selftests/bpf: add btf_dedup test of FWD/STRUCT resolution

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@redhat.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/testing/selftests/bpf/test_btf.c b/tools/testing/selftests/bpf/test_btf.c
index 1426c0a905c89605ff9c6c69b08aeb51c1650faf..38797aa627a732f31d333aaa6cf8020ceb3a211d 100644 (file)
--- 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 = {