port-mips/54309: gdb doesn't work on mips64 (32bit userland, 64bit kernel)

[coypu%sdf.org@localhost]

>Number:         54309
>Category:       port-mips
>Synopsis:       gdb doesn't work on mips64 (32bit userland, 64bit kernel)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-mips-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 19 10:30:00 +0000 2019
>Originator:     coypu
>Release:        NetBSD 8.99.45
>Organization:
>Environment:
NetBSD lite 8.99.45 NetBSD 8.99.45 (ERLITE) #0: Tue Jun 18 16:46:03 UTC 2019  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/evbmips/compile/ERLITE evbmips
>Description:
# ktruss -i -o /tmp/out gdb -q /usr/pkg/bin/sudo
Reading symbols from /usr/pkg/bin/sudo...
(No debugging symbols found in /usr/pkg/bin/sudo)
(gdb) r
Starting program: /usr/pkg/bin/sudo 
ptrace: Invalid argument.
(gdb) quit
A debugging session is active.

        Inferior 1 [process 29224] will be killed.

Quit anyway? (y or n) y
# kdump /tmp/out |grep ptrace
 29224      1 gdb      CALL  netbsd32_ptrace(PT_TRACE_ME,0,0,0)
 29224      1 gdb      RET   netbsd32_ptrace 0, 2013919680/0x7809f9c0
 28983      1 gdb      CALL  netbsd32_ptrace(PT_GET_PROCESS_STATE,0x7228,0x7fff6db8,8)
 28983      1 gdb      RET   netbsd32_ptrace 0, 65535/0xffff
 28983      1 gdb      CALL  netbsd32_ptrace(PT_GET_SIGINFO,0x7228,0x7fff6ed0,0x88)
 28983      1 gdb      RET   netbsd32_ptrace -1 errno 22 Invalid argument
       "ptrace: Invalid argument."
kdump: Unhandled size 168 for ktrpsig
kdump: Unhandled size 168 for ktrpsig
 28983      1 gdb      CALL  netbsd32_ptrace(PT_KILL,0x7228,0,0)
 28983      1 gdb      RET   netbsd32_ptrace 0, 8

>How-To-Repeat:

>Fix: