linux-kernel - next-20200528 - build error in kernel/rcu/refperf.c

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Message-ID: <538911.1590725791@turing-police>
Date:   Fri, 29 May 2020 00:16:31 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: next-20200528 - build error in kernel/rcu/refperf.c

commit 9088b449814f788d24f35a5840b6b2c2a23cd32a
Author: Paul E. McKenney <paulmck@...nel.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?

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