OpenBSD Guest under QEMU fails with pid 1 signal 11

I am trying to create OpenBSD images for use in Google Compute Engine using an expect script [1]. The expect script is able to drive the OpenBSD installation process successfully, but the created images fail to boot cleanly with a long stream of "Process (pid 1) got signal 11".

To reproduce try the following (please note that all my tests are on a macOS host with QEMU installed):

- Clone the GitHub project at [2]
- Assuming you have QEMU installed and install63.iso downloaded try the command:
./imgtool PATH/TO/install63.iso openbsd/base
- The openbsd/base expect script will boot the image and you should see the stream of "Process (pid 1) got signal 11". If not, try running the created image:
./imgtool install63-base.tar.gz shared/run

Thank you for your help.

Bill

[1] https://github.com/billziss-gh/pmci.img/blob/master/openbsd/base
[2] https://github.com/billziss-gh/pmci.img