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 <glider@xxxxxxxxxx>
To: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
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))
return 1;
}
return 0;
--
2.24.0.432.g9d3f5f5b63-goog
