1.. SPDX-License-Identifier: GPL-2.0 2 3Quick Start 4=========== 5 6This document describes how to get started with kernel development in Rust. 7 8 9Requirements: Building 10---------------------- 11 12This section explains how to fetch the tools needed for building. 13 14Some of these requirements might be available from Linux distributions 15under names like ``rustc``, ``rust-src``, ``rust-bindgen``, etc. However, 16at the time of writing, they are likely not to be recent enough unless 17the distribution tracks the latest releases. 18 19Prebuilt stable versions of LLVM+Rust are provided on `kernel.org 20<https://kernel.org/pub/tools/llvm/rust/>`_. These are the same slim and fast 21LLVM toolchains from :ref:`Getting LLVM <getting_llvm>` with versions of Rust 22added to them that Rust for Linux supports, depending on the Linux version. Two 23sets are provided: the "latest LLVM" and "matching LLVM" (please see the link 24for more information). 25 26To easily check whether the requirements are met, the following target 27can be used:: 28 29 make LLVM=1 rustavailable 30 31This triggers the same logic used by Kconfig to determine whether 32``RUST_IS_AVAILABLE`` should be enabled; but it also explains why not 33if that is the case. 34 35 36rustc 37***** 38 39A particular version of the Rust compiler is required. Newer versions may or 40may not work because, for the moment, the kernel depends on some unstable 41Rust features. 42 43If ``rustup`` is being used, enter the kernel build directory (or use 44``--path=<build-dir>`` argument to the ``set`` sub-command) and run:: 45 46 rustup override set $(scripts/min-tool-version.sh rustc) 47 48This will configure your working directory to use the correct version of 49``rustc`` without affecting your default toolchain. 50 51Note that the override applies to the current working directory (and its 52sub-directories). 53 54If you are not using ``rustup``, fetch a standalone installer from: 55 56 https://forge.rust-lang.org/infra/other-installation-methods.html#standalone 57 58 59Rust standard library source 60**************************** 61 62The Rust standard library source is required because the build system will 63cross-compile ``core`` and ``alloc``. 64 65If ``rustup`` is being used, run:: 66 67 rustup component add rust-src 68 69The components are installed per toolchain, thus upgrading the Rust compiler 70version later on requires re-adding the component. 71 72Otherwise, if a standalone installer is used, the Rust source tree may be 73downloaded into the toolchain's installation folder:: 74 75 curl -L "https://static.rust-lang.org/dist/rust-src-$(scripts/min-tool-version.sh rustc).tar.gz" | 76 tar -xzf - -C "$(rustc --print sysroot)/lib" \ 77 "rust-src-$(scripts/min-tool-version.sh rustc)/rust-src/lib/" \ 78 --strip-components=3 79 80In this case, upgrading the Rust compiler version later on requires manually 81updating the source tree (this can be done by removing ``$(rustc --print 82sysroot)/lib/rustlib/src/rust`` then rerunning the above command). 83 84 85libclang 86******** 87 88``libclang`` (part of LLVM) is used by ``bindgen`` to understand the C code 89in the kernel, which means LLVM needs to be installed; like when the kernel 90is compiled with ``LLVM=1``. 91 92Linux distributions are likely to have a suitable one available, so it is 93best to check that first. 94 95There are also some binaries for several systems and architectures uploaded at: 96 97 https://releases.llvm.org/download.html 98 99Otherwise, building LLVM takes quite a while, but it is not a complex process: 100 101 https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm 102 103Please see Documentation/kbuild/llvm.rst for more information and further ways 104to fetch pre-built releases and distribution packages. 105 106 107bindgen 108******* 109 110The bindings to the C side of the kernel are generated at build time using 111the ``bindgen`` tool. A particular version is required. 