arch_prctl — set architecture-specific thread state
#include <asm/prctl.h> #include <sys/prctl.h>
int
arch_prctl( |
int code, |
unsigned long addr); |
int
arch_prctl( |
int code, |
unsigned long *addr); |
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.
Subfunctions for x86-64 are:
ARCH_SET_FSSet the 64-bit base for the FS register to addr.
ARCH_GET_FSReturn the 64-bit base value for the FS register of the current thread in
the unsigned long pointed to
by addr.
ARCH_SET_GSSet the 64-bit base for the GS register to addr.
ARCH_GET_GSReturn the 64-bit base value for the GS register of the current thread in
the unsigned long pointed to
by addr.
On success, arch_prctl()
returns 0; on error, −1 is returned, and errno is set to indicate the error.
addr points
to an unmapped address or is outside the process
address space.
code is not
a valid subcommand.
addr is
outside the process address space.
arch_prctl() is a
Linux/x86-64 extension and should not be used in programs
intended to be portable.
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(2) 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 2GB of address space can be
allocated by using mmap(2) with the
MAP_32BIT flag.
Because of the aforementioned optimization, using arch_prctl(2) and set_thread_area(2) in the same thread is dangerous, as they may overwrite each other'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.
This page is part of release 4.07 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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