Fwd: VAX + Spectre

[Maciej W. Rozycki]

On Tue, 17 Sep 2019, Jon Elson via cctalk wrote:

> > "Spectre" is one of two notorious bugs of modern CPUs involving speculative
> > execution.  I rather doubt that VAX is affected by this but I suspect others
> > here have a lot more knowledge.
> >
> >
> You need an extremely high resolution timer to detect slight differences in
> execution time of speculatively-executed threads. The VAX 11/780 certainly did
> not do speculative execution, and my guess is that all VAXen did not, either.

 The NVAX and NVAX+ implementations include a branch predictor in their 
microarchitecture[1], so obviously they do execute speculatively.

> Also, I don't think the timer was high enough resolution to detect such a
> difference.

 I can't speak of timer availability offhand though.

References:

[1] G. Michael Uhler et al, "The NVAX and NVAX+ High-performance VAX 
    Microprocessors", Digital Technical Journal Vol. 4 No. 3 Summer 1992
    <ftp://ftp.linux-mips.org/pub/linux/mips/people/macro/DEC/DTJ/DTJ701/DTJ701PF.PDF>

  Maciej