kprobes: Add new KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag

Adding KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag to indicate that
attach address is on function entry. This is used in following
changes in get_func_ip helper to return correct function address.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-2-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/kprobes.h

@@ -103,6 +103,7 @@ struct kprobe {
 				   * this flag is only for optimized_kprobe.
 				   */
 #define KPROBE_FLAG_FTRACE	8 /* probe is using ftrace */
+#define KPROBE_FLAG_ON_FUNC_ENTRY	16 /* probe is on the function entry */
 
 /* Has this kprobe gone ? */
 static inline bool kprobe_gone(struct kprobe *p)

kernel/kprobes.c

@@ -1606,9 +1606,10 @@ int register_kprobe(struct kprobe *p)
 	struct kprobe *old_p;
 	struct module *probed_mod;
 	kprobe_opcode_t *addr;
+	bool on_func_entry;
 
 	/* Adjust probe address from symbol */
-	addr = kprobe_addr(p);
+	addr = _kprobe_addr(p->addr, p->symbol_name, p->offset, &on_func_entry);
 	if (IS_ERR(addr))
 		return PTR_ERR(addr);
 	p->addr = addr;
@@ -1628,6 +1629,9 @@ int register_kprobe(struct kprobe *p)
 
 	mutex_lock(&kprobe_mutex);
 
+	if (on_func_entry)
+		p->flags |= KPROBE_FLAG_ON_FUNC_ENTRY;
+
 	old_p = get_kprobe(p->addr);
 	if (old_p) {
 		/* Since this may unoptimize 'old_p', locking 'text_mutex'. */