commit 9088b449814f788d24f35a5840b6b2c2a23cd32a
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Mon May 25 17:22:24 2020 -0700

    refperf: Provide module parameter to specify number of experiments

changes this line of code (line 389)

-               reader_tasks[exp].result_avg = 1000 * process_durations(exp) / ((exp + 1) * loops);
+               result_avg[exp] = 1000 * process_durations(nreaders) / (nreaders * loops);

On a 32-bit ARM make allmodconfig with gcc 8.3, this results in:

ERROR: modpost: "__aeabi_uldivmod" [kernel/rcu/refperf.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:103: __modpost] Error 1

I admit not understanding why the original line of code worked and the new one doesn't.
Maybe gcc is smarter/dumber about the ranges of 'exp' and 'nreaders' than we thought?