buildroot/board/asus/tinker/genimage.cfg

image sdcard.img {
	hdimage {
	}

	partition u-boot-spl-dtb {
		in-partition-table = "no"
		image = "u-boot-spl-dtb.img"
		offset = 32K
	}

	partition rootfs {
		partition-type = 0x83
		image = "rootfs.ext4"
	}
}