PowerMac G5 crashes with "instruction storage interrupt" on recent 13

Hi all,

I have a PowerMac G5 that’s running an old build of FreeBSD 13 stable (from around October of last year) that I’m trying to upgrade to recent stable/13.

Booting into a new kernel brings two issues: the first is that the fans spin up to jet engine levels right before transferring control to userspace. An old patch I have locally to mitigate this (which I got from whichever outstanding bug exists for this in the bug tracker) doesn’t seem to work any longer.

The second is that the kernel crashes (apparently) as soon as it tries to mount a ZFS pool during early stages of the boot process, but after successfully transferring control to userspace. Typing this from a photo of the crash so omitting details that I think aren’t going to be relevant here, like addresses, here is what I get:

----
Setting hostid: …
ZFS filesystem version: 5
ZFS storage pool version: features support (500)

Fatal kernel trap:

Exception = 0x400 (instruction storage interrupt)
…
pid = 64, comm = zpool

panic: instruction storage interrupt trap
cpuid = 1
time = …
KDB: stack backtrace:
#0 kdb_backtrace
#1 vpanic
#2 panic
#3 trap
#4 powerpc_interrupt
Uptime: 7s
----

Any thoughts about what I could look into? Any “recent” commits that you think may be at fault?

Thanks!