linux-kernel - Re: [PATCH] arm64: stacktrace: Stop unwinding when the PC is zero

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Message-ID: <20210430173255.GE18574@arm.com>
Date:   Fri, 30 Apr 2021 18:32:55 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Leo Yan <leo.yan@...aro.org>, Will Deacon <will@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
Subject: Re: [PATCH] arm64: stacktrace: Stop unwinding when the PC is zero

On Thu, Apr 29, 2021 at 11:48:13AM +0100, Mark Rutland wrote:
> From b99e647b34b74059f3013c09f12fbd542c7679fd Mon Sep 17 00:00:00 2001
> From: Mark Rutland <mark.rutland@....com>
> Date: Thu, 29 Apr 2021 11:20:04 +0100
> Subject: [PATCH] arm64: stacktrace: restore terminal records
> 
> We removed the terminal frame records in commit:
> 
>    6106e1112cc69a36 ("arm64: remove EL0 exception frame record")
> 
> ... on the assumption that as we no longer used them to find the pt_regs
> at exception boundaries, they were no longer necessary.
> 
> However, Leo reports that as an unintended side-effect, this causes
> traces which cross secondary_start_kernel to terminate one entry too
> late, with a spurious "0" entry.
> 
> There are a few ways we could sovle this, but as we're planning to use
> terminal records for RELIABLE_STACKTRACE, let's revert the logic change
> for now, keeping the update comments and accounting for the changes in
> commit:
> 
>   3c02600144bdb0a1 ("arm64: stacktrace: Report when we reach the end of the stack")
> 
> This is effectively a partial revert of commit:
> 
>   6106e1112cc69a36 ("arm64: remove EL0 exception frame record")
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Fixes: 6106e1112cc69a36 ("arm64: remove EL0 exception frame record")
> Reported-by: Leo Yan <leo.yan@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>

Thanks Mark. I applied it to for-next/core (couldn't figure out the
combination of b4 and git am + the scissors and not replying to the top
message).

-- 
Catalin