buildroot/board/pc/genimage-bios.cfg

image disk.img {
	hdimage {
	}

	partition boot {
		in-partition-table = "no"
		image = "boot.img"
		offset = 0
		size = 512
		holes = {"(440; 512)"}
	}

	partition grub {
		in-partition-table = "no"
		image = "grub.img"
		offset = 512
	}

	partition root {
		partition-type = 0x83
		image = "rootfs.ext2"
	}
}