ftrace: Add another example of register_ftrace_direct() use case

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

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

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

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

#include <linux/module.h>

#include <linux/mm.h> /* for handle_mm_fault() */

#include <linux/ftrace.h>

void my_direct_func(struct vm_area_struct *vma,

			unsigned long address, unsigned int flags)

{

	trace_printk("handle mm fault vma=%p address=%lx flags=%x\n",

		     vma, address, flags);

}

extern void my_tramp(void *);

asm (

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

"   my_tramp:"

"	pushq %rbp\n"

"	movq %rsp, %rbp\n"

"	pushq %rdi\n"

"	pushq %rsi\n"

"	pushq %rdx\n"

"	call my_direct_func\n"

"	popq %rdx\n"

"	popq %rsi\n"

"	popq %rdi\n"

"	leave\n"

"	ret\n"

"	.popsection\n"

);

static int __init ftrace_direct_init(void)

{

	return register_ftrace_direct((unsigned long)handle_mm_fault,

				     (unsigned long)my_tramp);

}

static void __exit ftrace_direct_exit(void)

{

	unregister_ftrace_direct((unsigned long)handle_mm_fault,

				 (unsigned long)my_tramp);

}

module_init(ftrace_direct_init);

module_exit(ftrace_direct_exit);

MODULE_AUTHOR("Steven Rostedt");

MODULE_DESCRIPTION("Another example use case of using register_ftrace_direct()");

MODULE_LICENSE("GPL");