linux-kernel - Re: [PATCH] connector: Some fixes for ia64 unaligned access errors

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Message-Id: <20061211172907.305473cf.zaitcev@redhat.com>
Date:	Mon, 11 Dec 2006 17:29:07 -0800
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Erik Jacobson <erikj@....com>, guillaume.thouvenin@...l.net,
	linux-kernel@...r.kernel.org, zaitcev@...hat.com
Subject: Re: [PATCH] connector: Some fixes for ia64 unaligned access errors

On Mon, 11 Dec 2006 15:52:47 -0800, Matt Helsley <matthltc@...ibm.com> wrote:

> 	I'm shocked memcpy() introduces 8-byte stores that violate architecture
> alignment rules. Is there any chance this a bug in ia64's memcpy()
> implementation? I've tried to read it but since I'm not familiar with
> ia64 asm I can't make out significant parts of it in
> arch/ia64/lib/memcpy.S.

The arch/ia64/lib/memcpy.S is probably fine, it must be gcc doing
an inline substitution of a well-known function.

A commenter on my blog mentioned seeing the same thing in the past.
(http://zaitcev.livejournal.com/107185.html?thread=128945#t128945)

It's possible that applying (void *) cast to the first argument of memcpy
would disrupt this optimization. But since we have a well understood
patch by Erik, which only adds a penalty of 32 bytes of stack waste
and 32 bytes of memcpy, I thought it best not to bother with heaping
workarounds.

-- Pete
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