netdev - Re: [PATCH bpf-next 5/5] selftests/bpf: add btf

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Message-ID: <CAPhsuW6GhACUz9+Mahr2U=vFxzSNxirtfqEPuu1njqngdUrZCA@mail.gmail.com>
Date:   Thu, 28 Feb 2019 10:29:48 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>, kernel-team@...com,
        ast@...com, Arnaldo Carvalho de Melo <acme@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: add btf_dedup test of
 FWD/STRUCT resolution

On Wed, Feb 27, 2019 at 2:48 PM Andrii Nakryiko <andriin@...com> wrote:
>
> This patch adds a btf_dedup test exercising logic of STRUCT<->FWD
> resolution and validating that STRUCT is not resolved to a FWD. It also
> forces hash collisions, forcing both FWD and STRUCT to be candidates for
> each other. Previously this condition caused infinite loop due to FWD
> pointing to STRUCT and STRUCT pointing to its FWD.
>
> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Acked-by: Song Liu <songliubraving@...com>

> ---
>  tools/testing/selftests/bpf/test_btf.c | 45 ++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/test_btf.c b/tools/testing/selftests/bpf/test_btf.c
> index 1426c0a905c8..38797aa627a7 100644
> --- a/tools/testing/selftests/bpf/test_btf.c
> +++ b/tools/testing/selftests/bpf/test_btf.c
> @@ -5731,6 +5731,51 @@ const struct btf_dedup_test dedup_tests[] = {
>                 .dont_resolve_fwds = false,
>         },
>  },
> +{
> +       .descr = "dedup: struct <-> fwd resolution w/ hash collision",
> +       /*
> +        * // CU 1:
> +        * struct x;
> +        * struct s {
> +        *      struct x *x;
> +        * };
> +        * // CU 2:
> +        * struct x {};
> +        * struct s {
> +        *      struct x *x;
> +        * };
> +        */
> +       .input = {
> +               .raw_types = {
> +                       /* CU 1 */
> +                       BTF_FWD_ENC(NAME_TBD, 0 /* struct fwd */),      /* [1] fwd x      */
> +                       BTF_PTR_ENC(1),                                 /* [2] ptr -> [1] */
> +                       BTF_STRUCT_ENC(NAME_TBD, 1, 8),                 /* [3] struct s   */
> +                               BTF_MEMBER_ENC(NAME_TBD, 2, 0),
> +                       /* CU 2 */
> +                       BTF_STRUCT_ENC(NAME_TBD, 0, 0),                 /* [4] struct x   */
> +                       BTF_PTR_ENC(4),                                 /* [5] ptr -> [4] */
> +                       BTF_STRUCT_ENC(NAME_TBD, 1, 8),                 /* [6] struct s   */
> +                               BTF_MEMBER_ENC(NAME_TBD, 5, 0),
> +                       BTF_END_RAW,
> +               },
> +               BTF_STR_SEC("\0x\0s\0x\0x\0s\0x\0"),
> +       },
> +       .expect = {
> +               .raw_types = {
> +                       BTF_PTR_ENC(3),                                 /* [1] ptr -> [3] */
> +                       BTF_STRUCT_ENC(NAME_TBD, 1, 8),                 /* [2] struct s   */
> +                               BTF_MEMBER_ENC(NAME_TBD, 1, 0),
> +                       BTF_STRUCT_ENC(NAME_NTH(2), 0, 0),              /* [3] struct x   */
> +                       BTF_END_RAW,
> +               },
> +               BTF_STR_SEC("\0s\0x"),
> +       },
> +       .opts = {
> +               .dont_resolve_fwds = false,
> +               .dedup_table_size = 1, /* force hash collisions */
> +       },
> +},
>  {
>         .descr = "dedup: all possible kinds (no duplicates)",
>         .input = {
> --
> 2.17.1
>