kern_trap() broken fall-through for unhandled kernel-mode traps (T_PROTFLT/T_SEGNPFLT/T_BPTFLT/T_TRCTRAP): NULL p/lp deref for kernel threads, trapsignal(lp, i=0) sig-0 OOB read/call, and handler-returns-to-faulting-instruction livelock — pc64 ends these cases in trap_fatal

Summary

The vkernel copy breaks out of its switch where pc64 ends in trap_fatal: kernel threads (td_proc==NULL) deref NULL p inside the SA_NODEFER SIGSEGV handler -> recursive fault to stack exhaustion; emulated threads call trapsignal(sig=0) whose _SIG_WORD(0)=-1 reads one word below the sigset and a set bit 31 indexes ps_sigact[-1] and CALLS it; or silent 100%-CPU refault livelock instead of a diagnosable panic. Requires a partner vkernel kernel-mode #GP bug to reach. Match-pc64-trap_fatal fix.