Old amd64 Ubuntu won't start

Host environment

• Operating system: Gentoo
• OS/kernel version: Linux holo 6.6.41-gentoo-dist #1 SMP PREEMPT_DYNAMIC Thu Jul 18 14:37:53 -00 2024 x86_64 AMD Ryzen 3 2200G with Radeon Vega Graphics AuthenticAMD GNU/Linux
• Architecture: x86_64
• QEMU flavor: qemu-system-x86_64
• QEMU version: QEMU emulator version 9.0.91 (v9.1.0-rc1-21-g9eb51530c1-dirty)
• QEMU command line:

qemu-system-x86_64 -enable-kvm -m 1G -cdrom ubuntu-6.06.1-desktop-amd64.iso

Emulated/Virtualized environment

• Operating system: Ubuntu 6.06.1
• OS/kernel version: Linux ubuntu 2.6.15-26-amd64-generic #1 SMP PREEMPT Thu Aug 3 02:52:35 UTC 2006 x86_64 GNU/Linux
• Architecture: x86_64

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

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.