Section (2) arch_prctl
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
arch_prctl
() 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.
Subfunctions for x86-64 are:
ARCH_SET_FS
-
Set the 64-bit base for the
FS
register toaddr
. ARCH_GET_FS
-
Return the 64-bit base value for the
FS
register of the current thread in the unsigned long pointed to byaddr
. ARCH_SET_GS
-
Set the 64-bit base for the
GS
register toaddr
. ARCH_GET_GS
-
Return the 64-bit base value for the
GS
register of the current thread in the unsigned long pointed to byaddr
.
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 supported
only 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. As an optimization, if a 32-bit TLS base address
is used, arch_prctl
() may use a
real TLS entry as if set_thread_area(2) had been
called, instead of manipulating the segment base register
directly. Memory in the first 2 GB of address space can be
allocated by using mmap(2) with the
MAP_32BIT
flag.
Because of the aforementioned optimization, using
arch_prctl
() and set_thread_area(2) in the
same thread is dangerous, as they may overwrite each other_zsingle_quotesz_s
TLS entries.
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. Programs that use ARCH_SET_FS
directly are very likely to
crash.
SEE ALSO
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer_zsingle_quotesz_s manual
COLOPHON
This page is part of release 4.16 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (C) 2003 Andi Kleen %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |