating how many times the terminal has been resized.
This setting is intended for use by the test suite, where it would
otherwise be difficult to determine when a resize and refresh has
been completed.

`maint set tui-left-margin-verbose'

`maint show tui-left-margin-verbose'
Control whether the left margin of the TUI source and disassembly
windows uses `_' and `0' at locations where otherwise there would
be a space. The default is `off', which means spaces are used.
The setting is intended to make it clear where the left margin
begins and ends, to avoid incorrectly interpreting a space as
being part of the the left margin.

`maint set per-command'
`maint show per-command'
GDB can display the resources used by each command. This is
useful in debugging performance problems.

`maint set per-command space [on|off]'
`maint show per-command space'
Enable or disable the printing of the memory used by GDB for
each command. If enabled, GDB will display how much memory
each command took, following the command's own output. This
can also be requested by invoking GDB with the `--statistics'
command-line switch (*note Mode Options::).

`maint set per-command time [on|off]'
`maint show per-command time'
Enable or disable the printing of the execution time of GDB
for each command. If enabled, GDB will display how much time
it took to execute each command, following the command's own
output. Both CPU time and wallclock time are printed.
Printing both is useful when trying to determine whether the
cost is CPU or, e.g., disk/network latency. Note that the
CPU time printed is for GDB only, it does not include the
execution time of the inferior because there's no mechanism
currently to compute how much time was spent by GDB and how
much time was spent by the program been debugged. This can
also be requested by invoking GDB with the `--statistics'
command-line switch (*note Mode Options::).

`maint set per-command symtab [on|off]'
`maint show per-command symtab'
Enable or disable the printing of basic symbol table
statistics for each command. If enabled, GDB will display
the following information:

a. number of symbol tables

b. number of primary symbol tables

c. number of blocks in the blockvector

`maint set check-libthread-db [on|off]'
`maint show check-libthread-db'
Control whether GDB should run integrity checks on inferior
specific thread debugging libraries as they are loaded. The
default is not to perform such checks. If any check fails GDB will
unload the library and continue searching for a suitable candidate
as described in *Note set libthread-db-search-path::. For more
information about the tests, see *Note maint check libthread-db::.

`maint set gnu-source-highlight enabled [on|off]'
`maint show gnu-source-highlight enabled'
Control whether GDB should use the GNU Source Highlight library
for applying styling to source code (*note Output Styling::).
This will be `on' by default if the GNU Source Highlight library
is available. If the GNU Source Highlight library is not
available, then this will be `off' by default, and attempting to
change this value to `on' will give an error.

If the GNU Source Highlight library is not being used, then GDB
will use the Python Pygments package for source code styling, if
it is available.

This option is useful for debugging GDB's use of the Pygments
library when GDB is linked against the GNU Source Highlight
library.

`maint set libopcodes-styling enabled [on|off]'
`maint show libopcodes-styling enabled'
Control whether GDB should use its builtin disassembler
(`libopcodes') to style disassembler output (*note Output
Styling::). The builtin disassembler does not support styling for
all architectures.

When this option is `off' the builtin disassembler will not be
used for styling, GDB will fall back to using the Python Pygments
package if possible.

Trying to set this option `on' for an architecture that the
builtin disassembler is unable to style will give an error,
otherwise, the builtin disassembler will be used to style
disassembler output.

This option is `on' by default for supported architectures.

This option is useful for debugging GDB's use of the Pygments
library when GDB is built for an architecture that supports
styling with the builtin disassembler

`maint info screen'
Print various characteristics of the screen, such as various
notions of width and height.

`maint space VALUE'
An alias for `maint set per-command space'. A non-zero value
enables it, zero disables it.

`maint time VALUE'
An alias for `maint set per-command time'. A non-zero value
enables it, zero disables it.

`maint translate-address [SECTION] ADDR'
Find the symbol stored at the location specified by the address
ADDR and an optional section name SECTION. If found, GDB prints
the name of the closest symbol and an offset from the symbol's
location to the specified address. This is similar to the `info
address' command (*note Symbols::), except that this command also
allows to find symbols in other sections.

If section was not specified, the section in which the symbol was
found is also printed. For dynamically linked executables, the
name of executable or shared library containing the symbol is
printed as well.

`maint test-options require-delimiter'
`maint test-options unknown-is-error'
`maint test-options unknown-is-operand'
These commands are used by the testsuite to validate the command
options framework. The `require-delimiter' variant requires a
double-dash delimiter to indicate end of options. The
`unknown-is-error' and `unknown-is-operand' do not. The
`unknown-is-error' variant throws an error on unknown option,
while `unknown-is-operand' treats unknown options as the start of
the command's operands. When run, the commands output the result
of the processed options. When completed, the commands store the
internal result of completion in a variable exposed by the `maint
show test-options-completion-result' command.

`maint show test-options-completion-result'
Shows the result of completing the `maint test-options'
subcommands. This is used by the testsuite to validate completion
support in the command options framework.

`maint set test-settings KIND'
`maint show test-settings KIND'
These are representative commands for each KIND of setting type
GDB supports. They are used by the testsuite for exercising the
settings infrastructure.

`maint set backtrace-on-fatal-signal [on|off]'
`maint show backtrace-on-fatal-signal'
When this setting is `on', if GDB itself terminates with a fatal
signal (e.g. SIGSEGV), then a limited backtrace will be printed to
the standard error stream. This backtrace can be used to help
diagnose crashes within GDB in situations where a user is unable
to share a corefile with the GDB developers.

If the functionality to provide this backtrace is not available for
the platform on which GDB is running then this feature will be
`off' by default, and attempting to turn this feature on will give
an error.

For platforms that do support creating the backtrace this feature
is `on' by default.

`maint wait-for-index-cache'
Wait until all pending writes to the index cache have completed.
This is used by the test suite to avoid races when the index cache
is being updated by a worker thread.

`maint with SETTING [VALUE] [-- COMMAND]'
Like the `with' command, but works with `maintenance set'
variables. This is used by the testsuite to exercise the `with'
command's infrastructure.

`maint ignore-probes [-V|-VERBOSE] [PROVIDER [NAME [OBJFILE]]]'
`maint ignore-probes -RESET'
Set or reset the ignore-probes filter. The PROVIDER, NAME and
OBJFILE arguments are as in `enable probes' and `disable probes'
(*note enable probes::). Only supported for SystemTap probes.

