Re: [PATCH 1/2 v2] tracing/arm64: Have max stack tracer handle the case of return address after data

From: Will Deacon <will@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jiping Ma <Jiping.Ma2@windriver.com>,
	catalin.marinas@arm.com, will.deacon@arm.com,
	linux-kernel@vger.kernel.org, mingo@redhat.com,
	Joel Fernandes <joel@joelfernandes.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2 v2] tracing/arm64: Have max stack tracer handle the case of return address after data
Date: Tue, 13 Aug 2019 18:31:14 +0100	[thread overview]
Message-ID: <20190813173114.himeal2ublebx7ea@willie-the-truck> (raw)
In-Reply-To: <20190808222440.2f99c50e@oasis.local.home>

Hi Steve,

On Thu, Aug 08, 2019 at 10:24:40PM -0400, Steven Rostedt wrote:
> On Fri, 9 Aug 2019 10:17:19 +0800
> Jiping Ma <Jiping.Ma2@windriver.com> wrote:
> > On 2019年08月09日 01:24, Steven Rostedt wrote:
> > > On Thu, 8 Aug 2019 18:11:53 +0100
> > > Will Deacon <will@kernel.org> wrote:
> > >  
> > >>> We could make it more descriptive of what it will do and not the reason
> > >>> for why it is done...
> > >>>
> > >>>
> > >>>    ARCH_FTRACE_SHIFT_STACK_TRACER  
> > >> Acked-by: Will Deacon <will@kernel.org>  
> > > Thanks Will!
> > >
> > > Here's the official patch.
> > >
> > > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> > >
> > > Most archs (well at least x86) store the function call return address on the
> > > stack before storing the local variables for the function. The max stack
> > > tracer depends on this in its algorithm to display the stack size of each
> > > function it finds in the back trace.
> > >
> > > Some archs (arm64), may store the return address (from its link register)
> > > just before calling a nested function. There's no reason to save the link
> > > register on leaf functions, as it wont be updated. This breaks the algorithm
> > > of the max stack tracer.
> > >
> > > Add a new define ARCH_RET_ADDR_AFTER_LOCAL_VARS that an architecture may set  
> > 
> > ARCH_FTRACE_SHIFT_STACK_TRACER is used in the code.
> 
> Ah, I did a s/x/y/ to the diff of the patch, but not the change log.
> Thanks for pointing that out. I also need to update the comment in 2/2.

Are you going to post another version of this or have you queued it already?
Just want to make sure it doesn't slip through the cracks.

Cheers,

Will

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