Commit 6b6e6b1d authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201105043402.2530976-10-andrii@kernel.org
parent f86524ef

tools/lib/bpf/btf.c

+25 −2
Original line number Diff line number Diff line
@@ -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;