Here's an example of using `maint ignore-probes':
(gdb) maint ignore-probes -verbose libc ^longjmp$
ignore-probes filter has been set to:
PROVIDER: 'libc'
PROBE_NAME: '^longjmp$'
OBJNAME: ''
(gdb) start
<... more output ...>
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M

The following command is useful for non-interactive invocations of
GDB, such as in the test suite.

`set watchdog NSEC'
Set the maximum number of seconds GDB will wait for the target
operation to finish. If this time expires, GDB reports and error
and the command is aborted.

`show watchdog'
Show the current setting of the target wait timeout.

File: gdb.info, Node: Remote Protocol, Next: Agent Expressions, Prev: Maintenance Commands, Up: Top

Appendix E GDB Remote Serial Protocol
*************************************

* Menu:

* Overview::
* Standard Replies::
* Packets::
* Stop Reply Packets::
* General Query Packets::
* Architecture-Specific Protocol Details::
* Tracepoint Packets::
* Host I/O Packets::
* Interrupts::
* Notification Packets::
* Remote Non-Stop::
* Packet Acknowledgment::
* Examples::
* File-I/O Remote Protocol Extension::
* Library List Format::
* Library List Format for SVR4 Targets::
* Memory Map Format::
* Thread List Format::
* Traceframe Info Format::
* Branch Trace Format::
* Branch Trace Configuration Format::

File: gdb.info, Node: Overview, Next: Standard Replies, Up: Remote Protocol

E.1 Overview
============

There may be occasions when you need to know something about the
protocol--for example, if there is only one serial port to your target
machine, you might want your program to do something special if it
recognizes a packet meant for GDB.

In the examples below, `->' and `<-' are used to indicate
transmitted and received data, respectively.

All GDB commands and responses (other than acknowledgments and
notifications, see *Note Notification Packets::) are sent as a PACKET.
A PACKET is introduced with the character `$', the actual PACKET-DATA,
and the terminating character `#' followed by a two-digit CHECKSUM:

`$'PACKET-DATA`#'CHECKSUM
The two-digit CHECKSUM is computed as the modulo 256 sum of all
characters between the leading `$' and the trailing `#' (an eight bit
unsigned checksum).

Implementors should note that prior to GDB 5.0 the protocol
specification also included an optional two-digit SEQUENCE-ID:

`$'SEQUENCE-ID`:'PACKET-DATA`#'CHECKSUM

That SEQUENCE-ID was appended to the acknowledgment. GDB has never
output SEQUENCE-IDs. Stubs that handle packets added since GDB 5.0
must not accept SEQUENCE-ID.

When either the host or the target machine receives a packet, the
first response expected is an acknowledgment: either `+' (to indicate
the package was received correctly) or `-' (to request retransmission):

-> `$'PACKET-DATA`#'CHECKSUM
<- `+'
The `+'/`-' acknowledgments can be disabled once a connection is
established. *Note Packet Acknowledgment::, for details.

The host (GDB) sends COMMANDs, and the target (the debugging stub
incorporated in your program) sends a RESPONSE. In the case of step
and continue COMMANDs, the response is only sent when the operation has
completed, and the target has again stopped all threads in all attached
processes. This is the default all-stop mode behavior, but the remote
protocol also supports GDB's non-stop execution mode; see *Note Remote
Non-Stop::, for details.

PACKET-DATA consists of a sequence of characters with the exception
of `#' and `$' (see `X' packet for additional exceptions).

Fields within the packet should be separated using `,' `;' or `:'.
Except where otherwise noted all numbers are represented in HEX with
leading zeros suppressed.

Implementors should note that prior to GDB 5.0, the character `:'
could not appear as the third character in a packet (as it would
potentially conflict with the SEQUENCE-ID).

Binary data in most packets is encoded as two hexadecimal digits per
byte of binary data. This allowed the traditional remote protocol to
work over connections which were only seven-bit clean. Some packets
designed more recently assume an eight-bit clean connection, and use a
more efficient encoding to send and receive binary data.

The binary data representation uses `7d' (ASCII `}') as an escape
character. Any escaped byte is transmitted as the escape character
followed by the original character XORed with `0x20'. For example, the
byte `0x7d' would be transmitted as the two bytes `0x7d 0x5d'. The
bytes `0x23' (ASCII `#'), `0x24' (ASCII `$'), and `0x7d' (ASCII `}')
must always be escaped. Responses sent by the stub must also escape
`0x2a' (ASCII `*'), so that it is not interpreted as the start of a
run-length encoded sequence (described next).

Response DATA can be run-length encoded to save space. Run-length
encoding replaces runs of identical characters with one instance of the
repeated character, followed by a `*' and a repeat count. The repeat
count is itself sent encoded, to avoid binary characters in DATA: a
value of N is sent as `N+29'. For a repeat count greater or equal to
3, this produces a printable ASCII character, e.g. a space (ASCII code
32) for a repeat count of 3. (This is because run-length encoding
starts to win for counts 3 or more.) Thus, for example, `0* ' is a
run-length encoding of "0000": the space character after `*' means
repeat the leading `0' `32 - 29 = 3' more times.

The printable characters `#' and `$' or with a numeric value greater
than 126 must not be used. Runs of six repeats (`#') or seven repeats
(`$') can be expanded using a repeat count of only five (`"'). For
example, `00000000' can be encoded as `0*"00'.

*Note Standard Replies:: for standard error responses, and how to
respond indicating a command is not supported.

In describing packets (commands and responses), each description has
a template showing the overall syntax, followed by an explanation of the
packet's meaning. We include spaces in some of the templates for
clarity; these are not part of the packet's syntax. No GDB packet uses
spaces to separate its components. For example, a template like `foo
BAR BAZ' describes a packet beginning with the three ASCII bytes `foo',
followed by a BAR, followed directly by a BAZ. GDB does not transmit a
space character between the `foo' and the BAR, or between the BAR and
the BAZ.

We place optional portions of a packet in [square brackets]; for
example, a template like `c [ADDR]' describes a packet beginning with
the single ASCII character `c', possibly followed by an ADDR.

At a minimum, a stub is required to support the `?' command to tell
GDB the reason for halting, `g' and `G' commands for register access,
and the `m' and `M' commands for memory access. Stubs that only
control single-threaded targets can implement run control with the `c'
(continue) command, and if the target architecture supports
hardware-assisted single-stepping, the `s' (step) command. Stubs that
support multi-threading targets should support the `vCont' command.
All other commands are optional.

File: gdb.info, Node: Standard Replies, Next: Packets, Prev: Overview, Up: Remote Protocol

E.2 Standard Replies
====================

The remote protocol specifies a few standard replies. All commands
support these, except as noted in the individual command descriptions.

empty response
An empty response (raw character sequence `$#00') means the
COMMAND is not supported by the stub. This way it is possible to
extend the protocol. A newer GDB can tell if a command is
supported based on that response (but see also *Note qSupported::).

