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Wed, 27 Nov 2019 06:22:56 -0800 (PST) MIME-Version: 1.0 References: <20191122112621.204798-1-glider@google.com> <20191122112621.204798-3-glider@google.com> In-Reply-To: <20191122112621.204798-3-glider@google.com> From: Marco Elver Date: Wed, 27 Nov 2019 15:22:44 +0100 Message-ID: Subject: Re: [PATCH RFC v3 02/36] stackdepot: build with -fno-builtin To: Alexander Potapenko Cc: Vegard Nossum , Dmitry Vyukov , Sergey Senozhatsky , Arnd Bergmann , Andrey Ryabinin , Linux Memory Management List , Al Viro , adilger.kernel@dilger.ca, Andrew Morton , Andrey Konovalov , Andy Lutomirski , Ard Biesheuvel , hch@infradead.org, hch@lst.de, darrick.wong@oracle.com, davem@davemloft.net, dmitry.torokhov@gmail.com, ebiggers@google.com, Eric Dumazet , ericvh@gmail.com, gregkh@linuxfoundation.org, harry.wentland@amd.com, herbert@gondor.apana.org.au, iii@linux.ibm.com, mingo@elte.hu, jasowang@redhat.com, axboe@kernel.dk, m.szyprowski@samsung.com, Mark Rutland , martin.petersen@oracle.com, schwidefsky@de.ibm.com, Matthew Wilcox , mst@redhat.com, monstr@monstr.eu, pmladek@suse.com, Qian Cai , Randy Dunlap , robin.murphy@arm.com, Steven Rostedt , tiwai@suse.com, tytso@mit.edu, Thomas Gleixner , gor@linux.ibm.com, wsa@the-dreams.de 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: On Fri, 22 Nov 2019 at 12:26, wrote: > > Clang may replace stackdepot_memcmp() with a call to instrumented bcmp(), > which is exactly what we wanted to avoid creating stackdepot_memcmp(). > Building the file with -fno-builtin prevents such optimizations. > > Signed-off-by: Alexander Potapenko > To: Alexander Potapenko > Cc: Vegard Nossum > Cc: Dmitry Vyukov > Cc: Sergey Senozhatsky > Cc: Arnd Bergmann > Cc: Andrey Ryabinin > Cc: linux-mm@kvack.org > --- > This patch was previously called "stackdepot: prevent Clang from optimizing > away stackdepot_memcmp()". > > v3: > - use -fno-builtin instead of a barrier > > Change-Id: I4495b617b15c0ab003a61c1f0d54d0026fa8b144 > --- > lib/Makefile | 4 ++++ > lib/stackdepot.c | 2 +- > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/lib/Makefile b/lib/Makefile > index c5892807e06f..58a3e1b1a868 100644 > --- a/lib/Makefile > +++ b/lib/Makefile > @@ -215,6 +215,10 @@ obj-$(CONFIG_SG_POOL) += sg_pool.o > obj-$(CONFIG_STMP_DEVICE) += stmp_device.o > obj-$(CONFIG_IRQ_POLL) += irq_poll.o > > +# stackdepot.c should not be instrumented or call instrumented functions. > +# Prevent the compiler from calling builtins like memcmp() or bcmp() from this > +# file. > +CFLAGS_stackdepot.o += -fno-builtin > obj-$(CONFIG_STACKDEPOT) += stackdepot.o > KASAN_SANITIZE_stackdepot.o := n > KCOV_INSTRUMENT_stackdepot.o := n > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index 0bc6182bc7a6..6d1123123e56 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -163,7 +163,7 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, > unsigned int n) > { > for ( ; n-- ; u1++, u2++) { > - if (*u1 != *u2) > + if ((*u1) != (*u2)) Why this change? Can stackdepot.c be reverted? > return 1; > } > return 0; > -- > 2.24.0.432.g9d3f5f5b63-goog >