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The community wiki for GLIBC

The official and canonical GLIBC website is http://www.gnu.org/software/libc/

1. Overview

Any Unix-like operating system needs a C library: the library which defines the "system calls" and other basic facilities such as fopen, malloc, printf, exit etc.

The GNU C Library is used as the C library in the GNU systems and most systems with the Linux kernel.

1.1. Project Goals

The GNU C Library is primarily designed to be a portable and high performance C library.

It follows all relevant standards including ISO C11 and POSIX.1-2008. It is also internationalized and has one of the most complete internationalization interfaces known.

1.2. Project Features

• POSIX Threading

  • A History of Threading in GLIBC (todo) - Describes the GLIBC version history of POSIX NPTL as well as mutex and futex constructs.

• ... and more!

1.3. History

The history of Unix and various standards determine much of the interface of the C library. In general the GNU C library supports the ISO C and POSIX standards. We also try to support the features of popular Unix variants (including BSD and System V) when those do not conflict with the standards. Different compatibility modes (selectable when you compile an application) allow the peaceful coexistence of compatibility support for different varieties of Unix.

1.4. Editing the wiki

Owing to automated spammers we have switched to only allowing those people in the EditorGroup to edit the wiki. If you would like to participate in the wiki please email your request to libc-alpha@sourceware.org or contact one of the editors in EditorGroup and have them vouch for you and add you to the list. We are sorry for the inconvenience. Please help make the world a better place by helping prevent spam.

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2. Obtaining the Official Source

The "Download" section of the GLIBC website contains instructions on obtaining the official sources for the latest GLIBC release.

You can obtain official tarballs from the standard location, ftp://ftp.gnu.org/gnu/glibc/.

Source snapshots are available from ftp://sourceware.org/pub/glibc/snapshots/.

The working source tree is located in GIT, look here for instructions.

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3. FAQ

Consult the GLIBC FAQ for common questions and answers.

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4. Development

4.1. Contributing

• glibc coding style and conventions

• Contribution checklist

• Committer checklist

• MAINTAINERS

• Consensus

If you wish to contribute to glibc please post your idea or patch to libc-help@sourceware.org for initial review.

Review the contribution checklist before emailing libc-alpha@sourceware.org with your contribution.

glibc has maintainers for each architecture. Please CC them on any libc-alpha emails related to the architecture of your interest.

For help subscribing to the mailing-lists, simply send an empty e-mail to libc-help-info@sourceware.org or libc-alpha-info@sourceware.org

Developers with commit access should follow the committer checklist prior to pushing patches to the upstream source code repository.

4.2. Resources

4.2.1. Developer Resources

• The IRC channel is on Freenode at #glibc.

• Glibc Git Repository Information

• Regenerating and updating files not maintained as source in glibc

• Deprecating and removing obsolete code

• Glibc Locales/Charsets Guide

• Guidelines on the API

• The Austin Group (POSIX maintainers)

• Linux Standard Base

4.2.2. Standards and Documentation References

• Open Group reference for POSIX 1003.1-2008

• Linux man-pages

• Open Standards - ISO/IEC JTC1/SC22 WG14, WG15, WG20, WG21 ...

4.3. Release management

• Release process

• Glibc release timeline

4.4. Internals Documentation

• Using errlist-compat

• Dynamic Loader Internals

• Platform specific headers

• PTR_MANGLE & friends: http://udrepper.livejournal.com/13393.html

• SymbolVersioning

  • How to version a structure and create a change-proof function wrapper.

• Namespace control: __-prefixed symbols

• Conditional Code: PIC, SHARED, etc.

• AddOns: Working with addon dirs

• Destructor support for thread_local variables

• Environment Variable Guidelines

• System Call Wrappers

4.5. Issue Tracking

• Bugzilla Procedures

Do you want to help with GLIBC? The GLIBC Bug Triage initiative is a great way to get involved.

If you think the GLIBC bugzilla version selection drop-down is missing a version number, please contact libc-help < libc-help@sourceware.org >.

If you think that bugs aren't being fixed fast enough or that new features aren't being implemented fast enough, please take the time to read this email http://sourceware.org/ml/libc-help/2008-08/msg00009.html

4.6. Testing

• The glibc testsuite

• Testing results by target

• Testing a GLIBC build

• Testing against Gnulib's test suite

• Finding and fixing test-suite failures associated with check-localplt

• Writing a white box test for glibc internals

4.7. Debugging

• Debugging techniques for GLIBC development.

• GLIBC 'configure' debugging (todo).

• GLIBC 'make' debugging (todo).

• Debugging applications which use GLIBC (todo).

4.8. Tips and Tricks

• Loader tips and tricks.

• Compiling for x32.

• Providing your own version of FOO.

• Another recipe for intercepting syscalls and providing your own version of FOO (instructions specifically for Ubuntu Linux systems).

• The Plash project has some hints about GLIBC (mainly about build issues).

• rtldi can be used to install multiple versions of GLIBC simultaneously (specifically, multiple versions of the dynamic linker, ld.so).

• How to build an appication with your own custom glibc.

• How to use secure_getenv

4.8.1. Project TODO

We have one master TODO list. The links below are pages dedicated to specific entries in the master list.

• The master project TODO list

• Small Projects

• Generic

• Power Architecture

4.9. Project Wishlist by Developer

If you are looking for a GLIBC project this is the place to start.

• Agner Fog's Wishlists

• Ryan Arnold's Wishlist

4.10. Website Maintenance

The current website maintenance procedure is documented here.

4.11. Project Ports

4.11.1. External

• Port to Google Native Client (announcement)

• Port to OpenSolaris (announcement)

• Port to FreeBSD and NetBSD

4.11.2. How to Submit a New Port

• http://sourceware.org/ml/libc-alpha/2012-02/msg00376.html

• Section Porting on http://www.gnu.org/software/libc/development.html

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5. Feedback

We look forward to your feedback! Please be aware that this wiki uses text captchas to deter spam. If you have any problems answering the text captchas please contact libc-help@sourceware.org.

• Feedback and GLIBC Wiki FAQ - Leave a question about GLIBC here and a developer may answer it.

• GLIBC Wiki TODO List - A list of suggestions for improving the quality and breadth of the GLIBC wiki.