NAME

       getauxval - retrieve a value from the auxiliary vector

SYNOPSIS

       #include <sys/auxv.h>

       unsigned long getauxval(unsigned long type);

DESCRIPTION

       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
              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
              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 /proc/cpuinfo.

       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 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 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.

RETURN VALUE

       On success, getauxval() returns the value corresponding to type.  If type is not found, 0 is returned.

ERRORS

       No errors are diagnosed.

VERSIONS

       The getauxval() function was added to glibc in version 2.16.

CONFORMING TO

       This function is a nonstandard glibc extension.

NOTES

       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.

SEE ALSO

       secure_getenv(3), ld-linux.so(8)

       The kernel source file Documentation/ABI/stable/vdso

COLOPHON

       This page is part of release 3.54 of the Linux man-pages project.  A  description  of  the  project,  and
       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

GNU                                                2012-11-07                                       GETAUXVAL(3)