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