libbpf: Generalize BTF and BTF.ext type ID and strings iteration

Extract and generalize the logic to iterate BTF type ID and string offset
fields within BTF types and .BTF.ext data. Expose this internally in libbpf
for re-use by bpf_linker.

Additionally, complete strings deduplication handling for BTF.ext (e.g., CO-RE
access strings), which was previously missing. There previously was no
case of deduplicating .BTF.ext data, but bpf_linker is going to use it.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/btf.c

···
 	return d;
 }
 
-typedef int (*str_off_fn_t)(__u32 *str_off_ptr, void *ctx);
-
 /*
  * Iterate over all possible places in .BTF and .BTF.ext that can reference
  * string and pass pointer to it to a provided callback `fn`.
  */
-static int btf_for_each_str_off(struct btf_dedup *d, str_off_fn_t fn, void *ctx)
+static int btf_for_each_str_off(struct btf_dedup *d, str_off_visit_fn fn, void *ctx)
 {
-	void *line_data_cur, *line_data_end;
-	int i, j, r, rec_size;
-	struct btf_type *t;
+	int i, r;
 
 	for (i = 0; i < d->btf->nr_types; i++) {
-		t = btf_type_by_id(d->btf, d->btf->start_id + i);
-		r = fn(&t->name_off, ctx);
+		struct btf_type *t = btf_type_by_id(d->btf, d->btf->start_id + i);
+
+		r = btf_type_visit_str_offs(t, fn, ctx);
 		if (r)
 			return r;
-
-		switch (btf_kind(t)) {
-		case BTF_KIND_STRUCT:
-		case BTF_KIND_UNION: {
-			struct btf_member *m = btf_members(t);
-			__u16 vlen = btf_vlen(t);
-
-			for (j = 0; j < vlen; j++) {
-				r = fn(&m->name_off, ctx);
-				if (r)
-					return r;
-				m++;
-			}
-			break;
-		}
-		case BTF_KIND_ENUM: {
-			struct btf_enum *m = btf_enum(t);
-			__u16 vlen = btf_vlen(t);
-
-			for (j = 0; j < vlen; j++) {
-				r = fn(&m->name_off, ctx);
-				if (r)
-					return r;
-				m++;
-			}
-			break;
-		}
-		case BTF_KIND_FUNC_PROTO: {
-			struct btf_param *m = btf_params(t);
-			__u16 vlen = btf_vlen(t);
-
-			for (j = 0; j < vlen; j++) {
-				r = fn(&m->name_off, ctx);
-				if (r)
-					return r;
-				m++;
-			}
-			break;
-		}
-		default:
-			break;
-		}
 	}
 
 	if (!d->btf_ext)
 		return 0;
 
-	line_data_cur = d->btf_ext->line_info.info;
-	line_data_end = d->btf_ext->line_info.info + d->btf_ext->line_info.len;
-	rec_size = d->btf_ext->line_info.rec_size;
-
-	while (line_data_cur < line_data_end) {
-		struct btf_ext_info_sec *sec = line_data_cur;
-		struct bpf_line_info_min *line_info;
-		__u32 num_info = sec->num_info;
-
-		r = fn(&sec->sec_name_off, ctx);
-		if (r)
-			return r;
-
-		line_data_cur += sizeof(struct btf_ext_info_sec);
-		for (i = 0; i < num_info; i++) {
-			line_info = line_data_cur;
-			r = fn(&line_info->file_name_off, ctx);
-			if (r)
-				return r;
-			r = fn(&line_info->line_off, ctx);
-			if (r)
-				return r;
-			line_data_cur += rec_size;
-		}
-	}
+	r = btf_ext_visit_str_offs(d->btf_ext, fn, ctx);
+	if (r)
+		return r;
 
 	return 0;
 }
···
  * then mapping it to a deduplicated type ID, stored in btf_dedup->hypot_map,
  * which is populated during compaction phase.
  */
-static int btf_dedup_remap_type_id(struct btf_dedup *d, __u32 type_id)
+static int btf_dedup_remap_type_id(__u32 *type_id, void *ctx)
 {
+	struct btf_dedup *d = ctx;
 	__u32 resolved_type_id, new_type_id;
 
-	resolved_type_id = resolve_type_id(d, type_id);
+	resolved_type_id = resolve_type_id(d, *type_id);
 	new_type_id = d->hypot_map[resolved_type_id];
 	if (new_type_id > BTF_MAX_NR_TYPES)
 		return -EINVAL;
-	return new_type_id;
+
+	*type_id = new_type_id;
+	return 0;
 }
 
