libbpf: Accomodate DWARF/compiler bug with duplicated identical arrays

In some cases compiler seems to generate distinct DWARF types for identical
arrays within the same CU. That seems like a bug, but it's already out there
and breaks type graph equivalence checks, so accommodate it anyway by checking
for identical arrays, regardless of their type ID.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201105043402.2530976-10-andrii@kernel.org

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 8d04d9becb67a327e8f95c6684edda81c1923c0f..2d0d064c6d31ae863a397ebdef1489ebd5e33cec 100644 (file)
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -3785,6 +3785,19 @@ static inline __u16 btf_fwd_kind(struct btf_type *t)
        return btf_kflag(t) ? BTF_KIND_UNION : BTF_KIND_STRUCT;
 }
 
+/* Check if given two types are identical ARRAY definitions */
+static int btf_dedup_identical_arrays(struct btf_dedup *d, __u32 id1, __u32 id2)
+{
+       struct btf_type *t1, *t2;
+
+       t1 = btf_type_by_id(d->btf, id1);
+       t2 = btf_type_by_id(d->btf, id2);
+       if (!btf_is_array(t1) || !btf_is_array(t2))
+               return 0;
+
+       return btf_equal_array(t1, t2);
+}
+
 /*
  * Check equivalence of BTF type graph formed by candidate struct/union (we'll
  * call it "candidate graph" in this description for brevity) to a type graph
@@ -3895,8 +3908,18 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
        canon_id = resolve_fwd_id(d, canon_id);
 
        hypot_type_id = d->hypot_map[canon_id];
-       if (hypot_type_id <= BTF_MAX_NR_TYPES)
-               return hypot_type_id == cand_id;
+       if (hypot_type_id <= BTF_MAX_NR_TYPES) {
+               /* In some cases compiler will generate different DWARF types
+                * for *identical* array type definitions and use them for
+                * different fields within the *same* struct. This breaks type
+                * equivalence check, which makes an assumption that candidate
+                * types sub-graph has a consistent and deduped-by-compiler
+                * types within a single CU. So work around that by explicitly
+                * allowing identical array types here.
+                */
+               return hypot_type_id == cand_id ||
+                      btf_dedup_identical_arrays(d, hypot_type_id, cand_id);
+       }
 
        if (btf_dedup_hypot_map_add(d, canon_id, cand_id))
                return -ENOMEM;