linux-kernel - Re: [PATCH v6 4/7] arm64: Add ftrace support

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Date:	Sat, 15 Mar 2014 01:13:52 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Will Deacon <will.deacon@....com>
CC:	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"tim.bird@...ymobile.com" <tim.bird@...ymobile.com>,
	"gkulkarni@...iumnetworks.com" <gkulkarni@...iumnetworks.com>,
	"dsaxena@...aro.org" <dsaxena@...aro.org>,
	"arndb@...db.de" <arndb@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 4/7] arm64: Add ftrace support

On 03/14/2014 07:07 PM, Will Deacon wrote:
> On Fri, Mar 14, 2014 at 04:45:13AM +0000, AKASHI Takahiro wrote:
>> On 03/14/2014 02:08 AM, Will Deacon wrote:
>>> On Thu, Mar 13, 2014 at 10:13:47AM +0000, AKASHI Takahiro wrote:
>>>> This patch implements arm64 specific part to support function tracers,
>>>> such as function (CONFIG_FUNCTION_TRACER), function_graph
>>>> (CONFIG_FUNCTION_GRAPH_TRACER) and function profiler
>>>> (CONFIG_FUNCTION_PROFILER).
>>>>
>>>> With 'function' tracer, all the functions in the kernel are traced with
>>>> timestamps in ${sysfs}/tracing/trace. If function_graph tracer is
>>>> specified, call graph is generated.
>>>>
>>>> The kernel must be compiled with -pg option so that _mcount() is inserted
>>>> at the beginning of functions. This function is called on every function's
>>>> entry as long as tracing is enabled.
>>>> In addition, function_graph tracer also needs to be able to probe function's
>>>> exit. ftrace_graph_caller() & return_to_handler do this by faking link
>>>> register's value to intercept function's return path.
>>>>
>>>> More details on architecture specific requirements are described in
>>>> Documentation/trace/ftrace-design.txt.
>>>
>>> [...]
>>
>> You seem not to like this statement :-)
>
> Huh? I was just using '[...]' to signify that I'd removed a lot of context
> (since the code all looked fine there). Otherwise, review emails can get
> really long.

Please ignore my comment.

>>>> +       str     x0, [sp, #-16]!
>>>> +       mov     x0, x29                 //     parent's fp
>>>> +       bl      ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
>>>> +       mov     x30, x0                 // restore the original return address
>>>> +       ldr     x0, [sp], #16
>>>> +       ret
>>>
>>> and an ENDPROC here.
>>
>> Fix it.
>> But please note that this (return_to_handler) is not a real function.
>> Declaring it as ENDPROC is not very useful.
>
> Then use END(...). The opening macro was the main point, since that avoid
> the need for an explicit .globl.

Fix it.

-Takahiro AKASHI

> Will
>
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