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
  8extern void my_direct_func1(void);
  9extern void my_direct_func2(void);
 10
 11void my_direct_func1(void)
 12{
 13	trace_printk("my direct func1\n");
 14}
 15
 16void my_direct_func2(void)
 17{
 18	trace_printk("my direct func2\n");
 19}
 20
 21extern void my_tramp1(void *);
 22extern void my_tramp2(void *);
 23
 24static unsigned long my_ip = (unsigned long)schedule;
 25
 26#ifdef CONFIG_X86_64
 27
 28#include <asm/ibt.h>
 29
 30asm (
 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
 62asm (
 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
 99static unsigned long my_tramp = (unsigned long)my_tramp1;
100static unsigned long tramps[2] = {
101	(unsigned long)my_tramp1,
102	(unsigned long)my_tramp2,
103};
104
105static 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
126static struct task_struct *simple_tsk;
127
128static 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
138static void __exit ftrace_direct_exit(void)
139{
140	kthread_stop(simple_tsk);
141	unregister_ftrace_direct(my_ip, my_tramp);
142}
143
144module_init(ftrace_direct_init);
145module_exit(ftrace_direct_exit);
146
147MODULE_AUTHOR("Steven Rostedt");
148MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
149MODULE_LICENSE("GPL");