Re: [PATCH v1] sched/topology: Make compiler happy about unused constant definitions
From: Andy Shevchenko
Date: Tue Aug 25 2020 - 07:35:17 EST
On Tue, Aug 25, 2020 at 11:12:21AM +0100, Valentin Schneider wrote:
> On 25/08/20 10:03, Valentin Schneider wrote:
> > On 25/08/20 09:26, Andy Shevchenko wrote:
> >> 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.
>
> > Sorry, that's what I get for trying to be too succinct; what I tried to say
> > was that SD_DEGENERATE_GROUPS_MASK should very much be used for SMP. If the
> > build is !SMP, it shouldn't even be defined, IOW I'm perplexed as to where
> > this is coming from.
>
> So I see how having this as a constvar rather than a constexpr is somewhat
> daft (we get an instance per compilation unit), but none of my compilers
> seem to complain (even with W=1). AFAIA the kernelbot didn't catch any of
> it either.
>
> Out of curiosity, what's your compiler & compiler version?
% gcc --version
gcc (Debian 10.2.0-5) 10.2.0
% make O=... W=1 C=1 CF=-D__CHECK_ENDIAN__ -j64
> Alternatively we can make this a "proper" constant expression with the
> below.
It doesn't fix another static const in the same file, though that one requires
DEBUG_SCHED to be enabled.
Do you want me to split this fix and fix only the other case?
> ---
>
> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
> index 2d59ca77103e..b1331c4c48e9 100644
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -27,9 +27,11 @@ enum {
>
> /* Generate a mask of SD flags with the SDF_NEEDS_GROUPS metaflag */
> #define SD_FLAG(name, mflags) (name * !!((mflags) & SDF_NEEDS_GROUPS)) |
> -static const unsigned int SD_DEGENERATE_GROUPS_MASK =
> +enum {
> + SD_DEGENERATE_GROUPS_MASK =
> #include <linux/sched/sd_flags.h>
> -0;
> +0
> +};
> #undef SD_FLAG
>
> #ifdef CONFIG_SCHED_DEBUG
--
With Best Regards,
Andy Shevchenko