libbpf: Support BTF_KIND_TYPE_TAG

Add libbpf support for BTF_KIND_TYPE_TAG.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211112012614.1505315-1-yhs@fb.com

tools/lib/bpf/btf.c

@@ -299,6 +299,7 @@ static int btf_type_size(const struct btf_type *t)
 	case BTF_KIND_TYPEDEF:
 	case BTF_KIND_FUNC:
 	case BTF_KIND_FLOAT:
+	case BTF_KIND_TYPE_TAG:
 		return base_size;
 	case BTF_KIND_INT:
 		return base_size + sizeof(__u32);
@@ -349,6 +350,7 @@ static int btf_bswap_type_rest(struct btf_type *t)
 	case BTF_KIND_TYPEDEF:
 	case BTF_KIND_FUNC:
 	case BTF_KIND_FLOAT:
+	case BTF_KIND_TYPE_TAG:
 		return 0;
 	case BTF_KIND_INT:
 		*(__u32 *)(t + 1) = bswap_32(*(__u32 *)(t + 1));
@@ -649,6 +651,7 @@ int btf__align_of(const struct btf *btf, __u32 id)
 	case BTF_KIND_VOLATILE:
 	case BTF_KIND_CONST:
 	case BTF_KIND_RESTRICT:
+	case BTF_KIND_TYPE_TAG:
 		return btf__align_of(btf, t->type);
 	case BTF_KIND_ARRAY:
 		return btf__align_of(btf, btf_array(t)->type);
@@ -2235,6 +2238,22 @@ int btf__add_restrict(struct btf *btf, int ref_type_id)
 	return btf_add_ref_kind(btf, BTF_KIND_RESTRICT, NULL, ref_type_id);
 }
 
+/*
+ * Append new BTF_KIND_TYPE_TAG type with:
+ *   - *value*, non-empty/non-NULL tag value;
+ *   - *ref_type_id* - referenced type ID, it might not exist yet;
+ * Returns:
+ *   - >0, type ID of newly added BTF type;
+ *   - <0, on error.
+ */
+int btf__add_type_tag(struct btf *btf, const char *value, int ref_type_id)
+{
+	if (!value|| !value[0])
+		return libbpf_err(-EINVAL);
+
+	return btf_add_ref_kind(btf, BTF_KIND_TYPE_TAG, value, ref_type_id);
+}
+
 /*
  * Append new BTF_KIND_FUNC type with:
  *   - *name*, non-empty/non-NULL name;
@@ -3639,6 +3658,7 @@ static int btf_dedup_prep(struct btf_dedup *d)
 		case BTF_KIND_TYPEDEF:
 		case BTF_KIND_FUNC:
 		case BTF_KIND_FLOAT:
+		case BTF_KIND_TYPE_TAG:
 			h = btf_hash_common(t);
 			break;
 		case BTF_KIND_INT:
@@ -3699,6 +3719,7 @@ static int btf_dedup_prim_type(struct btf_dedup *d, __u32 type_id)
 	case BTF_KIND_VAR:
 	case BTF_KIND_DATASEC:
 	case BTF_KIND_DECL_TAG:
+	case BTF_KIND_TYPE_TAG:
 		return 0;
 
 	case BTF_KIND_INT:
@@ -4297,6 +4318,7 @@ static int btf_dedup_ref_type(struct btf_dedup *d, __u32 type_id)
 	case BTF_KIND_PTR:
 	case BTF_KIND_TYPEDEF:
 	case BTF_KIND_FUNC:
+	case BTF_KIND_TYPE_TAG:
 		ref_type_id = btf_dedup_ref_type(d, t->type);
 		if (ref_type_id < 0)
 			return ref_type_id;
@@ -4603,6 +4625,7 @@ int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ct
 	case BTF_KIND_FUNC:
 	case BTF_KIND_VAR:
 	case BTF_KIND_DECL_TAG:
+	case BTF_KIND_TYPE_TAG:
 		return visit(&t->type, ctx);
 
