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
FSregister toaddr. ARCH_GET_FS-
Return the 64-bit base value for the
FSregister of the current thread in the unsigned long pointed to byaddr. ARCH_SET_GS-
Set the 64-bit base for the
GSregister toaddr. ARCH_GET_GS-
Return the 64-bit base value for the
GSregister 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
-
addrpoints to an unmapped address or is outside the process address space. - EINVAL
-
codeis not a valid subcommand. - EPERM
-
addris 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/.
|
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