4 Feb
2019
4 Feb
'19
4:25 p.m.
From: Fritz Mueller
I've had a bit of time in front of the machine to
repro this and take a
look. What I actually see is:
R0 177770
R1 0
R2 0
R3 0
R4 0
R5 34
R6 141774
PC 000254
Argh. (Very red face!)
I worked out the trap stack layout by looking at m40.s and trap.c, and
totally forgot about the return PC (that's the 0444) from the call to
trap():
0001740 000013 141756 022050 000013 000000 000000 000000 000034
0001760 000444 000031 177760 000000 030351 177770 010210 170010
I clearly should have looked at core(V) in the V6 manual!
The R6 you have recorded is correct for just after the trap; that's
the kernel mode SP, which points to the top of the kernel stack,
in segment 6 (in the swappable per-process kernel area, which runs
from 140000-1776).
So there is no R5 mystery, I was just confused. Back to the other two!
Noel