Rockchip's boot image is different from standard Android boot image in that it does not contain a kernel image. actually, it's a gizped cpio ramdisk image that takes over the booting process from the kernel. In addition, there is a 8 byte header in the boot image and you need to strip that part off before you can uncompress it using gzip command.
unpack the boot images
As mentioned before, first we need to remove the 8 byte header from the image. The command is
dd if=boot.img of=boot.img.gz skip=8 bs=1 count=100000000000