linux-kernel - Re: [PATCH] static_call: fix function type mismatch

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Message-ID: <20210322153214.25d869b1@gandalf.local.home>
Date:   Mon, 22 Mar 2021 15:32:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] static_call: fix function type mismatch

On Mon, 22 Mar 2021 18:06:37 +0100
Arnd Bergmann <arnd@...nel.org> wrote:

> From: Arnd Bergmann <arnd@...db.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 the function to return 'int' as well, but remove the cast to
> ensure we get a warning if any of the types ever change.

I think the answer is the other way around. That is, to make the functions
it references return long instead. __static_call_return0 is part of the
dynamic call infrastructure. Perhaps it is currently only used by functions
that return int, but what happens when it is used for a function that
returns a pointer?

-- Steve


> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---