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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/x86/elf_auxvec.rst | 53 | ||||
| -rw-r--r-- | Documentation/x86/index.rst | 1 |
2 files changed, 54 insertions, 0 deletions
diff --git a/Documentation/x86/elf_auxvec.rst b/Documentation/x86/elf_auxvec.rst new file mode 100644 index 000000000000..18e4744717f9 --- /dev/null +++ b/Documentation/x86/elf_auxvec.rst @@ -0,0 +1,53 @@ +.. 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.) diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 0004f5d2283e..383048396336 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -36,3 +36,4 @@ x86-specific Documentation sva sgx features + elf_auxvec |