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Acid Manual
AU
Phil Winterbottom
[email protected]
SH
Introduction
PP
Acid is a general purpose, source level symbolic debugger.
The debugger is built around a simple command language.
The command language, distinct from the language of the program being debugged,
provides a flexible user interface that allows the debugger
interface to be customized for a specific application or architecture.
Moreover, it provides an opportunity to write test and
verification code independently of a program's source code.
Acid is able to debug multiple
processes provided they share a common set of symbols, such as the processes in
a threaded program.
PP
Like other language-based solutions, Acid presents a poor user interface but
provides a powerful debugging tool.
Application of Acid to hard problems is best approached by writing functions off-line
(perhaps loading them with the
CW include
function or using the support provided by
I acme (1)),
rather than by trying to type intricate Acid operations
at the interactive prompt.
PP
Acid allows the execution of a program to be controlled by operating on its
state while it is stopped and by monitoring and controlling its execution
when it is running. Each program action that causes a change
of execution state is reflected by the execution
of an Acid function, which may be user defined.
A library of default functions provides the functionality of a normal debugger.
PP
A Plan 9 process is controlled by writing messages to a control file in the
I proc (3)
file system. Each control message has a corresponding Acid function, which
sends the message to the process. These functions take a process id
I pid ) (
as an
argument. The memory and text file of the program may be manipulated using
the indirection operators. The symbol table, including source cross reference,
is available to an Acid program. The combination allows complex operations
to be performed both in terms of control flow and data manipulation.
SH
Input format and \f(CWwhatis\fP
PP
Comments start with
CW //
and continue to the end of the line.
Input is a series of statements and expressions separated by semicolons.
At the top level of the interpreter, the builtin function
CW print
is called automatically to display the result of all expressions except function calls.
A unary
CW +
may be used as a shorthand to force the result of a function call to be printed.
PP
Also at the top level, newlines are treated as semicolons
by the parser, so semicolons are unnecessary when evaluating expressions.
PP
When Acid starts, it loads the default program modules,
enters interactive mode, and prints a prompt. In this state Acid accepts
either function definitions or statements to be evaluated.
In this interactive mode
statements are evaluated immediately, while function definitions are
stored for later invocation.
PP
The
CW whatis
operator can be used to report the state of identifiers known to the interpreter.
With no argument,
CW whatis
reports the name of all defined Acid functions; when supplied with an identifier
as an argument it reports any variable, function, or type definition
associated with the identifier.
Because of the way the interpreter handles semicolons,
the result of a
CW whatis
statement can be returned directly to Acid without adding semicolons.
A syntax error or interrupt returns Acid to the normal evaluation
mode; any partially evaluated definitions are lost.
SH
Using the Library Functions
PP
After loading the program binary, Acid loads the portable and architecture-specific
library functions that form the standard debugging environment.
These files are Acid source code and are human-readable.
The following example uses the standard debugging library to show how
language and program interact:
P1
% acid /bin/ls
/bin/ls:mips plan 9 executable
/sys/lib/acid/port
/sys/lib/acid/mips
acid: new()
75721: system call _main ADD $-0x14,R29
75721: breakpoint main+0x4 MOVW R31,0x0(R29)
acid: bpset(ls)
acid: cont()
75721: breakpoint ls ADD $-0x16c8,R29
acid: stk()
At pc:0x0000141c:ls /sys/src/cmd/ls.c:87
ls(s=0x0000004d,multi=0x00000000) /sys/src/cmd/ls.c:87
called from main+0xf4 /sys/src/cmd/ls.c:79
main(argc=0x00000000,argv=0x7ffffff0) /sys/src/cmd/ls.c:48
called from _main+0x20 /sys/src/libc/mips/main9.s:10
acid: PC
0xc0000f60
acid: *PC
0x0000141c
acid: ls
0x0000141c
P2
The function
CW new()
creates a new process and stops it at the first instruction.
This change in state is reported by a call to the
Acid function
CW stopped ,
which is called by the interpreter whenever the debugged program stops.
CW Stopped
prints the status line giving the pid, the reason the program stopped
and the address and instruction at the current PC.
The function
CW bpset
makes an entry in the breakpoint table and plants a breakpoint in memory.
The
CW cont
function continues the process, allowing it to run until some condition
causes it to stop. In this case the program hits the breakpoint placed on
the function
CW ls
in the C program. Once again the
CW stopped
routine is called to print the status of the program. The function
CW stk
prints a C stack trace of the current process. It is implemented using
a builtin Acid function that returns the stack trace as a list; the code
that formats the information is all written in Acid.
The Acid variable
CW PC
holds the address of the
cell where the current value of the processor register
CW PC
is stored. By indirecting through
the value of
CW PC
the address where the program is stopped can be found.
All of the processor registers are available by the same mechanism.
SH
Types
PP
An Acid variable has one of four types:
I integer ,
I float ,
I list ,
or
I string .
The type of a variable is inferred from the type of the right-hand
side of the assignment expression which last set its value.
Referencing a variable that has not yet
been assigned draws a "used but not set" error. Many of the operators may
be applied to more than
one type; for these operators the action of the operator is determined by
the types of its operands. The action of each operator is defined in the
I Expressions
section of this manual.
SH
Variables
PP
Acid has three kinds of variables: variables defined by the symbol table
of the debugged program, variables that are defined and maintained
by the interpreter as the debugged program changes state, and variables
defined and used by Acid programs.
PP
Some examples of variables maintained by the interpreter are the register
pointers listed by name in the Acid list variable
CW registers ,
and the symbol table listed by name and contents in the Acid variable
CW symbols .
PP
The variable
CW pid
is updated by the interpreter to select the most recently created process
or the process selected by the
CW setproc
builtin function.
SH 1
Formats
PP
In addition to a type, variables have formats. The format is a code
letter that determines the printing style and the effect of some of the
operators on that variable. The format codes are derived from the format
letters used by
I db (1).
By default, symbol table variables and numeric constants
are assigned the format code
CW X ,
which specifies 32-bit hexadecimal.
Printing a variable with this code yields the output
CW 0x00123456 .
The format code of a variable may be changed from the default by using the
builtin function
CW fmt .
This function takes two arguments, an expression and a format code. After
the expression is evaluated the new format code is attached to the result
and forms the return value from
CW fmt .
The backslash operator is a short form of
CW fmt .
The format supplied by the backslash operator must be the format character
rather than an expression.
If the result is assigned to a variable the new format code is maintained
in the variable. For example:
P1
acid: x=10
acid: print(x)
0x0000000a
acid: x = fmt(x, 'D')
acid: print(x, fmt(x, 'X'))
10 0x0000000a
acid: x
10
acid: x\eo
12
P2
The supported format characters are:
RS
IP \f(CWo\fP
Print two-byte integer in octal.
IP \f(CWO\fP
Print four-byte integer in octal.
IP \f(CWq\fP
Print two-byte integer in signed octal.
IP \f(CWQ\fP
Print four-byte integer in signed octal.
IP \f(CWB\fP
Print four-byte integer in binary.
IP \f(CWd\fP
Print two-byte integer in signed decimal.
IP \f(CWD\fP
Print four-byte integer in signed decimal.
IP \f(CWV\fP
Print eight-byte integer in signed decimal.
IP \f(CWZ\fP
Print eight-byte integer in unsigned decimal.
IP \f(CWx\fP
Print two-byte integer in hexadecimal.
IP \f(CWX\fP
Print four-byte integer in hexadecimal.
IP \f(CWY\fP
Print eight-byte integer in hexadecimal.
IP \f(CWu\fP
Print two-byte integer in unsigned decimal.
IP \f(CWU\fP
Print four-byte integer in unsigned decimal.
IP \f(CWf\fP
Print single-precision floating point number.
