kern/51148: i386 install floppies no longer boot

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

>Number:         51148
>Category:       kern
>Synopsis:       i386 install floppies no longer boot
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 17 13:00:00 +0000 2016
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2016.05.14.21.19.05
>Organization:

>Environment:
System: NetBSD
Architecture: i386
Machine: i386
>Description:

The automated i386 tests on babylon5 are failing at the install stage,
hanging immediately after the kernel load.

The problem started with one of the following commits:

  2016.05.14.21.19.05 chs src/external/cddl/osnet/dev/dtrace/amd64/dtrace_isa.c 1.5
  2016.05.14.21.19.05 chs src/external/cddl/osnet/dev/dtrace/i386/dtrace_asm.S 1.4
  2016.05.14.21.19.05 chs src/external/cddl/osnet/dev/dtrace/i386/dtrace_isa.c 1.4
  2016.05.14.21.19.05 chs src/external/cddl/osnet/dist/uts/common/dtrace/dtrace.c 1.31
  2016.05.14.21.32.50 mlelstv src/doc/roadmaps/storage 1.14
  2016.05.15.07.01.36 maxv src/sys/arch/amd64/amd64/locore.S 1.91
  2016.05.15.07.01.36 maxv src/sys/arch/i386/i386/locore.S 1.123
  2016.05.15.07.17.53 maxv src/sys/arch/amd64/amd64/locore.S 1.92
  2016.05.15.07.17.53 maxv src/sys/arch/i386/i386/locore.S 1.124
  2016.05.15.10.35.54 maxv src/sys/arch/amd64/amd64/machdep.c 1.217
  2016.05.15.10.35.54 maxv src/sys/arch/i386/i386/machdep.c 1.755
  2016.05.15.10.35.54 maxv src/sys/arch/x86/x86/pmap.c 1.195
  2016.05.15.13.59.36 skrll src/sys/dev/ic/sl811hs.c 1.71
  2016.05.15.14.00.08 skrll src/sys/dev/ic/sl811hs.c 1.72
  2016.05.15.15.26.04 chs src/sys/arch/i386/include/asm.h 1.42

I can't auto-bisect it more closely because of build breakage.
For log data, see

  http://releng.netbsd.org/b5reports/i386/commits-2016.05.html#2016.05.14.21.19.05

It looks like the problem only affects installing from floppies and
not installing from a CD, based on some separate tests I did on my
own testbed.

>How-To-Repeat:

>Fix: