netdev - [PATCH net-next] ipv6: revert misguided compiler warning fix on ipv6_exthdrs

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Date:	Sun, 15 Dec 2013 18:18:06 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Jerry Chu <hkchu@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next] ipv6: revert misguided compiler warning fix on ipv6_exthdrs_len

This essentlally reverts commit f52d81dc27c3456c702e83183035142c222acdc7
("ipv6: fix compiler warning in ipv6_exthdrs_len") and silences the
warning with uninitialized_var.

Cc: Jerry Chu <hkchu@...gle.com>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
---

On Mon, Dec 16, 2013 at 12:20:22AM +0800, Jerry Chu wrote:
> On Sat, Dec 14, 2013 at 3:02 PM, David Miller <davem@...emloft.net> wrote:
> > From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> > Date: Sat, 14 Dec 2013 07:29:29 +0100
> >
> >> Commit 299603e8370a93dd5d8e8d800f0dff1ce2c53d36 ("net-gro: Prepare GRO
> >> stack for the upcoming tunneling support") used an uninitialized variable
> >> which leads to the following compiler warning:
> >>
> >> net/ipv6/ip6_offload.c: In function ‘ipv6_gro_complete’:
> >> net/ipv6/ip6_offload.c:178:24: warning: ‘optlen’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> >>     opth = (void *)opth + optlen;
> >>                         ^
> >> net/ipv6/ip6_offload.c:164:22: note: ‘optlen’ was declared here
> >>   int len = 0, proto, optlen;
> >>                       ^
> >> Fix it up.
> >>
> >> Cc: Jerry Chu <hkchu@...gle.com>
> >> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> >
> > Applied.
> 
> Please back out the above "fix" - it actually breaks the original code because
> the fix will cause exthdrs_len to be one optlen short.
>
> There was no bug in the original code, just the compiler warning (and I do not
> get any warning, although I admit I did not run with the -W flag).

Sorry, I see now, of course. Btw. I didn't use any special flags, just
a normal kernel build with gcc 4.8.2.

> In any case I will submit a revision shortly that will silent any
> warning if exists.

I hope you are ok with this.

Sorry,

  Hannes

 net/ipv6/ip6_offload.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index 08861f1..0a578fc 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -161,7 +161,7 @@ static int ipv6_exthdrs_len(struct ipv6hdr *iph,
 			    const struct net_offload **opps)
 {
 	struct ipv6_opt_hdr *opth = NULL;
-	int len = 0, optlen = 0, proto;
+	int len = 0, proto, uninitialized_var(optlen);
 
 	proto = iph->nexthdr;
 	for (;;) {
@@ -172,12 +172,11 @@ static int ipv6_exthdrs_len(struct ipv6hdr *iph,
 			if (!((*opps)->flags & INET6_PROTO_GSO_EXTHDR))
 				break;
 		}
-		if (opth == NULL) {
+		if (opth == NULL)
 			opth = (void *)(iph+1);
-		} else {
-			optlen = ipv6_optlen(opth);
+		else
 			opth = (void *)opth + optlen;
-		}
+		optlen = ipv6_optlen(opth);
 		len += optlen;
 		proto = opth->nexthdr;
 	}
-- 
1.8.3.1



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