[Simh] simh/VAX: DIVW3 problem ?

[Peter R. Trimmel]

When trying to run some VAX S/W on simh 3.2-0 I encountered sudden and
unexpected crashes
that can't be seen on 'real' H/W. I traced them down and found a 'DIVW3' VAX
instruction
that caused the pain by unexpectedly writing a LONG to the destination
instead of a WORD, destroying the memory location right after the
destination operand's address.

This instruction is used rarely by VMS but extensively by our S/W, which
used to be portable among PDP/11 and VAXen and therefore uses a 16bit
compiler (for the language RTL) to generate MACRO/11 code. So, all INTs are
16Bit, arithmetic operations are 16bit; we use MOVW, DIVW, ADDW all over the
place.

I looked at the code in VAX/vax_cpu.c and realised that it would take some
time to understand what's going on there. Maybe someone with a deeper
understanding of the VAX instruction emulation can provide some hints.

Please find attached some forensic investigations.

regards,
Peter

PS: we successfully run the Austrian Air Traffic Control System S/W on simh
now. Well, not for live operations ;-) but for inhouse tests it prooved to
be a very reliable environment.
This can be seen as a huge success for this project!

attached: rdp.crash.txt
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