arch_prctl — set architecture specific thread state
#include <asm/prctl.h> #include <sys/prctl.h>
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.
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 GS
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.
On sucess, 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 only
supported on Linux/x86-64 for 64bit programs currently.
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.
As of version 2.3.5, 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.
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual
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