Re: [PATCH v4 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot

[Song Liu]

> On Aug 31, 2021, at 9:08 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> 
> On Tue, Aug 31, 2021 at 7:01 PM Song Liu <songliubraving@xxxxxx> 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 <songliubraving@xxxxxx>
>> ---
> 
> LGTM, few minor nits below
> 
> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> 
>> .../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()

Will fix. 
> 
>> +
>> +       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()

Oops.. I added/removed it for every version, but forgot this time. Will fix 
in v5. 

Thanks,
Song