From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Tom Herbert <tom@herbertland.com>,
David Miller <davem@davemloft.net>,
Netdev <netdev@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH net] net: Allow flow dissector to handle non 4-byte aligned headers
Date: Tue, 2 Feb 2016 13:35:09 -0500 [thread overview]
Message-ID: <20160202183509.GA26588@oracle.com> (raw)
In-Reply-To: <CAKgT0UfjLEBUeiV3WS2BC=yRkxi9JBF4mqJ=niXOUQnhkiMhvA@mail.gmail.com>
On (02/01/16 19:56), Alexander Duyck wrote:
> > @@ -394,7 +407,7 @@ ip_proto_again:
> > data, hlen, &_eth);
> > if (!eth)
> > goto out_bad;
> > - proto = eth->h_proto;
> > + proto = get_unaligned_be16(ð->h_proto);
> > nhoff += sizeof(*eth);
> > }
>
> This piece doesn't make any sense to me. It is already only 2 bytes
> wide. I'm not sure why we should be seeing this trigger an unaligned
> access. Are you sure it wasn't something like the keyid causing the
> issue? I'd be interested in seeing what the compiler did here that it
> is triggering the problem.
You're right- I was getting blinded by all the unaligned-access
messages swimming by and making a mistake. It was actually the
memcpy(&key_addrs->v4addrs, &iph->saddr,
sizeof(key_addrs->v4addrs));
The assembler code is this:
0x8d3298 <__skb_flow_dissect+500>: ld [ %l5 + 0xc ], %g3
0x8d329c <__skb_flow_dissect+504>: add %i2, %g1, %g2
0x8d32a0 <__skb_flow_dissect+508>: st %g3, [ %i2 + %g1 ]
0x8d32a4 <__skb_flow_dissect+512>: ld [ %l5 + 0x10 ], %g1
0x8d32a8 <__skb_flow_dissect+516>: st %g1, [ %g2 + 4 ]
0x8d32ac <__skb_flow_dissect+520>: mov 2, %g1
I get unaligned access traps at __skb_flow_dissect+500 and
__skb_flow_dissect+512 (corresponding to saddr and daddr), once for
each interface (gretap/eth0 and eth1).
--Sowmini
next prev parent reply other threads:[~2016-02-02 18:35 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-31 21:37 [PATCH net] net: Allow flow dissector to handle non 4-byte aligned headers Tom Herbert
2016-01-31 21:47 ` kbuild test robot
2016-01-31 22:06 ` Florian Westphal
2016-02-01 0:24 ` Eric Dumazet
2016-02-01 0:39 ` Florian Fainelli
2016-02-01 15:20 ` Nicolas Dichtel
2016-02-01 16:01 ` Sowmini Varadhan
2016-02-01 0:43 ` Sowmini Varadhan
2016-02-01 12:32 ` Sergei Shtylyov
2016-02-02 0:31 ` Sowmini Varadhan
2016-02-02 0:46 ` Tom Herbert
2016-02-02 3:56 ` Alexander Duyck
2016-02-02 13:41 ` Hannes Frederic Sowa
2016-02-02 18:35 ` Sowmini Varadhan [this message]
2016-02-03 17:07 ` Tom Herbert
2016-02-03 17:31 ` Sowmini Varadhan
2016-02-03 17:51 ` Tom Herbert
2016-02-03 17:59 ` Sowmini Varadhan
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