Re: VAX + Spectre

[Paul Koning <paulkoning%comcast.net@localhost>]

> 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