ftrace: Do not let direct or IPMODIFY ftrace_ops be added to module and set trampolines

When inserting a module, we find all ftrace_ops referencing it on the
ftrace_ops_list. But FTRACE_OPS_FL_DIRECT and FTRACE_OPS_FL_IPMODIFY
flags are special, and should not be set automatically. So warn and
skip ftrace_ops that have these two flags set and adding new code.
Also check if only one ftrace_ops references the module, in which case
we can use a trampoline as an optimization.

Link: https://lkml.kernel.org/r/20200728180554.65203-2-zhouchengming@bytedance.comSigned-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -6199,9 +6199,17 @@ static int referenced_filters(struct dyn_ftrace *rec)
 
 	for (ops = ftrace_ops_list; ops != &ftrace_list_end; ops = ops->next) {
 		if (ops_references_rec(ops, rec)) {
+			if (WARN_ON_ONCE(ops->flags & FTRACE_OPS_FL_DIRECT))
+				continue;
+			if (WARN_ON_ONCE(ops->flags & FTRACE_OPS_FL_IPMODIFY))
+				continue;
 			cnt++;
 			if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
 				rec->flags |= FTRACE_FL_REGS;
+			if (cnt == 1 && ops->trampoline)
+				rec->flags |= FTRACE_FL_TRAMP;
+			else
+				rec->flags &= ~FTRACE_FL_TRAMP;
 		}
 	}