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| -rw-r--r-- | Documentation/rust/arch-support.rst | 25 | ||||
| -rw-r--r-- | Documentation/rust/coding-guidelines.rst | 412 | ||||
| -rw-r--r-- | Documentation/rust/general-information.rst | 161 | ||||
| -rw-r--r-- | Documentation/rust/index.rst | 67 | ||||
| -rw-r--r-- | Documentation/rust/quick-start.rst | 366 | ||||
| -rw-r--r-- | Documentation/rust/testing.rst | 236 |
6 files changed, 1267 insertions, 0 deletions
diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst new file mode 100644 index 000000000000..6e6a515d0899 --- /dev/null +++ b/Documentation/rust/arch-support.rst @@ -0,0 +1,25 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Arch Support +============ + +Currently, the Rust compiler (``rustc``) uses LLVM for code generation, +which limits the supported architectures that can be targeted. In addition, +support for building the kernel with LLVM/Clang varies (please see +Documentation/kbuild/llvm.rst). This support is needed for ``bindgen`` +which uses ``libclang``. + +Below is a general summary of architectures that currently work. Level of +support corresponds to ``S`` values in the ``MAINTAINERS`` file. + +============= ================ ============================================== +Architecture Level of support Constraints +============= ================ ============================================== +``arm`` Maintained ARMv7 Little Endian only. +``arm64`` Maintained Little Endian only. +``loongarch`` Maintained \- +``riscv`` Maintained ``riscv64`` and LLVM/Clang only. +``um`` Maintained \- +``x86`` Maintained ``x86_64`` only. +============= ================ ============================================== + diff --git a/Documentation/rust/coding-guidelines.rst b/Documentation/rust/coding-guidelines.rst new file mode 100644 index 000000000000..6ff9e754755d --- /dev/null +++ b/Documentation/rust/coding-guidelines.rst @@ -0,0 +1,412 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Coding Guidelines +================= + +This document describes how to write Rust code in the kernel. + + +Style & formatting +------------------ + +The code should be formatted using ``rustfmt``. In this way, a person +contributing from time to time to the kernel does not need to learn and +remember one more style guide. More importantly, reviewers and maintainers +do not need to spend time pointing out style issues anymore, and thus +less patch roundtrips may be needed to land a change. + +.. note:: Conventions on comments and documentation are not checked by + ``rustfmt``. Thus those are still needed to be taken care of. + +The default settings of ``rustfmt`` are used. This means the idiomatic Rust +style is followed. For instance, 4 spaces are used for indentation rather +than tabs. + +It is convenient to instruct editors/IDEs to format while typing, +when saving or at commit time. However, if for some reason reformatting +the entire kernel Rust sources is needed at some point, the following can be +run:: + + make LLVM=1 rustfmt + +It is also possible to check if everything is formatted (printing a diff +otherwise), for instance for a CI, with:: + + make LLVM=1 rustfmtcheck + +Like ``clang-format`` for the rest of the kernel, ``rustfmt`` works on +individual files, and does not require a kernel configuration. Sometimes it may +even work with broken code. + + +Comments +-------- + +"Normal" comments (i.e. ``//``, rather than code documentation which starts +with ``///`` or ``//!``) are written in Markdown the same way as documentation +comments are, even though they will not be rendered. This improves consistency, +simplifies the rules and allows to move content between the two kinds of +comments more easily. For instance: + +.. code-block:: rust + + // `object` is ready to be handled now. + f(object); + +Furthermore, just like documentation, comments are capitalized at the beginning +of a sentence and ended with a period (even if it is a single sentence). This +includes ``// SAFETY:``, ``// TODO:`` and other "tagged" comments, e.g.: + +.. code-block:: rust + + // FIXME: The error should be handled properly. + +Comments should not be used for documentation purposes: comments are intended +for implementation details, not users. This distinction is useful even if the +reader of the source file is both an implementor and a user of an API. In fact, +sometimes it is useful to use both comments and documentation at the same time. +For instance, for a ``TODO`` list or to comment on the documentation itself. +For the latter case, comments can be inserted in the middle; that is, closer to +the line of documentation to be commented. For any other case, comments are +written after the documentation, e.g.: + +.. code-block:: rust + + /// Returns a new [`Foo`]. + /// + /// # Examples + /// + // TODO: Find a better