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 7 extern void my_direct_func1(void); 8 extern void my_direct_func2(void); 9 10 void my_direct_func1(void) 11 { 12 trace_printk("my direct func1\n"); 13 } 14 15 void my_direct_func2(void) 16 { 17 trace_printk("my direct func2\n"); 18 } 19 20 extern void my_tramp1(void *); 21 extern void my_tramp2(void *); 22 23 static unsigned long my_ip = (unsigned long)schedule; 24 25 #ifdef CONFIG_X86_64 26 27 #include <asm/ibt.h> 28 #include <asm/nospec-branch.h> 29 30 asm ( 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 62 asm ( 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 99 static struct ftrace_ops direct; 100 101 static unsigned long my_tramp = (unsigned long)my_tramp1; 102 static unsigned long tramps[2] = { 103 (unsigned long)my_tramp1, 104 (unsigned long)my_tramp2, 105 }; 106 107 static int simple_thread(void *arg) 108 { 109 static int t; 110 int ret = 0; 111 112 while (!kthread_should_stop()) { 113 set_current_state(TASK_INTERRUPTIBLE); 114 schedule_timeout(2 * HZ); 115 116 if (ret) 117 continue; 118 t ^= 1; 119 ret = modify_ftrace_direct(&direct, tramps[t]); 120 if (!ret) 121 my_tramp = tramps[t]; 122 WARN_ON_ONCE(ret); 123 } 124 125 return 0; 126 } 127 128 static struct task_struct *simple_tsk; 129 130 static int __init ftrace_direct_init(void) 131 { 132 int ret; 133 134 ftrace_set_filter_ip(&direct, (unsigned long) my_ip, 0, 0); 135 ret = register_ftrace_direct(&direct, my_tramp); 136 137 if (!ret) 138 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn"); 139 return ret; 140 } 141 142 static void __exit ftrace_direct_exit(void) 143 { 144 kthread_stop(simple_tsk); 145 unregister_ftrace_direct(&direct, my_tramp, true); 146 } 147 148 module_init(ftrace_direct_init); 149 module_exit(ftrace_direct_exit); 150 151 MODULE_AUTHOR("Steven Rostedt"); 152 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()"); 153 MODULE_LICENSE("GPL"); 154