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Date:   Mon, 24 Jun 2019 09:11:21 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Phong Tran <tranmanphong@gmail.com>
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Subject: Re: [PATCH 01/15] arm: perf: cleanup cppcheck shifting error
Message-ID: <20190624071121.GN3436@hirez.programming.kicks-ass.net>
References: <20190623151313.970-1-tranmanphong@gmail.com>
 <20190623151313.970-2-tranmanphong@gmail.com>
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On Sun, Jun 23, 2019 at 10:12:59PM +0700, Phong Tran wrote:
> fix "Shifting signed 32-bit value by 31 bits is undefined behaviour
> errors"
> 
> [arch/arm/kernel/perf_event_v7.c:1080]: (error) Shifting signed 32-bit
> value by 31 bits is undefined behaviour
> [arch/arm/kernel/perf_event_v7.c:1436]: (error) Shifting signed 32-bit
> value by 31 bits is undefined behaviour
> [arch/arm/kernel/perf_event_v7.c:1783]: (error) Shifting signed 32-bit
> value by 31 bits is undefined behaviour

I don't think that is true; the kernel uses -fno-strict-overflow (which
implies -fwrapv) and that takes away all the signed UB.