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 #include <asm/nospec-branch.h>
29
30 asm (
31 " .pushsection .text, \"ax\", @progbits\n"
32 " .type my_tramp1, @function\n"
33 " .globl my_tramp1\n"
34 " my_tramp1:"
35 ASM_ENDBR
36 " pushq %rbp\n"
37 " movq %rsp, %rbp\n"
38 CALL_DEPTH_ACCOUNT
39 " call my_direct_func1\n"
40 " leave\n"
41 " .size my_tramp1, .-my_tramp1\n"
42 ASM_RET
43
44 " .type my_tramp2, @function\n"
45 " .globl my_tramp2\n"
46 " my_tramp2:"
47 ASM_ENDBR
48 " pushq %rbp\n"
49 " movq %rsp, %rbp\n"
50 CALL_DEPTH_ACCOUNT
51 " call my_direct_func2\n"
52 " leave\n"
53 ASM_RET
54 " .size my_tramp2, .-my_tramp2\n"
55 " .popsection\n"
56 );
57
58 #endif /* CONFIG_X86_64 */
59
60 #ifdef CONFIG_S390
61
62 asm (
63 " .pushsection .text, \"ax\", @progbits\n"
64 " .type my_tramp1, @function\n"
65 " .globl my_tramp1\n"
66 " my_tramp1:"
67 " lgr %r1,%r15\n"
68 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
69 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
70 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
71 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
72 " brasl %r14,my_direct_func1\n"
73 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
74 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
75 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
76 " lgr %r1,%r0\n"
77 " br %r1\n"
78 " .size my_tramp1, .-my_tramp1\n"
79 " .type my_tramp2, @function\n"
80 " .globl my_tramp2\n"
81 " my_tramp2:"
82 " lgr %r1,%r15\n"
83 " stmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
84 " stg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
85 " aghi %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
86 " stg %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
87 " brasl %r14,my_direct_func2\n"
88 " aghi %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
89 " lmg %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
90 " lg %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
91 " lgr %r1,%r0\n"
92 " br %r1\n"
93 " .size my_tramp2, .-my_tramp2\n"
94 " .popsection\n"
95 );
96
97 #endif /* CONFIG_S390 */
98
99 static unsigned long my_tramp = (unsigned long)my_tramp1;
100 static unsigned long tramps[2] = {
101 (unsigned long)my_tramp1,
102 (unsigned long)my_tramp2,
103 };
104
simple_thread(void * arg)105 static int simple_thread(void *arg)
106 {
107 static int t;
108 int ret = 0;
109
110 while (!kthread_should_stop()) {
111 set_current_state(TASK_INTERRUPTIBLE);
112 schedule_timeout(2 * HZ);
113
114 if (ret)
115 continue;
116 t ^= 1;
117 ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
118 if (!ret)
119 my_tramp = tramps[t];
120 WARN_ON_ONCE(ret);
121 }
122
123 return 0;
124 }
125
126 static struct task_struct *simple_tsk;
127
ftrace_direct_init(void)128 static int __init ftrace_direct_init(void)
129 {
130 int ret;
131
132 ret = register_ftrace_direct(my_ip, my_tramp);
133 if (!ret)
134 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
135 return ret;
136 }
137
ftrace_direct_exit(void)138 static void __exit ftrace_direct_exit(void)
139 {
140 kthread_stop(simple_tsk);
141 unregister_ftrace_direct(my_ip, my_tramp);
142 }
143
144 module_init(ftrace_direct_init);
145 module_exit(ftrace_direct_exit);
146
147 MODULE_AUTHOR("Steven Rostedt");
148 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
149 MODULE_LICENSE("GPL");
150