Ubuntu Manpage: getauxval - retrieve a value from the auxiliary vector

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_HWCAP2 (since glibc 2.18)
Further machine-dependent hints about processor capabilities.

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)). 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

       ENOENT (since glibc 2.19)
              No entry corresponding to type could be found in the auxiliary vector.

VERSIONS

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

ATTRIBUTES

       For an explanation of the terms used in this section, see 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 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.

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.

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/.