linux-kernel - Re: arch/arm64/kvm/perf.c:58:36: error: implicit declaration of function 'perf_num

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Message-ID: <87o8ehmayd.wl-maz@kernel.org>
Date:   Wed, 14 Apr 2021 11:12:26 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexandru Elisei <alexandru.elisei@....com>
Subject: Re: arch/arm64/kvm/perf.c:58:36: error: implicit declaration of function 'perf_num_counters'

On Tue, 13 Apr 2021 21:00:57 +0100,
Nathan Chancellor <nathan@...nel.org> wrote:

[...]

> I just ran into this again. It is not a clang specific issue, it
> reproduces quite easily with arm64 defconfig minus CONFIG_PERF_EVENTS
> and gcc 10.3.0:
> 
> arch/arm64/kvm/perf.c: In function 'kvm_perf_init':
> arch/arm64/kvm/perf.c:58:36: error: implicit declaration of function
> 'perf_num_counters'; did you mean 'dec_mm_counter'?
> [-Werror=implicit-function-declaration]
>    58 |  if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0)
>       |                                    ^~~~~~~~~~~~~~~~~
>       |                                    dec_mm_counter
> cc1: some warnings being treated as errors
> 
> I am not sure what the cleanest solution would be for providing a static
> inline version of perf_num_counters() would be, as only arm64 actually
> uses it (sh and s390 define it but it does not appear to be used) but it
> is only available through CONFIG_ARM_PMU instead of just
> CONFIG_PERF_EVENTS like the other two architectures mentioned above.

As you point out, KVM/arm64 is the only user of perf_num_counters()
across the whole kernel. The whole oprofile subsystem has been
removed, so maybe a a bigger cleanup is in order.

I'll post something shortly.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.