Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) .. _programming_language:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) Programming Language
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) The kernel is written in the C programming language [c-language]_.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) More precisely, the kernel is typically compiled with ``gcc`` [gcc]_
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) under ``-std=gnu89`` [gcc-c-dialect-options]_: the GNU dialect of ISO C90
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) (including some C99 features). ``clang`` [clang]_ is also supported, see
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) This dialect contains many extensions to the language [gnu-extensions]_,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) and many of them are used within the kernel as a matter of course.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) There is some support for compiling the kernel with ``icc`` [icc]_ for several
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) of the architectures, although at the time of writing it is not completed,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) requiring third-party patches.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) Attributes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) ----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) One of the common extensions used throughout the kernel are attributes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) [gcc-attribute-syntax]_. Attributes allow to introduce
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) implementation-defined semantics to language entities (like variables,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) functions or types) without having to make significant syntactic changes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) to the language (e.g. adding a new keyword) [n2049]_.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) In some cases, attributes are optional (i.e. a compiler not supporting them
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) should still produce proper code, even if it is slower or does not perform
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) as many compile-time checks/diagnostics).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) The kernel defines pseudo-keywords (e.g. ``__pure``) instead of using
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) directly the GNU attribute syntax (e.g. ``__attribute__((__pure__))``)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) in order to feature detect which ones can be used and/or to shorten the code.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) Please refer to ``include/linux/compiler_attributes.h`` for more information.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) .. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) .. [gcc] https://gcc.gnu.org
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) .. [clang] https://clang.llvm.org
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) .. [icc] https://software.intel.com/en-us/c-compilers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) .. [gcc-c-dialect-options] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) .. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) .. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) .. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)