Patchwork [net-next] net-ipv6: Fix alleged compiler warning in ipv6_exthdrs_len()

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Submitter Jerry Chu
Date Dec. 15, 2013, 5:19 p.m.
Message ID <1387127947-2075-1-git-send-email-hkchu@google.com>
Download mbox | patch
Permalink /patch/301370/
State Not Applicable
Delegated to: David Miller
Headers show

Comments

Jerry Chu - Dec. 15, 2013, 5:19 p.m.
From: Jerry Chu <hkchu@google.com>

It was reported that Commit 299603e8370a93dd5d8e8d800f0dff1ce2c53d36
("net-gro: Prepare GRO stack for the upcoming tunneling support")
triggered a compiler warning in ipv6_exthdrs_len():

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-u
    opth = (void *)opth + optlen;
    			^
    net/ipv6/ip6_offload.c:164:22: note: ‘optlen’ was declared here
    int len = 0, proto, optlen;
                        ^
Note that there was no real bug here - optlen was never uninitialized
before use. (Was the version of gcc I used smarter to not complain?)

Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
---
 net/ipv6/ip6_offload.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)
David Miller - Dec. 16, 2013, 1:31 a.m.
From: "H.K. Jerry Chu" <hkchu@google.com>

Date: Sun, 15 Dec 2013 09:19:07 -0800

> From: Jerry Chu <hkchu@google.com>

> 

> It was reported that Commit 299603e8370a93dd5d8e8d800f0dff1ce2c53d36

> ("net-gro: Prepare GRO stack for the upcoming tunneling support")

> triggered a compiler warning in ipv6_exthdrs_len():

> 

> 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-u

>     opth = (void *)opth + optlen;

>     			^

>     net/ipv6/ip6_offload.c:164:22: note: ‘optlen’ was declared here

>     int len = 0, proto, optlen;

>                         ^

> Note that there was no real bug here - optlen was never uninitialized

> before use. (Was the version of gcc I used smarter to not complain?)

> 

> Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

> Signed-off-by: H.K. Jerry Chu <hkchu@google.com>


What is this patch against?

It gets rejects when I try to apply it both with Hannes's patch reverted
and without it reverted.
Jerry Chu - Dec. 16, 2013, 2:30 a.m.
On Mon, Dec 16, 2013 at 9:31 AM, David Miller <davem@davemloft.net> wrote:
> From: "H.K. Jerry Chu" <hkchu@google.com>
> Date: Sun, 15 Dec 2013 09:19:07 -0800
>
>> From: Jerry Chu <hkchu@google.com>
>>
>> It was reported that Commit 299603e8370a93dd5d8e8d800f0dff1ce2c53d36
>> ("net-gro: Prepare GRO stack for the upcoming tunneling support")
>> triggered a compiler warning in ipv6_exthdrs_len():
>>
>> 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-u
>>     opth = (void *)opth + optlen;
>>                       ^
>>     net/ipv6/ip6_offload.c:164:22: note: ‘optlen’ was declared here
>>     int len = 0, proto, optlen;
>>                         ^
>> Note that there was no real bug here - optlen was never uninitialized
>> before use. (Was the version of gcc I used smarter to not complain?)
>>
>> Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
>> Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
>
> What is this patch against?
>
> It gets rejects when I try to apply it both with Hannes's patch reverted
> and without it reverted.

It was against net-next of a few days old (and w/o Hannes's patch):

commit 68536053600425c24aba031c45f053d447eedd9c (netnext/master)
Author: Florent Fourcot <florent.fourcot@enst-bretagne.fr>
Date:   Thu Dec 12 17:07:58 2013 +0100

    ipv6: fix incorrect type in declaration

I just did a git pull and will submit one against the latest net-next.
(I did not see any conflict though. Not sure why you can't apply the patch.)

Jerry
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Patch

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index 7540a0e..6fb4162 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -160,8 +160,8 @@  out:
 static int ipv6_exthdrs_len(struct ipv6hdr *iph,
 			    const struct net_offload **opps)
 {
-	struct ipv6_opt_hdr *opth = NULL;
-	int len = 0, proto, optlen;
+	struct ipv6_opt_hdr *opth = (void *)iph;
+	int len = 0, proto, optlen = sizeof(*iph);
 
 	proto = iph->nexthdr;
 	for (;;) {
@@ -172,10 +172,7 @@  static int ipv6_exthdrs_len(struct ipv6hdr *iph,
 			if (!((*opps)->flags & INET6_PROTO_GSO_EXTHDR))
 				break;
 		}
-		if (opth == NULL)
-			opth = (void *)(iph+1);
-		else
-			opth = (void *)opth + optlen;
+		opth = (void *)opth + optlen;
 		optlen = ipv6_optlen(opth);
 		len += optlen;
 		proto = opth->nexthdr;