perf record: Always record id index

In preparation for recording sideband events in a virtual machine guest so
that they can be injected into a host perf.data file.

Adjust the logic so that if there are IDs then the id index is recorded.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220610113316.6682-3-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -1834,13 +1834,11 @@ static int record__synthesize(struct record *rec, bool tail)
 		goto out;
 
 	/* Synthesize id_index before auxtrace_info */
-	if (rec->opts.auxtrace_sample_mode || rec->opts.full_auxtrace) {
 	err = perf_event__synthesize_id_index(tool,
 					      process_synthesized_event,
 					      session->evlist, machine);
 	if (err)
 		goto out;
-	}
 
 	if (rec->opts.full_auxtrace) {
 		err = perf_event__synthesize_auxtrace_info(rec->itr, tool,

tools/perf/util/synthetic-events.c

@@ -1719,14 +1719,17 @@ int perf_event__synthesize_id_index(struct perf_tool *tool, perf_event__handler_
 	size_t nr = 0, i = 0, sz, max_nr, n;
 	int err;
 
-	pr_debug2("Synthesizing id index\n");
-
 	max_nr = (UINT16_MAX - sizeof(struct perf_record_id_index)) /
 		 sizeof(struct id_index_entry);
 
 	evlist__for_each_entry(evlist, evsel)
 		nr += evsel->core.ids;
 
+	if (!nr)
+		return 0;
+
+	pr_debug2("Synthesizing id index\n");
+
 	n = nr > max_nr ? max_nr : nr;
 	sz = sizeof(struct perf_record_id_index) + n * sizeof(struct id_index_entry);
 	ev = zalloc(sz);