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Date:   Thu, 18 Jun 2020 11:31:18 +0200
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Subject: [PATCH 3/3] kcsan: Disable branch tracing in core runtime
From:   Marco Elver <elver@google.com>
To:     elver@google.com, paulmck@kernel.org
Cc:     will@kernel.org, peterz@infradead.org, bp@alien8.de,
        tglx@linutronix.de, mingo@kernel.org, dvyukov@google.com,
        cai@lca.pw, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org
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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@mail.gmail.com/

Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index fea064afc4f7..65ca5539c470 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
-- 
2.27.0.290.gba653c62da-goog