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 #include <asm/ibt.h>
28
29 asm (
30 " .pushsection .text, \"ax\", @progbits\n"
31 " .type my_tramp1, @function\n"
32 " .globl my_tramp1\n"
33 " my_tramp1:"
34 ASM_ENDBR
35 " pushq %rbp\n"
36 " movq %rsp, %rbp\n"
37 " call my_direct_func1\n"
38 " leave\n"
39 " .size my_tramp1, .-my_tramp1\n"
40 ASM_RET
41
42 " .type my_tramp2, @function\n"
43 " .globl my_tramp2\n"
44 " my_tramp2:"
45 ASM_ENDBR
46 " pushq %rbp\n"
47 " movq %rsp, %rbp\n"
48 " call my_direct_func2\n"
49 " leave\n"
50 ASM_RET
51 " .size my_tramp2, .-my_tramp2\n"
52 " .popsection\n"
53 );
54
55 #endif /* CONFIG_X86_64 */
56
57 #ifdef CONFIG_S390
58
59 asm (
60 " .pushsection .text, \"ax\", @progbits\n"
61 " .type my_tramp1, @function\n"
62 " .globl my_tramp1\n"
63 " my_tramp1:"
64 " lgr %r1,%r15\n"
65 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
66 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
67 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
68 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
69 " brasl %r14,my_direct_func1\n"
70 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
71 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
72 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
73 " lgr %r1,%r0\n"
74 " br %r1\n"
75 " .size my_tramp1, .-my_tramp1\n"
76 " .type my_tramp2, @function\n"
77 " .globl my_tramp2\n"
78 " my_tramp2:"
79 " lgr %r1,%r15\n"
80 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
81 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
82 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
83 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
84 " brasl %r14,my_direct_func2\n"
85 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
86 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
87 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
88 " lgr %r1,%r0\n"
89 " br %r1\n"
90 " .size my_tramp2, .-my_tramp2\n"
91 " .popsection\n"
92 );
93
94 #endif /* CONFIG_S390 */
95
96 static unsigned long my_tramp = (unsigned long)my_tramp1;
97 static unsigned long tramps[2] = {
98 (unsigned long)my_tramp1,
99 (unsigned long)my_tramp2,
100 };
101
simple_thread(void * arg)102 static int simple_thread(void *arg)
103 {
104 static int t;
105 int ret = 0;
106
107 while (!kthread_should_stop()) {
108 set_current_state(TASK_INTERRUPTIBLE);
109 schedule_timeout(2 * HZ);
110
111 if (ret)
112 continue;
113 t ^= 1;
114 ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
115 if (!ret)
116 my_tramp = tramps[t];
117 WARN_ON_ONCE(ret);
118 }
119
120 return 0;
121 }
122
123 static struct task_struct *simple_tsk;
124
ftrace_direct_init(void)125 static int __init ftrace_direct_init(void)
126 {
127 int ret;
128
129 ret = register_ftrace_direct(my_ip, my_tramp);
130 if (!ret)
131 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
132 return ret;
133 }
134
ftrace_direct_exit(void)135 static void __exit ftrace_direct_exit(void)
136 {
137 kthread_stop(simple_tsk);
138 unregister_ftrace_direct(my_ip, my_tramp);
139 }
140
141 module_init(ftrace_direct_init);
142 module_exit(ftrace_direct_exit);
143
144 MODULE_AUTHOR("Steven Rostedt");
145 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
146 MODULE_LICENSE("GPL");
147
