bpf: Compute bpf_skc_to_*() helper socket btf ids at build time

Currently, socket types (struct tcp_sock, udp_sock, etc.)
used by bpf_skc_to_*() helpers are computed when vmlinux_btf
is first built in the kernel.

Commit 5a2798a
("bpf: Add BTF_ID_LIST/BTF_ID/BTF_ID_UNUSED macros")
implemented a mechanism to compute btf_ids at kernel build
time which can simplify kernel implementation and reduce
runtime overhead by removing in-kernel btf_id calculation.
This patch did exactly this, removing in-kernel btf_id
computation and utilizing build-time btf_id computation.

If CONFIG_DEBUG_INFO_BTF is not defined, BTF_ID_LIST will
define an array with size of 5, which is not enough for
btf_sock_ids. So define its own static array if
CONFIG_DEBUG_INFO_BTF is not defined.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200720163358.1393023-1-yhs@fb.com

include/linux/bpf.h

@@ -1541,7 +1541,6 @@ static inline bool bpf_map_is_dev_bound(struct bpf_map *map)
 
 struct bpf_map *bpf_map_offload_map_alloc(union bpf_attr *attr);
 void bpf_map_offload_map_free(struct bpf_map *map);
-void init_btf_sock_ids(struct btf *btf);
 #else
 static inline int bpf_prog_offload_init(struct bpf_prog *prog,
 					union bpf_attr *attr)
@@ -1567,9 +1566,6 @@ static inline struct bpf_map *bpf_map_offload_map_alloc(union bpf_attr *attr)
 static inline void bpf_map_offload_map_free(struct bpf_map *map)
 {
 }
-static inline void init_btf_sock_ids(struct btf *btf)
-{
-}
 #endif /* CONFIG_NET && CONFIG_BPF_SYSCALL */
 
 #if defined(CONFIG_BPF_STREAM_PARSER)

kernel/bpf/btf.c

@@ -3672,7 +3672,6 @@ struct btf *btf_parse_vmlinux(void)
 		goto errout;
 
 	bpf_struct_ops_init(btf, log);
-	init_btf_sock_ids(btf);
 
 	btf_verifier_env_free(env);
 	refcount_set(&btf->refcnt, 1);

net/core/filter.c

@@ -9426,19 +9426,19 @@ void bpf_prog_change_xdp(struct bpf_prog *prev_prog, struct bpf_prog *prog)
  * sock_common as the first argument in its memory layout.
  */
 #define BTF_SOCK_TYPE_xxx \
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET, "inet_sock")			\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_CONN, "inet_connection_sock")	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_REQ, "inet_request_sock")	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, "inet_timewait_sock")	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_REQ, "request_sock")		\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK, "sock")			\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK_COMMON, "sock_common")		\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP, "tcp_sock")			\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_REQ, "tcp_request_sock")	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, "tcp_timewait_sock")	\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, "tcp6_sock")			\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, "udp_sock")			\
-	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, "udp6_sock")
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET, inet_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_CONN, inet_connection_sock)	\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_REQ, inet_request_sock)	\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, inet_timewait_sock)	\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_REQ, request_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK, sock)				\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK_COMMON, sock_common)		\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP, tcp_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_REQ, tcp_request_sock)		\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)		\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, tcp6_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, udp_sock)			\
+	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)
 
 enum {
 #define BTF_SOCK_TYPE(name, str) name,
@@ -9447,26 +9447,13 @@ BTF_SOCK_TYPE_xxx
 MAX_BTF_SOCK_TYPE,
 };
 
-static int btf_sock_ids[MAX_BTF_SOCK_TYPE];
-
-#ifdef CONFIG_BPF_SYSCALL
-static const char *bpf_sock_types[] = {
-#define BTF_SOCK_TYPE(name, str) str,
+#ifdef CONFIG_DEBUG_INFO_BTF
+BTF_ID_LIST(btf_sock_ids)
+#define BTF_SOCK_TYPE(name, type) BTF_ID(struct, type)
 BTF_SOCK_TYPE_xxx
 #undef BTF_SOCK_TYPE
-};
-
-void init_btf_sock_ids(struct btf *btf)
-{
-	int i, btf_id;
-
-	for (i = 0; i < MAX_BTF_SOCK_TYPE; i++) {
-		btf_id = btf_find_by_name_kind(btf, bpf_sock_types[i],
-					       BTF_KIND_STRUCT);
-		if (btf_id > 0)
-			btf_sock_ids[i] = btf_id;
-	}
-}
+#else
+static u32 btf_sock_ids[MAX_BTF_SOCK_TYPE];
 #endif
 
 static bool check_arg_btf_id(u32 btf_id, u32 arg)