IP \f(CWF\fP
Print double-precision floating point number.
IP \f(CWg\fP
Print a single precision floating point number in string format.
IP \f(CWG\fP
Print a double precision floating point number in string format.
IP \f(CWb\fP
Print byte in hexadecimal.
IP \f(CWc\fP
Print byte as an ASCII character.
IP \f(CWC\fP
Like
CW c ,
with
printable ASCII characters represented normally and
others printed in the form \f(CW\ex\fInn\fR.
IP \f(CWs\fP
Interpret the addressed bytes as UTF characters
and print successive characters until a zero byte is reached.
IP \f(CWr\fP
Print a two-byte integer as a rune.
IP \f(CWR\fP
Print successive two-byte integers as runes
until a zero rune is reached.
IP \f(CWi\fP
Print as machine instructions.
IP \f(CWI\fP
As
CW i
above, but print the machine instructions in
an alternate form if possible:
CW sunsparc
and
CW mipsco
reproduce the manufacturers' syntax.
IP \f(CWa\fP
Print the value in symbolic form.
RE
SH
Complex types
PP
Acid permits the definition of the layout of memory.
The usual method is to use the
CW -a
flag of the compilers to produce Acid-language descriptions of data structures (see
I 2c (1))
although such definitions can be typed interactively.
The keywords
CW complex ,
CW adt ,
CW aggr ,
and
CW union
are all equivalent; the compiler uses the synonyms to document the declarations.
A complex type is described as a set of members, each containing a format letter,
an offset in the structure, and a name. For example, the C structure
P1
struct List {
int type;
struct List *next;
};
P2
is described by the Acid statement
P1
complex List {
'D' 0 type;
'X' 4 next;
};
P2
SH
Scope
PP
Variables are global unless they are either parameters to functions
or are declared as
CW local
in a function body. Parameters and local variables are available only in
the body of the function in which they are instantiated.
Variables are dynamically bound: if a function declares a local variable
with the same name as a global variable, the global variable will be hidden
whenever the function is executing.
For example, if a function
CW f
has a local called
CW main ,
any function called below
CW f
will see the local version of
CW main ,
not the external symbol.
SH 1
Addressing
PP
Since the symbol table specifies addresses,
to access the value of program variables
an extra level of indirection
is required relative to the source code.
For consistency, the registers are maintained as pointers as well; Acid variables with the names
of processor registers point to cells holding the saved registers.
PP
The location in a file or memory image associated with
an address is calculated from a map
associated with the file.
Each map contains one or more quadruples (\c
I t ,
I b ,
I e ,
I f \|),
defining a segment named
I t
(usually
CW text ,
CW data ,
CW regs ,
or
CW fpregs )
mapping addresses in the range
I b
through
I e
to the part of the file
beginning at
offset
I f .
The memory model of a Plan 9 process assumes
that segments are disjoint. There
can be more than one segment of a given type (e.g., a process
may have more than one text segment) but segments
may not overlap.
An address
I a
is translated
to a file address
by finding a segment
for which
I b
+
I a
<
I e ;
the location in the file
is then
I address
+
I f
\-
I b .
PP
Usually,
the text and initialized data of a program
are mapped by segments called
CW text
and
CW data .
Since a program file does not contain bss, stack, or register data,
these data are
not mapped by the data segment.
The text segment is mapped similarly in the memory image of
a normal (i.e., non-kernel) process.
However, the segment called
CW *data
maps memory from the beginning to the end of the program's data space.
This region contains the program's static data, the bss, the
heap and the stack. A segment
called
CW *regs
maps the registers;
CW *fpregs
maps the floating point registers.
PP
Sometimes it is useful to define a map with a single segment
mapping the region from 0 to 0xFFFFFFFF; such a map
allows the entire file to be examined
without address translation. The builtin function
CW map
examines and modifies Acid's map for a process.
SH 1
Name Conflicts
PP
Name conflicts between keywords in the Acid language, symbols in the program,
and previously defined functions are resolved when the interpreter starts up.
Each name is made unique by prefixing enough
CW $
characters to the front of the name to make it unique. Acid reports
a list of each name change at startup. The report looks like this:
P1
/bin/sam: mips plan 9 executable
/lib/acid/port
/lib/acid/mips
Symbol renames:
append=$append T/0xa4e40
acid:
P2
The symbol
CW append
is both a keyword and a text symbol in the program. The message reports
that the text symbol is now named
CW $append .
SH
Expressions
PP
Operators have the same
binding and precedence as in C.
For operators of equal precedence, expressions are evaluated from left to right.
SH 1
Boolean expressions
PP
If an expression is evaluated for a boolean condition the test
performed depends on the type of the result. If the result is of
I integer
or
I floating
type the result is true if the value is non-zero. If the expression is a
I list
the result is true if there are any members in the list.
If the expression is a
I string
the result is true if there are any characters in the string.
DS
primary-expression:
identifier
identifier \f(CW:\fP identifier
constant
\f(CW(\fP expression \f(CW)\fP
\f(CW{\fP elist \f(CW}\fP
elist:
expression
elist , expression
DE
An identifier may be any legal Acid variable. The colon operator returns the
address of parameters or local variables in the current stack of a program.
For example:
P1
*main:argc
P2
prints the number of arguments passed into main. Local variables and parameters
can only be referenced after the frame has been established. It may be necessary to
step a program over the first few instructions of a breakpointed function to properly set
the frame.
PP
Constants follow the same lexical rules as C.
A list of expressions delimited by braces forms a list constructor.
A new list is produced by evaluating each expression when the constructor is executed.
The empty list is formed from
CW {} .
P1
acid: x = 10
acid: l = { 1, x, 2\eD }
acid: x = 20
acid: l
{0x00000001 , 0x0000000a , 2 }
P2
SH 1
Lists
PP
Several operators manipulate lists.
DS
list-expression:
primary-expression
\f(CWhead\fP primary-expression
\f(CWtail\fP primary-expression
\f(CWappend\fP expression \f(CW,\fP primary-expression
\f(CWdelete\fP expression \f(CW,\fP primary-expression
DE
The
I primary-expression
for
CW head
and
CW tail
must yield a value of type
I list .
If there are no elements in the list the value of
CW head
or
CW tail
will be the empty list. Otherwise
CW head
evaluates to the first element of the list and
CW tail
evaluates to the rest.
P1
acid: head {}
{}
acid: head {1, 2, 3, 4}
0x00000001
acid: tail {1, 2, 3, 4}
{0x00000002 , 0x00000003 , 0x00000004 }
P2
The first operand of
CW append
and
CW delete
must be an expression that yields a
I list .
CW Append
places the result of evaluating
I primary-expression
at the end of the list.
The
I primary-expression
supplied to
CW delete
must evaluate to an integer;
CW delete
removes the
I n 'th
item from the list, where
I n
is integral value of
I primary-expression.
List indices are zero-based.
P1
acid: append {1, 2}, 3
{0x00000001 , 0x00000002 , 0x00000003 }
acid: delete {1, 2, 3}, 1
{0x00000001 , 0x00000003 }
P2
PP
Assigning a list to a variable copies a reference to the list; if a list variable
is copied it still points at the same list. To copy a list, the elements must
be copied piecewise using
CW head
and
CW append .
SH 1
Operators
PP
DS
postfix-expression:
list-expression
postfix-expression \f(CW[\fP expression \f(CW]\fP
postfix-expression \f(CW(\fP argument-list \f(CW)\fP
postfix-expression \f(CW.\fP tag
postfix-expression \f(CW->\fP tag
postfix-expression \f(CW++\fP
postfix-expression \f(CW--\fP
argument-list:
expression
argument-list , expression
DE
The
CW [
I expression
CW ]
operator performs indexing.
The indexing expression must result in an expression of
I integer
type, say
I n .
