From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julia Lawall Date: Tue, 29 Jan 2013 16:19:43 +0000 Subject: Re: coccinelle and bitmask arithmetic (was: Re: [patch] TTY: synclink, small cleanup in dtr_rts()) Message-Id: List-Id: References: <20130127194039.GA18787@elgon.mountain> <1359317078.14406.12.camel@joe-AO722> <20130127201947.GO16282@mwanda> <9561.1359474916@turing-police.cc.vt.edu> <1359475998.4196.26.camel@joe-AO722> In-Reply-To: <1359475998.4196.26.camel@joe-AO722> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: cocci@systeme.lip6.fr On Tue, 29 Jan 2013, Joe Perches wrote: > 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. If the definition of a bitmask is an identifier in all capital letters, that would be easy. Another possibility is such an identifier that is defined to a value expressed beginning with 0x. Another possibility is such an identifier that is sometimes used with & and | and sometimes used with an arithmetic operation. I will give them a try. julia