linux-kernel - RE: [PATCH v1] sched/topology: Make compiler happy about unused constant definitions

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Date:   Tue, 25 Aug 2020 10:23:05 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>,
        Valentin Schneider <valentin.schneider@....com>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: RE: [PATCH v1] sched/topology: Make compiler happy about unused
 constant definitions

From: Andy Shevchenko
> Sent: 25 August 2020 09:27
> 
> On Mon, Aug 24, 2020 at 06:09:41PM +0100, Valentin Schneider wrote:
> > On 24/08/20 16:39, Andy Shevchenko wrote:
> > > Compilation of almost each file ends up with
> > >
> > >  In file included from .../include/linux/energy_model.h:10,
> > >                 from .../include/linux/device.h:16,
> > >                 from .../drivers/spi/spi.c:8:
> > >  .../include/linux/sched/topology.h:30:27: warning: ‘SD_DEGENERATE_GROUPS_MASK’ defined but not
> used [-Wunused-const-variable=]
> > >     30 | static const unsigned int SD_DEGENERATE_GROUPS_MASK =
> > >        |                           ^~~~~~~~~~~~~~~~~~~~~~~~~
> > >  ...
> > >
> > > Make compiler happy by annotating the static constants with __maybwe_unused.
> > >
> >
> > That should see some use as long as the build is for SMP. This whole region
> > is guarded by #ifdef CONFIG_SMP, so an !SMP build shouldn't trigger this.
> 
> Isn't SMP is default for most of the kernel builds?
> And honestly I didn't get the purpose of this comment.

The real fix is to not use 'static const' in C.
IIRC it is still a memory location (that can be patched) not
a compile time constant.

	David

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