Re: [PATCH] [v2] static_call: fix function type mismatch

From: Peter Zijlstra <peterz@infradead.org>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] [v2] static_call: fix function type mismatch
Date: Tue, 23 Mar 2021 08:33:37 +0100	[thread overview]
Message-ID: <YFmZ0a1I+PvyPvne@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210322214309.730556-1-arnd@kernel.org>

On Mon, Mar 22, 2021 at 10:42:24PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The __static_call_return0() function is declared to return a 'long',
> while it aliases a couple of functions that all return 'int'. When
> building with 'make W=1', gcc warns about this:
> 
> kernel/sched/core.c:5420:37: error: cast between incompatible function types from 'long int (*)(void)' to 'int (*)(void)' [-Werror=cast-function-type]
>  5420 |   static_call_update(might_resched, (typeof(&__cond_resched)) __static_call_return0);
> 
> Change all these function to return 'long' as well, but remove the cast to
> ensure we get a warning if any of the types ever change.

I still think it's utter batshit.

Please explain which architecture ABI is affected and why the warning is
sane.