ftrace/samples: Add a sample module that implements modify_ftrace_direct()

obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct.o

obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-too.o

obj-$(CONFIG_SAMPLE_FTRACE_DIRECT) += ftrace-direct-modify.o

// SPDX-License-Identifier: GPL-2.0-only

#include <linux/module.h>

#include <linux/kthread.h>

#include <linux/ftrace.h>

void my_direct_func1(void)

{

	trace_printk("my direct func1\n");

}

void my_direct_func2(void)

{

	trace_printk("my direct func2\n");

}

extern void my_tramp1(void *);

extern void my_tramp2(void *);

static unsigned long my_ip = (unsigned long)schedule;

asm (

"	.pushsection    .text, \"ax\", @progbits\n"

"   my_tramp1:"

"	pushq %rbp\n"

"	movq %rsp, %rbp\n"

"	call my_direct_func1\n"

"	leave\n"

"	ret\n"

"   my_tramp2:"

"	pushq %rbp\n"

"	movq %rsp, %rbp\n"

"	call my_direct_func2\n"

"	leave\n"

"	ret\n"

"	.popsection\n"

);

static unsigned long my_tramp = (unsigned long)my_tramp1;

static unsigned long tramps[2] = {

	(unsigned long)my_tramp1,

	(unsigned long)my_tramp2,

};

static int simple_thread(void *arg)

{

	static int t;

	int ret = 0;

	while (!kthread_should_stop()) {

		set_current_state(TASK_INTERRUPTIBLE);

		schedule_timeout(2 * HZ);

		if (ret)

			continue;

		t ^= 1;

		ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);

		if (!ret)

			my_tramp = tramps[t];

		WARN_ON_ONCE(ret);

	}

	return 0;

}

static struct task_struct *simple_tsk;

static int __init ftrace_direct_init(void)

{

	int ret;

	ret = register_ftrace_direct(my_ip, my_tramp);

	if (!ret)

		simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");

	return ret;

}

static void __exit ftrace_direct_exit(void)

{

	kthread_stop(simple_tsk);

	unregister_ftrace_direct(my_ip, my_tramp);

}

module_init(ftrace_direct_init);

module_exit(ftrace_direct_exit);

MODULE_AUTHOR("Steven Rostedt");

MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");

MODULE_LICENSE("GPL");