[Cocci] coccinelle and bitmask arithmetic (was: Re: [patch] TTY: synclink, small cleanup in dtr_rts())

[joe@perches.com (Joe Perches)]

On Tue, 2013-01-29 at 10:55 -0500, Valdis.Kletnieks at vt.edu wrote:
> On Sun, 27 Jan 2013 23:19:47 +0300, Dan Carpenter said:
> 
> > Yeah.  I think it would be, but adding bitflags together instead of
> > doing bitwise ORs is very common as well.
> 
> The fact it's common doesn't mean it's good programming practice,
> or even correct.  Consider:
> 
> #define F_FOO 0x01
> #define F_BAR 0x02
> #define F_BAZ 0x04
> 
> unsigned int flags = F_FOO;
> ...
>       flags |= F_BAR;
> 
> Now some time later, another code path does this:
> 
>       flags += F_FOO;
> 
> If it was another |, it would be a no harm no foul class of bug.
> But how long is it going to take you to figure out who set F_BAZ?
> 
> I wonder if there's a way to write a coccinelle patch to find places
> where we do arithmetic operations on bitmasks....

Not so far as I know, but maybe someone on the
cocci lists does. (cc'd)

I could imagine a test for variables that have
uses of both arithmetic and bit operations but
not a discriminator for when one type is
appropriate and the other is not.