tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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" 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
38static unsigned long my_tramp = (unsigned long)my_tramp1;
39static unsigned long tramps[2] = {
40 (unsigned long)my_tramp1,
41 (unsigned long)my_tramp2,
42};
43
44static 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
65static struct task_struct *simple_tsk;
66
67static 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
77static void __exit ftrace_direct_exit(void)
78{
79 kthread_stop(simple_tsk);
80 unregister_ftrace_direct(my_ip, my_tramp);
81}
82
83module_init(ftrace_direct_init);
84module_exit(ftrace_direct_exit);
85
86MODULE_AUTHOR("Steven Rostedt");
87MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
88MODULE_LICENSE("GPL");