linux-kernel - [PATCH] kcov: Don't trace the code coverage code

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Message-Id: <1460564557-2817-1-git-send-email-james.morse@arm.com>
Date:	Wed, 13 Apr 2016 17:22:37 +0100
From:	James Morse <james.morse@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Potapenko <glider@...gle.com>,
	James Morse <james.morse@....com>
Subject: [PATCH] kcov: Don't trace the code coverage code

Kcov causes the compiler to add a call to __sanitizer_cov_trace_pc() in
every basic block. Ftrace patches in a call to _mcount() to each function
it has annotated.

Letting these mechanisms annotate each other is a bad thing. Break the
loop by adding 'notrace' to __sanitizer_cov_trace_pc() so that ftrace
won't try to patch this code.

Signed-off-by: James Morse <james.morse@....com>
---
This patch lets arm64 with KCOV and STACK_TRACER boot.

 kernel/kcov.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 3efbee0834a8..78bed7125515 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -43,7 +43,7 @@ struct kcov {
  * Entry point from instrumented code.
  * This is called once per basic-block/edge.
  */
-void __sanitizer_cov_trace_pc(void)
+void notrace __sanitizer_cov_trace_pc(void)
 {
 	struct task_struct *t;
 	enum kcov_mode mode;
-- 
2.8.0.rc3