Documentation/process/programming-language.rst
.. _programming_language:
The Linux kernel is written in the C programming language [c-language].
More precisely, it is typically compiled with gcc [gcc]
under -std=gnu11 [gcc-c-dialect-options]: the GNU dialect of ISO C11.
clang [clang] is also supported; see documentation on
:ref:Building Linux with Clang/LLVM <kbuild_llvm>.
This dialect contains many extensions to the language [gnu-extensions]_, and many of them are used within the kernel as a matter of course.
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.
The kernel has support for the Rust programming language
[rust-language]_ under CONFIG_RUST. It is compiled with rustc [rustc]_
under --edition=2021 [rust-editions]_. Editions are a way to introduce
small changes to the language that are not backwards compatible.
On top of that, some unstable features [rust-unstable-features]_ are used in the kernel. Unstable features may change in the future, thus it is an important goal to reach a point where only stable features are used.
Please refer to Documentation/rust/index.rst 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 .. [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 .. [rust-language] https://www.rust-lang.org .. [rustc] https://doc.rust-lang.org/rustc/ .. [rust-editions] https://doc.rust-lang.org/edition-guide/editions/ .. [rust-unstable-features] https://github.com/Rust-for-Linux/linux/issues/2