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Date:   Fri, 15 Apr 2022 17:56:09 -0700
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Chen Zhongjin <chenzhongjin@huawei.com>
Cc:     "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
        mark.rutland@arm.com, broonie@kernel.org, ardb@kernel.org,
        nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com,
        catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org,
        linux-arm-kernel@lists.infradead.org,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v1 0/9] arm64: livepatch: Use DWARF Call Frame
 Information for frame pointer validation
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On Tue, Apr 12, 2022 at 04:32:22PM +0800, Chen Zhongjin wrote:
> By the way, I was thinking about a corner case, because arm64 CALL
> instruction won't push LR onto stack atomically as x86. Before push LR, FP
> to save frame there still can be some instructions such as bti, paciasp. If
> an irq happens here, the stack frame is not constructed so the FP unwinder
> will omit this function and provides a wrong stack trace to livepatch.
> 
> It's just a guess and I have not built the test case. But I think it's a
> defect on arm64 that FP unwinder can't work properly on prologue and
> epilogue. Do you have any idea about this?

x86 has similar issues with frame pointers, if for example preemption or
page fault exception occurs in a leaf function, or in a function
prologue or epilogue, before or after the frame pointer setup.

This issue is solved by the "reliable" unwinder which detects
irqs/exceptions on the stack and reports the stack as unreliable.

-- 
Josh