`E XX'
An error has occurred; XX is a two-digit hexadecimal error number.
In almost all cases, the protocol does not specify the meaning of
the error numbers; GDB usually ignores the numbers, or displays
them to the user without further interpretation.

`E.ERRTEXT'
An error has occurred; ERRTEXT is the textual error message,
encoded in ASCII.

File: gdb.info, Node: Packets, Next: Stop Reply Packets, Prev: Standard Replies, Up: Remote Protocol

E.3 Packets
===========

The following table provides a complete list of all currently defined
COMMANDs and their corresponding response DATA. *Note File-I/O Remote
Protocol Extension::, for details about the File I/O extension of the
remote protocol.

Each packet's description has a template showing the packet's overall
syntax, followed by an explanation of the packet's meaning. We include
spaces in some of the templates for clarity; these are not part of the
packet's syntax. No GDB packet uses spaces to separate its components.
For example, a template like `foo BAR BAZ' describes a packet
beginning with the three ASCII bytes `foo', followed by a BAR, followed
directly by a BAZ. GDB does not transmit a space character between the
`foo' and the BAR, or between the BAR and the BAZ.

Several packets and replies include a THREAD-ID field to identify a
thread. Normally these are positive numbers with a target-specific
interpretation, formatted as big-endian hex strings. A THREAD-ID can
also be a literal `-1' to indicate all threads, or `0' to pick any
thread.

In addition, the remote protocol supports a multiprocess feature in
which the THREAD-ID syntax is extended to optionally include both
process and thread ID fields, as `pPID.TID'. The PID (process) and TID
(thread) components each have the format described above: a positive
number with target-specific interpretation formatted as a big-endian
hex string, literal `-1' to indicate all processes or threads
(respectively), or `0' to indicate an arbitrary process or thread.
Specifying just a process, as `pPID', is equivalent to `pPID.-1'. It
is an error to specify all processes but a specific thread, such as
`p-1.TID'. Note that the `p' prefix is _not_ used for those packets
and replies explicitly documented to include a process ID, rather than
a THREAD-ID.

The multiprocess THREAD-ID syntax extensions are only used if both
GDB and the stub report support for the `multiprocess' feature using
`qSupported'. *Note multiprocess extensions::, for more information.

Note that all packet forms beginning with an upper- or lower-case
letter, other than those described here, are reserved for future use.

Here are the packet descriptions.

`!'
Enable extended mode. In extended mode, the remote server is made
persistent. The `R' packet is used to restart the program being
debugged.

Reply:
`OK'
The remote target both supports and has enabled extended mode.

`?'
This is sent when connection is first established to query the
reason the target halted. The reply is the same as for step and
continue. This packet has a special interpretation when the
target is in non-stop mode; see *Note Remote Non-Stop::.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`A ARGLEN,ARGNUM,ARG,...'
Initialized `argv[]' array passed into program. ARGLEN specifies
the number of bytes in the hex encoded byte stream ARG. See
`gdbserver' for more details.

Reply:
`OK'
The arguments were set.

`b BAUD'
(Don't use this packet; its behavior is not well-defined.) Change
the serial line speed to BAUD.

JTC: _When does the transport layer state change? When it's
received, or after the ACK is transmitted. In either case, there
are problems if the command or the acknowledgment packet is
dropped._

Stan: _If people really wanted to add something like this, and get
it working for the first time, they ought to modify ser-unix.c to
send some kind of out-of-band message to a specially-setup stub
and have the switch happen "in between" packets, so that from
remote protocol's point of view, nothing actually happened._

`B ADDR,MODE'
Set (MODE is `S') or clear (MODE is `C') a breakpoint at ADDR.

Don't use this packet. Use the `Z' and `z' packets instead (*note
insert breakpoint or watchpoint packet::).

`bc'
Backward continue. Execute the target system in reverse. No
parameter. *Note Reverse Execution::, for more information.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`bs'
Backward single step. Execute one instruction in reverse. No
parameter. *Note Reverse Execution::, for more information.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`c [ADDR]'
Continue at ADDR, which is the address to resume. If ADDR is
omitted, resume at current address.

This packet is deprecated for multi-threading support. *Note
vCont packet::.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`C SIG[;ADDR]'
Continue with signal SIG (hex signal number). If `;ADDR' is
omitted, resume at same address.

This packet is deprecated for multi-threading support. *Note
vCont packet::.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`d'
Toggle debug flag.

Don't use this packet; instead, define a general set packet (*note
General Query Packets::).

`D'
`D;PID'
The first form of the packet is used to detach GDB from the remote
system. It is sent to the remote target before GDB disconnects
via the `detach' command.

The second form, including a process ID, is used when multiprocess
protocol extensions are enabled (*note multiprocess extensions::),
to detach only a specific process. The PID is specified as a
big-endian hex string.

Reply:
`OK'
for success

`F RC,EE,CF;XX'
A reply from GDB to an `F' packet sent by the target. This is
part of the File-I/O protocol extension. *Note File-I/O Remote
Protocol Extension::, for the specification.

`g'
Read general registers.

Reply:
`XX...'
Each byte of register data is described by two hex digits.
The bytes with the register are transmitted in target byte
order. The size of each register and their position within
the `g' packet are determined by the target description
(*note Target Descriptions::); in the absence of a target
description, this is done using code internal to GDB;
typically this is some customary register layout for the
architecture in question.

When reading registers, the stub may also return a string of
literal `x''s in place of the register data digits, to
indicate that the corresponding register's value is
unavailable. For example, when reading registers from a
trace frame (*note Using the Collected Data: Analyze
Collected Data.), this means that the register has not been
collected in the trace frame. When reading registers from a
live program, this indicates that the stub has no means to
access the register contents, even though the corresponding
register is known to exist. Note that if a register truly
does not exist on the target, then it is better to not
include it in the target description in the first place.

For example, for an architecture with 4 registers of 4 bytes
each, the following reply indicates to GDB that registers 0
and 2 are unavailable, while registers 1 and 3 are available,
and both have zero value:

-> `g'
<- `xxxxxxxx00000000xxxxxxxx00000000'

`G XX...'
Write general registers. *Note read registers packet::, for a
description of the XX... data.

