With this patch in place, ARMv7 NixOS can be booted in QEMU:
qemu-system-arm -kernel u-boot -M vexpress-a9 -serial stdio -sd nixos-sd-image-armv7l-linux.img -m 1024
...with all the features that boot.loader.generic-extlinux-compatible
supports, like the boot generation menu and seamless kernel upgrades
in the VM.