 /*
···
  * referenced from any BTF type (e.g., struct fields, func proto args, etc) to
  * their final deduped type IDs.
  */
-static int btf_dedup_remap_type(struct btf_dedup *d, __u32 type_id)
-{
-	struct btf_type *t = btf_type_by_id(d->btf, type_id);
-	int i, r;
-
-	switch (btf_kind(t)) {
-	case BTF_KIND_INT:
-	case BTF_KIND_ENUM:
-	case BTF_KIND_FLOAT:
-		break;
-
-	case BTF_KIND_FWD:
-	case BTF_KIND_CONST:
-	case BTF_KIND_VOLATILE:
-	case BTF_KIND_RESTRICT:
-	case BTF_KIND_PTR:
-	case BTF_KIND_TYPEDEF:
-	case BTF_KIND_FUNC:
-	case BTF_KIND_VAR:
-		r = btf_dedup_remap_type_id(d, t->type);
-		if (r < 0)
-			return r;
-		t->type = r;
-		break;
-
-	case BTF_KIND_ARRAY: {
-		struct btf_array *arr_info = btf_array(t);
-
-		r = btf_dedup_remap_type_id(d, arr_info->type);
-		if (r < 0)
-			return r;
-		arr_info->type = r;
-		r = btf_dedup_remap_type_id(d, arr_info->index_type);
-		if (r < 0)
-			return r;
-		arr_info->index_type = r;
-		break;
-	}
-
-	case BTF_KIND_STRUCT:
-	case BTF_KIND_UNION: {
-		struct btf_member *member = btf_members(t);
-		__u16 vlen = btf_vlen(t);
-
-		for (i = 0; i < vlen; i++) {
-			r = btf_dedup_remap_type_id(d, member->type);
-			if (r < 0)
-				return r;
-			member->type = r;
-			member++;
-		}
-		break;
-	}
-
-	case BTF_KIND_FUNC_PROTO: {
-		struct btf_param *param = btf_params(t);
-		__u16 vlen = btf_vlen(t);
-
-		r = btf_dedup_remap_type_id(d, t->type);
-		if (r < 0)
-			return r;
-		t->type = r;
-
-		for (i = 0; i < vlen; i++) {
-			r = btf_dedup_remap_type_id(d, param->type);
-			if (r < 0)
-				return r;
-			param->type = r;
-			param++;
-		}
-		break;
-	}
-
-	case BTF_KIND_DATASEC: {
-		struct btf_var_secinfo *var = btf_var_secinfos(t);
-		__u16 vlen = btf_vlen(t);
-
-		for (i = 0; i < vlen; i++) {
-			r = btf_dedup_remap_type_id(d, var->type);
-			if (r < 0)
-				return r;
-			var->type = r;
-			var++;
-		}
-		break;
-	}
-
-	default:
-		return -EINVAL;
-	}
-
-	return 0;
-}
-
 static int btf_dedup_remap_types(struct btf_dedup *d)
 {
 	int i, r;
 
 	for (i = 0; i < d->btf->nr_types; i++) {
-		r = btf_dedup_remap_type(d, d->btf->start_id + i);
-		if (r < 0)
+		struct btf_type *t = btf_type_by_id(d->btf, d->btf->start_id + i);
+
+		r = btf_type_visit_type_ids(t, btf_dedup_remap_type_id, d);
+		if (r)
 			return r;
 	}
+
+	if (!d->btf_ext)
+		return 0;
+
+	r = btf_ext_visit_type_ids(d->btf_ext, btf_dedup_remap_type_id, d);
+	if (r)
+		return r;
+
 	return 0;
 }
 
