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Date: Fri, 20 Jul 2007 10:38:09 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: build fix for x86_64...
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To: Andi Kleen <ak@suse.de>
Cc: "Luck, Tony" <tony.luck@intel.com>, Randy Dunlap <randy.dunlap@oracle.com>, Andi Kleen <ak@novell.com>, Arthur Jones <arthur.jones@qlogic.com>, Vasily Tarasov <vtaras@openvz.org>, linux-kernel@vger.kernel.org, Jan Kara <jack@ucw.cz>, linux-arch@vger.kernel.org
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Andi Kleen wrote:
> 
> That doesn't help for any old interfaces, like the one here. For those
> still ifdefs are needed. Interfaces that use compat_u64 just use
> a normal #ifdef CONFIG_COMPAT.
> 
> Besides I have my doubts compat_u64 will be the solution
> to these worries. We have hundreds of people adding various interfaces
> to Linux and it's unlikely they all heard about it. So likely
> these cases will occur again and again.
> 

Of course they will.  compat_u64 will have no effect on a properly
designed interface where everything is aligned.

To me, the whole point with compat_u64 is that when someone has designed
an interface improperly (so it's alignment-dependent) then we can
replace u64 with compat_u64 and use the same structure on 64 bits even
though the original interface was broken.

	-hpa