Hi,
Jack Truong wrote:
> I have copied the contents of efi.img to the FAT partition and it does boot
> on my EFI firmware now. Thank you!
So your EFI indeed hopped on that partition.
Possibly only because it sees no other indication where to start
the boot process.
I now wonder whether the MBR partition 2 is actually intended
as EFI System Partition.
The partition type 0x01 generally indicates a FAT12 filesystem.
An EFI partition should have type 0xef.
Regrettably there is no file /.disk/mkisofs in the ISO which
tells the used xorriso -as mkisofs options.
I guess that /boot/grub/efi.img got marked by an option like
-e boot/grub/efi.img
To mark this file in MBR and GPT, one may add option
-isohybrid-gpt-basdat
directly after -e and its argument.
I tested by extracting the MBR and partition 2 from mini.iso,
mounting it, and repacking a new mini_with_gpt.iso by:
$ dd if=mini.iso bs=512 count=1 of=mini_template.mbr
$ dd if=mini.iso bs=512 skip=45056 count=12288 of=mini_partition2.img
$ mount -o loop mini.iso /mnt/iso
$ xorriso -as mkisofs -R \
-o mini_with_gpt.iso \
-isohybrid-mbr mini_template.mbr \
-c '/boot.cat' \
-b '/isolinux.bin' \
-no-emul-boot -boot-load-size 4 -boot-info-table \
-eltorito-alt-boot \
-e '/boot/grub/efi.img' \
-isohybrid-gpt-basdat -no-emul-boot \
-append_partition 3 0x01 mini_partition2.img \
/mnt/iso
This yields:
Volume id : 'ISOIMAGE'
El Torito catalog : 45 1
El Torito cat path : /boot.catalog
El Torito images : N Pltf B Emul Ld_seg Hdpt Ldsiz LBA
El Torito boot img : 1 BIOS y none 0x0000 0x00 4 46
El Torito boot img : 2 UEFI y none 0x0000 0x00 832 66
El Torito img path : 1 /isolinux.bin
El Torito img opts : 1 boot-info-table isohybrid-suitable
El Torito img path : 2 /boot/grub/efi.img
System area options: 0x00000102
System area summary: MBR isohybrid cyl-align-on GPT
ISO image size/512 : 45056
Partition offset : 0
MBR heads per cyl : 64
MBR secs per head : 32
MBR partition table: N Status Type Start Blocks
MBR partition : 1 0x80 0x00 0 45056
MBR partition : 2 0x00 0xef 264 832
MBR partition : 3 0x00 0x01 45056 12288
MBR partition path : 2 /boot/grub/efi.img
GPT : N Info
GPT disk GUID : 61bf3bd0595c364488002bde6f8fecfb
GPT entry array : 2 248 overlapping
GPT lba range : 64 44992 45055
GPT partition name : 1 490053004f00480079006200720069006400
GPT partname local : 1 ISOHybrid
GPT partition GUID : 1 61bf3bd0595c364488022bde6f8fecfb
GPT type GUID : 1 a2a0d0ebe5b9334487c068b6b72699c7
GPT partition flags: 1 0x1000000000000001
GPT start and size : 1 0 44992
GPT partition name : 2 490053004f004800790062007200690064003100
GPT partname local : 2 ISOHybrid1
GPT partition GUID : 2 61bf3bd0595c364488032bde6f8fecfb
GPT type GUID : 2 a2a0d0ebe5b9334487c068b6b72699c7
GPT partition flags: 2 0x1000000000000001
GPT start and size : 2 264 832
GPT partition path : 2 /boot/grub/efi.img
Now the empty FAT12 filesystem is in MBR partition 3.
It is unclear whether it is usiable on a system that knows about GPT.
(Maybe i should enhance -append_partition so that it publishes
the partition in GPT too.)
Of course, if the empty 6 MB partition is undesired in a 22.5 MB
ISO, then one can omit option
-append_partition 3 0x01 mini_partition2.img \
from above xorriso run.
If one wants to eradicate GPT and only keep MBR:
$ cp mini_with_gpt.iso mini_with_mbr_efi.iso
$ dd if=/dev/zero bs=512 count=1 seek=1 conv=notrunc of=mini_with_mbr_efi.iso
$ dd if=/dev/zero bs=512 count=1 seek=45055 conv=notrunc
of=mini_with_mbr_efi.iso
(The backup GPT header is the last 512 block of the ISO
filesystem range. Probably the appended partition data
prevent it from being recognized at all.)
Have a nice day :)
Thomas
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