1// SPDX-License-Identifier: GPL-2.0-only
2#include <linux/module.h>
3#include <linux/kthread.h>
4#include <linux/ftrace.h>
5#ifndef CONFIG_ARM64
6#include <asm/asm-offsets.h>
7#endif
8
9extern void my_direct_func1(void);
10extern void my_direct_func2(void);
11
12void my_direct_func1(void)
13{
14	trace_printk("my direct func1\n");
15}
16
17void my_direct_func2(void)
18{
19	trace_printk("my direct func2\n");
20}
21
22extern void my_tramp1(void *);
23extern void my_tramp2(void *);
24
25static unsigned long my_ip = (unsigned long)schedule;
26
27#ifdef CONFIG_X86_64
28
29#include <asm/ibt.h>
30#include <asm/nospec-branch.h>
31
32asm (
33"	.pushsection    .text, \"ax\", @progbits\n"
34"	.type		my_tramp1, @function\n"
35"	.globl		my_tramp1\n"
36"   my_tramp1:"
37	ASM_ENDBR
38"	pushq %rbp\n"
39"	movq %rsp, %rbp\n"
40	CALL_DEPTH_ACCOUNT
41"	call my_direct_func1\n"
42"	leave\n"
43"	.size		my_tramp1, .-my_tramp1\n"
44	ASM_RET
45
46"	.type		my_tramp2, @function\n"
47"	.globl		my_tramp2\n"
48"   my_tramp2:"
49	ASM_ENDBR
50"	pushq %rbp\n"
51"	movq %rsp, %rbp\n"
52	CALL_DEPTH_ACCOUNT
53"	call my_direct_func2\n"
54"	leave\n"
55	ASM_RET
56"	.size		my_tramp2, .-my_tramp2\n"
57"	.popsection\n"
58);
59
60#endif /* CONFIG_X86_64 */
61
62#ifdef CONFIG_S390
63
64asm (
65"	.pushsection	.text, \"ax\", @progbits\n"
66"	.type		my_tramp1, @function\n"
67"	.globl		my_tramp1\n"
68"   my_tramp1:"
69"	lgr		%r1,%r15\n"
70"	stmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
71"	stg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
72"	aghi		%r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
73"	stg		%r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
74"	brasl		%r14,my_direct_func1\n"
75"	aghi		%r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
76"	lmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
77"	lg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
78"	lgr		%r1,%r0\n"
79"	br		%r1\n"
80"	.size		my_tramp1, .-my_tramp1\n"
81"	.type		my_tramp2, @function\n"
82"	.globl		my_tramp2\n"
83"   my_tramp2:"
84"	lgr		%r1,%r15\n"
85"	stmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
86"	stg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
87"	aghi		%r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
88"	stg		%r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
89"	brasl		%r14,my_direct_func2\n"
90"	aghi		%r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
91"	lmg		%r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
92"	lg		%r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
93"	lgr		%r1,%r0\n"
94"	br		%r1\n"
95"	.size		my_tramp2, .-my_tramp2\n"
96"	.popsection\n"
97);
98
99#endif /* CONFIG_S390 */
100
101#ifdef CONFIG_ARM64
102
103asm (
104"	.pushsection    .text, \"ax\", @progbits\n"
105"	.type		my_tramp1, @function\n"
106"	.globl		my_tramp1\n"
107"   my_tramp1:"
108"	hint	34\n" // bti	c
109"	sub	sp, sp, #16\n"
110"	stp	x9, x30, [sp]\n"
111"	bl	my_direct_func1\n"
112"	ldp	x30, x9, [sp]\n"
113"	add	sp, sp, #16\n"
114"	ret	x9\n"
115"	.size		my_tramp1, .-my_tramp1\n"
116
117"	.type		my_tramp2, @function\n"
118"	.globl		my_tramp2\n"
119"   my_tramp2:"
120"	hint	34\n" // bti	c
121"	sub	sp, sp, #16\n"
122"	stp	x9, x30, [sp]\n"
123"	bl	my_direct_func2\n"
124"	ldp	x30, x9, [sp]\n"
125"	add	sp, sp, #16\n"
126"	ret	x9\n"
127"	.size		my_tramp2, .-my_tramp2\n"
128"	.popsection\n"
129);
130
131#endif /* CONFIG_ARM64 */
132
133#ifdef CONFIG_LOONGARCH
134
135asm (
136"	.pushsection    .text, \"ax\", @progbits\n"
137"	.type		my_tramp1, @function\n"
138"	.globl		my_tramp1\n"
139"   my_tramp1:\n"
140"	addi.d	$sp, $sp, -16\n"
141"	st.d	$t0, $sp, 0\n"
142"	st.d	$ra, $sp, 8\n"
143"	bl	my_direct_func1\n"
144"	ld.d	$t0, $sp, 0\n"
145"	ld.d	$ra, $sp, 8\n"
146"	addi.d	$sp, $sp, 16\n"
147"	jr	$t0\n"
148"	.size		my_tramp1, .-my_tramp1\n"
149
150"	.type		my_tramp2, @function\n"
151"	.globl		my_tramp2\n"
152"   my_tramp2:\n"
153"	addi.d	$sp, $sp, -16\n"
154"	st.d	$t0, $sp, 0\n"
155"	st.d	$ra, $sp, 8\n"
156"	bl	my_direct_func2\n"
157"	ld.d	$t0, $sp, 0\n"
158"	ld.d	$ra, $sp, 8\n"
159"	addi.d	$sp, $sp, 16\n"
160"	jr	$t0\n"
161"	.size		my_tramp2, .-my_tramp2\n"
162"	.popsection\n"
163);
164
165#endif /* CONFIG_LOONGARCH */
166
167static struct ftrace_ops direct;
168
169static unsigned long my_tramp = (unsigned long)my_tramp1;
170static unsigned long tramps[2] = {
171	(unsigned long)my_tramp1,
172	(unsigned long)my_tramp2,
173};
174
175static int simple_thread(void *arg)
176{
177	static int t;
178	int ret = 0;
179
180	while (!kthread_should_stop()) {
181		set_current_state(TASK_INTERRUPTIBLE);
182		schedule_timeout(2 * HZ);
183
184		if (ret)
185			continue;
186		t ^= 1;
187		ret = modify_ftrace_direct(&direct, tramps[t]);
188		if (!ret)
189			my_tramp = tramps[t];
190		WARN_ON_ONCE(ret);
191	}
192
193	return 0;
194}
195
196static struct task_struct *simple_tsk;
197
198static int __init ftrace_direct_init(void)
199{
200	int ret;
201
202	ftrace_set_filter_ip(&direct, (unsigned long) my_ip, 0, 0);
203	ret = register_ftrace_direct(&direct, my_tramp);
204
205	if (!ret)
206		simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
207	return ret;
208}
209
210static void __exit ftrace_direct_exit(void)
211{
212	kthread_stop(simple_tsk);
213	unregister_ftrace_direct(&direct, my_tramp, true);
214}
215
216module_init(ftrace_direct_init);
217module_exit(ftrace_direct_exit);
218
219MODULE_AUTHOR("Steven Rostedt");
220MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
221MODULE_LICENSE("GPL");
222