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Fri, 18 Oct 2019 02:43:19 -0700 (PDT) Date: Fri, 18 Oct 2019 11:42:40 +0200 In-Reply-To: <20191018094304.37056-1-glider@google.com> Message-Id: <20191018094304.37056-3-glider@google.com> Mime-Version: 1.0 References: <20191018094304.37056-1-glider@google.com> X-Mailer: git-send-email 2.23.0.866.gb869b98d4c-goog Subject: [PATCH RFC v1 02/26] stackdepot: prevent Clang from optimizing away stackdepot_memcmp() From: glider@google.com To: Alexander Potapenko Cc: Vegard Nossum , Dmitry Vyukov , linux-mm@kvack.org 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; }