linux-kernel - Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint for uprobes

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Date:	Mon, 23 Dec 2013 19:50:10 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...nel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"David A. Long" <dave.long@...aro.org>, systemtap@...rceware.org,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint
 for uprobes

(2013/12/23 16:46), Namhyung Kim wrote:
> On Mon, 23 Dec 2013 06:54:38 +0900, Masami Hiramatsu wrote:
>> (2013/12/21 3:03), Arnaldo Carvalho de Melo wrote:
>>> Em Fri, Dec 20, 2013 at 10:03:02AM +0000, Masami Hiramatsu escreveu:
>> BTW, I'm not sure why debuginfo and nm shows symbol address + 0x400000,
>> and why the perf's map/symbol can remove this offset. Could you tell me
>> how it works?
>> If I can get the offset (0x400000) from binary, I don't need this kind
>> of ugly hacks...
> 
> AFAIK the actual symbol address is what nm (and debuginfo) shows.  But
> perf adjusts symbol address to have a relative address from the start of
> mapping (i.e. file offset) like below:
> 
> 	sym.st_value -= shdr.sh_addr - shdr.sh_offset;

Thanks! this is what I really need!

> This way, we can handle mmap and symbol address almost uniformly
> (i.e. ip = map->start + symbol->address).  But this requires the mmap
> event during perf record.  For perf probe, we might need to synthesize
> mapping info from the section/segment header since it doesn't have the
> mmap event.  Currently, the dso__new_map() just creates a map starts
> from 0.

I think the uprobe requires only the relative address, doesn't that?

Thank you,

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


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