From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <smatch-owner@vger.kernel.org>
Received: from movementarian.org ([178.79.150.28]:47168 "EHLO
        movementarian.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726098AbfKMRwe (ORCPT
        <rfc822;smatch@vger.kernel.org>); Wed, 13 Nov 2019 12:52:34 -0500
Date: Wed, 13 Nov 2019 17:52:33 +0000
From: John Levon <levon@movementarian.org>
Subject: Re: check_signed.c false negative
Message-ID: <20191113175233.GA11603@movementarian.org>
References: <20191111232115.GA19963@movementarian.org>
 <20191112055759.GA1959@kadam.lan>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191112055759.GA1959@kadam.lan>
Sender: smatch-owner@vger.kernel.org
List-ID: <smatch.vger.kernel.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: smatch@vger.kernel.org

On Wed, Nov 13, 2019 at 08:39:13PM +0300, Dan Carpenter wrote:

> On Mon, Nov 11, 2019 at 11:21:15PM +0000, John Levon wrote:
> > 
> > Given:
> > 
> > enum ib_qp_state {
> >         IB_QPS_RESET,
> >         IB_QPS_INIT,
> >         IB_QPS_RTR,
> >         IB_QPS_RTS,
> >         IB_QPS_SQD,
> >         IB_QPS_SQE,
> >         IB_QPS_ERR
> > };
> > 
> > int p(enum ib_qp_state cur_state, enum ib_qp_state next_state)
> > {
> > #if 0
> >        if (cur_state  < 0 || cur_state > IB_QPS_ERR ||
> >          next_state < 0 || next_state > IB_QPS_ERR) {
> >                 return (5);
> >         }
> > #else
> >        if (next_state < 0 || next_state > IB_QPS_ERR) {
> >                 return (5);
> >         }
> > #endif
> > 
> >         return (0);
> > }
> > 
> > current smatch is happy. But "#if 1" above instead, and:
> > 
> > jlevon@sent:~/src/smatch$ ./smatch a.c
> > ./smatch: a.c:15 p() warn: unsigned 'cur_state' is never less than zero.
> > 
> > Why is "next_state" not reported equally?
> 
> My plan was that neither one would print a warning.  When people do
> 
> 	if (foo < 0 || foo > max)
> 
> then normally it's not a real life bug...  Linus said at kernel summit
> that he doesn't like when people send patches for those.

Right, in fact the code this comes from is similar: it's a
belt-and-braces check that we didn't somehow get a bad state value.

There's definitely other cases where this might be useful, though I
wouldn't object to disabling it by default altogether.

thanks
john