Re: [PATCH 2/3] hw/misc: Add mmio-debug-exit device

[Ilya Leoshkevich]

On Tue, 2022-07-12 at 10:42 +0530, Richard Henderson wrote:
> On 7/12/22 00:26, Ilya Leoshkevich wrote:
> > System tests on x86 use isa-debug-exit device in order to signal
> > success or failure to the test runner. Unfortunately it's not
> > easily
> > usable on other architectures, since a guest needs to access
> > address_space_io, which may not be as straightforward as on x86.
> > Also, it requires adding ISA bus, which an architecture might not
> > otherwise need.
> > 
> > Introduce mmio-debug-exit device, which has the same semantics, but
> > is
> > triggered by writes to memory.
> > 
> > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> 
> You shouldn't need this for s390x, as there are already (at least)
> two other paths to 
> qemu_system_shutdown_request.
> 
> E.g. SIGP, which has a stop option.
> 
> 
> r~
> 

I would normally use lpswe + disabled wait, but this always gives me
exit status code 0, which doesn't allow easily distinguishing between
success and failure.

Code-wise SIGP seems to do roughly the same thing, and a quick
experiment with:

    lgfi %r4,-1
    lgfi %r5,-1
    larl %r6,_cpuaddr
    stap 0(%r6)
    lh %r6,0(%r6)
    nilh %r6,0
    sigp %r4,%r6,5
_cpuaddr: .short 0

confirmed that we get exit status code 0 as well.

Best regards,
Ilya