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[Xen-devel] Re: [PATCH] Linux: 6 arguments hypercall v2

To: Jean Guyader <jean.guyader@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] Linux: 6 arguments hypercall v2
From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Date: Fri, 24 Jun 2011 16:07:35 +0100
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jean Guyader <Jean.Guyader@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On Fri, 2011-06-24 at 15:59 +0100, Jean Guyader wrote:
> On 24/06 03:46, Ian Campbell wrote:
> > On Fri, 2011-06-24 at 15:00 +0100, Jean Guyader wrote:
> > > Hi,
> > > 
> > > This patch implements the 6 arguments hypercalls.
> > > The sixth argument is passed using ebp or r9.
> > 
> > Looks pretty good.
> > 
> > I was able to get rid of more of the ifdefery etc with the following. It
> > appears to do the right thing (by inspection of compiled code, not
> > actual testing).
> > 
> > Defining both __res and __arg6 as register("eax") seems slightly
> > dubious, as is including them both in  __HYPERCALL_6PARAM, but gcc
> > doesn't seem to mind and it makes  __HYPERCALL_6PARAM the same in both
> > cases and gets rid of __HYPERCALL_DECLS6.
> > 
> > Your version is probably less likely to tickle ggc bugs/behaviour
> > changes in the future, so it's likely safer I think.
> > 
> Thanks that makes the code much nicer, I didn't really want to declare
> to variable in eax but if that works fine.

Well, with my specific version of gcc (4.4.5-8)... I didn't check the
docs to see if it supposed to be ok or not or anything like that.

> Also my patch modifies  HYPERVISOR_set_trap_table by mistake but
> shouldn't. I only used that for testing _hypercall6.

I did the same ;-)

>  I'll send
> another version with your changes in but without the mistake
> at the end.


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