DF-0715: issuing SMBIOC_OPENSESSION with ioc_svlen=0
  expected: kernel panic (fatal trap: read of sa->sa_len at (void*)-8 == 0xFFFFFFFFFFFFFFF8, non-canonical x86-64 GPF)
[ssh session hangs — guest panicked; serial console captures the panic:]

--- from dfbsd-qemu/boot.log (unpatched #0 kernel) ---
Fatal trap 12: page fault while in kernel mode
fault virtual address	= 0xfffffffffffffff8
fault code		= supervisor read data, page not present
instruction pointer	= 0x8:0xffffffff806c9c98
stack pointer	        = 0x10:0xfffff80118483518
frame pointer	        = 0x10:0xfffff80118483528
code segment		= base 0x0, limit 0xfffff, type 0x1b
Stopped at      dup_sockaddr+0x18:      movzbl  (%rdi),%edi
db>
[guest down — ssh connection lost]