[PATCH v2] selftests: harness: Mark test fixture objects __maybe_unused

[PATCH v2] selftests: harness: Mark test fixture objects __maybe_unused

[David Matlack]

Mark global test fixture object pointers __maybe_unused since they may
not ever be read (e.g. if fixture variants are used instead).

clang made a change to -Wunused-but-set-variable (split out into its own
subwarning, -Wunused-but-set-global) that causes this warning to be
emitted for various selftests and can be upgraded to an error in
selftest that set -Werror.

VFIO selftests have been broken since commit ff556bd98348 ("vfio:
selftests: Add -Wall and -Werror to the Makefile"), and the net
selftests builds have been noisy due to -Wall.

Fixes: 24cf65a62266 ("selftests/harness: Share _metadata between forked processes")
Reported-by: Kuniyuki Iwashima <kuniyu@google.com>
Reported-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
v2:
 - Update commit message about the change to clang (Nathan)
 - Correct the Fixes: tag (Nathan)

v1: https://lore.kernel.org/linux-kselftest/20260630213341.1664345-1-dmatlack@google.com/

Note: The fixes tag is commit 24cf65a62266 ("selftests/harness: Share
_metadata between forked processes"), which refactored TEST_F to share
test metadata across processes using mmap and convereted the test
fixture object from a static struct to a static pointer. Prior to commit
24cf65a62266 the static struct was always used once (the address of it
was taken and passed to __register_test()), but after the static pointer
was always assigned but potentially never read.

Cc: Nathan Chancellor <nathan@kernel.org>

 tools/testing/selftests/kselftest_harness.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 261e4df94d9d..29a19bc87084 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -467,7 +467,7 @@ static inline void __kselftest_memset_safe(void *s, int c, size_t n)
 				!__atomic_test_and_set(_metadata->no_teardown, __ATOMIC_RELAXED)) \
 			fixture_name##_teardown(_metadata, self, variant); \
 	} \
-	static struct __test_metadata *_##fixture_name##_##test_name##_object; \
+	static struct __test_metadata *_##fixture_name##_##test_name##_object __maybe_unused; \
 	static void __attribute__((constructor(KSELFTEST_PRIO_TEST))) \
 			_register_##fixture_name##_##test_name(void) \
 	{ \

base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
-- 
2.55.0.rc2.803.g1fd1e6609c-goog

Re: [PATCH v2] selftests: harness: Mark test fixture objects __maybe_unused

[David Matlack]

On Mon, Jul 6, 2026 at 10:52 AM David Matlack <dmatlack@google.com> wrote:
>
> Mark global test fixture object pointers __maybe_unused since they may
> not ever be read (e.g. if fixture variants are used instead).
>
> clang made a change to -Wunused-but-set-variable (split out into its own
> subwarning, -Wunused-but-set-global) that causes this warning to be
> emitted for various selftests and can be upgraded to an error in
> selftest that set -Werror.
>
> VFIO selftests have been broken since commit ff556bd98348 ("vfio:
> selftests: Add -Wall and -Werror to the Makefile"), and the net
> selftests builds have been noisy due to -Wall.
>
> Fixes: 24cf65a62266 ("selftests/harness: Share _metadata between forked processes")
> Reported-by: Kuniyuki Iwashima <kuniyu@google.com>
> Reported-by: Aaron Lewis <aaronlewis@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>

Sorry I forgot to apply Alex's Reviewed-by tag from v1:

   https://lore.kernel.org/linux-kselftest/20260630165244.0d013bbc@shazbot.org/

Re: [PATCH v2] selftests: harness: Mark test fixture objects __maybe_unused

[Kuniyuki Iwashima]

On Mon, Jul 6, 2026 at 10:52 AM David Matlack <dmatlack@google.com> wrote:
>
> Mark global test fixture object pointers __maybe_unused since they may
> not ever be read (e.g. if fixture variants are used instead).

Not very accurate; using fixtures w/ XFAIL_ADD() does not trigger
the warning.

>
> clang made a change to -Wunused-but-set-variable (split out into its own
> subwarning, -Wunused-but-set-global) that causes this warning to be
> emitted for various selftests and can be upgraded to an error in
> selftest that set -Werror.
>
> VFIO selftests have been broken since commit ff556bd98348 ("vfio:
> selftests: Add -Wall and -Werror to the Makefile"), and the net
> selftests builds have been noisy due to -Wall.
>
> Fixes: 24cf65a62266 ("selftests/harness: Share _metadata between forked processes")
> Reported-by: Kuniyuki Iwashima <kuniyu@google.com>
> Reported-by: Aaron Lewis <aaronlewis@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>

Not sure why Shuah didn't pick my patch though :/
https://lore.kernel.org/all/20260530054722.271157-1-kuniyu@google.com/