NAME
arch_prctl - set architecture specific thread state
SYNOPSIS
#include <asm/prctl.h>
#include <sys/prctl.h>
I int arch_prctl(int code, unsigned long addr)
DESCRIPTION
The
R 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
R 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
R 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.
RETURN VALUE
On sucess,
R arch_prctl ()
returns 0; on error, -1 is returned, and
errno
is set to indicate the error.
ERRORS
EFAULT
addr
points to an unmapped address or is outside the process address space.
EINVAL
code
is not a valid subcommand.
EPERM
addr
is outside the process address space.
CONFORMING TO
R arch_prctl ()
is a Linux/x86-64 extension and should not be used in programs intended
to be portable.
NOTES
R 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.
R 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
R 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.
SEE ALSO
