To: openib-general@openib.org
Cc: linux-kernel@vger.kernel.org
Subject: dealing with gcc 'comparison is always false' warnings (was: [PATCH] drivers/infiniband: fix comparsion between unsigned and negative)
References: <20070530080518.GA29195@nostromo.devel.redhat.com>
From: Roland Dreier <rdreier@cisco.com>
Date: Wed, 30 May 2007 08:30:00 -0700
In-Reply-To: <20070530080518.GA29195@nostromo.devel.redhat.com> (Bill Nottingham's message of "Wed, 30 May 2007 04:05:18 -0400")
Message-ID: <adazm3mqqh3.fsf@cisco.com>
User-Agent: Gnus/5.1007 (Gnus v5.10.7) XEmacs/21.4.19 (linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1064
Lines: 24

thanks... I'm wondering if there's a consensus among kernel hackers
about changes like:

 > -	if (hdr.cmd < 0 || hdr.cmd >= ARRAY_SIZE(ucma_cmd_table))
 > +	if (hdr.cmd >= ARRAY_SIZE(ucma_cmd_table))
 >  		return -EINVAL;

I understand that new gcc sees that hdr.cmd is unsigned and hence
can't be < 0, and generates a warning for that, and having a build
cluttered with warnings hides bugs and so on.  However the code here
looks quite sensible to me -- otherwise we end up with missing range
checking if hdr.cmd ever changes to a signed type.  This seems like a
good way to introduce bugs: delete valid range checking code to shut
up a silly gcc warning, and then change the type of a variable.

Can't we just make gcc shut up about the comparison and generate no
code for it because it knows it can't be true?

 - R.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/