Re: [Qemu-devel] Re: 440 emulation?

[Hollis Blanchard <hollisb@us.ibm.com>]

On Mon, 2009-03-16 at 14:41 -0500, Rob Landley wrote:
> On Monday 16 March 2009 14:15:06 Hollis Blanchard wrote:
> > On Mon, 2009-03-16 at 14:05 -0500, Rob Landley wrote:
> > > I'm trying to come up with a working 440 toolchain and root filesystem,
> > > and I think I've built one (--with-cpu=440 for the binutils and gcc
> > > config seems to be the magic), but my attempt to test it under qemu with
> > > -M bamboo led to an "Unable to initialize CPU" message, because
> > > apparently the 440 isn't actually supported.
> >
> > Correct, 440 is not supported by TCG, so I'm not sure what you're trying
> > to do?
> 
> Test a 440 toolchain on an emulated bamboo board.  I discovered that it wasn't 
> supported when I got the "Unable to initialize CPU" message, and investigated.  
> I was hoping that either another processor could run 440 code (ala armv5 
> running armv4 code), or that 440 support was pending and simply hadn't been 
> merged yet.  Couldn't find anything about it in the archives, so I asked.  
> (Not particularly coherently, as it turns out.)

While Power Architecture allows you to run userspace code across
different cores, the same is not true for supervisor code.

As far as I know, nobody is working on 440 TCG emulation. I think the
most difficult part would be the new MMU model; there are some other
changes relative to 405 but I think they're pretty simple.

> > > I tried feeding in "-cpu 405" in hopes of getting something to at least
> > > launch (that's what the source code does when it's using kvm, anyway),
> > > but it still said it couldn't initialize the cpu.
> >
> > As you can see from quick inspection, none of the code involved pays any
> > attention to your -cpu option. If you want to make that work, it should
> > simply be a matter of plumbing 'cpu_model' through ppc440ep_init().
> 
> I might take a stab at that...

As long as you know you're testing 405 support, not 440. If you build a
405 Linux kernel with device tree support, it might just work.

> > > Presumably this works for somebody, but I dunno how to get it to do
> > > anything interesting.  What is the status of the bamboo board?
> >
> > It works, as long as you can provide working core emulation.
> 
> I take it the only way to do this currently is to run kvm on actual 440 
> hardware?

Yes; KVM doesn't translate instruction sets.

(In theory you could do a little intra-architecture emulation to e.g.
run a 405 guest on 440 host, but this has not been implemented.)

-- 
Hollis Blanchard
IBM Linux Technology Center