samples/ftrace/ftrace-direct-modify.c

   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");