[Info-vax] VMS internals design, was: Re: BASIC and AST routines

[abrsvc]

On Friday, November 26, 2021 at 2:41:59 PM UTC-5, Simon Clubley wrote:
> On 2021-11-26, Félim Doyle <felim... at gmail.com> wrote: 
> > On Thursday, 25 November 2021 at 15:48:37 UTC, Dave Froble wrote: 
> >> VMS was designed and implemented for VAX, not generic computers. 
> > 
> > As I remember it, VAX/VMS was designed by DEC to be its best ever OS then the VAX hardware was designed and built to run it not the other way around. There were probably some mistakes made, unforeseen implementation issues and some miscommunications during parallel development of the hardware and software but the facilities that this combination provided, especially in comparison to the price range of other systems at the time, was revolutionary. 
> >
> One of the biggest mistakes made is that DEC went to the trouble of 
> implementing a 4-mode architecture and then completely blew how it was 
> used. 
> 
> That 4-mode architecture could have provided some really truly radical 
> internal security separation within VMS, but once you are in any of the 
> 3 inner modes, you can get to any of the other inner modes so all those 
> extra modes were wasted from a security isolation point of view. 
> 
> In case you are wondering, you can escalate from supervisor mode because 
> DCL has access to the privileges of the programs it runs even though it 
> doesn't actually need them. That kind of thing should have stayed within 
> the kernel so DCL never sees those privileges. 
> 
> Just yet another VMS design "feature". :-)
> Simon. 
> 
> -- 
> Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP 
> Walking destinations on a map are further away than they appear.
I find these kind of comments somewhat offensive since it is easy to criticize the decisions of people made 40 years ago using the context of knowledge today.  VMS was designed as a cooperative pairing of both hardware and software.  The use of R0 and R1 was for consistency across calls and had nothing to do with MACRO32 at all.  Bliss used the same register conventions.  If the VMS and VAX engineers knew in the late 70's what was known now, I suspect things would have been done differently.