The operation depends on the type of
I postfix-expression .
If the
I postfix-expression
yields an
I integer
it is assumed to be the base address of an array in the memory image.
The index offsets into this array; the size of the array members is
determined by the format associated with the
I postfix-expression .
If the
I postfix-expression
yields a
I string
the index operator fetches the
I n 'th
character
of the string. If the index points beyond the end
of the string, a zero is returned.
If the
I postfix-expression
yields a
I list
then the indexing operation returns the
I n 'th
item of the list.
If the list contains less than
I n
items the empty list
CW {}
is returned.
PP
The
CW ++
and
CW --
operators increment and decrement integer variables.
The amount of increment or decrement depends on the format code. These postfix
operators return the value of the variable before the increment or decrement
has taken place.
DS
unary-expression:
postfix-expression
\f(CW++\fP unary-expression
\f(CW--\fP unary-expression
unary-operator: one of
\f(CW*\fP \f(CW@\fP \f(CW+\fP \f(CW-\fP ~ \f(CW!\fP
DE
The operators
CW *
and
CW @
are the indirection operators.
CW @
references a value from the text file of the program being debugged.
The size of the value depends on the format code. The
CW *
operator fetches a value from the memory image of a process. If either
operator appears on the left-hand side of an assignment statement, either the file
or memory will be written. The file can only be modified when Acid is invoked
with the
CW -w
option.
The prefix
CW ++
and
CW --
operators perform the same operation as their postfix counterparts but
return the value after the increment or decrement has been performed. Since the
CW ++
and
CW *
operators fetch and increment the correct amount for the specified format,
the following function prints correct machine instructions on a machine with
variable length instructions, such as the 68020 or 386:
P1
defn asm(addr)
{
addr = fmt(addr, 'i');
loop 1, 10 do
print(*addr++, "\en");
}
P2
The operators
CW ~
and
CW !
perform bitwise and logical negation respectively. Their operands must be of
I integer
type.
DS
cast-expression:
unary-expression
unary-expression \f(CW\e\fP format-char
\f(CW(\fP complex-name \f(CW)\fP unary-expression
DE
A unary expression may be preceded by a cast. The cast has the effect of
associating the value of
I unary-expression
with a complex type structure.
The result may then be dereferenced using the
CW .
and
CW ->
operators.
PP
An Acid variable may be associated with a complex type
to enable accessing the type's members:
P1
acid: complex List {
'D' 0 type;
'X' 4 next;
};
acid: complex List lhead
acid: lhead.type
10
acid: lhead = ((List)lhead).next
acid: lhead.type
-46
P2
Note that the
CW next
field cannot be given a complex type automatically.
PP
When entered at the top level of the interpreter,
an expression of complex type
is treated specially.
If the type is called
CW T
and an Acid function also called
CW T
exists,
then that function will be called with the expression as its argument.
The compiler options
CW -a
and
CW -aa
will generate Acid source code defining such complex types and functions; see
I 2c (1).
PP
A
I unary-expression
may be qualified with a format specifier using the
CW \e
operator. This has the same effect as passing the expression to the
CW fmt
builtin function.
DS
multiplicative-expression:
cast-expression
multiplicative-expression \f(CW*\fP multiplicative-expression
multiplicative-expression \f(CW/\fP multiplicative-expression
multiplicative-expression \f(CW%\fP multiplicative-expression
DE
These operate on
I integer
and
I float
types and perform the expected operations:
CW *
multiplication,
CW /
division,
CW %
modulus.
DS
additive-expression:
multiplicative-expression
additive-expression \f(CW+\fP multiplicative-expression
additive-expression \f(CW-\fP multiplicative-expression
DE
These operators perform as expected for
I integer
and
I float
operands.
Unlike in C,
CW +
and
CW -
do not scale the addition based on the format of the expression.
This means that
CW i=i+1
will always add 1 but
CW i++
will add the size corresponding to the format stored with
CW i .
If both operands are of either
I string
or
I list
type then addition is defined as concatenation.
Adding a string and an integer is treated as concatenation
with the Unicode character corresponding to the integer.
Subtraction is undefined for strings and lists.
DS
shift-expression:
additive-expression
shift-expression \f(CW<<\fP additive-expression
shift-expression \f(CW>>\fP additive-expression
DE
The
CW >>
and
CW <<
operators perform bitwise right and left shifts respectively. Both
require operands of
I integer
type.
DS
relational-expression:
relational-expression \f(CW<\fP shift-expression
relational-expression \f(CW>\fP shift-expression
relational-expression \f(CW<=\fP shift-expression
relational-expression \f(CW>=\fP shift-expression
equality-expression:
relational-expression
relational-expression \f(CW==\fP equality-expression
relational-expression \f(CW!=\fP equality-expression
DE
The comparison operators are
CW <
(less than),
CW >
(greater than),
CW <=
(less than or equal to),
CW >=
(greater than or equal to),
CW ==
(equal to) and
CW !=
(not equal to). The result of a comparison is 0
if the condition is false, otherwise 1. The relational operators can only be
applied to operands of
I integer
and
I float
type. The equality operators apply to all types. Comparing mixed types is legal.
Mixed integer and float compare on the integral value. Other mixtures are always unequal.
Two lists are equal if they
have the same number of members and a pairwise comparison of the members results
in equality.
DS
AND-expression:
equality-expression
AND-expression \f(CW&\fP equality-expression
XOR-expression:
AND-expression
XOR-expression \f(CW^\fP AND-expression
OR-expression:
XOR-expression
OR-expression \f(CW|\fP XOR-expression
DE
These operators perform bitwise logical operations and apply only to the
I integer
type.
The operators are
CW &
(logical and),
CW ^
(exclusive or) and
CW |
(inclusive or).
DS
logical-AND-expression:
OR-expression
logical-AND-expression \f(CW&&\fP OR-expression
logical-OR-expression:
logical-AND-expression
logical-OR-expression \f(CW||\fP logical-AND-expression
DE
The
CW &&
operator returns 1 if both of its operands evaluate to boolean true, otherwise 0.
The
CW ||
operator returns 1 if either of its operands evaluates to boolean true,
otherwise 0.
SH
Statements
PP
DS
\f(CWif\fP expression \f(CWthen\fP statement \f(CWelse\fP statement
\f(CWif\fP expression \f(CWthen\fP statement
DE
The
I expression
is evaluated as a boolean. If its value is true the statement after
the
CW then
is executed, otherwise the statement after the
CW else
is executed. The
CW else
portion may be omitted.
DS
\f(CWwhile\fP expression \f(CWdo\fP statement
DE
In a while loop, the
I statement
is executed while the boolean
I expression
evaluates
true.
DS
\f(CWloop\fP startexpr, endexpr \f(CWdo\fP statement
DE
The two expressions
I startexpr
and
I endexpr
are evaluated prior to loop entry.
I Statement
is evaluated while the value of
I startexpr
is less than or equal to
I endexpr .
Both expressions must yield
I integer
values. The value of
I startexpr
is
incremented by one for each loop iteration.
Note that there is no explicit loop variable; the
I expressions
are just values.
DS
\f(CWreturn\fP expression
DE
CW return
terminates execution of the current function and returns to its caller.
The value of the function is given by expression. Since
CW return
requires an argument, nil-valued functions should return the empty list
CW {} .
DS
\f(CWlocal\fP variable
DE
The
CW local
statement creates a local instance of
I variable ,
which exists for the duration
of the instance of the function in which it is declared. Binding is dynamic: the local variable,
rather than the previous value of
I variable ,
is visible to called functions.
After a return from the current function the previous value of
I variable
is
restored.
PP
If Acid is interrupted, the values of all local variables are lost,
as if the function returned.
