[PATCH v1] perf header: Fix missing PMU caps

[Ian Rogers]

PMU caps are written as HEADER_PMU_CAPS or for the special case of the
PMU "cpu" as HEADER_CPU_PMU_CAPS. As the PMU "cpu" is special, and not
any "core" PMU, the logic had become broken and core PMUs not called
"cpu" were not having their caps written. This affects ARM and s390
non-hybrid PMUs.

Simplify the PMU caps writing logic to scan one fewer time and to be
more explicit in its behavior.

Reported-by: Wei Li <liwei391@xxxxxxxxxx>
Fixes: 178ddf3bad98 ("perf header: Avoid hybrid PMU list in write_pmu_caps")
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/header.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 52fbf526fe74..13c71d28e0eb 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1605,8 +1605,15 @@ static int write_pmu_caps(struct feat_fd *ff,
 	int ret;
 
 	while ((pmu = perf_pmus__scan(pmu))) {
-		if (!pmu->name || !strcmp(pmu->name, "cpu") ||
-		    perf_pmu__caps_parse(pmu) <= 0)
+		if (!strcmp(pmu->name, "cpu")) {
+			/*
+			 * The "cpu" PMU is special and covered by
+			 * HEADER_CPU_PMU_CAPS. Note, core PMUs are
+			 * counted/written here for ARM, s390 and Intel hybrid.
+			 */
+			continue;
+		}
+		if (perf_pmu__caps_parse(pmu) <= 0)
 			continue;
 		nr_pmu++;
 	}
@@ -1619,23 +1626,17 @@ static int write_pmu_caps(struct feat_fd *ff,
 		return 0;
 
 	/*
-	 * Write hybrid pmu caps first to maintain compatibility with
-	 * older perf tool.
+	 * Note older perf tools assume core PMUs come first, this is a property
+	 * of perf_pmus__scan.
 	 */
-	if (perf_pmus__num_core_pmus() > 1) {
-		pmu = NULL;
-		while ((pmu = perf_pmus__scan_core(pmu))) {
-			ret = __write_pmu_caps(ff, pmu, true);
-			if (ret < 0)
-				return ret;
-		}
-	}
-
 	pmu = NULL;
 	while ((pmu = perf_pmus__scan(pmu))) {
-		if (pmu->is_core || !pmu->nr_caps)
+		if (!strcmp(pmu->name, "cpu")) {
+			/* Skip as above. */
+			continue;
+		}
+		if (perf_pmu__caps_parse(pmu) <= 0)
 			continue;
-
 		ret = __write_pmu_caps(ff, pmu, true);
 		if (ret < 0)
 			return ret;
-- 
2.42.0.rc1.204.g551eb34607-goog