linux-kernel - Re: [RFC 2/3] arm64: refactor save_stack

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Date:	Fri, 17 Jul 2015 11:09:26 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Mark Rutland <mark.rutland@....com>
CC:	Jungseok Lee <jungseoklee85@...il.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"david.griego@...aro.org" <david.griego@...aro.org>,
	"olof@...om.net" <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 2/3] arm64: refactor save_stack_trace()

On 07/16/2015 11:34 PM, Steven Rostedt wrote:
> On Thu, 16 Jul 2015 15:28:34 +0100
> Mark Rutland <mark.rutland@....com> wrote:
>
>
>>> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
>>> index c5534fa..868d6f1 100644
>>> --- a/arch/arm64/include/asm/ftrace.h
>>> +++ b/arch/arm64/include/asm/ftrace.h
>>> @@ -15,6 +15,7 @@
>>>
>>>    #define MCOUNT_ADDR		((unsigned long)_mcount)
>>>    #define MCOUNT_INSN_SIZE	AARCH64_INSN_SIZE
>>> +#define FTRACE_STACK_FRAME_OFFSET 4 /* sync it up with stacktrace.c */
>>
>> Is there any reason we couldn't have the arch code dump the stack depth
>> for each function when it walks the stack to generate the stack trace?
>>
>> That means we can provide a more precise result (because we know the
>> layour of our own stackframes), and we only need walk the stack once to
>> do so.
>>
>> The downside is that we need a new function per-arch to do so.
>
> Or we make check_patch() a weak function, and let archs override it. I
> can possibly break up the code a bit to have helper functions where
> things are the same.

Yeah, that is exactly what I meant in my cover letter[0/3] if the series
of patches are not acceptable.

-Takahiro AKASHI

> I want x86 to be able to track irq stacks as well, but there's no way
> to do that generically yet, so having arch specific functions has been
> on my todo list.
>
> -- Steve
>
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