kumquat-buildroot/board/pc/genimage-efi.cfg

image efi-part.vfat {
  vfat {
    file startup.nsh {
      image = "efi-part/startup.nsh"
    }
    file EFI {
      image = "efi-part/EFI"
    }
    file bzImage {
      image = "bzImage"
    }
  }
  # 16MB - 32KB
  size = 16744448
}

image disk.img {
  hdimage {
    gpt = true
  }

  partition boot {
    image = "efi-part.vfat"
    partition-type-uuid = c12a7328-f81f-11d2-ba4b-00a0c93ec93b
    offset = 32768
    bootable = true
  }

  partition root {
    partition-type-uuid = 44479540-f297-41b2-9af7-d131d5f0458a
    partition-uuid = UUID_TMP
    image = "rootfs.ext2"
  }
}