Re: [PATCH 1/2] rust: kbuild: treat `build_error` and `rustdoc` as kernel objects

[Justin Forbes <jmforbes@linuxtx.org>]

On Mon, Nov 3, 2025 at 3:29 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Sun, Nov 02, 2025 at 10:28:52PM +0100, Miguel Ojeda wrote:
> > Even if normally `build_error` isn't a kernel object, it should still
> > be treated as such so that we pass the same flags. Similarly, `rustdoc`
> > targets are never kernel objects, but we need to treat them as such.
> >
> > Otherwise, starting with Rust 1.91.0 (released 2025-10-30), `rustc`
> > will complain about missing sanitizer flags since `-Zsanitizer` is a
> > target modifier too [1]:
> >
> >     error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `build_error`
> >      --> rust/build_error.rs:3:1
> >       |
> >     3 | //! Build-time error.
> >       | ^
> >       |
> >       = help: the `-Zsanitizer` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
> >       = note: unset `-Zsanitizer` in this crate is incompatible with `-Zsanitizer=kernel-address` in dependency `core`
> >       = help: set `-Zsanitizer=kernel-address` in this crate or unset `-Zsanitizer` in `core`
> >       = help: if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch=sanitizer` to silence this error
> >
> > Thus explicitly mark them as kernel objects.
> >
> > Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> > Link: https://github.com/rust-lang/rust/pull/138736 [1]
> > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>

I can verify that this fixes kernel builds with rust 1.91 in Fedora.

Tested-by: Justin M. Forbes <jforbes@fedoraproject.org>