From: Miguel Ojeda <ojeda@kernel.org>
To: Masahiro Yamada <masahiroy@kernel.org>,
Miguel Ojeda <ojeda@kernel.org>,
Wedson Almeida Filho <wedsonaf@gmail.com>,
Alex Gaynor <alex.gaynor@gmail.com>
Cc: "Nathan Chancellor" <nathan@kernel.org>,
"Nick Desaulniers" <ndesaulniers@google.com>,
"Nicolas Schier" <nicolas@fjasle.eu>,
"Boqun Feng" <boqun.feng@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Benno Lossin" <benno.lossin@proton.me>,
"Andreas Hindborg" <a.hindborg@samsung.com>,
"Alice Ryhl" <aliceryhl@google.com>,
linux-kbuild@vger.kernel.org, rust-for-linux@vger.kernel.org,
linux-kernel@vger.kernel.org, patches@lists.linux.dev,
stable@vger.kernel.org,
"Daniel Almeida" <daniel.almeida@collabora.com>,
"Julian Stecklina" <julian.stecklina@cyberus-technology.de>
Subject: [PATCH] kbuild: rust: force `alloc` extern to allow "empty" Rust files
Date: Mon, 22 Apr 2024 11:06:44 +0200 [thread overview]
Message-ID: <20240422090644.525520-1-ojeda@kernel.org> (raw)
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@vger.kernel.org # v6.6+
Reported-by: Daniel Almeida <daniel.almeida@collabora.com>
Reported-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>
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]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
scripts/Makefile.build | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
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 \
base-commit: 4cece764965020c22cff7665b18a012006359095
--
2.44.0
next reply other threads:[~2024-04-22 9:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-22 9:06 Miguel Ojeda [this message]
2024-04-22 9:13 ` [PATCH] kbuild: rust: force `alloc` extern to allow "empty" Rust files Alice Ryhl
2024-04-23 0:42 ` Miguel Ojeda
2024-04-25 14:15 ` Gary Guo
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