[PATCH v16 bpf-next 3/9] libbpf: Use layout to compute an unknown kind size

[Alan Maguire <alan.maguire@oracle.com>]

This allows BTF parsing to proceed even if we do not know the
kind.  Fall back to base BTF layout if layout information is
not in split BTF.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/lib/bpf/btf.c | 52 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 43 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 2c6c524175c0..291691171ca7 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -386,7 +386,42 @@ static int btf_parse_layout_sec(struct btf *btf)
 	return 0;
 }
 
-static int btf_type_size(const struct btf_type *t)
+/* for unknown kinds, consult kind layout. */
+static int btf_type_size_unknown(const struct btf *btf, const struct btf_type *t)
+{
+	__u32 l_cnt = btf->hdr.layout_len / sizeof(struct btf_layout);
+	struct btf_layout *l = btf->layout;
+	__u16 vlen = btf_vlen(t);
+	__u32 kind = btf_kind(t);
+
+	/* Fall back to base BTF if needed as they share layout information */
+	if (!l) {
+		struct btf *base_btf = btf->base_btf;
+
+		if (base_btf) {
+			l = base_btf->layout;
+			l_cnt = base_btf->hdr.layout_len / sizeof(struct btf_layout);
+		}
+	}
+	if (!l || kind >= l_cnt) {
+		pr_debug("Unsupported BTF_KIND: %u\n", btf_kind(t));
+		return -EINVAL;
+	}
+	if (l[kind].info_sz % 4) {
+		pr_debug("Unsupported info_sz %u for kind %u\n",
+			  l[kind].info_sz, kind);
+		return -EINVAL;
+	}
+	if (l[kind].elem_sz % 4) {
+		pr_debug("Unsupported elem_sz %u for kind %u\n",
+			 l[kind].elem_sz, kind);
+		return -EINVAL;
+	}
+
+	return sizeof(struct btf_type) + l[kind].info_sz + vlen * l[kind].elem_sz;
+}
+
+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);
@@ -422,8 +457,7 @@ 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);
 	}
 }
 
@@ -521,7 +555,7 @@ 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) {
@@ -2102,7 +2136,7 @@ static int btf_add_type(struct btf_pipe *p, const struct btf_type *src_type)
 	__u32 *str_off;
 	int sz, err;
 
-	sz = btf_type_size(src_type);
+	sz = btf_type_size(p->src, src_type);
 	if (sz < 0)
 		return libbpf_err(sz);
 
@@ -2192,7 +2226,7 @@ int btf__add_btf(struct btf *btf, const struct btf *src_btf)
 		struct btf_field_iter it;
 		__u32 *type_id, *str_off;
 
-		sz = btf_type_size(t);
+		sz = btf_type_size(src_btf, t);
 		if (sz < 0) {
 			/* unlikely, has to be corrupted src_btf */
 			err = sz;
@@ -5560,7 +5594,7 @@ 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;
 
@@ -6222,7 +6256,7 @@ int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
 
 		id = order_map[i];
 		t = btf__type_by_id(btf, id);
-		type_size = btf_type_size(t);
+		type_size = btf_type_size(btf, t);
 		memcpy(nt, t, type_size);
 
 		/* fix up referenced IDs for BTF */
@@ -6248,7 +6282,7 @@ int btf__permute(struct btf *btf, __u32 *id_map, __u32 id_map_cnt,
 
 	for (nt = new_types, i = 0; i < id_map_cnt - start_offs; i++) {
 		btf->type_offs[i] = nt - new_types;
-		nt += btf_type_size(nt);
+		nt += btf_type_size(btf, nt);
 	}
 
 	free(order_map);
-- 
2.39.3