ARCH_PRCTL

Section: Linux Programmer's Manual (2)
Updated: 2007-12-26
Index Return to Main Contents

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 TO

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

NOTES

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

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.

COLOPHON

This page is part of release 3.22 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/.

This document was created by man2html, using the manual pages.
Time: 05:33:03 GMT, December 24, 2015