perf pmus: Add placeholder core PMU

If loading a core PMU fails, legacy hardware/cache events may segv due
to there being no PMU. Create a placeholder empty PMU for this
case. This was discussed in:
https://lore.kernel.org/lkml/20230614151625.2077-1-yangjihong1@huawei.com/

Reported-by: Yang Jihong <yangjihong1@huawei.com>
Tested-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/r/20230627182834.117565-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 8d5ecd4ff1a9..7f984a7f16ca 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -928,6 +928,31 @@ err:
 	return NULL;
 }
 
+/* Creates the PMU when sysfs scanning fails. */
+struct perf_pmu *perf_pmu__create_placeholder_core_pmu(struct list_head *core_pmus)
+{
+	struct perf_pmu *pmu = zalloc(sizeof(*pmu));
+
+	if (!pmu)
+		return NULL;
+
+	pmu->name = strdup("cpu");
+	if (!pmu->name) {
+		free(pmu);
+		return NULL;
+	}
+
+	pmu->is_core = true;
+	pmu->type = PERF_TYPE_RAW;
+	pmu->cpus = cpu_map__online();
+
+	INIT_LIST_HEAD(&pmu->format);
+	INIT_LIST_HEAD(&pmu->aliases);
+	INIT_LIST_HEAD(&pmu->caps);
+	list_add_tail(&pmu->list, core_pmus);
+	return pmu;
+}
+
 void perf_pmu__warn_invalid_formats(struct perf_pmu *pmu)
 {
 	struct perf_pmu_format *format;