linux-kernel - Re: [PATCH -tip 6/7] perf bts trace: print function+offset

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Date:	Mon, 06 Dec 2010 19:28:49 +0900
From:	Akihiro Nagai <akihiro.nagai.hw@...achi.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH -tip  6/7] perf bts trace: print function+offset

(2010/12/06 11:42), Frederic Weisbecker wrote:
> On Fri, Dec 03, 2010 at 01:00:15PM +0900, Akihiro Nagai wrote:
>> Provide the function to print function+offset.
>> And, set it as the default behavior of 'perf bts trace'.
>> To use this function, users can also specify the option '-s' or '--symbol'.
>>
>> Example: 'perf bts -as trace'
>> This command prints address and function+offset.
>>
>> Output sample:
>> address            function+offset
>> 0xffffffff8146fe0e irq_return+0x0         =>  0x00007fd4038e3b20 _start+0x0
>> ...
>> 0x000000380661ee79 __libc_start_main+0xf9 =>  0x00000000004035c3 main+0x0
>> 0xffffffff8146ef4e irq_return+0x0         =>  0x00000000004035c3 main+0x0
>> 0x00000000004035e8 main+0x25              =>  0x000000000040bca0 set_program_name+0x0
>> 0xffffffff8146ef4e irq_return+0x0         =>  0x000000000040bca0 set_program_name+0x0
>> 0x000000000040bcae set_program_name+0xe   =>  0x00000000004023d0 strrchr@...+0x0
>> 0x00000000004023d0 strrchr@...+0x0        =>  0x00000000004023d6 strrchr@...+0x6
>> ...
>> 0x0000000000403e0c main+0x849             =>  0x00000000004021f0 exit@...+0x0
>> 0x00000000004021f0 exit@...+0x0           =>  0x00000000004021f6 exit@...+0x6
>> 0x00000000004021fb exit@...+0xb           =>  0x00000000004020d0 _init+0x18
>> 0x00000000004020d6 _init+0x1e             =>  0x00000038062149d0 _dl_runtime_resolve+0x0
>> ...
>
> There is another kind of mode that I suspect would be very useful: something like
> a userspace function graph tracer (you can have a look into the kernel function
> graph tracer we have in ftrace to get an overview).
>
> So, the idea would be to rebuild the whole function call flow:
>
> main() {
> 	func1()
> 	func2() {
> 		func3()
> 	}
> }
>
>
> This would require to deref the instructions into the dso addresses from
> the bts trace, keep only the "call" and the "ret" (there would be a small arch
> backend for this mode) and rebuild the whole tree of calls.
> We already have all the dso address mapping API in place with perf.
>
> I really think this could be a very useful tool. Also we can even later
> expand this to the branches, as Peter suggested. But starting with calls
> would a very great start already.
>
> Thanks.
It's very good idea!
I'll try it.

Thank you for your suggestion!

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