arch_prctl man page on CentOS

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ARCH_PRCTL(2)		   Linux Programmer's Manual		 ARCH_PRCTL(2)

NAME
       arch_prctl - set architecture specific thread state

SYNOPSIS
       #include <asm/prctl.h>

       #include <sys/prctl.h>

       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.

       Sub functions for x86-64 are:

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

       ARCH_GET_FS
	      Return the 64bit base value for the FS register of  the  current
	      thread in the unsigned long pointed to by the address parameter

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

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

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

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

       ARCH_SET_GS is disabled in some kernels.

       Context	switches  for 64bit segment bases are rather expensive. It may
       be a faster alternative to set a 32bit base using a segment selector by
       setting	up  an	LDT with modify_ldt(2) or using the set_thread_area(2)
       system call in a 2.5 kernel.  arch_prctl() is only needed when you want
       to  set	bases  that  are  larger than 4GB.  Memory in the first 2GB of
       address space can be allocated by  using	 mmap(2)  with	the  MAP_32BIT
       flag.

       As of version 2.3.5, glibc provides no prototype for arch_prctl().  You
       have to declare it yourself for now.  This may be fixed in future glibc
       versions.

       FS may be already used by the threading library.

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.

AUTHOR
       Man page written by Andi Kleen.

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

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

       AMD X86-64 Programmer's manual

Linux 2.4.20			  2003-02-02			 ARCH_PRCTL(2)
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