example. + /// ``` + /// let foo = f(42); + /// ``` + // FIXME: Use fallible approach. + pub fn f(x: i32) -> Foo { + // ... + } + +This applies to both public and private items. This increases consistency with +public items, allows changes to visibility with less changes involved and will +allow us to potentially generate the documentation for private items as well. +In other words, if documentation is written for a private item, then ``///`` +should still be used. For instance: + +.. code-block:: rust + + /// My private function. + // TODO: ... + fn f() {} + +One special kind of comments are the ``// SAFETY:`` comments. These must appear +before every ``unsafe`` block, and they explain why the code inside the block is +correct/sound, i.e. why it cannot trigger undefined behavior in any case, e.g.: + +.. code-block:: rust + + // SAFETY: `p` is valid by the safety requirements. + unsafe { *p = 0; } + +``// SAFETY:`` comments are not to be confused with the ``# Safety`` sections +in code documentation. ``# Safety`` sections specify the contract that callers +(for functions) or implementors (for traits) need to abide by. ``// SAFETY:`` +comments show why a call (for functions) or implementation (for traits) actually +respects the preconditions stated in a ``# Safety`` section or the language +reference. + + +Code documentation +------------------ + +Rust kernel code is not documented like C kernel code (i.e. via kernel-doc). +Instead, the usual system for documenting Rust code is used: the ``rustdoc`` +tool, which uses Markdown (a lightweight markup language). + +To learn Markdown, there are many guides available out there. For instance, +the one at: + + https://commonmark.org/help/ + +This is how a well-documented Rust function may look like: + +.. code-block:: rust + + /// Returns the contained [`Some`] value, consuming the `self` value, + /// without checking that the value is not [`None`]. + /// + /// # Safety + /// + /// Calling this method on [`None`] is *[undefined behavior]*. + /// + /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html + /// + /// # Examples + /// + /// ``` + /// let x = Some("air"); + /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); + /// ``` + pub unsafe fn unwrap_unchecked(self) -> T { + match self { + Some(val) => val, + + // SAFETY: The safety contract must be upheld by the caller. + None => unsafe { hint::unreachable_unchecked() }, + } + } + +This example showcases a few ``rustdoc`` features and some conventions followed +in the kernel: + +- The first paragraph must be a single sentence briefly describing what + the documented item does. Further explanations must go in extra paragraphs. + +- Unsafe functions must document their safety preconditions under + a ``# Safety`` section. + +- While not shown here, if a function may panic, the conditions under which + that happens must be described under a ``# Panics`` section. + + Please note that panicking should be very rare and used only with a good + reason. In almost all cases, a fallible approach should be used, typically + returning a ``Result``. + +- If providing examples of usage would help readers, they must be written in + a section called ``# Examples``. + +- Rust items (functions, types, constants...) must be linked appropriately + (``rustdoc`` will create a link automatically). + +- Any ``unsafe`` block must be preceded by a ``// SAFETY:`` comment + describing why the code inside is sound. + + While sometimes the reason might look trivial and therefore unneeded, + writing these comments is not just a good way of documenting what has been + taken into account, but most importantly, it provides a way to know that + there are no *extra* implicit constraints. + +To learn more about how to write documentation for Rust and extra features, +please take a look at the ``rustdoc`` book at: + + https://doc.rust-lang.org/rustdoc/how-to-write-documentation.html + +In addition, the kernel supports creating links relative to the source tree by +prefixing the link destination with ``srctree/``. For instance: + +.. code-block:: rust + + //! C header: [`include/linux/printk.h`](srctree/include/linux/printk.h) + +or: + +.. code-block:: rust + + /// [`struct mutex`]: srctree/include/linux/mutex.h + + +C FFI types +----------- + +Rust kernel code refers to C types, such as ``int``, using type aliases such as +``c_int``, which are readily available from the ``kernel`` prelude. Please do +not use the aliases from ``core::ffi`` -- they may not map to the correct types. + +These aliases should generally be referred directly by their identifier, i.e. +as a single segment path. For instance: + +.. code-block:: rust + + fn f(p: *const c_char) -> c_int { + // ... + } + + +Naming +------ + +Rust kernel code follows the usual Rust naming conventions: + + https://rust-lang.github.io/api-guidelines/naming.html + +When existing C concepts (e.g. macros, functions, objects...) are wrapped into +a Rust abstraction, a name as close as reasonably possible to the C side should +be used in order to avoid confusion and to improve readability when switching +back and forth between the C and Rust sides. For instance, macros such as +``pr_info`` from C are named the same in the Rust side. + +Having said that, casing should be adjusted to follow the Rust naming +conventions, and namespacing introduced by modules and types should not be +repeated in the item names. For instance, when wrapping constants like: + +.. code-block:: c + + #define GPIO_LINE_DIRECTION_IN 0 + #define GPIO_LINE_DIRECTION_OUT 1 + +The equivalent in Rust may look like (ignoring documentation): + +.. code-block:: rust + + pub mod gpio { + pub enum LineDirection { + In = bindings::GPIO_LINE_DIRECTION_IN as _, + Out = bindings::GPIO_LINE_DIRECTION_OUT as _, + } + } + +That is, the equivalent of ``GPIO_LINE_DIRECTION_IN`` would be referred to as +``gpio::LineDirection::In``. In particular, it should not be named +``gpio::gpio_line_direction::GPIO_LINE_DIRECTION_IN``. + + +Lints +----- + +In Rust, it is possible to ``allow`` particular warnings (diagnostics, lints) +locally, making the compiler ignore instances of a given warning within a given +function, module, block, etc. + +It is similar to ``#pragma GCC diagnostic push`` + ``ignored`` + ``pop`` in C +[#]_: + +.. code-block:: c + + #pragma GCC diagnostic push + #pragma GCC diagnostic ignored "-Wunused-function" + static void f(void) {} + #pragma GCC diagnostic pop + +.. [#] In this particular case, the kernel's ``__{always,maybe}_unused`` + attributes (C23's ``[[maybe_unused]]``) may be used; however, the example + is meant to reflect the equivalent lint in Rust discussed afterwards. + +But way less verbose: + +.. code-block:: rust + + #[allow(dead_code)] + fn f() {} + +By that virtue, it makes it possible to comfortably enable more diagnostics by +default (i.e. outside ``W=`` levels). In particular, those that may have some +false positives but that are otherwise quite useful to keep enabled to catch +potential mistakes. + +On top of that, Rust provides the ``expect`` attribute which takes this further. +It makes the compiler warn if the warning was not produced. For instance, the +following will ensure that, when ``f()`` is called somewhere, we will have to +remove the attribute: + +.. code-block:: rust + + #[expect(dead_code)] + fn f() {} + +If we do not, we get a warning from the compiler:: + + warning: this lint expectation is unfulfilled + --> x.rs:3:10 + | + 3 | #[expect(dead_code)] + | ^^^^^^^^^ + | + = note: `#[warn(unfulfilled_lint_expectations)]` on by default + +This means that ``expect``\ s do not get forgotten when they are not needed, which +may happen in several situations, e.g.: + +- Temporary attributes added while developing. + +- Improvements in lints in the compiler, Clippy or custom tools which may + remove a false positive. + +- When the lint is not needed anymore because it was expected that it would be + removed at some point, such as the ``dead_code`` example above. + +It also increases the visibility of the remaining ``allow``\ s and reduces the +chance of misapplying one. + +Thus prefer ``expect`` over ``allow`` unless: + +- Conditional compilation triggers the warning in some cases but not others. + + If there are only a few cases where the warning triggers (or does not + trigger) compared to the total number of cases, then one may consider using + a conditional ``expect`` (i.e. ``cfg_attr(..., expect(...))``). Otherwise, + it is likely simpler to just use ``allow``. + +- Inside macros, when the different invocations may create expanded code that + triggers the warning in some cases but not in others. + +- When code may trigger a warning for some architectures but not others, such + as an ``as`` cast to a C FFI type. + +As a more developed example, consider for instance this program: + +.. code-block:: rust + + fn g() {} + + fn main() { + #[cfg(CONFIG_X)] + g(); + } + +Here, function ``g()`` is dead code if ``CONFIG_X`` is not set. Can we use +``expect`` here? + +.. code-block:: rust + + #[expect(dead_code)] + fn g() {} + + fn main() { + #[cfg(CONFIG_X)] + g(); + } + +This would emit a lint if ``CONFIG_X`` is set, since it is not dead code in that +configuration. Therefore, in cases like this, we cannot use ``expect`` as-is. + +A simple possibility is using ``allow``: + +.. code-block:: rust + + #[allow(dead_code)] + fn g() {} + + fn main() { + #[cfg(CONFIG_X)] + g(); + } + +An alternative would be using a conditional ``expect``: + +.. code-block:: rust + + #[cfg_attr(not(CONFIG_X), expect(dead_code))] + fn g() {} + + fn main() { + #[cfg(CONFIG_X)] + g(); + } + +This would ensure that, if someone introduces another