.. 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 #include #include #include #include #include #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.)