What is the "do_BUG" and why does my rtl.o want it?

Please bear with me, I'm going to ramble a little because the situation
isn't quite clear in my own mind.

I'm trying to bring up a backup system HD whose RTLinux never worked right.
I have several kernel images on it but the most recent one was made
specifically for the current Single Board Computer and the next most recent
one was made for the last SBC I was using.
                    Old Board                                        Current
Board
CPU        2 x 600 MHz Celeron                    1x1.3GHz P-III but dual
capable
RAM            384 MB                                               512 MB
                        ...
...
I don't have enough information on the other differences -- like the chip
set -- to comment intelligently.  It's interesting to me that both kernels
work with the new board, but the RTLinux doesn't work with either.  AFAICT
the RTLinux modules were made after the most recent kernel -- I'm judging by
the date stamp which is the day after the new kernel was build and 4 months
after the previous one.

SO .. I apparently have a kernel that's built for the current board and
RTLinux modules that were made for it too.

BUT ...  With the new kernel, if I start loading RTLinux with the simplest
command I know
        insmod        /usr/src/rtlinux/modules/rtl.o
the system hangs.  Every time.  It takes a power cycle to recover.

If I boot with the older kernel, the system seems to work perfectly as a
normal Linux system.  But if I try to load the RTLinux modules, I get
"unresolved symbol:    do_BUG"    -- I'm not positive of the exact text of
the message but I think you understand what the system is saying.

I checked the new kernel with
        ksyms -a  |  grep  do_BUG
and it is defined in the P3 kernel but not in the old, Celeron one.  But
both kernels have the RTLinux patch installed which I've checked with
        ksyms  -a  | grep rtl
and I see the normal RTLinux symbols in both.

THE DIRTY DETAILS:
    The kernel is a "raw" 2.4.18 source tree downloaded from kernel.org and
both kernels were patched with RTL3.2-pre1 and were in fact, made from
exactly the same source tree.  What's really puzzling is that I had another
HD with the same setup -- 2.4.28 patched with RTL3.2-pre1 -- and it worked
just fine [until a system crash destroyed the root partition, but that's a
different problem].  The current HD is a secondary disk which isn't an exact
backup but contains much the same stuff.

SO ...
    1.  What is do_BUG?  Is it something that's only included in RTLinux
with a P-III?  Could I remake RTLinux to avoid it?
    2.  Other than completely downloading a kernel and rtlinux patch and
completely remaking the system, what's the most reasonable strategy for
solving the system hang problem?  [If I have no choice, then I have no
choice and I'll do it but I'm trying to save a full day's work in
downloading and compiling if I can.]

TIA

Norman Dresner
Fellow Support Avionics Systems Engineer  & Advanced Signal Processing
(SGI) Laboratory Administrator
Radar Systems Engineering Department
Northrop Grumman Corporation
Electronic Systems

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