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\" Id: dwarf_child.3 3961 2022-03-12 15:13:22Z jkoshy
\"
Dd December 21, 2014
Dt DWARF_CHILD 3
Os
Sh NAME
Nm dwarf_child ,
Nm dwarf_offdie ,
Nm dwarf_offdie_b ,
Nm dwarf_siblingof ,
Nm dwarf_siblingof_b
Nd retrieve DWARF Debugging Information Entry descriptors
Sh LIBRARY
Lb libdwarf
Sh SYNOPSIS
In libdwarf.h
Ft int
Fn dwarf_child "Dwarf_Die die" "Dwarf_Die *ret_die" "Dwarf_Error *err"
Ft int
Fo dwarf_offdie
Fa "Dwarf_Debug dbg"
Fa "Dwarf_Off offset"
Fa "Dwarf_Die *ret_die"
Fa "Dwarf_Error *err"
Fc
Ft int
Fo dwarf_offdie_b
Fa "Dwarf_Debug dbg"
Fa "Dwarf_Off offset"
Fa "Dwarf_Bool is_info"
Fa "Dwarf_Die *ret_die"
Fa "Dwarf_Error *err"
Fc
Ft int
Fo dwarf_siblingof
Fa "Dwarf_Debug dbg"
Fa "Dwarf_Die die"
Fa "Dwarf_Die *ret_die"
Fa "Dwarf_Error *err"
Fc
Ft int
Fo dwarf_siblingof_b
Fa "Dwarf_Debug dbg"
Fa "Dwarf_Die die"
Fa "Dwarf_Die *ret_die"
Fa "Dwarf_Bool is_info"
Fa "Dwarf_Error *err"
Fc
Sh DESCRIPTION
These functions are used to retrieve and traverse DWARF
Debugging Information Entry (DIE) descriptors associated with
a compilation unit.
These descriptors are arranged in the form of a tree, traversable
using
Dq child
and
Dq sibling
links; see
Xr dwarf 3
for more information.
DWARF Debugging Information Entry descriptors are represented
by the
Vt Dwarf_Die
opaque type.
Pp
Function
Fn dwarf_child
retrieves the child of descriptor denoted by argument
Fa die ,
and stores it in the location pointed to by argument
Fa ret_die .
Pp
Function
Fn dwarf_siblingof
retrieves the sibling of the descriptor denoted by argument
Fa die ,
and stores it in the location pointed to by argument
Fa ret_die .
If argument
Fa die
is
Dv NULL ,
the first debugging information entry descriptor for the
current compilation unit will be returned.
This function and function
Fn dwarf_child
may be used together to traverse the tree of debugging information
entry descriptors for a compilation unit.
Pp
Function
Fn dwarf_siblingof_b
is identical to the function
Fn dwarf_siblingof
except that it can retrieve the sibling descriptor from either the
current compilation unit or type unit.
If argument
Fa is_info
is non-zero, the function behaves identically to function
Fn dwarf_siblingof .
If argument
Fa is_info
is zero, the descriptor referred by argument
Fa die
should be associated with a debugging information entry in the
type unit.
The function will store the sibling of the descriptor in the location
pointed to by argument
Fa ret_die .
If argument
Fa is_info
is zero and argument
Fa die
is
Dv NULL ,
the first debugging information entry descriptor for the
current type unit will be returned.
Pp
Function
Fn dwarf_offdie
retrieves the debugging information entry descriptor at global offset
Fa offset
in the
Dq .debug_info
section of the object associated with argument
Fa dbg .
The returned descriptor is written to the location pointed to by argument
Fa ret_die .
Pp
Function
Fn dwarf_offdie_b
is identical to the function
Fn dwarf_offdie
except that it can retrieve the debugging information entry descriptor at
global offset
Fa offset
from either of the
Dq .debug_info
and
Dq .debug_types
sections of the object associated with argument
Fa dbg .
If argument
Fa is_info
is non-zero, the function will retrieve the debugging information
entry from the
Dq .debug_info
section, otherwise the function will retrieve the debugging
information entry from the
Dq .debug_types
section.
The returned descriptor is written to the location pointed to by argument
Fa ret_die .
Ss Memory Management
The memory area used for the
Vt Dwarf_Die
descriptor returned in argument
Fa ret_die
is allocated by the
Lb libdwarf .
Application code should use function
Fn dwarf_dealloc
with the allocation type
Dv DW_DLA_DIE
to free the memory area when the
Vt Dwarf_Die
descriptor is no longer needed.
Sh RETURN VALUES
These functions return the following values:
Bl -tag -width ".Bq Er DW_DLV_NO_ENTRY"
It Bq Er DW_DLV_OK
The call succeeded.
It Bq Er DW_DLV_ERROR
The requested operation failed.
Additional information about the error encountered will be recorded in
argument
Fa err ,
if it is not
Dv NULL .
It Bq Er DW_DLV_NO_ENTRY
For functions
Fn dwarf_child ,
Fn dwarf_siblingof
and
Fn dwarf_siblingof_b ,
the descriptor denoted by argument
Fa die
did not have a child or sibling.
Pp
For functions
Fn dwarf_offdie
and
Fn dwarf_offdie_b ,
there was no debugging information entry at the offset specified by
argument
Fa offset .
El
Sh EXAMPLES
To retrieve the first DWARF Debugging Information Entry descriptor for
the first compilation unit associated with a
Vt Dwarf_Debug
instance, and to traverse all its children, use:
Bd -literal -offset indent
Dwarf_Debug dbg;
Dwarf_Die die, die0;
Dwarf_Error de;

\&... allocate dbg using dwarf_init() etc ...

if (dwarf_next_cu_header(dbg, NULL, NULL, NULL, NULL, NULL, &de) !=
   DW_DLV_OK)
       errx(EXIT_FAILURE, "dwarf_next_cu_header: %s",
           dwarf_errmsg(de));

/* Get the first DIE for the current compilation unit. */
die = NULL;
if (dwarf_siblingof(dbg, die, &die0, &de) != DW_DLV_OK)
       errx(EXIT_FAILURE, "dwarf_siblingof: %s", dwarf_errmsg(de));

/* Get the first child of this DIE. */
die = die0;
if (dwarf_child(die, &die0, &de) != DW_DLV_OK)
       errx(EXIT_FAILURE, "dwarf_child: %s", dwarf_errmsg(de));

/* Get the rest of children. */
do {
       die = die0;
       if (dwarf_siblingof(dbg, die, &die0, &de) == DW_DLV_ERROR)
               errx(EXIT_FAILURE, "dwarf_siblingof: %s",
                   dwarf_errmsg(de));
} while (die0 != NULL);
Ed
Sh ERRORS
These functions may fail with the following errors:
Bl -tag -width ".Bq Er DW_DLE_DIE_NO_CU_CONTEXT"
It Bq Er DW_DLE_ARGUMENT
Arguments
Fa dbg ,
Fa die
or
Fa ret_die
were
Dv NULL .
It Bq Er DW_DLE_DIE_NO_CU_CONTEXT
Argument
Fa dbg
was not associated with a compilation unit.
It Bq Er DW_DLE_NO_ENTRY
The descriptor denoted by argument
Fa die
had no child or sibling, or there was no DWARF debugging information
entry at the offset specified by argument
Va offset .
El
Sh SEE ALSO
Xr dwarf 3 ,
Xr dwarf_errmsg 3 ,
Xr dwarf_get_die_infotypes_flag 3 ,
Xr dwarf_next_cu_header 3

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