linux-kernel - Re: [PATCH v2 2/2] Documentation: dev-tools: Enhance static analysis section with discussion

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Date:   Fri, 1 Apr 2022 08:19:13 +0800
From:   David Gow <davidgow@...gle.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Marcelo Schmitt <marcelo.schmitt1@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Daniel Latypov <dlatypov@...gle.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-sparse@...r.kernel.org, cocci@...ia.fr,
        smatch@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>, julia.lawall@...ia.fr
Subject: Re: [PATCH v2 2/2] Documentation: dev-tools: Enhance static analysis
 section with discussion

On Thu, Mar 31, 2022 at 4:14 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> On Wed, Mar 30, 2022 at 10:48:13AM +0800, David Gow wrote:
> > > +
> > > +Smatch does flow analysis and, if allowed to build the function database, it
> > > +also does cross function analysis. Smatch tries to answer questions like where
> > > +is this buffer allocated? How big is it? Can this index be controlled by the
> > > +user? Is this variable larger than that variable?
> > > +
> > > +It's generally easier to write checks in Smatch than it is to write checks in
> > > +Sparse. Nevertheless, there are some overlaps between Sparse and Smatch checks
> > > +because there is no reason for re-implementing Sparse's check in Smatch.
> >
> > This last sentence isn't totally clear to me. Should this "because" be "so"?
> >
>
> I stopped reading your email when you wrote "Cheers, David" but I should
> have scrolled down.
>
> There is not very much overlap between Sparse and Smatch.  Both have a
> warning for if (!x & y).  That is a tiny thing.  The big overlap is when
> it comes to the locking checks.  The Smatch check for locking is
> honestly way better and more capable.
>
> I always run both Sparse and Smatch on my patches.  I should run
> Coccinelle as well, but I'm more familiar with Sparse and Smatch.

Makes sense. I agree that the overlap doesn't seem particularly
important: it's the differences which should be more evident.

v3[1] of the patch cuts this down to just "Nevertheless, there are
some overlaps between Sparse and Smatch checks.", which I think is an
improvement.

Thanks,
-- David

[1]: https://lore.kernel.org/all/62f461a20600b95e694016c4e5348ef2e260fa87.1648674305.git.marcelo.schmitt1@gmail.com/