linux-kernel - Re: [RFC/PATCH 2/2] perf probe: Allow weak symbols to be probed

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Date:	Fri, 6 Mar 2015 16:28:11 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCH 2/2] perf probe: Allow weak symbols to be probed

On Fri, Mar 6, 2015 at 4:05 PM, Masami Hiramatsu
<masami.hiramatsu.pt@...achi.com> wrote:
> (2015/03/04 22:52), Namhyung Kim wrote:
>> It currently prevents adding probes in weak symbols.  But there're cases
>> that given name is an only weak symbol so that we cannot add probe.
>>
>>   $ perf probe -x /usr/lib/libc.so.6 -a calloc
>>   Failed to find symbol calloc in /usr/lib/libc-2.21.so
>>     Error: Failed to add events.
>>
>>   $ nm /usr/lib/libc.so.6 | grep calloc
>>   000000000007b1f0 t __calloc
>>   000000000007b1f0 T __libc_calloc
>>   000000000007b1f0 W calloc
>>
>> This change will result in duplicate probes when strong and weak symbols
>> co-exist in a binary.  But I think it's not a big problem since probes
>> at the weak symbol will never be hit anyway.
>>
>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/util/probe-event.c | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 1c570c2fa7cc..12b7d018106e 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -2339,8 +2339,7 @@ static int find_probe_functions(struct map *map, char *name)
>>       struct symbol *sym;
>>
>>       map__for_each_symbol_by_name(map, name, sym) {
>> -             if (sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL)
>> -                     found++;
>> +             found++;
>>       }
>
> Ah, I've found this is the magic...
> Here, we need another fix on my series.

Oops, right.  I didn't base on your patch so missed this function.

Thanks,
Namhyung


>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 22392b06..f9c1e53 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -309,10 +309,8 @@ static int find_alternative_probe_point(struct debuginfo *d
>
>         /* Find the address of given function */
>         map__for_each_symbol_by_name(map, pp->function, sym) {
> -               if (sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL) {
> -                       address = sym->start;
> -                       break;
> -               }
> +               address = sym->start;
> +               break;
>         }
>         if (!address) {
>                 ret = -ENOENT;
> -------
>
> With this fix, I could get variables on waitpid and calloc.
> -----
> # ./perf probe -x /lib64/libc-2.17.so -V waitpid
> Available variables at waitpid
>         @<__libc_waitpid+0>
>                 __pid_t pid
>                 int     oldtype
>                 int     options
>                 int*    stat_loc
> -----
>
> I'll update and include it my series.
>
> Thank you!
>
>>
>>       return found;
>> @@ -2708,8 +2707,7 @@ static struct strfilter *available_func_filter;
>>  static int filter_available_functions(struct map *map __maybe_unused,
>>                                     struct symbol *sym)
>>  {
>> -     if ((sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL) &&
>> -         strfilter__compare(available_func_filter, sym->name))
>> +     if (strfilter__compare(available_func_filter, sym->name))
>>               return 0;
>>       return 1;
>>  }
>>
>
>
> --
> Masami HIRAMATSU
> Software Platform Research Dept. Linux Technology Research Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu.pt@...achi.com
>
>



-- 
Thanks,
Namhyung
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