[Simh] VAX emulation issues on Raspberry Pi

[Mark Pizzolato]

On Tuesday, July 31, 2018 at 10:06 AM, Paul Koning wrote:
> > On Jul 31, 2018, at 12:36 PM, Mark Pizzolato <Mark at infocomm.com> wrote:
> >
> > ...
> >> Interesting, and not too surprising.  Given that, it may be useful to
> >> use a recent GCC which supports LTO -- Link Time Optimization.
> >> That's a scheme that allows whole-program optimization, rather than
> >> the normal per-sourcefile optimization.
> >
> > LTO was actually the default for most environments a few years back,
> > but I think that was one of the first things that broke some
> > simulators on some platforms.  It has been backed out when there were
> problems.
> 
> If that's still true with the latest GCC, especially with the in-development one
> (V9.0, from Subversion), those issues might be undefined code problems in
> SIMH.  It is of course also possible that they are LTO bugs, in which case finding
> and reporting them would be a useful thing.

The preponderance of issues are undefined code problems.  Given these 
being pervasive, chasing down corner case problems that LTO might cause (and 
identifying the actual details) hasn't been on the radar.

Being able to rigorously verify the reworked VAX code (and fix remaining or 
newly introduced issues) would be a priority given the right tools.  
I hope to hear back from Tim's contact to further this project.

Thanks.

- Mark