v4.19.13 snapshot.
diff --git a/tools/perf/tests/backward-ring-buffer.c b/tools/perf/tests/backward-ring-buffer.c
new file mode 100644
index 0000000..6d598cc
--- /dev/null
+++ b/tools/perf/tests/backward-ring-buffer.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test backward bit in event attribute, read ring buffer from end to
+ * beginning
+ */
+
+#include <perf.h>
+#include <evlist.h>
+#include <sys/prctl.h>
+#include "tests.h"
+#include "debug.h"
+#include <errno.h>
+
+#define NR_ITERS 111
+
+static void testcase(void)
+{
+ int i;
+
+ for (i = 0; i < NR_ITERS; i++) {
+ char proc_name[10];
+
+ snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
+ prctl(PR_SET_NAME, proc_name);
+ }
+}
+
+static int count_samples(struct perf_evlist *evlist, int *sample_count,
+ int *comm_count)
+{
+ int i;
+
+ for (i = 0; i < evlist->nr_mmaps; i++) {
+ struct perf_mmap *map = &evlist->overwrite_mmap[i];
+ union perf_event *event;
+
+ perf_mmap__read_init(map);
+ while ((event = perf_mmap__read_event(map)) != NULL) {
+ const u32 type = event->header.type;
+
+ switch (type) {
+ case PERF_RECORD_SAMPLE:
+ (*sample_count)++;
+ break;
+ case PERF_RECORD_COMM:
+ (*comm_count)++;
+ break;
+ default:
+ pr_err("Unexpected record of type %d\n", type);
+ return TEST_FAIL;
+ }
+ }
+ perf_mmap__read_done(map);
+ }
+ return TEST_OK;
+}
+
+static int do_test(struct perf_evlist *evlist, int mmap_pages,
+ int *sample_count, int *comm_count)
+{
+ int err;
+ char sbuf[STRERR_BUFSIZE];
+
+ err = perf_evlist__mmap(evlist, mmap_pages);
+ if (err < 0) {
+ pr_debug("perf_evlist__mmap: %s\n",
+ str_error_r(errno, sbuf, sizeof(sbuf)));
+ return TEST_FAIL;
+ }
+
+ perf_evlist__enable(evlist);
+ testcase();
+ perf_evlist__disable(evlist);
+
+ err = count_samples(evlist, sample_count, comm_count);
+ perf_evlist__munmap(evlist);
+ return err;
+}
+
+
+int test__backward_ring_buffer(struct test *test __maybe_unused, int subtest __maybe_unused)
+{
+ int ret = TEST_SKIP, err, sample_count = 0, comm_count = 0;
+ char pid[16], sbuf[STRERR_BUFSIZE];
+ struct perf_evlist *evlist;
+ struct perf_evsel *evsel __maybe_unused;
+ struct parse_events_error parse_error;
+ struct record_opts opts = {
+ .target = {
+ .uid = UINT_MAX,
+ .uses_mmap = true,
+ },
+ .freq = 0,
+ .mmap_pages = 256,
+ .default_interval = 1,
+ };
+
+ snprintf(pid, sizeof(pid), "%d", getpid());
+ pid[sizeof(pid) - 1] = '\0';
+ opts.target.tid = opts.target.pid = pid;
+
+ evlist = perf_evlist__new();
+ if (!evlist) {
+ pr_debug("Not enough memory to create evlist\n");
+ return TEST_FAIL;
+ }
+
+ err = perf_evlist__create_maps(evlist, &opts.target);
+ if (err < 0) {
+ pr_debug("Not enough memory to create thread/cpu maps\n");
+ goto out_delete_evlist;
+ }
+
+ bzero(&parse_error, sizeof(parse_error));
+ /*
+ * Set backward bit, ring buffer should be writing from end. Record
+ * it in aux evlist
+ */
+ err = parse_events(evlist, "syscalls:sys_enter_prctl/overwrite/", &parse_error);
+ if (err) {
+ pr_debug("Failed to parse tracepoint event, try use root\n");
+ ret = TEST_SKIP;
+ goto out_delete_evlist;
+ }
+
+ perf_evlist__config(evlist, &opts, NULL);
+
+ err = perf_evlist__open(evlist);
+ if (err < 0) {
+ pr_debug("perf_evlist__open: %s\n",
+ str_error_r(errno, sbuf, sizeof(sbuf)));
+ goto out_delete_evlist;
+ }
+
+ ret = TEST_FAIL;
+ err = do_test(evlist, opts.mmap_pages, &sample_count,
+ &comm_count);
+ if (err != TEST_OK)
+ goto out_delete_evlist;
+
+ if ((sample_count != NR_ITERS) || (comm_count != NR_ITERS)) {
+ pr_err("Unexpected counter: sample_count=%d, comm_count=%d\n",
+ sample_count, comm_count);
+ goto out_delete_evlist;
+ }
+
+ err = do_test(evlist, 1, &sample_count, &comm_count);
+ if (err != TEST_OK)
+ goto out_delete_evlist;
+
+ ret = TEST_OK;
+out_delete_evlist:
+ perf_evlist__delete(evlist);
+ return ret;
+}