Re: VAX + Spectre

[coypu%sdf.org@localhost]

On Tue, Sep 17, 2019 at 04:33:38PM -0400, Paul Koning wrote:
> 
> 
> > On Sep 17, 2019, at 5:32 AM, coypu%sdf.org@localhost wrote:
> > 
> > So, this is a bug report:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86811
> > 
> > GCC would like to know if VAX needs Spectre-related work.
> > Are any of the VAXes ever made capable of speculative execution? the
> > first tech for doing it was in 1967, so not entirely far-fetched.
> 
> I asked the experts on some other lists, and got this answer from Bob Supnik (lead author of SIMH and long-time VAX hardware specialist):
> 
> > Funny you should ask. The short answer is no. No VAX ever did speculative or out of order execution.
> > 
> > Three developments had to come together for Spectre-style bugs:
> > 
> > 1. Speculative execution that affects the cache or other indirectly testable state.
> > 2. A high-precision, user-mode timer (for measuring cache or branch table perturbation effects).
> > 3. A 'close-in' entity that can do low-latency measurements - the other thread(s) in a hyper-threaded CPU; another core in a multi-core chip; another processor on a SMP bus with extremely fast response time.
> 
> 
> So the answer is that GCC should mark the VAX architecture as "not an issue" just as was done with, say, the PDP11 port.
> 
> 	paul
> 

Thanks!

Very cool to have Bob Supnik as a source.