kunit/fortify: Add back "volatile" for sizeof() constants

It seems the Clang can see through OPTIMIZER_HIDE_VAR when the constant
is coming from sizeof. Adding "volatile" back to these variables solves
this false positive without reintroducing the issues that originally led
to switching to OPTIMIZER_HIDE_VAR in the first place[1].

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/2075 [1]
Cc: Jannik Glückert <jannik.glueckert@gmail.com>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Fixes: 6ee149f61bcc ("kunit/fortify: Replace "volatile" with OPTIMIZER_HIDE_VAR()")
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250628234034.work.800-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

diff --git a/lib/tests/fortify_kunit.c b/lib/tests/fortify_kunit.c
index 29ffc62a71e3f9684ed9ed54b8072e2a9c7aaf96..fc9c76f026d636e4e3a74292be40988df38dec44 100644 (file)
--- a/lib/tests/fortify_kunit.c
+++ b/lib/tests/fortify_kunit.c
@@ -1003,8 +1003,8 @@ static void fortify_test_memcmp(struct kunit *test)
 {
        char one[] = "My mind is going ...";
        char two[] = "My mind is going ... I can feel it.";
-       size_t one_len = sizeof(one) - 1;
-       size_t two_len = sizeof(two) - 1;
+       volatile size_t one_len = sizeof(one) - 1;
+       volatile size_t two_len = sizeof(two) - 1;
 
        OPTIMIZER_HIDE_VAR(one_len);
        OPTIMIZER_HIDE_VAR(two_len);