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Quick Start

This document describes how to get started with kernel development in Rust.

Requirements: Building

This section explains how to fetch the tools needed for building.

Some of these requirements might be available from Linux distributions under names like rustc, rust-src, rust-bindgen, etc. However, at the time of writing, they are likely not to be recent enough unless the distribution tracks the latest releases.

To easily check whether the requirements are met, the following target can be used:

make LLVM=1 rustavailable

This triggers the same logic used by Kconfig to determine whether RUST_IS_AVAILABLE should be enabled; but it also explains why not if that is the case.

rustc

A particular version of the Rust compiler is required. Newer versions may or may not work because, for the moment, the kernel depends on some unstable Rust features.

If rustup is being used, enter the kernel build directory (or use --path=<build-dir> argument to the set sub-command) and run:

rustup override set $(scripts/min-tool-version.sh rustc)

This will configure your working directory to use the correct version of rustc without affecting your default toolchain.

Note that the override applies to the current working directory (and its sub-directories).

If you are not using rustup, fetch a standalone installer from:

Rust standard library source

The Rust standard library source is required because the build system will cross-compile core and alloc.

If rustup is being used, run:

rustup component add rust-src

The components are installed per toolchain, thus upgrading the Rust compiler version later on requires re-adding the component.

Otherwise, if a standalone installer is used, the Rust source tree may be downloaded into the toolchain’s installation folder:

curl -L "https://static.rust-lang.org/dist/rust-src-$(scripts/min-tool-version.sh rustc).tar.gz" |
        tar -xzf - -C "$(rustc --print sysroot)/lib" \
        "rust-src-$(scripts/min-tool-version.sh rustc)/rust-src/lib/" \
        --strip-components=3

In this case, upgrading the Rust compiler version later on requires manually updating the source tree (this can be done by removing $(rustc --print sysroot)/lib/rustlib/src/rust then rerunning the above command).

libclang

libclang (part of LLVM) is used by bindgen to understand the C code in the kernel, which means LLVM needs to be installed; like when the kernel is compiled with LLVM=1.

Linux distributions are likely to have a suitable one available, so it is best to check that first.

There are also some binaries for several systems and architectures uploaded at:

Otherwise, building LLVM takes quite a while, but it is not a complex process:

Please see Building Linux with Clang/LLVM for more information and further ways to fetch pre-built releases and distribution packages.

bindgen

The bindings to the C side of the kernel are generated at build time using the bindgen tool. A particular version is required.

Install it via (note that this will download and build the tool from source):

cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli

bindgen needs to find a suitable libclang in order to work. If it is not found (or a different libclang than the one found should be used), the process can be tweaked using the environment variables understood by clang-sys (the Rust bindings crate that bindgen uses to access libclang):

  • LLVM_CONFIG_PATH can be pointed to an llvm-config executable.

  • Or LIBCLANG_PATH can be pointed to a libclang shared library or to the directory containing it.

  • Or CLANG_PATH can be pointed to a clang executable.

For details, please see clang-sys’s documentation at:

Requirements: Developing

This section explains how to fetch the tools needed for developing. That is, they are not needed when just building the kernel.

rustfmt

The rustfmt tool is used to automatically format all the Rust kernel code, including the generated C bindings (for details, please see Coding Guidelines).

If rustup is being used, its default profile already installs the tool, thus nothing needs to be done. If another profile is being used, the component can be installed manually:

rustup component add rustfmt

The standalone installers also come with rustfmt.

clippy

clippy is a Rust linter. Running it provides extra warnings for Rust code. It can be run by passing CLIPPY=1 to make (for details, please see General Information).

If rustup is being used, its default profile already installs the tool, thus nothing needs to be done. If another profile is being used, the component can be installed manually:

rustup component add clippy

The standalone installers also come with clippy.

cargo

cargo is the Rust native build system. It is currently required to run the tests since it is used to build a custom standard library that contains the facilities provided by the custom alloc in the kernel. The tests can be run using the rusttest Make target.

If rustup is being used, all the profiles already install the tool, thus nothing needs to be done.

The standalone installers also come with cargo.

rustdoc

rustdoc is the documentation tool for Rust. It generates pretty HTML documentation for Rust code (for details, please see General Information).

rustdoc is also used to test the examples provided in documented Rust code (called doctests or documentation tests). The rusttest Make target uses this feature.

If rustup is being used, all the profiles already install the tool, thus nothing needs to be done.

The standalone installers also come with rustdoc.

rust-analyzer

The rust-analyzer language server can be used with many editors to enable syntax highlighting, completion, go to definition, and other features.

rust-analyzer needs a configuration file, rust-project.json, which can be generated by the rust-analyzer Make target:

make LLVM=1 rust-analyzer

Configuration

Rust support (CONFIG_RUST) needs to be enabled in the General setup menu. The option is only shown if a suitable Rust toolchain is found (see above), as long as the other requirements are met. In turn, this will make visible the rest of options that depend on Rust.

Afterwards, go to:

Kernel hacking
    -> Sample kernel code
        -> Rust samples

And enable some sample modules either as built-in or as loadable.

Building

Building a kernel with a complete LLVM toolchain is the best supported setup at the moment. That is:

make LLVM=1

Using GCC also works for some configurations, but it is very experimental at the moment.

Hacking

To dive deeper, take a look at the source code of the samples at samples/rust/, the Rust support code under rust/ and the Rust hacking menu under Kernel hacking.

If GDB/Binutils is used and Rust symbols are not getting demangled, the reason is the toolchain does not support Rust’s new v0 mangling scheme yet. There are a few ways out:

  • Install a newer release (GDB >= 10.2, Binutils >= 2.36).

  • Some versions of GDB (e.g. vanilla GDB 10.1) are able to use the pre-demangled names embedded in the debug info (CONFIG_DEBUG_INFO).