isohybrid: Generate GPT and Mac bootable images
EFI systems typically don't support booting off ISO 9660 filesystems,
even if written to USB sticks. This patch adds support for generating a
GPT that covers the stick as well, with an additional partition entry
pointing purely at the secondary El Torito image. When burned to CD the
secondary El Torito will be used as an EFI boot image, and when written
to a USB stick the GPT partition will be found and may be booted from.
However, some earlier EFI Macs don't support booting from El Torito
images via EFI. To cater for them this also supports generating an Apple
partition table, allowing a third El Torito image in HFS+ format to be
made available to the firmware. This requires padding the MBR images
slightly in order to leave space for the Apple header, but should have
no functional impact.
Sadly, this breaks the workaround for Acer BIOSes (magic xor
instruction) when Mac support is enabled via -m... not much that can
be done about that.
Signed-off-by: Matthew Garrett <mjg@…>
Signed-off-by: H. Peter Anvin <hpa@…>
