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Revision 1.20 - (show annotations)
Sat Mar 31 12:34:54 2007 UTC (14 years, 9 months ago) by haible
Branch: MAIN
Changes since 1.19: +30 -11 lines
Talk primarily about git, not CVS.

1 Gnulib
2 ======
4 Gnulib is intended to be the canonical source for most of the important
5 "portability" and/or common files for GNU projects. These are files
6 intended to be shared at the source level; Gnulib is not a library meant
7 to be installed and linked against. Unlike most projects, Gnulib does
8 not normally generate a source tarball distribution; instead, developers
9 should just grab modules directly from the repository.
11 While portability across operating systems is not one of GNU's primary
12 goals, it has helped introduce many people to the GNU system, and is
13 worthwhile when it can be achieved at a low cost. This collection helps
14 lower that cost.
17 Contributing to Gnulib
18 ======================
19 All software here is Copyright (c) Free Software Foundation - you need
20 to have filled out an assignment form for a project that uses the
21 module for that contribution to be accepted here.
23 If you have a piece of code that you would like to contribute, please
24 email bug-gnulib@gnu.org. You can review the archives, subscribe, etc.,
25 via http://lists.gnu.org/mailman/listinfo/bug-gnulib.
27 Generally we are looking for files that fulfill at least one of the
28 following requirements:
30 * If your .c and .h files define functions that are broken or
31 missing on some other system, we should be able to include it.
33 * If your functions remove arbitrary limits from existing
34 functions (either under the same name, or as a slightly different
35 name), we should be able to include it.
37 If your functions define completely new but rarely used functionality,
38 you should probably consider packaging it as a separate library.
41 License
42 -------
43 Gnulib contains code both under GPL and LGPL. Because several packages
44 that use Gnulib are GPL, the files state they are licensed under GPL.
45 However, to support LGPL projects as well, you may use some of the
46 files under LGPL. The "License:" information in the files under
47 modules/ clarifies the real license that applies to the module source.
49 Keep in mind that if you submit patches to files in Gnulib, you should
50 license them under a compatible license, which means that sometimes
51 the contribution will have to be LGPL, if the original file is
52 available under LGPL via a "License: LGPL" information in the
53 projects' modules/ file.
56 How to add a new module
57 -----------------------
58 * Add the header files and source files to lib/.
59 * If the module needs configure-time checks, write an autoconf
60 macro for it in m4/<module>.m4. See m4/README for details.
61 * Write a module description modules/<module>, based on modules/TEMPLATE.
62 * If the module contributes a section to the end-user documentation,
63 put this documentation in doc/<module>.texi and add it to the "Files"
64 section of modules/<module>. Most modules don't do this; they have only
65 documentation for the programmer (= gnulib user). Such documentation
66 usually goes into the lib/ source files. It may also go into doc/;
67 but don't add it to the module description in this case.
68 * Add the module to the list in MODULES.html.sh.
70 You can test that a module builds correctly with:
71 $ ./gnulib-tool --create-testdir --dir=/tmp/testdir module1 ... moduleN
72 $ cd /tmp/testdir
73 $ ./configure && make
75 Other things:
76 * Check the license and copyright year of headers.
77 * Check that the source code follows the GNU coding standards;
78 see <http://www.gnu.org/prep/standards>.
79 * Add source files to config/srclist* if they are identical to upstream
80 and should be upgraded in gnulib whenever the upstream source changes.
81 * Include header files in source files to verify the function prototypes.
82 * Make sure a replacement function doesn't cause warnings or clashes on
83 systems that have the function.
84 * Autoconf functions can use gl_* prefix. The AC_* prefix is for
85 autoconf internal functions.
86 * Build files only if they are needed on a platform. Look at the
87 alloca and fnmatch modules for how to achieve this. If for some
88 reason you cannot do this, and you have a .c file that leads to an
89 empty .o file on some platforms (through some big #if around all the
90 code), then ensure that the compilation unit is not empty after
91 preprocessing. One way to do this is to #include <stddef.h> or
92 <stdio.h> before the big #if.
