linux-kernel - [PATCH v2 nolibc 01/15] tools/nolibc: tests: use volatile to force stack smashing

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Date:   Thu, 18 May 2023 07:55:07 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     gwml@...r.gnuweeb.org, kernel-team@...a.com, w@....eu,
        Thomas Weißschuh <linux@...ssschuh.net>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH v2 nolibc 01/15] tools/nolibc: tests: use volatile to force stack smashing

From: Thomas Weißschuh <linux@...ssschuh.net>

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

Reported-by: Alexey Dobriyan <adobriyan@...il.com>
Link: https://lore.kernel.org/lkml/c0584807-511c-4496-b062-1263ea38f349@p183/
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 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;
 }
-- 
2.40.1