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

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Message-ID: <CA+fCnZckGWuo=wViH8xfwXKjq9WH7URZqhxh-7bdHFTr67r8fQ@mail.gmail.com>
Date: Fri, 14 Jun 2024 00:51:18 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org, 
	syzkaller@...glegroups.com, elver@...gle.com, glider@...gle.com, 
	nogikh@...gle.com, tarasmadan@...gle.com
Subject: Re: [PATCH v2 4/4] x86: Ignore stack unwinding in KCOV

On Tue, Jun 11, 2024 at 9:50 AM 'Dmitry Vyukov' via syzkaller
<syzkaller@...glegroups.com> 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.
>
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> Reviewed-by: Alexander Potapenko <glider@...gle.com>
> Reviewed-by: Marco Elver <elver@...gle.com>
> Cc: x86@...nel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: syzkaller@...glegroups.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
>
> --

Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>