Re: [PATCH v4] rust: Makefile: bound rustdoc workaround to affected versions

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Feb 04, 2026 at 08:48:43AM +0900, HeeSu Kim wrote:
> The `-Cunsafe-allow-abi-mismatch=fixed-x18` workaround was added to
> handle a rustdoc bug where target modifiers were not properly saved [1].
> 
> This bug was fixed in Rust 1.90.0 [2]. Restrict the workaround to only
> apply for Rust 1.88.x and 1.89.x versions that are affected by the
> bug, preserving ABI compatibility checks on newer compiler versions.
> 
> Add `rustc-max-version` macro to `scripts/Makefile.compiler` for
> version upper bound checks, mirroring the existing `rustc-min-version`.
> 
> Link: https://github.com/rust-lang/rust/issues/144521 [1]
> Link: https://github.com/rust-lang/rust/pull/144523 [2]
> Suggested-by: Gary Guo <gary@garyguo.net>
> Link: https://lore.kernel.org/rust-for-linux/DG4JM9PU51M0.1YRGM9HVTY24U@garyguo.net/
> Suggested-by: Miguel Ojeda <ojeda@kernel.org>
> Link: https://lore.kernel.org/rust-for-linux/CANiq72n39eU9WE=Yh0_yJzmqMxo=QAaU2pN0UqP9jZ7bT7rhgA@mail.gmail.com/
> Cc: stable@vger.kernel.org # Useful in 6.18.y and later.
> Signed-off-by: HeeSu Kim <mlksvender@gmail.com>

Acked-by: Nathan Chancellor <nathan@kernel.org>

I assume Miguel will pick this up.

> ---
> Changes in v4:
> - Add rustc-max-version macro for cleaner version bounds
> - Use rustc-max-version instead of test-lt for readability
> 
> Changes in v3:
> - Remove Fixes: tag (this is a feature, not a fix)
> - Use full URLs with Link: tags instead of GitHub-style references
> - Add Link: to lore.kernel.org for Suggested-by attribution
> - Add Cc: stable for potential backporting to 6.18.y
> 
> Changes in v2:
> - Change approach: bound to affected Rust versions instead of ARM64-only
>   (the flag is simply ignored on non-ARM64 architectures)
> 
>  rust/Makefile             | 3 ++-
>  scripts/Makefile.compiler | 4 ++++
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/Makefile b/rust/Makefile
> index 5c0155b83454..1e8a75bc2878 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -136,7 +136,8 @@ pin_init-flags := \
>  
>  # `rustdoc` did not save the target modifiers, thus workaround for
>  # the time being (https://github.com/rust-lang/rust/issues/144521).
> -rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
> +# The bug was fixed in Rust 1.90.0, so only apply for 1.88.x and 1.89.x.
> +rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),$(if $(call rustc-max-version,108999),-Cunsafe-allow-abi-mismatch=fixed-x18))
>  
>  # Similarly, for doctests (https://github.com/rust-lang/rust/issues/146465).
>  doctests_modifiers_workaround := $(rustdoc_modifiers_workaround)$(if $(call rustc-min-version,109100),$(comma)sanitizer)
> diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
> index ef91910de265..85268f6f1494 100644
> --- a/scripts/Makefile.compiler
> +++ b/scripts/Makefile.compiler
> @@ -71,6 +71,10 @@ clang-min-version = $(call test-ge, $(CONFIG_CLANG_VERSION), $1)
>  # Usage: rustc-$(call rustc-min-version, 108500) += -Cfoo
>  rustc-min-version = $(call test-ge, $(CONFIG_RUSTC_VERSION), $1)
>  
> +# rustc-max-version
> +# Usage: rustc-$(call rustc-max-version, 109000) += -Cfoo
> +rustc-max-version = $(call test-le, $(CONFIG_RUSTC_VERSION), $1)

Minor meta comment: It is generally perferred to add a macro like this
in a separate change to make it easier to backport if it is needed in
the future.

>  # ld-option
>  # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
>  ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))
> -- 
> 2.52.0
>