1.. _programming_language:
2
3Programming Language
4====================
5
6The kernel is written in the C programming language [c-language]_.
7More precisely, the kernel is typically compiled with ``gcc`` [gcc]_
8under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
9(including some C99 features).
10
11This dialect contains many extensions to the language [gnu-extensions]_,
12and many of them are used within the kernel as a matter of course.
13
14There is some support for compiling the kernel with ``clang`` [clang]_
15and ``icc`` [icc]_ for several of the architectures, although at the time
16of writing it is not completed, requiring third-party patches.
17
18Attributes
19----------
20
21One of the common extensions used throughout the kernel are attributes
22[gcc-attribute-syntax]_. Attributes allow to introduce
23implementation-defined semantics to language entities (like variables,
24functions or types) without having to make significant syntactic changes
25to the language (e.g. adding a new keyword) [n2049]_.
26
27In some cases, attributes are optional (i.e. a compiler not supporting them
28should still produce proper code, even if it is slower or does not perform
29as many compile-time checks/diagnostics).
30
31The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using
32directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``)
33in order to feature detect which ones can be used and/or to shorten the code.
34
35Please refer to ``include/linux/compiler_attributes.h`` for more information.
36
37.. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards
38.. [gcc] https://gcc.gnu.org
39.. [clang] https://clang.llvm.org
40.. [icc] https://software.intel.com/en-us/c-compilers
41.. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
42.. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
43.. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
44.. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
45
46