Subject: Re: NFS structure allocation alignment patch
From: David Woodhouse <dwmw2@infradead.org>
To: Richard Curnow <Richard.Curnow@superh.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Paul Mundt <lethal@linux-sh.org>,
       Ben Gaster <Benedict.Gaster@superh.com>,
       Sean McGoogan <sean.mcgoogan@superh.com>,
       Boyd Moffat <boyd.moffat@superh.com>
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Date: Fri, 18 Jul 2003 17:10:39 +0100
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On Wed, 2003-07-16 at 16:03, Richard Curnow wrote:
> Apart from this issue, we haven't seen any code- or compiler-related
> problems due to misaligned loads and stores occurring.

That doesn't mean they don't exist. Various parts of the network code
_require_ alignment fixups -- the common case is that it'll be aligned,
and we take the hit only in the _rare_ case of misalignment rather than
using get_unaligned() in the fast path.

Also the flash code does the same in places too. It _did_ use
get_unaligned() for a while but it was removed since it's never valid
for an architecture to _not_ fix up unaligned in-kernel accesses.

> I bet someone will wonder how the misalignment hadn't shown up before.

Because all other architectures implement alignment fixups.

-- 
dwmw2

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