port-mips/53538: MIPS install fails with "exec /sbin/init: error 8"

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

>Number:         53538
>Category:       port-mips
>Synopsis:       MIPS install fails with "exec /sbin/init: error 8"
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    port-mips-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Aug 19 09:20:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2018.08.08.07.50.12
>Organization:

>Environment:
System: NetBSD
Architecture: mips
Machine: hpcmips
>Description:

Since simonb's commit of src/sys/arch/mips/mips/cpu_exec.c 1.66, the
hpcmips and pmax testbeds are unable to boot the install kernel:

[   3.0855438] root on md0a dumps on md0b
[   3.0855438] root file system type: ffs
[   3.0855438] kern.module.path=/stand/hpcmips/8.99.24/modules
[   3.0898467] exec /sbin/init: error 8
[   3.0898467] init: trying /sbin/oinit
[   3.0898467] exec /sbin/oinit: error 2
[   3.0898467] init: trying /sbin/init.bak
[   3.0898467] exec /sbin/init.bak: error 2
[   3.0898467] init: trying /rescue/init
[   3.0898467] exec /rescue/init: error 2
[   3.0898467] init path (default /sbin/init):

The above was extracted from
http://releng.netbsd.org/b5reports/hpcmips/2018/2018.08.18.03.09.37/install.log

More logs at:
http://releng.netbsd.org/b5reports/hpcmips/commits-2018.08.html#2018.08.08.07.50.12
http://releng.netbsd.org/b5reports/pmax/commits-2018.08.html#2018.08.08.07.50.12

>How-To-Repeat:

Inspect the test reports.

>Fix: