Hi, Chris Murphy wrote: > Is there a possibility of dropping MBR? i.e. use GPT containing both a > biosboot partition type, and EFI System partition type? I am not aware that legacy BIOS would hop directly on any GPT partition or any MBR partition table partition. The convention for hard-disk-like devices is to start the x86 code in bytes 0 to 439 (or maybe to byte 445) of the MBR as 16-bit program. In case of ISOLINUX or GRUB hybrid MBR, the only goal is to hand over program execution to the El Torito boot image which is allowed to be larger and is also the starting point for booting from DVD. The connection is made by xorriso by patching the LBA of the boot image into the x86 code of the MBR. Format and byte address for this patching depends on the boot loader. Thus the mutually exclusive options -isohybrid-mbr and --grub2-mbr. > The advantage of this is not just to get rid of MBR really. We have the room for those 440 bytes anyways if we have GPT. The magic number of GPT is the "protective" MBR partition table at bytes 446 to 509. There must be one partition slot of type 0xee and no other valid partition marked by the other three slots. The content of bytes 0 to 439 is specified by UEFI for "Protective MBR" as "Unused by UEFI systems". In contrast to that, the bytes from 440 to 445 are specified as "Unused. Set to zero." (UEFI 2.4 Table 15, UEFI 2.8 Table 19) > But if > there are still some systems out there that will face plant on GPT > anyway, it's probably best if they face plant when booting the > installation media rather than getting all the way to a successful > installation, just to face plant upon reboot. Legacy BIOS does not care for partition tables. At least to my knowledge from supporting production of bootable ISOs. My mileage may vary. Problems with partitions will arise only after BIOS handed control to the MBR x86 code on USB stick or the El Torito boot image on DVD. Possibly this here describes what is needed for GRUB if started by legacy BIOS and facing GPT: https://wiki.archlinux.org/title/GRUB#BIOS_systems I understand that the GPT boot partition substitutes for the traditional gap between MBR block and the start of the first MBR partition. 1 MiB of "embedded area" if i remember correctly. But grub-mkrescue ISOs have GPT without a dedicated boot partition. Probably that job is fulfilled by the El Torito boot image which has a few more KiB than the MBR x86 code. So i assume that face planting will happen only at later stages if the booted system makes false assumptions like "GPT means EFI". Have a nice day :) Thomas _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
