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). ``clang`` [clang]_ is also supported, see 10docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`. 11 12This dialect contains many extensions to the language [gnu-extensions]_, 13and many of them are used within the kernel as a matter of course. 14 15There is some support for compiling the kernel with ``icc`` [icc]_ for several 16of the architectures, although at the time of writing it is not completed, 17requiring third-party patches. 18 19Attributes 20---------- 21 22One of the common extensions used throughout the kernel are attributes 23[gcc-attribute-syntax]_. Attributes allow to introduce 24implementation-defined semantics to language entities (like variables, 25functions or types) without having to make significant syntactic changes 26to the language (e.g. adding a new keyword) [n2049]_. 27 28In some cases, attributes are optional (i.e. a compiler not supporting them 29should still produce proper code, even if it is slower or does not perform 30as many compile-time checks/diagnostics). 31 32The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using 33directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) 34in order to feature detect which ones can be used and/or to shorten the code. 35 36Please refer to ``include/linux/compiler_attributes.h`` for more information. 37 38.. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards 39.. [gcc] https://gcc.gnu.org 40.. [clang] https://clang.llvm.org 41.. [icc] https://software.intel.com/en-us/c-compilers 42.. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html 43.. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html 44.. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html 45.. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf 46 47