linux-kernel - Re: [PATCH] kcov: improve documentation

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Date:   Tue, 28 Feb 2023 21:01:01 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     andrey.konovalov@...ux.dev, Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH] kcov: improve documentation

On Tue, Feb 28, 2023 at 10:37 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Mon, 27 Feb 2023 at 18:17, <andrey.konovalov@...ux.dev> wrote:
> >
> > From: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > Improve KCOV documentation:
> >
> > - Use KCOV instead of kcov, as the former is more widely-used.
> >
> > - Mention Clang in compiler requirements.
> >
> > - Use ``annotations`` for inline code.
> >
> > - Rework remote coverage collection documentation for better clarity.
> >
> > - Various smaller changes.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > ---
> >  Documentation/dev-tools/kcov.rst | 169 +++++++++++++++++++------------
> >  1 file changed, 102 insertions(+), 67 deletions(-)
> >
> > diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
> > index d83c9ab49427..a113a03a475f 100644
> > --- a/Documentation/dev-tools/kcov.rst
> > +++ b/Documentation/dev-tools/kcov.rst
> > @@ -1,42 +1,50 @@
> > -kcov: code coverage for fuzzing
> > +KCOV: code coverage for fuzzing
> >  ===============================
> >
> > -kcov exposes kernel code coverage information in a form suitable for coverage-
> > -guided fuzzing (randomized testing). Coverage data of a running kernel is
> > -exported via the "kcov" debugfs file. Coverage collection is enabled on a task
> > -basis, and thus it can capture precise coverage of a single system call.
> > +KCOV collects and exposes kernel code coverage information in a form suitable
> > +for coverage-guided fuzzing. Coverage data of a running kernel is exported via
> > +the ``kcov`` debugfs file. Coverage collection is enabled on a task basis, and
> > +thus KCOV can capture precise coverage of a single system call.
> >
> > -Note that kcov does not aim to collect as much coverage as possible. It aims
> > -to collect more or less stable coverage that is function of syscall inputs.
> > -To achieve this goal it does not collect coverage in soft/hard interrupts
> > -and instrumentation of some inherently non-deterministic parts of kernel is
> > -disabled (e.g. scheduler, locking).
> > +Note that KCOV does not aim to collect as much coverage as possible. It aims
> > +to collect more or less stable coverage that is a function of syscall inputs.
> > +To achieve this goal, it does not collect coverage in soft/hard interrupts
> > +(unless remove coverage collection is enabled, see below) and from some
> > +inherently non-deterministic parts of the kernel (e.g. scheduler, locking).
> >
> > -kcov is also able to collect comparison operands from the instrumented code
> > -(this feature currently requires that the kernel is compiled with clang).
> > +Besides collecting code coverage, KCOV can also collect comparison operands.
> > +See the "Comparison operands collection" section for details.
> > +
> > +Besides collecting coverage data from syscall handlers, KCOV can also collect
> > +coverage for annotated parts of the kernel executing in background kernel
> > +tasks or soft interrupts. See the "Remote coverage collection" section for
> > +details.
> >
> >  Prerequisites
> >  -------------
> >
> > -Configure the kernel with::
> > +KCOV relies on compiler instrumentation and requires GCC 6.1.0 or later
> > +or any Clang version supported by the kernel.
> >
> > -        CONFIG_KCOV=y
> > +Collecting comparison operands is only supported with Clang.
>
> Are you sure?
> I see -fsanitize-coverage=trace-cmp in gcc sources and man page.

Right, supported too starting with version 8.

Will fix in v2.

> Otherwise looks good to me.

I'll add your Reviewed-by to v2 then.

Thank you!