DS
\f(CWdefn\fP function-name \f(CW(\fP parameter-list \f(CW)\fP body
parameter-list:
variable
parameter-list , variable
body:
\f(CW{\fP statement \f(CW}\fP
DE
Functions are introduced by the
CW defn
statement. The definition of parameter names suppresses any variables
of the same name until the function returns. The body of a function is a list
of statements enclosed by braces.
SH
Code variables
PP
Acid permits the delayed evaluation of a parameter to a function. The parameter
may then be evaluated at any time with the
CW eval
operator. Such parameters are called
I "code variables
and are defined by prefixing their name with an asterisk in their declaration.
PP
For example, this function wraps up an expression for later evaluation:
P1
acid: defn code(*e) { return e; }
acid: x = code(v+atoi("100")\eD)
acid: print(x)
(v+atoi("100"))\eD;
acid: eval x
<stdin>:5: (error) v used but not set
acid: v=5
acid: eval x
105
P2
SH
Source Code Management
PP
Acid provides the means to examine source code. Source code is
represented by lists of strings. Builtin functions provide mapping
from address to lines and vice-versa. The default debugging environment
has the means to load and display source files.
SH
Builtin Functions
PP
The Acid interpreter has a number of builtin functions, which cannot be redefined.
These functions perform machine- or operating system-specific functions such as
symbol table and process management.
The following section presents a description of each builtin function.
The notation
CW {}
is used to denote the empty list, which is the default value of a function that
does not execute a
CW return
statement.
The type and number of parameters for each function are specified in the
description; where a parameter can be of any type it is specified as type
I item .
de Ip
KS
in 0
LP
ie h \&\f2\\$1\fP\ \ \f(CW\\$2(\f2\\$3\f(CW)\f1\ \ \ \ \ \ \ \ \\$4
el .tl '\f2\\$1\fP\ \ \f(CW\\$2(\f2\\$3\f(CW)\f1''\\$4'
IP
.
de Ex
KE
KS
IP
ft CW
ta 4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n +4n
nf
in +4n
br
.
de Ee
fi
ft 1
br
KE
.
\"
\"
\"
Ip integer access string "Check if a file can be read
CW Access
returns the integer 1 if the file name in
I string
can be read by the builtin functions
CW file ,
CW readfile ,
or
CW include ,
otherwise 0. A typical use of this function is to follow
a search path looking for a source file; it is used by
CW findsrc .
Ex
if access("main.c") then
return file("main.c");
Ee
\"
\"
\"
Ip float atof string "Convert a string to float
CW atof
converts the string supplied as its argument into a floating point
number. The function accepts strings in the same format as the C
function of the same name. The value returned has the format code
CW f .
CW atof
returns the value 0.0 if it is unable to perform the conversion.
Ex
acid: +atof("10.4e6")
1.04e+07
Ee
\"
\"
\"
Ip integer atoi string "Convert a string to an integer
CW atoi
converts the argument
i string
to an integer value.
The function accepts strings in the same format as the C function of the
same name. The value returned has the format code
CW D .
CW atoi
returns the integer 0 if it is unable to perform a conversion.
Ex
acid: +atoi("-1255")
-1255
Ee
\"
\"
\"
Ip \f(CW{}\fP error string "Generate an interpreter error
CW error
generates an error message and returns the interpreter to interactive
mode. If an Acid program is running, it is aborted.
Processes being debugged are not affected. The values of all local variables are lost.
CW error
is commonly used to stop the debugger when some interesting condition arises
in the debugged program.
Ex
while 1 do {
step();
if *main != @main then
error("memory corrupted");
}
Ee
\"
\"
\"
Ip list file string "Read the contents of a file into a list
CW file
reads the contents of the file specified by
I string
into a list.
Each element in the list is a string corresponding to a line in the file.
CW file
breaks lines at the newline character, but the newline
characters are not returned as part each string.
CW file
returns the empty list if it encounters an error opening or reading the data.
Ex
acid: print(file("main.c")[0])
#include <u.h>
Ee
\"
\"
\"
Ip integer filepc string "Convert source address to text address
CW filepc
interprets its
I string
argument as a source file address in the form of a file name and line offset.
CW filepc
uses the symbol table to map the source address into a text address
in the debugged program. The
I integer
return value has the format
CW X .
CW filepc
returns an address of -1 if the source address is invalid.
The source file address uses the same format as
I acme (1).
This function is commonly used to set breakpoints from the source text.
Ex
acid: bpset(filepc("main:10"))
acid: bptab()
0x00001020 usage ADD $-0xc,R29
Ee
\"
\"
\"
Ip item fmt item,fmt "Set print, \f(CW@\fP and \f(CW*\fP formats
CW fmt
evaluates the expression
I item
and sets the format of the result to
I fmt .
The format of a value determines how it will be printed and
what kind of object will be fetched by the
CW *
and
CW @
operators. The
CW \e
operator is a short-hand form of the
CW fmt
builtin function. The
CW fmt
function leaves the format of the
I item
unchanged.
Ex
acid: main=fmt(main, 'i') // as instructions
acid: print(main\eX, "\et", *main)
0x00001020 ADD $-64,R29
Ee
\"
\"
\"
Ip fmt fmtof item "Get format
CW fmtof
evaluates the expression
I item
and returns the format of the result.
Ex
acid: +fmtof(33)
W
acid: +fmtof("string")
s
Ee
\"
\"
\"
Ip integer fmtsize item "Get format size
CW fmtsize
evaluates the expression
I item
and returns the size in bytes of a single element of result's format.
Ex
acid: +fmtsize('c')
8
acid: +fmtsize('c'\ec)
1
acid: +fmtsize(0\eX)
4
acid: +fmtsize('c'\e3)
10
Ee
\"
\"
\"
Ip list fnbound integer "Find start and end address of a function
CW fnbound
interprets its
I integer
argument as an address in the text of the debugged program.
CW fnbound
returns a list containing two integers corresponding to
the start and end addresses of the function containing the supplied address.
If the
I integer
address is not in the text segment of the program then the empty list is returned.
CW fnbound
is used by
CW next
to detect stepping into new functions.
Ex
acid: print(fnbound(main))
{0x00001050, 0x000014b8}
Ee
\"
\"
\"
Ip \f(CW{}\fP follow integer "Compute follow set
The follow set is defined as the set of program counter values that could result
from executing an instruction.
CW follow
interprets its
I integer
argument as a text address, decodes the instruction at
that address and, with the current register set, builds a list of possible
next program counter values. If the instruction at the specified address
cannot be decoded
CW follow
raises an error.
CW follow
is used to plant breakpoints on
all potential paths of execution. The following code fragment
plants breakpoints on top of all potential following instructions.
Ex
lst = follow(*PC);
while lst do
{
*head lst = bpinst;
lst = tail lst;
}
Ee
\"
\"
\"
Ip \f(CW{}\fP include string "Take input from a new file
CW include
opens the file specified by
I string
and uses its contents as command input to the interpreter.
The interpreter restores input to its previous source when it encounters
either an end of file or an error.
CW include
can be used to incrementally load symbol table information without
leaving the interpreter.
Ex
acid: include("/sys/src/cmd/acme/syms")
Ee
\"
\"
\"
Ip \f(CW{}\fP interpret string "Take input from a string
CW interpret
evaluates the
I string
expression and uses its result as command input for the interpreter.
The interpreter restores input to its previous source when it encounters
either the end of string or an error. The
CW interpret
function allows Acid programs to write Acid code for later evaluation.
Ex
acid: interpret("main+10;")
0x0000102a
Ee
\"
\"
\"
Ip string itoa integer[,string] "Convert integer to string
CW itoa
takes an integer argument and converts it into an ASCII string
in the
CW D
format.
an alternate format string
may be provided in the
CW %
style of
I print (2).
This function is commonly used to build
CW rc
command lines.
