Once make finishes successfully the configured output results can be found in the folder:
The cpio archive can be used as a ramdisk for mkbootimg (learn more in the guide How to build Linux mainline kernel for Xperia devices):
mkbootimg … --ramdisk output/images/rootfs.cpio ...
However, the size of the ramdisk is restricted by the size of the boot partition, so once more components are compiled in we need to flash the ext4 image in one of the partitions.
fastboot flash system output/images/rootfs.ext4
We can either use this partition directly or via an ramdisk that uses pivot_root. As we have working eMMC we can use the former for now. To do this we need to add an empty ramdisk to our boot.img and specify the partition as root on the kernel command line:
dd if=/dev/zero of=dummy.img bs=4096 count=1
mkbootimg … --ramdisk dummy.img ...
To configure the Linux kernel to wait for the eMMC to become ready and use the “system” partition as root filesystem, use:
Make sure to replace “25” with the partition number for the “system” partition on your device.
This will provide a basic Linux environment that can be used for testing new kernel features.