perf intel-pt: Support itrace d+o option to direct debug log to stdout

It can be useful to see debug output in between normal output.

Add support for AUXTRACE_LOG_FLG_USE_STDOUT to Intel PT.
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20211027080334.365596-7-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-intel-pt.txt

@@ -953,6 +953,7 @@ by flags which affect what debug messages will or will not be logged. Each flag
 must be preceded by either '+' or '-'. The flags support by Intel PT are:
 		-a	Suppress logging of perf events
 		+a	Log all perf events
+		+o	Output to stdout instead of "intel_pt.log"
 By default, logged perf events are filtered by any specified time ranges, but
 flag +a overrides that.
 

tools/perf/util/intel-pt-decoder/intel-pt-log.c

@@ -82,10 +82,10 @@ static int intel_pt_log_open(void)
 	if (f)
 		return 0;
 
-	if (!log_name[0])
-		return -1;
-
+	if (log_name[0])
 		f = fopen(log_name, "w+");
+	else
+		f = stdout;
 	if (!f) {
 		intel_pt_enable_logging = false;
 		return -1;

tools/perf/util/intel-pt.c

@@ -3736,8 +3736,6 @@ int intel_pt_process_auxtrace_info(union perf_event *event,
 	if (err)
 		goto err_free;
 
-	intel_pt_log_set_name(INTEL_PT_PMU_NAME);
-
 	if (session->itrace_synth_opts->set) {
 		pt->synth_opts = *session->itrace_synth_opts;
 	} else {
@@ -3752,6 +3750,9 @@ int intel_pt_process_auxtrace_info(union perf_event *event,
 		pt->synth_opts.thread_stack = opts->thread_stack;
 	}
 
+	if (!(pt->synth_opts.log_plus_flags & AUXTRACE_LOG_FLG_USE_STDOUT))
+		intel_pt_log_set_name(INTEL_PT_PMU_NAME);
+
 	pt->session = session;
 	pt->machine = &session->machines.host; /* No kvm support */
 	pt->auxtrace_type = auxtrace_info->type;