How to read the reason for Kernel reboot?

Currently i am using __setup("warmboot=",myfunc)

But it looks like i can use this on only one time. If i do this for two times in two drivers only one guy is getting called.

Is there any way i could read the reason for reboot.

I want to read it so that i can get the reason that is stored.

like 0xABADBABE is watchdog 0xCODEDEAD is panic. Etc..

Please suggest an alternative approach.

Thanks,
manty