X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;ds=sidebyside;f=doc%2Falloca.texi;h=a6395868e9be64844783c9f68ccb50b8754888cb;hb=cd56634a4a8179fd5a4419fbb3e27211b042ab1c;hp=e1421f0b0d51345799a7f3c6b4eff642df8eb549;hpb=ce5de1c1b35f8fcc69b9a2c2f1fcc59f1f3ee5cc;p=gnulib.git diff --git a/doc/alloca.texi b/doc/alloca.texi index e1421f0b0..a6395868e 100644 --- a/doc/alloca.texi +++ b/doc/alloca.texi @@ -1,19 +1,43 @@ @c Documentation of gnulib module 'alloca'. -The alloca 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 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 -module provides a malloc() based emulation. This emulation will not free a +module provides a @code{malloc} based emulation. This emulation will not free a memory block immediately when the calling function returns, but rather will -wait until the next alloca() call from a function with the same or a shorter -stack length. Thus, in some cases, a few memory blocks will be kept although -they are not needed any more. +wait until the next @code{alloca} call from a function with the same or a +shorter stack length. Thus, in some cases, a few memory blocks will be kept +although they are not needed any more. + +The user can @code{#include } and use @code{alloca} on all platforms. +Note that the @code{#include } 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 and use alloca() on all platforms. Note -that the #include 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 -An alternative to this module is the 'alloca-opt' module. +An alternative to this module is the @samp{alloca-opt} module.