1// SPDX-License-Identifier: GPL-2.0-only
 2#include <linux/module.h>
 3#include <linux/kthread.h>
 4#include <linux/ftrace.h>
 5
 6void my_direct_func1(void)
 7{
 8	trace_printk("my direct func1\n");
 9}
10
11void my_direct_func2(void)
12{
13	trace_printk("my direct func2\n");
14}
15
16extern void my_tramp1(void *);
17extern void my_tramp2(void *);
18
19static unsigned long my_ip = (unsigned long)schedule;
20
21asm (
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
42static unsigned long my_tramp = (unsigned long)my_tramp1;
43static unsigned long tramps[2] = {
44	(unsigned long)my_tramp1,
45	(unsigned long)my_tramp2,
46};
47
48static 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
69static struct task_struct *simple_tsk;
70
71static 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
81static void __exit ftrace_direct_exit(void)
82{
83	kthread_stop(simple_tsk);
84	unregister_ftrace_direct(my_ip, my_tramp);
85}
86
87module_init(ftrace_direct_init);
88module_exit(ftrace_direct_exit);
89
90MODULE_AUTHOR("Steven Rostedt");
91MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
92MODULE_LICENSE("GPL");