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 "	.type		my_tramp1, @function\n"
24 "   my_tramp1:"
25 "	pushq %rbp\n"
26 "	movq %rsp, %rbp\n"
27 "	call my_direct_func1\n"
28 "	leave\n"
29 "	.size		my_tramp1, .-my_tramp1\n"
30 "	ret\n"
31 "	.type		my_tramp2, @function\n"
32 "   my_tramp2:"
33 "	pushq %rbp\n"
34 "	movq %rsp, %rbp\n"
35 "	call my_direct_func2\n"
36 "	leave\n"
37 "	ret\n"
38 "	.size		my_tramp2, .-my_tramp2\n"
39 "	.popsection\n"
40 );
41 
42 static unsigned long my_tramp = (unsigned long)my_tramp1;
43 static unsigned long tramps[2] = {
44 	(unsigned long)my_tramp1,
45 	(unsigned long)my_tramp2,
46 };
47 
48 static int simple_thread(void *arg)
49 {
50 	static int t;
51 	int ret = 0;
52 
53 	while (!kthread_should_stop()) {
54 		set_current_state(TASK_INTERRUPTIBLE);
55 		schedule_timeout(2 * HZ);
56 
57 		if (ret)
58 			continue;
59 		t ^= 1;
60 		ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
61 		if (!ret)
62 			my_tramp = tramps[t];
63 		WARN_ON_ONCE(ret);
64 	}
65 
66 	return 0;
67 }
68 
69 static struct task_struct *simple_tsk;
70 
71 static int __init ftrace_direct_init(void)
72 {
73 	int ret;
74 
75 	ret = register_ftrace_direct(my_ip, my_tramp);
76 	if (!ret)
77 		simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
78 	return ret;
79 }
80 
81 static void __exit ftrace_direct_exit(void)
82 {
83 	kthread_stop(simple_tsk);
84 	unregister_ftrace_direct(my_ip, my_tramp);
85 }
86 
87 module_init(ftrace_direct_init);
88 module_exit(ftrace_direct_exit);
89 
90 MODULE_AUTHOR("Steven Rostedt");
91 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
92 MODULE_LICENSE("GPL");
93