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);
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 TOarch_prctl() is a Linux/x86-64 extension and should not be used in pro‐
grams intended to be portable.
NOTESarch_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.
Context switches for 64-bit segment bases are rather expensive. It may
be a faster alternative to set a 32-bit base using a segment selector
by setting up an LDT with modify_ldt(2) or using the set_thread_area(2)
system call in kernel 2.5 or later. 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 2.7, 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.
SEE ALSOmmap(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/.
Linux 2007-12-26 ARCH_PRCTL(2)
