1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/module.h>
3 #include <linux/kthread.h>
4 #include <linux/ftrace.h>
5 
6 void my_direct_func1(void)
7 {
8 	trace_printk("my direct func1\n");
9 }
10 
11 void my_direct_func2(void)
12 {
13 	trace_printk("my direct func2\n");
14 }
15 
16 extern void my_tramp1(void *);
17 extern void my_tramp2(void *);
18 
19 static unsigned long my_ip = (unsigned long)schedule;
20 
21 asm (
22 "	.pushsection    .text, \"ax\", @progbits\n"
23 "   my_tramp1:"
24 "	pushq %rbp\n"
25 "	movq %rsp, %rbp\n"
26 "	call my_direct_func1\n"
27 "	leave\n"
28 "	ret\n"
29 "   my_tramp2:"
30 "	pushq %rbp\n"
31 "	movq %rsp, %rbp\n"
32 "	call my_direct_func2\n"
33 "	leave\n"
34 "	ret\n"
35 "	.popsection\n"
36 );
37 
38 static unsigned long my_tramp = (unsigned long)my_tramp1;
39 static unsigned long tramps[2] = {
40 	(unsigned long)my_tramp1,
41 	(unsigned long)my_tramp2,
42 };
43 
44 static int simple_thread(void *arg)
45 {
46 	static int t;
47 	int ret = 0;
48 
49 	while (!kthread_should_stop()) {
50 		set_current_state(TASK_INTERRUPTIBLE);
51 		schedule_timeout(2 * HZ);
52 
53 		if (ret)
54 			continue;
55 		t ^= 1;
56 		ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
57 		if (!ret)
58 			my_tramp = tramps[t];
59 		WARN_ON_ONCE(ret);
60 	}
61 
62 	return 0;
63 }
64 
65 static struct task_struct *simple_tsk;
66 
67 static int __init ftrace_direct_init(void)
68 {
69 	int ret;
70 
71 	ret = register_ftrace_direct(my_ip, my_tramp);
72 	if (!ret)
73 		simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
74 	return ret;
75 }
76 
77 static void __exit ftrace_direct_exit(void)
78 {
79 	kthread_stop(simple_tsk);
80 	unregister_ftrace_direct(my_ip, my_tramp);
81 }
82 
83 module_init(ftrace_direct_init);
84 module_exit(ftrace_direct_exit);
85 
86 MODULE_AUTHOR("Steven Rostedt");
87 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
88 MODULE_LICENSE("GPL");
89