Look at common-vars.sh for some variables that can be changed (disk name, amount of memory).
Run install-vm.sh to create a new VM.
- Install with the basic Ubuntu server configuration. I recommend LVM if you decide to resize the image later.
Run extract-kernel.sh to get the linux kernel/initrd from the install disk image. This should work for LVM qcow2 images. You'll need to install libguestfs-tools.
Run run-vm.sh every time you want to start the VM. ^a-x to kill qemu.
Once you get the VM working, reinstall Lapidary inside the VM and do all of your gem5 work within the VM.
I know that there are many ways to do this, but I find the raw qemu approach to work the best across a variety of setups.