selftests/harness: Handle TEST_F()'s explicit exit codes

If TEST_F() explicitly calls exit(code) with code different than 0, then
_metadata->exit_code is set to this code (e.g. KVM_ONE_VCPU_TEST()).  We
need to keep in mind that _metadata->exit_code can be KSFT_SKIP while
the process exit code is 0.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Reported-by: Sean Christopherson <seanjc@google.com>
Tested-by: Sean Christopherson <seanjc@google.com>
Closes: https://lore.kernel.org/r/ZjPelW6-AbtYvslu@google.com
Fixes: 0710a1a ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Link: https://lore.kernel.org/r/20240511171445.904356-11-mic@digikod.net
Signed-off-by: Mickaël Salaün <mic@digikod.net>

tools/testing/selftests/kselftest_harness.h

@@ -462,9 +462,13 @@ static inline pid_t clone3_vfork(void)
 		munmap(teardown, sizeof(*teardown)); \
 		if (self && fixture_name##_teardown_parent) \
 			munmap(self, sizeof(*self)); \
-		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
+		if (WIFEXITED(status)) { \
+			if (WEXITSTATUS(status)) \
+				_metadata->exit_code = WEXITSTATUS(status); \
+		} else if (WIFSIGNALED(status)) { \
 			/* Forward signal to __wait_for_test(). */ \
 			kill(getpid(), WTERMSIG(status)); \
+		} \
 		__test_check_assert(_metadata); \
 	} \
 	static struct __test_metadata *_##fixture_name##_##test_name##_object; \