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Manual Pages  — DWARF_CHILD

NAME

dwarf_child, dwarf_offdie, dwarf_offdie_b, dwarf_siblingof, dwarf_siblingof_b – retrieve DWARF Debugging Information Entry descriptors

CONTENTS

LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

SYNOPSIS

#include <libdwarf.h>

int
dwarf_child(Dwarf_Die die, Dwarf_Die *ret_die, Dwarf_Error *err);

int
dwarf_offdie(Dwarf_Debug dbg, Dwarf_Off offset, Dwarf_Die *ret_die, Dwarf_Error *err);

int
dwarf_offdie_b(Dwarf_Debug dbg, Dwarf_Off offset, Dwarf_Bool is_info, Dwarf_Die *ret_die, Dwarf_Error *err);

int
dwarf_siblingof(Dwarf_Debug dbg, Dwarf_Die die, Dwarf_Die *ret_die, Dwarf_Error *err);

int
dwarf_siblingof_b(Dwarf_Debug dbg, Dwarf_Die die, Dwarf_Die *ret_die, Dwarf_Bool is_info, Dwarf_Error *err);

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 "child" and "sibling" links; see dwarf(3) for more information. DWARF Debugging Information Entry descriptors are represented by the Dwarf_Die opaque type.

Function dwarf_child() retrieves the child of descriptor denoted by argument die, and stores it in the location pointed to by argument ret_die.

Function dwarf_siblingof() retrieves the sibling of the descriptor denoted by argument die, and stores it in the location pointed to by argument ret_die. If argument die is NULL, the first debugging information entry descriptor for the current compilation unit will be returned. This function and function dwarf_child() may be used together to traverse the tree of debugging information entry descriptors for a compilation unit.

Function dwarf_siblingof_b() is identical to the function dwarf_siblingof() except that it can retrieve the sibling descriptor from either the current compilation unit or type unit. If argument is_info is non-zero, the function behaves identically to function dwarf_siblingof(). If argument is_info is zero, the descriptor referred by argument 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 ret_die. If argument is_info is zero and argument die is NULL, the first debugging information entry descriptor for the current type unit will be returned.

Function dwarf_offdie() retrieves the debugging information entry descriptor at global offset offset in the ".debug_info" section of the object associated with argument dbg. The returned descriptor is written to the location pointed to by argument ret_die.

Function dwarf_offdie_b() is identical to the function dwarf_offdie() except that it can retrieve the debugging information entry descriptor at global offset offset from either of the ".debug_info" and ".debug_types" sections of the object associated with argument dbg. If argument is_info is non-zero, the function will retrieve the debugging information entry from the ".debug_info" section, otherwise the function will retrieve the debugging information entry from the ".debug_types" section. The returned descriptor is written to the location pointed to by argument ret_die.

Memory Management

The memory area used for the Dwarf_Die descriptor returned in argument ret_die is allocated by the DWARF Access Library (libdwarf, -ldwarf)Application code should use function dwarf_dealloc() with the allocation type DW_DLA_DIE to free the memory area when the Dwarf_Die descriptor is no longer needed.

RETURN VALUES

These functions return the following values:
[DW_DLV_OK] The call succeeded.
[DW_DLV_ERROR] The requested operation failed. Additional information about the error encountered will be recorded in argument err, if it is not NULL.
[DW_DLV_NO_ENTRY] For functions dwarf_child(), dwarf_siblingof() and dwarf_siblingof_b(), the descriptor denoted by argument die did not have a child or sibling.

For functions dwarf_offdie() and dwarf_offdie_b(), there was no debugging information entry at the offset specified by argument offset.

EXAMPLES

To retrieve the first DWARF Debugging Information Entry descriptor for the first compilation unit associated with a Dwarf_Debug instance, and to traverse all its children, use: 
Dwarf_Debug dbg;
Dwarf_Die die, die0;
Dwarf_Error de;


amp;... 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);

ERRORS

These functions may fail with the following errors:
[DW_DLE_ARGUMENT] Arguments dbg, die or ret_die were NULL.
[DW_DLE_DIE_NO_CU_CONTEXT] Argument dbg was not associated with a compilation unit.
[DW_DLE_NO_ENTRY] The descriptor denoted by argument die had no child or sibling, or there was no DWARF debugging information entry at the offset specified by argument offset.

SEE ALSO

dwarf(3), dwarf_errmsg(3), dwarf_get_die_infotypes_flag(3), dwarf_next_cu_header(3)
DWARF_CHILD (3) December 21, 2014
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“ As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs. ”
— Maurice Wilkes