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
The QEMU project is currently considering to move its bug tracking to another system. For this we need to know which bugs are still valid and which could be closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state back to "New" within the next 60 days, otherwise this report will be marked as "Expired". Or mark it as "Fix Released" if the problem has been solved with a newer version of QEMU already. Thank you and sorry for the inconvenience.