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

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Sun, Mar 29, 2020 at 6:10 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:
>
> > On Sat, Mar 28, 2020 at 11:29 AM Toke Høiland-Jørgensen <toke@redhat.com> 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 <toke@redhat.com>
> >> ---
> >>  .../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:

Right, because test_global_data uses BPF-only struct definitions. In
real life those types should be shared in a common header file.

For this feature, I'd suggest to create a separate trivial BPF program
with a simple trivial BPF program and single global variable. There is
nothing you really need from test_global_data setup.

>
> 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
>