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