linux-kernel - Re: Re: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save

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Message-ID: <5004D85C.70704@hitachi.com>
Date:	Tue, 17 Jul 2012 12:13:32 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, yrl.pp-manager.tt@...achi.com
Subject: Re: Re: Re: [RFC][PATCH 2/4 v4] ftrace/x86: Add save_regs for
 i386 function calls

(2012/07/17 12:05), Steven Rostedt wrote:
> On Tue, 2012-07-17 at 11:08 +0900, Masami Hiramatsu wrote:
> 
>>> I found that regs_get_register() doesn't honor this either. Thus,
>>> kprobes in tracing gets this:
>>>
>>>  # echo 'p:ftrace sys_read+4 s=%sp' > /debug/tracing/kprobe_events
>>>  # echo 1 > /debug/tracing/events/kprobes/enable
>>>  # cat trace
>>>             sshd-1345  [000] d...   489.117168: ftrace: (sys_read+0x4/0x70) s=b7e96768
>>>             sshd-1345  [000] d...   489.117191: ftrace: (sys_read+0x4/0x70) s=b7e96768
>>>              cat-1447  [000] d...   489.117392: ftrace: (sys_read+0x4/0x70) s=5a7
>>>              cat-1447  [001] d...   489.118023: ftrace: (sys_read+0x4/0x70) s=b77ad05f
>>>             less-1448  [000] d...   489.118079: ftrace: (sys_read+0x4/0x70) s=b7762e06
>>>             less-1448  [000] d...   489.118117: ftrace: (sys_read+0x4/0x70) s=b7764970
>>>
>>
>> Yes, that is by design, since I made it so. :)
>> Instead of %sp, kprobe tracer provides $stack special argument
>> for stack address, because "sp" is not always means the stack
>> address on every arch.
> 
> But is that useful? Wouldn't the actual stack pointer be more
> informative?

It is just FYI :). I rather like your "%sp" enhancement
than current meaningless "%sp" on i386...

However, I think "$stack" is more general and informative
for users, thus, at least perf probe uses it for getting
variables from stack.

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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