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

[David Matlack <dmatlack@google.com>]

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