112 113Install it via (note that this will download and build the tool from source):: 114 115 cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli 116 117``bindgen`` needs to find a suitable ``libclang`` in order to work. If it is 118not found (or a different ``libclang`` than the one found should be used), 119the process can be tweaked using the environment variables understood by 120``clang-sys`` (the Rust bindings crate that ``bindgen`` uses to access 121``libclang``): 122 123* ``LLVM_CONFIG_PATH`` can be pointed to an ``llvm-config`` executable. 124 125* Or ``LIBCLANG_PATH`` can be pointed to a ``libclang`` shared library 126 or to the directory containing it. 127 128* Or ``CLANG_PATH`` can be pointed to a ``clang`` executable. 129 130For details, please see ``clang-sys``'s documentation at: 131 132 https://github.com/KyleMayes/clang-sys#environment-variables 133 134 135Requirements: Developing 136------------------------ 137 138This section explains how to fetch the tools needed for developing. That is, 139they are not needed when just building the kernel. 140 141 142rustfmt 143******* 144 145The ``rustfmt`` tool is used to automatically format all the Rust kernel code, 146including the generated C bindings (for details, please see 147coding-guidelines.rst). 148 149If ``rustup`` is being used, its ``default`` profile already installs the tool, 150thus nothing needs to be done. If another profile is being used, the component 151can be installed manually:: 152 153 rustup component add rustfmt 154 155The standalone installers also come with ``rustfmt``. 156 157 158clippy 159****** 160 161``clippy`` is a Rust linter. Running it provides extra warnings for Rust code. 162It can be run by passing ``CLIPPY=1`` to ``make`` (for details, please see 163general-information.rst). 164 165If ``rustup`` is being used, its ``default`` profile already installs the tool, 166thus nothing needs to be done. If another profile is being used, the component 167can be installed manually:: 168 169 rustup component add clippy 170 171The standalone installers also come with ``clippy``. 172 173 174rustdoc 175******* 176 177``rustdoc`` is the documentation tool for Rust. It generates pretty HTML 178documentation for Rust code (for details, please see 179general-information.rst). 180 181``rustdoc`` is also used to test the examples provided in documented Rust code 182(called doctests or documentation tests). The ``rusttest`` Make target uses 183this feature. 184 185If ``rustup`` is being used, all the profiles already install the tool, 186thus nothing needs to be done. 187 188The standalone installers also come with ``rustdoc``. 189 190 191rust-analyzer 192************* 193 194The `rust-analyzer <https://rust-analyzer.github.io/>`_ language server can 195be used with many editors to enable syntax highlighting, completion, go to 196definition, and other features. 197 198``rust-analyzer`` needs a configuration file, ``rust-project.json``, which 199can be generated by the ``rust-analyzer`` Make target:: 200 201 make LLVM=1 rust-analyzer 202 203 204Configuration 205------------- 206 207``Rust support`` (``CONFIG_RUST``) needs to be enabled in the ``General setup`` 208menu. The option is only shown if a suitable Rust toolchain is found (see 209above), as long as the other requirements are met. In turn, this will make 210visible the rest of options that depend on Rust. 211 212Afterwards, go to:: 213 214 Kernel hacking 215 -> Sample kernel code 216 -> Rust samples 217 218And enable some sample modules either as built-in or as loadable. 219 220 221Building 222-------- 223 224Building a kernel with a complete LLVM toolchain is the best supported setup 225at the moment. That is:: 226 227 make LLVM=1 228 229Using GCC also works for some configurations, but it is very experimental at 230the moment. 231 232 233Hacking 234------- 235 236To dive deeper, take a look at the source code of the samples 237at ``samples/rust/``, the Rust support code under ``rust/`` and 238the ``Rust hacking`` menu under ``Kernel hacking``. 239 240If GDB/Binutils is used and Rust symbols are not getting demangled, the reason 241is the toolchain does not support Rust's new v0 mangling scheme yet. 242There are a few ways out: 243 244 - Install a newer release (GDB >= 10.2, Binutils >= 2.36). 245 246 - Some versions of GDB (e.g. vanilla GDB 10.1) are able to use 247 the pre-demangled names embedded in the debug info (``CONFIG_DEBUG_INFO``). 248