Hmm. I don't know if this means anything, but I installed s390-tools-2.19.0-3.1 from openSUSE:Factory:zSystems, and read_values now works as expected. I would pursue this further, but first I would need to know how to get my hands on all the various debuginfo and debugsource RPMs for things like s390-tools, qclib, glibc, etc.