From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Perches Date: Tue, 29 Jan 2013 16:13:18 +0000 Subject: coccinelle and bitmask arithmetic (was: Re: [patch] TTY: synclink, small cleanup in dtr_rts()) Message-Id: <1359475998.4196.26.camel@joe-AO722> List-Id: References: <20130127194039.GA18787@elgon.mountain> <1359317078.14406.12.camel@joe-AO722> <20130127201947.GO16282@mwanda> <9561.1359474916@turing-police.cc.vt.edu> In-Reply-To: <9561.1359474916@turing-police.cc.vt.edu> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: cocci@systeme.lip6.fr 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.