Re: Using coccinelle for (quick?) syntax fixing

[Antti Kantee <pooka%cs.hut.fi@localhost>]

On Mon Aug 09 2010 at 18:19:28 +0200, Jean-Yves Migeon wrote:
> > That said, if $someone can produce a set of rules which showably find
> > bugs in NetBSD code and do not produce a lot of false positives, I'm
> > very interested in seeing nightly runs.
> 
> Alright, let's get a bit more practical. Warning: patch may not apply
> cleanly, and I am working with a "month-old" src:
> 
> - logical not with bitwise "&" (attached: notvsand.diff)
> 
> This one should be checked, I am not familiar with this code.

Those definitely look fishy.  I'm surprised gcc doesn't give a warning.

> - more serious: NULL check then dereference (attached: nullderef.diff)
> 
> IMHO, the last ones would be easier to spot with "if (foo == NULL)..."
> instead of having "if (!foo)..." Clarity does help (guess it did not for
> the other half, anyway :/ )

Well, at least the first one is under #ifdef __FreeBSD__, and would panic
anyway already in malloc ;)

But, sure, it's always useful to check error branches are not a highly
complex call to uvm_fault().

> > ... especially if there are no TAILQ false positives ;)
> 
> Only true negatives with that one :p
> 
> Purpose was to gather opinions (if it got wildly rejected, I would have
> stop doing anything with it now). Note that I view coccinelle more like a
> tool making rototilling easier than full blown static analyzer; there are
> probably better ones out there (clang).

IIRC, there were some private discussions earlier (year or so ago?) and it
was suggested that rototills should accompany a public spatch.  But given
that in practise applying the spatch is usually a combination of using
spatch, sed, etc., there would need to be accompanying documentation too.
Anyway, someone needs to work out the details and drive the issue.

I think your examples are useful to run every now and then in a static
analyzer capacity.  Just because there are "better" ones, doesn't mean
others are obsolete, especially if the results are different.