linux-kernel - Re: [PATCH] mpparse.c:231: warning: comparison is always false

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Message-Id: <20060915012302.d459c2dc.akpm@osdl.org>
Date:	Fri, 15 Sep 2006 01:23:02 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Jarek Poplawski <jarkao2@...pl>
Cc:	Andi Kleen <ak@....de>, Dave Jones <davej@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mpparse.c:231: warning: comparison is always false

On Fri, 15 Sep 2006 10:11:23 +0200
Jarek Poplawski <jarkao2@...pl> wrote:

> On Thu, Sep 14, 2006 at 06:17:54PM -0700, Andrew Morton wrote:
> > On Wed, 13 Sep 2006 08:50:10 +0200
> > Jarek Poplawski <jarkao2@...pl> wrote:
> > 
> > > Hello,
> > > 
> > > Probably after 2.6.18-rc6-git1 there is this cc warning: 
> > > "arch/i386/kernel/mpparse.c:231: warning: comparison is
> > > always false due to limited range of data type".
> > > Maybe this patch will be helpful.
> > > 
> > 
> > Thanks.   Andi has already queued a similar patch.
> > 
> > Andi, you might as well scoot that upstream, otherwise we'll get lots of
> > emails about it.
> ...
> > > +#if 0xFF >= MAX_MP_BUSSES
> > >  	if (m->mpc_busid >= MAX_MP_BUSSES) {
> 
> As a matter of fact today I think my patch is wrong.

No, I think it's OK.  Well, you had an off-by-one...

> I don't know how Andi has fixed it,

Same thing.  (He has `#if MAX_MP_BUSSES < 256').

> but after rethinking
> the question of Dave Jones I see it's fixing the result
> instead of the source of a problem (char or not char).

The mpc_busid field is set to eight-bits by BIOS; there's nothing we can do
about that...

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