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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]_ | |
8 | under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90 | |
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9 | (including some C99 features). ``clang`` [clang]_ is also supported, see |
10 | docs on :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 | There is some support for compiling the kernel with ``icc`` [icc]_ for several |
16 | of the architectures, although at the time of writing it is not completed, | |
17 | requiring third-party patches. | |
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18 | |
19 | Attributes | |
20 | ---------- | |
21 | ||
22 | One of the common extensions used throughout the kernel are attributes | |
23 | [gcc-attribute-syntax]_. Attributes allow to introduce | |
24 | implementation-defined semantics to language entities (like variables, | |
25 | functions or types) without having to make significant syntactic changes | |
26 | to the language (e.g. adding a new keyword) [n2049]_. | |
27 | ||
28 | In some cases, attributes are optional (i.e. a compiler not supporting them | |
29 | should still produce proper code, even if it is slower or does not perform | |
30 | as many compile-time checks/diagnostics). | |
31 | ||
32 | The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using | |
33 | directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``) | |
34 | in order to feature detect which ones can be used and/or to shorten the code. | |
35 | ||
36 | Please 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 |