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

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

[Miguel Ojeda]

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>
---
 rust/Makefile | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/rust/Makefile b/rust/Makefile
index 23c7ae905bd2..5de103e20841 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -127,9 +127,14 @@ rustdoc-core: private rustc_target_flags = --edition=$(core-edition) $(core-cfgs
 rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs rustdoc-clean FORCE
 	+$(call if_changed,rustdoc)
 
+# Even if `rustdoc` targets are not kernel objects, they should still be
+# treated as such so that we pass the same flags. Otherwise, for instance,
+# `rustc` will complain about missing sanitizer flags causing an ABI mismatch.
+rustdoc-compiler_builtins: private is-kernel-object := y
 rustdoc-compiler_builtins: $(src)/compiler_builtins.rs rustdoc-core FORCE
 	+$(call if_changed,rustdoc)
 
+rustdoc-ffi: private is-kernel-object := y
 rustdoc-ffi: $(src)/ffi.rs rustdoc-core FORCE
 	+$(call if_changed,rustdoc)
 
@@ -147,6 +152,7 @@ rustdoc-pin_init: $(src)/pin-init/src/lib.rs rustdoc-pin_init_internal \
     rustdoc-macros FORCE
 	+$(call if_changed,rustdoc)
 
+rustdoc-kernel: private is-kernel-object := y
 rustdoc-kernel: private rustc_target_flags = --extern ffi --extern pin_init \
     --extern build_error --extern macros \
     --extern bindings --extern uapi
@@ -522,6 +528,10 @@ $(obj)/pin_init.o: $(src)/pin-init/src/lib.rs $(obj)/compiler_builtins.o \
     $(obj)/$(libpin_init_internal_name) $(obj)/$(libmacros_name) FORCE
 	+$(call if_changed_rule,rustc_library)
 
+# Even if normally `build_error` is not a kernel object, it should still be
+# treated as such so that we pass the same flags. Otherwise, for instance,
+# `rustc` will complain about missing sanitizer flags causing an ABI mismatch.
+$(obj)/build_error.o: private is-kernel-object := y
 $(obj)/build_error.o: private skip_gendwarfksyms = 1
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_rule,rustc_library)
-- 
2.51.2

[PATCH 2/2] rust: kbuild: workaround `rustdoc` doctests modifier bug

[Miguel Ojeda]

The `rustdoc` modifiers bug [1] was fixed in Rust 1.90.0 [2], for which
we added a workaround in commit abbf9a449441 ("rust: workaround `rustdoc`
target modifiers bug").

However, `rustdoc`'s doctest generation still has a similar issue [3],
being fixed at [4], which does not affect us because we apply the
workaround to both, and now, starting with Rust 1.91.0 (released
2025-10-30), `-Zsanitizer` is a target modifier too [5], which means we
fail with:

      RUSTDOC TK rust/kernel/lib.rs
    error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `kernel`
     --> rust/kernel/lib.rs:3:1
      |
    3 | //! The `kernel` crate.
      | ^
      |
      = 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

A simple way around is to add the sanitizer to the list in the existing
workaround (especially if we had not started to pass the sanitizer
flags in the previous commit, since in that case that would not be
necessary). However, that still applies the workaround in more cases
than necessary.

Instead, only modify the doctests flags to ignore the check for
sanitizers, so that it is more local (and thus the compiler keeps checking
it for us in the normal `rustdoc` calls). Since the previous commit
already treated the `rustdoc` calls as kernel objects, this should allow
us in the future to easily remove this workaround when the time comes.

By the way, the `-Cunsafe-allow-abi-mismatch` flag overwrites previous
ones rather than appending, so it needs to be all done in the same flag.
Moreover, unknown modifiers are rejected, and thus we have to gate based
on the version too.

Finally, `-Zsanitizer-cfi-normalize-integers` is not affected, so it is
not needed in the workaround.

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/issues/144521 [1]
Link: https://github.com/rust-lang/rust/pull/144523 [2]
Link: https://github.com/rust-lang/rust/issues/146465 [3]
Link: https://github.com/rust-lang/rust/pull/148068 [4]
Link: https://github.com/rust-lang/rust/pull/138736 [5]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/rust/Makefile b/rust/Makefile
index 5de103e20841..ce6d9c9d9727 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -69,6 +69,9 @@ core-edition := $(if $(call rustc-min-version,108700),2024,2021)
 # 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)
 
+# 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)
+
 # `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
@@ -236,7 +239,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 		--extern bindings --extern uapi \
 		--no-run --crate-name kernel -Zunstable-options \
 		--sysroot=/dev/null \
-		$(rustdoc_modifiers_workaround) \
+		$(doctests_modifiers_workaround) \
 		--test-builder $(objtree)/scripts/rustdoc_test_builder \
 		$< $(rustdoc_test_kernel_quiet); \
 	$(objtree)/scripts/rustdoc_test_gen
-- 
2.51.2

Re: [PATCH 2/2] rust: kbuild: workaround `rustdoc` doctests modifier bug

[Alice Ryhl]

