netdev - Re: Seeing new kernel unaligned access messages in linux-next on ia64

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Date:	Thu, 25 Mar 2010 00:17:01 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Andreas Schwab <schwab@...ux-m68k.org>
cc:	David Miller <davem@...emloft.net>, tony.luck@...el.com,
	netdev@...r.kernel.org
Subject: Re: Seeing new kernel unaligned access messages in linux-next on
 ia64


On Wednesday 2010-03-24 23:47, Andreas Schwab wrote:
>Jan Engelhardt writes:
>
>> Using a temporary and memcpying it off would normally fix this,
>> as in the patch below. During testing however, I still get
>> unaligned messages even with the patch - and I would not know
>> what causes this.
>
>The memcpy will not fix the alignment issue because the copy operation
>is fully equivalent to a direct assignment, and the compiler can still
>take advantage of the known alignment of the types.  You have to
>explicitly tell the compiler about the reduced alignment guarantee.

You're right, I remember seeing that sort of optimization before. So I 
have changed the function's signature to read

-static void copy_rtnl_link_stats64(struct rtnl_link_stats64 *v,
-                                  const struct net_device_stats *b)
+static void copy_rtnl_link_stats64(void *v, const struct net_device_stats *b)
 {
 ...
 	memcpy(v, &a, sizeof(a));
 }

No more unaligned messages - but is this an acceptable solution?

thanks,
Jan
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