Ex
acid: rc("cat /proc/"+itoa(pid)+"/segment")
Stack 7fc00000 80000000 1
Data 00001000 00009000 1
Data 00009000 0000a000 1
Bss 0000a000 0000c000 1
Ee
\"
\"
\"
Ip \f(CW{}\fP kill integer "Kill a process
CW kill
writes a kill control message into the control file of the process
specified by the
I integer
pid.
If the process was previously installed by
CW setproc
it will be removed from the list of active processes.
If the
I integer
has the same value as
CW pid ,
then
CW pid
will be set to 0.
To continue debugging, a new process must be selected using
CW setproc .
For example, to kill all the active processes:
Ex
while proclist do {
kill(head proclist);
proclist = tail proclist;
}
Ee
\"
\"
\"
Ip list map list "Set or retrieve process memory map
CW map
either retrieves all the mappings associated with a process or sets a single
map entry to a new value.
If the
I list
argument is omitted then
CW map
returns a list of lists. Each sublist has four values and describes a
single region of contiguous addresses in the
memory or file image of the debugged program. The first entry is the name of the
mapping. If the name begins with
CW *
it denotes a map into the memory of an active process.
The second and third values specify the base and end
address of the region and the fourth number specifies the offset in the file
corresponding to the first location of the region.
A map entry may be set by supplying a list in the same format as the sublist
described above. The name of the mapping must match a region already defined
by the current map.
Maps are set automatically for Plan 9 processes and some kernels; they may
need to be set by hand for other kernels and programs that run on bare hardware.
Ex
acid: map({"text", _start, end, 0x30})
Ee
\"
\"
\"
Ip integer match item,list "Search list for matching value
CW match
compares each item in
I list
using the equality operator
CW ==
with
I item .
The
I item
can be of any type. If the match succeeds the result is the integer index
of the matching value, otherwise -1.
Ex
acid: list={8,9,10,11}
acid: print(list[match(10, list)]\eD)
10
Ee
\"
\"
\"
Ip \f(CW{}\fP newproc string "Create a new process
CW newproc
starts a new process with an argument vector constructed from
I string .
The argument vector excludes the name of the program to execute and
each argument in
I string
must be space separated. A new process can accept no more
than 512 arguments. The internal variable
CW pid
is set to the pid of the newly created process. The new pid
is also appended to the list of active processes stored in the variable
CW proclist .
The new process is created then halted at the first instruction, causing
the debugger to call
CW stopped .
The library functions
CW new
and
CW win
should be used to start processes when using the standard debugging
environment.
Ex
acid: newproc("-l .")
56720: system call _main ADD $-0x14,R29
Ee
\"
\"
\"
Ip string pcfile integer "Convert text address to source file name
CW pcfile
interprets its
I integer
argument as a text address in the debugged program. The address and symbol table
are used to generate a string containing the name of the source file
corresponding to the text address. If the address does not lie within the
program the string
CW ?file?
is returned.
Ex
acid: print("Now at ", pcfile(*PC), ":", pcline(*PC))
Now at ls.c:46
Ee
\"
\"
\"
Ip integer pcline integer "Convert text address to source line number
CW pcline
interprets its
I integer
argument as a text address in the debugged program. The address and symbol table
are used to generate an integer containing the line number in the source file
corresponding to the text address. If the address does not lie within the
program the integer 0 is returned.
Ex
acid: +file("main.c")[pcline(main)]
main(int argc, char *argv[])
Ee
\"
\"
\"
Ip \f(CW{}\fP print item,item,... "Print expressions
CW print
evaluates each
I item
supplied in its argument list and prints it to standard output. Each
argument will be printed according to its associated format character.
When the interpreter is executing, output is buffered and flushed every
5000 statements or when the interpreter returns to interactive mode.
CW print
accepts a maximum of 512 arguments.
Ex
acid: print(10, "decimal ", 10\eD, "octal ", 10\eo)
0x0000000a decimal 10 octal 000000000012
acid: print({1, 2, 3})
{0x00000001 , 0x00000002 , 0x00000003 }
acid: print(main, main\ea, "\et", @main\ei)
0x00001020 main ADD $-64,R29
Ee
\"
\"
\"
Ip \f(CW{}\fP printto string,item,item,... "Print expressions to file
CW printto
offers a limited form of output redirection. The first
I string
argument is used as the path name of a new file to create.
Each
I item
is then evaluated and printed to the newly created file. When all items
have been printed the file is closed.
CW printto
accepts a maximum of 512 arguments.
Ex
acid: printto("/env/foo", "hello")
acid: rc("echo -n $foo")
hello
Ee
\"
\"
\"
Ip string rc string "Execute a shell command
CW rc
evaluates
I string
to form a shell command. A new command interpreter is started
to execute the command. The Acid interpreter blocks until the command
completes. The return value is the empty string
if the command succeeds, otherwise the exit status of the failed command.
Ex
acid: rc("B "+itoa(-pcline(addr))+" "+pcfile(addr));
Ee
\"
\"
\"
Ip string readfile string "Read file contents into a string
CW readfile
takes the contents of the file specified by
I string
and returns its contents as a new string.
If
CW readfile
encounters a zero byte in the file, it terminates.
If
CW readfile
encounters an error opening or reading the file then the empty list
is returned.
CW readfile
can be used to read the contents of device files whose lines are not
terminated with newline characters.
Ex
acid: ""+readfile("/dev/label")
helix
Ee
\"
\"
\"
Ip string reason integer "Print cause of program stoppage
CW reason
uses machine-dependent information to generate a string explaining
why a process has stopped. The
I integer
argument is the value of an architecture dependent status register,
for example
CW CAUSE
on the MIPS.
Ex
acid: print(reason(*CAUSE))
system call
Ee
\"
\"
\"
Ip integer regexp pattern,string "Regular expression match
CW regexp
matches the
I pattern
string supplied as its first argument with the
I string
supplied as its second.
If the pattern matches the result is the value 1, otherwise 0.
Ex
acid: print(regexp(".*bar", "foobar"))
1
Ee
\"
\"
\"
Ip \f(CW{}\fP setproc integer "Set debugger focus
CW setproc
selects the default process used for memory and control operations. It effectively
shifts the focus of control between processes. The
I integer
argument specifies the pid of the process to look at.
The variable
CW pid
is set to the pid of the selected process. If the process is being
selected for the first time its pid is added to the list of active
processes
CW proclist .
Ex
acid: setproc(68382)
acid: procs()
>68382: Stopped at main+0x4 setproc(68382)
Ee
\"
\"
\"
Ip \f(CW{}\fP start integer "Restart execution
CW start
writes a
CW start
message to the control file of the process specified by the pid
supplied as its
I integer
argument.
CW start
draws an error if the process is not in the
CW Stopped
state.
Ex
acid: start(68382)
acid: procs()
>68382: Running at main+0x4 setproc(68382)
Ee
\"
\"
\"
Ip \f(CW{}\fP startstop integer "Restart execution, block until stopped
CW startstop
performs the same actions as a call to
CW start
followed by a call to
CW stop .
The
I integer
argument specifies the pid of the process to control. The process
must be in the
CW Stopped
state.
Execution is restarted, the debugger then waits for the process to
return to the
CW Stopped
state. A process will stop if a startstop message has been written to its control
file and any of the following conditions becomes true: the process executes or returns from
a system call, the process generates a trap or the process receives a note.
CW startstop
is used to implement single stepping.
Ex
acid: startstop(pid)
75374: breakpoint ls ADD $-0x16c8,R29
Ee
\"
\"
\"
Ip string status integer "Return process state
CW status
uses the pid supplied by its
I integer
argument to generate a string describing the state of the process.
The string corresponds to the state returned by the
sixth column of the
I ps (1)
command.
