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_FSSet the 64bit base for the FS register to addr.
ARCH_GET_FSReturn the 64bit base value for the FS register of the current thread in
the unsigned
long pointed to by the address parameter
ARCH_SET_GSSet the 64bit base for the GS register to addr.
ARCH_GET_GSReturn the 64bit base value for the GS register of the current thread in
the unsigned
long pointed to by the address parameter.
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.
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.
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual
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