arch_prctl(2) -- Linux man page
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)
DESCRIPTION
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.
NOTES
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.
No prototype for
arch_prctl
in glibc 2.2. You have to declare it yourself for now.
This will be fixed in future glibc versions.
FS
may be already used by the threading library.
ERRORS
- EINVAL
-
code
is not a valid subcommand.
- EPERM
-
addr
is outside the process address space.
- EFAULT
-
addr
points to an unmapped address or is outside the process address space.
AUTHOR
Man page written by Andi Kleen.
CONFORMANCE
arch_prctl
is a Linux/x86-64 extension and should not be used in programs intended to be portable.
SEE ALSO
mmap(2),
modify_ldt(2),
prctl(2),
set_thread_area(2)
AMD X86-64 Programmer's manual
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