[bpf-next,v4,2/6] bpf/libbpf: BTF support for typed ksyms

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a4f55f8a460d..9b36c52b8511 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -390,6 +390,12 @@  struct extern_desc {
 		} kcfg;
 		struct {
 			unsigned long long addr;
+
+			/* target btf_id of the corresponding kernel var. */
+			int vmlinux_btf_id;
+
+			/* local btf_id of the ksym extern's type. */
+			__u32 type_id;
 		} ksym;
 	};
 };
@@ -2522,12 +2528,23 @@  static int bpf_object__load_vmlinux_btf(struct bpf_object *obj)
 {
 	bool need_vmlinux_btf = false;
 	struct bpf_program *prog;
-	int err;
+	int i, err;
 
 	/* CO-RE relocations need kernel BTF */
 	if (obj->btf_ext && obj->btf_ext->core_relo_info.len)
 		need_vmlinux_btf = true;
 
+	/* Support for typed ksyms needs kernel BTF */
+	for (i = 0; i < obj->nr_extern; i++) {
+		const struct extern_desc *ext;
+
+		ext = &obj->externs[i];
+		if (ext->type == EXT_KSYM && ext->ksym.type_id) {
+			need_vmlinux_btf = true;
+			break;
+		}
+	}
+
 	bpf_object__for_each_program(prog, obj) {
 		if (!prog->load)
 			continue;
@@ -3156,16 +3173,10 @@  static int bpf_object__collect_externs(struct bpf_object *obj)
 				return -ENOTSUP;
 			}
 		} else if (strcmp(sec_name, KSYMS_SEC) == 0) {
-			const struct btf_type *vt;
-
 			ksym_sec = sec;
 			ext->type = EXT_KSYM;
-
-			vt = skip_mods_and_typedefs(obj->btf, t->type, NULL);
-			if (!btf_is_void(vt)) {
-				pr_warn("extern (ksym) '%s' is not typeless (void)\n", ext_name);
-				return -ENOTSUP;
-			}
+			skip_mods_and_typedefs(obj->btf, t->type,
+					       &ext->ksym.type_id);
 		} else {
 			pr_warn("unrecognized extern section '%s'\n", sec_name);
 			return -ENOTSUP;
@@ -5800,8 +5811,13 @@  bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 				insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
 				insn[1].imm = ext->kcfg.data_off;
 			} else /* EXT_KSYM */ {
-				insn[0].imm = (__u32)ext->ksym.addr;
-				insn[1].imm = ext->ksym.addr >> 32;
+				if (ext->ksym.type_id) { /* typed ksyms */
+					insn[0].src_reg = BPF_PSEUDO_BTF_ID;
+					insn[0].imm = ext->ksym.vmlinux_btf_id;
+				} else { /* typeless ksyms */
+					insn[0].imm = (__u32)ext->ksym.addr;
+					insn[1].imm = ext->ksym.addr >> 32;
+				}
 			}
 			relo->processed = true;
 			break;
@@ -6933,10 +6949,72 @@  static int bpf_object__read_kallsyms_file(struct bpf_object *obj)
 	return err;
 }
 
+static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
+{
+	struct extern_desc *ext;
+	int i, id;
+
+	for (i = 0; i < obj->nr_extern; i++) {
+		const struct btf_type *targ_var, *targ_type;
+		__u32 targ_type_id, local_type_id;
+		const char *targ_var_name;
+		int ret;
+
+		ext = &obj->externs[i];
+		if (ext->type != EXT_KSYM || !ext->ksym.type_id)
+			continue;
+
+		id = btf__find_by_name_kind(obj->btf_vmlinux, ext->name,
+					    BTF_KIND_VAR);
+		if (id <= 0) {
+			pr_warn("extern (ksym) '%s': failed to find BTF ID in vmlinux BTF.\n",
+				ext->name);
+			return -ESRCH;
+		}
+
+		/* find local type_id */
+		local_type_id = ext->ksym.type_id;
+
+		/* find target type_id */
+		targ_var = btf__type_by_id(obj->btf_vmlinux, id);
+		targ_var_name = btf__name_by_offset(obj->btf_vmlinux,
+						    targ_var->name_off);
+		targ_type = skip_mods_and_typedefs(obj->btf_vmlinux,
+						   targ_var->type,
+						   &targ_type_id);
+
+		ret = bpf_core_types_are_compat(obj->btf, local_type_id,
+						obj->btf_vmlinux, targ_type_id);
+		if (ret <= 0) {
+			const struct btf_type *local_type;
+			const char *targ_name, *local_name;
+
+			local_type = btf__type_by_id(obj->btf, local_type_id);
+			local_name = btf__name_by_offset(obj->btf,
+							 local_type->name_off);
+			targ_name = btf__name_by_offset(obj->btf_vmlinux,
+							targ_type->name_off);
+
+			pr_warn("extern (ksym) '%s': incompatible types, expected [%d] %s %s, but kernel has [%d] %s %s\n",
+				ext->name, local_type_id,
+				btf_kind_str(local_type), local_name, targ_type_id,
+				btf_kind_str(targ_type), targ_name);
+			return -EINVAL;
+		}
+
+		ext->is_set = true;
+		ext->ksym.vmlinux_btf_id = id;
+		pr_debug("extern (ksym) '%s': resolved to [%d] %s %s\n",
+			 ext->name, id, btf_kind_str(targ_var), targ_var_name);
+	}
+	return 0;
+}
+
 static int bpf_object__resolve_externs(struct bpf_object *obj,
 				       const char *extra_kconfig)
 {
 	bool need_config = false, need_kallsyms = false;
+	bool need_vmlinux_btf = false;
 	struct extern_desc *ext;
 	void *kcfg_data = NULL;
 	int err, i;
@@ -6967,7 +7045,10 @@  static int bpf_object__resolve_externs(struct bpf_object *obj,
 			   strncmp(ext->name, "CONFIG_", 7) == 0) {
 			need_config = true;
 		} else if (ext->type == EXT_KSYM) {
-			need_kallsyms = true;
+			if (ext->ksym.type_id)
+				need_vmlinux_btf = true;
+			else
+				need_kallsyms = true;
 		} else {
 			pr_warn("unrecognized extern '%s'\n", ext->name);
 			return -EINVAL;
@@ -6996,6 +7077,11 @@  static int bpf_object__resolve_externs(struct bpf_object *obj,
 		if (err)
 			return -EINVAL;
 	}
+	if (need_vmlinux_btf) {
+		err = bpf_object__resolve_ksyms_btf_id(obj);
+		if (err)
+			return -EINVAL;
+	}
 	for (i = 0; i < obj->nr_extern; i++) {
 		ext = &obj->externs[i];
 
@@ -7028,10 +7114,10 @@  int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
 	}
 
 	err = bpf_object__probe_loading(obj);
+	err = err ? : bpf_object__load_vmlinux_btf(obj);
 	err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
 	err = err ? : bpf_object__sanitize_and_load_btf(obj);
 	err = err ? : bpf_object__sanitize_maps(obj);
-	err = err ? : bpf_object__load_vmlinux_btf(obj);
 	err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
 	err = err ? : bpf_object__create_maps(obj);
 	err = err ? : bpf_object__relocate(obj, attr->target_btf_path);