Re: [PATCH] rust: upgrade to Rust 1.74.1

[David Gow <davidgow@google.com>]

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On Thu, 14 Dec 2023 at 17:30, Miguel Ojeda <ojeda@kernel.org> wrote:
>
> This is the next upgrade to the Rust toolchain, from 1.73.0 to 1.74.1
> (i.e. the latest) [1].
>
> See the upgrade policy [2] and the comments on the first upgrade in
> commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2").
>
> # Unstable features
>
> No unstable features (that we use) were stabilized.
>
> Therefore, the only unstable features allowed to be used outside the
> `kernel` crate are still `new_uninit,offset_of`, though other code to
> be upstreamed may increase the list (e.g. `offset_of` was added recently).
>
> Please see [3] for details.
>
> # Other improvements
>
> Rust 1.74.0 allows to use `#[repr(Rust)]` explicitly [4], which can be
> useful to be explicit about particular cases that would normally use
> e.g. the C representation, such as silencing lints like the upcoming
> additions we requested [5] to the `no_mangle_with_rust_abi` Clippy lint
> (which in turn triggered the `#[repr(Rust)]` addition).
>
> Rust 1.74.0 includes a fix for one of the false negative cases we reported
> in Clippy's `disallowed_macros` lint [6] that we would like to use in
> the future.
>
> Rust 1.74.1 fixes an ICE that the Apple AGX GPU driver was hitting [7].
>
> # Required changes
>
> For this upgrade, no changes were required (i.e. on our side).
>
> # `alloc` upgrade and reviewing
>
> The vast majority of changes are due to our `alloc` fork being upgraded
> at once.
>
> There are two kinds of changes to be aware of: the ones coming from
> upstream, which we should follow as closely as possible, and the updates
> needed in our added fallible APIs to keep them matching the newer
> infallible APIs coming from upstream.
>
> Instead of taking a look at the diff of this patch, an alternative
> approach is reviewing a diff of the changes between upstream `alloc` and
> the kernel's. This allows to easily inspect the kernel additions only,
> especially to check if the fallible methods we already have still match
> the infallible ones in the new version coming from upstream.
>
> Another approach is reviewing the changes introduced in the additions in
> the kernel fork between the two versions. This is useful to spot
> potentially unintended changes to our additions.
>
> To apply these approaches, one may follow steps similar to the following
> to generate a pair of patches that show the differences between upstream
> Rust and the kernel (for the subset of `alloc` we use) before and after
> applying this patch:
>
>     # Get the difference with respect to the old version.
>     git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
>     git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
>         cut -d/ -f3- |
>         grep -Fv README.md |
>         xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
>     git -C linux diff --patch-with-stat --summary -R > old.patch
>     git -C linux restore rust/alloc
>
>     # Apply this patch.
>     git -C linux am rust-upgrade.patch
>
>     # Get the difference with respect to the new version.
>     git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
>     git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
>         cut -d/ -f3- |
>         grep -Fv README.md |
>         xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
>     git -C linux diff --patch-with-stat --summary -R > new.patch
>     git -C linux restore rust/alloc
>
> Now one may check the `new.patch` to take a look at the additions (first
> approach) or at the difference between those two patches (second
> approach). For the latter, a side-by-side tool is recommended.
>
> Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1741-2023-12-07 [1]
> Link: https://rust-for-linux.com/rust-version-policy [2]
> Link: https://github.com/Rust-for-Linux/linux/issues/2 [3]
> Link: https://github.com/rust-lang/rust/pull/114201 [4]
> Link: https://github.com/rust-lang/rust-clippy/issues/11219 [5]
> Link: https://github.com/rust-lang/rust-clippy/issues/11431 [6]
> Link: https://github.com/rust-lang/rust/issues/117976#issuecomment-1822225691 [7]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---

KUnit tests pass on x86_64 and UML.

Tested-by: David Gow <davidgow@google.com>

Cheers,
-- David

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