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1.. SPDX-License-Identifier: GPL-2.02 3==================================4x86-specific ELF Auxiliary Vectors5==================================6 7This document describes the semantics of the x86 auxiliary vectors.8 9Introduction10============11 12ELF Auxiliary vectors enable the kernel to efficiently provide13configuration-specific parameters to userspace. In this example, a program14allocates an alternate stack based on the kernel-provided size::15 16 #include <sys/auxv.h>17 #include <elf.h>18 #include <signal.h>19 #include <stdlib.h>20 #include <assert.h>21 #include <err.h>22 23 #ifndef AT_MINSIGSTKSZ24 #define AT_MINSIGSTKSZ 5125 #endif26 27 ....28 stack_t ss;29 30 ss.ss_sp = malloc(ss.ss_size);31 assert(ss.ss_sp);32 33 ss.ss_size = getauxval(AT_MINSIGSTKSZ) + SIGSTKSZ;34 ss.ss_flags = 0;35 36 if (sigaltstack(&ss, NULL))37 err(1, "sigaltstack");38 39 40The exposed auxiliary vectors41=============================42 43AT_SYSINFO is used for locating the vsyscall entry point. It is not44exported on 64-bit mode.45 46AT_SYSINFO_EHDR is the start address of the page containing the vDSO.47 48AT_MINSIGSTKSZ denotes the minimum stack size required by the kernel to49deliver a signal to user-space. AT_MINSIGSTKSZ comprehends the space50consumed by the kernel to accommodate the user context for the current51hardware configuration. It does not comprehend subsequent user-space stack52consumption, which must be added by the user. (e.g. Above, user-space adds53SIGSTKSZ to AT_MINSIGSTKSZ.)54