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libbpf: Resolve enum fwd as full enum64 and vice versa

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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
This commit is contained in:
Eduard Zingerman
2022-11-02 01:54:12 +02:00
committed by Andrii Nakryiko
parent a2eba90326
commit 3a387f5a8f
1 changed files with 25 additions and 50 deletions
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75
src/btf.c
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@@ -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 */
/* 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;
}
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 */
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: