illumos gate

Debugging another issue, I have mdb repeatedly crashing while trying to walk a list_t

> $C
fffffd7fffdfe7f0 genunix.so`list_walk_step+0xac()
fffffd7fffdfe820 walk_step+0x5e()
fffffd7fffdfe840 walk_common+0x71()
fffffd7fffdfe870 mdb_pwalk+0x3f()
fffffd7fffdfe8b0 cmd_walk+0x138()
fffffd7fffdfe900 dcmd_invoke+0x64()
fffffd7fffdfe970 mdb_call_idcmd+0x1f8()
fffffd7fffdfea40 mdb_call+0x1fc()
fffffd7fffdfeb30 yyparse+0x50d()
fffffd7fffdfec50 mdb_run+0x2cd()
fffffd7fffdffa50 main+0x13af()
fffffd7fffdffa60 0x42687c()

The list I am walking is, presumed to be partially trashed (that's why I'm walking it, in fact, as confirmation), but mdb should be resilient to that.