mirror of https://github.com/mkerrisk/man-pages
131 lines
3.3 KiB
Groff
131 lines
3.3 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 2003 Andi Kleen
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.TH ARCH_PRCTL 2 2003-02-02 "Linux 2.4.20" "Linux Programmer's Manual"
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.SH NAME
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arch_prctl \- set architecture specific thread state
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.SH SYNOPSIS
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.B #include <asm/prctl.h>
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.B #include <sys/prctl.h>
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.sp
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.BI "int arch_prctl(int code, unsigned long addr)"
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.SH DESCRIPTION
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The
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.BR arch_prctl ()
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function sets architecture specific process or thread state.
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.I code
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selects a subfunction
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and passes argument
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.I addr
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to it.
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.LP
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Sub functions for x86-64 are:
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.TP
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.B ARCH_SET_FS
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Set the 64bit base for the
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.I FS
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register to
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.IR addr .
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.TP
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.B ARCH_GET_FS
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Return the 64bit base value for the
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.I FS
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register of the current thread in the
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.I unsigned long
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pointed to by the
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.I address
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parameter
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.TP
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.B ARCH_SET_GS
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Set the 64bit base for the
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.I GS
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register to
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.IR addr .
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.TP
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.B ARCH_GET_GS
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Return the 64bit base value for the
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.I GS
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register of the current thread in the
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.I unsigned long
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pointed to by the
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.I address
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parameter.
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.SH NOTES
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.BR arch_prctl ()
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is only supported on Linux/x86-64 for 64bit programs currently.
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The 64bit base changes when a new 32bit segment selector is loaded.
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.B ARCH_SET_GS
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is disabled in some kernels.
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Context switches for 64bit segment bases are rather expensive.
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It may be a
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faster alternative to set a 32bit base using a segment selector by setting up
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an LDT with
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.BR modify_ldt (2)
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or using the
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.BR set_thread_area (2)
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system call in a 2.5 kernel.
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.BR arch_prctl ()
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is only needed when you want to set bases that are larger than 4GB.
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Memory in the first 2GB of address space can be allocated by using
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.BR mmap (2)
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with the
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.I MAP_32BIT
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flag.
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As of version 2.3.5, glibc provides no prototype for
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.BR arch_prctl ().
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You have to declare it yourself for now.
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This may be fixed in future glibc versions.
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.I FS
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may be already used by the threading library.
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.SH ERRORS
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.TP
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.B EFAULT
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.I addr
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points to an unmapped address or is outside the process address space.
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.TP
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.B EINVAL
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.I code
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is not a valid subcommand.
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.TP
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.B EPERM
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.I addr
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is outside the process address space.
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.SH AUTHOR
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Man page written by Andi Kleen.
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.SH "CONFORMING TO"
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.BR arch_prctl ()
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is a Linux/x86-64 extension and should not be used in programs intended
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to be portable.
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.SH "SEE ALSO"
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.BR mmap (2),
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.BR modify_ldt (2),
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.BR prctl (2),
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.BR set_thread_area (2)
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.sp
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AMD X86-64 Programmer's manual
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