ELF_AUX_INFO(3)

💖 NAME 💖

okay so ELF_AUX_INFO(3) is the page for elf_aux_info(), and it's literally about extracting data from the elf auxiliary vector of the current process. bestie, it's giving “libc girlie asks the process for one specific auxv item” and honestly? iconic. 💅

🫶 LIBRARY 🫶

Standard C Library (libc, -lc) — yeah, she lives in libc. 🎀

✨ SYNOPSIS ✨

#include <sys/auxv.h>

int
elf_aux_info(int aux, void *buf, int buflen);

🌸 DESCRIPTION 🌸

okay so elf_aux_info() retrieves the auxiliary info vector requested in aux. the info gets stored into the provided buffer if it will fit. 🫶

The following values, defined in <sys/elf_common.h>, can be requested (corresponding buffer sizes are specified in parenthesis):

• AT_CANARY — the canary value for SSP. arbitrary sized buffer: as many bytes are returned as it fits into it, rest is zeroed. 🛡️
• AT_EXECPATH — the path of executed program (MAXPATHLEN). heads up: this may not be present if the process was initialized by fexecve(2) and the namecache no longer contains the file's name. 😭
• AT_HWCAP — CPU / hardware feature flags (sizeof(u_long)). 🔥
• AT_HWCAP2 — CPU / hardware feature flags (sizeof(u_long)). 🔥
• AT_HWCAP3 — CPU / hardware feature flags (sizeof(u_long)). 🔥
• AT_HWCAP4 — CPU / hardware feature flags (sizeof(u_long)). 🔥
• AT_NCPUS — number of CPUs (sizeof(int)). 🧚
• AT_OSRELDATE — the OSRELDATE of the kernel or jail the program is running on (sizeof(int)). 🌈
• AT_PAGESIZES — vector of page sizes (arbitrary sized buffer, as many elements of the pagesizes array are returned as it fits). 🦋
• AT_PAGESZ — page size in bytes (sizeof(int)). 📏
• AT_TIMEKEEP — pointer to VDSO timehands (for library internal use, sizeof(void *)). ⏰
• AT_USRSTACKBASE — top of the user stack for main thread. 🥞
• AT_USRSTACKLIM — limit for grow of the user stack for main thread. 🥞

🦋 RETURN VALUES 🦋

Returns zero on success, or an error number on failure. zero is the slay outcome, no cap. 🌟

💀 ERRORS 💀

• [EINVAL] — an unknown item was requested. 🙈
• [EINVAL] — the provided buffer was not the right size for the requested item. 😬
• [ENOENT] — the requested item is not available. 💔

🍓 HISTORY 🍓

The elf_aux_info() function appeared in FreeBSD 12.0. periodt. ✨

🌺 BUGS 🌺

Only a small subset of available auxiliary info vector items are accessible with this function. Some items require a "right-sized" buffer while others just require a "big enough" buffer. lowkey important — don't assume every auxv item is reachable, bestie. 💀

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💌 cute sign-off: source/version Debian, date June 24, 2025, manual ELF_AUX_INFO(3). catch u later, bestie — go extract that data and slay 💅✨