port-mips/43431: mips trap handling broken

[martin%NetBSD.org@localhost]

>Number:         43431
>Category:       port-mips
>Synopsis:       mips trap handling broken
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-mips-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 07 19:15:00 +0000 2010
>Originator:     Martin Husemann
>Release:        NetBSD 5.99.30
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD 5.99.30 (CUBE) #22: Mon Jun  7 20:53:59 CEST 2010 evbmips-el, 
alchemy au1550
Architecture: mips
Machine: mips32
>Description:
Trying to boot an old userland with a current kernel fails in init:

init: copying out path `/sbin/init' 11
pid 1(init): ABI set to O32 (e_flags=0x1007)
trap: pid 1(init): sig 11: cause=0x8 epc=0x50505050 va=0x50505050
registers:
[ 0]=00000000 [ 1]=00000001 [ 2]=00000000 [ 3]=00000000
[ 4]=7dffb918 [ 5]=7fffdc14 [ 6]=00000000 [ 7]=7fffdbfc
[ 8]=7fffdc14 [ 9]=50505050 [10]=00000018 [11]=056de450
[12]=00000002 [13]=00000003 [14]=00000001 [15]=83f185e0
[16]=50505050 [17]=50505050 [18]=50505050 [19]=50505050
[20]=50505050 [21]=50505050 [22]=50505050 [23]=50505050
[24]=7dfa0000 [25]=7dfac2d8 [26]=00000000 [27]=00000000
[28]=7dff7150 [29]=7fffd724 [30]=50505050 [31]=50505050
Stopped in pid 1.1 (init) at    netbsd:cpu_Debugger+0x4:        jr      ra
                bdslot: nop
db> bt
cpu_Debugger+4 (804114d0,80360f40,b2,80360f5c) ra 80267524 sz 0
trap+35c (804114d0,8,50505050,50505050) ra 801b88e4 sz 144
mips32_UserGenException+d8 (804114d0,8,50505050,50505050) ra 0 sz 0
User-level: pid 1.1

Note the bogus register dump; this would have send a SIGSEGV to init - I
assume the args passed to from UserGenException() to trap() are bogus.
Maybe this was just a page fault misinterpreted some way?

>How-To-Repeat:
s/a

>Fix:
n/a