[TUHS] Another odd comment in V6

Noel Chiappa jnc at mercury.lcs.mit.edu
Wed Feb 15 01:40:04 AEST 2017


    > From: Lars Brinkhoff

    > Nick Downing <downing.nick at gmail.com> writes:

    >> By contrast the MIT guy probably was working with a much smaller/more
    >> economical system that didn't maintain a kernel stack per process.

I'm not sure I'd call ITS 'smaller'... :-)

    > PCLSRing is a feature of MIT' ITS operating system, and it does have a
    > separate stack for the kernel.

I wasn't sure if there was a separate kernel stack for each process; I checked
the ITS source, and there is indeed a separate stack per process. There are
also three other stacks in the kernel that are used from time to time (look
for 'MOVE P,' for places where the SP is loaded).

Oddly enough, it doesn't seem to ever _save_ the SP - there are no 'MOVEM P,'
instructions that I could find!

	Noel


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