The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x ded103c7eb23753f22597afa500a7c1ad34116ba # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2024042909-whimsical-drapery-40d1@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: ded103c7eb23 ("kbuild: rust: force `alloc` extern to allow "empty" Rust files") 295d8398c67e ("kbuild: specify output names separately for each emission type from rustc") 16169a47d5c3 ("kbuild: refactor host*_flags") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From ded103c7eb23753f22597afa500a7c1ad34116ba Mon Sep 17 00:00:00 2001 From: Miguel Ojeda <ojeda@xxxxxxxxxx> Date: Mon, 22 Apr 2024 11:06:44 +0200 Subject: [PATCH] kbuild: rust: force `alloc` extern to allow "empty" Rust files 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> diff --git a/scripts/Makefile.build b/scripts/Makefile.build index baf86c0880b6..533a7799fdfe 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -273,7 +273,7 @@ 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 $@)) \ --sysroot=/dev/null \
