glibc

The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. It is a wrapper around the system calls of the Linux kernel for application use. Despite its name, it now also directly supports C++ (and, indirectly, other programming languages). It was started in the 1980s by the Free Software Foundation (FSF) for the GNU operating system.

Not to be confused with GLib or Gnulib.

GNU C Library
Original author(s)Roland McGrath
Developer(s)GNU Project, most contributions by Ulrich Drepper
Initial release1987 (1987)[1]
Stable release
2.38[2] Edit this on Wikidata / 31 July 2023
Repository
Written inC
Operating systemUnix-like
TypeRuntime library
License2001: LGPL-2.1-or-later[lower-alpha 1]
1992: LGPL-2.0-or-later[lower-alpha 2]
Websitewww.gnu.org/software/libc/

Released under the GNU Lesser General Public License,[3] glibc is free software. The GNU C Library project provides the core libraries for the GNU system, as well as many systems that use Linux as the kernel. These libraries provide critical APIs including ISO C11, POSIX.1-2008, BSD, OS-specific APIs and more. These APIs include such foundational facilities as open, read, write, malloc, printf, getaddrinfo, dlopen, pthread_create, crypt, login, exit and more.

History
Version Date Highlights
0.1 – 0.6October 1991 – February 1992
1.0February 1992
1.01 – 1.09.3March 1992 – December 1994
1.90 – 1.102May 1996 – January 1997
2.0January 1997
2.0.1January 1997
2.0.2February 1997
2.0.91December 1997
2.0.95July 1998
2.1February 1999
2.1.1March 1999
2.2November 2000
2.2.1January 2001
2.2.2February 2001
2.2.3March 2001
2.2.4July 2001
2.3October 2002
2.3.1October 2002
2.3.2February 2003
2.3.3December 2003
2.3.4December 2004Minimum for Linux Standard Base (LSB) 3.0
2.3.5April 2005
2.3.6November 2005
2.4March 2006Minimum for LSB 4.0, initial inotify support
2.5September 2006Full inotify support. RHEL5 end of support was November 30, 2020 (2020-11-30)
2.6May 2007
2.7October 2007
2.8April 2008
2.9November 2008
2.10May 2009Minimum for LSB 5.0. Initial psiginfo support.
2.11October 2009SLES11 reached end of long term support in March 2022.
2.12May 2010
2.13January 2011
2.14June 2011
2.15March 2012
2.16June 2012x32 ABI support, ISO C11 compliance, SystemTap
2.17December 201264-bit ARM support
2.18August 2013Improved C++11 support. Support for Intel TSX lock elision. Support for the Xilinx MicroBlaze and IBM POWER8 microarchitectures.
2.19February 2014SystemTap 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.
2.20September 2014Support for file description locks
2.21February 2015New semaphore implementation
2.22August 2015Support to enable Google Native Client (NaCl), that originally ran on x86, running on ARMv7-A, Unicode 7.0
2.23February 2016Unicode 8.0
2.24August 2016Some deprecated features have been removed
2.25February 2017The getentropy and getrandom functions, and the <sys/random.h> header file have been added.
2.26August 2017Improved performance (per-thread cache for malloc), Unicode 10 support
2.27February 2018Performance optimizations. RISC-V support.
2.28August 2018statx, renameat2, Unicode 11.0.0
2.29February 2019
  • getcpu wrapper
  • build and install all locales as directories with files
  • optimized trigonomical functions
  • Transactional Lock Elision for powercp64le ABI
  • posix_spawn_file_actions_addchdir_np and posix_spawn_file_actions_addfchdir_np
  • popen and system do not run atfork handlers anymore
  • support for the C-SKY ABIV2 running on Linux
  • strftime's default formatting of a locale's alternative year; the '_' and '-' flags can now be applied to its "%EY"[7]
2.30August 2019Unicode 12.1.0, the dynamic linker accepts the --preload argument to preload shared objects, the gettid function has been added on Linux, Minguo (Republic of China) calendar support, new Japanese era added to ja_JP locale, memory allocation functions fail with total object size larger than PTRDIFF_MAX; CVE-2019-7309 and CVE-2019-9169 fixed[8]
2.31February 2020Initial C23 standard support
2.32August 2020Unicode 13.0, 'access' attribute for better warnings in GCC 10, i.e. to "help detect buffer overflows and other out-of-bounds accesses"[9]
2.33February 2021HWCAPS
2.34August 2021libpthread, libdl, libutil, libanl has been integrated into libc.
2.35February 2022Unicode 14.0, C.UTF-8 locale, restartable sequences. Removed Intel MPX support.
2.36August 2022
2.37February 2023
2.38August 2023The strlcpy and strlcat functions added. libmvec support for ARM64.
Ulrich Drepper in 2007, the main author of glibc
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 glibc project was initially written mostly by Roland McGrath, working for the Free Software Foundation (FSF) in the summer of 1987 as a teenager.[10] In February 1988, FSF described glibc as having nearly completed the functionality required by ANSI C.[11] By 1992, it had the ANSI C-1989 and POSIX.1-1990 functions implemented and work was under way on POSIX.2.[12] In September 1995 Ulrich Drepper made his first contribution to the glibc and by 1997 most commits were made by him. Drepper held the maintainership position for many years and until 2012 accumulated 63% of all commits to the project.[13]

