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Message-ID: <54B7ADF2.9090409@hitachi.com>
Date: Thu, 15 Jan 2015 21:09:22 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...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>,
David Ahern <dsahern@...il.com>
Subject: Re: Re: [PATCH v2 3/4] perf probe: Do not rely on map__load()
filter to find symbols
(2015/01/14 22:54), Arnaldo Carvalho de Melo wrote:
> Em Wed, Jan 14, 2015 at 08:18:07PM +0900, Namhyung Kim escreveu:
>> The find_probe_trace_events_from_map() searches matching symbol from a
>> map (so from a backing dso). For uprobes, it'll create a new map (and
>> dso) and loads it using a filter. It's a little bit inefficient in that
>> it'll read out the symbol table everytime but works well anyway.
>>
>> For kprobes however, it'll reuse existing kernel map which might be
>> loaded before. In this case map__load() just returns with no result.
>> It makes kprobes always failed to find symbol even if it exists in the
>> map (dso).
>>
>> To fix it, use map__find_symbol_by_name() instead. It'll load a map
>> with full symbols and sorts them by name. It needs to search sibing
>> nodes since there can be multiple (local) symbols with same name.
>>
>> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>> tools/perf/util/probe-event.c | 32 +++++++++++++++-----------------
>> 1 file changed, 15 insertions(+), 17 deletions(-)
>>
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 94a717bf007d..b1406d79b271 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -2193,18 +2193,18 @@ static int __add_probe_trace_events(struct perf_probe_event *pev,
>> return ret;
>> }
>>
>> -static char *looking_function_name;
>> -static int num_matched_functions;
>> -
>> -static int probe_function_filter(struct map *map __maybe_unused,
>> - struct symbol *sym)
>> +static int find_probe_functions(struct map *map, char *name)
>> {
>> - if ((sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL) &&
>> - strcmp(looking_function_name, sym->name) == 0) {
>> - num_matched_functions++;
>> - return 0;
>> + struct symbol *sym, *link = NULL;
>> + int found = 0;
>> +
>> + while ((sym = map__find_symbol_by_name(map, name, NULL, link)) != NULL) {
>> + if (sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL)
>> + found++;
>> + link = sym;
>> }
>> - return 1;
>> +
>> + return found;
>> }
>
> How about using the "from" (that you called "link") to follow the list.h
> style and provide:
>
> map__find_symbol_by_name_from(map, sym, filter, from);
>
> And use it to implement map__find_symbol_by_name():
>
> map__find_symbol_by_name(map, sym, filter)
> {
> return map__find_symbol_by_name_from(map, sym, filter, NULL);
> }
>
> Your loop would then become:
>
> link = NULL;
>
> while ((sym = map__find_symbol_by_name_from(map, name, NULL, link)) != NULL) {
> if (sym->binding == STB_GLOBAL || sym->binding == STB_LOCAL)
> found++;
> link = sym;
> }
+1 ;)
Would it be nicer to rename "link" local variable to "from" ?
>
> And no map__find_symbol_by_name() callsites would have to be touched.
BTW, such other callsites has no similar issues?
Thank you,
>
> - Arnaldo
>
>> #define strdup_or_goto(str, label) \
>> @@ -2221,11 +2221,11 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>> struct map *map = NULL;
>> struct kmap *kmap = NULL;
>> struct ref_reloc_sym *reloc_sym = NULL;
>> - struct symbol *sym;
>> - struct rb_node *nd;
>> + struct symbol *sym, *link = NULL;
>> struct probe_trace_event *tev;
>> struct perf_probe_point *pp = &pev->point;
>> struct probe_trace_point *tp;
>> + int num_matched_functions;
>> int ret, i;
>>
>> /* Init maps of given executable or kernel */
>> @@ -2242,10 +2242,8 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>> * Load matched symbols: Since the different local symbols may have
>> * same name but different addresses, this lists all the symbols.
>> */
>> - num_matched_functions = 0;
>> - looking_function_name = pp->function;
>> - ret = map__load(map, probe_function_filter);
>> - if (ret || num_matched_functions == 0) {
>> + num_matched_functions = find_probe_functions(map, pp->function);
>> + if (num_matched_functions == 0) {
>> pr_err("Failed to find symbol %s in %s\n", pp->function,
>> target ? : "kernel");
>> ret = -ENOENT;
>> @@ -2275,7 +2273,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>> }
>>
>> ret = 0;
>> - map__for_each_symbol(map, sym, nd) {
>> + while ((sym = map__find_symbol_by_name(map, pp->function, NULL, link))) {
>> tev = (*tevs) + ret;
>> tp = &tev->point;
>> if (ret == num_matched_functions) {
>> --
>> 2.2.1
> --
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--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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