A process must be in the
CW Stopped
state to modify its memory or registers.
Ex
acid: ""+status(pid)
Stopped
Ee
\"
\"
\"
Ip \f(CW{}\fP stop integer "Wait for a process to stop
CW stop
writes a
CW stop
message to the control file of the process specified by the
pid supplied as its
I integer
argument.
The interpreter blocks until the debugged process enters the
CW Stopped
state.
A process will stop if a stop message has been written to its control
file and any of the following conditions becomes true: the process executes or returns from
a system call, the process generates a trap, the process is scheduled or the
process receives a note.
CW stop
is used to wait for a process to halt before planting a breakpoint since Plan 9
only allows a process's memory to be written while it is in the
CW Stopped
state.
Ex
defn bpset(addr) {
if (status(pid)!="Stopped") then {
print("Waiting...\en");
stop(pid);
}
...
}
Ee
\"
\"
\"
Ip list strace pc,sp,linkreg "Stack trace
CW strace
generates a list of lists corresponding to procedures called by the debugged
program. Each sublist describes a single stack frame in the active process.
The first element is an
I integer
of format
CW X
specifying the address of the called function. The second element is the value
of the program counter when the function was called. The third and fourth elements
contain lists of parameter and automatic variables respectively.
Each element of these lists
contains a string with the name of the variable and an
I integer
value of format
CW X
containing the current value of the variable.
The arguments to
CW strace
are the current value of the program counter, the current value of the
stack pointer, and the address of the link register. All three parameters
must be integers.
The setting of
I linkreg
is architecture dependent. On the MIPS linkreg is set to the address of saved
CW R31 ,
on the SPARC to the address of saved
CW R15 .
For the other architectures
I linkreg
is not used, but must point to valid memory.
Ex
acid: print(strace(*PC, *SP, linkreg))
{{0x0000141c, 0xc0000f74,
{{"s", 0x0000004d}, {"multi", 0x00000000}},
{{"db", 0x00000000}, {"fd", 0x000010a4},
{"n", 0x00000001}, {"i", 0x00009824}}}}
Ee
\"
\"
\"
Ip \f(CW{}\fP waitstop integer "Wait for a process to stop
CW waitstop
writes a waitstop message to the control file of the process specified by the
pid supplied as its
I integer
argument.
The interpreter will remain blocked until the debugged process enters the
CW Stopped
state.
A process will stop if a waitstop message has been written to its control
file and any of the following conditions becomes true: the process generates a trap
or receives a note. Unlike
CW stop ,
the
CW waitstop
function is passive; it does not itself cause the program to stop.
Ex
acid: waitstop(pid)
75374: breakpoint ls ADD $-0x16c8,R29
Ee
\"
\"
\"
SH
Library Functions
PP
A standard debugging environment is provided by modules automatically
loaded when
Acid is started.
These modules are located in the directory
CW /sys/lib/acid .
These functions may be overridden, personalized, or added to by code defined in
CW $home/lib/acid .
The implementation of these functions can be examined using the
CW whatis
operator and then modified during debugging sessions.
\"
\"
\"
Ip \f(CW{}\fP Bsrc integer "Load editor with source
CW Bsrc
interprets the
I integer
argument as a text address. The text address is used to produce a pathname
and line number suitable for the
CW B
command
to send to the text editor
I sam (1)
or
I acme (1).
CW Bsrc
builds an
I rc (1)
command to invoke
CW B ,
which either selects an existing source file or loads a new source file into the editor.
The line of source corresponding to the text address is then selected.
In the following example
CW stopped
is redefined so that the editor
follows and displays the source line currently being executed.
Ex
defn stopped(pid) {
pstop(pid);
Bsrc(*PC);
}
Ee
\"
\"
\"
Ip \f(CW{}\fP Fpr "" "Display double precision floating registers
For machines equipped with floating point,
CW Fpr
displays the contents of the floating point registers as double precision
values.
Ex
acid: Fpr()
F0 0. F2 0.
F4 0. F6 0.
F8 0. F10 0.
\&...
Ee
\"
\"
\"
Ip \f(CW{}\fP Ureg integer "Display contents of Ureg structure
CW Ureg
interprets the integer passed as its first argument as the address of a
kernel
CW Ureg
structure. Each element of the structure is retrieved and printed.
The size and contents of the
CW Ureg
structure are architecture dependent.
This function can be used to decode the first argument passed to a
I notify (2)
function after a process has received a note.
Ex
acid: Ureg(*notehandler:ur)
status 0x3000f000
pc 0x1020
sp 0x7ffffe00
cause 0x00004002
\&...
Ee
\"
\"
\"
Ip \f(CW{}\fP acidinit "" "Interpreter startup
CW acidinit
is called by the interpreter after all
modules have been loaded at initialization time.
It is used to set up machine specific variables and the default source path.
CW acidinit
should not be called by user code.
KE
\"
\"
\"
Ip \f(CW{}\fP addsrcdir string "Add element to source search path
CW addsrcdir
interprets its string argument as a new directory
CW findsrc
should search when looking for source code files.
CW addsrcdir
draws an error if the directory is already in the source search path. The search
path may be examined by looking at the variable
CW srcpath .
Ex
acid: rc("9fs fornax")
acid: addsrcpath("/n/fornax/sys/src/cmd")
Ee
\"
\"
\"
Ip \f(CW{}\fP asm integer "Disassemble machine instructions
CW asm
interprets its integer argument as a text address from which to disassemble
machine instructions.
CW asm
prints the instruction address in symbolic and hexadecimal form, then prints
the instructions with addressing modes. Up to twenty instructions will
be disassembled.
CW asm
stops disassembling when it reaches the end of the current function.
Instructions are read from the file image using the
CW @
operator.
Ex
acid: asm(main)
main 0x00001020 ADD $-0x64,R29
main+0x4 0x00001024 MOVW R31,0x0(R29)
main+0x8 0x00001028 MOVW R1,argc+4(FP)
main+0xc 0x0000102c MOVW $bin(SB),R1
Ee
\"
\"
\"
Ip \f(CW{}\fP bpdel integer "Delete breakpoint
CW bpdel
removes a previously set breakpoint from memory.
The
I integer
supplied as its argument must be the address of a previously set breakpoint.
The breakpoint address is deleted from the active breakpoint list
CW bplist ,
then the original instruction is copied from the file image to the memory
image so that the breakpoint is removed.
Ex
acid: bpdel(main+4)
Ee
\"
\"
\"
Ip \f(CW{}\fP bpset integer "Set a breakpoint
CW bpset
places a breakpoint instruction at the address specified
by its
I integer
argument, which must be in the text segment.
CW bpset
draws an error if a breakpoint has already been set at the specified address.
A list of current breakpoints is maintained in the variable
CW bplist .
Unlike in
I db (1),
breakpoints are left in memory even when a process is stopped, and
the process must exist, perhaps by being
created by either
CW new
or
CW win ,
in order to place a breakpoint.
CW Db "" (
accepts breakpoint commands before the process is started.)
On the
MIPS and SPARC architectures,
breakpoints at function entry points should be set 4 bytes into the function
because the
instruction scheduler may fill
CW JAL
branch delay slots with the first instruction of the function.
Ex
acid: bpset(main+4)
Ee
\"
\"
\"
Ip \f(CW{}\fP bptab "" "List active breakpoints
CW bptab
prints a list of currently installed breakpoints. The list contains the
breakpoint address in symbolic and hexadecimal form as well as the instruction
the breakpoint replaced. Breakpoints are not maintained across process creation
using
CW new
and
CW win .
They are maintained across a fork, but care must be taken to keep control of
the child process.
