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Re: [Qemu-devel] [RFC PATCH] s390x-linux-user
From: |
Blue Swirl |
Subject: |
Re: [Qemu-devel] [RFC PATCH] s390x-linux-user |
Date: |
Fri, 26 Jun 2009 21:22:25 +0300 |
On 6/26/09, Paul Brook <address@hidden> wrote:
> On Friday 26 June 2009, Blue Swirl wrote:
> > On 6/26/09, Paul Brook <address@hidden> wrote:
> > > On Friday 26 June 2009, Blue Swirl wrote:
> > > > On 6/26/09, Ulrich Hecht <address@hidden> 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.
> >
> > Then add the second byte of the referenced instruction to TB flags? Or
> > maybe just the result of the OR operation for compactness?
>
>
> No. You need the whole instruction. Which is fetched from memory, so is not
> easily available when you're checking TB flags.
> To do it this way, I think you'd need to split the instruction in two. The
> first part would load the whole instruciton from memory, or with r0, then
> store the result in an internal CPU pseudo-register to the whole instruction,
> and cuse annother TB lookup. The second would generate code that cleared the
> pseudo-register then executed the code that was stored in it.
> You'd have to include the whole of the pseudo-register in TB_FLAGS, and I
> doubt you've got enough bits for that.
How about cs_base then?
> OTOH, tweaking the TCG interface so that it works as an interpreter shouldn't
> be all that hard. It's something I've been considering to do for a while, and
> would mean that you can build both interpreter and translator from the same
> source.
Like by adding an interpreter TCG target? If it were in C only, it
could also serve as a portable (low performance) translator runtime.
Re: [Qemu-devel] [RFC PATCH] s390x-linux-user, Stuart Brady, 2009/06/26