Merge branch 'libbpf: deprecate legacy BPF map definitions'

Andrii Nakryiko says:

====================

Officially deprecate legacy BPF map definitions in libbpf. They've been slated
for deprecation for a while in favor of more powerful BTF-defined map
definitions and this patch set adds warnings and a way to enforce this in
libbpf through LIBBPF_STRICT_MAP_DEFINITIONS strict mode flag.

Selftests are fixed up and updated, BPF documentation is updated, bpftool's
strict mode usage is adjusted to avoid breaking users unnecessarily.

v1->v2:
  - replace missed bpf_map_def case in Documentation/bpf/btf.rst (Alexei).
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/bpf/btf.rst

@@ -565,18 +565,15 @@ A map can be created with ``btf_fd`` and specified key/value type id.::
 In libbpf, the map can be defined with extra annotation like below:
 ::
 
-    struct bpf_map_def SEC("maps") btf_map = {
-        .type = BPF_MAP_TYPE_ARRAY,
-        .key_size = sizeof(int),
-        .value_size = sizeof(struct ipv_counts),
-        .max_entries = 4,
-    };
-    BPF_ANNOTATE_KV_PAIR(btf_map, int, struct ipv_counts);
+    struct {
+        __uint(type, BPF_MAP_TYPE_ARRAY);
+        __type(key, int);
+        __type(value, struct ipv_counts);
+        __uint(max_entries, 4);
+    } btf_map SEC(".maps");
 
-Here, the parameters for macro BPF_ANNOTATE_KV_PAIR are map name, key and
-value types for the map. During ELF parsing, libbpf is able to extract
-key/value type_id's and assign them to BPF_MAP_CREATE attributes
-automatically.
+During ELF parsing, libbpf is able to extract key/value type_id's and assign
+them to BPF_MAP_CREATE attributes automatically.
 
 .. _BPF_Prog_Load:
 
@@ -824,13 +821,12 @@ structure has bitfields. For example, for the following map,::
            ___A b1:4;
            enum A b2:4;
       };
-      struct bpf_map_def SEC("maps") tmpmap = {
-           .type = BPF_MAP_TYPE_ARRAY,
-           .key_size = sizeof(__u32),
-           .value_size = sizeof(struct tmp_t),
-           .max_entries = 1,
-      };
-      BPF_ANNOTATE_KV_PAIR(tmpmap, int, struct tmp_t);
+      struct {
+           __uint(type, BPF_MAP_TYPE_ARRAY);
+           __type(key, int);
+           __type(value, struct tmp_t);
+           __uint(max_entries, 1);
+      } tmpmap SEC(".maps");
 
 bpftool is able to pretty print like below:
 ::

tools/bpf/bpftool/main.c

@@ -478,7 +478,14 @@ int main(int argc, char **argv)
 	}
 
 	if (!legacy_libbpf) {
-		ret = libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+		enum libbpf_strict_mode mode;
+
+		/* Allow legacy map definitions for skeleton generation.
+		 * It will still be rejected if users use LIBBPF_STRICT_ALL
+		 * mode for loading generated skeleton.
+		 */
+		mode = (__LIBBPF_STRICT_LAST - 1) & ~LIBBPF_STRICT_MAP_DEFINITIONS;
+		ret = libbpf_set_strict_mode(mode);
 		if (ret)
 			p_err("failed to enable libbpf strict mode: %d", ret);
 	}

tools/lib/bpf/bpf_helpers.h

@@ -133,7 +133,7 @@ struct bpf_map_def {
 	unsigned int value_size;
 	unsigned int max_entries;
 	unsigned int map_flags;
-};
+} __attribute__((deprecated("use BTF-defined maps in .maps section")));
 
 enum libbpf_pin_type {
 	LIBBPF_PIN_NONE,

tools/lib/bpf/libbpf.c

@@ -1937,6 +1937,11 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 	if (obj->efile.maps_shndx < 0)
 		return 0;
 
+	if (libbpf_mode & LIBBPF_STRICT_MAP_DEFINITIONS) {
+		pr_warn("legacy map definitions in SEC(\"maps\") are not supported\n");
+		return -EOPNOTSUPP;
+	}
+
 	if (!symbols)
 		return -EINVAL;
 
