linux-kernel - Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

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Message-ID: <45FF3CB1.7080301@goop.org>
Date:	Mon, 19 Mar 2007 18:45:21 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Zachary Amsden <zach@...are.com>
CC:	Andi Kleen <ak@....de>, David Miller <davem@...emloft.net>,
	rusty@...tcorp.com.au, mingo@...e.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, chrisw@...s-sol.org,
	anthony@...emonkey.ws, torvalds@...ux-foundation.org,
	netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops
 callsites to make them patchable

Zachary Amsden wrote:
> Jeremy Fitzhardinge wrote:
>>  If we then work out in each direction and see matched push/pops,
>> then we know what registers can be trashed in the call.  This also
>> allows us to determine the callsite size, and therefore how much space
>> we need for inlining.
>>   
>
> No, that is a very dangerous suggestion.  You absolutely *cannot* do
> this safely without explicitly marking the start EIP of this code. 
> You *must* use metadata to do that.  It is never safe to disassemble
> backwards or "rewind" EIP for x86 code. 

What do you mean the instruction before is "mov $0x52515000,%eax"?

Yeah, you're right.  Oh well.

    J
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