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

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Message-ID: <20151020153227.GL11226@e104818-lin.cambridge.arm.com>
Date:	Tue, 20 Oct 2015 16:32:28 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>, zhouchengming1@...wei.com,
	Arnd Bergmann <arnd@...db.de>, xiexiuqi@...wei.com,
	Punit Agrawal <punit.agrawal@....com>, guohanjun@...wei.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Li Bin <huawei.libin@...wei.com>, dingtianhong@...wei.com,
	Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [PATCH] arm64: ftrace: function_graph: dump real return addr in
 call trace

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?

Thanks.

-- 
Catalin
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