linux-kernel - Re: [PATCH 2/2] rust: upgrade to Rust 1.72.0

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Date:   Wed, 23 Aug 2023 23:28:34 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>
Cc:     Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Jonathan Corbet <corbet@....net>,
        workflows@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: upgrade to Rust 1.72.0

On 8/23/23 13:02, Miguel Ojeda wrote:
> This is the second upgrade to the Rust toolchain, from 1.71.1 to 1.72.0
> (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 feature allowed to be used outside
> the `kernel` crate is still `new_uninit`, though other code to be
> upstreamed may increase the list.
> 
> Please see [3] for details.
> 
> # Other improvements
> 
> Previously, the compiler could incorrectly generate a `.eh_frame`
> section under `-Cpanic=abort`. We were hitting this bug in our
> old `rust` branch [4]. Gary fixed the issue in Rust 1.72.0 [5].
> 
> # Required changes
> 
> For the upgrade, the following changes are required:
> 
>    - A call to `Box::from_raw` in `rust/kernel/sync/arc.rs` now requires
>      an explicit `drop()` call. See previous patch for details.
> 
> # `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-1720-2023-08-24 [1]
> Link: https://rust-for-linux.com/rust-version-policy [2]
> Link: https://github.com/Rust-for-Linux/linux/issues/2 [3]
> Closes: https://github.com/Rust-for-Linux/linux/issues/1012 [4]
> Link: https://github.com/rust-lang/rust/pull/112403 [5]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
> [...]
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>