[TUHS] 2.9 kernel compile

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Feb 12 07:14:08 AEST 2015

    > From: Jacob Ritorto

    > I set simh to 11/34 and I managed to get actual panics before (that I
    > didn't record)


    > now I'm just getting hangs, mostly when hitting ctrl-D to bring system to
    > mutiuser.

The fact that it boots to the shell OK indicates things are mostly OK. I
wonder what it's trying to do, in going to multi-user, that's wedging the

    > Same if I mount -a in single user and then try to access /usr (works for
    > a while, then hangs.).

Ah. That sounds very much like a 'lost' interrupt. The process is waiting
(inside the kernel) for the device to complete, and ..... crickets.

    > When hung, I can still get character echo to my terminal

So the machine is still running OK (most echoing is done inside the TTY
interrupt handler).

    >  but can't interrupt or background the running command, etc.

Like I said, it's sleeping inside the kernel, and missed the wakeup event.

If you have another console logged in, it would be interesting to see if that
one is frozen too. If not, we can use tools like 'ps', running on the second
line, to look at the first process and see what it's waiting for.

Single user, the following hack:

  sh < /dev/ttyX > /dev/ttyX &

can be used to start a shell on another tty line (since going full multi-user
seems to wedge it).

    > Would it help if I traced memory and single-stepped through the
    > (apparently) infinite loop?

No, because it's very likely not a loop! ;-)

    > here are some examples of crashes on the real pdp11/34 (booting via
    > vtserver, then bringing in system from the MSCP disk), with the original
    > 2.9bsd-MSCP kernel (the one specifically built for 11/23):
    >  ka6 = 2200
    >  aps = 141572
    >  pc = 50456 ps = 30250
    >  __ovno = 7
    >  trap type 11
    >  panic: trap

That's a segmentation fault. Very odd trap to get! 2.9 uses overlays right?
Maybe there's a problem with how some overlay fits, or something? I don't know
much about the overlay feature, never used it, sorry.

Most of the other data (PS address, PC, KDSA6 contents, etc) aren't much use
without a dump.

    > and another: plain boring old hang at boot when trying to size devices.
    > Can't even echo characters this time.

If the init process hasn't got as far an opening the TTY, you might not get
character echoing.

If that randomly lost interrupt got lost very early on, you might could see
this sort of behaviour.

    > One thing I think is interesting is that it's claiming 158720KW of
    > memory. Is that weird? ...  Where's it getting that odd number?  Vanilla
    > 2.9.1 on the real 11/34 boots with
    >  Berkeley UNIX (Rev. 2.9.1) Sun Nov 20 14:55:50 PST 1983
    >  mem = 135872

No idea where it's coming from, but remember Beowulf Schaeffer's advice to
Gregory Pelton in "Flatlander".

And now that I think about it, if the system thinks it has more memory than it
actually does, that would definitely cause problems.

Probably you should put some printf()'s in startup() and see where it's coming


More information about the TUHS mailing list