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 extern void my_direct_func1(void);
   7 extern void my_direct_func2(void);
   8
   9 void my_direct_func1(void)
  10 {
  11         trace_printk("my direct func1\n");
  12 }
  13
  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
  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
  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
  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");