DWARF_GET_RELOCATION_INFO(3)

✨ NAME ✨

dwarf_get_relocation_info — retrieve generated relocation arrays

Okay bestie, this page is from the Library Functions Manual, and it's all about getting those relocation arrays that libdwarf generated for you. Slay.

💖 LIBRARY 💖

DWARF Access Library (libdwarf, -ldwarf)

🎀 SYNOPSIS 🎀

#include <libdwarf.h>

int
dwarf_get_relocation_info(Dwarf_P_Debug dbg,
    Dwarf_Signed *elf_section_index, Dwarf_Signed *elf_section_link,
    Dwarf_Unsigned *reloc_entry_count, Dwarf_Relocation_Data *reloc_buf,
    Dwarf_Error *err);

🦋 DESCRIPTION 🦋

Okay so here's the tea, bestie. dwarf_get_relocation_info() is the function you call to retrieve the relocation arrays that were generated by a prior call to dwarf_transform_to_disk_form(3). No cap.

Each call to this function snags the next available relocation array. So you're gonna want to call it repeatedly to get all of them. The total number of generated relocation arrays you can retrieve is available via dwarf_get_relocation_info_count(3). Iconic.

Argument dbg should reference a DWARF producer instance allocated using dwarf_producer_init(3) in sequence. or dwarf_producer_init_b(3). The DW_DLC_SYMBOLIC_RELOCATIONS flag should have been set on that DWARF producer instance.

💅 Lowkey important: if that DW_DLC_SYMBOLIC_RELOCATIONS flag wasn't set, you're gonna get DW_DLV_NO_ENTRY back. Not me warning you.

Argument elf_section_index should point to a location that will be set to the ELF section index of the relocation section to which the retrieved relocation array belongs. It's giving "where does this even go" energy.

Argument elf_section_link should point to a location that will be set to the section index of the ELF section to which the retrieved relocation array applies. Periodt.

Argument reloc_entry_count should point to a location that will be set to the total number of relocation entries contained in the relocation array. So you know how many you're working with.

Argument reloc_buf should point to a location that will be set to a pointer to the retrieved array of relocation entries. That's your actual data, bestie.

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

The retrieved relocation entries are described using structure Dwarf_Relocation_Data_s, which is defined in the header file <libdwarf.h>:

typedef struct Dwarf_Relocation_Data_s {
        unsigned char drd_type;
        unsigned char drd_length;
        Dwarf_Unsigned drd_offset;
        Dwarf_Unsigned drd_symbol_index;
} *Dwarf_Relocation_Data;

Struct Dwarf_Relocation_Data_s consists of the following fields:

• drd_type — the type code of the relocation entry. The Dwarf_Rel_Type enumeration defined in the header file <libdwarf.h> specifies legal values for this field. It's giving "type check" realness.
• drd_length — the size in bytes of the field to be relocated. Basically how chunky it is.
• drd_offset — the section-relative offset of the field to be relocated. Where it lives, lowkey.
• drd_symbol_index — the symbol index associated with the relocation entry. The main character symbol, if you will.

🧚 Memory Management 🧚

The memory area used for the relocation arrays is managed by the DWARF Access Library (libdwarf, -ldwarf). So you don't have to free it yourself, bestie. The function dwarf_producer_finish() may be used to release it, along with other resources associated with the producer instance. Slay.

🌈 RETURN VALUES 🌈

On success, dwarf_get_relocation_info() returns DW_DLV_OK. It returns DW_DLV_NO_ENTRY if there were no more relocation arrays to retrieve, or if the flag DW_DLC_SYMBOLIC_RELOCATIONS was not set on the producer instance. In case of an error, dwarf_get_relocation_info() returns DW_DLV_ERROR and sets the argument err. That's the vibe check.

💀 EXAMPLES 💀

To generate relocation entries and retrieve them, use this:

Dwarf_P_Debug dbg;
Dwarf_Relocation_Data buf;
Dwarf_Signed count, index, link;
Dwarf_Unsigned reloc_cnt, entry_cnt;
Dwarf_Error de;
int version, i, j;

/*
 * Assume that dbg refers to a DWARF producer instance created
 * created with DW_DLC_SYMBOLIC_RELOCATIONS flag set and that
 * application code has added DWARF debugging information
 * to the producer instance.
 */
if ((count = dwarf_transform_to_disk_form(dbg, &de)) ==
    DW_DLV_NOCOUNT) {
        warnx("dwarf_transform_to_disk_form failed: %s",
            dwarf_errmsg(-1));
        return;
}

/* ... process generated section byte streams ... */
if (dwarf_get_relocation_info_count(dbg, &reloc_cnt, &version, &de) !=
    DW_DLV_OK) {
        warnx("dwarf_get_relocation_info_count failed: %s",
            dwarf_errmsg(-1));
        return;
}

for (i = 0; (Dwarf_Unsigned) i < reloc_cnt; i++) {
        if (dwarf_get_relocation_info(dbg, &index, &link, &entry_cnt,
            &buf, &de) != DW_DLV_OK) {
                warnx("dwarf_get_relocation_info failed: %s",
                    dwarf_errmsg(-1));
                continue;
        }
        for (j = 0; (Dwarf_Unsigned) j < entry_cnt; j++) {
                /* ...use each reloc data in buf[j]... */
        }
}

dwarf_producer_finish(dbg, &de);

🙈 ERRORS 🙈

Function dwarf_get_relocation_info() can fail with these:

• [DW_DLE_ARGUMENT] — one of the arguments dbg, elf_section_index, elf_section_link, reloc_entry_count or reloc_buf was NULL. Not me forgetting an argument. 💀
• [DW_DLE_NO_ENTRY] — there were no more ELF relocation arrays to retrieve. You've collected them all, bestie.
• [DW_DLE_NO_ENTRY] — the flag DW_DLC_SYMBOLIC_RELOCATIONS was not set on the producer instance. Oops.
• [DW_DLE_NO_ENTRY] — function dwarf_transform_to_disk_form(3) was not called prior to calling function dwarf_get_relocation_info(). You gotta do the first step first, fr fr.

🫶 SEE ALSO 🫶

dwarf(3), dwarf_get_relocation_info_count(3), dwarf_producer_finish(3), dwarf_producer_init(3), dwarf_producer_init_b(3), dwarf_reset_section_bytes(3), dwarf_transform_to_disk_form(3)

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And that's the page, bestie! This gem was brought to you by Debian, dated September 3, 2011, and it's the DWARF_GET_RELOCATION_INFO(3) manual page. Stay iconic. 💅✨