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

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Date:	Tue, 21 Jul 2015 08:53:34 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>,
	Jungseok Lee <jungseoklee85@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Catalin Marinas <Catalin.Marinas@....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()

Hi

So i don't have to repost my patch here. Please use the original
commit log message[1/3] as is.
But please keep in mind that there is still an issue that I mentioned
in the cover letter; 'Size' field is inaccurate.
  <reported size> = <its own dynamic local variables>
                         + <child's local variables>
and
  <real size> = <reported size> + <its local variables>
                                - <child's local variables>
where "dynamic" means, for example, a variable allocated like the below:
   int foo(int num) {
     int array[num];
     ...
   }
(See more details in my ascii art.)

Such usage is seldom seen in the kernel, and <reported size> is
likely equal to <child's local variables>. In other words, we will
see one-line *displacement* in most cases.

(We'd better mention it explicitly in the commmit?)

Thanks,
-Takahiro AKASHI


On 07/21/2015 01:20 AM, Will Deacon wrote:
> Hi all,
>
> On Fri, Jul 17, 2015 at 04:34:21PM +0100, Jungseok Lee wrote:
>> On Jul 17, 2015, at 11:59 PM, Jungseok Lee wrote:
>>> On Jul 17, 2015, at 11:41 PM, Steven Rostedt wrote:
>>>> Thanks! Can you repost patch 1 with the changes I recommended, so that
>>>> I can get an Acked-by from the arm64 maintainers and pull all the
>>>> changes in together. This is fine for a 4.3 release, right? That is, it
>>>> doesn't need to go into 4.2-rcs.
>>>>
>>>
>>> It's not hard to repost a patch, but I feel like we have to wait for Akashi's response.
>>> Also, it might be needed to consider Mark's comment on arch part.
>>>
>>> If they are okay, I will proceed.
>>
>> The [RFC 1/3] patch used in my environment is shaped as follows.
>> I leave the hunk for *only* clear synchronization. This is why I choose this format
>> instead of reposting a patch. I hope it would help to track down this thread.
>>
>> I think this is my best at this point.
>>
>> ----8<----
>> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
>> index c5534fa..2b43e20 100644
>> --- a/arch/arm64/include/asm/ftrace.h
>> +++ b/arch/arm64/include/asm/ftrace.h
>> @@ -13,8 +13,9 @@
>>
>>   #include <asm/insn.h>
>>
>> -#define MCOUNT_ADDR		((unsigned long)_mcount)
>> -#define MCOUNT_INSN_SIZE	AARCH64_INSN_SIZE
>> +#define MCOUNT_ADDR			((unsigned long)_mcount)
>> +#define MCOUNT_INSN_SIZE		AARCH64_INSN_SIZE
>> +#define FTRACE_STACK_FRAME_OFFSET	AARCH64_INSN_SIZE
>>
>>   #ifndef __ASSEMBLY__
>>   #include <linux/compat.h>
>> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
>> index 407991b..9ab67af 100644
>> --- a/arch/arm64/kernel/stacktrace.c
>> +++ b/arch/arm64/kernel/stacktrace.c
>> @@ -20,6 +20,7 @@
>>   #include <linux/sched.h>
>>   #include <linux/stacktrace.h>
>>
>> +#include <asm/insn.h>
>>   #include <asm/stacktrace.h>
>>
>>   /*
>> @@ -52,7 +53,7 @@ int notrace unwind_frame(struct stackframe *frame)
>>   	 * -4 here because we care about the PC at time of bl,
>>   	 * not where the return will go.
>>   	 */
>> -	frame->pc = *(unsigned long *)(fp + 8) - 4;
>> +	frame->pc = *(unsigned long *)(fp + 8) - AARCH64_INSN_SIZE;
>>
>>   	return 0;
>>   }
>
> The arm64 bits look fine to me:
>
>    Acked-by: Will Deacon <will.deacon@....com>
>
> Steve: feel free to take this along with the other ftrace changes. I don't
> anticipate any conflicts, but if anything crops up in -next we can sort
> it out then.
>
> Thanks!
>
> Will
>
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