kern/53280: amd64 panics since recent compat/netbsd32 commits

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

>Number:         53280
>Category:       kern
>Synopsis:       amd64 panics since recent compat/netbsd32 commits
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 12 14:50:00 +0000 2018
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date >= 2018.05.10.02.36.26
>Organization:
>Environment:
System: NetBSD guava.gson.org 7.1.1 NetBSD 7.1.1 (GENERIC.201712222334Z) amd64
Architecture: x86_64
Machine: amd64
>Description:

Running the lib/libbpfjit/t_bpfjit test, NetBSD/amd64 panics with:

    libbpfjit_opt_ld_abs_3: [0.009291s] Passed.
    libbpfj[ 893.0457576] panic: mbuf 0xffffe407d8f81800 already freed
[ 893.1124434] cpu0: Begin traceback...
[ 893.1572333] vpanic() at netbsd:vpanic+0x16f
i[ 893.2072275] snprintf() at netbsd:snprintf
t[ 893.2561867] m_cat() at netbsd:m_cat
[ 893.2968113] m_freem() at netbsd:m_freem+0xe
_[ 893.3468085] unp_send() at netbsd:unp_send+0x9b
[ 893.4009719] sosend() at netbsd:sosend+0x83b
[ 893.4509703] do_sys_sendmsg_so() at netbsd:do_sys_sendmsg_so+0x27d
[ 893.5259668] do_sys_sendmsg() at netbsd:do_sys_sendmsg+0x73
[ 893.5895060] netbsd32_sendmsg() at netbsd:netbsd32_sendmsg+0x7b
[ 893.6592946] netbsd32_syscall() at netbsd:netbsd32_syscall+-0x1e5b9e
[ 893.7363745] cpu0: End traceback...

Bisection shows the problem started with the following commits:

  2018.05.10.02.36.07 christos src/sys/compat/netbsd32/netbsd32.h 1.118
  2018.05.10.02.36.07 christos src/sys/compat/netbsd32/netbsd32_compat_20.c 1.37
  2018.05.10.02.36.07 christos src/sys/compat/netbsd32/netbsd32_conv.h 1.35
  2018.05.10.02.36.07 christos src/sys/compat/netbsd32/netbsd32_socket.c 1.46
  2018.05.10.02.36.07 christos src/sys/compat/netbsd32/syscalls.master 1.121
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_syscall.h 1.135
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_syscallargs.h 1.135
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_syscalls.c 1.133
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_syscalls_autoload.c 1.14
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_sysent.c 1.133
  2018.05.10.02.36.26 christos src/sys/compat/netbsd32/netbsd32_systrace_args.c 1.25

>How-To-Repeat:

Run the ATF tests.

>Fix: