[Qemu-devel] Bug: FC6 x86_64 guest causes illegal instructions on QEMU 0.8.2 on 32-bit P4 host

[Kevin Kofler]

I have encountered an issue which I think is a bug in QEMU. I'm running QEMU 
0.8.2 (from the Fedora Extras RPM: qemu-0.8.2-3.fc6.i386.rpm) on a 32-bit 
Pentium IV running Fedora Core 6 (as host OS). (And yes, that RPM is built with 
compat-gcc-32 (GCC 3.2), not GCC 4.x, so that's not the problem.) Using 
qemu-system-x86_64, I can install (using the x86_64 boot.iso and a HTTP 
installation) and run CentOS 4.4 x86_64 (as the guest) with no problems. (Even 
the speed is acceptable when keeping in mind that this is an emulated 
instruction set.)

Unfortunately, trying to do the same thing with Fedora Core 6 as the guest 
doesn't work:
* If I try to boot the FC6 x86_64 boot.iso, it only goes as far as "Booting 
kernel." and then the emulated machine locks up. Trying to boot the vmlinuz 
directly (bypassing the syslinux bootloader) doesn't change anything. Looking 
at the debugging logs, I see the installer hits an "illegal" instruction (an 
instruction unknown to QEMU actually, as the boot.iso is known to work on real 
x86_64 hardware) early in the kernel.
* So what I tried next is setting up an FC6 x86_64 chroot in the installed 
CentOS 4.4 x86_64 guest using the "mock" tool. This works as long as it is only 
setting up the chroot from the host system, but as soon as a binary from the 
FC6 chroot is run, it hits an illegal instruction again. (This time it just 
kills the FC6 executable and returns to CentOS 4.4 bash with the error.) So 
it's not just the kernel which doesn't work.

Is this enough information to reproduce and fix the problem? (The images I used 
are all publically available.) Or do you want me to provide some logs? (Which 
ones?)

        Kevin Kofler