linux-kernel - Re: [PATCH -tip v2 4/8] perf-probe: Use _stext based address instead of the symbol name

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Message-ID: <52EF541E.8040802@hitachi.com>
Date:	Mon, 03 Feb 2014 17:32:30 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"David A. Long" <dave.long@...aro.org>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip v2 4/8] perf-probe: Use _stext based address instead
 of the symbol name

(2014/02/03 16:49), Namhyung Kim wrote:
> On Wed, 29 Jan 2014 09:14:59 +0000, Masami Hiramatsu wrote:
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 4a9f43b..120954b 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -387,6 +387,44 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
>>  	return ret;
>>  }
>>  
>> +/* Post processing the probe events */
>> +static int post_process_probe_trace_events(struct probe_trace_event *tevs,
>> +					   int ntevs, const char *module,
>> +					   bool uprobe)
>> +{
>> +	struct symbol *sym;
>> +	struct map *map;
>> +	unsigned long stext = 0;
>> +	char *tmp;
>> +	int i;
>> +
>> +	if (uprobe)
>> +		return add_exec_to_probe_trace_events(tevs, ntevs, module);
>> +
>> +	/* Note that currently _stext based probe is not for drivers */
>> +	if (module)
>> +		return add_module_to_probe_trace_events(tevs, ntevs, module);
>> +
>> +	sym = __find_kernel_function_by_name("_stext", &map);
> 
> Couldn't we just use kmap->ref_reloc_sym instead of the hard-coded
> "_stext"?  You might want to check the Adrian's recent kaslr fixes (now
> in tip/perf/urgent).

Yeah, I just found Adrian's work and this series must be updated for that,
because symbol's address is now based on the real (relocated) address.
OK, I'll try to use a symbol in ref_reloc_sym. ;) Thank you for pointed it out!

Thanks!

-- 
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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