In May 2009 glibc was migrated to a Git repository.[13]

In 2010, a licensing issue was resolved which was caused by the Sun RPC implementation in glibc that was not GPL compatible. It was fixed by re-licensing the Sun RPC components under the BSD license.[14][15]

In 2014, glibc suffered from an ABI breakage bug on s390.[16]

In July 2017, 30 years after he started glibc, Roland McGrath announced his departure, "declaring myself maintainer emeritus and withdrawing from direct involvement in the project. These past several months, if not the last few years, have proven that you don't need me anymore".[10]

In 2018, maintainer Raymond Nicholson removed a joke about abortion from the glibc source code. It was restored later by Alexandre Oliva after Richard Stallman demanded to have it returned.[17]

In 2021, the copyright assignment requirement to the Free Software Foundation was removed from the project.[18]

Fork and variant

In 1994, the developers of the Linux kernel forked glibc. Their fork, "Linux libc", was maintained separately until around 1998. Because the copyright attribution was insufficient, changes could not be merged back to the GNU Libc.[19] When the FSF released glibc 2.0 in January 1997, the kernel developers discontinued Linux libc due to glibc 2.0's superior compliance with POSIX standards.[20] glibc 2.0 also had better internationalisation and more in-depth translation, IPv6 capability, 64-bit data access, facilities for multithreaded applications, future version compatibility, and the code was more portable.[21] 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[22]

In 2009, Debian and a number of derivatives switched from glibc to the variant[24] eglibc.[25] Eglibc was supported by a consortium consisting of Freescale, MIPS, MontaVista and Wind River.[26] It contained changes that made it more suitable for embedded usage and had added support for architectures that were not supported by glibc, such as the PowerPC e500. The code of eglibc was merged back into glibc at version 2.20.[27] Since 2014, eglibc is discontinued. The Yocto Project and Debian also moved back to glibc since the release of Debian Jessie.[28]

Steering committee

Starting in 2001 the library's development had been overseen by a committee,[29] with Ulrich Drepper[30] kept as the lead contributor and maintainer. The steering committee installation was surrounded by a public controversy, as it was openly described by Ulrich Drepper as a failed hostile takeover maneuver by Richard Stallman.[31][32][33][34]

In March 2012, the steering committee voted to disband itself and remove Drepper in favor of a community-driven development process, with Ryan Arnold, Maxim Kuvyrkov, Joseph Myers, Carlos O'Donell, and Alexandre Oliva holding the responsibility of GNU maintainership (but no extra decision-making power).[35][36][37]

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.

