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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | BUGS | SEE ALSO | COLOPHON |
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getauxval(3) Library Functions Manual getauxval(3)
getauxval - retrieve a value from the auxiliary vector
Standard C library (libc, -lc)
#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 pointer to a string (PowerPC and MIPS only). On
PowerPC, this identifies the real platform; may differ
from AT_PLATFORM. On MIPS, this identifies the ISA level
(since Linux 5.7).
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
A pointer to a string containing the pathname used to
execute the 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_L1D_CACHEGEOMETRY
Geometry of the L1 data cache, encoded with the cache line
size in bytes in the bottom 16 bits and the cache
associativity in the next 16 bits. The associativity is
such that if N is the 16-bit value, the cache is N-way set
associative.
AT_L1D_CACHESIZE
The L1 data cache size.
AT_L1I_CACHEGEOMETRY
Geometry of the L1 instruction cache, encoded as for
AT_L1D_CACHEGEOMETRY.
AT_L1I_CACHESIZE
The L1 instruction cache size.
AT_L2_CACHEGEOMETRY
Geometry of the L2 cache, encoded as for
AT_L1D_CACHEGEOMETRY.
AT_L2_CACHESIZE
The L2 cache size.
AT_L3_CACHEGEOMETRY
Geometry of the L3 cache, encoded as for
AT_L1D_CACHEGEOMETRY.
AT_L3_CACHESIZE
The L3 cache 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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ getauxval() │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
GNU.
glibc 2.16.
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.
execve(2), secure_getenv(3), vdso(7), ld-linux.so(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
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2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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Linux man-pages 6.9.1 2024-05-02 getauxval(3)
Pages that refer to this page: execve(2), getunwind(2), getenv(3), proc_pid_auxv(5), libc(7), random(7), vdso(7), ld.so(8), systemd-coredump(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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