From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <ak@suse.de>
Subject: Re: 32/64-bit hypercall interface
Date: 04 Oct 2005 14:11:10 +0200
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To: "Nakajima, Jun" <jun.nakajima@intel.com>
Cc: Jeremy Katz <katzj@redhat.com>, xen-devel@lists.xensource.com, Ian Pratt <Ian.Pratt@cl.cam.ac.uk>
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"Nakajima, Jun" <jun.nakajima@intel.com> writes:
> 
> The 32-bit and 64-bit hypercall ABI cannot be identical on x86 because
> of the generic ABI difference between 32-bit and 64-bit. 

You use a custom ABI for hypercalls anyways, so you can define
it to be the same with some care. That is the approach that is 
used by some newer subsystems in the Linux kernel.

In my experience even people with the best intentions tend to get that
wrong at some point because there are some subtle issues so having the
additional safety net of a compat layer is still a good idea. It would
only emulate the ones that went wrong.

-Andi