.. SPDX-License-Identifier: GPL-2.0
==================================
x86-specific ELF Auxiliary Vectors
==================================
This document describes the semantics of the x86 auxiliary vectors.
Introduction
============
ELF Auxiliary vectors enable the kernel to efficiently provide
configuration-specific parameters to userspace. In this example, a program
allocates an alternate stack based on the kernel-provided size::
#include <sys/auxv.h>
#include <elf.h>
#include <signal.h>
#include <stdlib.h>
#include <assert.h>
#include <err.h>
#ifndef AT_MINSIGSTKSZ
#define AT_MINSIGSTKSZ 51
#endif
....
stack_t ss;
ss.ss_sp = malloc(ss.ss_size);
assert(ss.ss_sp);
ss.ss_size = getauxval(AT_MINSIGSTKSZ) + SIGSTKSZ;
ss.ss_flags = 0;
if (sigaltstack(&ss, NULL))
err(1, "sigaltstack");
The exposed auxiliary vectors
=============================
AT_SYSINFO is used for locating the vsyscall entry point. It is not
exported on 64-bit mode.
AT_SYSINFO_EHDR is the start address of the page containing the vDSO.
AT_MINSIGSTKSZ denotes the minimum stack size required by the kernel to
deliver a signal to user-space. AT_MINSIGSTKSZ comprehends the space
consumed by the kernel to accommodate the user context for the current
hardware configuration. It does not comprehend subsequent user-space stack
consumption, which must be added by the user. (e.g. Above, user-space adds
SIGSTKSZ to AT_MINSIGSTKSZ.)
