Re: ISO installer image: GPT versus MBR partitions

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i plan to ask at gru-devel about mformat, its MBR, and the partition entry,
as soon as the last experiment is made (LBA 1 rather than LBA 0 as start
of the inner partition).

For that discussion i could also need the exact model name of the Macbook.
If its EFI has a name, then this too.


Florian Pelz wrote:
> +--- grub-2.02/util/grub-mkrescue.c     2019-04-21 08:17:18.880000000 +0200
> ++++ grub-2.02/util/grub-mkrescue.c     2019-04-21 08:17:52.588000000 +0200
> [...]
> +-      { "mformat", "-C", "-f", "2880", "-L", "16",
> ++      { "mformat", "-k", "-C", "-f", "2880", "-L", "16",

The difference between the contents of the first image block with and
without option -k is significant, at least if we ask program "file".

If a special version of gub-mkrescue is acceptable, then i would rather
propose to apply the dd treatment to   efiimgfat  after mformat created
it without option -k.

We could ask at grub-devel for advise how to write 16 bytes to that file
without needing another shell command. (It's C language, after all.)

The binary differences between both blocks 0, except partition entry, are:

/efi.img from Guix 0.16.0
#########################
Image from mformat -k

00000000 :    eb  3c  90  4d  54  4f  4f  34  30  32  31  00  02  01  01  00
             ### ### ### ### ### ### ### ### ### ### ###
00000000 :    00  00  00  00  00  00  00  00  00  00  00  00  02  01  01  00

00000020 :    00  00  00  00  00  00  29  a7  48  66  33  4e  4f  20  4e  41
                                         ### ### ### ###
00000020 :    00  00  00  00  00  00  29  42  87  4b  7d  4e  4f  20  4e  41

00000030 :    4d  45  20  20  20  20  46  41  54  31  32  20  20  20  fa  31
                                                                     ### ###
00000030 :    4d  45  20  20  20  20  46  41  54  31  32  20  20  20  00  00

00000040 :    c0  8e  d8  8e  c0  fc  b9  00  01  be  00  7c  bf  00  80  f3
             ### ### ### ### ### ### ###     ### ###     ### ###     ### ###
00000040 :    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00

00000050 :    a5  ea  56  00  00  08  b8  01  02  bb  00  7c  ba  80  00  b9
             ### ### ###         ### ### ### ### ###     ### ### ###     ###
00000050 :    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00

00000060 :    01  00  cd  13  72  05  ea  00  7c  00  00  cd  19  00  00  00
             ###     ### ### ### ### ###     ###         ### ###
00000060 :    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00

...

000001f0 :    00  00  00  00  00  00  00  00  00  00  00  00  00  00  55  aa
                                                                     ### ###
000001f0 :    00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00


Have a nice day :)

Thomas