Qemu refuses to multiboot Elf64 kernels

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1811888
Reported by 'Lukasz Janyst' on 2019-01-15 :

Qemu does not multiboot Elf64 bit kernels when emulating x86_64 systems.
This is unfortunate because it renders the `-kernel` option quite useless.
It's true that a multiboot compatible bootloader puts you in protected
mode by default, and you have to set up the long mode yourself. While it
is easy to put such 32-bit bootstrap code in a 64 bit binary, it is not
possible to compile a 64 bit kernel into a 32 bit binary.

After quick search, it turned out that loading 64 bit elf binaries has
been disabled to be compatible with GRUB. However, since that time, both
GRUB and Syslinux load 64 bit ELF kernels just fine, which makes qemu
incompatible with them. Furthermore, it seems that this feature does and
has always worked fine and that people have since submitted patches to re-
enable it.

https://patchwork.ozlabs.org/patch/62142/
https://patchwork.kernel.org/patch/9770523/

Please consider applying the attached patch.

Best Regards,
Lukasz Janyst