From de048b6ee86597c6079a5ed3a1cca996089a83d3 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Wed, 2 Nov 2022 01:54:12 +0200 Subject: [PATCH] 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 Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20221101235413.1824260-1-eddyz87@gmail.com --- tools/lib/bpf/btf.c | 75 ++++++++++++++++++----------------------------------- 1 file changed, 25 insertions(+), 50 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 675a0df..71d68bf 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -3404,23 +3404,17 @@ static long btf_hash_enum(struct btf_type *t) { long h; - /* don't hash vlen and enum members to support enum fwd resolving */ + /* don't hash vlen, enum members and size to support enum fwd resolving */ h = hash_combine(0, t->name_off); - h = hash_combine(h, t->info & ~0xffff); - h = hash_combine(h, t->size); return h; } -/* Check structural equality of two ENUMs. */ -static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2) +static bool btf_equal_enum_members(struct btf_type *t1, struct btf_type *t2) { const struct btf_enum *m1, *m2; __u16 vlen; int i; - if (!btf_equal_common(t1, t2)) - return false; - vlen = btf_vlen(t1); m1 = btf_enum(t1); m2 = btf_enum(t2); @@ -3433,15 +3427,12 @@ static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2) return true; } -static bool btf_equal_enum64(struct btf_type *t1, struct btf_type *t2) +static bool btf_equal_enum64_members(struct btf_type *t1, struct btf_type *t2) { const struct btf_enum64 *m1, *m2; __u16 vlen; int i; - if (!btf_equal_common(t1, t2)) - return false; - vlen = btf_vlen(t1); m1 = btf_enum64(t1); m2 = btf_enum64(t2); @@ -3455,6 +3446,19 @@ static bool btf_equal_enum64(struct btf_type *t1, struct btf_type *t2) return true; } +/* Check structural equality of two ENUMs or ENUM64s. */ +static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2) +{ + if (!btf_equal_common(t1, t2)) + return false; + + /* t1 & t2 kinds are identical because of btf_equal_common */ + if (btf_kind(t1) == BTF_KIND_ENUM) + return btf_equal_enum_members(t1, t2); + else + return btf_equal_enum64_members(t1, t2); +} + static inline bool btf_is_enum_fwd(struct btf_type *t) { return btf_is_any_enum(t) && btf_vlen(t) == 0; @@ -3464,21 +3468,14 @@ static bool btf_compat_enum(struct btf_type *t1, struct btf_type *t2) { if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2)) return btf_equal_enum(t1, t2); - /* ignore vlen when comparing */ - return t1->name_off == t2->name_off && - (t1->info & ~0xffff) == (t2->info & ~0xffff) && - t1->size == t2->size; -} - -static bool btf_compat_enum64(struct btf_type *t1, struct btf_type *t2) -{ - if (!btf_is_enum_fwd(t1) && !btf_is_enum_fwd(t2)) - return btf_equal_enum64(t1, t2); - - /* ignore vlen when comparing */ + /* At this point either t1 or t2 or both are forward declarations, thus: + * - skip comparing vlen because it is zero for forward declarations; + * - skip comparing size to allow enum forward declarations + * to be compatible with enum64 full declarations; + * - skip comparing kind for the same reason. + */ return t1->name_off == t2->name_off && - (t1->info & ~0xffff) == (t2->info & ~0xffff) && - t1->size == t2->size; + btf_is_any_enum(t1) && btf_is_any_enum(t2); } /* @@ -3763,6 +3760,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id) break; case BTF_KIND_ENUM: + case BTF_KIND_ENUM64: h = btf_hash_enum(t); for_each_dedup_cand(d, hash_entry, h) { cand_id = (__u32)(long)hash_entry->value; @@ -3783,27 +3781,6 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id) } break; - case BTF_KIND_ENUM64: - h = btf_hash_enum(t); - for_each_dedup_cand(d, hash_entry, h) { - cand_id = (__u32)(long)hash_entry->value; - cand = btf_type_by_id(d->btf, cand_id); - if (btf_equal_enum64(t, cand)) { - new_id = cand_id; - break; - } - if (btf_compat_enum64(t, cand)) { - if (btf_is_enum_fwd(t)) { - /* resolve fwd to full enum */ - new_id = cand_id; - break; - } - /* resolve canonical enum fwd to full enum */ - d->map[cand_id] = type_id; - } - } - break; - case BTF_KIND_FWD: case BTF_KIND_FLOAT: h = btf_hash_common(t); @@ -4099,10 +4076,8 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, return btf_equal_int_tag(cand_type, canon_type); case BTF_KIND_ENUM: - return btf_compat_enum(cand_type, canon_type); - case BTF_KIND_ENUM64: - return btf_compat_enum64(cand_type, canon_type); + return btf_compat_enum(cand_type, canon_type); case BTF_KIND_FWD: case BTF_KIND_FLOAT: -- 2.7.4