Merge tag 'rust-6.11' of https://github.com/Rust-for-Linux/linux

Pull Rust updates from Miguel Ojeda:
 "The highlight is the establishment of a minimum version for the Rust
  toolchain, including 'rustc' (and bundled tools) and 'bindgen'.

  The initial minimum will be the pinned version we currently have, i.e.
  we are just widening the allowed versions. That covers three stable
  Rust releases: 1.78.0, 1.79.0, 1.80.0 (getting released tomorrow),
  plus beta, plus nightly.

  This should already be enough for kernel developers in distributions
  that provide recent Rust compiler versions routinely, such as Arch
  Linux, Debian Unstable (outside the freeze period), Fedora Linux,
  Gentoo Linux (especially the testing channel), Nix (unstable) and
  openSUSE Slowroll and Tumbleweed.

  In addition, the kernel is now being built-tested by Rust's pre-merge
  CI. That is, every change that is attempting to land into the Rust
  compiler is tested against the kernel, and it is merged only if it
  passes. Similarly, the bindgen tool has agreed to build the kernel in
  their CI too.

  Thus, with the pre-merge CI in place, both projects hope to avoid
  unintentional changes to Rust that break the kernel. This means that,
  in general, apart from intentional changes on their side (that we will
  need to workaround conditionally on our side), the upcoming Rust
  compiler versions should generally work.

  In addition, the Rust project has proposed getting the kernel into
  stable Rust (at least solving the main blockers) as one of its three
  flagship goals for 2024H2 [1].

  I would like to thank Niko, Sid, Emilio et al. for their help
  promoting the collaboration between Rust and the kernel.

  Toolchain and infrastructure:

   - Support several Rust toolchain versions.

   - Support several bindgen versions.

   - Remove 'cargo' requirement and simplify 'rusttest', thanks to
     'alloc' having been dropped last cycle.

   - Provide proper error reporting for the 'rust-analyzer' target.

  'kernel' crate:

   - Add 'uaccess' module with a safe userspace pointers abstraction.

   - Add 'page' module with a 'struct page' abstraction.

   - Support more complex generics in workqueue's 'impl_has_work!'
     macro.

  'macros' crate:

   - Add 'firmware' field support to the 'module!' macro.

   - Improve 'module!' macro documentation.

  Documentation:

   - Provide instructions on what packages should be installed to build
     the kernel in some popular Linux distributions.

   - Introduce the new kernel.org LLVM+Rust toolchains.

   - Explain '#[no_std]'.

  And a few other small bits"

Link: https://rust-lang.github.io/rust-project-goals/2024h2/index.html#flagship-goals [1]

* tag 'rust-6.11' of https://github.com/Rust-for-Linux/linux: (26 commits)
  docs: rust: quick-start: add section on Linux distributions
  rust: warn about `bindgen` versions 0.66.0 and 0.66.1
  rust: start supporting several `bindgen` versions
  rust: work around `bindgen` 0.69.0 issue
  rust: avoid assuming a particular `bindgen` build
  rust: start supporting several compiler versions
  rust: simplify Clippy warning flags set
  rust: relax most deny-level lints to warnings
  rust: allow `dead_code` for never constructed bindings
  rust: init: simplify from `map_err` to `inspect_err`
  rust: macros: indent list item in `paste!`'s docs
  rust: add abstraction for `struct page`
  rust: uaccess: add typed accessors for userspace pointers
  uaccess: always export _copy_[from|to]_user with CONFIG_RUST
  rust: uaccess: add userspace pointers
  kbuild: rust-analyzer: improve comment documentation
  kbuild: rust-analyzer: better error handling
  docs: rust: no_std is used
  rust: alloc: add __GFP_HIGHMEM flag
  rust: alloc: fix typo in docs for GFP_NOWAIT
  ...

4 files changed, 111 insertions, 54 deletions

diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
index 1497e80f030e..3fc63f27c226 100644
--- a/Documentation/process/changes.rst
+++ b/Documentation/process/changes.rst
@@ -89,14 +89,7 @@ docs on :ref:`Building Linux with Clang/LLVM <kbuild_llvm>`.
 Rust (optional)
 ---------------
 
-A particular version of the Rust toolchain is required. Newer versions may or
-may not work because the kernel depends on some unstable Rust features, for
-the moment.
-
-Each Rust toolchain comes with several "components", some of which are required
-(like ``rustc``) and some that are optional. The ``rust-src`` component (which
-is optional) needs to be installed to build the kernel. Other components are
-useful for developing.
+A recent version of the Rust compiler is required.
 
 Please see Documentation/rust/quick-start.rst for instructions on how to
 satisfy the build requirements of Rust support. In particular, the ``Makefile``
diff --git a/Documentation/rust/general-information.rst b/Documentation/rust/general-information.rst
index 4bb6ac12d482..e3f388ef4ee4 100644
--- a/Documentation/rust/general-information.rst
+++ b/Documentation/rust/general-information.rst
@@ -7,6 +7,14 @@ 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.
+
+
 Code documentation
 ------------------
 
diff --git a/Documentation/rust/quick-start.rst b/Documentation/rust/quick-start.rst
index cc3f11e0d441..d06a36106cd4 100644
--- a/Documentation/rust/quick-start.rst
+++ b/Documentation/rust/quick-start.rst
@@ -5,17 +5,93 @@ 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 Unstable (Sid), outside of the freeze period, provides recent Rust
+releases and thus it 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
+
 
 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::
 
@@ -29,16 +105,15 @@ 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.
+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::
+``--path=<build-dir>`` argument to the ``set`` sub-command) and run,
+for instance::
 
-	rustup override set $(scripts/min-tool-version.sh rustc)
+	rustup override set stable
 
-This will configure your working directory to use the correct version of
+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
@@ -65,9 +140,9 @@ 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-$(scripts/min-tool-version.sh rustc).tar.gz" |
+	curl -L "https://static.rust-lang.org/dist/rust-src-$(rustc --version | cut -d' ' -f2).tar.gz" |
 		tar -xzf - -C "$(rustc --print sysroot)/lib" \
-		"rust-src-$(scripts/min-tool-version.sh rustc)/rust-src/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
@@ -101,26 +176,22 @@ bindgen
 *******
 
 The bindings to the C side of the kernel are generated at build time using
-the ``bindgen`` tool. A particular version is required.
+the ``bindgen`` tool.
 
-Install it via (note that this will download and build the tool from source)::
+Install it, for instance, via (note that this will download and build the tool
+from source)::
 
-	cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli
+	cargo install --locked 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``):
+``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:
 
-* ``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:
+	https://github.com/KyleMayes/clang-sys#linking
 
 	https://github.com/KyleMayes/clang-sys#environment-variables
 
@@ -164,20 +235,6 @@ can be installed manually::
 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
 *******
 
diff --git a/Documentation/rust/testing.rst b/Documentation/rust/testing.rst
index acfd0c2be48d..568b71b415a4 100644
--- a/Documentation/rust/testing.rst
+++ b/Documentation/rust/testing.rst
@@ -131,9 +131,8 @@ Additionally, there are the ``#[test]`` tests. These can be run using the
 
 	make LLVM=1 rusttest
 
-This requires the kernel ``.config`` and downloads external repositories. It
-runs the ``#[test]`` tests on the host (currently) and thus is fairly limited in
-what these tests can test.
+This requires the kernel ``.config``. It runs the ``#[test]`` tests on the host
+(currently) and thus is fairly limited in what these tests can test.
 
 The Kselftests
 --------------