SYNOPSIS
       #include <asm/prctl.h>
       #include <sys/prctl.h>

       int arch_prctl(int code, unsigned long addr);
       int arch_prctl(int code, unsigned long *addr);

DESCRIPTION
       The  arch_prctl() function sets architecture-specific process or thread
       state.  code selects a subfunction and passes argument addr to it; addr
       is  interpreted as either an unsigned long for the "set" operations, or
       as an unsigned long *, for the "get" operations.

       Sub functions for x86-64 are:

       ARCH_SET_FS
              Set the 64-bit base for the FS register to addr.

       ARCH_GET_FS
              Return the 64-bit base value for the FS register of the  current
              thread in the unsigned long pointed to by addr.

       ARCH_SET_GS
              Set the 64-bit base for the GS register to addr.

       ARCH_GET_GS
              Return  the 64-bit base value for the GS register of the current
              thread in the unsigned long pointed to by addr.

RETURN VALUE
       On success, arch_prctl() returns 0; on error, -1 is returned, and errno
       is set to indicate the error.

ERRORS
       EFAULT addr  points  to  an  unmapped address or is outside the process
              address space.

       EINVAL code is not a valid subcommand.

       EPERM  addr is outside the process address space.

CONFORMING TO
       arch_prctl() is a Linux/x86-64 extension and should not be used in pro-
       grams intended to be portable.

NOTES
       arch_prctl() is only supported on Linux/x86-64 for 64-bit programs cur-
       rently.

       The 64-bit base changes when a new 32-bit segment selector is loaded.

       ARCH_SET_GS is disabled in some kernels.

       FS may be already used by the threading library.

SEE ALSO
       mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)

       AMD X86-64 Programmer's manual

COLOPHON
       This page is part of release 3.23 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/.