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

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Message-ID: <20190808222440.2f99c50e@oasis.local.home>
Date:   Thu, 8 Aug 2019 22:24:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jiping Ma <Jiping.Ma2@...driver.com>
Cc:     Will Deacon <will@...nel.org>, <linux-kernel@...r.kernel.org>,
        <catalin.marinas@....com>, <will.deacon@....com>,
        <mingo@...hat.com>, Joel Fernandes <joel@...lfernandes.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2 v2] tracing/arm64: Have max stack tracer handle the
 case of return address after data

On Fri, 9 Aug 2019 10:17:19 +0800
Jiping Ma <Jiping.Ma2@...driver.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@...nel.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@...nel.org>  
> > Thanks Will!
> >
> > Here's the official patch.
> >
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.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.

-- Steve

> 
> Jiping
> 
>