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1 | .. _programming_language: |
2 | ||
3 | Programming Language | |
4 | ==================== | |
5 | ||
6 | The kernel is written in the C programming language [c-language]_. | |
7 | More precisely, the kernel is typically compiled with ``gcc`` [gcc]_ | |
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8 | under ``-std=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11. |
9 | ``clang`` [clang]_ is also supported, see docs on | |
10 | :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`. | |
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11 | |
12 | This dialect contains many extensions to the language [gnu-extensions]_, | |
13 | and many of them are used within the kernel as a matter of course. | |
14 | ||
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15 | Attributes |
16 | ---------- | |
17 | ||
18 | One of the common extensions used throughout the kernel are attributes | |
19 | [gcc-attribute-syntax]_. Attributes allow to introduce | |
20 | implementation-defined semantics to language entities (like variables, | |
21 | functions or types) without having to make significant syntactic changes | |
22 | to the language (e.g. adding a new keyword) [n2049]_. | |
23 | ||
24 | In some cases, attributes are optional (i.e. a compiler not supporting them | |
25 | should still produce proper code, even if it is slower or does not perform | |
26 | as many compile-time checks/diagnostics). | |
27 | ||
28 | The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using | |
29 | directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) | |
30 | in order to feature detect which ones can be used and/or to shorten the code. | |
31 | ||
32 | Please refer to ``include/linux/compiler_attributes.h`` for more information. | |
33 | ||
34 | .. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards | |
35 | .. [gcc] https://gcc.gnu.org | |
36 | .. [clang] https://clang.llvm.org | |
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37 | .. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html |
38 | .. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html | |
39 | .. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html | |
40 | .. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf | |
41 |