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Re: Test Proposal for [bug #46716] Protective MBR partition is not marke

From: Thomas Schmitt
Subject: Re: Test Proposal for [bug #46716] Protective MBR partition is not marked as bootable
Date: Mon, 04 Jan 2016 22:10:08 +0100


Alexander E. Patrakov wrote:
> Robert Jones found an
> iMac (iMac5,2, boot ROM version IM52.0090.B00) that boots from "mbr_only"
> but doesn't boot from "mjg" when attepted to boot from USB

Can you get him to test a Debian netinst image ?
They are ISOLINUX/GRUB2 hybrids in "mjg" layout. See below for
URL and layout description.

> Please inspect these iso images to make absolutely sure that we are talking
> about the same thing:

So let's classify the ISOs:

> shows one working EFI option

Looks like "mbr_only" with MKRESCUE_SED_PROTECTIVE=no.
Partition 1 of type 0xcd is mountable as ISO, which is good.
Partition 2 0xef is outside ISO range, which is not optimal
(but inavoidable since ISO is caged in partition 1 and EFI forbids
partition overlapping).

One can have it vice versa: not mountable and partition 2 inside ISO

> doesn't show up in the menu

Partition 1 0xcd is not mountable, which is not optimal.
Partition 2 0xef is outside ISO range, which is not optimal.
GPT marks EFI partition but is not announced by MBR with single
partition of type 0xee and thus should be ignored by EFI.
HFS+ filesystem and EFI partition are announced in Apple Partition Map.

> doesn't show up in the menu

"mjg" with MKRESCUE_SED_PARTNO=1 and option --mbr-force-bootable.
Partition 1 0xef for EFI, outside the ISO (i should improve this case
by expanding the ISO to the end of partition 2).
Partition 2 is a dummy of type 0x00 with "bootable/active" flag.
GPT, HFS+, and APM like in minimal-mjg-p2.iso.

> shows two working EFI options

"original" with CPPFLAGS="-DLibisofs_mjg_boot_for_grub2 and option
Partition 1 is of type 0xee and points EFI to the GPT.
Partition 2 is a dummy of type 0x00 with "bootable/active" flag.
GPT marks EFI and HFS+.
APM marks HFS+.
No gap filler partitions because of -DLibisofs_mjg_boot_for_grub2.

I really can see only one path to the EFI partition.
Vladimir's HFS+ files must contain the magic for the second EFI offer.

These Debian ISOs show the original mjg layout


Mountable partition 1 of type 0x00 with "bootable/active" flag
encloses partition 2 of type 0xef which points to EFI FAT image
(the file which serves as EFI El Torito boot image).
The same in GPT: partition 1 covers the ISO and would be mountable
if recognized. Partition 2 is inside partition 1 and marks the
APM points to EFI FAT. (I am nagging since years that it shall
be removed. But debian-cd has big inertia.)

Have a nice day :)


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