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Date: Tue, 2 Feb 2016 13:35:09 -0500
From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: Tom Herbert <tom@...bertland.com>,
David Miller <davem@...emloft.net>,
Netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net] net: Allow flow dissector to handle non 4-byte
aligned headers
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
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