linux-kernel - Re: [PATCH 1/2] drivers/telephony/ixj.c::add_caps(): don't rely on undefined behaviour

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Date:	Tue, 20 Mar 2012 00:40:50 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Joe Perches <joe@...ches.com>
cc:	linux-kernel@...r.kernel.org,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Ed Okerson <eokerson@...cknet.net>,
	Greg Herlein <gherlein@...cknet.net>,
	"David W. Erhart" <derhart@...cknet.net>,
	John Sellers <jsellers@...cknet.net>,
	Mike Preston <mpreston@...cknet.net>,
	David Huggins-Daines <dhd@...stral.com>,
	Fabio Ferrari <fabio.ferrari@...itro.com.br>,
	Artis Kugevics <artis@...lv>,
	Daniele Bellucci <bellucda@...cali.it>
Subject: Re: [PATCH 1/2] drivers/telephony/ixj.c::add_caps(): don't rely on
 undefined behaviour

On Mon, 19 Mar 2012, Joe Perches wrote:

> On Tue, 2012-03-20 at 00:19 +0100, Jesper Juhl wrote:
> > On Mon, 19 Mar 2012, Joe Perches wrote:
> > > On Mon, 2012-03-19 at 23:46 +0100, Jesper Juhl wrote:
> > > > On Mon, 19 Mar 2012, Joe Perches wrote:
> > > > > On Mon, 2012-03-19 at 23:37 +0100, Jesper Juhl wrote:
> > > > > > In drivers/telephony/ixj.c::add_caps() we have several statements like this:
> > > > > >   	j->caplist[j->caps].handle = j->caps++;
> > > > > > That's undefined behaviour right there.
> > > > > telephony has been moved to staging.
> > > > Since when? Where?
> > > > In my up-to-date Linus tree with HEAD at 
> > > > c16fa4f2ad19908a47c63d8fa436a1178438c7e7, that file is is still in 
> > > > drivers/telephony/, not in staging/...
> > > > /confused
> > > In the -next tree.
> > Ok, seems I've missed that.
> > > Yes, it's a bug fix, but drivers/telephony is pretty dead.
> > Dead or not, as long as it's in the tree I think that fixing bugs is 
> > relevant.
> > Besides, who knows if/when it'll get ressurrected ;)
> 
> Sorry, I didn't mean to suggest it shouldn't
> be fixed.
> 
> I meant that it probably didn't need to be
> fixed during the merge window or maybe even
> not backported to stable unless you're sure
> the order of operations is now done correctly
> and with no real change in current operation
> by inspecting the object.  I presume it worked
> before but it's likely not too many people
> actually still use this hardware with the
> current kernel.
> 
I never intended to push it for -stable, it probably "works" in its 
current form with any relevant compiler. I just spotted a bug and wanted 
to fix it :-)
If it gets fixed during the merge window or at some other time I don't 
really care - but I don't see any reason to not just fix it as soon as 
possible.

I have no idea how many people still use this hardware with current 
kernels, but even if just a few do, they deserve to get code that has 
well-defined behaviour with standards conforming C compilers and not what 
is currently there that can change with different compilers/different 
compiler versions.

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
Don't top-post http://www.catb.org/jargon/html/T/top-post.html
Plain text mails only, please.

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