DWARF_LOCLIST(3)

💖 NAME 💖

okay so bestie, this is the DWARF_LOCLIST(3) page from the Library Functions Manual — iconic. It covers dwarf_loclist and dwarf_loclist_n, and their whole job is to retrieve DWARF location expression information. ✨

🫶 LIBRARY 🫶

DWARF Access Library (libdwarf, -ldwarf) — yes, that exact library, no cap. 💅

🌸 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. That’s the whole vibe. 🦋

⚠️ Deprecated notice, bestie: function dwarf_loclist() is deprecated. New application code should instead use function dwarf_loclist_n(). Don’t make it weird. 💀

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.

🍓 EXAMPLES 🍓

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);

💀 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.

🔥 SEE ALSO 🔥

dwarf(3), dwarf_dealloc(3), dwarf_get_loclist_entry(3), dwarf_loclist_from_expr(3), dwarf_loclist_from_expr_a(3) — go read the whole friend group. 👑

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xoxo, Debian — November 9, 2011 💖