From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751507AbdFGNMX (ORCPT <rfc822;w@1wt.eu>);
        Wed, 7 Jun 2017 09:12:23 -0400
Received: from mail-oi0-f41.google.com ([209.85.218.41]:34470 "EHLO
        mail-oi0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751403AbdFGNMW (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 7 Jun 2017 09:12:22 -0400
MIME-Version: 1.0
In-Reply-To: <20170607085803.04829eb5@gandalf.local.home>
References: <20170530181306.GV141096@google.com> <20170531235519.GX141096@google.com>
 <CAK8P3a3nrxvTVx8zjgf+_byAX82FG8jFD73L2nPSJBwK5grdXA@mail.gmail.com>
 <CA+55aFyhgWGr-=9t7131XAUyNy8Zs_vUfp-PGu_eaLkMAa6=sg@mail.gmail.com>
 <20170606212354.GZ141096@google.com> <eb3f47af-b622-f898-44b8-3174ca871ab1@kernel.dk>
 <CAK8P3a2H6enP0dsFRcf9pumRg1wxhVpynQYJooiMQRUGpCvQHQ@mail.gmail.com> <20170607085803.04829eb5@gandalf.local.home>
From: Arnd Bergmann <arnd@arndb.de>
Date: Wed, 7 Jun 2017 15:12:21 +0200
X-Google-Sender-Auth: FKbjkms-hnzbFSYNuBQqAoVNnQ8
Message-ID: <CAK8P3a22M5hJG=9uzN6fRMffsGfkt9sWeOYVy8ENN+dB13A1yg@mail.gmail.com>
Subject: Re: [RFC] clang: 'unused-function' warning on static inline functions
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jens Axboe <axboe@kernel.dk>, Matthias Kaehlcke <mka@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@lst.de>, David Rientjes <rientjes@google.com>,
        Douglas Anderson <dianders@chromium.org>,
        Guenter Roeck <linux@roeck-us.net>, Mark Brown <broonie@kernel.org>,
        David Miller <davem@davemloft.net>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Jun 7, 2017 at 2:58 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 7 Jun 2017 10:17:18 +0200
> Arnd Bergmann <arnd@arndb.de> wrote:

>> > where it is truly just dead junk. I'd rather just leave the dead junk
>> > than have pointless warnings, if I have to choose one of the two
>> > outcomes.
>>
>> This is a relatively rare case, with an inline function defined by a macro, and
>> I sent a patch for a similar one in 1f318a8bafcf ("modules: mark
>> __inittest/__exittest
>> as __maybe_unused"). I think this is a case where the __maybe_unused
>> annotation is reasonable, though for the other instances of unused inline
>> functions in .c files, there is often a better way: typically the only caller
>> of a function is inside of an #ifdef and moving the inline function definition
>> into the same #ifdef block makes it clearer what is going on.
>>
>
> How many warnings does the TRACE_EVENT() macros produce? That macro
> creates a lot of static inline functions for every event. For example,
> it will create an rcuidle() version of a tracepoint for those locations
> that need to be called where RCU is not watching. It also adds a
> trace_#tracepoint#_enabled() function for those that want to test if
> the tracepoint is enabled or not.
>
> That is, every tracepoint creates static inlined functions for cases
> that are used by only a few. I'm sure they will cause lots of warnings
> because there will be a lot of unused static inlined functions.

The TRACE_EVENT() macro is always invoked from header files, so
clang does not warn about unused instances. The only other header
I found that defines macros that cause unused inline functions is
include/linux/interval_tree_generic.h, but I only saw two warnings
from that in the whole allmodconfig build.

        Arnd