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Subject: Re: next-20200528 - build error in kernel/rcu/refperf.c
To:     =?UTF-8?Q?Valdis_Kl=c4=93tnieks?= <valdis.kletnieks@vt.edu>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org
References: <538911.1590725791@turing-police>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <9d8b13db-9d77-416d-e283-9ea509ce43d1@infradead.org>
Date:   Thu, 28 May 2020 21:48:18 -0700
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On 5/28/20 9:16 PM, Valdis Klētnieks wrote:
> 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?
> 

Paul has already responded: (unfortunately)

"So I am restricting to 64BIT for the time being.  Yeah, I know, lazy of
me.  ;-)"

https://lore.kernel.org/lkml/20200528180855.GP2869@paulmck-ThinkPad-P72/

-- 
~Randy