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btf: resolve enum fwds in btf_dedup

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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: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2019-03-10 17:44:09 -07:00 committed by Alexei Starovoitov
parent f48a920504
commit 9768095ba9
1 changed files with 38 additions and 13 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

51
tools/lib/bpf/btf.c
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@ -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:
return btf_equal_enum(cand_type, canon_type);
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: {