linux-kernel - RE: Re: [RFC PATCH perf/core v3 00/17] perf-probe --cache and SDT support

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Date:	Wed, 19 Aug 2015 15:15:30 +0000
From:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
To:	"'Namhyung Kim'" <namhyung@...nel.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Ingo Molnar" <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Jiri Olsa <jolsa@...nel.org>, Borislav Petkov <bp@...e.de>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>
Subject: RE: Re: [RFC PATCH perf/core v3 00/17] perf-probe --cache and
 SDT support

Hi Namhyung,

> From: Namhyung Kim [mailto:namhyung@...il.com] On Behalf Of Namhyung Kim
> >  - (ftrace) Support multiple SDTs on single event.
> >
> > Since multiple same SDTs are defined in a single binary (e.g. libc:setjump
> > has 3 different entries on libc-2.17.so), we need the last feature on
> > ftrace, so that a single uprobe event can occur several different
> > probe points.
> 
> Do you want to have multiple events of same name in the kernel?  Or
> to make perf handle those same names with different kernel events?

Good point, I meant the former. But the latter is also possible.

Here is my idea;

Suppose to define an event "foo" at "bar" function + 10byte offset with
2 arguments as below:
 # echo p:foo bar+10 arg1=%ax arg2=%dx > kprobe_events

To add a probe point on the same event, use "+p" or "+r" instead of "p" or "r"
and we can also change the assignment for each argument.
 # echo +p:foo bar+20 arg1=%cx arg2=0 >> kprobe_events

Also, I guess we'll need to support a fixed value assignment because sometimes
local valiables are optimized out.

Thank you,