···
 
 	pr_warn("failed to find valid kernel BTF\n");
 	return ERR_PTR(-ESRCH);
+}
+
+int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx)
+{
+	int i, n, err;
+
+	switch (btf_kind(t)) {
+	case BTF_KIND_INT:
+	case BTF_KIND_FLOAT:
+	case BTF_KIND_ENUM:
+		return 0;
+
+	case BTF_KIND_FWD:
+	case BTF_KIND_CONST:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_PTR:
+	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_FUNC:
+	case BTF_KIND_VAR:
+		return visit(&t->type, ctx);
+
+	case BTF_KIND_ARRAY: {
+		struct btf_array *a = btf_array(t);
+
+		err = visit(&a->type, ctx);
+		err = err ?: visit(&a->index_type, ctx);
+		return err;
+	}
+
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION: {
+		struct btf_member *m = btf_members(t);
+
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->type, ctx);
+			if (err)
+				return err;
+		}
+		return 0;
+	}
+
+	case BTF_KIND_FUNC_PROTO: {
+		struct btf_param *m = btf_params(t);
+
+		err = visit(&t->type, ctx);
+		if (err)
+			return err;
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->type, ctx);
+			if (err)
+				return err;
+		}
+		return 0;
+	}
+
+	case BTF_KIND_DATASEC: {
+		struct btf_var_secinfo *m = btf_var_secinfos(t);
+
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->type, ctx);
+			if (err)
+				return err;
+		}
+		return 0;
+	}
+
+	default:
+		return -EINVAL;
+	}
+}
+
+int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx)
+{
+	int i, n, err;
+
+	err = visit(&t->name_off, ctx);
+	if (err)
+		return err;
+
+	switch (btf_kind(t)) {
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION: {
+		struct btf_member *m = btf_members(t);
+
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->name_off, ctx);
+			if (err)
+				return err;
+		}
+		break;
+	}
+	case BTF_KIND_ENUM: {
+		struct btf_enum *m = btf_enum(t);
+
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->name_off, ctx);
+			if (err)
+				return err;
+		}
+		break;
+	}
+	case BTF_KIND_FUNC_PROTO: {
+		struct btf_param *m = btf_params(t);
+
+		for (i = 0, n = btf_vlen(t); i < n; i++, m++) {
+			err = visit(&m->name_off, ctx);
+			if (err)
+				return err;
+		}
+		break;
+	}
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+int btf_ext_visit_type_ids(struct btf_ext *btf_ext, type_id_visit_fn visit, void *ctx)
+{
+	const struct btf_ext_info *seg;
+	struct btf_ext_info_sec *sec;
+	int i, err;
+
+	seg = &btf_ext->func_info;
+	for_each_btf_ext_sec(seg, sec) {
+		struct bpf_func_info_min *rec;
+
+		for_each_btf_ext_rec(seg, sec, i, rec) {
+			err = visit(&rec->type_id, ctx);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	seg = &btf_ext->core_relo_info;
+	for_each_btf_ext_sec(seg, sec) {
+		struct bpf_core_relo *rec;
+
+		for_each_btf_ext_rec(seg, sec, i, rec) {
+			err = visit(&rec->type_id, ctx);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+
+int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void *ctx)
+{
+	const struct btf_ext_info *seg;
+	struct btf_ext_info_sec *sec;
+	int i, err;
+
+	seg = &btf_ext->func_info;
+	for_each_btf_ext_sec(seg, sec) {
+		err = visit(&sec->sec_name_off, ctx);
+		if (err)
+			return err;
+	}
+
+	seg = &btf_ext->line_info;
+	for_each_btf_ext_sec(seg, sec) {
+		struct bpf_line_info_min *rec;
+
+		err = visit(&sec->sec_name_off, ctx);
+		if (err)
+			return err;
+
+		for_each_btf_ext_rec(seg, sec, i, rec) {
+			err = visit(&rec->file_name_off, ctx);
+			if (err)
+				return err;
+			err = visit(&rec->line_off, ctx);
+			if (err)
+				return err;
+		}
+	}
+
+	seg = &btf_ext->core_relo_info;
+	for_each_btf_ext_sec(seg, sec) {
+		struct bpf_core_relo *rec;
+
+		err = visit(&sec->sec_name_off, ctx);
+		if (err)
+			return err;
+
+		for_each_btf_ext_rec(seg, sec, i, rec) {
+			err = visit(&rec->access_str_off, ctx);
+			if (err)
+				return err;
+		}
+	}
+
+	return 0;
 }

tools/lib/bpf/libbpf_internal.h

···
 	enum bpf_core_relo_kind kind;
 };
 
+typedef int (*type_id_visit_fn)(__u32 *type_id, void *ctx);
+typedef int (*str_off_visit_fn)(__u32 *str_off, void *ctx);
+int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx);
+int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx);
+int btf_ext_visit_type_ids(struct btf_ext *btf_ext, type_id_visit_fn visit, void *ctx);
+int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void *ctx);
+
 #endif /* __LIBBPF_LIBBPF_INTERNAL_H */