[RFC bpf-next 3/8] libbpf: use metadata to compute an unknown kind size

[Alan Maguire <alan.maguire@xxxxxxxxxx>]

This allows BTF parsing to proceed even if we do not know the
kind.

Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
 tools/lib/bpf/btf.c | 50 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 036dc1505969..77a072716d58 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -336,7 +336,40 @@ static int btf_parse_meta_sec(struct btf *btf)
 	return 0;
 }
 
-static int btf_type_size(const struct btf_type *t)
+/* for unknown kinds, consult kind metadata. */
+static int btf_type_size_unknown(const struct btf *btf, const struct btf_type *t)
+{
+	int size = sizeof(struct btf_type);
+	struct btf_kind_meta *m = NULL;
+	__u16 vlen = btf_vlen(t);
+	__u8 kind = btf_kind(t);
+
+	if (btf->meta_data) {
+		struct btf_metadata *meta = btf->meta_data;
+
+		if (kind < meta->kind_meta_cnt)
+			m = &meta->kind_meta[kind];
+	}
+
+	if (!m || (void *)m > (btf->meta_data + btf->hdr->meta_header.meta_len)) {
+		pr_debug("Unsupported BTF_KIND: %u\n", btf_kind(t));
+		return -EINVAL;
+	}
+
+	if (!(m->flags & BTF_KIND_META_OPTIONAL)) {
+		/* a required kind, and we do not know about it.. */
+		pr_debug("unknown but required kind: %s(%u)\n",
+			 btf__name_by_offset(btf, m->name_off), kind);
+		return -EINVAL;
+	}
+
+	size += m->info_sz;
+	size += vlen * m->elem_sz;
+
+	return size;
+}
+
+static int btf_type_size(const struct btf *btf, const struct btf_type *t)
 {
 	const int base_size = sizeof(struct btf_type);
 	__u16 vlen = btf_vlen(t);
@@ -372,8 +405,7 @@ static int btf_type_size(const struct btf_type *t)
 	case BTF_KIND_DECL_TAG:
 		return base_size + sizeof(struct btf_decl_tag);
 	default:
-		pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
-		return -EINVAL;
+		return btf_type_size_unknown(btf, t);
 	}
 }
 
@@ -472,7 +504,7 @@ static int btf_parse_type_sec(struct btf *btf)
 		if (btf->swapped_endian)
 			btf_bswap_type_base(next_type);
 
-		type_size = btf_type_size(next_type);
+		type_size = btf_type_size(btf, next_type);
 		if (type_size < 0)
 			return type_size;
 		if (next_type + type_size > end_type) {
@@ -952,10 +984,8 @@ static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
 	btf->types_data = btf->raw_data + btf->hdr->hdr_len + btf->hdr->type_off;
 
 	err = btf_parse_str_sec(btf);
+	err = err ?: btf_parse_meta_sec(btf);
 	err = err ?: btf_parse_type_sec(btf);
-	if (err)
-		goto done;
-	err = btf_parse_meta_sec(btf);
 
 done:
 	if (err) {
@@ -1687,7 +1717,7 @@ int btf__add_type(struct btf *btf, const struct btf *src_btf, const struct btf_t
 	struct btf_type *t;
 	int sz, err;
 
-	sz = btf_type_size(src_type);
+	sz = btf_type_size(src_btf, src_type);
 	if (sz < 0)
 		return libbpf_err(sz);
 
@@ -1768,7 +1798,7 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 	memcpy(t, src_btf->types_data, data_sz);
 
 	for (i = 0; i < cnt; i++) {
-		sz = btf_type_size(t);
+		sz = btf_type_size(src_btf, t);
 		if (sz < 0) {
 			/* unlikely, has to be corrupted src_btf */
 			err = sz;
@@ -4764,7 +4794,7 @@ static int btf_dedup_compact_types(struct btf_dedup *d)
 			continue;
 
 		t = btf__type_by_id(d->btf, id);
-		len = btf_type_size(t);
+		len = btf_type_size(d->btf, t);
 		if (len < 0)
 			return len;
 
-- 
2.31.1