[PATCH bpf-next 1/2] libbpf: fix a couple of missed btf_type_tag handling in btf.c

[Yonghong Song <yhs@fb.com>]

Commit 2dc1e488e5cd ("libbpf: Support BTF_KIND_TYPE_TAG") added
BTF_KIND_TYPE_TAG support. But to test vmlinux build with
  #define __user __attribute__((btf_type_tag("user")))
I need to sync libbpf repo and manually copy libbpf sources
to pahole. To simplify process, I used BTF_KIND_RESTRICT to
simulate BTF_KIND_TYPE_TAG with vmlinux build as "restrict"
modifier is barely used in kernel. But this approach missed
one case in dedup with structures where BTF_KIND_RESTRICT is
handled and BTF_KIND_TYPE_TAG is not handled in
btf_dedup_is_equiv(), and this will result in pahole dedup
failure. This patch fixed this issue and a selftest is added in
the subsequent patch to test this scenario.

The other missed handling is in btf__resolve_size().
Currently the compiler always emit like PTR->TYPE_TAG->...
so in practice we don't hit the missing BTF_KIND_TYPE_TAG handling
issue with compiler generated code. But let us added
case BTF_KIND_TYPE_TAG in the switch statement
to be future proof.

Fixes: 2dc1e488e5cd ("libbpf: Support BTF_KIND_TYPE_TAG")
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/btf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index fadf089ae8fe..b6be579e0dc6 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -610,6 +610,7 @@ __s64 btf__resolve_size(const struct btf *btf, __u32 type_id)
 		case BTF_KIND_RESTRICT:
 		case BTF_KIND_VAR:
 		case BTF_KIND_DECL_TAG:
+		case BTF_KIND_TYPE_TAG:
 			type_id = t->type;
 			break;
 		case BTF_KIND_ARRAY:
@@ -4023,6 +4024,7 @@ 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:
+	case BTF_KIND_TYPE_TAG:
 		if (cand_type->info != canon_type->info)
 			return 0;
 		return btf_dedup_is_equiv(d, cand_type->type, canon_type->type);
-- 
2.30.2