Name
arch_prctl — set architecture specific thread
state
Synopsis
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.
RETURN VALUE
On sucess, 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
arch_prctl() is a
Linux/x86-64 extension and should not be used in programs
intended to be portable.
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.
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.
SEE ALSO
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual
Copyright (C) 2003 Andi Kleen
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