samples/ftrace/ftrace-direct.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/module.h>
   3
   4 #include <linux/sched.h> /* for wake_up_process() */
   5 #include <linux/ftrace.h>
   6 #include <asm/asm-offsets.h>
   7
   8 extern void my_direct_func(struct task_struct *p);
   9
  10 void my_direct_func(struct task_struct *p)
  11 {
  12         trace_printk("waking up %s-%d\n", p->comm, p->pid);
  13 }
  14
  15 extern void my_tramp(void *);
  16
  17 #ifdef CONFIG_X86_64
  18
  19 asm (
  20 "       .pushsection    .text, \"ax\", @progbits\n"
  21 "       .type           my_tramp, @function\n"
  22 "       .globl          my_tramp\n"
  23 "   my_tramp:"
  24 "       pushq %rbp\n"
  25 "       movq %rsp, %rbp\n"
  26 "       pushq %rdi\n"
  27 "       call my_direct_func\n"
  28 "       popq %rdi\n"
  29 "       leave\n"
  30         ASM_RET
  31 "       .size           my_tramp, .-my_tramp\n"
  32 "       .popsection\n"
  33 );
  34
  35 #endif /* CONFIG_X86_64 */
  36
  37 #ifdef CONFIG_S390
  38
  39 asm (
  40 "       .pushsection    .text, \"ax\", @progbits\n"
  41 "       .type           my_tramp, @function\n"
  42 "       .globl          my_tramp\n"
  43 "   my_tramp:"
  44 "       lgr             %r1,%r15\n"
  45 "       stmg            %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  46 "       stg             %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  47 "       aghi            %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
  48 "       stg             %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
  49 "       brasl           %r14,my_direct_func\n"
  50 "       aghi            %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
  51 "       lmg             %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  52 "       lg              %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  53 "       lgr             %r1,%r0\n"
  54 "       br              %r1\n"
  55 "       .size           my_tramp, .-my_tramp\n"
  56 "       .popsection\n"
  57 );
  58
  59 #endif /* CONFIG_S390 */
  60
  61 static int __init ftrace_direct_init(void)
  62 {
  63         return register_ftrace_direct((unsigned long)wake_up_process,
  64                                      (unsigned long)my_tramp);
  65 }
  66
  67 static void __exit ftrace_direct_exit(void)
  68 {
  69         unregister_ftrace_direct((unsigned long)wake_up_process,
  70                                  (unsigned long)my_tramp);
  71 }
  72
  73 module_init(ftrace_direct_init);
  74 module_exit(ftrace_direct_exit);
  75
  76 MODULE_AUTHOR("Steven Rostedt");
  77 MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
  78 MODULE_LICENSE("GPL");