Hi,
another experiment proposal for Dominik 'Rathann' Mierzejewski:
Zeroize the GPT of a copy of boot-grub2-f36.iso and adjust MBR partition 1.
Do this in bash for the $'\x...' gestures:
# Create the playground
cp boot-grub2-f36.iso test.iso
# Zeroize the main GPT
dd if=/dev/zero bs=1 seek=512 count=32256 conv=notrunc of=test.iso
# Zeroize the header block of the backup GPT
dd if=/dev/zero bs=512 seek=1334219 count=1 conv=notrunc of=test.iso
# Set the boot flag to MBR partition 1
echo $'\x80' | dd bs=1 seek=446 count=1 conv=notrunc of=test.iso
# Change the partition type to 0x17 (as with BIOS-only ISOLINUX isohybrid)
echo $'\x17' | dd bs=1 seek=450 count=1 conv=notrunc of=test.iso
# Set the start of MBR partition 1 to LBA 64, so that it is mountable
echo $'\x40' | dd bs=1 seek=454 count=1 conv=notrunc of=test.iso
# Append 63 blocks of 512 bytes to compensate for the new start LBA
# with the old partition size. (Else partition editors will hate the
# image because it is too small for the partition.)
dd if=/dev/zero bs=512 count=63 >>test.iso
Check whether partition editors like the result and see the boot flag:
$ /sbin/fdisk -l test.iso
...
Disklabel type: dos
...
Device Boot Start End Sectors Size Id Type
test.iso1 * 64 1334282 1334219 651.5M 17 Hidden HPFS/NTFS
Put test.iso onto the USB stick as usual.
The result is supposed to boot from USB stick only via legacy BIOS.
EFI would still see the System Partition on a CD or DVD because it is
announced by the El Torito catalog.
If it does not boot on the Dell XPS 15 L502X, try whether it boots on
some other BIOS machine.
I only roughly tested that
qemu-system-x86_64 -enable-kvm -m 512 -hda test.iso
boots to the GRUB menu.
Have a nice day :)
Thomas