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 #include <asm/nospec-branch.h>
7 
8 extern void my_direct_func1(void);
9 extern void my_direct_func2(void);
10 
11 void my_direct_func1(void)
12 {
13 	trace_printk("my direct func1\n");
14 }
15 
16 void my_direct_func2(void)
17 {
18 	trace_printk("my direct func2\n");
19 }
20 
21 extern void my_tramp1(void *);
22 extern void my_tramp2(void *);
23 
24 static unsigned long my_ip = (unsigned long)schedule;
25 
26 #ifdef CONFIG_X86_64
27 
28 #include <asm/ibt.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 
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 
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 
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