I have been trying to port ubuntu touch using ubport's source tree and currently i was able to finish building. I flashed boot.img using heimdall and was able to boot into recovery.
After that I used rootstock to install the ubuntu preinstalled tar and system.img. It didn't work initially but after bunch of checking around I finally got it working. So after rootstock finished its job my device rebooted and stuck in bootloop.

I rebooted into recovery and check /proc/last_kmsg and this was what the last line said:
Starting kernel at 0x81808000...

So anyone have any idea what went wrong and what can I do to get to working?
Thanks.