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libbpf: Resolve enum fwd as full enum64 and vice versa
Changes de-duplication logic for enums in the following way: - update btf_hash_enum to ignore size and kind fields to get ENUM and ENUM64 types in a same hash bucket; - update btf_compat_enum to consider enum fwd to be compatible with full enum64 (and vice versa); This allows BTF de-duplication in the following case: // CU #1 enum foo; struct s { enum foo *a; } *x; // CU #2 enum foo { x = 0xfffffffff // big enough to force enum64 }; struct s { enum foo *a; } *y; De-duplicated BTF prior to this commit: [1] ENUM64 'foo' encoding=UNSIGNED size=8 vlen=1 'x' val=68719476735ULL [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none) [3] STRUCT 's' size=8 vlen=1 'a' type_id=4 bits_offset=0 [4] PTR '(anon)' type_id=1 [5] PTR '(anon)' type_id=3 [6] STRUCT 's' size=8 vlen=1 'a' type_id=8 bits_offset=0 [7] ENUM 'foo' encoding=UNSIGNED size=4 vlen=0 [8] PTR '(anon)' type_id=7 [9] PTR '(anon)' type_id=6 De-duplicated BTF after this commit: [1] ENUM64 'foo' encoding=UNSIGNED size=8 vlen=1 'x' val=68719476735ULL [2] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none) [3] STRUCT 's' size=8 vlen=1 'a' type_id=4 bits_offset=0 [4] PTR '(anon)' type_id=1 [5] PTR '(anon)' type_id=3 Enum forward declarations in C do not provide information about enumeration values range. Thus the `btf_type->size` field is meaningless for forward enum declarations. In fact, GCC does not encode size in DWARF for forward enum declarations (but dwarves sets enumeration size to a default value of `sizeof(int) * 8` when size is not specified see dwarf_loader.c:die__create_new_enumeration). Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20221101235413.1824260-1-eddyz87@gmail.com
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@ -3404,23 +3404,17 @@ static long btf_hash_enum(struct btf_type *t)
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{
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long h;
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/* don't hash vlen and enum members to support enum fwd resolving */
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/* don't hash vlen, enum members and size to support enum fwd resolving */
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h = hash_combine(0, t->name_off);
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h = hash_combine(h, t->info & ~0xffff);
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h = hash_combine(h, t->size);
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return h;
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}
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/* Check structural equality of two ENUMs. */
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static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2)
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static bool btf_equal_enum_members(struct btf_type *t1, struct btf_type *t2)
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{
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const struct btf_enum *m1, *m2;
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__u16 vlen;
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int i;
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if (!btf_equal_common(t1, t2))
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return false;
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vlen = btf_vlen(t1);
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m1 = btf_enum(t1);
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m2 = btf_enum(t2);
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@ -3433,15 +3427,12 @@ static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2)
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return true;
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}
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static bool btf_equal_enum64(struct btf_type *t1, struct btf_type *t2)
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static bool btf_equal_enum64_members(struct btf_type *t1, struct btf_type *t2)
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{
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const struct btf_enum64 *m1, *m2;
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__u16 vlen;
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int i;
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if (!btf_equal_common(t1, t2))
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return false;
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vlen = btf_vlen(t1);
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m1 = btf_enum64(t1);
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m2 = btf_enum64(t2);
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@ -3455,6 +3446,19 @@ static bool btf_equal_enum64(struct btf_type *t1, struct btf_type *t2)
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return true;
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}
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/* Check structural equality of two ENUMs or ENUM64s. */
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static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2)
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{
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if (!btf_equal_common(t1, t2))
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return false;
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/* t1 & t2 kinds are identical because of btf_equal_common */
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if (btf_kind(t1) == BTF_KIND_ENUM)
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return btf_equal_enum_members(t1, t2);
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else
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return btf_equal_enum64_members(t1, t2);
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}
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static inline bool btf_is_enum_fwd(struct btf_type *t)
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{
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return btf_is_any_enum(t) && btf_vlen(t) == 0;
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@ -3464,21 +3468,14 @@ static bool btf_compat_enum(struct btf_type *t1, struct btf_type *t2)
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{
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if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2))
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return btf_equal_enum(t1, t2);
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/* ignore vlen when comparing */
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/* At this point either t1 or t2 or both are forward declarations, thus:
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* - skip comparing vlen because it is zero for forward declarations;
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* - skip comparing size to allow enum forward declarations
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* to be compatible with enum64 full declarations;
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* - skip comparing kind for the same reason.
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*/
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return t1->name_off == t2->name_off &&
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(t1->info & ~0xffff) == (t2->info & ~0xffff) &&
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t1->size == t2->size;
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}
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static bool btf_compat_enum64(struct btf_type *t1, struct btf_type *t2)
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{
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if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2))
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return btf_equal_enum64(t1, t2);
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/* ignore vlen when comparing */
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return t1->name_off == t2->name_off &&
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(t1->info & ~0xffff) == (t2->info & ~0xffff) &&
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t1->size == t2->size;
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btf_is_any_enum(t1) && btf_is_any_enum(t2);
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}
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/*
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@ -3763,6 +3760,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
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break;
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case BTF_KIND_ENUM:
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case BTF_KIND_ENUM64:
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h = btf_hash_enum(t);
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for_each_dedup_cand(d, hash_entry, h) {
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cand_id = (__u32)(long)hash_entry->value;
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@ -3783,27 +3781,6 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
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}
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break;
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case BTF_KIND_ENUM64:
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h = btf_hash_enum(t);
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for_each_dedup_cand(d, hash_entry, h) {
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cand_id = (__u32)(long)hash_entry->value;
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cand = btf_type_by_id(d->btf, cand_id);
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if (btf_equal_enum64(t, cand)) {
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new_id = cand_id;
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break;
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}
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if (btf_compat_enum64(t, cand)) {
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if (btf_is_enum_fwd(t)) {
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/* resolve fwd to full enum */
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new_id = cand_id;
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break;
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}
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/* resolve canonical enum fwd to full enum */
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d->map[cand_id] = type_id;
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}
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}
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break;
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case BTF_KIND_FWD:
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case BTF_KIND_FLOAT:
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h = btf_hash_common(t);
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@ -4099,10 +4076,8 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
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return btf_equal_int_tag(cand_type, canon_type);
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case BTF_KIND_ENUM:
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return btf_compat_enum(cand_type, canon_type);
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case BTF_KIND_ENUM64:
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return btf_compat_enum64(cand_type, canon_type);
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return btf_compat_enum(cand_type, canon_type);
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case BTF_KIND_FWD:
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case BTF_KIND_FLOAT:
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