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.\" $Id: dwarf_child.3 3644 2018-10-15 19:55:01Z 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
.Ar die ,
and stores it in the location pointed to by argument
.Ar ret_die .
.Pp
Function
.Fn dwarf_siblingof
retrieves the sibling of the descriptor denoted by argument
.Ar die ,
and stores it in the location pointed to by argument
.Ar ret_die .
If argument
.Ar die
is 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
.Ar is_info
is non-zero, the function behaves identically to function
.Fn dwarf_siblingof .
If argument
.Ar is_info
is zero, the descriptor referred by argument
.Ar 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
.Ar ret_die .
If argument
.Ar is_info
is zero and argument
.Ar 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
.Ar offset
in the
.Dq .debug_info
section of the object associated with argument
.Ar dbg .
The returned descriptor is written to the location pointed to by argument
.Ar 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
.Ar offset
from either of the
.Dq .debug_info
and
.Dq .debug_types
sections of the object associated with argument
.Ar dbg .
If argument
.Ar 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
.Ar ret_die .
.Ss Memory Management
The memory area used for the
.Vt Dwarf_Die
descriptor returned in argument
.Ar 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
.Ar err ,
if it is not 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
.Ar 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
.Ar 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
.Ar dbg ,
.Ar die
or
.Ar ret_die
were NULL.
.It Bq Er DW_DLE_DIE_NO_CU_CONTEXT
Argument
.Ar dbg
was not associated with a compilation unit.
.It Bq Er DW_DLE_NO_ENTRY
The descriptor denoted by argument
.Ar 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