Hi, there is a copy of the -G image file in the ISO:
/boot/grub/sparc64-ieee1275/cdboot.img It has only 512 bytes. Very non-zero. But block 0 is for the SUN disk label (partition table). libisofs overwrites it completely at ISO production time. See https://sources.debian.org/src/libisofs/1.5.0-1/libisofs/system_area.c/#L776 grub-mkrescue copies stuff to bytes 512 to 767 of its -G image. Maybe you should prepend 512 0-bytes to your cdboot.img. Have a nice day :) Thomas