Reply:
`OK'
for success

`H OP THREAD-ID'
Set thread for subsequent operations (`m', `M', `g', `G', et.al.).
Depending on the operation to be performed, OP should be `c' for
step and continue operations (note that this is deprecated,
supporting the `vCont' command is a better option), and `g' for
other operations. The thread designator THREAD-ID has the format
and interpretation described in *Note thread-id syntax::.

Reply:
`OK'
for success

`i [ADDR[,NNN]]'
Step the remote target by a single clock cycle. If `,NNN' is
present, cycle step NNN cycles. If ADDR is present, cycle step
starting at that address.

`I'
Signal, then cycle step. *Note step with signal packet::. *Note
cycle step packet::.

`k'
Kill request.

The exact effect of this packet is not specified.

For a bare-metal target, it may power cycle or reset the target
system. For that reason, the `k' packet has no reply.

For a single-process target, it may kill that process if possible.

A multiple-process target may choose to kill just one process, or
all that are under GDB's control. For more precise control, use
the vKill packet (*note vKill packet::).

If the target system immediately closes the connection in response
to `k', GDB does not consider the lack of packet acknowledgment to
be an error, and assumes the kill was successful.

If connected using `target extended-remote', and the target does
not close the connection in response to a kill request, GDB probes
the target state as if a new connection was opened (*note ?
packet::).

`m ADDR,LENGTH'
Read LENGTH addressable memory units starting at address ADDR
(*note addressable memory unit::). Note that ADDR may not be
aligned to any particular boundary.

The stub need not use any particular size or alignment when
gathering data from memory for the response; even if ADDR is
word-aligned and LENGTH is a multiple of the word size, the stub
is free to use byte accesses, or not. For this reason, this
packet may not be suitable for accessing memory-mapped I/O devices.

Reply:
`XX...'
Memory contents; each byte is transmitted as a two-digit
hexadecimal number. The reply may contain fewer addressable
memory units than requested if the server was able to read
only part of the region of memory.

Unlike most packets, this packet does not support
`E.ERRTEXT'-style textual error replies (*note textual error
reply::).

`M ADDR,LENGTH:XX...'
Write LENGTH addressable memory units starting at address ADDR
(*note addressable memory unit::). The data is given by XX...;
each byte is transmitted as a two-digit hexadecimal number.

Reply:
`OK'
All the data was written successfully. (If only part of the
data was written, this command returns an error.)

`p N'
Read the value of register N; N is in hex. *Note read registers
packet::, for a description of how the returned register value is
encoded.

Reply:
`XX...'
the register's value

`P N...=R...'
Write register N... with value R.... The register number N is in
hexadecimal, and R... contains two hex digits for each byte in the
register (target byte order).

Reply:
`OK'
for success

`q NAME PARAMS...'
`Q NAME PARAMS...'
General query (`q') and set (`Q'). These packets are described
fully in *Note General Query Packets::.

`r'
Reset the entire system.

Don't use this packet; use the `R' packet instead.

`R XX'
Restart the program being debugged. The XX, while needed, is
ignored. This packet is only available in extended mode (*note
extended mode::).

The `R' packet has no reply.

`s [ADDR]'
Single step, resuming at ADDR. If ADDR is omitted, resume at same
address.

This packet is deprecated for multi-threading support. *Note
vCont packet::.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`S SIG[;ADDR]'
Step with signal. This is analogous to the `C' packet, but
requests a single-step, rather than a normal resumption of
execution.

This packet is deprecated for multi-threading support. *Note
vCont packet::.

Reply: *Note Stop Reply Packets::, for the reply specifications.

`t ADDR:PP,MM'
Search backwards starting at address ADDR for a match with pattern
PP and mask MM, both of which are are 4 byte long. There must be
at least 3 digits in ADDR.

`T THREAD-ID'
Find out if the thread THREAD-ID is alive. *Note thread-id
syntax::.

Reply:
`OK'
thread is still alive

`v'
Packets starting with `v' are identified by a multi-letter name,
up to the first `;' or `?' (or the end of the packet).

`vAttach;PID'
Attach to a new process with the specified process ID PID. The
process ID is a hexadecimal integer identifying the process. In
all-stop mode, all threads in the attached process are stopped; in
non-stop mode, it may be attached without being stopped if that is
supported by the target.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`Any stop packet'
for success in all-stop mode (*note Stop Reply Packets::)

`OK'
for success in non-stop mode (*note Remote Non-Stop::)

`vCont[;ACTION[:THREAD-ID]]...'
Resume the inferior, specifying different actions for each thread.

For each inferior thread, the leftmost action with a matching
THREAD-ID is applied. Threads that don't match any action remain
in their current state. Thread IDs are specified using the syntax
described in *Note thread-id syntax::. If multiprocess extensions
(*note multiprocess extensions::) are supported, actions can be
specified to match all threads in a process by using the `pPID.-1'
form of the THREAD-ID. An action with no THREAD-ID matches all
threads. Specifying no actions is an error.

Currently supported actions are:

`c'
Continue.

`C SIG'
Continue with signal SIG. The signal SIG should be two hex
digits.

`s'
Step.

`S SIG'
Step with signal SIG. The signal SIG should be two hex
digits.

`t'
Stop.

`r START,END'
Step once, and then keep stepping as long as the thread stops
at addresses between START (inclusive) and END (exclusive).
The remote stub reports a stop reply when either the thread
goes out of the range or is stopped due to an unrelated
reason, such as hitting a breakpoint. *Note range stepping::.

If the range is empty (START == END), then the action becomes
equivalent to the `s' action. In other words, single-step
once, and report the stop (even if the stepped instruction
jumps to START).

(A stop reply may be sent at any point even if the PC is
still within the stepping range; for example, it is valid to
implement this packet in a degenerate way as a single
instruction step operation.)

The optional argument ADDR normally associated with the `c', `C',
`s', and `S' packets is not supported in `vCont'.

The `t' action is only relevant in non-stop mode (*note Remote
Non-Stop::) and may be ignored by the stub otherwise. A stop
reply should be generated for any affected thread not already
stopped. When a thread is stopped by means of a `t' action, the
corresponding stop reply should indicate that the thread has
stopped with signal `0', regardless of whether the target uses
some other signal as an implementation detail.

The server must ignore `c', `C', `s', `S', and `r' actions for
threads that are already running. Conversely, the server must
ignore `t' actions for threads that are already stopped.

_Note:_ In non-stop mode, a thread is considered running until GDB
acknowledges an asynchronous stop notification for it with the
`vStopped' packet (*note Remote Non-Stop::).

The stub must support `vCont' if it reports support for
multiprocess extensions (*note multiprocess extensions::).

Reply: *Note Stop Reply Packets::, for the reply specifications.

