bpf: Add initial poke descriptor table for jit images

Add initial poke table data structures and management to the BPF
prog that can later be used by JITs. Also add an instance of poke
specific data for tail call maps; plan for later work is to extend
this also for BPF static keys.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/1db285ec2ea4207ee0455b3f8e191a4fc58b9ade.1574452833.git.daniel@iogearbox.net

include/linux/bpf.h

@@ -488,6 +488,24 @@ struct bpf_func_info_aux {
 	bool unreliable;
 };
 
+enum bpf_jit_poke_reason {
+	BPF_POKE_REASON_TAIL_CALL,
+};
+
+/* Descriptor of pokes pointing /into/ the JITed image. */
+struct bpf_jit_poke_descriptor {
+	void *ip;
+	union {
+		struct {
+			struct bpf_map *map;
+			u32 key;
+		} tail_call;
+	};
+	bool ip_stable;
+	u8 adj_off;
+	u16 reason;
+};
+
 struct bpf_prog_aux {
 	atomic64_t refcnt;
 	u32 used_map_cnt;
@@ -513,6 +531,8 @@ struct bpf_prog_aux {
 	const char *attach_func_name;
 	struct bpf_prog **func;
 	void *jit_data; /* JIT specific data. arch dependent */
+	struct bpf_jit_poke_descriptor *poke_tab;
+	u32 size_poke_tab;
 	struct latch_tree_node ksym_tnode;
 	struct list_head ksym_lnode;
 	const struct bpf_prog_ops *ops;