[PATCH] kcov: disable tracing and branch profiling in kcov

[PATCH] kcov: disable tracing and branch profiling in kcov

[Andrey Ryabinin]

Tracing of __sanitizer_cov_trace_pc() causes unbound recursion and crash,
because __sanitizer_cov_trace_pc() is also called from tracer code.
For the same reason we need to disable profiling of 'if' branches.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 kernel/kcov.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 3efbee0..7919253 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -1,5 +1,6 @@
 #define pr_fmt(fmt) "kcov: " fmt
 
+#define DISABLE_BRANCH_PROFILING
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/file.h>
@@ -43,7 +44,7 @@ struct kcov {
  * Entry point from instrumented code.
  * This is called once per basic-block/edge.
  */
-void __sanitizer_cov_trace_pc(void)
+notrace void __sanitizer_cov_trace_pc(void)
 {
 	struct task_struct *t;
 	enum kcov_mode mode;
-- 
2.7.3

Re: [PATCH] kcov: disable tracing and branch profiling in kcov

[Dmitry Vyukov]

On Thu, Apr 21, 2016 at 12:32 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
> Tracing of __sanitizer_cov_trace_pc() causes unbound recursion and crash,
> because __sanitizer_cov_trace_pc() is also called from tracer code.
> For the same reason we need to disable profiling of 'if' branches.
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
>  kernel/kcov.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 3efbee0..7919253 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -1,5 +1,6 @@
>  #define pr_fmt(fmt) "kcov: " fmt
>
> +#define DISABLE_BRANCH_PROFILING
>  #include <linux/compiler.h>
>  #include <linux/types.h>
>  #include <linux/file.h>
> @@ -43,7 +44,7 @@ struct kcov {
>   * Entry point from instrumented code.
>   * This is called once per basic-block/edge.
>   */
> -void __sanitizer_cov_trace_pc(void)
> +notrace void __sanitizer_cov_trace_pc(void)
>  {
>         struct task_struct *t;
>         enum kcov_mode mode;
> --
> 2.7.3


There was a similar patch "kcov: Don't trace the code coverage code"
recently. But it did not add DISABLE_BRANCH_PROFILING.

[PATCH v2] kcov: don't profile branches in kcov

[Andrey Ryabinin]

Profiling 'if' statements in __sanitizer_cov_trace_pc() leads to
unbound recursion and crash:
	__sanitizer_cov_trace_pc() ->
		ftrace_likely_update ->
			__sanitizer_cov_trace_pc() ...

Define DISABLE_BRANCH_PROFILING to disable this tracer.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 kernel/kcov.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 3efbee0..aee961f 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -1,5 +1,6 @@
 #define pr_fmt(fmt) "kcov: " fmt
 
+#define DISABLE_BRANCH_PROFILING
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/file.h>
-- 
2.7.3