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rust: workaround rustdoc target modifiers bug

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commit abbf9a4494 upstream.

Starting with Rust 1.88.0 (released 2025-06-26), `rustdoc` complains
about a target modifier mismatch in configurations where `-Zfixed-x18`
is passed:

    error: mixing `-Zfixed-x18` will cause an ABI mismatch in crate `rust_out`
      |
      = help: the `-Zfixed-x18` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
      = note: unset `-Zfixed-x18` in this crate is incompatible with `-Zfixed-x18=` in dependency `core`
      = help: set `-Zfixed-x18=` in this crate or unset `-Zfixed-x18` in `core`
      = help: if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch=fixed-x18` to silence this error

The reason is that `rustdoc` was not passing the target modifiers when
configuring the session options, and thus it would report a mismatch
that did not exist as soon as a target modifier is used in a dependency.

We did not notice it in the kernel until now because `-Zfixed-x18` has
been a target modifier only since 1.88.0 (and it is the only one we use
so far).

The issue has been reported upstream [1] and a fix has been submitted
[2], including a test similar to the kernel case.

  [ This is now fixed upstream (thanks Guillaume for the quick review),
    so it will be fixed in Rust 1.90.0 (expected 2025-09-18).

      - Miguel ]

Meanwhile, conditionally pass `-Cunsafe-allow-abi-mismatch=fixed-x18`
to workaround the issue on our side.

Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Reported-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Closes: https://lore.kernel.org/rust-for-linux/36cdc798-524f-4910-8b77-d7b9fac08d77@oss.qualcomm.com/
Link: https://github.com/rust-lang/rust/issues/144521 [1]
Link: https://github.com/rust-lang/rust/pull/144523 [2]
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250727092317.2930617-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Miguel Ojeda 2025-07-27 11:23:17 +02:00 committed by Greg Kroah-Hartman
parent 1b39c9a886
commit b8980ac45b
1 changed files with 6 additions and 0 deletions
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6
rust/Makefile
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@ -62,6 +62,10 @@ core-cfgs = \
core-edition := $(if $(call rustc-min-version,108700),2024,2021)
# `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)
# `rustc` recognizes `--remap-path-prefix` since 1.26.0, but `rustdoc` only
# since Rust 1.81.0. Moreover, `rustdoc` ICEs on out-of-tree builds since Rust
# 1.82.0 (https://github.com/rust-lang/rust/issues/138520). Thus workaround both
@ -74,6 +78,7 @@ quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
-Zunstable-options --generate-link-to-definition \
--output $(rustdoc_output) \
--crate-name $(subst rustdoc-,,$@) \
$(rustdoc_modifiers_workaround) \
$(if $(rustdoc_host),,--sysroot=/dev/null) \
@$(objtree)/include/generated/rustc_cfg $<
@ -216,6 +221,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
--extern bindings --extern uapi \
--no-run --crate-name kernel -Zunstable-options \
--sysroot=/dev/null \
$(rustdoc_modifiers_workaround) \
--test-builder $(objtree)/scripts/rustdoc_test_builder \
$< $(rustdoc_test_kernel_quiet); \
$(objtree)/scripts/rustdoc_test_gen