GNU C Library

"glibc" redirects here. It is not to be confused with GLib or Gnulib.
GNU C Library
Original author(s) Roland McGrath
Developer(s) GNU Project
Initial release 1987[1]
Stable release 2.21 (February 6, 2015[2]) [±]
Development status Active
Written in C
Operating system Unix-like
Type Runtime library
License GNU Lesser General Public License
Website www.gnu.org/software/libc/
The Linux API is composed out of the System Call Interface of the Linux kernel, the GNU C Library (by GNU), libdrm, libalsa and libevdev (by freedesktop.org).
The GNU C Library is a wrapper around the system calls of the Linux kernel.
The Linux kernel and GNU C Library together form the Linux API. After compilation, the binaries offer an ABI.

The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. Despite its name, it now also directly supports C++ (and indirectly other programming languages). Originally written by the Free Software Foundation (FSF) for the GNU operating system, the library's development had been overseen by a committee since 2001,[3] with Ulrich Drepper[4] as the lead contributor and maintainer. In March 2012, the steering committee voted to disband itself, in favor of a community-driven development process, with Ryan Arnold, Maxim Kuvyrkov, Joseph Myers, Carlos O'Donell, and Alexandre Oliva as non-decision making project stewards.[5][6]

Released under the GNU Lesser General Public License, glibc is free software.

History

glibc was initially written mostly by Roland McGrath, working for the Free Software Foundation (FSF) in the 1980s.

In February 1988, FSF described glibc as having nearly completed the functionality required by ANSI C.[7] By 1992, it had the ANSI C-1989 and POSIX.1-1990 functions implemented and work was under way on POSIX.2.[8]

A temporary fork

In the early 1990s, the developers of the Linux kernel forked glibc. Their fork, called "Linux libc", was maintained separately for years and released versions 2 through 5.

When FSF released glibc 2.0 in January 1997, it had much more complete POSIX standards compliance, better internationalisation and multilingual function, IPv6 capability, 64-bit data access, facilities for multithreaded applications, future version compatibility, and the code was more portable.[9] At this point, the Linux kernel developers discontinued their fork and returned to using FSF's glibc.[10]

The last used version of Linux libc used the internal name (soname) libc.so.5. Following on from this, glibc 2.x on Linux uses the soname libc.so.6[11] (Alpha and IA64 architectures now use libc.so.6.1, instead). The *.so file name is often abbreviated as libc6 (for example in the package name in Debian) following the normal conventions for libraries.

According to Richard Stallman, the changes that had been made in Linux libc could not be merged back into glibc because the authorship status of that code was unclear and the GNU project is quite strict about recording copyright and authors.[12]

Version history

For most systems, the version of glibc can be obtained by executing the lib file (for example, /lib/libc.so.6).

Version Date Notes Adoption
0.1 – 0.6 Oct 1991 – February 1992
1.0 February 1992
1.01 – 1.09.3 March 1992 – December 1994
1.90 – 1.102 May 1996 – January 1997
2.0 January 1997
2.0.1 January 1997
2.0.2 February 1997
2.0.91 December 1997
2.0.95 July 1998
2.1 February 1999
2.1.1 March 1999
2.2 November 2000
2.2.1 January 2001
2.2.2 February 2001
2.2.3 March 2001
2.2.4 July 2001
2.3 October 2002
2.3.1 October 2002
2.3.2 February 2003 Debian 3.1 (Sarge)
2.3.3 December 2003
2.3.4 December 2004 Standard for Linux Standard Base (LSB) 3.0 RHEL 4 (Update 5)
2.3.5 April 2005 SLES 9
2.3.6 November 2005 Debian 4.0 (Etch)
2.4 March 2006 Standard for LSB 4.0, initial inotify support SLES 10
2.5 September 2006 Full inotify support RHEL 5
2.6 May 2007
2.7 October 2007 Debian 5 (Lenny), Ubuntu 8.04
2.8 April 2008
2.9 November 2008
2.10 May 2009
2.11 October 2009 SLES 11, Ubuntu 10.04, eglibc used in Debian 6 (Squeeze)
2.12 May 2010 RHEL 6
2.13 January 2011 eglibc 2.13 used in Debian 7 (Wheezy)
2.14 June 2011
2.15 March 2012 Ubuntu 12.04 and 12.10
2.16 June 2012 x32 ABI support, ISO C11 compliance, SystemTap
2.17 December 2012 64-bit ARM support; Ubuntu 13.04, RHEL 7
2.18 August 2013 Improved C++11 support. Support for Intel TSX lock elision. Support for the Xilinx MicroBlaze and IBM POWER8 microarchitectures. Fedora 20
2.19 February 2014 SystemTap probes for malloc. GNU Indirect Function (IFUNC) support for ppc32 and ppc64. New feature test macro _DEFAULT_SOURCE to replace _SVID_SOURCE and _BSD_SOURCE. Preliminary safety documentation for all functions in the manual. ABI change in ucontext and jmp_buf for s390/s390x. Ubuntu 14.04
2.20 September 2014 Support for file description locks Fedora 21
2.21 February 2015 New semaphore implementation Ubuntu 15.04, Debian experimental, Fedora 22

