DWARF_LOCLIST_FROM_EXPR(3) | Library Functions Manual | DWARF_LOCLIST_FROM_EXPR(3)

# NAME

`dwarf_loclist_from_expr`, `dwarf_loclist_from_expr_a`, `dwarf_loclist_from_expr_b` —
translate DWARF location expression bytes

# LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

# SYNOPSIS

`#include <libdwarf.h>`

int
`dwarf_loclist_from_expr`(Dwarf_Debug dbg, Dwarf_Ptr bytes_in, Dwarf_Unsigned bytes_len, Dwarf_Locdesc **llbuf, Dwarf_Signed *listlen, Dwarf_Error *err);

int
`dwarf_loclist_from_expr_a`(Dwarf_Debug dbg, Dwarf_Ptr bytes_in, Dwarf_Unsigned bytes_len, Dwarf_Half addr_size, Dwarf_Locdesc **llbuf, Dwarf_Signed *listlen, Dwarf_Error *err);

int
`dwarf_loclist_from_expr_b`(Dwarf_Debug dbg, Dwarf_Ptr bytes_in, Dwarf_Unsigned bytes_len, Dwarf_Half addr_size, Dwarf_Half offset_size, Dwarf_Small version, Dwarf_Locdesc **llbuf, Dwarf_Signed *listlen, Dwarf_Error *error);

# DESCRIPTION

Function `dwarf_loclist_from_expr`() translates DWARF location expression bytes into a Dwarf_Locdesc descriptor. The size for address related data is taken to be the default address size for the object being read.

Argument dbg should reference a DWARF debug context allocated using dwarf_init(3).

Argument bytes_in should point to an array of DWARF location expression bytes.

Argument bytes_len should specify the number of the location expression bytes to be translated.

Argument llbuf should point to a location which will be set to a pointer to a returned Dwarf_Locdesc descriptor.

Argument listlen should point to a location which will hold the number of the Dwarf_Locdesc descriptors returned. In this case it is always set to 1.

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

Function `dwarf_loclist_from_expr_a`() is identical to function `dwarf_loclist_from_expr`(), except that it requires one additional argument addr_size, which specifies the address size to use when translating the location expression bytes.

Function `dwarf_loclist_from_expr_b`() is identical to function `dwarf_loclist_from_expr_a`() except that it requires two additional arguments for translating the location expression bytes. Argument offset_size specifies the offset size, and argument version specifies the DWARF version. These values are required to correctly translate the `DW_OP_GNU_implicit_pointer` opcode.

## Memory Management

The memory area used for the descriptor returned in argument llbuf is allocated by DWARF Access Library (libdwarf, -ldwarf). When the descriptor is no longer needed, application code should use function dwarf_dealloc(3) to free the memory area in two steps:

1. First, the array of Dwarf_Loc descriptors pointed to by the ld_s field of the Dwarf_Locdesc descriptor should be deallocated using the allocation type `DW_DLA_LOC_BLOCK`.
2. Next, the application should free the llbuf pointer using the allocation type `DW_DLA_LOCDESC`.

# RETURN VALUES

On success, these functions returns `DW_DLV_OK`. In case of an error, they return `DW_DLV_ERROR` and set the argument err.

# ERRORS

These functions may fail with the following errors:

[`DW_DLE_ARGUMENT`]
  One of the arguments dbg, bytes_in, llbuf or listlen was NULL.
[`DW_DLE_ARGUMENT`]
  Argument bytes_len was 0.
[`DW_DLE_ARGUMENT`]
  The value of argument addr_size was invalid.
[`DW_DLE_LOC_EXPR_BAD`]
  An unknown or invalid operation was found in the location expression bytes provided in argument bytes_in.
[`DW_DLE_MEMORY`]
  An out of memory condition was encountered during the execution of this function.

# SEE ALSO

dwarf(3), dwarf_dealloc(3), dwarf_loclist_n(3), dwarf_get_fde_info_for_all_regs3(3), dwarf_get_fde_info_for_cfa_reg3(3), dwarf_get_fde_info_for_reg3(3), dwarf_get_loclist_entry(3)

December 21, 2014 | NetBSD 9.1