94 Portability guidelines
95 ----------------------
97 Gnulib code is intended to be portable to a wide variety of platforms,
98 not just GNU platforms.
100 Many Gnulib modules exist so that applications need not worry about
101 undesirable variability in implementations. For example, an
102 application that uses the 'malloc' module need not worry about (malloc
103 (0)) returning NULL on some Standard C platforms; and 'time_r' users
104 need not worry about localtime_r returning int (not char *) on some
105 platforms that predate POSIX 1003.1-2001.
107 Originally much of the Gnulib code was portable to ancient hosts like
108 4.2BSD, but it is a maintenance hassle to maintain compatibility with
109 unused hosts, so currently we assume at least a freestanding C89
110 compiler, possibly operating with a C library that predates C89. The
111 oldest environment currently ported to is probably SunOS 4 + GCC 1.x,
112 though we haven't tested this exact combination. SunOS 4 last shipped
113 on 1998-09-30, and Sun dropped support for it on 2003-10-01, so at
114 some point we may start assuming a C89 library as well.
116 Because we assume a freestanding C89 compiler, Gnulib code can include
117 <float.h>, <limits.h>, <stdarg.h>, and <stddef.h> unconditionally. It
118 can also include hosted headers like <errno.h> that were present in
119 Unix Version 7 and are thus widely available. Similarly, many modules
120 include <sys/types.h> even though it's not even in C99; that's OK
121 since <sys/types.h> has been around nearly forever. <string.h> and
122 <stdlib.h> were not in Unix Version 7, so they weren't universally
123 available on ancient hosts, but they are both in SunOS 4 (the oldest
124 platform still in relatively-common use) so Gnulib assumes them now.
126 Even if the include files exist, they may not conform to C89.
127 However, GCC has a "fixincludes" script that attempts to fix most
128 C89-conformance problems. So Gnulib currently assumes include files
129 largely conform to C89 or better. People still using ancient hosts
130 should use fixincludes or fix their include files manually.
132 Even if the include files conform to C89, the library itself may not.
133 For example, SunOS 4's (free (NULL)) can dump core, so Gnulib code
134 must avoid freeing a null pointer, even though C89 allows it.
135 You can work around some of these problems by requiring the relevant
136 modules, e.g., the Gnulib 'free' module supplies a conforming 'free'.
138 The GNU coding standards allow one departure from strict C99: Gnulib
139 code can assume that standard internal types like size_t are no wider
140 than 'long'. POSIX 1003.1-2001 and the GNU coding standards both
141 require 'int' to be at least 32 bits wide, so Gnulib code assumes this
142 as well. Gnulib code makes the following additional assumptions:
144 * With one exception noted below, signed integer arithmetic is two's
145 complement, without runtime overflow checking. This is the
146 traditional behavior, and is supported by C99 implementations that
147 conform to ISO/IEC 10967-1 (LIA-1) and that define signed integer
148 types as being modulo.
150 The exception is signed loop indexes. Here, the behavior is
151 undefined if any signed expression derived from the loop index
152 overflows. For example, the following code contains two such
153 overflows (the "i++" and the "i + 1") and therefore has undefined
154 behavior:
156 int i;
157 for (i = INT_MAX - 10; i <= INT_MAX; i++)
158 if (i + 1 < 0)
159 {
160 report_overflow ();
161 break;
162 }
164 This exception is a concession to modern optimizing compilers,
165 which can turn the above loop into code that executes the loop body
166 11 times, even though wraparound arithmetic would cause the loop to
167 iterate forever.
169 * There are no "holes" in integer values: all the bits of an integer
170 contribute to its value in the usual way.
172 * If two nonoverlapping objects have sizes S and T represented as
173 size_t values, then S + T cannot overflow. This assumption is true
174 for all practical hosts with flat address spaces, but it is not
175 always true for hosts with segmented address spaces.
