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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: Sun, 20 Dec 2015 13:24:36 +0100


i wrote:
> >    error: disk `' not found.

Alexander E. Patrakov wrote:
> The "ls" command in this case finds only (hd0), (fd0), (fd1) and (cd0)

I meanwhile found the strings in /efi.img
  disk `%s' not found
  grub rescue> 

So OVMF starts GRUB2.

To clarify whether via MBR x86 code in BIOS legacy mode or
via partition 2 in EFI MBR legacy mode, i kill the MBR x86 code:
  $ dd conv=notrunc of=minimal-grub2-repacked.iso \
       bs=1 count=446 if=/dev/zero

OVMF still brings me to "grub rescue>".

So the running GRUB2 indeed stems from partition 2.

But then GRUB2 lacks info from OVMF about the partitions ?

> Given this failure, I will not test this repacked iso on real hardware.

Your choice, of course.
It would be interesting, though, to see what happens on a
different EFI implementation. Maybe OVMF is too much addicted
to GPT.
(Not that we could ignore it. But at least we could blame it.)

> I'd try to repack the iso with the command that was similar to the one
> passed to xorriso by grub-mkrescue.

The goal was to try a layout with MBR boot flag, without GPT, and
with mountable ISO partition.

The current grub-mkrescue layout seems to work better with OVMF
... if i did not make a stupid mistake with my repack proposal.

I will try whether MBR partition table manipulations can make it
more tasty for OVMF. But together with Andrei's opinion:

> > Also I am sure some people will be rather reluctant to add duplicate ESP

my proposal seems to be dead.

(It does work for Debian arm64 ISOs, afaik.)


Do you want to try whether the wrapper partition of type 0x00 with
boot flag works on all your machines ? 
You would have to manipulate the MBR partition table to become either

  MBR partition table:   N Status  Type        Start       Blocks
  MBR partition      :   1   0x00  0xef          336         5760
  MBR partition      :   2   0x80  0x00            0        32852

or with swapped partition entries

  MBR partition      :   1   0x80  0x00            0        32852
  MBR partition      :   2   0x00  0xef          336         5760

The rest would stay as comes out of current grub-mkrescue.

Have a nice day :)


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