Ex
acid: bpset(ls+4)
acid: bptab()
0x00001420 ls+0x4 MOVW R31,0x0(R29)
Ee
\"
\"
\"
Ip \f(CW{}\fP casm "" "Continue disassembly
CW casm
continues to disassemble instructions from where the last
CW asm
or
CW casm
command stopped. Like
CW asm ,
this command stops disassembling at function boundaries.
Ex
acid: casm()
main+0x10 0x00001030 MOVW $0x1,R3
main+0x14 0x00001034 MOVW R3,0x8(R29)
main+0x18 0x00001038 MOVW $0x1,R5
main+0x1c 0x0000103c JAL Binit(SB)
Ee
\"
\"
\"
Ip \f(CW{}\fP cont "" "Continue program execution
CW cont
restarts execution of the currently active process.
If the process is stopped on a breakpoint, the breakpoint is first removed,
the program is single stepped, the breakpoint is replaced and the program
is then set executing. This may cause
CW stopped()
to be called twice.
CW cont
causes the interpreter to block until the process enters the
CW Stopped
state.
Ex
acid: cont()
95197: breakpoint ls+0x4 MOVW R31,0x0(R29)
Ee
\"
\"
\"
Ip \f(CW{}\fP dump integer,integer,string "Formatted memory dump
CW dump
interprets its first argument as an address, its second argument as a
count and its third as a format string.
CW dump
fetches an object from memory at the current address and prints it according
to the format. The address is incremented by the number of bytes specified by
the format and the process is repeated count times. The format string is any
combination of format characters, each preceded by an optional count.
For each object,
CW dump
prints the address in hexadecimal, a colon, the object and then a newline.
CW dump
uses
CW mem
to fetch each object.
Ex
acid: dump(main+35, 4, "X2bi")
0x00001043: 0x0c8fa700 108 143 lwc2 r0,0x528f(R4)
0x0000104d: 0xa9006811 0 0 swc3 r0,0x0(R24)
0x00001057: 0x2724e800 4 37 ADD $-0x51,R23,R31
0x00001061: 0xa200688d 6 0 NOOP
0x0000106b: 0x2710c000 7 0 BREAK
Ee
\"
\"
\"
Ip \f(CW{}\fP findsrc string "Use source path to load source file
CW findsrc
interprets its
I string
argument as a source file. Each directory in the source path is searched
in turn for the file. If the file is found, the source text is loaded using
CW file
and stored in the list of active source files called
CW srctext .
The name of the file is added to the source file name list
CW srcfiles .
Users are unlikely to call
CW findsrc
from the command line, but may use it from scripts to preload source files
for a debugging session. This function is used by
CW src
and
CW line
to locate and load source code. The default search path for the MIPS
is
CW ./ ,
CW /sys/src/libc/port ,
CW /sys/src/libc/9sys ,
CW /sys/src/libc/mips .
Ex
acid: findsrc(pcfile(main));
Ee
\"
\"
\"
Ip \f(CW{}\fP fpr "" "Display single precision floating registers
For machines equipped with floating point,
CW fpr
displays the contents of the floating point registers as single precision
values. When the interpreter stores or manipulates floating point values
it converts into double precision values.
Ex
acid: fpr()
F0 0. F1 0.
F2 0. F3 0.
F4 0. F5 0.
\&...
Ee
\"
\"
\"
Ip \f(CW{}\fP func "" "Step while in function
CW func
single steps the active process until it leaves the current function
by either calling another function or returning to its caller.
CW func
will execute a single instruction after leaving the current function.
Ex
acid: func()
95197: breakpoint ls+0x8 MOVW R1,R8
95197: breakpoint ls+0xc MOVW R8,R1
95197: breakpoint ls+0x10 MOVW R8,s+4(FP)
95197: breakpoint ls+0x14 MOVW $0x2f,R5
95197: breakpoint ls+0x18 JAL utfrrune(SB)
95197: breakpoint utfrrune ADD $-0x18,R29
Ee
\"
\"
\"
Ip \f(CW{}\fP gpr "" "Display general purpose registers
CW gpr
prints the values of the general purpose processor registers.
Ex
acid: gpr()
R1 0x00009562 R2 0x000010a4 R3 0x00005d08
R4 0x0000000a R5 0x0000002f R6 0x00000008
\&...
Ee
\"
\"
\"
Ip \f(CW{}\fP labstk integer "Print stack trace from label
CW labstk
performs a stack trace from a Plan 9
I label.
The kernel,
C compilers store continuations in a common format. Since the
compilers all use caller save conventions a continuation may be saved by
storing a
CW PC
and
CW SP
pair. This data structure is called a label and is used by the
the C function
CW longjmp
and the kernel to schedule threads and processes.
CW labstk
interprets its
I integer
argument as the address of a label and produces a stack trace for
the thread of execution. The value of the function
CW ALEF_tid
is a suitable argument for
CW labstk .
Ex
acid: labstk(*mousetid)
At pc:0x00021a70:Rendez_Sleep+0x178 rendez.l:44
Rendez_Sleep(r=0xcd7d8,bool=0xcd7e0,t=0x0) rendez.l:5
called from ALEF_rcvmem+0x198 recvmem.l:45
ALEF_rcvmem(c=0x000cd764,l=0x00000010) recvmem.l:6
\&...
Ee
\"
\"
\"
Ip \f(CW{}\fP lstk "" "Stack trace with local variables
CW lstk
produces a long format stack trace.
The stack trace includes each function in the stack,
where it was called from, and the value of the parameters and automatic
variables for each function.
CW lstk
displays the value rather than the address of each variable and all
variables are assumed to be an integer in format
CW X .
To print a variable in its correct format use the
CW :
operator to find the address and apply the appropriate format before indirection
with the
CW *
operator. It may be necessary to single step a couple of instructions into
a function to get a correct stack trace because the frame pointer adjustment
instruction may get scheduled down into the body of the function.
Ex
acid: lstk()
At pc:0x00001024:main+0x4 ls.c:48
main(argc=0x00000001,argv=0x7fffefec) ls.c:48
called from _main+0x20 main9.s:10
_argc=0x00000000
_args=0x00000000
fd=0x00000000
buf=0x00000000
i=0x00000000
Ee
\"
\"
\"
Ip \f(CW{}\fP mem integer,string "Print memory object
CW mem
interprets its first
I integer
argument as the address of an object to be printed according to the
format supplied in its second
I string
argument.
The format string can be any combination of format characters, each preceded
by an optional count.
Ex
acid: mem(bdata+0x326, "2c2Xb")
P = 0xa94bc464 0x3e5ae44d 19
Ee
\"
\"
\"
Ip \f(CW{}\fP new "" "Create new process
CW new
starts a new copy of the debugged program. The new program is started
with the program arguments set by the variable
CW progargs .
The new program is stopped in the second instruction of
CW main .
The breakpoint list is reinitialized.
CW new
may be used several times to instantiate several copies of a program
simultaneously. The user can rotate between the copies using
CW setproc .
Ex
acid: progargs="-l"
acid: new()
60: external interrupt _main ADD $-0x14,R29
60: breakpoint main+0x4 MOVW R31,0x0(R29)
Ee
\"
\"
\"
Ip \f(CW{}\fP next "" "Step through language statement
CW next
steps through a single language level statement without tracing down
through each statement in a called function. For each statement,
CW next
prints the machine instructions executed as part of the statement. After
the statement has executed, source lines around the current program
counter are displayed.
Ex
acid: next()
60: breakpoint Binit+0x4 MOVW R31,0x0(R29)
60: breakpoint Binit+0x8 MOVW f+8(FP),R4
binit.c:93
88
89 int
90 Binit(Biobuf *bp, int f, int mode)
91 {
>92 return Binits(bp, f, mode, bp->b, BSIZE);
93 }
Ee
\"
\"
\"
Ip \f(CW{}\fP notestk integer "Stack trace after receiving a note
CW notestk
interprets its
I integer
argument as the address of a
CW Ureg
structure passed by the kernel to a
I notify (2)
function during note processing.
