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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: 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
zero-sugar-mainline-defconfig
Andrii Nakryiko 2020-11-04 20:33:59 -08:00 committed by Alexei Starovoitov
parent f86524efcf
commit 6b6e6b1d09
1 changed files with 25 additions and 2 deletions
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27
tools/lib/bpf/btf.c
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@ -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;