ftrace: Show subops in enabled_functions

The function graph infrastructure uses subops of the function tracer.
These are not shown in enabled_functions. Add a "subops:" section to the
enabled_functions line to show what functions are attached via subops. If
the subops is from the function_graph infrastructure, then show the entry
and return callbacks that are attached.

Here's an example of the output:

schedule_on_each_cpu (1)                tramp: 0xffffffffc03ef000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60     subops: {ent:trace_graph_entry+0x0/0x20 ret:trace_graph_return+0x0/0x150}

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250410153830.5d97f108@gandalf.local.home
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/ftrace.h

@@ -328,6 +328,7 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
  * DIRECT - Used by the direct ftrace_ops helper for direct functions
  *            (internal ftrace only, should not be used by others)
  * SUBOP  - Is controlled by another op in field managed.
+ * GRAPH  - Is a component of the fgraph_ops structure
  */
 enum {
 	FTRACE_OPS_FL_ENABLED			= BIT(0),
@@ -349,6 +350,7 @@ enum {
 	FTRACE_OPS_FL_PERMANENT                 = BIT(16),
 	FTRACE_OPS_FL_DIRECT			= BIT(17),
 	FTRACE_OPS_FL_SUBOP			= BIT(18),
+	FTRACE_OPS_FL_GRAPH			= BIT(19),
 };
 
 #ifndef CONFIG_DYNAMIC_FTRACE_WITH_ARGS

kernel/trace/fgraph.c

@@ -1382,6 +1382,8 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 	/* Always save the function, and reset at unregistering */
 	gops->saved_func = gops->entryfunc;
 
+	gops->ops.flags |= FTRACE_OPS_FL_GRAPH;
+
 	ret = ftrace_startup_subops(&graph_ops, &gops->ops, command);
 	if (!ret)
 		fgraph_array[i] = gops;

kernel/trace/ftrace.c

@@ -4373,6 +4373,42 @@ static inline int print_rec(struct seq_file *m, unsigned long ip)
 }
 #endif
 
+static void print_subops(struct seq_file *m, struct ftrace_ops *ops, struct dyn_ftrace *rec)
+{
+	struct ftrace_ops *subops;
+	bool first = true;
+
+	list_for_each_entry(subops, &ops->subop_list, list) {
+		if (!((subops->flags & FTRACE_OPS_FL_ENABLED) &&
+		      hash_contains_ip(rec->ip, subops->func_hash)))
+			continue;
+		if (first) {
+			seq_printf(m, "\tsubops:");
+			first = false;
+		}
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+		if (subops->flags & FTRACE_OPS_FL_GRAPH) {
+			struct fgraph_ops *gops;
+
+			gops = container_of(subops, struct fgraph_ops, ops);
+			seq_printf(m, " {ent:%pS ret:%pS}",
+				   (void *)gops->entryfunc,
+				   (void *)gops->retfunc);
+			continue;
+		}
+#endif
+		if (subops->trampoline) {
+			seq_printf(m, " {%pS (%pS)}",
+				   (void *)subops->trampoline,
+				   (void *)subops->func);
+			add_trampoline_func(m, subops, rec);
+		} else {
+			seq_printf(m, " {%pS}",
+				   (void *)subops->func);
+		}
+	}
+}
+
 static int t_show(struct seq_file *m, void *v)
 {
 	struct ftrace_iterator *iter = m->private;
@@ -4425,6 +4461,7 @@ static int t_show(struct seq_file *m, void *v)
 						   (void *)ops->trampoline,
 						   (void *)ops->func);
 					add_trampoline_func(m, ops, rec);
+					print_subops(m, ops, rec);
 					ops = ftrace_find_tramp_ops_next(rec, ops);
 				} while (ops);
 			} else
@@ -4437,6 +4474,7 @@ static int t_show(struct seq_file *m, void *v)
 			if (ops) {
 				seq_printf(m, "\tops: %pS (%pS)",
 					   ops, ops->func);
+				print_subops(m, ops, rec);
 			} else {
 				seq_puts(m, "\tops: ERROR!");
 			}