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Re: [bug #46716] Protective MBR partition is not marked as bootable

From: Thomas Schmitt
Subject: Re: [bug #46716] Protective MBR partition is not marked as bootable
Date: Sat, 19 Dec 2015 16:50:37 +0100


[resending to bug-grub after rejection message]

Alexander E. Patrakov wrote:
> > http://www.syslinux.org/wiki/index.php/Isohybrid

This is quite independent of what GRUB2 does.
(SYSLINUX and GRUB2 meet at BIOS and EFI, of course.)

Andrei Borzenkov wrote:
> Command from syslinux wiki does not create protective MBR; it creates
> normal DOS partition of type 17 and marks it as bootable.

Especially the SYSLINUX partition is mountable as it starts
at the begin of the ISO filesystem. :))

Looking at the source code of libisofs, i'd expect that the
bootability flag is set if GRUB2 related option
is given. At least Vladimir Serbinenko prescribed it to me.


>>> 3) Put 0x80 (for bootable partition), 0, 2, 0 (C/H/S of the start), 0xcd
>>> (partition type), [3 bytes of C/H/S end], 0x01, 0x00, 0x00, 0x00 (LBA
>>> start in little endian), [LBA end in little endian] at 446-462

This might be a regression which nobody noticed yet.

> Marking protective partition as bootable may trigger bugs on EFI, so I
> am not sure if it is reallu desirable.

If the needs for BIOS and EFI are incompatible, then we should
add an option to xorriso which controls this.
Probably an alternative to --protective-msdos-label.
But first i must find out what's going on inside libisofs.

For the investigation i could need:

- An ISO produced by grub-mkrescue as used by Alexander.
  Lean would be nice. Please post download URL.
  Newest xorriso releases can deduce the used options from the
  ISO and replay them.
  Please also tell your exact grub-mkreascue arguments.

- A quick starter for Debian Jessie or Sid how i get to the same
  GRUB2 environment in which Alexander runs grub-mkrescue.
  (This is on my todo list since half a year. I apologize.)

Have a nice day :)


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