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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,  getaux-
       val() 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 usu-
       ally 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 3.53 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)
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