This is a note to let you know that I've just added the patch titled
kbuild: rust: force `alloc` extern to allow "empty" Rust files
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kbuild-rust-force-alloc-extern-to-allow-empty-rust-f.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit cb22155fdf04820451fcb5386eefe655f9f39941
Author: Miguel Ojeda <ojeda@xxxxxxxxxx>
Date: Mon Apr 22 11:06:44 2024 +0200
kbuild: rust: force `alloc` extern to allow "empty" Rust files
[ Upstream commit ded103c7eb23753f22597afa500a7c1ad34116ba ]
If one attempts to build an essentially empty file somewhere in the
kernel tree, it leads to a build error because the compiler does not
recognize the `new_uninit` unstable feature:
error[E0635]: unknown feature `new_uninit`
--> <crate attribute>:1:9
|
1 | feature(new_uninit)
| ^^^^^^^^^^
The reason is that we pass `-Zcrate-attr='feature(new_uninit)'` (together
with `-Zallow-features=new_uninit`) to let non-`rust/` code use that
unstable feature.
However, the compiler only recognizes the feature if the `alloc` crate
is resolved (the feature is an `alloc` one). `--extern alloc`, which we
pass, is not enough to resolve the crate.
Introducing a reference like `use alloc;` or `extern crate alloc;`
solves the issue, thus this is not seen in normal files. For instance,
`use`ing the `kernel` prelude introduces such a reference, since `alloc`
is used inside.
While normal use of the build system is not impacted by this, it can still
be fairly confusing for kernel developers [1], thus use the unstable
`force` option of `--extern` [2] (added in Rust 1.71 [3]) to force the
compiler to resolve `alloc`.
This new unstable feature is only needed meanwhile we use the other
unstable feature, since then we will not need `-Zcrate-attr`.
Cc: stable@xxxxxxxxxxxxxxx # v6.6+
Reported-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
Reported-by: Julian Stecklina <julian.stecklina@xxxxxxxxxxxxxxxxxxxxx>
Closes: https://rust-for-linux.zulipchat.com/#narrow/stream/288089-General/topic/x/near/424096982 [1]
Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
Link: https://github.com/rust-lang/rust/issues/111302 [2]
Link: https://github.com/rust-lang/rust/pull/109421 [3]
Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240422090644.525520-1-ojeda@xxxxxxxxxx
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 1827bc1db1e98..78f9cf73d96b2 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -285,7 +285,7 @@ rust_common_cmd = \
-Zallow-features=$(rust_allowed_features) \
-Zcrate-attr=no_std \
-Zcrate-attr='feature($(rust_allowed_features))' \
- --extern alloc --extern kernel \
+ -Zunstable-options --extern force:alloc --extern kernel \
--crate-type rlib -L $(objtree)/rust/ \
--crate-name $(basename $(notdir $@)) \
--out-dir $(dir $@) --emit=dep-info=$(depfile)
