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Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions

From: Thomas Schmitt
Subject: Re: [Bug-xorriso] ISO installer image: GPT versus MBR partitions
Date: Thu, 25 Apr 2019 17:09:05 +0200


Florian Pelz wrote:
> I do not know and did not try yet how to configure GRUB to produce
> both 32-bit and 64-bit EFI.

As Debian user i am in the comfortable position to install the
three binary packages for BIOS, x86 EFI 32 bit, and x86 EFI 64 bit.
Then grub-mkrescue knows what to do.

Some digging in the source of grub-mkrescue and util/grub-install-common.c
reveils that it is about the existence of $cpu-$firmware directories
with lots of .mod files in them:

  $ ls /usr/lib/grub
  grub-mkconfig_lib  i386-efi  i386-pc  x86_64-efi

The binary Debian packages nearly entirely consist of one of these
directories, each:

But i don't know the tool which is to be used for creating those
directories and for filling them with .mod files.

Maybe you find some GRUB tool usage in the Guix ISO production which
uses parameters like "x86_64" "efi".
Or the name "grub-mkconfig_lib" gives a hint ? man grub-mkconfig and
info chapter are quite sparse.

> (Would putting both 32-bit and 64-bit
> bootefi files in EFI/Boot/ be a good idea for Guix ISOs in general, or
> could this lead to problems with 64-bit machines or lead to confusing
> boot selection screens?)

It should be perfectly ok to combine several EFI start programs in
one EFI partition. The firmware is supposed to pick what it deems
UEFI 2.4 "Removable Media Boot Behavior":

  "[...] the system firmware will attempt to boot from a removable media
   FilePathList[0] by adding a default file name in the form
     \EFI\BOOT\BOOT{machine type short-name}.EFI.
   Each file only contains one UEFI image type, and a system may
   support booting from one or more images types."

You could even combine "IA32", "X64", "ARM", and "AA64" programs if you
manage to keep all CPU specific files apart in the course of the further
operating system run.

> The Lenovo Ideapad 100S’s owner tried a USB drive prepared with a
> purely 32-bit GRUB [...]
>   export MKRESCUE_SED_MODE=mbr_hfs
>   export MKRESCUE_SED_IN_EFI_NO_PT=yes
>   grub-mkrescue --xorriso=./grub-mkrescue-sed.sh  \
>                 -iso_mbr_part_type 0x83 -partition_offset 16 \

> and it boots fine.

So that's not the mad EFI which hates all MBR partitions except one 0xef.

> a DVD with an untreated Guix
> git master could not be booted but very likely due to an error with my
> external DVD drive (it often does not work)

We could start a separate endeavor in private for diagnosing that.
(My other sport besides ISO 9660 is burning flat round things.)

> I will try a current git master Guix iso built for 32-bit next.  If it
> does not work (guixsd-install-0.15.0.i686-linux.iso did not work), I
> will try the same with
> dd if=/dev/zero bs=1 count=16 seek=446 of=/dev/sdc2

Was the machine similarly stuck as the Macbook ?
That would probably be the partition problem, indeed.

But failure when GRUB or a Linux kernel have taken over would be a
different problem. The minimal grub-mkrescue ISO would then possibly
work because it prompts the user before the problem can occur.
Or maybe because it has a .mod file that is needed for that machine ?

Have a nice day :)


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