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[38] includes: ARM, ARC, C-SKY, DEC Alpha, IA-64, Motorola m68k, MicroBlaze, MIPS, Nios II, PA-RISC, PowerPC, RISC-V, s390, SPARC, and x86 (old versions support TILE). 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.[39] It is also used (in an edited form) and named libroot.so in BeOS and Haiku.[40]

Use in small devices

glibc has been criticized as being "bloated" and slower than other libraries in the past, e.g. by Linus Torvalds[41] and embedded Linux programmers. For this reason, several alternative C standard libraries have been created which emphasize a smaller footprint. However, many small-device projects use GNU libc over the smaller alternatives because of its application support, standards compliance, and completeness. Examples include Openmoko[42] and Familiar Linux for iPaq handhelds (when using the GPE display software).[43]

Compatibility layers

There are compatibility layers ("shims") to allow programs written for other ecosystems to run on glibc interface offering systems. These include libhybris, a compatibility layer for Android's Bionic, and Wine, which can be seen as a compatibility layer from Windows APIs to glibc and other native APIs available on Unix-like systems.

See also

Notes
  1. LGPL-2.1-or-later since 2001-07-06, version 2.2.4.[3][4]
  2. LGPL-2.0-or-later from 1992 to 2001-07-05. Version 1.04? to 2.2.3.[5][6]