@@ -1999,6 +2004,8 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 			return -LIBBPF_ERRNO__FORMAT;
 		}
 
+		pr_warn("map '%s' (legacy): legacy map definitions are deprecated, use BTF-defined maps instead\n", map_name);
+
 		if (ELF64_ST_BIND(sym->st_info) == STB_LOCAL) {
 			pr_warn("map '%s' (legacy): static maps are not supported\n", map_name);
 			return -ENOTSUP;
@@ -4190,6 +4197,7 @@ static int bpf_map_find_btf_info(struct bpf_object *obj, struct bpf_map *map)
 		return 0;
 
 	if (!bpf_map__is_internal(map)) {
+		pr_warn("Use of BPF_ANNOTATE_KV_PAIR is deprecated, use BTF-defined maps in .maps section instead\n");
 		ret = btf__get_map_kv_tids(obj->btf, map->name, def->key_size,
 					   def->value_size, &key_type_id,
 					   &value_type_id);

tools/lib/bpf/libbpf_legacy.h

@@ -73,6 +73,11 @@ enum libbpf_strict_mode {
 	 * operation.
 	 */
 	LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK = 0x10,
+	/*
+	 * Error out on any SEC("maps") map definition, which are deprecated
+	 * in favor of BTF-defined map definitions in SEC(".maps").
+	 */
+	LIBBPF_STRICT_MAP_DEFINITIONS = 0x20,
 
 	__LIBBPF_STRICT_LAST,
 };

tools/testing/selftests/bpf/Makefile

@@ -21,7 +21,7 @@ endif
 
 BPF_GCC		?= $(shell command -v bpf-gcc;)
 SAN_CFLAGS	?=
-CFLAGS += -g -O0 -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)		\
+CFLAGS += -g -O0 -rdynamic -Wall -Werror $(GENFLAGS) $(SAN_CFLAGS)	\
 	  -I$(CURDIR) -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)		\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(OUTPUT)
 LDFLAGS += $(SAN_CFLAGS)
@@ -292,7 +292,7 @@ IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null | \
 MENDIAN=$(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
 
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
-BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 			\
+BPF_CFLAGS = -g -Werror -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) 		\
 	     -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR)			\
 	     -I$(abspath $(OUTPUT)/../usr/include)
 

tools/testing/selftests/bpf/prog_tests/btf.c

@@ -4560,6 +4560,8 @@ static void do_test_file(unsigned int test_num)
 	has_btf_ext = btf_ext != NULL;
 	btf_ext__free(btf_ext);
 
+	/* temporary disable LIBBPF_STRICT_MAP_DEFINITIONS to test legacy maps */
+	libbpf_set_strict_mode((__LIBBPF_STRICT_LAST - 1) & ~LIBBPF_STRICT_MAP_DEFINITIONS);
 	obj = bpf_object__open(test->file);
 	err = libbpf_get_error(obj);
 	if (CHECK(err, "obj: %d", err))
@@ -4684,6 +4686,8 @@ static void do_test_file(unsigned int test_num)
 	fprintf(stderr, "OK");
 
 done:
+	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+
 	btf__free(btf);
 	free(func_info);
 	bpf_object__close(obj);

tools/testing/selftests/bpf/progs/freplace_cls_redirect.c

@@ -7,12 +7,12 @@
 #include <bpf/bpf_endian.h>
 #include <bpf/bpf_helpers.h>
 
-struct bpf_map_def SEC("maps") sock_map = {
-	.type = BPF_MAP_TYPE_SOCKMAP,
-	.key_size = sizeof(int),
-	.value_size = sizeof(int),
-	.max_entries = 2,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__type(key, int);
+	__type(value, int);
+	__uint(max_entries, 2);
+} sock_map SEC(".maps");
 
 SEC("freplace/cls_redirect")
 int freplace_cls_redirect_test(struct __sk_buff *skb)

tools/testing/selftests/bpf/progs/sample_map_ret0.c

@@ -2,19 +2,19 @@
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 
-struct bpf_map_def SEC("maps") htab = {
-	.type = BPF_MAP_TYPE_HASH,
-	.key_size = sizeof(__u32),
-	.value_size = sizeof(long),
-	.max_entries = 2,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, __u32);
+	__type(value, long);
+	__uint(max_entries, 2);
+} htab SEC(".maps");
 
