NEWS.stable: log cherry-pick [e446f25]->[c092018] relocatable-shell: Update suggested...

[gnulib.git] / doc / alloca-opt.texi

diff --git a/doc/alloca-opt.texi b/doc/alloca-opt.texi
index 86f17cf..5b052c8 100644 (file)
--- a/doc/alloca-opt.texi
+++ b/doc/alloca-opt.texi
@@ -1,16 +1,41 @@
 @c Documentation of gnulib module 'alloca-opt'.
 
-The alloca-opt module provides for a function alloca() which allocates memory
-on the stack, where the system allows it. A memory block allocated with alloca()
-exists only until the function that calls alloca() returns or exits abruptly.
+@c Copyright (C) 2004, 2007, 2009-2014 Free Software Foundation, Inc.
+
+@c Permission is granted to copy, distribute and/or modify this document
+@c under the terms of the GNU Free Documentation License, Version 1.3 or
+@c any later version published by the Free Software Foundation; with no
+@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+@c Texts.  A copy of the license is included in the ``GNU Free
+@c Documentation License'' file as part of this distribution.
+
+The alloca-opt module provides for a function @code{alloca} which allocates
+memory on the stack, where the system allows it. A memory block allocated with
+@code{alloca} exists only until the function that calls @code{alloca} returns
+or exits abruptly.
 
 There are a few systems where this is not possible: HP-UX systems, and some
-other platforms when the C++ compiler is used. On these platforms the alloca-opt
-module provides no replacement, just a preprocessor macro HAVE_ALLOCA.
+other platforms when the C++ compiler is used. On these platforms the
+alloca-opt module provides no replacement, just a preprocessor macro
+HAVE_ALLOCA.
+
+The user can @code{#include <alloca.h>} on all platforms, and use
+@code{alloca} on those platforms where the preprocessor macro HAVE_ALLOCA
+evaluates to true. If HAVE_ALLOCA is false, the code should use a heap-based
+memory allocation based on @code{malloc} or (in C++) @code{new}. Note that
+the @code{#include <alloca.h>} must be the first one after the
+autoconf-generated @file{config.h}, for AIX 3 compatibility. Thanks to IBM for
+this nice restriction!
+
+Note that GCC 3.1 and 3.2 can @emph{inline} functions that call @code{alloca}.
+When this happens, the memory blocks allocated with @code{alloca} will not be
+freed until @emph{the end of the calling function}. If this calling function
+runs a loop calling the function that uses @code{alloca}, the program easily
+gets a stack overflow and crashes. To protect against this compiler behaviour,
+you can mark the function that uses @code{alloca} with the following attribute:
 
-The user can #include <alloca.h> on all platforms, and use alloca() on those
-platforms where the preprocessor macro HAVE_ALLOCA evaluates to true. If
-HAVE_ALLOCA is false, the code should use a heap-based memory allocation
-based on malloc() or - in C++ - 'new'. Note that the #include <alloca.h> must be
-the first one after the autoconf-generated config.h. Thanks to AIX for this nice
-restriction!
+@smallexample
+#ifdef __GNUC__
+__attribute__ ((__noinline__))
+#endif
+@end smallexample