46 lines
2.0 KiB
ReStructuredText
46 lines
2.0 KiB
ReStructuredText
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.. _programming_language:
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Programming Language
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====================
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The kernel is written in the C programming language [c-language]_.
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More precisely, the kernel is typically compiled with ``gcc`` [gcc]_
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under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
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(including some C99 features).
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This dialect contains many extensions to the language [gnu-extensions]_,
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and many of them are used within the kernel as a matter of course.
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There is some support for compiling the kernel with ``clang`` [clang]_
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and ``icc`` [icc]_ for several of the architectures, although at the time
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of writing it is not completed, requiring third-party patches.
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Attributes
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----------
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One of the common extensions used throughout the kernel are attributes
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[gcc-attribute-syntax]_. Attributes allow to introduce
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implementation-defined semantics to language entities (like variables,
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functions or types) without having to make significant syntactic changes
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to the language (e.g. adding a new keyword) [n2049]_.
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In some cases, attributes are optional (i.e. a compiler not supporting them
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should still produce proper code, even if it is slower or does not perform
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as many compile-time checks/diagnostics).
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The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using
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directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``)
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in order to feature detect which ones can be used and/or to shorten the code.
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Please refer to ``include/linux/compiler_attributes.h`` for more information.
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.. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards
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.. [gcc] https://gcc.gnu.org
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.. [clang] https://clang.llvm.org
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.. [icc] https://software.intel.com/en-us/c-compilers
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.. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
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.. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
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.. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
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.. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
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