-struct bpf_map_def SEC("maps") array = {
-	.type = BPF_MAP_TYPE_ARRAY,
-	.key_size = sizeof(__u32),
-	.value_size = sizeof(long),
-	.max_entries = 2,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, long);
+	__uint(max_entries, 2);
+} array SEC(".maps");
 
 /* Sample program which should always load for testing control paths. */
 SEC(".text") int func()

tools/testing/selftests/bpf/progs/test_btf_haskv.c

@@ -9,12 +9,15 @@ struct ipv_counts {
 	unsigned int v6;
 };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 struct bpf_map_def SEC("maps") btf_map = {
 	.type = BPF_MAP_TYPE_ARRAY,
 	.key_size = sizeof(int),
 	.value_size = sizeof(struct ipv_counts),
 	.max_entries = 4,
 };
+#pragma GCC diagnostic pop
 
 BPF_ANNOTATE_KV_PAIR(btf_map, int, struct ipv_counts);
 

tools/testing/selftests/bpf/progs/test_btf_newkv.c

@@ -9,6 +9,8 @@ struct ipv_counts {
 	unsigned int v6;
 };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 /* just to validate we can handle maps in multiple sections */
 struct bpf_map_def SEC("maps") btf_map_legacy = {
 	.type = BPF_MAP_TYPE_ARRAY,
@@ -16,6 +18,7 @@ struct bpf_map_def SEC("maps") btf_map_legacy = {
 	.value_size = sizeof(long long),
 	.max_entries = 4,
 };
+#pragma GCC diagnostic pop
 
 BPF_ANNOTATE_KV_PAIR(btf_map_legacy, int, struct ipv_counts);
 

tools/testing/selftests/bpf/progs/test_btf_nokv.c

@@ -8,12 +8,12 @@ struct ipv_counts {
 	unsigned int v6;
 };
 
-struct bpf_map_def SEC("maps") btf_map = {
-	.type = BPF_MAP_TYPE_ARRAY,
-	.key_size = sizeof(int),
-	.value_size = sizeof(struct ipv_counts),
-	.max_entries = 4,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(key_size, sizeof(int));
+	__uint(value_size, sizeof(struct ipv_counts));
+	__uint(max_entries, 4);
+} btf_map SEC(".maps");
 
 __attribute__((noinline))
 int test_long_fname_2(void)

tools/testing/selftests/bpf/progs/test_skb_cgroup_id_kern.c

@@ -10,12 +10,12 @@
 
 #define NUM_CGROUP_LEVELS	4
 
-struct bpf_map_def SEC("maps") cgroup_ids = {
-	.type = BPF_MAP_TYPE_ARRAY,
-	.key_size = sizeof(__u32),
-	.value_size = sizeof(__u64),
-	.max_entries = NUM_CGROUP_LEVELS,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(max_entries, NUM_CGROUP_LEVELS);
+} cgroup_ids SEC(".maps");
 
 static __always_inline void log_nth_level(struct __sk_buff *skb, __u32 level)
 {

tools/testing/selftests/bpf/progs/test_tc_edt.c

@@ -17,12 +17,12 @@
 #define THROTTLE_RATE_BPS (5 * 1000 * 1000)
 
 /* flow_key => last_tstamp timestamp used */
-struct bpf_map_def SEC("maps") flow_map = {
-	.type = BPF_MAP_TYPE_HASH,
-	.key_size = sizeof(uint32_t),
-	.value_size = sizeof(uint64_t),
-	.max_entries = 1,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, uint32_t);
+	__type(value, uint64_t);
+	__uint(max_entries, 1);
+} flow_map SEC(".maps");
 
 static inline int throttle_flow(struct __sk_buff *skb)
 {

tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c

@@ -16,12 +16,12 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 
-struct bpf_map_def SEC("maps") results = {
-	.type = BPF_MAP_TYPE_ARRAY,
-	.key_size = sizeof(__u32),
-	.value_size = sizeof(__u32),
-	.max_entries = 3,
-};
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__type(key, __u32);
+	__type(value, __u32);
+	__uint(max_entries, 3);
+} results SEC(".maps");
 
 static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
 					   void *iph, __u32 ip_size,