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>
intarch_prctl(intcode,unsignedlongaddr)
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 FS 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.
No prototype for arch_prctl in glibc 2.2. You have to declare it your-
self for now. This will be fixed in future glibc versions.
FS may be already used by the threading library.
ERRORS
EINVAL code is not a valid subcommand.
EPERM addr is outside the process address space.
EFAULT addr points to an unmapped address or is outside the process
address space.
AUTHOR
Man page written by Andi Kleen.
CONFORMANCE
arch_prctl is a Linux/x86-64 extension and should not be used in pro-
grams intended to be portable.
SEEALSO
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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