netdev - Re: alignment faults in 3.6

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Date:	Thu, 11 Oct 2012 12:00:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Måns Rullgård <mans@...sr.com>
Cc:	David Laight <David.Laight@...LAB.COM>,
	Jon Masters <jonathan@...masters.org>,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: alignment faults in 3.6

On Thu, 2012-10-11 at 10:45 +0100, Måns Rullgård wrote:
> "David Laight" <David.Laight@...LAB.COM> writes:
> 
> >> -----Original Message-----
> >> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On Behalf Of Måns Rullgård
> >> Sent: 11 October 2012 03:27
> >> To: Jon Masters
> >> Cc: linux-arm-kernel@...ts.infradead.org; netdev@...r.kernel.org
> >> Subject: Re: alignment faults in 3.6
> >> 
> >> Jon Masters <jonathan@...masters.org> writes:
> >> 
> >> > Hi everyone,
> >> >
> >> > On 10/05/2012 10:33 AM, Rob Herring wrote:
> >> >> On 10/05/2012 09:05 AM, Russell King - ARM Linux wrote:
> >> >>> On Fri, Oct 05, 2012 at 07:24:44AM -0500, Rob Herring wrote:
> >> >>>> On 10/05/2012 03:24 AM, Russell King - ARM Linux wrote:
> >> >>>>> Does it matter?  I'm just relaying the argument against adding __packed
> >> >>>>> which was used before we were forced (by the networking folk) to implement
> >> >>>>> the alignment fault handler.
> >> >>>>
> >> >>>> It doesn't really matter what will be accepted or not as adding __packed
> >> >>>> to struct iphdr doesn't fix the problem anyway. 
> > ...
> >> There are exactly two possible solutions:
> >> 
> >> 1. Change the networking code so those structs are always aligned.  This
> >>    might not be (easily) possible.
> >> 2. Mark the structs __packed and fix any typecasts like the ones seen in
> >>    this thread.  This will have an adverse effect in cases where the
> >>    structs are in fact aligned.
> >> 
> >> Both solutions lie squarely in the networking code.  It's time to
> >> involve that list, or we'll never get anywhere.
> >
> > It might be enough to use __attribute__((aligned(2))) on some structure
> > members (actually does 'ldm' need 8 byte alignment?? - in which case
> > aligned(4) is enough).
> 
> The aligned attribute can only increase alignment.
> 

I have no idea what is the problem, 

-ENOTENOUGHCONTEXT



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