Re: [PATCH v2 3/4] perf probe: Do not rely on map__load() filter to find symbols

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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@hitachi.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.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;
	}

And no map__find_symbol_by_name() callsites would have to be touched.

- 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