|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
GETAUXVAL(3) Linux Programmer's Manual GETAUXVAL(3)
getauxval - retrieve a value from the auxiliary vector
#include <sys/auxv.h>
unsigned long getauxval(unsigned long type);
The 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 type, getauxval() returns the corresponding
value.
The value returned for each type is given in the following list. Not
all type values are present on all architectures.
AT_BASE
The base address of the program interpreter (usually, the
dynamic linker).
AT_BASE_PLATFORM
A string identifying the real platform; may differ from
AT_PLATFORM (PowerPC only).
AT_CLKTCK
The frequency with which times(2) counts. This value can also
be obtained via sysconf(_SC_CLK_TCK).
AT_DCACHEBSIZE
The data cache block size.
AT_EGID
The effective group ID of the thread.
AT_ENTRY
The entry address of the executable.
AT_EUID
The effective user ID of the thread.
AT_EXECFD
File descriptor of program.
AT_EXECFN
Pathname used to execute program.
AT_FLAGS
Flags (unused).
AT_FPUCW
Used FPU control word (SuperH architecture only). This gives
some information about the FPU initialization performed by the
kernel.
AT_GID The real group ID of the thread.
AT_HWCAP
An architecture and ABI dependent bit-mask whose settings
indicate detailed processor capabilities. The contents of the
bit mask are hardware dependent (for example, see the kernel
source file arch/x86/include/asm/cpufeature.h for details
relating to the Intel x86 architecture; the value returned is
the first 32-bit word of the array described there). A human-
readable version of the same information is available via
/proc/cpuinfo.
AT_HWCAP2 (since glibc 2.18)
Further machine-dependent hints about processor capabilities.
AT_ICACHEBSIZE
The instruction cache block size.
AT_PAGESZ
The system page size (the same value returned by
sysconf(_SC_PAGESIZE)).
AT_PHDR
The address of the program headers of the executable.
AT_PHENT
The size of program header entry.
AT_PHNUM
The number of program headers.
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 rpath values.
AT_RANDOM
The address of sixteen bytes containing a random value.
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 binary (so
that its real and effective UIDs or GIDs differ from one
another), or that it gained capabilities by executing a binary
file that has capabilities (see capabilities(7)).
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
ld-linux.so(8)) and glibc changes other aspects of its
behavior. (See also secure_getenv(3).)
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).
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.
AT_UCACHEBSIZE
The unified cache block size.
AT_UID The real user ID of the thread.
On success, getauxval() returns the value corresponding to type. If
type is not found, 0 is returned.
ENOENT (since glibc 2.19)
No entry corresponding to type could be found in the auxiliary
vector.
The getauxval() function was added to glibc in version 2.16.
For an explanation of the terms used in this section, see
attributes(7).
┌────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────┼───────────────┼─────────┤
│getauxval() │ Thread safety │ MT-Safe │
└────────────┴───────────────┴─────────┘
This function is a nonstandard glibc extension.
The primary consumer of the information in the auxiliary vector is
the dynamic linker 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 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 /proc/[pid]/auxv; see proc(5) for more information.
Before the addition of the ENOENT error in glibc 2.19, there was no
way to unambiguously distinguish the case where type could not be
found from the case where the value corresponding to type was zero.
secure_getenv(3), vdso(7), ld-linux.so(8)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2016-07-17 GETAUXVAL(3)
Pages that refer to this page: getunwind(2), getenv(3), proc(5), libc(7), random(7), vdso(7), ld.so(8)