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Re: xorriso and EFI boot images

From: Thomas Schmitt
Subject: Re: xorriso and EFI boot images
Date: Thu, 22 Apr 2010 20:00:13 +0200


the fresh development upload of xorriso-0.5.5
with timestamp 2010.04.22.160615 implements the
wish about --efi-boot :

Vladimir Serbinenko wrote 17 Apr 2010:
> I would like to have efi+bios cd with 2 eltorito
> entries: one with platformid=0 and another one with platformid=0xef.
> [...]
> I would like that on hybrid BIOS always come in
> default entry to avoid hitting BIOS bugs
> In case of just EFI the Section header entry and Section entry become
> Validation entry and default entry.

So now xorriso -as mkisofs has this provisory

-b is for 80x86 BIOS images, platform ID 0.
Options -boot-load-size, -no-emul-boot,
-boot-info-table affect this -b boot image.

--efi-boot is for EFI images, platform id 0xef.
Hardcoded are: no emulation, no boot info table.
The load size is obtained from the size of the
EFI image file and rounded up to full 512 byte

Prone to change is the current rule that the
EFI image always is second if a BIOS image is
present. I will probably make this depending on
the sequence of options in future.
Please take care in grub-mkrescue to express
your desired sorting by giving -b before


Quote from El Torito 1.0 paragraph 2.3
"The section header has an identification string.
 If the BIOS understands the ID, string it may
 choose to boot the system using one of these
 entries in place of the INITIAL/DEFAULT entry."

What does that mean: "the BIOS understands" ?
Do we have to write something particular in
there for EFI ?
Any idea what one would have to write in case of
a 80x86-BIOS image ?

The Validation Entry has an ID too.
But that is defined as quite meaningless:
"This is intended to identify the
 manufacturer/developer of the CD-ROM."


Currently libisofs is able to write and read up
to 32 boot images. It writes each image entry
into an own section, but i plan to allow sections
of more than one image entry and user provided
ID strings.

xorriso on the other hand got only a primitive
extension efi_path, which lives beneath bin_path.
This is not flexible. So i plan for improvements.
Nevertheless, the option sequence
  -b ... --efi-boot ...
is promised to always lead to Vladimir's intended
boot catalog structure.


I tested with dummy boot images.
The boot catalog entries seem to be ok.
Now i am curious whether i misunderstood the
specs somewhere or whether it really would boot.

Have a nice day :)


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