This is part 3 of my blog post series about emulating BSD operating systems for 32-bit ARM with QEMU. Buckle up, today we will need to do an actual OS installation!

In OpenBSD/armv7, the miniroot image is an installer, so we also need a new empty drive image to install to. I recommend the qcow2 format, since it consumes only the space that is actually occupied. The 10G image created below is only 192 kilobytes initially. Here is how you create the root image:

qemu-img create -f qcow2 root.qcow2 10G

Next, we will need the pflash0.img and pflash1.img files created in the previous part.

As for the install image, there are several choices on the download page for OpenBSD 7.6/armv7. I went with miniroot-cubox-76.img but I don’t think it matters much which one you choose. They only differ in the platform-specific bootloader, and we will be booting from UEFI instead anyway.

Note that when booting, you might get an error message complaining that the size of the image is not a power of two. If that happens, just resize it to the next bigger one:

qemu-img resize miniroot-cubox-76.img 64M

Running the installer

Here is the command line to launch the installer then:

#!/bin/sh
qemu-system-arm \
	-M virt \
	-m 1024 \
	-nographic \
	-drive file=miniroot-cubox-76.img,format=raw \
	-drive file=root.qcow2,format=qcow2 \
	-drive file=pflash0.img,format=raw,if=pflash,readonly=on \
	-drive file=pflash1.img,format=raw,if=pflash \
	-device virtio-gpu-pci \
	-nic user,model=rtl8139

This time, we don’t have to type anything in the UEFI shell, it loads the bootloader directly, followed by the OpenBSD installer! At the boot> prompt, just press Enter.

I won’t go over the steps to install OpenBSD itself. The only thing to keep in mind is that OpenBSD calls the boot image (the miniroot) sd0 and the root disk we created sd1, so be sure to install onto sd1.

As always, you can get out of QEMU and back to the terminal by “powering down”, e.g. running halt -p from a shell.

After installation

To boot your newly installed system, use the exact same QEMU command line as before, except that you remove the miniroot disk entry:

#!/bin/sh
qemu-system-arm \
	-M virt \
	-m 1024 \
	-nographic \
	-drive file=root.qcow2,format=qcow2 \
	-drive file=pflash0.img,format=raw,if=pflash,readonly=on \
	-drive file=pflash1.img,format=raw,if=pflash \
	-device virtio-gpu-pci \
	-nic user,model=rtl8139

A dmesg output of this freshly installed system can be found here. Notably, it looks like the virtio GPU is not supported, so I am not sure if you can get X11 to work.

When I did this installation, a short time after the OpenBSD 7.6 release, there were no binary packages avaiable for 32-bit ARM. But it looks like this has changed! There is a full set of packages in https://cdn.openbsd.org/pub/OpenBSD/7.6/packages/arm/ now, so that a command like

pkg_add vim

will just work. That’s nice!

Some thoughts on machine types and emulation

When I started fiddling with this, I tried to get qemu to emulate a real machine corresponding to one of the OpenBSD miniroot image. But that’s fairly limiting: these boards came with too little RAM, too slow storage, too few cores, all of it.

The nice property of an emulator like QEMU is that you can kind of build your own machine from scratch. The virt machine type is a generic thing that you can build out just like you want it. Want 8G of RAM? More cores? No worries!

You can add a bunch of virtio devices that are virtualization-aware; if one of them doesn’t work right, replace with some other emulated hardware. This is also why my command lines above use an rtl8139 network device instead of a virtio-net.

And for booting this contraption, using the EDKII UEFI firmware allows just booting a generic kernel and bootloader, which is supported almost everywhere.

And that concludes my series of blog posts on emulating ARM systems with QEMU. I hope you enjoyed it!

For reference, here are links to the other parts in the series:

• Emulating *BSD on ARM, Part 1: Introduction
• Emulating *BSD on ARM, Part 2: FreeBSD