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[Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravi

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable
From: Ingo Molnar <mingo@xxxxxxx>
Date: Fri, 16 Mar 2007 10:24:45 +0100
Cc: Zachary Amsden <zach@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, Anthony Liguori <anthony@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
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* Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> Wrap a set of interesting paravirt_ops calls in a wrapper which makes 
> the callsites available for patching.  Unfortunately this is pretty 
> ugly because there's no way to get gcc to generate a function call, 
> but also wrap just the callsite itself with the necessary labels.
> 
> This patch supports functions with 0-4 arguments, and either void or 
> returning a value.  64-bit arguments must be split into a pair of 
> 32-bit arguments (lower word first).  Small structures are returned in 
> registers.

ugh. This is beyond ugly! Why dont we just compile two images, one for 
Xen and one for native, do two passes to get those two images and 
'merge' them into a single vmlinuz (so that we still have a 'single' 
kernel unit to deal with on the distro side). This way we avoid all this 
crazy, limited, fragile patchery business...

        Ingo

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