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[Xen-devel] Re: A proposal - binary

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: A proposal - binary
From: "Bill Rugolsky Jr." <brugolsky@xxxxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 4 Aug 2006 17:40:39 -0400
Cc: Andrew Morton <akpm@xxxxxxxx>, zach@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, jeremy@xxxxxxxxxxxxx, simon@xxxxxxxxxxxxx, jlo@xxxxxxxxxx, greg@xxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, Antonio Vargas <windenntw@xxxxxxxxx>, David Lang <dlang@xxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, ian.pratt@xxxxxxxxxxxxx, torvalds@xxxxxxxx, Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
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On Fri, Aug 04, 2006 at 02:26:20PM -0700, Jeremy Fitzhardinge wrote:
> >I also am missing something here. how can a system be compiled to do 
> >several different things for the same privilaged opcode (including 
> >running that opcode) without turning that area of code into a 
> >performance pig as it checks for each possible hypervisor being present?
> 
> Conceptually, the paravirtops structure is a structure of pointers to 
> functions which get filled in at runtime to support whatever hypervisor 
> we're running over.  But it also has the means to patch inline versions 
> of the appropriate code sequences for performance-critical operations.

Perhaps Ulrich and Jakub should join this discussion, as the whole
thing sounds like a rehash of the userland ld.so + glibc versioned ABI.
glibc has weathered 64-bit LFS changes to open(), SYSENTER, and vdso.

Isn't this discussion entirely analogous (except for the patching of
performance critical sections, perhaps) to taking a binary compiled
against glibc-2.0 back on Linux-2.2 and running it on glibc-2.4 + 2.6.17?
Or OpenSolaris, for that matter?

        Bill Rugolsky

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