Re: Regarding the ULTRIX and OSF1 compats

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> That borders on meaningless.  If Ultrix never ran on SPARC or x86_64
>> (which was the case AFAIK), what would it even mean to be compatible
>> with it?
> It doesn't mean anything - that's not the point.  The point is that
> these compat options are retained because people have old binaries
> which use them (on the appropriate architecture).  But those systems
> are somewhat rare (and often slow) and aren't the best place to test
> anything - especially since if an old binary hasn't triggered a
> particular bug in the past, it is unlikely to in the future either.

Yes, but if nothing trips that putative bug, then there is a sense in
which it doesn't matter.  (There are, of course, other senses in which
it does.)

> Just because we'd have no reason to ever change to a different ABI
> just for the fun of it, doesn't mean that we cannot (we shouldn't.
> but we could).   That's what these emulation compat layers are - they
> simply map the other system's ABI into ours.

True as far as it goes.  But if there is no Ultrix ABI for SPARC, there
is nothing to map.

It sounds as though you are proposing to, to pick a concrete example
for convenience of language, design a SPARC ABI which is in some ways
similar to the Ultrix ABI for VAX, then use that to test COMPAT_ULTRIX
on SPARC.

This would, perhaps, help find some of the more egregious bugs.  But
what you'll wind up with is COMPAT_ULTRIX that actually provides
compatability with your Ultrixish ABI on SPARC.  It can, and eventually
will, have bugs when it comes to compatability with Ultrix.

It's a little like the modern mania for cross-building.  It helps, but
only if you/we don't forget that it's only a rough approximation.  How
long was it VAX was broken because there was something wrong that
showed up on native builds but not cross-builds?  People got used to
thinking that because it cross-built, it was fine.  It's one reason I
insist on self-hosting on all my machines.

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