Re: [PATCH v3] selftests: harness: Mark test fixture objects __maybe_unused

[Nathan Chancellor <nathan@kernel.org>]

On Mon, Jul 06, 2026 at 06:31:54PM +0000, David Matlack wrote:
> Mark _##fixture_name##_##test_name##_object __maybe_unused since it may
> not ever be read. This pointer is only read in XFAIL_ADD(), which tests
> are not required to use.
> 
> 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>
> Reviewed-by: Alex Williamson <alex@shazbot.org>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>

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

> ---
> v3:
>  - Pick up Kuniyuki's Reviewed-by tag.
>  - Pick up Alex's Reviewed-by tag from v1.
>  - Fix commit description accuracy (Kuniyuki)
> 
> v2: https://lore.kernel.org/linux-kselftest/20260706175228.2468730-1-dmatlack@google.com/
> 
> 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
> 

-- 
Cheers,
Nathan