1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/module.h>
3 #include <linux/kthread.h>
4 #include <linux/ftrace.h>
5 #include <asm/asm-offsets.h>
6
7 extern void my_direct_func1(void);
8 extern void my_direct_func2(void);
9
my_direct_func1(void)10 void my_direct_func1(void)
11 {
12 trace_printk("my direct func1\n");
13 }
14
my_direct_func2(void)15 void my_direct_func2(void)
16 {
17 trace_printk("my direct func2\n");
18 }
19
20 extern void my_tramp1(void *);
21 extern void my_tramp2(void *);
22
23 static unsigned long my_ip = (unsigned long)schedule;
24
25 #ifdef CONFIG_X86_64
26
27 asm (
28 " .pushsection .text, \"ax\", @progbits\n"
29 " .type my_tramp1, @function\n"
30 " .globl my_tramp1\n"
31 " my_tramp1:"
32 " pushq %rbp\n"
33 " movq %rsp, %rbp\n"
34 " call my_direct_func1\n"
35 " leave\n"
36 " .size my_tramp1, .-my_tramp1\n"
37 " ret\n"
38 " .type my_tramp2, @function\n"
39 " .globl my_tramp2\n"
40 " my_tramp2:"
41 " pushq %rbp\n"
42 " movq %rsp, %rbp\n"
43 " call my_direct_func2\n"
44 " leave\n"
45 " ret\n"
46 " .size my_tramp2, .-my_tramp2\n"
47 " .popsection\n"
48 );
49
50 #endif /* CONFIG_X86_64 */
51
52 #ifdef CONFIG_S390
53
54 asm (
55 " .pushsection .text, \"ax\", @progbits\n"
56 " .type my_tramp1, @function\n"
57 " .globl my_tramp1\n"
58 " my_tramp1:"
59 " lgr %r1,%r15\n"
60 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
61 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
62 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
63 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
64 " brasl %r14,my_direct_func1\n"
65 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
66 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
67 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
68 " lgr %r1,%r0\n"
69 " br %r1\n"
70 " .size my_tramp1, .-my_tramp1\n"
71 " .type my_tramp2, @function\n"
72 " .globl my_tramp2\n"
73 " my_tramp2:"
74 " lgr %r1,%r15\n"
75 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
76 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
77 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
78 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
79 " brasl %r14,my_direct_func2\n"
80 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
81 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
82 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
83 " lgr %r1,%r0\n"
84 " br %r1\n"
85 " .size my_tramp2, .-my_tramp2\n"
86 " .popsection\n"
87 );
88
89 #endif /* CONFIG_S390 */
90
91 static unsigned long my_tramp = (unsigned long)my_tramp1;
92 static unsigned long tramps[2] = {
93 (unsigned long)my_tramp1,
94 (unsigned long)my_tramp2,
95 };
96
simple_thread(void * arg)97 static int simple_thread(void *arg)
98 {
99 static int t;
100 int ret = 0;
101
102 while (!kthread_should_stop()) {
103 set_current_state(TASK_INTERRUPTIBLE);
104 schedule_timeout(2 * HZ);
105
106 if (ret)
107 continue;
108 t ^= 1;
109 ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
110 if (!ret)
111 my_tramp = tramps[t];
112 WARN_ON_ONCE(ret);
113 }
114
115 return 0;
116 }
117
118 static struct task_struct *simple_tsk;
119
ftrace_direct_init(void)120 static int __init ftrace_direct_init(void)
121 {
122 int ret;
123
124 ret = register_ftrace_direct(my_ip, my_tramp);
125 if (!ret)
126 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
127 return ret;
128 }
129
ftrace_direct_exit(void)130 static void __exit ftrace_direct_exit(void)
131 {
132 kthread_stop(simple_tsk);
133 unregister_ftrace_direct(my_ip, my_tramp);
134 }
135
136 module_init(ftrace_direct_init);
137 module_exit(ftrace_direct_exit);
138
139 MODULE_AUTHOR("Steven Rostedt");
140 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
141 MODULE_LICENSE("GPL");
142