 	case BTF_KIND_ARRAY: {

tools/lib/bpf/btf.h

@@ -227,6 +227,7 @@ LIBBPF_API int btf__add_typedef(struct btf *btf, const char *name, int ref_type_
 LIBBPF_API int btf__add_volatile(struct btf *btf, int ref_type_id);
 LIBBPF_API int btf__add_const(struct btf *btf, int ref_type_id);
 LIBBPF_API int btf__add_restrict(struct btf *btf, int ref_type_id);
+LIBBPF_API int btf__add_type_tag(struct btf *btf, const char *value, int ref_type_id);
 
 /* func and func_proto construction APIs */
 LIBBPF_API int btf__add_func(struct btf *btf, const char *name,
@@ -458,7 +459,8 @@ static inline bool btf_is_mod(const struct btf_type *t)
 
 	return kind == BTF_KIND_VOLATILE ||
 	       kind == BTF_KIND_CONST ||
-	       kind == BTF_KIND_RESTRICT;
+	       kind == BTF_KIND_RESTRICT ||
+	       kind == BTF_KIND_TYPE_TAG;
 }
 
 static inline bool btf_is_func(const struct btf_type *t)
@@ -491,6 +493,11 @@ static inline bool btf_is_decl_tag(const struct btf_type *t)
 	return btf_kind(t) == BTF_KIND_DECL_TAG;
 }
 
+static inline bool btf_is_type_tag(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_TYPE_TAG;
+}
+
 static inline __u8 btf_int_encoding(const struct btf_type *t)
 {
 	return BTF_INT_ENCODING(*(__u32 *)(t + 1));

tools/lib/bpf/btf_dump.c

@@ -330,6 +330,7 @@ static int btf_dump_mark_referenced(struct btf_dump *d)
 		case BTF_KIND_FUNC:
 		case BTF_KIND_VAR:
 		case BTF_KIND_DECL_TAG:
+		case BTF_KIND_TYPE_TAG:
 			d->type_states[t->type].referenced = 1;
 			break;
 
@@ -573,6 +574,7 @@ static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr)
 	case BTF_KIND_VOLATILE:
 	case BTF_KIND_CONST:
 	case BTF_KIND_RESTRICT:
+	case BTF_KIND_TYPE_TAG:
 		return btf_dump_order_type(d, t->type, through_ptr);
 
 	case BTF_KIND_FUNC_PROTO: {
@@ -747,6 +749,7 @@ static void btf_dump_emit_type(struct btf_dump *d, __u32 id, __u32 cont_id)
 	case BTF_KIND_VOLATILE:
 	case BTF_KIND_CONST:
 	case BTF_KIND_RESTRICT:
+	case BTF_KIND_TYPE_TAG:
 		btf_dump_emit_type(d, t->type, cont_id);
 		break;
 	case BTF_KIND_ARRAY:
@@ -1167,6 +1170,7 @@ static void btf_dump_emit_type_decl(struct btf_dump *d, __u32 id,
 		case BTF_KIND_CONST:
 		case BTF_KIND_RESTRICT:
 		case BTF_KIND_FUNC_PROTO:
+		case BTF_KIND_TYPE_TAG:
 			id = t->type;
 			break;
 		case BTF_KIND_ARRAY:
@@ -1335,6 +1339,11 @@ static void btf_dump_emit_type_chain(struct btf_dump *d,
 		case BTF_KIND_RESTRICT:
 			btf_dump_printf(d, " restrict");
 			break;
+		case BTF_KIND_TYPE_TAG:
+			btf_dump_emit_mods(d, decls);
+			name = btf_name_of(d, t->name_off);
+			btf_dump_printf(d, " __attribute__((btf_type_tag(\"%s\")))", name);
+			break;
 		case BTF_KIND_ARRAY: {
 			const struct btf_array *a = btf_array(t);
 			const struct btf_type *next_t;

tools/lib/bpf/libbpf.c

@@ -197,6 +197,8 @@ enum kern_feature_id {
 	FEAT_PERF_LINK,
 	/* BTF_KIND_DECL_TAG support */
 	FEAT_BTF_DECL_TAG,
+	/* BTF_KIND_TYPE_TAG support */
+	FEAT_BTF_TYPE_TAG,
 	__FEAT_CNT,
 };
 
