[TUHS] Some notes on running UNIX v6 in 2015, using SimH and a healthy dose of documentation

Greg 'groggy' Lehey grog at lemis.com
Fri Dec 4 10:52:05 AEST 2015

On Thursday,  3 December 2015 at 10:42:00 -0500, Noel Chiappa wrote:

> E.g. switching processes probably requires a fair amount, since one
> needs to know about internal CPU registers, etc;

And there you missed your cue :-) From swtch() in sys/ken/slp.c:

	 * If the new process paused because it was
	 * swapped out, set the stack level to the last call
	 * to savu(u_ssav).  This means that the return
	 * which is executed immediately after the call to aretu
	 * actually returns from the last routine which did
	 * the savu.
	 * You are not expected to understand this.

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