// 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");