tools: Allow specifying base BTF file in resolve_btfids

This commit allows specifying the base BTF for resolving btf id
lists/sets during link time in the resolve_btfids tool. The base BTF is
set to NULL if no path is passed. This allows resolving BTF ids for
module kernel objects.

Also, drop the --no-fail option, as it is only used in case .BTF_ids
section is not present, instead make no-fail the default mode. The long
option name is same as that of pahole.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-5-memxor@gmail.com

tools/bpf/resolve_btfids/main.c

@@ -89,6 +89,7 @@ struct btf_id {
 struct object {
 	const char *path;
 	const char *btf;
+	const char *base_btf_path;
 
 	struct {
 		int		 fd;
@@ -477,16 +478,27 @@ static int symbols_resolve(struct object *obj)
 	int nr_structs  = obj->nr_structs;
 	int nr_unions   = obj->nr_unions;
 	int nr_funcs    = obj->nr_funcs;
+	struct btf *base_btf = NULL;
 	int err, type_id;
 	struct btf *btf;
 	__u32 nr_types;
 
-	btf = btf__parse(obj->btf ?: obj->path, NULL);
+	if (obj->base_btf_path) {
+		base_btf = btf__parse(obj->base_btf_path, NULL);
+		err = libbpf_get_error(base_btf);
+		if (err) {
+			pr_err("FAILED: load base BTF from %s: %s\n",
+			       obj->base_btf_path, strerror(-err));
+			return -1;
+		}
+	}
+
+	btf = btf__parse_split(obj->btf ?: obj->path, base_btf);
 	err = libbpf_get_error(btf);
 	if (err) {
 		pr_err("FAILED: load BTF from %s: %s\n",
 			obj->btf ?: obj->path, strerror(-err));
-		return -1;
+		goto out;
 	}
 
 	err = -1;
@@ -545,6 +557,7 @@ static int symbols_resolve(struct object *obj)
 
 	err = 0;
 out:
+	btf__free(base_btf);
 	btf__free(btf);
 	return err;
 }
@@ -678,7 +691,6 @@ static const char * const resolve_btfids_usage[] = {
 
 int main(int argc, const char **argv)
 {
-	bool no_fail = false;
 	struct object obj = {
 		.efile = {
 			.idlist_shndx  = -1,
@@ -695,8 +707,8 @@ int main(int argc, const char **argv)
 			 "be more verbose (show errors, etc)"),
 		OPT_STRING(0, "btf", &obj.btf, "BTF data",
 			   "BTF data"),
-		OPT_BOOLEAN(0, "no-fail", &no_fail,
-			   "do not fail if " BTF_IDS_SECTION " section is not found"),
+		OPT_STRING('b', "btf_base", &obj.base_btf_path, "file",
+			   "path of file providing base BTF"),
 		OPT_END()
 	};
 	int err = -1;
@@ -717,10 +729,8 @@ int main(int argc, const char **argv)
 	 */
 	if (obj.efile.idlist_shndx == -1 ||
 	    obj.efile.symbols_shndx == -1) {
-		if (no_fail)
-			return 0;
-		pr_err("FAILED to find needed sections\n");
-		return -1;
+		pr_debug("Cannot find .BTF_ids or symbols sections, nothing to do\n");
+		return 0;
 	}
 
 	if (symbols_collect(&obj))

tools/testing/selftests/bpf/Makefile

@@ -454,7 +454,7 @@ $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS)			\
 			     | $(TRUNNER_BINARY)-extras
 	$$(call msg,BINARY,,$$@)
 	$(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
-	$(Q)$(RESOLVE_BTFIDS) --no-fail --btf $(TRUNNER_OUTPUT)/btf_data.o $$@
+	$(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.o $$@
 
 endef