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Message-ID: <ZBSO/sWK1IGkoOxj@arm.com>
Date: Fri, 17 Mar 2023 16:02:06 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Kristina Martsenko <kristina.martsenko@....com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>,
Mark Rutland <mark.rutland@....com>,
Mark Brown <broonie@...nel.org>,
Luis Machado <luis.machado@....com>,
Vladimir Murzin <vladimir.murzin@....com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] arm64: mops: handle single stepping after MOPS
exception
On Thu, Feb 16, 2023 at 04:00:10PM +0000, Kristina Martsenko wrote:
> When a MOPS main or epilogue instruction is being executed, the task may
> get scheduled on a different CPU and restart execution from the prologue
> instruction. If the main or epilogue instruction is being single stepped
> then it makes sense to finish the step and take the step exception
> before starting to execute the next (prologue) instruction. So
> fast-forward the single step state machine when taking a MOPS exception.
>
> This means that if a main or epilogue instruction is single stepped with
> ptrace, the debugger will sometimes observe the PC moving back to the
> prologue instruction. (As already mentioned, this should be rare as it
> only happens when the task is scheduled to another CPU during the step.)
>
> This also ensures that perf breakpoints count prologue instructions
> consistently (i.e. every time they are executed), rather than skipping
> them when there also happens to be a breakpoint on a main or epilogue
> instruction.
>
> Signed-off-by: Kristina Martsenko <kristina.martsenko@....com>
Acked-by: Catalin Marinas <catalin.marinas@....com>
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