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