[PATCH bpf-next v3 11/15] libbpf: struct_ops in SEC("?.struct_ops") and SEC("?.struct_ops.link")

[Eduard Zingerman <eddyz87@gmail.com>]

Allow using two new section names for struct_ops maps:
- SEC("?.struct_ops")
- SEC("?.struct_ops.link")

To specify maps that have bpf_map->autocreate == false after open.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/lib/bpf/libbpf.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 4ef3902e65db..c0212244bdf7 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -497,6 +497,8 @@ struct bpf_struct_ops {
 #define KSYMS_SEC ".ksyms"
 #define STRUCT_OPS_SEC ".struct_ops"
 #define STRUCT_OPS_LINK_SEC ".struct_ops.link"
+#define OPT_STRUCT_OPS_SEC "?.struct_ops"
+#define OPT_STRUCT_OPS_LINK_SEC "?.struct_ops.link"
 
 enum libbpf_map_type {
 	LIBBPF_MAP_UNSPEC,
@@ -1324,6 +1326,15 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
 			return -ENOMEM;
 		map->btf_value_type_id = type_id;
 
+		/* Follow same convention as for programs autoload:
+		 * SEC("?.struct_ops") means map is not created by default.
+		 */
+		if (sec_name[0] == '?') {
+			map->autocreate = false;
+			/* from now on forget there was ? in section name */
+			sec_name++;
+		}
+
 		map->def.type = BPF_MAP_TYPE_STRUCT_OPS;
 		map->def.key_size = sizeof(int);
 		map->def.value_size = type->size;
@@ -3688,7 +3699,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 				sec_desc->shdr = sh;
 				sec_desc->data = data;
 			} else if (strcmp(name, STRUCT_OPS_SEC) == 0 ||
-				   strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
+				   strcmp(name, STRUCT_OPS_LINK_SEC) == 0 ||
+				   strcmp(name, OPT_STRUCT_OPS_SEC) == 0 ||
+				   strcmp(name, OPT_STRUCT_OPS_LINK_SEC) == 0) {
 				sec_desc->sec_type = SEC_ST_OPS;
 				sec_desc->shdr = sh;
 				sec_desc->data = data;
@@ -3708,6 +3721,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			if (!section_have_execinstr(obj, targ_sec_idx) &&
 			    strcmp(name, ".rel" STRUCT_OPS_SEC) &&
 			    strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
+			    strcmp(name, ".rel" OPT_STRUCT_OPS_SEC) &&
+			    strcmp(name, ".rel" OPT_STRUCT_OPS_LINK_SEC) &&
 			    strcmp(name, ".rel" MAPS_ELF_SEC)) {
 				pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
 					idx, name, targ_sec_idx,
-- 
2.43.0