@@ -2076,6 +2078,7 @@ static const char *__btf_kind_str(__u16 kind)
 	case BTF_KIND_DATASEC: return "datasec";
 	case BTF_KIND_FLOAT: return "float";
 	case BTF_KIND_DECL_TAG: return "decl_tag";
+	case BTF_KIND_TYPE_TAG: return "type_tag";
 	default: return "unknown";
 	}
 }
@@ -2588,8 +2591,10 @@ static bool btf_needs_sanitization(struct bpf_object *obj)
 	bool has_float = kernel_supports(obj, FEAT_BTF_FLOAT);
 	bool has_func = kernel_supports(obj, FEAT_BTF_FUNC);
 	bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
+	bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
 
-	return !has_func || !has_datasec || !has_func_global || !has_float || !has_decl_tag;
+	return !has_func || !has_datasec || !has_func_global || !has_float ||
+	       !has_decl_tag || !has_type_tag;
 }
 
 static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
@@ -2599,6 +2604,7 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
 	bool has_float = kernel_supports(obj, FEAT_BTF_FLOAT);
 	bool has_func = kernel_supports(obj, FEAT_BTF_FUNC);
 	bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
+	bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
 	struct btf_type *t;
 	int i, j, vlen;
 
@@ -2657,6 +2663,10 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
 			 */
 			t->name_off = 0;
 			t->info = BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 0);
+		} else if (!has_type_tag && btf_is_type_tag(t)) {
+			/* replace TYPE_TAG with a CONST */
+			t->name_off = 0;
+			t->info = BTF_INFO_ENC(BTF_KIND_CONST, 0, 0);
 		}
 	}
 }
@@ -4460,6 +4470,22 @@ static int probe_kern_btf_decl_tag(void)
 					     strs, sizeof(strs)));
 }
 
+static int probe_kern_btf_type_tag(void)
+{
+	static const char strs[] = "\0tag";
+	__u32 types[] = {
+		/* int */
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),		/* [1] */
+		/* attr */
+		BTF_TYPE_TYPE_TAG_ENC(1, 1),				/* [2] */
+		/* ptr */
+		BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 2),	/* [3] */
+	};
+
+	return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
+					     strs, sizeof(strs)));
+}
+
 static int probe_kern_array_mmap(void)
 {
 	struct bpf_create_map_attr attr = {
@@ -4657,6 +4683,9 @@ static struct kern_feature_desc {
 	[FEAT_BTF_DECL_TAG] = {
 		"BTF_KIND_DECL_TAG support", probe_kern_btf_decl_tag,
 	},
+	[FEAT_BTF_TYPE_TAG] = {
+		"BTF_KIND_TYPE_TAG support", probe_kern_btf_type_tag,
+	},
 };
 
 static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)

tools/lib/bpf/libbpf.map

@@ -403,6 +403,7 @@ LIBBPF_0.6.0 {
 		bpf_program__set_extra_flags;
 		btf__add_btf;
 		btf__add_decl_tag;
+		btf__add_type_tag;
 		btf__dedup;
 		btf__dedup_deprecated;
 		btf__raw_data;

tools/lib/bpf/libbpf_internal.h

@@ -73,6 +73,8 @@
 	BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_FLOAT, 0, 0), sz)
 #define BTF_TYPE_DECL_TAG_ENC(value, type, component_idx) \
 	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_DECL_TAG, 0, 0), type), (component_idx)
+#define BTF_TYPE_TYPE_TAG_ENC(value, type) \
+	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_TYPE_TAG, 0, 0), type)
 
 #ifndef likely
 #define likely(x) __builtin_expect(!!(x), 1)