call to ``g()`` somewhere +(e.g. unconditionally), then it would be spotted that it is not dead code +anymore. However, the ``cfg_attr`` is more complex than a simple ``allow``. + +Therefore, it is likely that it is not worth using conditional ``expect``\ s when +more than one or two configurations are involved or when the lint may be +triggered due to non-local changes (such as ``dead_code``). + +For more information about diagnostics in Rust, please see: + + https://doc.rust-lang.org/stable/reference/attributes/diagnostics.html + +Error handling +-------------- + +For some background and guidelines about Rust for Linux specific error handling, +please see: + + https://rust.docs.kernel.org/kernel/error/type.Result.html#error-codes-in-c-and-rust diff --git a/Documentation/rust/general-information.rst b/Documentation/rust/general-information.rst new file mode 100644 index 000000000000..6146b49b6a98 --- /dev/null +++ b/Documentation/rust/general-information.rst @@ -0,0 +1,161 @@ +.. SPDX-License-Identifier: GPL-2.0 + +General Information +=================== + +This document contains useful information to know when working with +the Rust support in the kernel. + + +``no_std`` +---------- + +The Rust support in the kernel can link only `core <https://doc.rust-lang.org/core/>`_, +but not `std <https://doc.rust-lang.org/std/>`_. Crates for use in the +kernel must opt into this behavior using the ``#![no_std]`` attribute. + + +.. _rust_code_documentation: + +Code documentation +------------------ + +Rust kernel code is documented using ``rustdoc``, its built-in documentation +generator. + +The generated HTML docs include integrated search, linked items (e.g. types, +functions, constants), source code, etc. They may be read at: + + https://rust.docs.kernel.org + +For linux-next, please see: + + https://rust.docs.kernel.org/next/ + +There are also tags for each main release, e.g.: + + https://rust.docs.kernel.org/6.10/ + +The docs can also be easily generated and read locally. This is quite fast +(same order as compiling the code itself) and no special tools or environment +are needed. This has the added advantage that they will be tailored to +the particular kernel configuration used. To generate them, use the ``rustdoc`` +target with the same invocation used for compilation, e.g.:: + + make LLVM=1 rustdoc + +To read the docs locally in your web browser, run e.g.:: + + xdg-open Documentation/output/rust/rustdoc/kernel/index.html + +To learn about how to write the documentation, please see coding-guidelines.rst. + + +Extra lints +----------- + +While ``rustc`` is a very helpful compiler, some extra lints and analyses are +available via ``clippy``, a Rust linter. To enable it, pass ``CLIPPY=1`` to +the same invocation used for compilation, e.g.:: + + make LLVM=1 CLIPPY=1 + +Please note that Clippy may change code generation, thus it should not be +enabled while building a production kernel. + + +Abstractions vs. bindings +------------------------- + +Abstractions are Rust code wrapping kernel functionality from the C side. + +In order to use functions and types from the C side, bindings are created. +Bindings are the declarations for Rust of those functions and types from +the C side. + +For instance, one may write a ``Mutex`` abstraction in Rust which wraps +a ``struct mutex`` from the C side and calls its functions through the bindings. + +Abstractions are not available for all the kernel internal APIs and concepts, +but it is intended that coverage is expanded as time goes on. "Leaf" modules +(e.g. drivers) should not use the C bindings directly. Instead, subsystems +should provide as-safe-as-possible abstractions as needed. + +.. code-block:: + + rust/bindings/ + (rust/helpers/) + + include/ -----+ <-+ + | | + drivers/ rust/kernel/ +----------+ <-+ | + fs/ | bindgen | | + .../ +-------------------+ +----------+ --+ | + | Abstractions | | | + +---------+ | +------+ +------+ | +----------+ | | + | my_foo | -----> | | foo | | bar | | -------> | Bindings | <-+ | + | driver | Safe | | sub- | | sub- | | Unsafe | | | + +---------+ | |system| |system| | | bindings | <-----+ + | | +------+ +------+ | | crate | | + | | kernel crate | +----------+ | + | +-------------------+ | + | | + +------------------# FORBIDDEN #--------------------------------+ + +The main idea is to encapsulate all direct interaction with the kernel's C APIs +into carefully reviewed and documented abstractions. Then users of these +abstractions cannot introduce undefined behavior (UB) as long as: + +#. The abstractions are correct ("sound"). +#. Any ``unsafe`` blocks respect the safety contract necessary to call the + operations inside the block. Similarly, any ``unsafe impl``\ s respect the + safety contract necessary to implement the trait. + +Bindings +~~~~~~~~ + +By including a C header from ``include/`` into +``rust/bindings/bindings_helper.h``, the ``bindgen`` tool will auto-generate the +bindings for the included subsystem. After building, see the ``*_generated.rs`` +output files in the ``rust/bindings/`` directory. + +For parts of the C header that ``bindgen`` does not auto generate, e.g. C +``inline`` functions or non-trivial macros, it is acceptable to add a small +wrapper function to ``rust/helpers/`` to make it available for the Rust side as +well. + +Abstractions +~~~~~~~~~~~~ + +Abstractions are the layer between the bindings and the in-kernel users. They +are located in ``rust/kernel/`` and their role is to encapsulate the unsafe +access to the bindings into an as-safe-as-possible API that they expose to their +users. Users of the abstractions include things like drivers or file systems +written in Rust. + +Besides the safety aspect, the abstractions are supposed to be "ergonomic", in +the sense that they turn the C interfaces into "idiomatic" Rust code. Basic +examples are to turn the C resource acquisition and release into Rust +constructors and destructors or C integer error codes into Rust's ``Result``\ s. + + +Conditional compilation +----------------------- + +Rust code has access to conditional compilation based on the kernel +configuration: + +.. code-block:: rust + + #[cfg(CONFIG_X)] // Enabled (`y` or `m`) + #[cfg(CONFIG_X="y")] // Enabled as a built-in (`y`) + #[cfg(CONFIG_X="m")] // Enabled as a module (`m`) + #[cfg(not(CONFIG_X))] // Disabled + +For other predicates that Rust's ``cfg`` does not support, e.g. expressions with +numerical comparisons, one may define a new Kconfig symbol: + +.. code-block:: kconfig + + config RUSTC_VERSION_MIN_107900 + def_bool y if RUSTC_VERSION >= 107900 diff --git a/Documentation/rust/index.rst b/Documentation/rust/index.rst new file mode 100644 index 000000000000..ec62001c7d8c --- /dev/null +++ b/Documentation/rust/index.rst @@ -0,0 +1,67 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Rust +==== + +Documentation related to Rust within the kernel. To start using Rust +in the kernel, please read the quick-start.rst guide. + + +The Rust experiment +------------------- + +The Rust support was merged in v6.1 into mainline in order to help in +determining whether Rust as a language was suitable for the kernel, i.e. worth +the tradeoffs. + +Currently, the Rust support is primarily intended for kernel developers and +maintainers interested in the Rust support, so that they can start working on +abstractions and drivers, as well as helping the development of infrastructure +and tools. + +If you are an end user, please note that there are currently no in-tree +drivers/modules suitable or intended for production use, and that the Rust +support is still in development/experimental, especially for certain kernel +configurations. + + +Code documentation +------------------ + +Given a kernel configuration, the kernel may generate Rust code documentation, +i.e. HTML rendered by the ``rustdoc`` tool. + +.. only:: rustdoc and html + + This kernel documentation was built with `Rust code documentation + <rustdoc/kernel/index.html>`_. + +.. only:: not rustdoc and html + + This kernel documentation was not built with Rust code documentation. + +A pregenerated version is provided at: + + https://rust.docs.kernel.org + +Please see the :ref:`Code documentation <rust_code_documentation>` section for +more details. + +.. toctree:: + :maxdepth: 1 + + quick-start + general-information + coding-guidelines + arch-support + testing + +You can also find learning materials for Rust in its section in +:doc:`../process/kernel-docs`. + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/rust/quick-start.rst b/Documentation/rust/quick-start.rst new file mode 100644 index 000000000000..155f7107329a --- /dev/null +++ b/Documentation/rust/quick-start.rst @@ -0,0 +1,366 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Quick Start +=========== + +This document describes how to get started with kernel development in Rust. + +There are a few ways to install a Rust toolchain needed for kernel development. +A simple way is to use the packages from your Linux distribution if they are +suitable -- the first section below explains this approach. An advantage of this +approach is that, typically, the distribution will match the LLVM used by Rust +and Clang. + +Another way is using the prebuilt stable versions of LLVM+Rust provided on +`kernel.org <https://kernel.org/pub/tools/llvm/rust/>`_. These are the same slim +and fast LLVM toolchains from :ref:`Getting LLVM <getting_llvm>` with versions +of Rust added to them that Rust for Linux supports. Two sets are provided: the +"latest LLVM" and "matching LLVM" (please see the link for more information). + +Alternatively, the next two "Requirements" sections explain each component and +how