Re: [PATCH v2 4/4] x86: Ignore stack unwinding in KCOV

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Jun 11, 2024 at 09:50:33AM +0200, Dmitry Vyukov wrote:
> Stack unwinding produces large amounts of uninteresting coverage.
> It's called from KASAN kmalloc/kfree hooks, fault injection, etc.
> It's not particularly useful and is not a function of system call args.
> Ignore that code.

This stems from KCOV's purpose being guiding syzkaller as opposed to it
being a more general coverage tool, right?

Is that spelled out anywhere?

Anyway,

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Reviewed-by: Alexander Potapenko <glider@google.com>
> Reviewed-by: Marco Elver <elver@google.com>
> Cc: x86@kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: syzkaller@googlegroups.com
> ---
>  arch/x86/kernel/Makefile | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 20a0dd51700a..cd49ebfae984 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -39,6 +39,14 @@ KMSAN_SANITIZE_sev.o					:= n
>  # first second.
>  KCOV_INSTRUMENT_head$(BITS).o				:= n
>  KCOV_INSTRUMENT_sev.o					:= n
> +# These are called from save_stack_trace() on debug paths,
> +# and produce large amounts of uninteresting coverage.
> +KCOV_INSTRUMENT_stacktrace.o				:= n
> +KCOV_INSTRUMENT_dumpstack.o				:= n
> +KCOV_INSTRUMENT_dumpstack_$(BITS).o			:= n
> +KCOV_INSTRUMENT_unwind_orc.o				:= n
> +KCOV_INSTRUMENT_unwind_frame.o				:= n
> +KCOV_INSTRUMENT_unwind_guess.o				:= n
>  
>  CFLAGS_irq.o := -I $(src)/../include/asm/trace
>  
> -- 
> 2.45.2.505.gda0bf45e8d-goog
>