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Wed, 30 Oct 2019 07:22:48 -0700 (PDT) Date: Wed, 30 Oct 2019 15:22:14 +0100 In-Reply-To: <20191030142237.249532-1-glider@google.com> Message-Id: <20191030142237.249532-3-glider@google.com> Mime-Version: 1.0 References: <20191030142237.249532-1-glider@google.com> X-Mailer: git-send-email 2.24.0.rc0.303.g954a862665-goog Subject: [PATCH RFC v2 02/25] stackdepot: prevent Clang from optimizing away stackdepot_memcmp() From: glider@google.com To: Vegard Nossum , Dmitry Vyukov , linux-mm@kvack.org Cc: viro@zeniv.linux.org.uk, akpm@linux-foundation.org, aryabinin@virtuozzo.com, luto@kernel.org, ard.biesheuvel@linaro.org, arnd@arndb.de, hch@lst.de, dmitry.torokhov@gmail.com, edumazet@google.com, ericvh@gmail.com, gregkh@linuxfoundation.org, harry.wentland@amd.com, herbert@gondor.apana.org.au, mingo@elte.hu, axboe@kernel.dk, martin.petersen@oracle.com, schwidefsky@de.ibm.com, mst@redhat.com, monstr@monstr.eu, pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org, tiwai@suse.com, tytso@mit.edu, tglx@linutronix.de, wsa@the-dreams.de, gor@linux.ibm.com, iii@linux.ibm.com, mark.rutland@arm.com, willy@infradead.org, rdunlap@infradead.org, andreyknvl@google.com, elver@google.com, Alexander Potapenko Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Clang may replace stackdepot_memcmp() with a call to instrumented bcmp(), which is exactly what we wanted to avoid creating stackdepot_memcmp(). Add a compiler barrier() to prevent optimizations. Signed-off-by: Alexander Potapenko To: Alexander Potapenko Cc: Vegard Nossum Cc: Dmitry Vyukov Cc: linux-mm@kvack.org --- Change-Id: I4495b617b15c0ab003a61c1f0d54d0026fa8b144 --- lib/stackdepot.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 0d00d2ac0c4b..785839298e08 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -163,6 +163,11 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, unsigned int n) { for ( ; n-- ; u1++, u2++) { + /* + * Prevent Clang from replacing this function with a bcmp() + * call. + */ + barrier(); if (*u1 != *u2) return 1; } -- 2.24.0.rc0.303.g954a862665-goog