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GETAUXVAL(3)               Linux Programmer's Manual              GETAUXVAL(3)

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_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_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 Secu-
              rity  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 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.
SEE ALSO
       secure_getenv(3), ld-linux.so(8)
       The kernel source file Documentation/ABI/stable/vdso
COLOPHON
       This  page  is  part of release 3.53 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)