NAME

dwarf_expand_frame_instructions —

expand frame instructions

LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

SYNOPSIS

#include <libdwarf.h>

int
dwarf_expand_frame_instructions(Dwarf_Cie cie, Dwarf_Ptr instructions, Dwarf_Unsigned len, Dwarf_Frame_Op **ret_ops, Dwarf_Signed *ret_opcnt, Dwarf_Error *error);

DESCRIPTION

Function dwarf_expand_frame_instructions() translates DWARF frame instruction bytes into an array of Dwarf_Frame_Op descriptors.

Argument cie should reference the CIE descriptor associated with the instructions to be translated.

Arugment instructions should point to an array of frame instruction bytes, as returned by the functions dwarf_get_cie_info(3) or dwarf_get_fde_instr_bytes(3).

Argument len should specify the number of the frame instruction bytes to be translated.

Argument ret_ops should point to a location that will be set to a pointer to an array of translated Dwarf_Frame_Op descriptors.

Argument ret_opcnt should point to a location that will hold the total number of the returned descriptors.

If argument err is not NULL, it will be used to store error information in case of an error.

Memory Management

The memory area used for the descriptor array returned in argument ret_ops is allocated by DWARF Access Library (libdwarf, -ldwarf). Application code should use function dwarf_dealloc(3) with type DW_DLA_FRAME_BLOCK to free the memory area when the descriptor array is no longer needed.

RETURN VALUES

Function dwarf_expand_frame_instructions() returns DW_DLV_OK when it succeeds. In case of an error, it returns DW_DLV_ERROR and sets the argument err.

EXAMPLES

To retrieve and expand the frame instructions for a given FDE descriptor, use:

Dwarf_Dbg dbg;
Dwarf_Cie cie;
Dwarf_Fde fde;
Dwarf_Ptr fde_inst;
Dwarf_Unsigned fde_instlen;
Dwarf_Frame_Op *ops;
Dwarf_Signed opcnt;
Dwarf_Error de;

/* ... assuming `dbg` references a valid DWARF debugging context,
  `fde` references a valid FDE descriptor and `cie` holds the CIE
  descriptor associated with the FDE descriptor ... */

if (dwarf_get_fde_instr_bytes(fde, &fde_inst, &fde_instlen,
    &de) != DW_DLV_OK)
	errx(EXIT_FAILURE, "dwarf_get_fde_instr_bytes failed: %s",
	    dwarf_errmsg(de));

if (dwarf_expand_frame_instructions(cie, fde_inst, fde_instlen,
    &ops, &opcnt, &de) != DW_DLV_OK)
	errx(EXIT_FAILURE,
	    "dwarf_expand_frame_instructions failed: %s",
	    dwarf_errmsg(de));

for (i = 0; i < opcnt; i++) {
	/* ... use ops[i] ... */
}

/* Free the memory area when no longer needed. */
dwarf_dealloc(dbg, ops, DW_DLA_FRAME_BLOCK);

ERRORS

Function dwarf_expand_frame_instructions() can fail with:

[DW_DLE_ARGUMENT]: One of the arguments cie, instructions, ret_ops or ret_opcnt was NULL.
[DW_DLE_ARGUMENT]: Argument len was 0.
[DW_DLE_MEMORY]: An out of memory condition was encountered during the execution of this function.
[DW_DLE_FRAME_INSTR_EXEC_ERROR]: An unknown instruction was found in the instruction bytes provided in argument instructions.