| .. _programming_language: |
| |
| Programming Language |
| ==================== |
| |
| The kernel is written in the C programming language [c-language]_. |
| More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ |
| under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11. |
| |
| This dialect contains many extensions to the language [gnu-extensions]_, |
| and many of them are used within the kernel as a matter of course. |
| |
| There is some support for compiling the kernel with ``clang`` [clang]_ |
| and ``icc`` [icc]_ for several of the architectures, although at the time |
| of writing it is not completed, requiring third-party patches. |
| |
| Attributes |
| ---------- |
| |
| One of the common extensions used throughout the kernel are attributes |
| [gcc-attribute-syntax]_. Attributes allow to introduce |
| implementation-defined semantics to language entities (like variables, |
| functions or types) without having to make significant syntactic changes |
| to the language (e.g. adding a new keyword) [n2049]_. |
| |
| In some cases, attributes are optional (i.e. a compiler not supporting them |
| should still produce proper code, even if it is slower or does not perform |
| as many compile-time checks/diagnostics). |
| |
| The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using |
| directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) |
| in order to feature detect which ones can be used and/or to shorten the code. |
| |
| Please refer to ``include/linux/compiler_attributes.h`` for more information. |
| |
| .. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards |
| .. [gcc] https://gcc.gnu.org |
| .. [clang] https://clang.llvm.org |
| .. [icc] https://software.intel.com/en-us/c-compilers |
| .. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html |
| .. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html |
| .. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html |
| .. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf |
| |