I'm not sure if this is of any interest to anyone but me, BUT the cal-tool works from the /sbin/preinit shell. So rdmod -p segmentation faults, but cal-tool -f (which does the same thing, prints the R&D mode string) works.

Eventually I'll start comparing straces and see what I can figure out, but it doesn't make sense to me why my program would fail at that stage of boot, as far as I can deduce, at the cal.h derived functions.