While trying to debug crashdump from GENERIC + debug options with default cflags and cputype, kgdb failed me:

(kgdb) bt full
#0  doadump (textdump=0x1) at /home/system/ghost/usr/src/sys/kern/kern_shutdown.c:265
No locals.
During symbol reading, Incomplete CFI data; unspecified registers at 0xffffffff80906019.
#1  0xffffffff80906584 in kern_reboot (howto=0x104) at /home/system/ghost/usr/src/sys/kern/kern_shutdown.c:448
        _ep = (struct eventhandler_entry *) 0x0
        _el = Variable "_el" is not available.
(kgdb)

(kgdb) bt
#0  doadump (textdump=0x1) at /home/system/ghost/usr/src/sys/kern/kern_shutdown.c:265
During symbol reading, Incomplete CFI data; unspecified registers at 0xffffffff80906019.
#1  0xffffffff80906584 in kern_reboot (howto=0x104) at /home/system/ghost/usr/src/sys/kern/kern_shutdown.c:448
#2  0xffffffff80906a87 in panic (fmt=0x1 <Address 0x1 out of bounds>)
    at /home/system/ghost/usr/src/sys/kern/kern_shutdown.c:636
#3  0xffffffff80b2dae0 in softdep_deallocate_dependencies (bp=Variable "bp" is not available.
)
    at /home/system/ghost/usr/src/sys/ufs/ffs/ffs_softdep.c:13350
During symbol reading, unsupported tag: 'DW_TAG_const_type'.
#4  0xffffffff80986480 in brelse (bp=0xffffff80f5ea2620) at buf.h:429
#5  0xffffffff80988dd8 in bufdone (bp=0xffffff80f5ea2620) at /home/system/ghost/usr/src/sys/kern/vfs_bio.c:3347
#6  0xffffffff8086f07c in g_io_schedule_up (tp=Variable "tp" is not available.
) at /home/system/ghost/usr/src/sys/geom/geom_io.c:679
#7  0xffffffff8086f61c in g_up_procbody (arg=Variable "arg" is not available.
) at /home/system/ghost/usr/src/sys/geom/geom_kern.c:97
#8  0xffffffff808d62bf in fork_exit (callout=0xffffffff8086f5c0 <g_up_procbody>, arg=0x0, frame=0xffffff8000252c40)
    at /home/system/ghost/usr/src/sys/kern/kern_fork.c:992
#9  0xffffffff80beba6e in fork_trampoline () at /home/system/ghost/usr/src/sys/amd64/amd64/exception.S:602
#10 0x0000000000000000 in ?? ()
#11 0x0000000000000000 in ?? ()
#12 0x0000000000000001 in ?? ()

[keeps repeating]

#34 0x000000000000000b in ?? ()
#35 0xffffffff81287380 in affinity ()
#36 0x0000000000000000 in ?? ()
#37 0xfffffe0002921000 in ?? ()
#38 0xffffff8000252600 in ?? ()
#39 0xffffff80002525a8 in ?? ()
#40 0xfffffe0002919000 in ?? ()
#41 0xffffffff8092f9a9 in sched_switch (td=0xffffffff8086f5c0, newtd=0x0, flags=Variable "flags" is not available.
)
    at /home/system/ghost/usr/src/sys/kern/sched_ule.c:1913
Previous frame inner to this frame (corrupt stack?)