The sources in general are very inconsistent in its use of tabs vs spaces.  I autoindented posix_timers.c and eval.c (which had very broken indentation) in vim with shiftwidth=4.  This gave an indentation style like what was used in uvalarm.c, which is where I did my initial prototyping.  I can switch both to shiftwidth=8, and that will at least make it consistent with main.c and backend.c

I'm not sure that additional messaging specifically about 'eval cost limitation' adds any value.  The driver is about to abort during startup, so nothing at all will function - not just eval cost.