Supported hardware and kernels

Glibc is used in systems that run many different kernels and different hardware architectures. Its most common use is in systems using the Linux kernel on x86 hardware, however, officially supported hardware includes: x86, Motorola 680x0, DEC Alpha, PowerPC, ETRAX CRIS, s390, and SPARC. It officially supports the Hurd and Linux kernels. Additionally, there are heavily patched versions that run on the kernels of FreeBSD and NetBSD (from which Debian GNU/kFreeBSD and Debian GNU/NetBSD systems are built, respectively), as well as a forked-version of OpenSolaris.[13] It is also used (in an edited form) and named libroot.so in BeOS and Haiku.[14]

Functionality

glibc provides the functionality required by the Single UNIX Specification, POSIX (1c, 1d, and 1j) and some of the functionality required by ISO C11, ISO C99, Berkeley Unix (BSD) interfaces, the System V Interface Definition (SVID) and the X/Open Portability Guide (XPG), Issue 4.2, with all extensions common to XSI (X/Open System Interface) compliant systems along with all X/Open UNIX extensions.

In addition, glibc also provides extensions that have been deemed useful or necessary while developing GNU.

Use in small devices

glibc has been criticized as being "bloated" and slower than other libraries in the past, e.g. by Linus Torvalds[15] and embedded Linux programmers. For this reason, several alternative C standard libraries have been created which emphasize a smaller footprint. Alternative libcs are Bionic (based mostly on libc from BSD and used in Android[16]), dietlibc, uClibc, Newlib, Klibc, musl, and EGLIBC.

However, many small-device projects use GNU libc over the smaller alternatives because of its application support, standards compliance, and completeness. Examples include Openmoko[17] and Familiar Linux for iPaq handhelds (when using the GPE display software).[18]

See also

Wikimedia Commons has media related to GNU C Library.
Other C standard libraries

References

  1. ↑ Corbet, Jonathan (28 March 2012). "A turning point for GNU libc". LWN.net.
  2. ↑ O'Donell, Carlos (2015-02-06). "The GNU C Library version 2.21 is now available." (Mailing list). info-gnu. Retrieved 2015-02-06.
  3. ↑ "glibc homepage". In 2001 The GNU C Library Steering Committee ..., was formed and currently consists of Mark Brown, Paul Eggert, Andreas Jaeger, Jakub Jelinek, Roland McGrath and Andreas Schwab.
  4. ↑ "Ulrich Drepper". LinkedIn. Retrieved 2012-06-13.
  5. ↑ McGrath, Roland (26 March 2012). "glibc steering committee dissolving". Sourceware.org. Retrieved 2012-06-13.
  6. ↑ Myers, Joseph S. (26 March 2012). "GNU C Library development and maintainers". Sourceware.org. Retrieved 2012-06-13.
  7. ↑ "https://www.gnu.org/bulletins/bull4.html". Most libraries are done. Roland McGrath [...] has a nearly complete set of ANSI C library functions. We hope they will be ready some time this spring.
  8. ↑ "GNU's Bulletin, vol. 1 no. 12". It now contains all of the ANSI C-1989 and POSIX.1-1990 functions, and work is in progress on POSIX.2 and Unix functions (BSD and System V)
  9. ↑ Lee, Elliot (2001). "A Technical Comparison of glibc 2.x With Legacy System Libraries". Archived from the original on 11 April 2004.
  10. ↑ "Forking: it could even happen to you". the split between GNU LIBC and the Linux LIBC -- it went on for years while Linux stabilized, and then the forks re-merged into one project
  11. ↑ "Fear of Forking essay, see "6. glibc --> Linux libc --> glibc"".
  12. ↑ "Fear of Forking, footnote on Stallman's merge comments".
  13. ↑ Bartley, David; Spang, Michael. "GNU/kOpenSolaris (GNU libc/base + OpenSolaris kernel)". Retrieved 2008-12-16.
  14. ↑ "Haiku Source". libroot.so is not part of GNU project and is included in Haiku source code.
  15. ↑ Torvalds, Linus (9 January 2002). "Posting to the glibc mailing list".
  16. ↑ "Bionic libc README".
  17. ↑ "OpenMoko components". We will use glibc (not uClibC) ... The alternatives may save more space and be more optimized, but are more likely to give us integration headaches
  18. ↑ "Re: [Familiar] Which glibc for Familiar 0.8.4 ?". Question: which version of the GLIBC was used to build the Familiar 0.8.4 ? Answer: 2.3.3

External links