1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/module.h>
3 
4 #include <linux/mm.h> /* for handle_mm_fault() */
5 #include <linux/ftrace.h>
6 #include <asm/asm-offsets.h>
7 
8 extern void my_direct_func(struct vm_area_struct *vma,
9 			   unsigned long address, unsigned int flags);
10 
my_direct_func(struct vm_area_struct * vma,unsigned long address,unsigned int flags)11 void my_direct_func(struct vm_area_struct *vma,
12 			unsigned long address, unsigned int flags)
13 {
14 	trace_printk("handle mm fault vma=%p address=%lx flags=%x\n",
15 		     vma, address, flags);
16 }
17 
18 extern void my_tramp(void *);
19 
20 #ifdef CONFIG_X86_64
21 
22 asm (
23 "	.pushsection    .text, \"ax\", @progbits\n"
24 "	.type		my_tramp, @function\n"
25 "	.globl		my_tramp\n"
26 "   my_tramp:"
27 "	pushq %rbp\n"
28 "	movq %rsp, %rbp\n"
29 "	pushq %rdi\n"
30 "	pushq %rsi\n"
31 "	pushq %rdx\n"
32 "	call my_direct_func\n"
33 "	popq %rdx\n"
34 "	popq %rsi\n"
35 "	popq %rdi\n"
36 "	leave\n"
37 "	ret\n"
38 "	.size		my_tramp, .-my_tramp\n"
39 "	.popsection\n"
40 );
41 
42 #endif /* CONFIG_X86_64 */
43 
44 #ifdef CONFIG_S390
45 
46 asm (
47 "	.pushsection	.text, \"ax\", @progbits\n"
48 "	.type		my_tramp, @function\n"
49 "	.globl		my_tramp\n"
50 "   my_tramp:"
51 "	lgr		%r1,%r15\n"
52 "	stmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
53 "	stg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
54 "	aghi		%r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
55 "	stg		%r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
56 "	brasl		%r14,my_direct_func\n"
57 "	aghi		%r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
58 "	lmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
59 "	lg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
60 "	lgr		%r1,%r0\n"
61 "	br		%r1\n"
62 "	.size		my_tramp, .-my_tramp\n"
63 "	.popsection\n"
64 );
65 
66 #endif /* CONFIG_S390 */
67 
ftrace_direct_init(void)68 static int __init ftrace_direct_init(void)
69 {
70 	return register_ftrace_direct((unsigned long)handle_mm_fault,
71 				     (unsigned long)my_tramp);
72 }
73 
ftrace_direct_exit(void)74 static void __exit ftrace_direct_exit(void)
75 {
76 	unregister_ftrace_direct((unsigned long)handle_mm_fault,
77 				 (unsigned long)my_tramp);
78 }
79 
80 module_init(ftrace_direct_init);
81 module_exit(ftrace_direct_exit);
82 
83 MODULE_AUTHOR("Steven Rostedt");
84 MODULE_DESCRIPTION("Another example use case of using register_ftrace_direct()");
85 MODULE_LICENSE("GPL");
86