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

Joe Perches
2013-01-29T16:13:23Z

On Tue, 2013-01-29 at 10:55 -0500, Valdis.Kletnieks@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.