[PATCH kcsan 3/3] kcsan: Disable branch tracing in core runtime

[paulmck]

From: Marco Elver <elver@xxxxxxxxxx>

Disable branch tracing in core KCSAN runtime if branches are being
traced (TRACE_BRANCH_PROFILING). This it to avoid its performance
impact, but also avoid recursion in case KCSAN is enabled for the branch
tracing runtime.

The latter had already been a problem for KASAN:
https://lore.kernel.org/lkml/CANpmjNOeXmD5E3O50Z3MjkiuCYaYOPyi+1rq=GZvEKwBvLR0Ug@xxxxxxxxxxxxxx/

Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/kcsan/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index fea064a..65ca553 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -8,7 +8,7 @@ CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
 CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
-	-fno-stack-protector
+	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 obj-y := core.o debugfs.o report.o
 obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o
-- 
2.9.5