References
  1. Corbet, Jonathan (28 March 2012). "A turning point for GNU libc". LWN.net.
  2. Andreas K. Huettel (31 July 2023). "The GNU C Library version 2.38 is now available". Retrieved 1 August 2023.
  3. "sourceware.org Git – glibc.git/blob – Makefile". sourceware.org. Retrieved 10 June 2021. LGPL-2.1-or-later in the headers
  4. "sourceware.org Git – glibc.git/commit – Update to LGPL v.2.1". sourceware.org. 6 July 2001. Retrieved 10 June 2021. LGPL-2.1-or-later in the headers
  5. "glibc-1.04.tar.Z". 4 September 1992. Retrieved 22 December 2021.
  6. "sourceware.org Git – glibc.git/commit – Initial import: Makefile". sourceware.org. 18 February 1995. Retrieved 10 June 2021. LGPL-2.0-or-later in the headers
  7. "sourceware.org Git – glibc.git/blob – NEWS".
  8. "sourceware.org Git – glibc.git/blob – NEWS".
  9. "The GNU C Library version 2.32 is now available". sourceware.org. Retrieved 13 August 2020.
  10. "Roland McGrath bows out as glibc maintainer [LWN.net]". lwn.net. 7 July 2017. Retrieved 8 July 2017.
  11. "GNU's Bulletin, vol. 1 no. 4, February, 1988". 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.
  12. "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)
  13. Corbet, Jonathan (28 March 2012). "A turning point for GNU libc". LWN.net. Of the nearly 19,000 commits found in the project's git repository (which contains changes back to 1995), over 12,000 were made by Ulrich.
  14. "Glibc finally free software – The H Open: News and Features". H-online. Retrieved 19 September 2021.
  15. Phipps, Simon (2 September 2010). "Gnu/Linux: Finally, it's really free software". InfoWorld. Retrieved 19 September 2021.
  16. Corbet, Jonathan. "The glibc s390 ABI break [LWN.net]". LWN.net. Retrieved 17 March 2022.
  17. Claburn, Thomas. "Glibc 'abortion joke' diff tiff leaves Richard Stallman miffed". The Register. Retrieved 17 January 2023.
  18. Halfacree, Gareth. "Open-source projects glibc and gnulib look to sever copyright ties with Free Software Foundation". The Register. Retrieved 17 January 2023.
  19. "History of glibc and Linux libc". Free Software Magazine. Retrieved 10 May 2021.
  20. "Forking: it could even happen to you". 24 October 2000. Archived from the original on 15 September 2009. 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
  21. Lee, Elliot (2001). "A Technical Comparison of glibc 2.x With Legacy System Libraries". Archived from the original on 11 April 2004.
  22. "Fear of Forking essay, see "6. glibc --> Linux libc --> glibc"".
  23. "EGLIBC: FAQ". eglibc.org. Retrieved 16 September 2021.
  24. The eglibc developers emphasized themselves that eglibc is not a fork of glibc, but a variant, accepting patches from the upstream glibc project.[23]
  25. Vaduva, Alexandru (2016). Linux : embedded development: leverage the power of Linux to develop captivating and powerful embedded Linux projects : a course in three modules. Alex Gonzalez, Chris Simmonds. Birmingham, UK. p. 24. ISBN 978-1-78712-445-5. OCLC 960471438.{{cite book}}: CS1 maint: location missing publisher (link)
  26. Stiebert, Julius (6 May 2009). "Debian wechselt zur Eglibc". golem.de. Retrieved 16 September 2021.
  27. Simmonds, Chris (2017). Mastering embedded Linux programming: unleash the full potential of embedded Linux (2nd ed.). Birmingham, UK. p. 26. ISBN 978-1-78728-885-0. OCLC 995052708.{{cite book}}: CS1 maint: location missing publisher (link)
  28. Vaduva, Alexandru (2015). Learning embedded Linux using the Yocto project: develop powerful embedded Linux systems with the Yocto project components. Birmingham, UK. p. 29. ISBN 978-1-78439-519-3. OCLC 914797028.{{cite book}}: CS1 maint: location missing publisher (link)
  29. "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.
  30. "Ulrich Drepper". LinkedIn. Retrieved 13 June 2012.
  31. online, heise (19 August 2001). "Open-Source-Entwickler kritisiert Stallman". heise online (in German). Retrieved 16 September 2021.
  32. Drepper, Ulrich (26 June 2000). "RMS is at it again". sourceware.org. Retrieved 20 November 2015. A few weeks ago RMS started the next attack on me (a single mail, followed by indirect tries to take influence, followed by another mail today). The essence is that he complains I am not following "GNU policies" and therefore have to be replaced by a steering committee of which I could be a part. Some of you (namely Roland and Andreas S.) probably know about this since he proposed both as other members of the committee. In addition there was Mark Brown listed (I know somebody of this name at IBM who would also fit in this group but I'm not sure whether it is really him.) Anyhow, I completely reject this. It is not helping at all, the opposite is true. First, I am not aware of any essential policies I'm violating. The only ones are that I'm not following orders from RMS which clearly have political intends (which is of course a sacrilege) and possibly that I do not care about Winblowz (if the latter counts at all). None of this will change in any way.
  33. Drepper, Ulrich (15 August 2001). "glibc 2.2.4". sourceware.com. Retrieved 29 November 2015. And now for some not so nice things. Stallman recently tried what I would call a hostile takeover of the glibc development. He tried to conspire behind my back and persuade the other main developers to take control so that in the end he is in control and can dictate whatever pleases him. This attempt failed but he kept on pressuring people everywhere and it got really ugly. In the end I agreed to the creation of a so-called "steering committee" (SC).
  34. rms-accused-of-attempting-glibc-hostile-takeover on slashdot.com on 19 August 2001
  35. "The GNU C Library Steering Committee disbands – The H Open: News and Features". H-Online. Retrieved 16 March 2023.
  36. McGrath, Roland (26 March 2012). "glibc steering committee dissolving". Sourceware.org. Retrieved 13 June 2012.
  37. Myers, Joseph S. (26 March 2012). "GNU C Library development and maintainers". Sourceware.org. Retrieved 13 June 2012.
  38. "The GNU C Library machine maintainers".
  39. Bartley, David; Spang, Michael. "GNU/kOpenSolaris (GNU libc/base + OpenSolaris kernel)". Archived from the original on 6 November 2019. Retrieved 16 December 2008.
  40. "Haiku Source". GitHub. libroot.so is not part of GNU project and is included in Haiku source code.
  41. Torvalds, Linus (9 January 2002). "Posting to the glibc mailing list".
  42. "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
  43. "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
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