linux-kernel - Re: [PATCH] perf/core: Drop __weak attribute from arch_perf_update

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Message-ID: <20230604160810.eu7egpjrcb6ettoh@google.com>
Date:   Sun, 4 Jun 2023 09:08:10 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] perf/core: Drop __weak attribute from
 arch_perf_update_userpage() prototype

On Sat, Jun 03, 2023 at 09:25:19AM +0100, Marc Zyngier wrote:
> Reiji reports that the arm64 implementation of arch_perf_update_userpage()
> is now ignored and replaced by the dummy stub in core code.
> This seems to happen since the PMUv3 driver was moved to driver/perf.
> 
> As it turns out, dropping the __weak attribute from the *prototype*
> of the function solves the problem. You're right, this doesn't seem
> to make much sense. And yet... It appears that both symbols get
> flagged as weak, and that the first one to appear in the link order
> wins:
> 
> $ nm drivers/perf/arm_pmuv3.o|grep arch_perf_update_userpage
> 0000000000001db0 W arch_perf_update_userpage
> 
> Dropping the attribute from the prototype restores the expected
> behaviour, and arm64 is able to enjoy arch_perf_update_userpage()
> again.
> 
> Reported-by: Reiji Watanabe <reijiw@...gle.com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>

Tested-by: Reiji Watanabe <reijiw@...gle.com>