Gnulib ====== Gnulib is intended to be the canonical source for most of the important "portability" and/or common files for GNU projects. These are files intended to be shared at the source level; Gnulib is not a library meant to be installed and linked against. Unlike most projects, Gnulib does not normally generate a source tarball distribution; instead, developers should just grab modules directly from the repository. While portability across operating systems is not one of GNU's primary goals, it has helped introduce many people to the GNU system, and is worthwhile when it can be achieved at a low cost. This collection helps lower that cost. Contributing to Gnulib ====================== All software here is Copyright (c) Free Software Foundation - you need to have filled out an assignment form for a project that uses the module for that contribution to be accepted here. If you have a piece of code that you would like to contribute, please email bug-gnulib@gnu.org. You can review the archives, subscribe, etc., via http://lists.gnu.org/mailman/listinfo/bug-gnulib. Generally we are looking for files that fulfill at least one of the following requirements: * If your .c and .h files define functions that are broken or missing on some other system, we should be able to include it. * If your functions remove arbitrary limits from existing functions (either under the same name, or as a slightly different name), we should be able to include it. If your functions define completely new but rarely used functionality, you should probably consider packaging it as a separate library. License ------- Gnulib contains code both under GPL and LGPL. Because several packages that use Gnulib are GPL, the files state they are licensed under GPL. However, to support LGPL projects as well, you may use some of the files under LGPL. The "License:" information in the files under modules/ clarifies the real license that applies to the module source. Keep in mind that if you submit patches to files in Gnulib, you should license them under a compatible license, which means that sometimes the contribution will have to be LGPL, if the original file is available under LGPL via a "License: LGPL" information in the projects' modules/ file. How to add a new module ----------------------- * Add the header files and source files to lib/. * If the module needs configure-time checks, write an autoconf macro for it in m4/.m4. See m4/README for details. * Write a module description modules/, based on modules/TEMPLATE. * If the module contributes a section to the end-user documentation, put this documentation in doc/.texi and add it to the "Files" section of modules/. Most modules don't do this; they have only documentation for the programmer (= gnulib user). Such documentation usually goes into the lib/ source files. It may also go into doc/; but don't add it to the module description in this case. * Add the module to the list in MODULES.html.sh. You can test that a module builds correctly with: $ ./gnulib-tool --create-testdir --dir=/tmp/testdir module1 ... moduleN $ cd /tmp/testdir $ ./configure && make Other things: * Check the license and copyright year of headers. * Check that the source code follows the GNU coding standards; see . * Add source files to config/srclist* if they are identical to upstream and should be upgraded in gnulib whenever the upstream source changes. * Include header files in source files to verify the function prototypes. * Make sure a replacement function doesn't cause warnings or clashes on systems that have the function. * Autoconf functions can use gl_* prefix. The AC_* prefix is for autoconf internal functions. * Build files only if they are needed on a platform. Look at the alloca and fnmatch modules for how to achieve this. If for some reason you cannot do this, and you have a .c file that leads to an empty .o file on some platforms (through some big #if around all the code), then ensure that the compilation unit is not empty after preprocessing. One way to do this is to #include or before the big #if. Portability guidelines ---------------------- Gnulib code is intended to be portable to a wide variety of platforms, not just GNU platforms. Many Gnulib modules exist so that applications need not worry about undesirable variability in implementations. For example, an application that uses the 'malloc' module need not worry about (malloc (0)) returning NULL on some Standard C platforms; and 'time_r' users need not worry about localtime_r returning int (not char *) on some platforms that predate POSIX 1003.1-2001. Originally much of the Gnulib code was portable to ancient hosts like 4.2BSD, but it is a maintenance hassle to maintain compatibility with unused hosts, so currently we assume at least a freestanding C89 compiler, possibly operating with a C library that predates C89. The oldest environment currently ported to is probably SunOS 4 + GCC 1.x, though we haven't tested this exact combination. SunOS 4 last shipped on 1998-09-30, and Sun dropped support for it on 2003-10-01, so at some point we may start assuming a C89 library as well. Because we assume a freestanding C89 compiler, Gnulib code can include , , , and unconditionally. It can also include hosted headers like that were present in Unix Version 7 and are thus widely available. Similarly, many modules include even though it's not even in C99; that's OK since has been around nearly forever. and were not in Unix Version 7, so they weren't universally available on ancient hosts, but they are both in SunOS 4 (the oldest platform still in relatively-common use) so