On Sun, Nov 02, 2025 at 10:28:53PM +0100, Miguel Ojeda wrote:
> The `rustdoc` modifiers bug [1] was fixed in Rust 1.90.0 [2], for which
> we added a workaround in commit abbf9a449441 ("rust: workaround `rustdoc`
> target modifiers bug").
> 
> However, `rustdoc`'s doctest generation still has a similar issue [3],
> being fixed at [4], which does not affect us because we apply the
> workaround to both, and now, starting with Rust 1.91.0 (released
> 2025-10-30), `-Zsanitizer` is a target modifier too [5], which means we
> fail with:
> 
>       RUSTDOC TK rust/kernel/lib.rs
>     error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `kernel`
>      --> rust/kernel/lib.rs:3:1
>       |
>     3 | //! The `kernel` crate.
>       | ^
>       |
>       = 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
> 
> A simple way around is to add the sanitizer to the list in the existing
> workaround (especially if we had not started to pass the sanitizer
> flags in the previous commit, since in that case that would not be
> necessary). However, that still applies the workaround in more cases
> than necessary.
> 
> Instead, only modify the doctests flags to ignore the check for
> sanitizers, so that it is more local (and thus the compiler keeps checking
> it for us in the normal `rustdoc` calls). Since the previous commit
> already treated the `rustdoc` calls as kernel objects, this should allow
> us in the future to easily remove this workaround when the time comes.
> 
> By the way, the `-Cunsafe-allow-abi-mismatch` flag overwrites previous
> ones rather than appending, so it needs to be all done in the same flag.
> Moreover, unknown modifiers are rejected, and thus we have to gate based
> on the version too.

Ah .. we may want to file a bug for that.

> Finally, `-Zsanitizer-cfi-normalize-integers` is not affected, so it is
> not needed in the workaround.
> 
> 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/issues/144521 [1]
> Link: https://github.com/rust-lang/rust/pull/144523 [2]
> Link: https://github.com/rust-lang/rust/issues/146465 [3]
> Link: https://github.com/rust-lang/rust/pull/148068 [4]
> Link: https://github.com/rust-lang/rust/pull/138736 [5]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

Re: [PATCH 2/2] rust: kbuild: workaround `rustdoc` doctests modifier bug

[Justin Forbes]

On Mon, Nov 3, 2025 at 3:28 AM Alice Ryhl <aliceryhl@google.com> wrote:
>
> On Sun, Nov 02, 2025 at 10:28:53PM +0100, Miguel Ojeda wrote:
> > The `rustdoc` modifiers bug [1] was fixed in Rust 1.90.0 [2], for which
> > we added a workaround in commit abbf9a449441 ("rust: workaround `rustdoc`
> > target modifiers bug").
> >
> > However, `rustdoc`'s doctest generation still has a similar issue [3],
> > being fixed at [4], which does not affect us because we apply the
> > workaround to both, and now, starting with Rust 1.91.0 (released
> > 2025-10-30), `-Zsanitizer` is a target modifier too [5], which means we
> > fail with:
> >
> >       RUSTDOC TK rust/kernel/lib.rs
> >     error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `kernel`
> >      --> rust/kernel/lib.rs:3:1
> >       |
> >     3 | //! The `kernel` crate.
> >       | ^
> >       |
> >       = 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
> >
> > A simple way around is to add the sanitizer to the list in the existing
> > workaround (especially if we had not started to pass the sanitizer
> > flags in the previous commit, since in that case that would not be
> > necessary). However, that still applies the workaround in more cases
> > than necessary.
> >
> > Instead, only modify the doctests flags to ignore the check for
> > sanitizers, so that it is more local (and thus the compiler keeps checking
> > it for us in the normal `rustdoc` calls). Since the previous commit
> > already treated the `rustdoc` calls as kernel objects, this should allow
> > us in the future to easily remove this workaround when the time comes.
> >
> > By the way, the `-Cunsafe-allow-abi-mismatch` flag overwrites previous
> > ones rather than appending, so it needs to be all done in the same flag.
> > Moreover, unknown modifiers are rejected, and thus we have to gate based
> > on the version too.
>
> Ah .. we may want to file a bug for that.
>
> > Finally, `-Zsanitizer-cfi-normalize-integers` is not affected, so it is
> > not needed in the workaround.
> >
> > 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/issues/144521 [1]
> > Link: https://github.com/rust-lang/rust/pull/144523 [2]
> > Link: https://github.com/rust-lang/rust/issues/146465 [3]
> > Link: https://github.com/rust-lang/rust/pull/148068 [4]
> > Link: https://github.com/rust-lang/rust/pull/138736 [5]
> > 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>

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

[Alice Ryhl]

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>

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

[Justin Forbes]

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>

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

[Miguel Ojeda]

On Sun, Nov 2, 2025 at 10:30 PM Miguel Ojeda <ojeda@kernel.org> 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>

Applied series to `rust-fixes` -- thanks everyone!

I will send another less urgent one for 1.92.0 (in beta now) that goes
on top of these here.

Cheers,
Miguel