netdev - [PATCH bpf-next 1/2] libbpf: do not resolve size on duplicate FUNCs

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Message-Id: <20240929-libbpf-dup-extern-funcs-v1-1-df15fbd6525b@hack3r.moe>
Date: Sun, 29 Sep 2024 16:48:00 +0800
From: Eric Long via B4 Relay <devnull+i.hack3r.moe@...nel.org>
To: bpf@...r.kernel.org
Cc: Andrii Nakryiko <andrii@...nel.org>, 
 Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org, 
 Eric Long <i@...k3r.moe>
Subject: [PATCH bpf-next 1/2] libbpf: do not resolve size on duplicate
 FUNCs

From: Eric Long <i@...k3r.moe>

FUNCs do not have sizes, thus currently btf__resolve_size will fail
with -EINVAL. Add conditions so that we only update size when the BTF
object is not function or function prototype.

Signed-off-by: Eric Long <i@...k3r.moe>
---
 tools/lib/bpf/linker.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 81dbbdd79a7c65a4b048b85e1dba99cb5f7cb56b..a2a7075038f898053b468a8256b93460edc29de6 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -2449,20 +2449,24 @@ static int linker_append_btf(struct bpf_linker *linker, struct src_obj *obj)
 			 * the same extern VARs/FUNCs.
 			 */
 			if (glob_sym && glob_sym->var_idx >= 0) {
+				const struct btf_type *t = btf__type_by_id(linker->btf, glob_sym->underlying_btf_id);
+				int kind = btf_kind(t);
 				__s64 sz;
 
 				dst_var = &dst_sec->sec_vars[glob_sym->var_idx];
-				/* Because underlying BTF type might have
-				 * changed, so might its size have changed, so
-				 * re-calculate and update it in sec_var.
-				 */
-				sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
-				if (sz < 0) {
-					pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
-						name, (int)sz);
-					return -EINVAL;
+				if (kind != BTF_KIND_FUNC && kind != BTF_KIND_FUNC_PROTO) {
+					/* Because underlying BTF type might have
+					 * changed, so might its size have changed, so
+					 * re-calculate and update it in sec_var.
+					 */
+					sz = btf__resolve_size(linker->btf, glob_sym->underlying_btf_id);
+					if (sz < 0) {
+						pr_warn("global '%s': failed to resolve size of underlying type: %d\n",
+							name, (int)sz);
+						return -EINVAL;
+					}
+					dst_var->size = sz;
 				}
-				dst_var->size = sz;
 				continue;
 			}
 

-- 
2.46.2