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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [RFC PATCH] s390x-linux-user
Date: Fri, 26 Jun 2009 18:40:09 +0100
References: <200906261849.43746.uli@suse.de>
	<f43fc5580906261017o1eace71dn8b6483fa354e693d@mail.gmail.com>
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To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>

On Friday 26 June 2009, Blue Swirl wrote:
> On 6/26/09, Ulrich Hecht <uli@suse.de> wrote:
> >  There is a very peculiar S/390 instruction called "EXECUTE". What it
> > does is to take another instruction stored somewhere in memory,
> > logical-OR the second byte of the instruction with the LSB of R0 and then
> > execute the result, without changing the instruction in memory or the
> > program counter. Any idea how to implement this in QEMU? Currently, I'm
> > interpreting the couple of instructions that GCC uses EXECUTE with, but
> > in the long run that would amount to implementing a second emulator...
>
> Maybe something like this: Make a special TB of the EXECUTE
> instruction and add LSB of R0 to TB flags for these TBs. Then you can
> examine R0, OR and generate code at translation time. The TBs linking
> to EXECUTE TB may need to be special too in order to track for R0.

That's not sufficient. The results also depend on the referenced instruction.

Paul