On Tue, Aug 31, 2021 at 7:01 PM Song Liu [off-list ref] wrote:

This test uses bpf_get_branch_snapshot from a fexit program. The test uses
a target function (bpf_testmod_loop_test) and compares the record against
kallsyms. If there isn't enough record matching kallsyms, the test fails.

Signed-off-by: Song Liu <redacted>
---

LGTM, few minor nits below

Acked-by: Andrii Nakryiko <andrii@kernel.org>

 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  14 ++-
 .../bpf/prog_tests/get_branch_snapshot.c      | 101 ++++++++++++++++++
 .../selftests/bpf/progs/get_branch_snapshot.c |  44 ++++++++
 tools/testing/selftests/bpf/trace_helpers.c   |  37 +++++++
 tools/testing/selftests/bpf/trace_helpers.h   |   5 +
 5 files changed, 200 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
 create mode 100644 tools/testing/selftests/bpf/progs/get_branch_snapshot.c

[...]

+
+void test_get_branch_snapshot(void)
+{
+       struct get_branch_snapshot *skel = NULL;
+       int err;
+
+       if (create_perf_events()) {
+               test__skip();  /* system doesn't support LBR */
+               goto cleanup;
+       }
+
+       skel = get_branch_snapshot__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "get_branch_snapshot__open_and_load"))
+               goto cleanup;
+
+       err = kallsyms_find("bpf_testmod_loop_test", &skel->bss->address_low);
+       if (!ASSERT_OK(err, "kallsyms_find"))
+               goto cleanup;
+
+       err = kallsyms_find_next("bpf_testmod_loop_test", &skel->bss->address_high);
+       if (!ASSERT_OK(err, "kallsyms_find_next"))
+               goto cleanup;
+
+       err = get_branch_snapshot__attach(skel);
+       if (!ASSERT_OK(err, "get_branch_snapshot__attach"))
+               goto cleanup;
+
+       /* trigger the program */
+       system("cat /sys/kernel/bpf_testmod > /dev/null 2>& 1");

ugh :( see prog_tests/module_attach.c, we can extract and reuse
trigger_module_test_read() and trigger_module_test_write()

+
+       if (skel->bss->total_entries < 16) {
+               /* too few entries for the hit/waste test */
+               test__skip();
+               goto cleanup;
+       }
+

[...]

+SEC("fexit/bpf_testmod_loop_test")
+int BPF_PROG(test1, int n, int ret)
+{
+       long i;
+
+       total_entries = bpf_get_branch_snapshot(entries, sizeof(entries), 0);
+       total_entries /= sizeof(struct perf_branch_entry);
+
+       bpf_printk("total_entries %lu\n", total_entries);
+
+       for (i = 0; i < PERF_MAX_BRANCH_SNAPSHOT; i++) {
+               if (i >= total_entries)
+                       break;
+               if (in_range(entries[i].from) && in_range(entries[i].to))
+                       test1_hits++;
+               else if (!test1_hits)
+                       wasted_entries++;
+               bpf_printk("i %d from %llx to %llx", i, entries[i].from,
+                          entries[i].to);

debug leftovers? this will be polluting trace_pipe unnecessarily; same
for above total_entries bpf_printk()

[...]