Gnulib assumes them now. Even if the include files exist, they may not conform to C89. However, GCC has a "fixincludes" script that attempts to fix most C89-conformance problems. So Gnulib currently assumes include files largely conform to C89 or better. People still using ancient hosts should use fixincludes or fix their include files manually. Even if the include files conform to C89, the library itself may not. For example, SunOS 4's (free (NULL)) can dump core, so Gnulib code must avoid freeing a null pointer, even though C89 allows it. You can work around some of these problems by requiring the relevant modules, e.g., the Gnulib 'free' module supplies a conforming 'free'. The GNU coding standards allow one departure from strict C99: Gnulib code can assume that standard internal types like size_t are no wider than 'long'. POSIX 1003.1-2001 and the GNU coding standards both require 'int' to be at least 32 bits wide, so Gnulib code assumes this as well. Gnulib code makes the following additional assumptions: * With one exception noted below, signed integer arithmetic is two's complement, without runtime overflow checking. This is the traditional behavior, and is supported by C99 implementations that conform to ISO/IEC 10967-1 (LIA-1) and that define signed integer types as being modulo. The exception is signed loop indexes. Here, the behavior is undefined if any signed expression derived from the loop index overflows. For example, the following code contains two such overflows (the "i++" and the "i + 1") and therefore has undefined behavior: int i; for (i = INT_MAX - 10; i <= INT_MAX; i++) if (i + 1 < 0) { report_overflow (); break; } This exception is a concession to modern optimizing compilers, which can turn the above loop into code that executes the loop body 11 times, even though wraparound arithmetic would cause the loop to iterate forever. * There are no "holes" in integer values: all the bits of an integer contribute to its value in the usual way. * If two nonoverlapping objects have sizes S and T represented as size_t values, then S + T cannot overflow. This assumption is true for all practical hosts with flat address spaces, but it is not always true for hosts with segmented address spaces. * If an existing object has size S, and if T is sufficiently small (e.g., 8 KiB), then S + T cannot overflow. Overflow in this case would mean that the rest of your program fits into T bytes, which can't happen in realistic flat-address-space hosts. * Objects with all bits zero are treated as 0 or NULL. For example, memset (A, 0, sizeof A) initializes an array A of pointers to NULL. * Adding zero to a null pointer does not change the pointer. For example, 0 + (char *) NULL == (char *) NULL. The above assumptions are not required by the C or POSIX standards but hold on all practical porting targets that we're familiar with. If you have a porting target where these assumptions are not true, we'd appreciate hearing of any fixes. We need fixes that do not increase runtime overhead on standard hosts and that are relatively easy to maintain. With the above caveats, Gnulib code should port without problem to new hosts, e.g., hosts conforming to C99 or to recent POSIX standards. Hence Gnulib code should avoid using constructs (e.g., undeclared functions return 'int') that do not conform to C99. High Quality ============ We will be developing a testsuite for these applications. The goal is to have a 100% firm interface so that maintainers can feel free to update to the code in git at *any* time and know that their application will not break. This means that before any change can be committed to the repository, a test suite program must be produced that exposes the bug for regression testing. All experimental work should be done on branches to help promote this. git and CVS =========== Gnulib is available for anonymous checkout. In any Bourne-shell the following should work: $ git clone git://git.sv.gnu.org/gnulib Or, if you prefer the CVS-like 'cogito' frontend to plain 'git': $ cg clone git://git.sv.gnu.org/gnulib git resources: Overview: http://en.wikipedia.org/wiki/Git_(software) Homepage: http://git.or.cz/ Download: http://www.kernel.org/pub/software/scm/git/ Tutorial: http://git.or.cz/course/ http://www.kernel.org/pub/software/scm/git/docs/tutorial.html FAQ: http://git.or.cz/gitwiki/GitFaq cogito resources: Overview: http://en.wikipedia.org/wiki/Cogito_(software) Homepage: http://git.or.cz/cogito/ Download: http://kernel.org/pub/software/scm/cogito/ Tutorial: http://git.or.cz/course/ For those among us who have tightly limited disk space and a fast network connection, CVS checkouts are also supported: $ cvs -d :pserver:anoncvs@cvs.gnu.org:/cvsroot/gnulib login (Just hit Enter or Return when prompted for a password) $ cvs -d :pserver:anoncvs@cvs.gnu.org:/cvsroot/gnulib checkout gnulib Gnulib is hosted on savannah.gnu.org. The project page is http://savannah.gnu.org/projects/gnulib. Keeping Up-to-date ================== The best way to work with Gnulib is to check it out of git. Subscribing to the bug-gnulib@gnu.org mailing list will help you to plan when to update your local copy of Gnulib (which you use to maintain your software) from git. To synchronize, you can use "git pull" or "cg update", or "cvs update -dP" if you are still using CVS. Sometimes, using an updated version of Gnulib will require you to use newer versions of GNU Automake or Autoconf. You may find it helpful to join the autotools-announce mailing list to be advised of such changes. ----- Copyright (C) 2001, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */