man2/arch_prctl.2

   1 .\" Hey Emacs! This file is -*- nroff -*- source.
   2 .\"
   3 .\" Copyright (C) 2003 Andi Kleen
   4 .\"
   5 .\" Permission is granted to make and distribute verbatim copies of this
   6 .\" manual provided the copyright notice and this permission notice are
   7 .\" preserved on all copies.
   8 .\"
   9 .\" Permission is granted to copy and distribute modified versions of this
  10 .\" manual under the conditions for verbatim copying, provided that the
  11 .\" entire resulting derived work is distributed under the terms of a
  12 .\" permission notice identical to this one.
  13 .\"
  14 .\" Since the Linux kernel and libraries are constantly changing, this
  15 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  16 .\" responsibility for errors or omissions, or for damages resulting from
  17 .\" the use of the information contained herein.  The author(s) may not
  18 .\" have taken the same level of care in the production of this manual,
  19 .\" which is licensed free of charge, as they might when working
  20 .\" professionally.
  21 .\"
  22 .\" Formatted or processed versions of this manual, if unaccompanied by
  23 .\" the source, must acknowledge the copyright and authors of this work.
  24 .TH ARCH_PRCTL 2 2007-12-26 "Linux" "Linux Programmer's Manual"
  25 .SH NAME
  26 arch_prctl \- set architecture-specific thread state
  27 .SH SYNOPSIS
  28 .nf
  29 .B #include <asm/prctl.h>
  30 .br
  31 .B #include <sys/prctl.h>
  32 .sp
  33 .BI "int arch_prctl(int " code ", unsigned long " addr );
  34 .BI "int arch_prctl(int " code ", unsigned long *" addr );
  35 .fi
  36 .SH DESCRIPTION
  37 The
  38 .BR arch_prctl ()
  39 function sets architecture-specific process or thread state.
  40 .I code
  41 selects a subfunction
  42 and passes argument
  43 .I addr
  44 to it;
  45 .I addr
  46 is interpreted as either an
  47 .I "unsigned long"
  48 for the "set" operations, or as an
  49 .IR "unsigned long *" ,
  50 for the "get" operations.
  51 .LP
  52 Sub functions for x86-64 are:
  53 .TP
  54 .B ARCH_SET_FS
  55 Set the 64-bit base for the
  56 .I FS
  57 register to
  58 .IR addr .
  59 .TP
  60 .B ARCH_GET_FS
  61 Return the 64-bit base value for the
  62 .I FS
  63 register of the current thread in the
  64 .I unsigned long
  65 pointed to by
  66 .IR addr .
  67 .TP
  68 .B ARCH_SET_GS
  69 Set the 64-bit base for the
  70 .I GS
  71 register to
  72 .IR addr .
  73 .TP
  74 .B ARCH_GET_GS
  75 Return the 64-bit base value for the
  76 .I GS
  77 register of the current thread in the
  78 .I unsigned long
  79 pointed to by
  80 .IR addr .
  81 .SH RETURN VALUE
  82 On success,
  83 .BR arch_prctl ()
  84 returns 0; on error, \-1 is returned, and
  85 .I errno
  86 is set to indicate the error.
  87 .SH ERRORS
  88 .TP
  89 .B EFAULT
  90 .I addr
  91 points to an unmapped address or is outside the process address space.
  92 .TP
  93 .B EINVAL
  94 .I code
  95 is not a valid subcommand.
  96 .TP
  97 .B EPERM
  98 .I addr
  99 is outside the process address space.
 100 .\" .SH AUTHOR
 101 .\" Man page written by Andi Kleen.
 102 .SH CONFORMING TO
 103 .BR arch_prctl ()
 104 is a Linux/x86-64 extension and should not be used in programs intended
 105 to be portable.
 106 .SH NOTES
 107 .BR arch_prctl ()
 108 is only supported on Linux/x86-64 for 64-bit programs currently.
 109
 110 The 64-bit base changes when a new 32-bit segment selector is loaded.
 111
 112 .B ARCH_SET_GS
 113 is disabled in some kernels.
 114
 115 Context switches for 64-bit segment bases are rather expensive.
 116 It may be a faster alternative to set a 32-bit base using a
 117 segment selector by setting up an LDT with
 118 .BR modify_ldt (2)
 119 or using the
 120 .BR set_thread_area (2)
 121 system call in kernel 2.5 or later.
 122 .BR arch_prctl ()
 123 is only needed when you want to set bases that are larger than 4GB.
 124 Memory in the first 2GB of address space can be allocated by using
 125 .BR mmap (2)
 126 with the
 127 .B MAP_32BIT
 128 flag.
 129
 130 As of version 2.7, glibc provides no prototype for
 131 .BR arch_prctl ().
 132 You have to declare it yourself for now.
 133 This may be fixed in future glibc versions.
 134
 135 .I FS
 136 may be already used by the threading library.
 137 .SH SEE ALSO
 138 .BR mmap (2),
 139 .BR modify_ldt (2),
 140 .BR prctl (2),
 141 .BR set_thread_area (2)
 142
 143 AMD X86-64 Programmer's manual