Commit 9768095b authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

btf: resolve enum fwds in btf_dedup 



GCC and clang support enum forward declarations as an extension. Such
forward-declared enums will be represented as normal BTF_KIND_ENUM types with
vlen=0. This patch adds ability to resolve such enums to their corresponding
fully defined enums. This helps to avoid duplicated BTF type graphs which only
differ by some types referencing forward-declared enum vs full enum.

One such example in kernel is enum irqchip_irq_state, defined in
include/linux/interrupt.h and forward-declared in include/linux/irq.h. This
causes entire struct task_struct and all referenced types to be duplicated in
btf_dedup output. This patch eliminates such duplication cases.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent f48a9205

tools/lib/bpf/btf.c

+38 −13
Original line number Diff line number Diff line
@@ -1602,16 +1602,12 @@ static bool btf_equal_int(struct btf_type *t1, struct btf_type *t2) 
/* Calculate type signature hash of ENUM. */

static __u32 btf_hash_enum(struct btf_type *t)

{

	struct btf_enum *member = (struct btf_enum *)(t + 1);

	__u32 vlen = BTF_INFO_VLEN(t->info);

	__u32 h = btf_hash_common(t);

	int i;

	__u32 h;



	for (i = 0; i < vlen; i++) {

		h = hash_combine(h, member->name_off);

		h = hash_combine(h, member->val);

		member++;

	}

	/* don't hash vlen and enum members 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;

}
@@ -1637,6 +1633,22 @@ static bool btf_equal_enum(struct btf_type *t1, struct btf_type *t2) 
	return true;

}



static inline bool btf_is_enum_fwd(struct btf_type *t)

{

	return BTF_INFO_KIND(t->info) == BTF_KIND_ENUM &&

	       BTF_INFO_VLEN(t->info) == 0;

}



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;

}



/*

 * Calculate type signature hash of STRUCT/UNION, ignoring referenced type IDs,

 * as referenced type IDs equivalence is established separately during type
@@ -1860,6 +1872,17 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id) 
				new_id = cand_node->type_id;

				break;

			}

			if (d->opts.dont_resolve_fwds)

				continue;

			if (btf_compat_enum(t, cand)) {

				if (btf_is_enum_fwd(t)) {

					/* resolve fwd to full enum */

					new_id = cand_node->type_id;

					break;

				}

				/* resolve canonical enum fwd to full enum */

				d->map[cand_node->type_id] = type_id;

			}

		}

		break;
@@ -2084,15 +2107,15 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, 
		return fwd_kind == real_kind;

	}



	if (cand_type->info != canon_type->info)

		return 0;



	switch (cand_kind) {

	case BTF_KIND_INT:

		return btf_equal_int(cand_type, canon_type);



	case BTF_KIND_ENUM:

		if (d->opts.dont_resolve_fwds)

			return btf_equal_enum(cand_type, canon_type);

		else

			return btf_compat_enum(cand_type, canon_type);



	case BTF_KIND_FWD:

		return btf_equal_common(cand_type, canon_type);
@@ -2103,6 +2126,8 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, 
	case BTF_KIND_PTR:

	case BTF_KIND_TYPEDEF:

	case BTF_KIND_FUNC:

		if (cand_type->info != canon_type->info)

			return 0;

		return btf_dedup_is_equiv(d, cand_type->type, canon_type->type);



	case BTF_KIND_ARRAY: {

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