Old amd64 Ubuntu won't start
Description of problem:
While taking a trip down memory lane, I noticed that old Ubuntu amd64 live CDs won't boot in qemu-system-x86_64, while i386 ones work fine. I can confirm this for 6.06 and prior releases, while 8.04 and forward are OK (I don't have interim releases isos).
Steps to reproduce:
1. Launch qemu-system-x86_64 with Ubuntu 6.06.1 amd64 live CD
2. Press "Start or install Ubuntu"
3. PANIC: early exception rip (etc, please see screenshot below)
Additional information:
![Schermata_da_2024-08-13_22-07-14](/uploads/b25474a5bc984e330c1cec32677db2bb/Schermata_da_2024-08-13_22-07-14.png)

I tried a few versions of QEMU and I can tell you that everything worked fine in 7.0.0 and it first broke in 7.1.0. I don't have a more precise bisect, sorry. I also tried in Fedora 40 with QEMU 8.2.2 and I have the same issue, so I don't think it's distro related.

On the other hand, on a completely different PC with an Intel Core i3-330M I have no issue at all, even with QEMU 8.2.3, so it might be AMD/Ryzen related.