samples/ftrace/ftrace-direct-modify.c

   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 void my_direct_func1(void)
   8 {
   9         trace_printk("my direct func1\n");
  10 }
  11
  12 void my_direct_func2(void)
  13 {
  14         trace_printk("my direct func2\n");
  15 }
  16
  17 extern void my_tramp1(void *);
  18 extern void my_tramp2(void *);
  19
  20 static unsigned long my_ip = (unsigned long)schedule;
  21
  22 #ifdef CONFIG_X86_64
  23
  24 asm (
  25 "       .pushsection    .text, \"ax\", @progbits\n"
  26 "       .type           my_tramp1, @function\n"
  27 "       .globl          my_tramp1\n"
  28 "   my_tramp1:"
  29 "       pushq %rbp\n"
  30 "       movq %rsp, %rbp\n"
  31 "       call my_direct_func1\n"
  32 "       leave\n"
  33 "       .size           my_tramp1, .-my_tramp1\n"
  34 "       ret\n"
  35 "       .type           my_tramp2, @function\n"
  36 "       .globl          my_tramp2\n"
  37 "   my_tramp2:"
  38 "       pushq %rbp\n"
  39 "       movq %rsp, %rbp\n"
  40 "       call my_direct_func2\n"
  41 "       leave\n"
  42 "       ret\n"
  43 "       .size           my_tramp2, .-my_tramp2\n"
  44 "       .popsection\n"
  45 );
  46
  47 #endif /* CONFIG_X86_64 */
  48
  49 #ifdef CONFIG_S390
  50
  51 asm (
  52 "       .pushsection    .text, \"ax\", @progbits\n"
  53 "       .type           my_tramp1, @function\n"
  54 "       .globl          my_tramp1\n"
  55 "   my_tramp1:"
  56 "       lgr             %r1,%r15\n"
  57 "       stmg            %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  58 "       stg             %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  59 "       aghi            %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
  60 "       stg             %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
  61 "       brasl           %r14,my_direct_func1\n"
  62 "       aghi            %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
  63 "       lmg             %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  64 "       lg              %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  65 "       lgr             %r1,%r0\n"
  66 "       br              %r1\n"
  67 "       .size           my_tramp1, .-my_tramp1\n"
  68 "       .type           my_tramp2, @function\n"
  69 "       .globl          my_tramp2\n"
  70 "   my_tramp2:"
  71 "       lgr             %r1,%r15\n"
  72 "       stmg            %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  73 "       stg             %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  74 "       aghi            %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
  75 "       stg             %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
  76 "       brasl           %r14,my_direct_func2\n"
  77 "       aghi            %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
  78 "       lmg             %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  79 "       lg              %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  80 "       lgr             %r1,%r0\n"
  81 "       br              %r1\n"
  82 "       .size           my_tramp2, .-my_tramp2\n"
  83 "       .popsection\n"
  84 );
  85
  86 #endif /* CONFIG_S390 */
  87
  88 static unsigned long my_tramp = (unsigned long)my_tramp1;
  89 static unsigned long tramps[2] = {
  90         (unsigned long)my_tramp1,
  91         (unsigned long)my_tramp2,
  92 };
  93
  94 static int simple_thread(void *arg)
  95 {
  96         static int t;
  97         int ret = 0;
  98
  99         while (!kthread_should_stop()) {
 100                 set_current_state(TASK_INTERRUPTIBLE);
 101                 schedule_timeout(2 * HZ);
 102
 103                 if (ret)
 104                         continue;
 105                 t ^= 1;
 106                 ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
 107                 if (!ret)
 108                         my_tramp = tramps[t];
 109                 WARN_ON_ONCE(ret);
 110         }
 111
 112         return 0;
 113 }
 114
 115 static struct task_struct *simple_tsk;
 116
 117 static int __init ftrace_direct_init(void)
 118 {
 119         int ret;
 120
 121         ret = register_ftrace_direct(my_ip, my_tramp);
 122         if (!ret)
 123                 simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
 124         return ret;
 125 }
 126
 127 static void __exit ftrace_direct_exit(void)
 128 {
 129         kthread_stop(simple_tsk);
 130         unregister_ftrace_direct(my_ip, my_tramp);
 131 }
 132
 133 module_init(ftrace_direct_init);
 134 module_exit(ftrace_direct_exit);
 135
 136 MODULE_AUTHOR("Steven Rostedt");
 137 MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
 138 MODULE_LICENSE("GPL");