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annotate doc/alloca.texi @ 14776:a3bd209aea02

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test-perror: rewrite to use init script Make the test simpler, and also check for correct exit status. * modules/perror-tests (Files): Add init.sh. * tests/test-perror.sh: Use temporary directory. Signed-off-by: Eric Blake <eblake@redhat.com>
author Eric Blake <eblake@redhat.com>
date Fri, 20 May 2011 08:57:54 -0600
parents 97fc9a21a8fb
children 8250f2777afc
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1 @c Documentation of gnulib module 'alloca'.
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2
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3 @c Copyright (C) 2004, 2007, 2009-2011 Free Software Foundation, Inc.
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4
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5 @c Permission is granted to copy, distribute and/or modify this document
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6 @c under the terms of the GNU Free Documentation License, Version 1.3 or
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7 @c any later version published by the Free Software Foundation; with no
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8 @c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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9 @c Texts. A copy of the license is included in the ``GNU Free
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10 @c Documentation License'' file as part of this distribution.
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11
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12 The alloca module provides for a function @code{alloca} which allocates
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13 memory on the stack, where the system allows it. A memory block allocated with
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14 @code{alloca} exists only until the function that calls @code{alloca} returns
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15 or exits abruptly.
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17 There are a few systems where this is not possible: HP-UX systems, and some
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18 other platforms when the C++ compiler is used. On these platforms the alloca
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19 module provides a @code{malloc} based emulation. This emulation will not free a
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20 memory block immediately when the calling function returns, but rather will
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21 wait until the next @code{alloca} call from a function with the same or a
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22 shorter stack length. Thus, in some cases, a few memory blocks will be kept
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23 although they are not needed any more.
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24
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25 The user can @code{#include <alloca.h>} and use @code{alloca} on all platforms.
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26 Note that the @code{#include <alloca.h>} must be the first one after the
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27 autoconf-generated @file{config.h}, for AIX 3 compatibility. Thanks to IBM for
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28 this nice restriction!
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30 Note that GCC 3.1 and 3.2 can @emph{inline} functions that call @code{alloca}.
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31 When this happens, the memory blocks allocated with @code{alloca} will not be
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32 freed until @emph{the end of the calling function}. If this calling function
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33 runs a loop calling the function that uses @code{alloca}, the program easily
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34 gets a stack overflow and crashes. To protect against this compiler behaviour,
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35 you can mark the function that uses @code{alloca} with the following attribute:
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37 @smallexample
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38 #ifdef __GNUC__
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39 __attribute__ ((__noinline__))
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40 #endif
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41 @end smallexample
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42
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43 An alternative to this module is the @samp{alloca-opt} module.