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Re: [Xen-devel] Re: [PATCH] Linux: 6 arguments hypercall v3

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] Linux: 6 arguments hypercall v3
From: James <James.McKenzie@xxxxxxxxxx>
Date: Mon, 27 Jun 2011 21:19:07 +0100
Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jean Guyader <jean.guyader@xxxxxxxxxxxxx>, Jean Guyader <Jean.Guyader@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On Fri, Jun 24, 2011 at 03:43:18PM -0700, Jeremy Fitzhardinge wrote:
> On 06/24/2011 03:15 PM, Jean Guyader wrote:
> > I only tested it gcc 4.4.
> >
> > We could still use the v2 which is not as nice, but it doesn't try to
> > load eax twice. Let me know which one you will feel better about.

Given "that loading r0 twice" is in the gcc documentation as an
example at


I think it's fair to use that.

> I feel best about the one you've successfully tested with a number of
> older compilers ;)

what compilers work to build modern linux? We'll give a goodly set of them
a try if that makes everyone feel better.

> Does it have to?  Couldn't it take a pointer to a struct or something?

Yes we could change the API, make sure the struct is visible on all
CPUs, making it incompatible with the existing code, but I think that
misses the point: Xen is written to support 6 argument hypercalls, but
32 bit dom0 is missing the functionality to call them. Surely that's 
something we should fix?


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