Hello Richard et al, I wrote a man page for the getauxval(3) function that you added in glibc 2.16. Would you be willing to take a look and correct anything that seems amiss? Cheers, Michael .\" Copyright 2012 Michael Kerrisk <mtk.manpages@xxxxxxxxx> .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" See also https://lwn.net/Articles/519085/ .\" .TH GETAUXVAL 3 2012-11-05 "GNU" "Linux Programmer's Manual" .SH NAME getauxval \- retrieve a value from the auxiliary vector .SH SYNOPSIS .nf .B #include <sys/auxv.h> .sp .BI "unsigned long getauxval(unsigned long " type ); .fi .SH DESCRIPTION The .BR getauxval () function retrieves values from the auxiliary vector, a mechanism that the kernel's ELF binary loader uses to pass certain information to user space when a program is executed. Each entry in the auxiliary vector consists of a pair of values: a type that identifies what this entry represents, and a value for that type. Given the argument .IR type , .BR getauxval () returns the corresponding value. The value returned for each .I type is given in the following list. Not all .I type values are present on all architectures. .TP .BR AT_BASE The base address of the program interpreter (usually, the dynamic linker). .TP .BR AT_BASE_PLATFORM A string identifying the real platform; may differ from .BR AT_PLATFORM (PowerPC only). .TP .BR AT_CLKTCK The frequency with which .BR times (2) counts. This value can also be obtained via .IR sysconf(_SC_CLK_TCK) . .TP .BR AT_DCACHEBSIZE The data cache block size. .TP .BR AT_EGID The effective group ID of the thread. .TP .BR AT_ENTRY The entry address of the executable. .TP .BR AT_EUID The effective user ID of the thread. .TP .BR AT_EXECFD File descriptor of program. .TP .BR AT_EXECFN Pathname used to execute program. .TP .BR AT_FLAGS Flags (unused). .TP .BR AT_FPUCW Used FPU control word (SuperH architecture only). This gives some information about the FPU initialization performed by the kernel. .TP .BR AT_GID The real group ID of the thread. .TP .BR AT_HWCAP A pointer to a multibyte mask of bits whose settings indicate detailed processor capabilities. The contents of the bit mask are hardware dependent (for example, see the kernel source file .IR arch/x86/include/asm/cpufeature.h for details relating to the Intel x86 architecture). A human-readable version of the same information is available via .IR /proc/cpuinfo . .TP .BR AT_ICACHEBSIZE The instruction cache block size. .\" .TP .\" .BR AT_IGNORE .\" .TP .\" .BR AT_IGNOREPPC .\" .TP .\" .BR AT_NOTELF .TP .BR AT_PAGESZ The system page size (the same value returned by .IR sysconf(_SC_PAGESIZE) . .TP .BR AT_PHDR The address of the program headers of the executable. .TP .BR AT_PHENT The size of program header entry. .TP .BR AT_PHNUM The number of program headers. .TP .BR AT_PLATFORM A pointer to a string that identifies the hardware platform that the program is running on. The dynamic linker uses this in the interpretation of .IR rpath values. .TP .BR AT_RANDOM The address of sixteen bytes containing a random value. .TP .BR AT_SECURE Has a nonzero value if this executable should be treated securely. Most commonly, a nonzero value indicates that the process is executing a set-user-ID or set-group-ID program; alternatively, a nonzero value may be triggered by a Linux Security Module. When this value is nonzero, the dynamic linker disables the use of certain environment variables (see .BR ld-linux.so (8)) and glibc changes other aspects of its behavior. (See also .BR secure_getenv (3).) .TP .BR AT_SYSINFO The entry point to the system call function in the VDSO. Not present/needed on all architectures (e.g., absent on x86-64). .TP .BR AT_SYSINFO_EHDR The address of a page containing the Virtual Dynamic Shared Object (VDSO) that the kernel creates in order to provide fast implementations of certain system calls. .TP .BR AT_UCACHEBSIZE The unified cache block size. .TP .BR AT_UID The real user ID of the thread. .SH RETURN VALUE On success, .BR getauxval () returns the value corresponding to .IR type . If .I type is not found, 0 is returned. .SH ERRORS No errors are diagnosed. .SH VERSIONS The .BR getauxval () function was added to glibc in version 2.16. .SH "CONFORMING TO" This function is a nonstandard glibc extension. .SH NOTES The primary consumer of the information in the auxiliary vector is the dynamic linker .BR ld-linux.so (8). The auxiliary vector is a convenient and efficient shortcut that allows the kernel to communicate a certain set of standard information that the dynamic linker usually or always needs. In some cases, the same information could be obtained by system calls, but using the auxiliary vector is cheaper. The auxiliary vector resides just above the argument list and environment in the process address space. The auxiliary vector supplied to a program can be viewed by setting the .B LD_SHOW_AUXV environment variable when running a program: $ LD_SHOW_AUXV=1 sleep 1 The auxiliary vector of any process can (subject to file permissions) be obtained via .IR /proc/PID/auxv ; see .BR proc (5) for more information. .SH "SEE ALSO" .BR secure_getenv (3), .BR ld-linux.so (8) The kernel source file .IR Documentation/ABI/stable/vdso -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
