perf parse-events: Tidy the setting of the default event name

Add comments. Pass ownership of the event name to save on a strdup.
Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Beeman Strong <beeman@rivosinc.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240416061533.921723-17-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/parse-events.c

@@ -1836,18 +1836,21 @@ int parse_events__modifier_event(struct parse_events_state *parse_state, void *l
 	return parse_events__modifier_list(parse_state, loc, list, mod, /*group=*/false);
 }
 
-int parse_events_name(struct list_head *list, const char *name)
+int parse_events__set_default_name(struct list_head *list, char *name)
 {
 	struct evsel *evsel;
+	bool used_name = false;
 
 	__evlist__for_each_entry(list, evsel) {
 		if (!evsel->name) {
-			evsel->name = strdup(name);
+			evsel->name = used_name ? strdup(name) : name;
+			used_name = true;
 			if (!evsel->name)
 				return -ENOMEM;
 		}
 	}
-
+	if (!used_name)
+		free(name);
 	return 0;
 }
 

tools/perf/util/parse-events.h

@@ -207,7 +207,7 @@ int parse_events__modifier_event(struct parse_events_state *parse_state, void *l
 				 struct list_head *list, struct parse_events_modifier mod);
 int parse_events__modifier_group(struct parse_events_state *parse_state, void *loc,
 				 struct list_head *list, struct parse_events_modifier mod);
-int parse_events_name(struct list_head *list, const char *name);
+int parse_events__set_default_name(struct list_head *list, char *name);
 int parse_events_add_tracepoint(struct list_head *list, int *idx,
 				const char *sys, const char *event,
 				struct parse_events_error *error,

tools/perf/util/parse-events.l

@@ -96,6 +96,11 @@ static int drv_str(yyscan_t scanner, int token)
 	return token;
 }
 
+/*
+ * Use yyless to return all the characaters to the input. Update the column for
+ * location debugging. If __alloc is non-zero set yylval to the text for the
+ * returned token's value.
+ */
 #define REWIND(__alloc)				\
 do {								\
 	YYSTYPE *__yylval = parse_events_get_lval(yyscanner);	\

tools/perf/util/parse-events.y

@@ -247,10 +247,14 @@ event_name
 event_name:
 PE_EVENT_NAME event_def
 {
-	int err;
+	/*
+	 * When an event is parsed the text is rewound and the entire text of
+	 * the event is set to the str of PE_EVENT_NAME token matched here. If
+	 * no name was on an event via a term, set the name to the entire text
+	 * taking ownership of the allocation.
+	 */
+	int err = parse_events__set_default_name($2, $1);
 
-	err = parse_events_name($2, $1);
-	free($1);
 	if (err) {
 		free_list_evsel($2);
 		YYNOMEM;