netdev - Re: [PATCH] netfilter: conntrack: remove uninitialized shadow variable

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Date:	Mon, 09 May 2016 22:12:31 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>,
	Florian Westphal <fw@...len.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Sasha Levin <sasha.levin@...cle.com>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfilter: conntrack: remove uninitialized shadow variable

On Monday 09 May 2016 22:01:17 Pablo Neira Ayuso wrote:
> On Mon, May 09, 2016 at 09:47:23PM +0200, Arnd Bergmann wrote:
> > A recent commit introduced an unconditional use of an uninitialized
> > variable, as reported in this gcc warning:
> > 
> > net/netfilter/nf_conntrack_core.c: In function '__nf_conntrack_confirm':
> > net/netfilter/nf_conntrack_core.c:632:33: error: 'ctinfo' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >    bytes = atomic64_read(&counter[CTINFO2DIR(ctinfo)].bytes);
> >                                  ^
> > net/netfilter/nf_conntrack_core.c:628:26: note: 'ctinfo' was declared here
> >    enum ip_conntrack_info ctinfo;
> > 
> > The problem is that a local variable shadows the function parameter.
> > This removes the local variable, which looks like what Pablo originally
> > intended.
> 
> Acked-by: Pablo Neira Ayuso <pablo@...filter.org>
> 
> Sorry for this, I wonder why gcc didn't catch up this here.
> 
> @David, you can integrate this into your net-next tree.
> 
> Thanks for fixing up this Arnd.

By default, an allmodconfig build will hide these warnings because of
excessive false positives from CONFIG_CC_OPTIMIZE_FOR_SIZE. I've
tried twice to get a patch merged that disables CONFIG_CC_OPTIMIZE_FOR_SIZE
in allmodconfig so we get better warnings, but that patch unfortunately
got ignored.

	Arnd