Default unpacking and repacking boot.img from stock rom
Hi all,
Since it took me some time to figure out the correct values I guess this info can be useful to someone out there

1) the boot partition is mmcblk0p20 but it is signed. To get something meaningful out of it you need to drop the head of it

Code:
dd if=/dev/block/mmcblk0p20 of=boot.img bs=256 skip=1
2) to repack you need to pass the options
Code:
 --pagesize 2048 --base 40400000
to mkbootimg