240 lines
4.9 KiB
HTML
240 lines
4.9 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of ARCH_PRCTL</TITLE>
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</HEAD><BODY>
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<H1>ARCH_PRCTL</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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arch_prctl - set architecture-specific thread state
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/asm/prctl.h">asm/prctl.h</A>></B>
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<B>#include <<A HREF="file:///usr/include/sys/prctl.h">sys/prctl.h</A>></B>
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<B>int arch_prctl(int </B><I>code</I><B>, unsigned long </B><I>addr</I><B>);</B>
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<B>int arch_prctl(int </B><I>code</I><B>, unsigned long *</B><I>addr</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>arch_prctl</B>()
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sets architecture-specific process or thread state.
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<I>code</I>
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selects a subfunction
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and passes argument
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<I>addr</I>
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to it;
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<I>addr</I>
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is interpreted as either an
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<I>unsigned long</I>
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for the "set" operations, or as an
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<I>unsigned long *</I>,
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for the "get" operations.
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<P>
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Subfunctions for x86-64 are:
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<DL COMPACT>
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<DT id="1"><B>ARCH_SET_FS</B>
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<DD>
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Set the 64-bit base for the
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<I>FS</I>
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register to
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<I>addr</I>.
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<DT id="2"><B>ARCH_GET_FS</B>
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<DD>
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Return the 64-bit base value for the
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<I>FS</I>
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register of the current thread in the
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<I>unsigned long</I>
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pointed to by
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<I>addr</I>.
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<DT id="3"><B>ARCH_SET_GS</B>
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<DD>
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Set the 64-bit base for the
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<I>GS</I>
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register to
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<I>addr</I>.
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<DT id="4"><B>ARCH_GET_GS</B>
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<DD>
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Return the 64-bit base value for the
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<I>GS</I>
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register of the current thread in the
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<I>unsigned long</I>
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pointed to by
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<I>addr</I>.
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</DL>
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>arch_prctl</B>()
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returns 0; on error, -1 is returned, and
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<I>errno</I>
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is set to indicate the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="5"><B>EFAULT</B>
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<DD>
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<I>addr</I>
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points to an unmapped address or is outside the process address space.
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<DT id="6"><B>EINVAL</B>
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<DD>
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<I>code</I>
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is not a valid subcommand.
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<DT id="7"><B>EPERM</B>
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<DD>
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<I>addr</I>
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is outside the process address space.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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<B>arch_prctl</B>()
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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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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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<B>arch_prctl</B>()
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is supported only on Linux/x86-64 for 64-bit programs currently.
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<P>
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The 64-bit base changes when a new 32-bit segment selector is loaded.
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<P>
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<B>ARCH_SET_GS</B>
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is disabled in some kernels.
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<P>
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Context switches for 64-bit segment bases are rather expensive.
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As an optimization, if a 32-bit TLS base address is used,
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<B>arch_prctl</B>()
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may use a real TLS entry as if
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<B><A HREF="/cgi-bin/man/man2html?2+set_thread_area">set_thread_area</A></B>(2)
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had been called, instead of manipulating the segment base register directly.
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Memory in the first 2 GB of address space can be allocated by using
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2)
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with the
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<B>MAP_32BIT</B>
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flag.
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<P>
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Because of the aforementioned optimization, using
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<B>arch_prctl</B>()
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and
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<B><A HREF="/cgi-bin/man/man2html?2+set_thread_area">set_thread_area</A></B>(2)
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in the same thread is dangerous, as they may overwrite each other's
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TLS entries.
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<P>
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As of version 2.7, glibc provides no prototype for
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<B>arch_prctl</B>().
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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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<P>
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<I>FS</I>
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may be already used by the threading library.
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Programs that use
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<B>ARCH_SET_FS</B>
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directly are very likely to crash.
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<A NAME="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+modify_ldt">modify_ldt</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+prctl">prctl</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+set_thread_area">set_thread_area</A></B>(2)
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<P>
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AMD X86-64 Programmer's manual
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<A NAME="lbAJ"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="8"><A HREF="#lbAB">NAME</A><DD>
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<DT id="9"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="10"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="11"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="12"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="13"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="14"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="15"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="16"><A HREF="#lbAJ">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:32 GMT, March 31, 2021
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</BODY>
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</HTML>
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