perf script: Add not taken event for branch stack

The branch stack has an existed field for printing mispredict, extend
the field for printing events and add support not-taken event.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250304111240.3378214-6-leo.yan@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/builtin-script.c

@@ -935,19 +935,25 @@ static int perf_sample__fprintf_start(struct perf_script *script,
 	return printed;
 }
 
-static inline char
-mispred_str(struct branch_entry *br)
+static inline size_t
+bstack_event_str(struct branch_entry *br, char *buf, size_t sz)
 {
-	if (!(br->flags.mispred  || br->flags.predicted))
-		return '-';
+	if (!(br->flags.mispred || br->flags.predicted || br->flags.not_taken))
+		return snprintf(buf, sz, "-");
 
-	return br->flags.predicted ? 'P' : 'M';
+	return snprintf(buf, sz, "%s%s",
+			br->flags.predicted ? "P" : "M",
+			br->flags.not_taken ? "N" : "");
 }
 
 static int print_bstack_flags(FILE *fp, struct branch_entry *br)
 {
-	return fprintf(fp, "/%c/%c/%c/%d/%s/%s ",
-		       mispred_str(br),
+	char events[16] = { 0 };
+	size_t pos;
+
+	pos = bstack_event_str(br, events, sizeof(events));
+	return fprintf(fp, "/%s/%c/%c/%d/%s/%s ",
+		       pos < 0 ? "-" : events,
 		       br->flags.in_tx ? 'X' : '-',
 		       br->flags.abort ? 'A' : '-',
 		       br->flags.cycles,

tools/perf/util/branch.h

@@ -25,7 +25,8 @@ struct branch_flags {
 			u64 spec:2;
 			u64 new_type:4;
 			u64 priv:3;
-			u64 reserved:31;
+			u64 not_taken:1;
+			u64 reserved:30;
 		};
 	};
 };