[TUHS] 211bsd: kernel panic after a 'here document' in tcsh

[Michael Kjörling]

On 5 Jun 2017 16:12 +0200, from w.f.j.mueller at retro11.de (Walter F.J. Mueller):
> I'm using 211bsd (Version 447) and found that a 'here document' in tcsh
> leads to a kernel panic. It's absolutely reproducible on my system, both
> when run it on my FPGA PDP-11 or in simh. Just doing
> 
>   tcsh
>   cat << EOF

I'm curious whether the same thing happens if you try that in some
other shell? (Not sure how widely here documents were supported back
then, but I'm asking anyway.)


> is enough, and I get
> 
>     ka6 31333 aps 147472
>     pc 161324 ps 30004
>     ov 4
>     cpuerr 20
>     trap type 0
>     panic: trap
>     syncing disks... done
> 
> looking at the crash dump gives
> 
>   cd /etc/crash
>   ./why 4
>     Backtrace:
>     0147372: _boot(05000,0100) from    ~panic+072
>     0147414: _etext(011350) from ~trap+0350
>     0147450: ~trap() from call+040
>     0147516: _psignal(0101520,0160750) from ~trap+0364
>     0147554: ~trap() from call+040
> 
> so the crash is in psignal, which is afaik the kernel internal
> mechanism to dispatch signals.

The PC value in the panic report ("pc 161324") strikes me as high, but
161324 octal is 58068 decimal, so it's not excessively so, and perhaps
in line with what one might expect to see with a kernel pinned near
top of memory. Are the offsets in the backtrace constant, i.e. does it
always crash on the same code?

Not knowing what cpuerr 20 is specifically doesn't help, and at least
http://www.retro11.de/ouxr/29bsd/usr/src/sys/sys/trap.c.html#n:112
(which doesn't seem to be too far from what you are running) isn't
terribly enlightening; CPUERR is simply a pointer into a memory-mapped
register of some kind, as seen at
http://www.retro11.de/ouxr/29bsd/usr/include/sys/iopage.h.html#m:CPUERR,
and at least pdp11_cpumod.c from the simh source code at
http://simh.trailing-edge.com/interim/pdp11_cpumod.c wasn't terribly
enlightening, though of course I could be looking in entirely the
wrong place.

-- 
Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)