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