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Date:   Mon, 18 Apr 2022 09:11:45 -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 Mon, Apr 18, 2022 at 08:28:33PM +0800, Chen Zhongjin wrote:
> Hi Josh,
> 
> IIUC, ORC on x86 can make reliable stack unwind for this scenario
> because objtool validates BP state.
> 
> I'm thinking that on arm64 there's no guarantee that LR will be pushed
> onto stack. When we meet similar scenario on arm64, we should recover
> (LR, FP) on pt_regs and continue to unwind the stack. And this is
> reliable only after we validate (LR, FP).
> 
> So should we track LR on arm64 additionally as track BP on x86? Or can
> we just treat (LR, FP) as a pair? because as I know they are always set
> up together.

Does the arm64 unwinder have a way to detect kernel pt_regs on the
stack?  If so, the simplest solution is to mark all stacks with kernel
regs as unreliable.  That's what the x86 FP unwinder does.

-- 
Josh