🚀 go-pugleaf

In article <44908@bbn.COM> dswartz@BBN.COM (Dan Swartzendruber) writes:
>	[ ... ]		The PDP-11 had
>the same problem.  I seem to recall they solved it by having a diagnostic
>register in which the CPU wrote which registers had been incremented or
>decremented and by how much.  That wasn't as bad as it might first seem.
>There are only two registers which can change as a result of any given
>instruction and they could only change by 1, 2 or 4.  It's been a while
>since I hacked on a PDP-11, so I might be off a little here, but that
>was the basic gist....

Some PDP-11s had this register, some did not.  It turns out
that the only time this was a problem was when an
auto-[in|de]crement *floating*point* instruction caused the
fault.  Unfortunately, DEC left this register out of the
PDP-11/60 (or was that the 11/44?), which implemented the
standard floating point instruction set.  Thus, for this
PDP-11 only, you had to do stack probes if you were going to
use *(double *)p++ into automatic storage.

Dennis Rockwell
Concurrent Engineering
Westford MA