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[thirdparty/man-pages.git] / man2 / arch_prctl.2

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.TH ARCH_PRCTL 2 2003-02-02 "Linux 2.4.20" "Linux Programmer's Manual"
.SH NAME
arch_prctl \- set architecture specific thread state
.SH SYNOPSIS
.B #include <asm/prctl.h>
.sp
.B #include <sys/prctl.h>
.sp
.BI "int arch_prctl(int code, unsigned long addr)"
.SH DESCRIPTION
The
.BR arch_prctl ()
function sets architecture specific process or thread state.
.I code
selects a subfunction
and passes argument
.I addr 
to it. 
.LP
Sub functions for x86-64 are:
.TP
.B ARCH_SET_FS
Set the 64bit base for the 
.I FS
register to
.IR addr .
.TP
.B ARCH_GET_FS
Return the 64bit base value for the
.I FS
register of the current thread in the 
.I unsigned long
pointed to by the 
.I address 
parameter
.TP
.B ARCH_SET_GS
Set the 64bit base for the 
.I GS
register to
.IR addr .
.TP
.B ARCH_GET_GS
Return the 64bit base value for the
.I GS
register of the current thread in the 
.I unsigned long
pointed to by the 
.I address 
parameter.
.SH NOTES
.IR 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.

.B 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
.BR modify_ldt (2)
or using the 
.BR set_thread_area (2)
system call in a 2.5 kernel. 
.BR 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
.BR mmap (2)
with the
.I MAP_32BIT
flag.

No prototype for 
.IR arch_prctl ()
in glibc 2.2. You have to declare it yourself for now.
This will be fixed in future glibc versions.

.I FS 
may be already used by the threading library.
.SH ERRORS
.TP
.B EFAULT
.I addr 
points to an unmapped address or is outside the process address space.
.TP
.B EINVAL
.I code 
is not a valid subcommand.
.TP
.B EPERM
.I addr
is outside the process address space.
.SH AUTHOR
Man page written by Andi Kleen.
.SH CONFORMANCE
.IR arch_prctl ()
is a Linux/x86-64 extension and should not be used in programs intended to be portable.
.SH "SEE ALSO"
.BR mmap (2),
.BR modify_ldt (2),
.BR prctl (2),
.BR set_thread_area (2)
.sp
AMD X86-64 Programmer's manual