CW notestk
uses the
CW PC ,
CW SP ,
and link register from the
CW Ureg
to print a stack trace corresponding to the point in the program where the note
was received.
To get a valid stack trace on the MIPS and SPARC architectures from a notify
routine, the program must stop in a new function called from the notify routine
so that the link register is valid and the notify routine's parameters are
addressable.
Ex
acid: notestk(*notify:ur)
Note pc:0x00001024:main+0x4 ls.c:48
main(argc=0x00000001,argv=0x7fffefec) ls.c:48
called from _main+0x20 main9.s:10
_argc=0x00000000
_args=0x00000000
Ee
\"
\"
\"
Ip \f(CW{}\fP pfl integer "Print source file and line
CW pfl
interprets its argument as a text address and uses it to print
the source file and line number corresponding to the address. The output
has the same format as file addresses in
I acme (1).
Ex
acid: pfl(main)
ls.c:48
Ee
\"
\"
\"
Ip \f(CW{}\fP procs "" "Print active process list
CW procs
prints a list of active process attached to the debugger. Each process
produces a single line of output giving the pid, process state, the address
the process is currently executing, and the
CW setproc
command required to make that process current.
The current process is marked in the first column with a
CW >
character. The debugger maintains a list of processes in the variable
CW proclist .
Ex
acid: procs()
>62: Stopped at main+0x4 setproc(62)
60: Stopped at Binit+0x8 setproc(60)
Ee
\"
\"
\"
Ip \f(CW{}\fP pstop integer "Print reason process stopped
CW pstop
prints the status of the process specified by the
I integer
pid supplied as its argument.
CW pstop
is usually called from
CW stopped
every time a process enters the
CW Stopped
state.
Ex
acid: pstop(62)
0x0000003e: breakpoint main+0x4 MOVW R31,0x0(R29)
Ee
\"
\"
\"
Ip \f(CW{}\fP regs "" "Print registers
CW regs
prints the contents of both the general and special purpose registers.
CW regs
calls
CW spr
then
CW gpr
to display the contents of the registers.
KE
\"
\"
\"
Ip \f(CW{}\fP source "" "Summarize source data base
CW source
prints the directory search path followed by a list of currently loaded
source files. The source management functions
CW src
and
CW findsrc
use the search path to locate and load source files. Source files are
loaded incrementally into a source data base during debugging. A list
of loaded files is stored in the variable
CW srcfiles
and the contents of each source file in the variable
CW srctext .
Ex
acid: source()
/n/bootes/sys/src/libbio/
/
/sys/src/libc/port/
/sys/src/libc/9sys/
/sys/src/libc/mips/
binit.c
Ee
\"
\"
\"
Ip \f(CW{}\fP spr "" "Print special purpose registers
CW spr
prints the contents of the processor control and memory management
registers. Where possible, the contents of the registers are decoded
to provide extra information; for example the
CW CAUSE
register on the MIPS is
printed both in hexadecimal and using the
CW reason
function.
Ex
acid: spr()
PC 0x00001024 main+0x4 ls.c:48
SP 0x7fffef68 LINK 0x00006264 _main+0x28 main9.s:12
STATUS 0x0000ff33 CAUSE 0x00000024 breakpoint
TLBVIR 0x000000d3 BADVADR 0x00001020
HI 0x00000004 LO 0x00001ff7
Ee
\"
\"
\"
Ip \f(CW{}\fP src integer "Print lines of source
CW src
interprets its
I integer
argument as a text address and uses this address to print 5 lines
of source before and after the address. The current line is marked with a
CW >
character.
CW src
uses the source search path maintained by
CW source
and
CW addsrcdir
to locate the required source files.
Ex
acid: src(*PC)
ls.c:47
42 Biobuf bin;
43
44 #define HUNK 50
45
46 void
>47 main(int argc, char *argv[])
48 {
49 int i, fd;
50 char buf[64];
51
52 Binit(&bin, 1, OWRITE);
Ee
\"
\"
\"
Ip \f(CW{}\fP step "" "Single step process
CW step
causes the debugged process to execute a single machine level instruction.
If the program is stopped on a breakpoint set by
CW bpset
it is first removed, the single step executed, and the breakpoint replaced.
CW step
uses
CW follow
to predict the address of the program counter after the current instruction
has been executed. A breakpoint is placed at each of these predicted addresses
and the process is started. When the process stops the breakpoints are removed.
Ex
acid: step()
62: breakpoint main+0x8 MOVW R1,argc+4(FP)
Ee
\"
\"
\"
Ip \f(CW{}\fP stk "" "Stack trace
CW stk
produces a short format stack trace. The stack trace includes each function
in the stack, where it was called from, and the value of the parameters.
The short format omits the values of automatic variables.
Parameters are assumed to be integer values in the format
CW X ;
to print a parameter in the correct format use the
CW :
to obtain its address, apply the correct format, and use the
CW *
indirection operator to find its value.
It may be necessary to single step a couple of instructions into
a function to get a correct stack trace because the frame pointer adjustment
instruction may get scheduled down into the body of the function.
Ex
acid: stk()
At pc:0x00001028:main+0x8 ls.c:48
main(argc=0x00000002,argv=0x7fffefe4) ls.c:48
called from _main+0x20 main9.s:10
Ee
\"
\"
\"
Ip \f(CW{}\fP stmnt "" "Execute a single statement
CW stmnt
executes a single language level statement.
CW stmnt
displays each machine level instruction as it is executed. When the executed
statement is completed the source for the next statement is displayed.
Unlike
CW next ,
the
CW stmnt
function will trace down through function calls.
Ex
acid: stmnt()
62: breakpoint main+0x18 MOVW R5,0xc(R29)
62: breakpoint main+0x1c JAL Binit(SB)
62: breakpoint Binit ADD $-0x18,R29
binit.c:91
89 int
90 Binit(Biobuf *bp, int f, int mode)
>91 {
Ee
\"
\"
\"
Ip \f(CW{}\fP stopped integer "Report status of stopped process
CW stopped
is called automatically by the interpreter
every time a process enters the
CW Stopped
state, such as when it hits a breakpoint.
The pid is passed as the
I integer
argument. The default implementation just calls
CW pstop ,
but the function may be changed to provide more information or perform fine control
of execution. Note that
CW stopped
should return; for example, calling
CW step
in
CW stopped
will recur until the interpreter runs out of stack space.
Ex
acid: defn stopped(pid) {
if *lflag != 0 then error("lflag modified");
}
acid: progargs = "-l"
acid: new();
acid: while 1 do step();
<stdin>:7: (error) lflag modified
acid: stk()
At pc:0x00001220:main+0x200 ls.c:54
main(argc=0x00000001,argv=0x7fffffe8) ls.c:48
called from _main+0x20 main9.s:10
Ee
\"
\"
\"
Ip \f(CW{}\fP symbols string "Search symbol table
CW symbols
uses the regular expression supplied by
I string
to search the symbol table for symbols whose name matches the
regular expression.
Ex
acid: symbols("main")
main T 0x00001020
_main T 0x0000623c
Ee
\"
\"
\"
Ip \f(CW{}\fP win "" "Start new process in a window
CW win
performs exactly the same function as
CW new
but uses the window system to create a new window for the debugged process.
The variable
CW progargs
supplies arguments to the new process.
The environment variable
CW $8½srv
must be set to allow the interpreter to locate the mount channel for the
window system.
The window is created in the top left corner of the screen and is
400x600 pixels in size. The
CW win
function may be modified to alter the geometry.
The window system will not be able to deliver notes in the new window
since the pid of the created process is not passed when the server is
mounted to create a new window.
Ex
acid: win()
Ee