to install them through ``rustup``, the standalone installers from Rust +and/or building them. + +The rest of the document explains other aspects on how to get started. + + +Distributions +------------- + +Arch Linux +********** + +Arch Linux provides recent Rust releases and thus it should generally work out +of the box, e.g.:: + + pacman -S rust rust-src rust-bindgen + + +Debian +****** + +Debian Testing and Debian Unstable (Sid), outside of the freeze period, provide +recent Rust releases and thus they should generally work out of the box, e.g.:: + + apt install rustc rust-src bindgen rustfmt rust-clippy + + +Fedora Linux +************ + +Fedora Linux provides recent Rust releases and thus it should generally work out +of the box, e.g.:: + + dnf install rust rust-src bindgen-cli rustfmt clippy + + +Gentoo Linux +************ + +Gentoo Linux (and especially the testing branch) provides recent Rust releases +and thus it should generally work out of the box, e.g.:: + + USE='rust-src rustfmt clippy' emerge dev-lang/rust dev-util/bindgen + +``LIBCLANG_PATH`` may need to be set. + + +Nix +*** + +Nix (unstable channel) provides recent Rust releases and thus it should +generally work out of the box, e.g.:: + + { pkgs ? import <nixpkgs> {} }: + pkgs.mkShell { + nativeBuildInputs = with pkgs; [ rustc rust-bindgen rustfmt clippy ]; + RUST_LIB_SRC = "${pkgs.rust.packages.stable.rustPlatform.rustLibSrc}"; + } + + +openSUSE +******** + +openSUSE Slowroll and openSUSE Tumbleweed provide recent Rust releases and thus +they should generally work out of the box, e.g.:: + + zypper install rust rust1.79-src rust-bindgen clang + + +Ubuntu +****** + +25.04 +~~~~~ + +The latest Ubuntu releases provide recent Rust releases and thus they should +generally work out of the box, e.g.:: + + apt install rustc rust-src bindgen rustfmt rust-clippy + +In addition, ``RUST_LIB_SRC`` needs to be set, e.g.:: + + RUST_LIB_SRC=/usr/src/rustc-$(rustc --version | cut -d' ' -f2)/library + +For convenience, ``RUST_LIB_SRC`` can be exported to the global environment. + + +24.04 LTS and older +~~~~~~~~~~~~~~~~~~~ + +Though Ubuntu 24.04 LTS and older versions still provide recent Rust +releases, they require some additional configuration to be set, using +the versioned packages, e.g.:: + + apt install rustc-1.80 rust-1.80-src bindgen-0.65 rustfmt-1.80 \ + rust-1.80-clippy + ln -s /usr/lib/rust-1.80/bin/rustfmt /usr/bin/rustfmt-1.80 + ln -s /usr/lib/rust-1.80/bin/clippy-driver /usr/bin/clippy-driver-1.80 + +None of these packages set their tools as defaults; therefore they should be +specified explicitly, e.g.:: + + make LLVM=1 RUSTC=rustc-1.80 RUSTDOC=rustdoc-1.80 RUSTFMT=rustfmt-1.80 \ + CLIPPY_DRIVER=clippy-driver-1.80 BINDGEN=bindgen-0.65 + +Alternatively, modify the ``PATH`` variable to place the Rust 1.80 binaries +first and set ``bindgen`` as the default, e.g.:: + + PATH=/usr/lib/rust-1.80/bin:$PATH + update-alternatives --install /usr/bin/bindgen bindgen \ + /usr/bin/bindgen-0.65 100 + update-alternatives --set bindgen /usr/bin/bindgen-0.65 + +``RUST_LIB_SRC`` needs to be set when using the versioned packages, e.g.:: + + RUST_LIB_SRC=/usr/src/rustc-$(rustc-1.80 --version | cut -d' ' -f2)/library + +For convenience, ``RUST_LIB_SRC`` can be exported to the global environment. + +In addition, ``bindgen-0.65`` is available in newer releases (24.04 LTS and +24.10), but it may not be available in older ones (20.04 LTS and 22.04 LTS), +thus ``bindgen`` may need to be built manually (please see below). + + +Requirements: Building +---------------------- + +This section explains how to fetch the tools needed for building. + +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 recent version of the Rust compiler is required. + +If ``rustup`` is being used, enter the kernel build directory (or use +``--path=<build-dir>`` argument to the ``set`` sub-command) and run, +for instance:: + + rustup override set stable + +This will configure your working directory to use the given 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: + + https://forge.rust-lang.org/infra/other-installation-methods.html#standalone + + +Rust standard library source +**************************** + +The Rust standard library source is required because the build system will +cross-compile ``core``. + +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-$(rustc --version | cut -d' ' -f2).tar.gz" | + tar -xzf - -C "$(rustc --print sysroot)/lib" \ + "rust-src-$(rustc --version | cut -d' ' -f2)/rust-src/lib/" \ + --strip-components=3 + +In this case, upgrading the Rust compiler version later on requires manually +updating the source tree (this can be done by removing ``$(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: + + https://releases.llvm.org/download.html + +Otherwise, building LLVM takes quite a while, but it is not a