linux-kernel - [PATCH] kasan/test: fix protection against compiler elision

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Message-Id: <20250728-kasan-kunit-fix-volatile-v1-1-e7157c9af82d@google.com>
Date: Mon, 28 Jul 2025 22:11:54 +0200
From: Jann Horn <jannh@...gle.com>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>, 
 Alexander Potapenko <glider@...gle.com>, 
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
 Vincenzo Frascino <vincenzo.frascino@....com>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 Nihar Chaithanya <niharchaithanya@...il.com>
Cc: kasan-dev@...glegroups.com, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, Jann Horn <jannh@...gle.com>
Subject: [PATCH] kasan/test: fix protection against compiler elision

The kunit test is using assignments to
"static volatile void *kasan_ptr_result" to prevent elision of memory
loads, but that's not working:
In this variable definition, the "volatile" applies to the "void", not to
the pointer.
To make "volatile" apply to the pointer as intended, it must follow
after the "*".

This makes the kasan_memchr test pass again on my system.
The kasan_strings test is still failing because all the definitions of
load_unaligned_zeropad() are lacking explicit instrumentation hooks and
ASAN does not instrument asm() memory operands.

Fixes: 5f1c8108e7ad ("mm:kasan: fix sparse warnings: Should it be static?")
Signed-off-by: Jann Horn <jannh@...gle.com>
---
 mm/kasan/kasan_test_c.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index 5f922dd38ffa..c9cdafdde132 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/mm/kasan/kasan_test_c.c
@@ -47,7 +47,7 @@ static struct {
  * Some tests use these global variables to store return values from function
  * calls that could otherwise be eliminated by the compiler as dead code.
  */
-static volatile void *kasan_ptr_result;
+static void *volatile kasan_ptr_result;
 static volatile int kasan_int_result;
 
 /* Probe for console output: obtains test_status lines of interest. */

---
base-commit: 01a412d06bc5786eb4e44a6c8f0f4659bd4c9864
change-id: 20250728-kasan-kunit-fix-volatile-d2b9f6bbadc7

-- 
Jann Horn <jannh@...gle.com>