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 onBuilding 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 introduceimplementation-defined semantics to language entities (like variables,functions or types) without having to make significant syntactic changesto the language (e.g. adding a new keyword) [n2049].
In some cases, attributes are optional (i.e. a compiler not supporting themshould still produce proper code, even if it is slower or does not performas many compile-time checks/diagnostics).
The kernel defines pseudo-keywords (e.g. __pure) instead of usingdirectly 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 introducesmall changes to the language that are not backwards compatible.
On top of that, some unstable features [rust-unstable-features] are used inthe kernel. Unstable features may change in the future, thus it is an importantgoal to reach a point where only stable features are used.
Please refer to Rust for more information.
[gcc]
[clang]
[gcc-c-dialect-options]
[gnu-extensions]
[gcc-attribute-syntax]
[rust-language]
[rust-editions]
[rust-unstable-features]
