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

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

[David Matlack]

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>
---
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

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

[Nathan Chancellor]

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

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

[David Matlack]

On Mon, Jul 6, 2026 at 11:32 AM David Matlack <dmatlack@google.com> 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>

Kees and Shuah, is it ok if Alex takes this through the VFIO tree? [1]
This fixes a bug exposed by recent VFIO selftests commit ff556bd98348
("vfio: selftests: Add -Wall and -Werror to the Makefile").

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

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

[Kees Cook]

On Tue, Jul 14, 2026 at 09:24:36AM -0700, David Matlack wrote:
> On Mon, Jul 6, 2026 at 11:32 AM David Matlack <dmatlack@google.com> 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>
> 
> Kees and Shuah, is it ok if Alex takes this through the VFIO tree? [1]
> This fixes a bug exposed by recent VFIO selftests commit ff556bd98348
> ("vfio: selftests: Add -Wall and -Werror to the Makefile").
> 
> [1] https://lore.kernel.org/linux-kselftest/20260630165244.0d013bbc@shazbot.org/

Yeah, please do. This has ample review. :)

-- 
Kees Cook