`vCont?'
Request a list of actions supported by the `vCont' packet.

Reply:
`vCont[;ACTION...]'
The `vCont' packet is supported. Each ACTION is a supported
command in the `vCont' packet.

`vCtrlC'
Interrupt remote target as if a control-C was pressed on the remote
terminal. This is the equivalent to reacting to the `^C' (`\003',
the control-C character) character in all-stop mode while the
target is running, except this works in non-stop mode. *Note
interrupting remote targets::, for more info on the all-stop
variant.

Reply:
`OK'
for success

`vFile:OPERATION:PARAMETER...'
Perform a file operation on the target system. For details, see
*Note Host I/O Packets::.

`vFlashErase:ADDR,LENGTH'
Direct the stub to erase LENGTH bytes of flash starting at ADDR.
The region may enclose any number of flash blocks, but its start
and end must fall on block boundaries, as indicated by the flash
block size appearing in the memory map (*note Memory Map
Format::). GDB groups flash memory programming operations
together, and sends a `vFlashDone' request after each group; the
stub is allowed to delay erase operation until the `vFlashDone'
packet is received.

Reply:
`OK'
for success

`vFlashWrite:ADDR:XX...'
Direct the stub to write data to flash address ADDR. The data is
passed in binary form using the same encoding as for the `X'
packet (*note Binary Data::). The memory ranges specified by
`vFlashWrite' packets preceding a `vFlashDone' packet must not
overlap, and must appear in order of increasing addresses
(although `vFlashErase' packets for higher addresses may already
have been received; the ordering is guaranteed only between
`vFlashWrite' packets). If a packet writes to an address that was
neither erased by a preceding `vFlashErase' packet nor by some
other target-specific method, the results are unpredictable.

Reply:
`OK'
for success

`E.memtype'
for vFlashWrite addressing non-flash memory

`vFlashDone'
Indicate to the stub that flash programming operation is finished.
The stub is permitted to delay or batch the effects of a group of
`vFlashErase' and `vFlashWrite' packets until a `vFlashDone'
packet is received. The contents of the affected regions of flash
memory are unpredictable until the `vFlashDone' request is
completed.

`vKill;PID'
Kill the process with the specified process ID PID, which is a
hexadecimal integer identifying the process. This packet is used
in preference to `k' when multiprocess protocol extensions are
supported; see *Note multiprocess extensions::.

Reply:
`OK'
for success

`vMustReplyEmpty'
The correct reply to an unknown `v' packet is to return the empty
string, however, some older versions of `gdbserver' would
incorrectly return `OK' for unknown `v' packets.

The `vMustReplyEmpty' is used as a feature test to check how
`gdbserver' handles unknown packets, it is important that this
packet be handled in the same way as other unknown `v' packets.
If this packet is handled differently to other unknown `v' packets
then it is possible that GDB may run into problems in other areas,
specifically around use of `vFile:setfs:'.

`vRun;FILENAME[;ARGUMENT]...'
Run the program FILENAME, passing it each ARGUMENT on its command
line. The file and arguments are hex-encoded strings. If
FILENAME is an empty string, the stub may use a default program
(e.g. the last program run). The program is created in the stopped
state.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`Any stop packet'
for success (*note Stop Reply Packets::)

`vStopped'
*Note Notification Packets::.

`X ADDR,LENGTH:XX...'
Write data to memory, where the data is transmitted in binary.
Memory is specified by its address ADDR and number of addressable
memory units LENGTH (*note addressable memory unit::); `XX...' is
binary data (*note Binary Data::).

Reply:
`OK'
for success

`z TYPE,ADDR,KIND'
`Z TYPE,ADDR,KIND'
Insert (`Z') or remove (`z') a TYPE breakpoint or watchpoint
starting at address ADDRESS of kind KIND.

Each breakpoint and watchpoint packet TYPE is documented
separately.

_Implementation notes: A remote target shall return an empty string
for an unrecognized breakpoint or watchpoint packet TYPE. A
remote target shall support either both or neither of a given
`ZTYPE...' and `zTYPE...' packet pair. To avoid potential
problems with duplicate packets, the operations should be
implemented in an idempotent way._

`z0,ADDR,KIND'
`Z0,ADDR,KIND[;COND_LIST...][;cmds:PERSIST,CMD_LIST...]'
Insert (`Z0') or remove (`z0') a software breakpoint at address
ADDR of type KIND.

A software breakpoint is implemented by replacing the instruction
at ADDR with a software breakpoint or trap instruction. The KIND
is target-specific and typically indicates the size of the
breakpoint in bytes that should be inserted. E.g., the ARM and
MIPS can insert either a 2 or 4 byte breakpoint. Some
architectures have additional meanings for KIND (*note
Architecture-Specific Protocol Details::); if no
architecture-specific value is being used, it should be `0'. KIND
is hex-encoded. COND_LIST is an optional list of conditional
expressions in bytecode form that should be evaluated on the
target's side. These are the conditions that should be taken into
consideration when deciding if the breakpoint trigger should be
reported back to GDB.

See also the `swbreak' stop reason (*note swbreak stop reason::)
for how to best report a software breakpoint event to GDB.

The COND_LIST parameter is comprised of a series of expressions,
concatenated without separators. Each expression has the following
form:

`X LEN,EXPR'
LEN is the length of the bytecode expression and EXPR is the
actual conditional expression in bytecode form.

The optional CMD_LIST parameter introduces commands that may be
run on the target, rather than being reported back to GDB. The
parameter starts with a numeric flag PERSIST; if the flag is
nonzero, then the breakpoint may remain active and the commands
continue to be run even when GDB disconnects from the target.
Following this flag is a series of expressions concatenated with no
separators. Each expression has the following form:

`X LEN,EXPR'
LEN is the length of the bytecode expression and EXPR is the
actual commands expression in bytecode form.

_Implementation note: It is possible for a target to copy or move
code that contains software breakpoints (e.g., when implementing
overlays). The behavior of this packet, in the presence of such a
target, is not defined._

Reply:
`OK'
success

`z1,ADDR,KIND'
`Z1,ADDR,KIND[;COND_LIST...][;cmds:PERSIST,CMD_LIST...]'
Insert (`Z1') or remove (`z1') a hardware breakpoint at address
ADDR.

A hardware breakpoint is implemented using a mechanism that is not
dependent on being able to modify the target's memory. The KIND,
COND_LIST, and CMD_LIST arguments have the same meaning as in `Z0'
packets.

