Re: [PATCH 1/2] rust: upgrade to Rust 1.71.0

[Miguel Ojeda]

On Sun, Jul 30, 2023 at 12:04 AM Miguel Ojeda <ojeda@xxxxxxxxxx> wrote:
>
> This is the second upgrade to the Rust toolchain, from 1.68.2 to 1.71.0
> (i.e. the latest).
>
> See the upgrade policy [1] 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 [2] for details.
>
> # Required changes
>
> For the upgrade, this patch requires the following changes:
>
>   - Removal of the `__rust_*` allocator functions, together with
>     the addition of the `__rust_no_alloc_shim_is_unstable` static.
>     See [3] for details.
>
>   - Some more compiler builtins added due to `<f{32,64}>::midpoint()`
>     that got added in Rust 1.71 [4].
>
> # `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://rust-for-linux.com/rust-version-policy [1]
> Link: https://github.com/Rust-for-Linux/linux/issues/2 [2]
> Link: https://github.com/rust-lang/rust/pull/86844 [3]
> Link: https://github.com/rust-lang/rust/pull/92048 [4]
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Applied to `rust-next` -- thanks everyone!

As mentioned earlier, I have moved to 1.71.1 instead that got released
meanwhile, since it does not require any changes w.r.t. this one
except the obvious ones and it is likely the one that people would
like to use/have (so less warnings).

Cheers,
Miguel