port-sparc/54789: Sparc boot fails with "Trap 0x21 while interrupts disabled"

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

>Number:         54789
>Category:       port-sparc
>Synopsis:       Sparc boot fails with "Trap 0x21 while interrupts disabled"
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-sparc-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Dec 20 09:35:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current
>Organization:
>Environment:
System: NetBSD
Architecture: sparc
Machine: sparc
>Description:

On the sparc testbeds, booting the install media has recently started
failing with:

  [   4.0516950] root on md0a dumps on md0b
  [   4.0516950] root file system type: ffs
  [   4.0617135] kern.module.path=/stand/sparc/9.99.26/modules
  [   4.0651650] WARNING: negative runtime; monotonic clock has gone backwards
  qemu: fatal: Trap 0x21 while interrupts disabled, Error state
  pc: 00000000  npc: 00000004
  %g0-7: 00000000 00000073 00000000 00000000 00000000 f4d29000 f02315e0 f010dd58
  %o0-7: 00000000 00000000 00000000 00000000 f0561020 f0561050 f4d2ada8 f00ff870
  %l0-7: 040000c7 f000a1cc f000a1d0 00000009 f0002068 00000000 f02315e0 f0008444
  %i0-7: f4d2aea1 effffffd 00000002 f4d29000 0000002d 00000000 f4d2ae38 f0009d80
  %f00:  0000000000000000 0000000000000000 0000000000000000 0000000000000000
  %f08:  0000000000000000 0000000000000000 0000000000000000 0000000000000000
  %f16:  0000000000000000 0000000000000000 0000000000000000 0000000000000000
  %f24:  0000000000000000 0000000000000000 0000000000000000 0000000000000000
  psr: 040000c7 (icc: ---- SPE: SP-) wim: 00000002
  fsr: 00000000 y: 00000000

For more log output, see:

  http://releng.netbsd.org/b5reports/sparc/commits-2019.12.html#2019.12.18.02.46.21
  http://www.gson.org/netbsd/bugs/build/sparc/commits-2019.12.html#2019.12.18.20.38.14

>How-To-Repeat:

>Fix: