Subject: Re: [PATCH v3 2/2] selftests: Add test for overriding global data value before load

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Sun, 29 Mar 2020 15:10:47 +0200

Andrii Nakryiko <[email-masked]> writes:

> On Sat, Mar 28, 2020 at 11:29 AM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> This extends the global_data test to also exercise the new
>> bpf_map__set_initial_value() function. The test simply overrides the global
>> data section with all zeroes, and checks that the new value makes it into
>> the kernel map on load.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
>> ---
>>  .../selftests/bpf/prog_tests/global_data.c    | 61 +++++++++++++++++++
>>  1 file changed, 61 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/global_data.c b/tools/testing/selftests/bpf/prog_tests/global_data.c
>> index c680926fce73..f018ce53a8d1 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/global_data.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/global_data.c
>> @@ -121,6 +121,65 @@ static void test_global_data_rdonly(struct bpf_object *obj, __u32 duration)
>>               "err %d errno %d\n", err, errno);
>>  }
>>
>> +static void test_global_data_set_rdonly(__u32 duration)
>> +{
>> +       const char *file = "./test_global_data.o";
>> +       int err = -ENOMEM, map_fd, zero = 0;
>> +       __u8 *buff = NULL, *newval = NULL;
>> +       struct bpf_program *prog;
>> +       struct bpf_object *obj;
>> +       struct bpf_map *map;
>> +       size_t sz;
>> +
>> +       obj = bpf_object__open_file(file, NULL);
>
> Try using skeleton open and load .o file, it will cut this code almost
> in half.

Doesn't work, though:

In file included from /home/build/linux/tools/testing/selftests/bpf/prog_tests/global_data_init.c:3:
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:31:14: error: field ‘struct1’ has incomplete type
   31 |   struct foo struct1;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:37:14: error: field ‘struct3’ has incomplete type
   37 |   struct foo struct3;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:45:14: error: field ‘struct0’ has incomplete type
   45 |   struct foo struct0;
      |              ^~~~~~~
/home/build/linux/tools/testing/selftests/bpf/test_global_data.skel.h:46:14: error: field ‘struct2’ has incomplete type
   46 |   struct foo struct2;
      |              ^~~~~~~
make: *** [Makefile:361: /home/build/linux/tools/testing/selftests/bpf/global_data_init.test.o] Error 1

Just fixing the program SEC name as you suggested below already gets rid
of half the setup code, though, so doesn't really make much difference
anyway :)

>> +       if (CHECK_FAIL(!obj))
>> +               return;
>> +       prog = bpf_program__next(NULL, obj);
>> +       if (CHECK_FAIL(!prog))
>> +               goto out;
>> +       err = bpf_program__set_sched_cls(prog);
>
> Please fix SEC() name for that program instead of setting type explicitly.

Yeah, that helps, thanks!

>> +       if (CHECK_FAIL(err))
>> +               goto out;
>> +
>> +       map = bpf_object__find_map_by_name(obj, "test_glo.rodata");
>> +       if (CHECK_FAIL(!map || !bpf_map__is_internal(map)))
>> +               goto out;
>> +
>> +       sz = bpf_map__def(map)->value_size;
>> +       newval = malloc(sz);
>> +       if (CHECK_FAIL(!newval))
>> +               goto out;
>> +       memset(newval, 0, sz);
>> +
>> +       /* wrong size, should fail */
>> +       err = bpf_map__set_initial_value(map, newval, sz - 1);
>> +       if (CHECK(!err, "reject set initial value wrong size", "err %d\n", err))
>> +               goto out;
>> +
>> +       err = bpf_map__set_initial_value(map, newval, sz);
>> +       if (CHECK_FAIL(err))
>> +               goto out;
>> +
>> +       err = bpf_object__load(obj);
>> +       if (CHECK_FAIL(err))
>> +               goto out;
>> +
>> +       map_fd = bpf_map__fd(map);
>> +       if (CHECK_FAIL(map_fd < 0))
>> +               goto out;
>> +
>> +       buff = malloc(sz);
>> +       if (buff)
>> +               err = bpf_map_lookup_elem(map_fd, &zero, buff);
>> +       CHECK(!buff || err || memcmp(buff, newval, sz),
>> +             "compare .rodata map data override",
>> +             "err %d errno %d\n", err, errno);
>> +out:
>> +       free(buff);
>> +       free(newval);
>> +       bpf_object__close(obj);
>> +}
>> +
>>  void test_global_data(void)
>>  {
>>         const char *file = "./test_global_data.o";
>> @@ -144,4 +203,6 @@ void test_global_data(void)
>>         test_global_data_rdonly(obj, duration);
>>
>>         bpf_object__close(obj);
>> +
>> +       test_global_data_set_rdonly(duration);
>
> This should either be a sub-test or better yet a separate test
> altogether.

Sure, will move it to its own file.

-Toke