177 * If an existing object has size S, and if T is sufficiently small
178 (e.g., 8 KiB), then S + T cannot overflow. Overflow in this case
179 would mean that the rest of your program fits into T bytes, which
180 can't happen in realistic flat-address-space hosts.
182 * Objects with all bits zero are treated as 0 or NULL. For example,
183 memset (A, 0, sizeof A) initializes an array A of pointers to NULL.
185 * Adding zero to a null pointer does not change the pointer.
186 For example, 0 + (char *) NULL == (char *) NULL.
188 The above assumptions are not required by the C or POSIX standards but
189 hold on all practical porting targets that we're familiar with. If
190 you have a porting target where these assumptions are not true, we'd
191 appreciate hearing of any fixes. We need fixes that do not increase
192 runtime overhead on standard hosts and that are relatively easy to
193 maintain.
195 With the above caveats, Gnulib code should port without problem to new
196 hosts, e.g., hosts conforming to C99 or to recent POSIX standards.
197 Hence Gnulib code should avoid using constructs (e.g., undeclared
198 functions return 'int') that do not conform to C99.
200 High Quality
201 ============
203 We will be developing a testsuite for these applications. The goal is
204 to have a 100% firm interface so that maintainers can feel free to
205 update to the code in git at *any* time and know that their
206 application will not break. This means that before any change can be
207 committed to the repository, a test suite program must be produced
208 that exposes the bug for regression testing. All experimental work
209 should be done on branches to help promote this.
211 git and CVS
212 ===========
214 Gnulib is available for anonymous checkout. In any Bourne-shell the
215 following should work:
216 $ git clone git://git.sv.gnu.org/gnulib
217 Or, if you prefer the CVS-like 'cogito' frontend to plain 'git':
218 $ cg clone git://git.sv.gnu.org/gnulib
220 git resources:
221 Overview: http://en.wikipedia.org/wiki/Git_(software)
222 Homepage: http://git.or.cz/
223 Download: http://www.kernel.org/pub/software/scm/git/
224 Tutorial: http://git.or.cz/course/
225 http://www.kernel.org/pub/software/scm/git/docs/tutorial.html
226 FAQ: http://git.or.cz/gitwiki/GitFaq
228 cogito resources:
229 Overview: http://en.wikipedia.org/wiki/Cogito_(software)
230 Homepage: http://git.or.cz/cogito/
231 Download: http://kernel.org/pub/software/scm/cogito/
232 Tutorial: http://git.or.cz/course/
234 For those among us who have tightly limited disk space and a fast network
235 connection, CVS checkouts are also supported:
236 $ cvs -d :pserver:anoncvs@cvs.gnu.org:/cvsroot/gnulib login
237 (Just hit Enter or Return when prompted for a password)
238 $ cvs -d :pserver:anoncvs@cvs.gnu.org:/cvsroot/gnulib checkout gnulib
240 Gnulib is hosted on savannah.gnu.org. The project page is
241 http://savannah.gnu.org/projects/gnulib.
243 Keeping Up-to-date
244 ==================
246 The best way to work with Gnulib is to check it out of git.
247 Subscribing to the bug-gnulib@gnu.org mailing list will help you to
248 plan when to update your local copy of Gnulib (which you use to
249 maintain your software) from git. To synchronize, you can use "git pull"
250 or "cg update", or "cvs update -dP" if you are still using CVS.
252 Sometimes, using an updated version of Gnulib will require you to use
253 newer versions of GNU Automake or Autoconf. You may find it helpful
254 to join the autotools-announce mailing list to be advised of such
255 changes.
258 -----
259 Copyright (C) 2001, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
261 This program is free software; you can redistribute it and/or modify
262 it under the terms of the GNU General Public License as published by
263 the Free Software Foundation; either version 2, or (at your option)
264 any later version.
266 This program is distributed in the hope that it will be useful,
267 but WITHOUT ANY WARRANTY; without even the implied warranty of
269 GNU General Public License for more details.
271 You should have received a copy of the GNU General Public License
272 along with this program; if not, write to the Free Software Foundation,
273 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */

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