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R: Program counter stuck at 0xFFFFFFFC when emulating e5500 processor on

From: luigi burdo
Subject: R: Program counter stuck at 0xFFFFFFFC when emulating e5500 processor on T4240-RDB board
Date: Wed, 11 Mar 2020 16:44:29 +0000

HI Devid,
the kvm full work on e5500 cpu personally tested this on P5020 and P5040 when i had the varisys beta boards AmigaOne
But is  not possible made kvm-pr from an e5500 to and e6500 and vice versa. 
the e5500 was not kvm-pr compatible with 604e instructions set, probably something is missing or locked in the cpu? just because i was using on the board standard PPC linux distros with only kernel with modules made for the e5500 machine and the system was working right.

Probably the e6500 is more compatible with 604e G3/G4 and 970 in Kvm-pr

Da: Qemu-ppc per conto di David Gibson
Inviato: Mercoledì, 11 Marzo, 2020 06:03
A: Philippe Mathieu-Daudé
Cc: Wayne Li; qemu-ppc; QEMU Developers
Oggetto: Re: Program counter stuck at 0xFFFFFFFC when emulating e5500 processor on T4240-RDB board

On Thu, Feb 20, 2020 at 09:44:13AM +0100, Philippe Mathieu-Daudé wrote:
> Hello,
> On 2/20/20 6:40 AM, Wayne Li wrote:
> > Dear QEMU list members,
> No subject: it is unlikely your question get noticed...
> Also you didn't Cc'ed the people who might help you (doing that for you):
> ./scripts/get_maintainer.pl -f target/ppc/cpu-models.c
> David Gibson <address@hidden> (maintainer:PowerPC TCG CPUs)
> address@hidden (open list:PowerPC TCG CPUs)
> address@hidden (open list:All patches CC here)

Right.  Unfortunately the embedded cpu support is barely maintained,
so there's only a little bit of help I can give.

> > This will kind of be a repost but I'd like to post my question again
> > because I've gained some more knowledge that makes me feel that my
> > question would be easier to answer.  So we developed a custom-made QEMU
> > VM that emulates a custom machine that has an e5500 processor.  I'm
> > running this VM on a T4240-RDB board which has an e6500 processor and
> > I'm trying to get the VM running with KVM enabled.  The problem I'm
> > having is the program counter refuses to increment at all.  It just
> > stays at the address 0xFFFFFFFC.  On a run without KVM enabled, the VM
> > will also start executing at this same address but the program counter
> > beings to increment immediately.  I know this is a custom QEMU VM and
> > maybe some of the startup stuff we do could be causing problems, but
> > what could possibly stop the program counter from incrementing
> > altogether?
> >
> > Also, I do have another side question.  When running with KVM enabled, I
> > see the kernel-level ioctl call KVM_RUN running and then returning over
> > and over again (by the way before the VM kinda grinds to a halt I only
> > see QEMU make the KVM_RUN call twice, but the kernel-level ioctl
> > function is being called over and over again for some reason).  And each
> > time the KVM_RUN call returns, the return-from-interrupt takes the VM to
> > the address 0xFFFFFFFC.  What is the KVM_RUN ioctl call used for?  Why
> > is it being called over and over again?  Maybe if I understood this
> > better I'd be able to figure out what's stopping my program counter from
> > incrementing.

I don't really know if KVM even attempts to support e5500 cpus.  We'd
need to at least know what your host kernel is and what KVM variant it
is using.  What's the instruction at 0xfffffffc which seems not to be
handled here properly?  It sounds like you might be getting some sort
of rolling trap, because KVM isn't handling that instruction correctly.

The KVM_RUN is what causes KVM to actual enter the guest and execute
instructions.  It returns when something triggers a guest exit - a
trap or various other events can do this.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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