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 extern void my_direct_func1(void);
7 extern void my_direct_func2(void);
8
my_direct_func1(void)9 void my_direct_func1(void)
10 {
11 trace_printk("my direct func1\n");
12 }
13
my_direct_func2(void)14 void my_direct_func2(void)
15 {
16 trace_printk("my direct func2\n");
17 }
18
19 extern void my_tramp1(void *);
20 extern void my_tramp2(void *);
21
22 static unsigned long my_ip = (unsigned long)schedule;
23
24 asm (
25 " .pushsection .text, \"ax\", @progbits\n"
26 " .type my_tramp1, @function\n"
27 " .globl my_tramp1\n"
28 " my_tramp1:"
29 " pushq %rbp\n"
30 " movq %rsp, %rbp\n"
31 " call my_direct_func1\n"
32 " leave\n"
33 " .size my_tramp1, .-my_tramp1\n"
34 ASM_RET
35 " .type my_tramp2, @function\n"
36 " .globl my_tramp2\n"
37 " my_tramp2:"
38 " pushq %rbp\n"
39 " movq %rsp, %rbp\n"
40 " call my_direct_func2\n"
41 " leave\n"
42 ASM_RET
43 " .size my_tramp2, .-my_tramp2\n"
44 " .popsection\n"
45 );
46
47 static unsigned long my_tramp = (unsigned long)my_tramp1;
48 static unsigned long tramps[2] = {
49 (unsigned long)my_tramp1,
50 (unsigned long)my_tramp2,
51 };
52
simple_thread(void * arg)53 static int simple_thread(void *arg)
54 {
55 static int t;
56 int ret = 0;
57
58 while (!kthread_should_stop()) {
59 set_current_state(TASK_INTERRUPTIBLE);
60 schedule_timeout(2 * HZ);
61
62 if (ret)
63 continue;
64 t ^= 1;
65 ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
66 if (!ret)
67 my_tramp = tramps[t];
68 WARN_ON_ONCE(ret);
69 }
70
71 return 0;
72 }
73
74 static struct task_struct *simple_tsk;
75
ftrace_direct_init(void)76 static int __init ftrace_direct_init(void)
77 {
78 int ret;
79
80 ret = register_ftrace_direct(my_ip, my_tramp);
81 if (!ret)
82 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
83 return ret;
84 }
85
ftrace_direct_exit(void)86 static void __exit ftrace_direct_exit(void)
87 {
88 kthread_stop(simple_tsk);
89 unregister_ftrace_direct(my_ip, my_tramp);
90 }
91
92 module_init(ftrace_direct_init);
93 module_exit(ftrace_direct_exit);
94
95 MODULE_AUTHOR("Steven Rostedt");
96 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
97 MODULE_LICENSE("GPL");
98