GELF_GETNOTE(3)

✨ GELF_GETNOTE(3) ✨

okay bestie, welcome to the gelf_getnote page from the Libelf Programmer's Manual 💅 this one's a lil niche but it's SO useful if you're out here wrangling ELF notes, i promise.

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🌸 NAME 🌸

gelf_getnote — get class-independent note information at the supplied offset 🦋

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🎀 SYNOPSIS 🎀

#include <gelf.h>

size_t gelf_getnote (Elf_Data *data, size_t offset, GElf_Nhdr *result, size_t *name_offset, size_t *desc_offset);

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💖 DESCRIPTION 💖

so the whole vibe here is: you've got some data, you've got an offset, and this function goes and grabs the ELF note header sitting at that offset and drops it into a class-independent representation pointed at by result. slay.

then it fills in the note name offset and note descriptor offset — both relative to the start of data — into *name_offset and *desc_offset respectively. periodt.

the GElf_Nhdr fields n_namesz, n_descsz, and n_type tell you the note's name length, descriptor length and type, respectively. and here's the cute part: alignment and padding of the note data entry are handled automatically by this function 🧚 you don't gotta do it yourself, bestie.

if you want the full lore on ELF notes, go read elf(5). iykyk.

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🫶 PARAMETERS 🫶

• data — a pointer to an Elf_Data that's associated with a SHT_NOTE section or a PT_NOTE segment. also, data->d_type should be ELF_T_NHDR or ELF_T_NHDR8. (yeah it matters, don't skip it 🙈)
• offset — the offset of a note header within data.
• result — a pointer to a caller-provided GElf_Nhdr structure where the requested note header gets stored. result must not be NULL.
• name_offset — a pointer to a caller-provided size_t for storing the name offset of the requested note. this offset is relative to data->d_buf. name_offset must not be NULL.
• desc_offset — a pointer to a caller-provided size_t for storing the descriptor offset of the requested note. this offset is relative to data->d_buf. desc_offset must not be NULL.

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🔥 RETURN VALUE 🔥

on success? iconic behaviour: this function updates *result, *name_offset, and *desc_offset, and returns the offset of the next note ✨

if there are no notes remaining, then the return value will be greater than or equal to the d_size of data. that's your little "we're done here" signal, bestie.

on failure, this function returns zero and sets elf_errno. 😭

and one lil special case: if data is NULL, then zero is returned without setting elf_errno. no drama, no errno, just a zero. 💀

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🌈 EXAMPLE 🌈

size_t offset = 0;
GElf_Nhdr nhdr;
size_t name_offset;
size_t desc_offset;
while (offset < data->d_size
       && (offset = gelf_getnote (data, offset,
                                  &nhdr, &name_offset, &desc_offset)) > 0)
  {
    const char *name = nhdr.n_namesz == 0 ? "" : data->d_buf + name_offset;
    const char *desc = nhdr.n_descsz == 0 ? "" : data->d_buf + desc_offset;

    /* Process note here.  name and desc are not guaranteed to be
       zero-terminated.  The presence of null characters should be
       verified using n_namesz and n_descsz.  */
    [...]
  }

okay real talk for a sec: name and desc are not guaranteed to be zero-terminated. do not just strlen() them and hope for the best, that's how you get a vibe check you did NOT ask for. verify the presence of null characters using n_namesz and n_descsz. 🚨

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👑 SEE ALSO 👑

libelf(3), elf(5)

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⭐ ATTRIBUTES ⭐

• gelf_getnote() — Thread safety: MT-Safe 💅

(no table energy today bestie, just the facts: this one is MT-Safe, go wild.)

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🍓 REPORTING BUGS 🍓

found a bug? don't suffer in silence, report it to <elfutils-devel@sourceware.org> or hit up https://sourceware.org/bugzilla/ 🫶

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💜 HISTORY 💜

gelf_getnote first appeared in elfutils 0.130.

and heads up — this function is an elfutils libelf extension and may not be available in other libelf implementations. so if you're porting somewhere else and it's missing, that's why, not you. 🧚

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okay that's the whole page, you ate that. 💖 this was from the Libelf manual, dated 2025-12-31 — go forth and read your notes, bestie ✨🎀🦋