768409cff6
This is the next upgrade to the Rust toolchain, from 1.75.0 to 1.76.0
(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 in Rust 1.76.0.
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.
Please see [3] for details.
# Required changes
`rustc` (and others) now warns when it cannot connect to the Make
jobserver, thus mark those invocations as recursive as needed. Please
see the previous commit for details.
# Other changes
Rust 1.76.0 does not emit the `.debug_pub{names,types}` sections anymore
for DWARFv4 [4][5]. For instance, in the uncompressed debug info case,
this debug information took:
samples/rust/rust_minimal.o ~64 KiB (~18% of total object size)
rust/kernel.o ~92 KiB (~15%)
rust/core.o ~114 KiB ( ~5%)
In the compressed debug info (zlib) case:
samples/rust/rust_minimal.o ~11 KiB (~6%)
rust/kernel.o ~17 KiB (~5%)
rust/core.o ~21 KiB (~1.5%)
In addition, the `rustc_codegen_gcc` backend now does not emit the
`.eh_frame` section when compiling under `-Cpanic=abort` [6], thus
removing the need for the patch in the CI to compile the kernel [7].
Moreover, it also now emits the `.comment` section too [6].
# `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-1760-2024-02-08 [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/compiler-team/issues/688 [4]
Link: https://github.com/rust-lang/rust/pull/117962 [5]
Link: https://github.com/rust-lang/rust/pull/118068 [6]
Link: https://github.com/Rust-for-Linux/ci-rustc_codegen_gcc [7]
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240217002638.57373-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
alloc
These source files come from the Rust standard library, hosted in the https://github.com/rust-lang/rust repository, licensed under "Apache-2.0 OR MIT" and adapted for kernel use. For copyright details, see https://github.com/rust-lang/rust/blob/master/COPYRIGHT.
Please note that these files should be kept as close as possible to upstream. In general, only additions should be performed (e.g. new methods). Eventually, changes should make it into upstream so that, at some point, this fork can be dropped from the kernel tree.
The Rust upstream version on top of which these files are based matches
the output of scripts/min-tool-version.sh rustc.
Rationale
On one hand, kernel folks wanted to keep alloc in-tree to have more
freedom in both workflow and actual features if actually needed
(e.g. receiver types if we ended up using them), which is reasonable.
On the other hand, Rust folks wanted to keep alloc as close as
upstream as possible and avoid as much divergence as possible, which
is also reasonable.
We agreed on a middle-ground: we would keep a subset of alloc
in-tree that would be as small and as close as possible to upstream.
Then, upstream can start adding the functions that we add to alloc
etc., until we reach a point where the kernel already knows exactly
what it needs in alloc and all the new methods are merged into
upstream, so that we can drop alloc from the kernel tree and go back
to using the upstream one.
By doing this, the kernel can go a bit faster now, and Rust can slowly incorporate and discuss the changes as needed.