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Compiler Attributes: add Doc/process/programming-language.rst

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Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # on top of v4.19-rc5, clang 7
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
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Miguel Ojeda 2018-09-03 18:32:11 +02:00
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Documentation/process/index.rst
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@ -23,6 +23,7 @@ Below are the essential guides that every developer should read.
code-of-conduct
development-process
submitting-patches
programming-language
coding-style
maintainer-pgp-guide
email-clients

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.. _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=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
(including some C99 features).
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