Re: [RFC/PATCH 2/2] perf probe: Allow weak symbols to be probed
From: Namhyung Kim
Date: Fri Mar 06 2015 - 02:28:38 EST
On Fri, Mar 6, 2015 at 4:05 PM, Masami Hiramatsu
<masami.hiramatsu.pt@xxxxxxxxxxx> 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@xxxxxxxxxxx>
>> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
>> ---
>> 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@xxxxxxxxxxx
>
>
--
Thanks,
Namhyung
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