_Implementation note: A hardware breakpoint is not affected by code
movement._

Reply:
`OK'
success

`z2,ADDR,KIND'
`Z2,ADDR,KIND'
Insert (`Z2') or remove (`z2') a write watchpoint at ADDR. The
number of bytes to watch is specified by KIND.

Reply:
`OK'
success

`z3,ADDR,KIND'
`Z3,ADDR,KIND'
Insert (`Z3') or remove (`z3') a read watchpoint at ADDR. The
number of bytes to watch is specified by KIND.

Reply:
`OK'
success

`z4,ADDR,KIND'
`Z4,ADDR,KIND'
Insert (`Z4') or remove (`z4') an access watchpoint at ADDR. The
number of bytes to watch is specified by KIND.

Reply:
`OK'
success

File: gdb.info, Node: Stop Reply Packets, Next: General Query Packets, Prev: Packets, Up: Remote Protocol

E.4 Stop Reply Packets
======================

The `C', `c', `S', `s', `vCont', `vAttach', `vRun', `vStopped', and `?'
packets can receive any of the below as a reply. Except for `?' and
`vStopped', that reply is only returned when the target halts. In the
below the exact meaning of "signal number" is defined by the header
`include/gdb/signals.h' in the GDB source code.

In non-stop mode, the server will simply reply `OK' to commands such
as `vCont'; any stop will be the subject of a future notification.
*Note Remote Non-Stop::.

As in the description of request packets, we include spaces in the
reply templates for clarity; these are not part of the reply packet's
syntax. No GDB stop reply packet uses spaces to separate its
components.

`S AA'
The program received signal number AA (a two-digit hexadecimal
number). This is equivalent to a `T' response with no N:R pairs.

`T AA N1:R1;N2:R2;...'
The program received signal number AA (a two-digit hexadecimal
number). This is equivalent to an `S' response, except that the
`N:R' pairs can carry values of important registers and other
information directly in the stop reply packet, reducing round-trip
latency. Single-step and breakpoint traps are reported this way.
Each `N:R' pair is interpreted as follows:

* If N is a hexadecimal number, it is a register number, and the
corresponding R gives that register's value. The data R is a
series of bytes in target byte order, with each byte given by
a two-digit hex number.

* If N is `thread', then R is the thread ID of the stopped
thread, as specified in *Note thread-id syntax::.

* If N is `core', then R is the hexadecimal number of the core
on which the stop event was detected.

* If N is a recognized "stop reason", it describes a more
specific event that stopped the target. The currently
defined stop reasons are listed below. The AA should be
`05', the trap signal. At most one stop reason should be
present.

* Otherwise, GDB should ignore this `N:R' pair and go on to the
next; this allows us to extend the protocol in the future.

The currently defined stop reasons are:

`watch'
`rwatch'
`awatch'
The packet indicates a watchpoint hit, and R is the data
address, in hex.

`syscall_entry'
`syscall_return'
The packet indicates a syscall entry or return, and R is the
syscall number, in hex.

`library'
The packet indicates that the loaded libraries have changed.
GDB should use `qXfer:libraries:read' to fetch a new list of
loaded libraries. The R part is ignored.

`replaylog'
The packet indicates that the target cannot continue replaying
logged execution events, because it has reached the end (or
the beginning when executing backward) of the log. The value
of R will be either `begin' or `end'. *Note Reverse
Execution::, for more information.

`swbreak'
The packet indicates a software breakpoint instruction was
executed, irrespective of whether it was GDB that planted the
breakpoint or the breakpoint is hardcoded in the program.
The R part must be left empty.

On some architectures, such as x86, at the architecture
level, when a breakpoint instruction executes the program
counter points at the breakpoint address plus an offset. On
such targets, the stub is responsible for adjusting the PC to
point back at the breakpoint address.

This packet should not be sent by default; older GDB versions
did not support it. GDB requests it, by supplying an
appropriate `qSupported' feature (*note qSupported::). The
remote stub must also supply the appropriate `qSupported'
feature indicating support.

This packet is required for correct non-stop mode operation.

`hwbreak'
The packet indicates the target stopped for a hardware
breakpoint. The R part must be left empty.

The same remarks about `qSupported' and non-stop mode above
apply.

`fork'
The packet indicates that `fork' was called, and R is the
thread ID of the new child process, as specified in *Note
thread-id syntax::. This packet is only applicable to
targets that support fork events.

This packet should not be sent by default; older GDB versions
did not support it. GDB requests it, by supplying an
appropriate `qSupported' feature (*note qSupported::). The
remote stub must also supply the appropriate `qSupported'
feature indicating support.

`vfork'
The packet indicates that `vfork' was called, and R is the
thread ID of the new child process, as specified in *Note
thread-id syntax::. This packet is only applicable to
targets that support vfork events.

This packet should not be sent by default; older GDB versions
did not support it. GDB requests it, by supplying an
appropriate `qSupported' feature (*note qSupported::). The
remote stub must also supply the appropriate `qSupported'
feature indicating support.

`vforkdone'
The packet indicates that a child process created by a vfork
has either called `exec' or terminated, so that the address
spaces of the parent and child process are no longer shared.
The R part is ignored. This packet is only applicable to
targets that support vforkdone events.

This packet should not be sent by default; older GDB versions
did not support it. GDB requests it, by supplying an
appropriate `qSupported' feature (*note qSupported::). The
remote stub must also supply the appropriate `qSupported'
feature indicating support.

`exec'
The packet indicates that `execve' was called, and R is the
absolute pathname of the file that was executed, in hex.
This packet is only applicable to targets that support exec
events.

This packet should not be sent by default; older GDB versions
did not support it. GDB requests it, by supplying an
appropriate `qSupported' feature (*note qSupported::). The
remote stub must also supply the appropriate `qSupported'
feature indicating support.

`clone'
The packet indicates that `clone' was called, and R is the
thread ID of the new child thread, as specified in *Note
thread-id syntax::. This packet is only applicable to
targets that support clone events.

This packet should not be sent by default; GDB requests it
with the *Note QThreadOptions:: packet.

`create'
The packet indicates that the thread was just created. The
new thread is stopped until GDB sets it running with a
resumption packet (*note vCont packet::). This packet should
not be sent by default; GDB requests it with the *Note
QThreadEvents:: packet. See also the `w' (*note thread exit
event::) remote reply below. The R part is ignored.

`W AA'
`W AA ; process:PID'
The process exited, and AA is the exit status. This is only
applicable to certain targets.

The second form of the response, including the process ID of the
exited process, can be used only when GDB has reported support for
multiprocess protocol extensions; see *Note multiprocess
extensions::. Both AA and PID are formatted as big-endian hex
strings.

