Definitions

gnu c

GNU C Library

The GNU C Library, commonly known as glibc, is the C standard library released by the GNU Project. Originally written by the Free Software Foundation (FSF) for the GNU operating system, the library's development has been overseen by a committee since 2001, with Ulrich Drepper from Red Hat as the lead contributor and maintainer.

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

History

glibc was initially written mostly by Roland McGrath, working for the FSF in the 1980s.

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

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 1996, it had much more complete POSIX standards support, better internationalisation/multilingual support, support for IPv6, 64-bit data access, support for multithreaded applications, future version compatibility support, and the code was more portable. At this point, the Linux kernel developers discontinued their fork and returned to using FSF's glibc.

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 (Alpha and IA64 architectures now use libc.so.6.1, instead). The soname 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.

Supported hardware and kernels

Glibc is used in systems which run many different kernels and different hardware architectures. Its most common use is in systems using the Linux kernel on x86 hardware, but officially supported hardware includes: x86, Motorola 680x0, DEC Alpha, PowerPC, ARM, ETRAX CRIS, s390, and SPARC. It officially supports the Hurd and Linux kernels, although 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). It is also used (in an edited form) as the libroot of BeOS and hence Haiku.

Functionality

glibc provides the functionality required by the Single UNIX Specification, POSIX (1c, 1d, and 1j) and some of the functionality required by 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 which 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 and embedded Linux programmers. For this reason, several alternative C standard libraries have been created which emphasize a smaller footprint. Among them are dietlibc, uClibc, Newlib, Klibc, 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 and Familiar Linux for iPaq handhelds (when using the GPE display software).

See also

References

External links

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