[PATCH 03/15] perf tools: Add a function to test for kernel support for AUX area sampling

[Adrian Hunter]

Architectures are expected to know if AUX area sampling is supported by the
hardware. Add a function perf_can_aux_sample() which will determine whether
the kernel supports it.

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
---
 tools/perf/util/evlist.h |  1 +
 tools/perf/util/record.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 13051409fd22..3655b9ebb147 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -176,6 +176,7 @@ void perf_evlist__set_id_pos(struct evlist *evlist);
 bool perf_can_sample_identifier(void);
 bool perf_can_record_switch_events(void);
 bool perf_can_record_cpu_wide(void);
+bool perf_can_aux_sample(void);
 void perf_evlist__config(struct evlist *evlist, struct record_opts *opts,
 			 struct callchain_param *callchain);
 int record_opts__config(struct record_opts *opts);
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index 8579505c29a4..e2321edcdd8f 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -136,6 +136,36 @@ bool perf_can_record_cpu_wide(void)
 	return true;
 }
 
+/*
+ * Architectures are expected to know if AUX area sampling is supported by the
+ * hardware. Here we check for kernel support.
+ */
+bool perf_can_aux_sample(void)
+{
+	struct perf_event_attr attr = {
+		.exclude_kernel = 1,
+		/*
+		 * Non-zero value causes the kernel to calculate the effective
+		 * attribute size up to that byte.
+		 */
+		.aux_sample_size = 1,
+	};
+	int fd;
+
+	fd = sys_perf_event_open(&attr, -1, 0, -1, 0);
+	/*
+	 * If the kernel attribute is big enough to contain aux_sample_size
+	 * then we assume that it is supported. We are relying on the kernel to
+	 * validate the attribute size before anything else that could be wrong.
+	 */
+	if (fd == -E2BIG)
+		return false;
+	if (fd >= 0)
+		close(fd);
+
+	return true;
+}
+
 void perf_evlist__config(struct evlist *evlist, struct record_opts *opts,
 			 struct callchain_param *callchain)
 {
-- 
2.17.1