`X AA'
`X AA ; process:PID'
The process terminated with signal AA.

The second form of the response, including the process ID of the
terminated process, can be used only when GDB has reported support
for multiprocess protocol extensions; see *Note multiprocess
extensions::. Both AA and PID are formatted as big-endian hex
strings.

`w AA ; TID'
The thread exited, and AA is the exit status. This response
should not be sent by default; GDB requests it with either the
*Note QThreadEvents:: or *Note QThreadOptions:: packets. See also
*Note thread create event:: above. AA is formatted as a
big-endian hex string.

`N'
There are no resumed threads left in the target. In other words,
even though the process is alive, the last resumed thread has
exited. For example, say the target process has two threads:
thread 1 and thread 2. The client leaves thread 1 stopped, and
resumes thread 2, which subsequently exits. At this point, even
though the process is still alive, and thus no `W' stop reply is
sent, no thread is actually executing either. The `N' stop reply
thus informs the client that it can stop waiting for stop replies.
This packet should not be sent by default; older GDB versions did
not support it. GDB requests it, by supplying an appropriate
`qSupported' feature (*note qSupported::). The remote stub must
also supply the appropriate `qSupported' feature indicating
support.

`O XX...'
`XX...' is hex encoding of ASCII data, to be written as the
program's console output. This can happen at any time while the
program is running and the debugger should continue to wait for
`W', `T', etc. This reply is not permitted in non-stop mode.

`F CALL-ID,PARAMETER...'
CALL-ID is the identifier which says which host system call should
be called. This is just the name of the function. Translation
into the correct system call is only applicable as it's defined in
GDB. *Note File-I/O Remote Protocol Extension::, for a list of
implemented system calls.

`PARAMETER...' is a list of parameters as defined for this very
system call.

The target replies with this packet when it expects GDB to call a
host system call on behalf of the target. GDB replies with an
appropriate `F' packet and keeps up waiting for the next reply
packet from the target. The latest `C', `c', `S' or `s' action is
expected to be continued. *Note File-I/O Remote Protocol
Extension::, for more details.

File: gdb.info, Node: General Query Packets, Next: Architecture-Specific Protocol Details, Prev: Stop Reply Packets, Up: Remote Protocol

E.5 General Query Packets
=========================

Packets starting with `q' are "general query packets"; packets starting
with `Q' are "general set packets". General query and set packets are
a semi-unified form for retrieving and sending information to and from
the stub.

The initial letter of a query or set packet is followed by a name
indicating what sort of thing the packet applies to. For example, GDB
may use a `qSymbol' packet to exchange symbol definitions with the
stub. These packet names follow some conventions:

* The name must not contain commas, colons or semicolons.

* Most GDB query and set packets have a leading upper case letter.

* The names of custom vendor packets should use a company prefix, in
lower case, followed by a period. For example, packets designed at
the Acme Corporation might begin with `qacme.foo' (for querying
foos) or `Qacme.bar' (for setting bars).

The name of a query or set packet should be separated from any
parameters by a `:'; the parameters themselves should be separated by
`,' or `;'. Stubs must be careful to match the full packet name, and
check for a separator or the end of the packet, in case two packet
names share a common prefix. New packets should not begin with `qC',
`qP', or `qL'(1).

Like the descriptions of the other packets, each description here
has a template showing the packet's overall syntax, followed by an
explanation of the packet's meaning. We include spaces in some of the
templates for clarity; these are not part of the packet's syntax. No
GDB packet uses spaces to separate its components.

Here are the currently defined query and set packets:

`QAgent:1'
`QAgent:0'
Turn on or off the agent as a helper to perform some debugging
operations delegated from GDB (*note Control Agent::).

`QAllow:OP:VAL...'
Specify which operations GDB expects to request of the target, as
a semicolon-separated list of operation name and value pairs.
Possible values for OP include `WriteReg', `WriteMem',
`InsertBreak', `InsertTrace', `InsertFastTrace', and `Stop'. VAL
is either 0, indicating that GDB will not request the operation,
or 1, indicating that it may. (The target can then use this to
set up its own internals optimally, for instance if the debugger
never expects to insert breakpoints, it may not need to install
its own trap handler.)

`qC'
Return the current thread ID.

Reply:
`QC THREAD-ID'
Where THREAD-ID is a thread ID as documented in *Note
thread-id syntax::.

`(anything else)'
Any other reply implies the old thread ID.

`qCRC:ADDR,LENGTH'
Compute the CRC checksum of a block of memory using CRC-32 defined
in IEEE 802.3. The CRC is computed byte at a time, taking the most
significant bit of each byte first. The initial pattern code
`0xffffffff' is used to ensure leading zeros affect the CRC.

_Note:_ This is the same CRC used in validating separate debug
files (*note Debugging Information in Separate Files: Separate
Debug Files.). However the algorithm is slightly different. When
validating separate debug files, the CRC is computed taking the
_least_ significant bit of each byte first, and the final result
is inverted to detect trailing zeros.

Reply:
`C CRC32'
The specified memory region's checksum is CRC32.

`QDisableRandomization:VALUE'
Some target operating systems will randomize the virtual address
space of the inferior process as a security feature, but provide a
feature to disable such randomization, e.g. to allow for a more
deterministic debugging experience. On such systems, this packet
with a VALUE of 1 directs the target to disable address space
randomization for processes subsequently started via `vRun'
packets, while a packet with a VALUE of 0 tells the target to
enable address space randomization.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

This packet is not probed by default; the remote stub must request
it, by supplying an appropriate `qSupported' response (*note
qSupported::). This should only be done on targets that actually
support disabling address space randomization.

`QStartupWithShell:VALUE'
On UNIX-like targets, it is possible to start the inferior using a
shell program. This is the default behavior on both GDB and
`gdbserver' (*note set startup-with-shell::). This packet is used
to inform `gdbserver' whether it should start the inferior using a
shell or not.

If VALUE is `0', `gdbserver' will not use a shell to start the
inferior. If VALUE is `1', `gdbserver' will use a shell to start
the inferior. All other values are considered an error.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

This packet is not probed by default; the remote stub must request
it, by supplying an appropriate `qSupported' response (*note
qSupported::). This should only be done on targets that actually
support starting the inferior using a shell.

Use of this packet is controlled by the `set startup-with-shell'
command; *note set startup-with-shell::.

`QEnvironmentHexEncoded:HEX-VALUE'
On UNIX-like targets, it is possible to set environment variables
that will be passed to the inferior during the startup process.
This packet is used to inform `gdbserver' of an environment
variable that has been defined by the user on GDB (*note set
environment::).

