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From:   =?utf-8?q?Thomas_Wei=C3=9Fschuh?= <linux@weissschuh.net>
Date:   Tue, 28 Mar 2023 14:50:35 +0000
Subject: [PATCH] tools/nolibc: tests: use volatile to force stack smashing
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Message-Id: <20230328-nolibc-smash-stack-volatile-v1-1-2b4aa7563a77@weissschuh.net>
To:     Willy Tarreau <w@1wt.eu>, Shuah Khan <shuah@kernel.org>
Cc:     linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        =?utf-8?q?Thomas_Wei=C3=9Fschuh?= <linux@weissschuh.net>
Precedence: bulk

Use a volatile pointer to write outside the buffer so the compiler can't
optimize it away.

Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Link: https://lore.kernel.org/lkml/c0584807-511c-4496-b062-1263ea38f349@p183/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---

This is based on the "dev" branch of the rcu tree.
---
 tools/testing/selftests/nolibc/nolibc-test.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 21bacc928bf7..47013b78972e 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -667,17 +667,13 @@ int run_stdlib(int min, int max)
 	return ret;
 }
 
-#if defined(__clang__)
-__attribute__((optnone))
-#elif defined(__GNUC__)
-__attribute__((optimize("O0")))
-#endif
 static int smash_stack(void)
 {
 	char buf[100];
+	volatile char *ptr = buf;
 
 	for (size_t i = 0; i < 200; i++)
-		buf[i] = 'P';
+		ptr[i] = 'P';
 
 	return 1;
 }

---
base-commit: 6e7cac3d5b8c77ddedfaa7efad23aa542cde53b2
change-id: 20230328-nolibc-smash-stack-volatile-0e87e9273fea

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>