.. _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=gnu11`` [gcc-c-dialect-options]_: the GNU dialect of ISO C11. ``clang`` [clang]_ is also supported, see docs on :ref:`Building Linux with Clang/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. 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. Rust ---- The kernel has experimental 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