Re: [Qemu-devel] [Qemu-ppc] Help needed testing on ppc

[Alexander Graf]

On 17.06.14 11:34, BALATON Zoltan wrote:
> On Tue, 17 Jun 2014, Alexander Graf wrote:
> > On 17.06.14 01:42, BALATON Zoltan wrote:
> > > On Thu, 12 Jun 2014, BALATON Zoltan wrote:
> > > > On Wed, 7 May 2014, Alexander Graf wrote:
> > > > > On 05/07/2014 05:31 PM, Tom Musta wrote:
> > > > > > On 5/6/2014 6:17 PM, BALATON Zoltan wrote:
> > > > > > > On Tue, 6 May 2014, Tom Musta wrote:
> > > > > > > > (2) Your patch makes some store instructions compliant with the 
> > > > > > > > most recent ISAs but there are many other instructions that are 
> > > > > > > > not addressed by the patch.  I think fixing only some will be a 
> > > > > > > > future source of confusion.>>
> > > > > > Alex:  do you have an opinion on this?  Are you OK with changing 
> > > > > > masks for a few stores but not all instructions in general?
> > > > >
> > > > > I would like to see someone just test all those load/store 
> > > > > instructions on old CPUs and see whether they fault. If none 
> > > > > faults, we should just be consistent and remove them for all. If 
> > > > > say a 750 really only ignores the Rc bit for stwx for some reason 
> > > > > we should just model it accordingly.
> > > >
> > > > To get some answers to this and other questions that are still open 
> > > > I've made a test program by stripping down yaboot and adding tests 
> > > > to it so that it should be possible to run from Open Firmware as a 
> > > > boot loader. It can be found here:
> > > >
> > > > http://goliat.eik.bme.hu/~balaton/oftest/
> > > >
> > > > The files there are:
> > > > * oftest - an ELF executable that you can put on some device OF can 
> > > > read
> > > >        and run it if it were a boot loader ( e.g. 0> boot 
> > > > hd0,0:\oftest )
> > > > * oftest.hfs.xz - the same file on an 800k HFS volume that can be 
> > > > put on
> > > >        e.g. a USB drive or CD then used as the previous one
> > > > * oftest-src.tar.xz - the source
> > > >
> > > > When run from Open Firmware it should print some information about 
> > > > memory layout, MSR setting, stack location, BAT registers and test 
> > > > the stwx opcode with and without reserved bit which should help us 
> > > > understand better the differences between QEMU and real hardware. I 
> > > > could only test it on QEMU though.
> > >
> > > I've got some results (but more are welcome) which can be seen here:
> > >
> > > http://goliat.eik.bme.hu/~balaton/oftest/results/
> > >
> > > The results show that the stwx instruction with reserved bit set 
> > > does not change status bits and does not generate an exception on 
> > > any CPU tested (G3 and G4) so it is most probably just ignored as we 
> > > thought.
> >
> > [adding qemu-ppc and tom to CC]
> >
> > Tom already commented on this. Is there a pattern that matches all 
> > the indexed load/store instructions or is stwx a one-off?
>
> Is this a question to whom? If to me I don't understand it.

stwx is part of a group of instructions. It's very rare that hardware 
only shows certain behavior (like ignore a reserved bit) for single 
instructions. Usually it happens on complete groups.


Alex