port-i386/53621: i386 panics on boot

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         53621
>Category:       port-i386
>Synopsis:       i386 panics on boot
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-i386-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Sep 20 08:50:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2018.09.20.06.54.36
>Organization:
>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

I tried to boot a -current/i386 kernel on the old Pentium-class
machine of PR 52569 to check whether said PR has been fixed, but
the machine paniced on boot.

Here's a brief summary of the backtrace manually transcribed from
the VGA console:

vpanic()
__x86_indirect_thunk_edx()
cv_signal()
fdcintr1()
fdcintr()
intr_biglock_wrapper()
-- switch to interrupt stack ---
Xintr_legacy6()
--- interrupt ---
outb()
intr_establish_xname()
(etc)

Full backtrace:

http://www.gson.org/netbsd/bugs/i386-panic/5.jpg
http://www.gson.org/netbsd/bugs/i386-panic/6.jpg
http://www.gson.org/netbsd/bugs/i386-panic/7.jpg

For a dmesg from a successful boot with an older -current, see PR 52553.

>How-To-Repeat:

>Fix: