[TUHS] Article on 'not meant to understand this'

Steve Johnson scj at yaccman.com
Tue Jan 17 05:10:37 AEST 2017

I was well aware of the comment in V6, but had no idea what it
referred to.   When Dennis and I were porting what became V7 to the
Interdata 8/32, we spent about 10 frustrating days dealing with savu
and retu.  Dennis did his most productive work between 10pm and 4am,
while I kept more normal hours.  We would pore over the crash dumps
(in hex, then a new thing for us--PDP-ll was all octal, all the
time).  I'd tinker with the compiler, he'd tinker with the code and
we would get it to limp, flap its wings, and then crash.  The problem
was that the Interdata had many more registers than the PDP-11, so the
compiler only saved the register variables across a call, where the
PDP-11 saved all the registers.  This was just fine inside a process,
but between processes it was deadly.  After we had tried everything
we could think of, Dennis concluded that the fundamental architecture
was broken.  In a couple of days, he came up with the scheme that
ended up in V7.

It was only several years later when I saw a T-shirt with savu and
retu on it along with the famous comment that I realized what it had
referred to, and enjoyed the irony that we hadn't understood it


----- Original Message -----
From: "Brantley Coile" <brantleycoile at me.com>
To:"Larry McVoy" <lm at mcvoy.com>
Cc:<tuhs at tuhs.org>
Sent:Mon, 16 Jan 2017 05:11:02 -0500
Subject:Re: [TUHS] Article on 'not meant to understand this'

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