linux-kernel - Re: [PATCH] arm64: ftrace: function_graph: dump real return addr in call trace

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Date:	Wed, 28 Oct 2015 15:21:31 +0000
From:	Will Deacon <will.deacon@....com>
To:	libin <huawei.libin@...wei.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mark Rutland <mark.rutland@....com>, zhouchengming1@...wei.com,
	Arnd Bergmann <arnd@...db.de>, xiexiuqi@...wei.com,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Punit Agrawal <punit.agrawal@....com>,
	linux-kernel@...r.kernel.org, dingtianhong@...wei.com,
	guohanjun@...wei.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: ftrace: function_graph: dump real return addr in
 call trace

On Thu, Oct 22, 2015 at 08:55:43AM +0800, libin wrote:
> 在 2015/10/20 23:32, Catalin Marinas 写道:
> >On Thu, Oct 15, 2015 at 10:18:12AM -0400, Steven Rostedt wrote:
> >>On Thu, 15 Oct 2015 13:51:33 +0100
> >>Will Deacon <will.deacon@....com> wrote:
> >>
> >>>Is this the same old problem caused by e306dfd06fcb ("ARM64: unwind: Fix
> >>>PC calculation")? I've said previously that I'm happy to revert that if
> >>>we're the only architecture with this behaviour, but Akashi resisted
> >>>because there are other issues with ftrace that he was hoping to address
> >>>and they would resolve this too.
> >>
> >>Just a reference, but this patch is pretty much exactly what x86
> >>currently has. I wonder if I should make that function generic for all
> >>archs to use.
> >>
> >>If you accept this patch, I can look at what archs do and pull out the
> >>common code and place it into the core code and have the archs call
> >>that instead.
> >
> >The difference I see from the sh and x86 version is that we have this -4
> >on arm64, introduced by e306dfd06fcb as Will mentioned above (it seemed
> >to have caused more problems that it solved). I think we should revert
> >that commit first just to be in line with other architectures and then
> >apply additional fixes as needed.
> >
> >Question for Li Bin: is your patch still needed if we revert commit
> >e306dfd06fcb?
> >
> 
> It still be needed, but it can be implemented in generic for all archs
> as Steve suggested.

Well, there's still an argument for reverting e306dfd06fcb because it
makes us behave differently to other architectures (in particular,
arch/arm).

Will
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