0001 .. _programming_language:
0002
0003 Programming Language
0004 ====================
0005
0006 The kernel is written in the C programming language [c-language]_.
0007 More precisely, the kernel is typically compiled with ``gcc`` [gcc]_
0008 under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11.
0009 ``clang`` [clang]_ is also supported, see docs on
0010 :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
0011
0012 This dialect contains many extensions to the language [gnu-extensions]_,
0013 and many of them are used within the kernel as a matter of course.
0014
0015 There is some support for compiling the kernel with ``icc`` [icc]_ for several
0016 of the architectures, although at the time of writing it is not completed,
0017 requiring third-party patches.
0018
0019 Attributes
0020 ----------
0021
0022 One of the common extensions used throughout the kernel are attributes
0023 [gcc-attribute-syntax]_. Attributes allow to introduce
0024 implementation-defined semantics to language entities (like variables,
0025 functions or types) without having to make significant syntactic changes
0026 to the language (e.g. adding a new keyword) [n2049]_.
0027
0028 In some cases, attributes are optional (i.e. a compiler not supporting them
0029 should still produce proper code, even if it is slower or does not perform
0030 as many compile-time checks/diagnostics).
0031
0032 The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using
0033 directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``)
0034 in order to feature detect which ones can be used and/or to shorten the code.
0035
0036 Please refer to ``include/linux/compiler_attributes.h`` for more information.
0037
0038 .. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards
0039 .. [gcc] https://gcc.gnu.org
0040 .. [clang] https://clang.llvm.org
0041 .. [icc] https://software.intel.com/en-us/c-compilers
0042 .. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
0043 .. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
0044 .. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
0045 .. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
0046
