netdev - Re: [RFC] Kernel unaligned access at __skb_flow

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Date:	Fri, 29 Jan 2016 18:04:24 -0500
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Michael Dalton <mwdalton@...gle.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [RFC] Kernel unaligned access at __skb_flow_dissect

On (01/29/16 15:00), Tom Herbert wrote:

> The sparc documentation is pretty clear
> http://docs.oracle.com/cd/E19253-01/816-4854/hwovr-2/index.html, seems
> like unaligned accesses are not allowed in the architecture.

yes, but looks like you  can paper over some of this with
memcpy (as was happening with the saddr ref in skb_flow_dissect
that puzzled me and Eric because it did not generate any traps).

I suppose one could sprinkele a few WARN_ON's for !IS_ALIGNED
but that's not a fool-proof detection method either (in addition
to all the ugly shouting in the code).

--Sowmini