linux-kernel - Re: [PATCH 25/25] [PATCH] add paravirtualization support for x86

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Date:	Thu, 9 Aug 2007 08:30:34 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Glauber de Oliveira Costa <glommer@...il.com>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	rusty@...tcorp.com.au, ak@...e.de, mingo@...e.hu,
	chrisw@...s-sol.org, avi@...ranet.com, anthony@...emonkey.ws,
	virtualization@...ts.linux-foundation.org, lguest@...abs.org
Subject: Re: [PATCH 25/25] [PATCH] add paravirtualization support for x86_64


--
On Thu, 9 Aug 2007, Jeremy Fitzhardinge wrote:

> Glauber de Oliveira Costa wrote:
> > On 8/9/07, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> >
> >>> Does it really matter?
> >>>
> >>>
> >> Well, yes, if alignment is an issue.
> >>
> > Of course, But the question rises from the context that they are both
> > together at the beginning. So they are not making anybody non-aligned.
> > Then the question: Why would putting it in the end be different to
> > putting them _together_, aligned at the beginning ?
> >
>
> Well, the point is that if you add new ones then alignment may be an
> issue.  Putting them at the end (with a comment explaining why they're
> there) will make it more robust.  Though splitting them into their own
> sub-structure would probably be better.

Glauber,

I was thinking of putting them at the end too, and that would make it all
work better. But I didn't mention it because I was in the mindset of "well
i386 has that there, we should too" :-(

>
> Hm.  So x86-64 doesn't make 64-bit pointers be 64-bit aligned?

yeah, it usually does. But it's one of those paranoid things, where you
want it to still work even if someone later on throws an
__attribute__((packed)) in on paravirt ops ;-)

-- Steve

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