KmodDebugging

Get your coredump.
Start kgdb: kgdb /var/crash/kern.X /var/crash/vmcore.X.
Load some handy helper commands when you're at the kgdb prompt: source /usr/src/test/debug/gdb.kernel.
Get the kld statistics from the kernel: kldstat at the kgdb prompt.
Background kgdb (^Z).
Execute a helper utility to create another gdb script: asf -s /modules.
Paste the output from the kgdb 'kldstat' command above.
Signal asf that you're ready (^D).
Foreground kgdb again: fg.
Load the gdb script created by asf above to load kmod symbols: source .asf at the kgdb prompt.
Print, list, backtrace to your heart's content! Be sure to have debug symbols compiled with your modules though ;).