253 lines
5.1 KiB
HTML
253 lines
5.1 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 BRK</TITLE>
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</HEAD><BODY>
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<H1>BRK</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2016-03-15<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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brk, sbrk - change data segment size
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<P>
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<B>int brk(void *</B><I>addr</I><B>);</B>
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<P>
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<B>void *sbrk(intptr_t </B><I>increment</I><B>);</B>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>brk</B>(),
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<B>sbrk</B>():
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<DL COMPACT><DT id="1"><DD>
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<DL COMPACT>
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<DT id="2">Since glibc 2.19:<DD>
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<PRE>
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_DEFAULT_SOURCE ||
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(_XOPEN_SOURCE >= 500) &&
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! (_POSIX_C_SOURCE >= 200112L)
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</PRE>
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<DT id="3">From glibc 2.12 to 2.19:<DD>
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<PRE>
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_BSD_SOURCE || _SVID_SOURCE ||
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(_XOPEN_SOURCE >= 500) &&
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! (_POSIX_C_SOURCE >= 200112L)
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</PRE>
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<DT id="4">Before glibc 2.12:<DD>
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
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</DL>
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>brk</B>()
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and
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<B>sbrk</B>()
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change the location of the
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<I>program break</I>,
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which defines the end of the process's data segment
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(i.e., the program break is the first location after the end of the
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uninitialized data segment).
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Increasing the program break has the effect of
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allocating memory to the process;
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decreasing the break deallocates memory.
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<P>
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<B>brk</B>()
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sets the end of the data segment to the value specified by
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<I>addr</I>,
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when that value is reasonable, the system has enough memory,
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and the process does not exceed its maximum data size (see
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<B><A HREF="/cgi-bin/man/man2html?2+setrlimit">setrlimit</A></B>(2)).
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<P>
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<B>sbrk</B>()
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increments the program's data space by
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<I>increment</I>
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bytes.
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Calling
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<B>sbrk</B>()
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with an
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<I>increment</I>
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of 0 can be used to find the current location of the program break.
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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>brk</B>()
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returns zero.
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On error, -1 is returned, and
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<I>errno</I>
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is set to
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<B>ENOMEM</B>.
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<P>
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On success,
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<B>sbrk</B>()
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returns the previous program break.
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(If the break was increased,
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then this value is a pointer to the start of the newly allocated memory).
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On error,
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<I>(void *) -1</I>
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is returned, and
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<I>errno</I>
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is set to
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<B>ENOMEM</B>.
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<A NAME="lbAF"> </A>
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<H2>CONFORMING TO</H2>
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4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
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<A NAME="lbAG"> </A>
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<H2>NOTES</H2>
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Avoid using
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<B>brk</B>()
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and
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<B>sbrk</B>():
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the
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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memory allocation package is the
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portable and comfortable way of allocating memory.
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<P>
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Various systems use various types for the argument of
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<B>sbrk</B>().
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Common are <I>int</I>, <I>ssize_t</I>, <I>ptrdiff_t</I>, <I>intptr_t</I>.
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<A NAME="lbAH"> </A>
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<H3>C library/kernel differences</H3>
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The return value described above for
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<B>brk</B>()
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is the behavior provided by the glibc wrapper function for the Linux
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<B>brk</B>()
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system call.
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(On most other implementations, the return value from
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<B>brk</B>()
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is the same; this return value was also specified in SUSv2.)
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However,
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the actual Linux system call returns the new program break on success.
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On failure, the system call returns the current break.
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The glibc wrapper function does some work
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(i.e., checks whether the new break is less than
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<I>addr</I>)
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to provide the 0 and -1 return values described above.
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<P>
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On Linux,
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<B>sbrk</B>()
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is implemented as a library function that uses the
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<B>brk</B>()
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system call, and does some internal bookkeeping so that it can
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return the old break value.
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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+execve">execve</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+getrlimit">getrlimit</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?3+end">end</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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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="5"><A HREF="#lbAB">NAME</A><DD>
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<DT id="6"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="7"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="8"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="9"><A HREF="#lbAF">CONFORMING TO</A><DD>
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<DT id="10"><A HREF="#lbAG">NOTES</A><DD>
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<DL>
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<DT id="11"><A HREF="#lbAH">C library/kernel differences</A><DD>
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</DL>
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<DT id="12"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="13"><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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