[Bug 237590] powerpc64 PowerMac11,2 and 7,2 context, -r330614 and later (including -r345758): "ofwdump -ap" crashes the system; probable -r330610 "cause"

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237590

--- Comment #4 from Mark Millard <marklmi26-fbsd at yahoo.com> ---
(In reply to Mark Millard from comment #3)

Based on register values values it looks like the
openfirmware code got something like, say, a Data
Storage Exception, that in turn went to generictrap,
that in turn went to k_trap:

<k_trap> mfsprg  r31,0
<k_trap+0x4> mfsrr0  r30
<k_trap+0x8> std     r30,288(r31)
<k_trap+0xc> mfsrr1  r30
<k_trap+0x10> std     r30,296(r31)
<k_trap+0x14> mfsprg  r31,1
<k_trap+0x18> mfmsr   r30
<k_trap+0x1c> ori     r30,r30,50
<k_trap+0x20> mtmsr   r30
<k_trap+0x24> isync
<k_trap+0x28> stdu    r31,-688(r1)

It failed at the last because the value r1 held
0xffff'ffff'ffb7'f400, apparently an openfirmware
stack address being handled by a FreeBSD exception
handler under the FreeBSD memory management.

(So far, I can not be sure of what, specifically,
initiated getting to k_trap.)

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