samples/ftrace/ftrace-direct.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/module.h>
   3
   4 #include <linux/sched.h> /* for wake_up_process() */
   5 #include <linux/ftrace.h>
   6
   7 extern void my_direct_func(struct task_struct *p);
   8
   9 void my_direct_func(struct task_struct *p)
  10 {
  11         trace_printk("waking up %s-%d\n", p->comm, p->pid);
  12 }
  13
  14 extern void my_tramp(void *);
  15
  16 asm (
  17 "       .pushsection    .text, \"ax\", @progbits\n"
  18 "       .type           my_tramp, @function\n"
  19 "       .globl          my_tramp\n"
  20 "   my_tramp:"
  21 "       pushq %rbp\n"
  22 "       movq %rsp, %rbp\n"
  23 "       pushq %rdi\n"
  24 "       call my_direct_func\n"
  25 "       popq %rdi\n"
  26 "       leave\n"
  27         ASM_RET
  28 "       .size           my_tramp, .-my_tramp\n"
  29 "       .popsection\n"
  30 );
  31
  32
  33 static int __init ftrace_direct_init(void)
  34 {
  35         return register_ftrace_direct((unsigned long)wake_up_process,
  36                                      (unsigned long)my_tramp);
  37 }
  38
  39 static void __exit ftrace_direct_exit(void)
  40 {
  41         unregister_ftrace_direct((unsigned long)wake_up_process,
  42                                  (unsigned long)my_tramp);
  43 }
  44
  45 module_init(ftrace_direct_init);
  46 module_exit(ftrace_direct_exit);
  47
  48 MODULE_AUTHOR("Steven Rostedt");
  49 MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
  50 MODULE_LICENSE("GPL");