[Bug 1062737] Re: hybrid images do not include a valid GPT

[Thomas Schmitt]

Hi,

> I've built a test image now using the cherry-picked patch from 1.2.5,
> and confirmed that the -partition_offset option now happily coexists
> with -isohybrid-gpt-basdat

Thanks a lot for testing.

> However, as the resultant image still appears to not have a valid MBR
> partition table, there doesn't seem to be any advantage to adding this
> option back to our builds for 12.10.  So I think we'll leave it as is
> with -partition_offset 16 disabled for now.

Do you rather mean "no valid GPT" ?
The MBR seems to be ok now. After all it made the difference
between boot and not-boot.

The GPT is there but it usually not recognized because the MBR
is not trivial enough (not a "protective MBR"). This should have
nothing to do with -partition_offset.
If it has, then this would be probably another bug.

I googled a bit and found:
  http://www.rodsbooks.com/gdisk/hybrid.html
The described "Hybrid MBR" would differ from mjg's mainly by the
type of the first MBR partition: 0xee rather than 0x00 im mjg's.

So does it help GPT visibility to set byte 450 of the ISO image
to the value 0xee ? (Byte count starting at 0)


Have a nice day :)

Thomas

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https://bugs.launchpad.net/bugs/1062737

Title:
  hybrid images do not include a valid GPT

Status in Ubuntu CD image build software:
  Fix Released
Status in “libisofs” package in Ubuntu:
  Triaged

Bug description:
  The insyde UEFI firmware implementation does not see the GPT on the
  hybrid images generated on nusakan (e.g., the 12.10 beta2 image).
  This appears to be consistent with what both gdisk and parted show:

  $ gdisk -l ~/devel/iso/ubuntu-12.10-beta2-desktop-amd64.iso 
  GPT fdisk (gdisk) version 0.8.5

  Partition table scan:
    MBR: MBR only
    BSD: not present
    APM: not present
    GPT: not present

  
  ***************************************************************
  Found invalid GPT and valid MBR; converting MBR to GPT format.
  ***************************************************************

  Disk /home/vorlon/devel/iso/ubuntu-12.10-beta2-desktop-amd64.iso: 1548288 sectors, 756.0 MiB
  Logical sector size: 512 bytes
  Disk identifier (GUID): 1ADDF8C9-5CE1-41A4-9124-2CC80EED991F
  Partition table holds up to 128 entries
  First usable sector is 34, last usable sector is 1548254
  Partitions will be aligned on 2048-sector boundaries
  Total free space is 1548221 sectors (756.0 MiB)

  Number  Start (sector)    End (sector)  Size       Code  Name
  $

  Removing the -partition_offset 16 option from the xorriso commandline
  is sufficient to generate an image with a recognizable partition
  table; but I imagine this causes other problems for hybrid systems.

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