getauxval

       #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_PLAT-
              FORM (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_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 it's 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)).   Alterna-
              tively,  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
       attributes(7).

       +------------+---------------+---------+
       |Interface   | Attribute     | Value   |
       +------------+---------------+---------+
       |getauxval() | Thread safety | MT-Safe |
       +------------+---------------+---------+
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  environ-
       ment  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.

BUGS
       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 zer0.

SEE ALSO
       secure_getenv(3), vdso(7), ld-linux.so(8)

COLOPHON
       This page is part of release 4.04 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
       http://www.kernel.org/doc/man-pages/.

GNU                               2015-12-05                      GETAUXVAL(3)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2019 Hurricane Electric. All Rights Reserved.