complex process: + + https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm + +Please see Documentation/kbuild/llvm.rst 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. + +Install it, for instance, via (note that this will download and build the tool +from source):: + + cargo install --locked bindgen-cli + +``bindgen`` uses the ``clang-sys`` crate to find a suitable ``libclang`` (which +may be linked statically, dynamically or loaded at runtime). By default, the +``cargo`` command above will produce a ``bindgen`` binary that will load +``libclang`` at runtime. If it is not found (or a different ``libclang`` than +the one found should be used), the process can be tweaked, e.g. by using the +``LIBCLANG_PATH`` environment variable. For details, please see ``clang-sys``'s +documentation at: + + https://github.com/KyleMayes/clang-sys#linking + + https://github.com/KyleMayes/clang-sys#environment-variables + + +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.rst). + +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.rst). + +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``. + + +rustdoc +******* + +``rustdoc`` is the documentation tool for Rust. It generates pretty HTML +documentation for Rust code (for details, please see +general-information.rst). + +``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 <https://rust-analyzer.github.io/>`_ 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``). diff --git a/Documentation/rust/testing.rst b/Documentation/rust/testing.rst new file mode 100644 index 000000000000..f43cb77bcc69 --- /dev/null +++ b/Documentation/rust/testing.rst @@ -0,0 +1,236 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Testing +======= + +This document contains useful information how to test the Rust code in the +kernel. + +There are three sorts of tests: + +- The KUnit tests. +- The ``#[test]`` tests. +- The Kselftests. + +The KUnit tests +--------------- + +These are the tests that come from the examples in the Rust documentation. They +get transformed into KUnit tests. + +Usage +***** + +These tests can be run via KUnit. For example via ``kunit_tool`` (``kunit.py``) +on the command line:: + + ./tools/testing/kunit/kunit.py run --make_options LLVM=1 --arch x86_64 --kconfig_add CONFIG_RUST=y + +Alternatively, KUnit can run them as kernel built-in at boot. Refer to +Documentation/dev-tools/kunit/index.rst for the general KUnit documentation +and Documentation/dev-tools/kunit/architecture.rst for the details of kernel +built-in vs. command line testing. + +To use these KUnit doctests, the following must be enabled:: + + CONFIG_KUNIT + Kernel hacking -> Kernel Testing and Coverage -> KUnit - Enable support for unit tests + CONFIG_RUST_KERNEL_DOCTESTS + Kernel hacking -> Rust hacking -> Doctests for the `kernel` crate + +in the kernel config system. + +KUnit tests are documentation tests +*********************************** + +These documentation tests are typically examples of usage of any item (e.g. +function, struct, module...). + +They are very convenient because they are just written alongside the +documentation. For instance: + +.. code-block:: rust + + /// Sums two numbers. + /// + /// ``` + /// assert_eq!(mymod::f(10, 20), 30); + /// ``` + pub fn f(a: i32, b: i32) -> i32 { + a + b + } + +In userspace, the tests are collected and run via ``rustdoc``. Using the tool +as-is would be useful already, since it allows verifying that examples compile +(thus enforcing they are kept in sync with the code they document) and as well +as running those that do not depend on in-kernel APIs. + +For the kernel, however, these tests get transformed into KUnit test suites. +This means that doctests get compiled as Rust kernel objects, allowing them to +run against a built kernel. + +A benefit of this KUnit integration is that Rust doctests get to reuse existing +testing facilities. For instance, the kernel log would look like:: + + KTAP version 1 + 1..1 + KTAP version 1 + # Subtest: rust_doctests_kernel + 1..59 + # rust_doctest_kernel_build_assert_rs_0.location: rust/kernel/build_assert.rs:13 + ok 1 rust_doctest_kernel_build_assert_rs_0 + # rust_doctest_kernel_build_assert_rs_1.location: rust/kernel/build_assert.rs:56 + ok 2 rust_doctest_kernel_build_assert_rs_1 + # rust_doctest_kernel_init_rs_0.location: rust/kernel/init.rs:122 + ok 3 rust_doctest_kernel_init_rs_0 + ... + # rust_doctest_kernel_types_rs_2.location: rust/kernel/types.rs:150 + ok 59 rust_doctest_kernel_types_rs_2 + # rust_doctests_kernel: pass:59 fail:0 skip:0 total:59 + # Totals: pass:59 fail:0 skip:0 total:59 + ok 1 rust_doctests_kernel + +Tests using the `? <https://doc.rust-lang.org/reference/expressions/operator-expr.html#the-question-mark-operator>`_ +operator are also supported as usual, e.g.: + +.. code-block:: rust + + /// ``` + /// # use kernel::{spawn_work_item, workqueue}; + /// spawn_work_item!