Buildroot is generating images for an embedded device where they should run. This is working very well. In those images, the rootfs is included.
I try to run Android from SD-card. This card is prepared. There are partitions: boot(FAT32), rootfs(ext4), system(ext4), cache(ext4) and usedata(ext4). Boot partitions has files to run u-boot: MLO, u-boot.bin and uImage. To run it I use commands