The packet is composed by HEX-VALUE, an hex encoded representation
of the NAME=VALUE format representing an environment variable.
The name of the environment variable is represented by NAME, and
the value to be assigned to the environment variable is
represented by VALUE. If the variable has no value (i.e., the
value is `null'), then VALUE will not be present.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

This packet is not probed by default; the remote stub must request
it, by supplying an appropriate `qSupported' response (*note
qSupported::). This should only be done on targets that actually
support passing environment variables to the starting inferior.

This packet is related to the `set environment' command; *note set
environment::.

`QEnvironmentUnset:HEX-VALUE'
On UNIX-like targets, it is possible to unset environment variables
before starting the inferior in the remote target. This packet is
used to inform `gdbserver' of an environment variable that has
been unset by the user on GDB (*note unset environment::).

The packet is composed by HEX-VALUE, an hex encoded representation
of the name of the environment variable to be unset.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

This packet is not probed by default; the remote stub must request
it, by supplying an appropriate `qSupported' response (*note
qSupported::). This should only be done on targets that actually
support passing environment variables to the starting inferior.

This packet is related to the `unset environment' command; *note
unset environment::.

`QEnvironmentReset'
On UNIX-like targets, this packet is used to reset the state of
environment variables in the remote target before starting the
inferior. In this context, reset means unsetting all environment
variables that were previously set by the user (i.e., were not
initially present in the environment). It is sent to `gdbserver'
before the `QEnvironmentHexEncoded' (*note
QEnvironmentHexEncoded::) and the `QEnvironmentUnset' (*note
QEnvironmentUnset::) packets.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

This packet is not probed by default; the remote stub must request
it, by supplying an appropriate `qSupported' response (*note
qSupported::). This should only be done on targets that actually
support passing environment variables to the starting inferior.

`QSetWorkingDir:[DIRECTORY]'
This packet is used to inform the remote server of the intended
current working directory for programs that are going to be
executed.

The packet is composed by DIRECTORY, an hex encoded representation
of the directory that the remote inferior will use as its current
working directory. If DIRECTORY is an empty string, the remote
server should reset the inferior's current working directory to
its original, empty value.

This packet is only available in extended mode (*note extended
mode::).

Reply:
`OK'
The request succeeded.

`qfThreadInfo'
`qsThreadInfo'
Obtain a list of all active thread IDs from the target (OS).
Since there may be too many active threads to fit into one reply
packet, this query works iteratively: it may require more than one
query/reply sequence to obtain the entire list of threads. The
first query of the sequence will be the `qfThreadInfo' query;
subsequent queries in the sequence will be the `qsThreadInfo'
query.

NOTE: This packet replaces the `qL' query (see below).

Reply:
`m THREAD-ID'
A single thread ID

`m THREAD-ID,THREAD-ID...'
a comma-separated list of thread IDs

`l'
(lower case letter `L') denotes end of list.

In response to each query, the target will reply with a list of
one or more thread IDs, separated by commas. GDB will respond to
each reply with a request for more thread ids (using the `qs' form
of the query), until the target responds with `l' (lower-case ell,
for "last"). Refer to *Note thread-id syntax::, for the format of
the THREAD-ID fields.

_Note: GDB will send the `qfThreadInfo' query during the initial
connection with the remote target, and the very first thread ID
mentioned in the reply will be stopped by GDB in a subsequent
message. Therefore, the stub should ensure that the first thread
ID in the `qfThreadInfo' reply is suitable for being stopped by
GDB._

`qGetTLSAddr:THREAD-ID,OFFSET,LM'
Fetch the address associated with thread local storage specified
by THREAD-ID, OFFSET, and LM.

THREAD-ID is the thread ID associated with the thread for which to
fetch the TLS address. *Note thread-id syntax::.

OFFSET is the (big endian, hex encoded) offset associated with the
thread local variable. (This offset is obtained from the debug
information associated with the variable.)

LM is the (big endian, hex encoded) OS/ABI-specific encoding of the
load module associated with the thread local storage. For example,
a GNU/Linux system will pass the link map address of the shared
object associated with the thread local storage under
consideration. Other operating environments may choose to
represent the load module differently, so the precise meaning of
this parameter will vary.

Reply:
`XX...'
Hex encoded (big endian) bytes representing the address of
the thread local storage requested.

`qGetTIBAddr:THREAD-ID'
Fetch address of the Windows OS specific Thread Information Block.

THREAD-ID is the thread ID associated with the thread.

Reply:
`XX...'
Hex encoded (big endian) bytes representing the linear
address of the thread information block.

`qL STARTFLAG THREADCOUNT NEXTTHREAD'
Obtain thread information from RTOS. Where: STARTFLAG (one hex
digit) is one to indicate the first query and zero to indicate a
subsequent query; THREADCOUNT (two hex digits) is the maximum
number of threads the response packet can contain; and NEXTTHREAD
(eight hex digits), for subsequent queries (STARTFLAG is zero), is
returned in the response as ARGTHREAD.

Don't use this packet; use the `qfThreadInfo' query instead (see
above).

Reply:
`qM COUNT DONE ARGTHREAD THREAD...'
Where: COUNT (two hex digits) is the number of threads being
returned; DONE (one hex digit) is zero to indicate more
threads and one indicates no further threads; ARGTHREADID
(eight hex digits) is NEXTTHREAD from the request packet;
THREAD... is a sequence of thread IDs, THREADID (eight hex
digits), from the target. See
`remote.c:parse_threadlist_response()'.

`qMemTags:START ADDRESS,LENGTH:TYPE'
Fetch memory tags of type TYPE from the address range
[START ADDRESS, START ADDRESS + LENGTH). The target is
responsible for calculating how many tags will be returned, as this
is architecture-specific.

START ADDRESS is the starting address of the memory range.

LENGTH is the length, in bytes, of the memory range.

TYPE is the type of tag the request wants to fetch. The type is a
signed integer.

GDB will only send this packet if the stub has advertised support
for memory tagging via `qSupported'.

Reply:
`MXX...'
Hex encoded sequence of uninterpreted bytes, XX...,
representing the tags found in the requested memory range.

`qIsAddressTagged:ADDRESS'
---------- Footnotes ----------

(1) The `qP' and `qL' packets predate these conventions, and
have arguments without any terminator for the packet name; we
suspect they are in widespread use in places that are difficult to
upgrade. The `qC' packet has no arguments, but some existing
stubs (e.g. RedBoot) are known to not check for the end of the
packet.