(workqueue::system(), || pr_info!("x\n"))?; + /// # Ok::<(), Error>(()) + /// ``` + +The tests are also compiled with Clippy under ``CLIPPY=1``, just like normal +code, thus also benefitting from extra linting. + +In order for developers to easily see which line of doctest code caused a +failure, a KTAP diagnostic line is printed to the log. This contains the +location (file and line) of the original test (i.e. instead of the location in +the generated Rust file):: + + # rust_doctest_kernel_types_rs_2.location: rust/kernel/types.rs:150 + +Rust tests appear to assert using the usual ``assert!`` and ``assert_eq!`` +macros from the Rust standard library (``core``). We provide a custom version +that forwards the call to KUnit instead. Importantly, these macros do not +require passing context, unlike those for KUnit testing (i.e. +``struct kunit *``). This makes them easier to use, and readers of the +documentation do not need to care about which testing framework is used. In +addition, it may allow us to test third-party code more easily in the future. + +A current limitation is that KUnit does not support assertions in other tasks. +Thus, we presently simply print an error to the kernel log if an assertion +actually failed. Additionally, doctests are not run for nonpublic functions. + +Since these tests are examples, i.e. they are part of the documentation, they +should generally be written like "real code". Thus, for example, instead of +using ``unwrap()`` or ``expect()``, use the ``?`` operator. For more background, +please see: + + https://rust.docs.kernel.org/kernel/error/type.Result.html#error-codes-in-c-and-rust + +The ``#[test]`` tests +--------------------- + +Additionally, there are the ``#[test]`` tests. Like for documentation tests, +these are also fairly similar to what you would expect from userspace, and they +are also mapped to KUnit. + +These tests are introduced by the ``kunit_tests`` procedural macro, which takes +the name of the test suite as an argument. + +For instance, assume we want to test the function ``f`` from the documentation +tests section. We could write, in the same file where we have our function: + +.. code-block:: rust + + #[kunit_tests(rust_kernel_mymod)] + mod tests { + use super::*; + + #[test] + fn test_f() { + assert_eq!(f(10, 20), 30); + } + } + +And if we run it, the kernel log would look like:: + + KTAP version 1 + # Subtest: rust_kernel_mymod + # speed: normal + 1..1 + # test_f.speed: normal + ok 1 test_f + ok 1 rust_kernel_mymod + +Like documentation tests, the ``assert!`` and ``assert_eq!`` macros are mapped +back to KUnit and do not panic. Similarly, the +`? <https://doc.rust-lang.org/reference/expressions/operator-expr.html#the-question-mark-operator>`_ +operator is supported, i.e. the test functions may return either nothing (i.e. +the unit type ``()``) or ``Result`` (i.e. any ``Result<T, E>``). For instance: + +.. code-block:: rust + + #[kunit_tests(rust_kernel_mymod)] + mod tests { + use super::*; + + #[test] + fn test_g() -> Result { + let x = g()?; + assert_eq!(x, 30); + Ok(()) + } + } + +If we run the test and the call to ``g`` fails, then the kernel log would show:: + + KTAP version 1 + # Subtest: rust_kernel_mymod + # speed: normal + 1..1 + # test_g: ASSERTION FAILED at rust/kernel/lib.rs:335 + Expected is_test_result_ok(test_g()) to be true, but is false + # test_g.speed: normal + not ok 1 test_g + not ok 1 rust_kernel_mymod + +If a ``#[test]`` test could be useful as an example for the user, then please +use a documentation test instead. Even edge cases of an API, e.g. error or +boundary cases, can be interesting to show in examples. + +The ``rusttest`` host tests +--------------------------- + +These are userspace tests that can be built and run in the host (i.e. the one +that performs the kernel build) using the ``rusttest`` Make target:: + + make LLVM=1 rusttest + +This requires the kernel ``.config``. + +Currently, they are mostly used for testing the ``macros`` crate's examples. + +The Kselftests +-------------- + +Kselftests are also available in the ``tools/testing/selftests/rust`` folder. + +The kernel config options required for the tests are listed in the +``tools/testing/selftests/rust/config`` file and can be included with the aid +of the ``merge_config.sh`` script:: + + ./scripts/kconfig/merge_config.sh .config tools/testing/selftests/rust/config + +The kselftests are built within the kernel source tree and are intended to +be executed on a system that is running the same kernel. + +Once a kernel matching the source tree has been installed and booted, the +tests can be compiled and executed using the following command:: + + make TARGETS="rust" kselftest + +Refer to Documentation/dev-tools/kselftest.rst for the general Kselftest +documentation. |