Re: [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr()

[Andrii Nakryiko]

On Wed, Aug 19, 2020 at 3:42 PM Hao Luo <haoluo@xxxxxxxxxx> wrote:
>
> Test bpf_per_cpu_ptr(). Test two paths in the kernel. If the base
> pointer points to a struct, the returned reg is of type PTR_TO_BTF_ID.
> Direct pointer dereference can be applied on the returned variable.
> If the base pointer isn't a struct, the returned reg is of type
> PTR_TO_MEM, which also supports direct pointer dereference.
>
> Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx>
> ---

Acked-by: Andrii Nakryiko <andriin@xxxxxx>

>  .../testing/selftests/bpf/prog_tests/ksyms_btf.c  |  4 ++++
>  .../testing/selftests/bpf/progs/test_ksyms_btf.c  | 15 ++++++++++++++-
>  2 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> index 1dad61ba7e99..bdedd4a76b42 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> @@ -71,6 +71,10 @@ void test_ksyms_btf(void)
>               "got %llu, exp %llu\n", data->out__runqueues, runqueues_addr);
>         CHECK(data->out__bpf_prog_active != bpf_prog_active_addr, "bpf_prog_active",
>               "got %llu, exp %llu\n", data->out__bpf_prog_active, bpf_prog_active_addr);
> +       CHECK(data->out__rq_cpu != 1, "rq_cpu",
> +             "got %u, exp %u\n", data->out__rq_cpu, 1);
> +       CHECK(data->out__process_counts == -1, "process_counts",
> +             "got %lu, exp != -1", data->out__process_counts);
>
>  cleanup:
>         test_ksyms_btf__destroy(skel);
> diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_btf.c b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> index e04e31117f84..78cf1ebb753d 100644
> --- a/tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> +++ b/tools/testing/selftests/bpf/progs/test_ksyms_btf.c
> @@ -7,16 +7,29 @@
>
>  __u64 out__runqueues = -1;
>  __u64 out__bpf_prog_active = -1;
> +__u32 out__rq_cpu = -1;
> +unsigned long out__process_counts = -1;

try to not use long for variables, it is 32-bit integer in user-space
but always 64-bit in BPF. This causes problems when using skeleton on
32-bit architecture.

>
> -extern const struct rq runqueues __ksym; /* struct type global var. */
> +extern const struct rq runqueues __ksym; /* struct type percpu var. */
>  extern const int bpf_prog_active __ksym; /* int type global var. */
> +extern const unsigned long process_counts __ksym; /* int type percpu var. */
>
>  SEC("raw_tp/sys_enter")
>  int handler(const void *ctx)
>  {
> +       struct rq *rq;
> +       unsigned long *count;
> +
>         out__runqueues = (__u64)&runqueues;
>         out__bpf_prog_active = (__u64)&bpf_prog_active;
>
> +       rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1);
> +       if (rq)
> +               out__rq_cpu = rq->cpu;

this is awesome!

Are there any per-cpu variables that are arrays? Would be nice to test
those too.


> +       count = (unsigned long *)bpf_per_cpu_ptr(&process_counts, 1);
> +       if (count)
> +               out__process_counts = *count;
> +
>         return 0;
>  }
>
> --
> 2.28.0.220.ged08abb693-goog
>