DWARF_LOCLIST(3)

DWARF_LOCLIST(3) | Library Functions Manual | DWARF_LOCLIST(3)

# NAME

`dwarf_loclist`, `dwarf_loclist_n` —
retrieve DWARF location expression information

# LIBRARY

DWARF Access Library (libdwarf, -ldwarf)

# SYNOPSIS

`#include <libdwarf.h>`

int
`dwarf_loclist`(Dwarf_Attribute at, Dwarf_Locdesc **llbuf, Dwarf_Signed *listlen, Dwarf_Error *error);

int
`dwarf_loclist_n`(Dwarf_Attribute at, Dwarf_Locdesc ***llbuf, Dwarf_Signed *listlen, Dwarf_Error *error);

# DESCRIPTION

These functions retrieve the location expressions associated with a DWARF attribute.

Note: function `dwarf_loclist`() is deprecated. New application code should instead use function `dwarf_loclist_n`()

Function `dwarf_loclist_n`() retrieves the list of location expressions associated with a DWARF attribute. Argument at should reference a valid DWARF attribute. Argument llbuf should point to a location which will hold a returned array of pointers to Dwarf_Locdesc descriptors. Argument listlen should point to a location which will be set to the number of elements contained in the returned array. If argument err is not NULL, it will be used to store error information in case of an error.

Function `dwarf_loclist`() retrieves the first location expression associated with an attribute. Argument at should reference a valid DWARF attribute. Argument llbuf should point to a location which will hold the returned pointer to a Dwarf_Locdesc descriptor. Argument listlen should point to a location which will be always set to 1. If argument err is not NULL, it will be used to store error information in case of an error.

Dwarf_Locdesc descriptors are defined in the header file `<libdwarf.h>`, and consist of following fields:

ld_lopc
  The lowest program counter address covered by the descriptor. This field will be set to 0 if the descriptor is not associated with an address range.
ld_hipc
  The highest program counter address covered by the descriptor. This field will be set to 0 if the descriptor is not associated with an address range.
ld_cents
  The number of entries returned in ld_s field.
ld_s
  Pointer to an array of Dwarf_Loc descriptors.

Each Dwarf_Loc descriptor represents one operation of a location expression. These descriptors are defined in the header file `<libdwarf.h>`, and consist of following fields:

lr_atom
  The operator name, one of the `DW_OP_*` constants defined in the header file `<dwarf.h>`.
lr_number
  The first operand of this operation.
lr_number2
  The second operand of this operation.
lr_offset
  The byte offset of this operation within the containing location expression.

## Memory Management

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

1. First, the ld_s field of each Dwarf_Locdesc descriptor should be deallocated using the allocation type `DW_DLA_LOC_BLOCK`.
2. Then, the application should free each Dwarf_Locdesc descriptor using the allocation type `DW_DLA_LOCDESC`.
3. Finally, the llbuf pointer should be deallocated using the allocation type `DW_DLA_LIST`.

# 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 can fail with:

[`DW_DLE_ARGUMENT`]
  One of the arguments at, llbuf or listlen was NULL.
[`DW_DLE_ARGUMENT`]
  The attribute provided by argument at does not contain a location expression or is not associated with a location expression list.

# EXAMPLE

To retrieve the location list associated with an attribute, use:

    Dwarf_Attribute at;
    Dwarf_Locdesc **llbuf;
    Dwarf_Signed lcnt;
    Dwarf_Loc *lr;
    Dwarf_Error de;
    int i;

    if (dwarf_loclist_n(at, &llbuf, &lcnt, &de) != DW_DLV_OK)
    	errx(EXIT_FAILURE, "dwarf_loclist_n failed: %s",
    	    dwarf_errmsg(de));

    for (i = 0; i < lcnt; i++) {
    	/* ... Use llbuf[i] ... */
    	for (j = 0; (Dwarf_Half) j < llbuf[i]->ld_cents; j++) {
    		lr = &llbuf[i]->ld_s[j];
    		/* ... Use each Dwarf_Loc descriptor ... */
    	}
    	dwarf_dealloc(dbg, llbuf[i]->ld_s, DW_DLA_LOC_BLOCK);
    	dwarf_dealloc(dbg, llbuf[i], DW_DLA_LOCDESC);
    }
    dwarf_dealloc(dbg, llbuf, DW_DLA_LIST);

# SEE ALSO

dwarf(3), dwarf_dealloc(3), dwarf_loclist_from_expr(3), dwarf_loclist_from_expr_a(3), dwarf_get_loclist_entry(3)

November 9, 2011 | NetBSD 9.4