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 #include <asm/nospec-branch.h>
   8
   9 extern void my_direct_func(struct task_struct *p);
  10
  11 void my_direct_func(struct task_struct *p)
  12 {
  13         trace_printk("waking up %s-%d\n", p->comm, p->pid);
  14 }
  15
  16 extern void my_tramp(void *);
  17
  18 #ifdef CONFIG_X86_64
  19
  20 #include <asm/ibt.h>
  21
  22 asm (
  23 "       .pushsection    .text, \"ax\", @progbits\n"
  24 "       .type           my_tramp, @function\n"
  25 "       .globl          my_tramp\n"
  26 "   my_tramp:"
  27         ASM_ENDBR
  28 "       pushq %rbp\n"
  29 "       movq %rsp, %rbp\n"
  30         CALL_DEPTH_ACCOUNT
  31 "       pushq %rdi\n"
  32 "       call my_direct_func\n"
  33 "       popq %rdi\n"
  34 "       leave\n"
  35         ASM_RET
  36 "       .size           my_tramp, .-my_tramp\n"
  37 "       .popsection\n"
  38 );
  39
  40 #endif /* CONFIG_X86_64 */
  41
  42 #ifdef CONFIG_S390
  43
  44 asm (
  45 "       .pushsection    .text, \"ax\", @progbits\n"
  46 "       .type           my_tramp, @function\n"
  47 "       .globl          my_tramp\n"
  48 "   my_tramp:"
  49 "       lgr             %r1,%r15\n"
  50 "       stmg            %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  51 "       stg             %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  52 "       aghi            %r15,"__stringify(-STACK_FRAME_OVERHEAD)"\n"
  53 "       stg             %r1,"__stringify(__SF_BACKCHAIN)"(%r15)\n"
  54 "       brasl           %r14,my_direct_func\n"
  55 "       aghi            %r15,"__stringify(STACK_FRAME_OVERHEAD)"\n"
  56 "       lmg             %r0,%r5,"__stringify(__SF_GPRS)"(%r15)\n"
  57 "       lg              %r14,"__stringify(__SF_GPRS+8*8)"(%r15)\n"
  58 "       lgr             %r1,%r0\n"
  59 "       br              %r1\n"
  60 "       .size           my_tramp, .-my_tramp\n"
  61 "       .popsection\n"
  62 );
  63
  64 #endif /* CONFIG_S390 */
  65
  66 static int __init ftrace_direct_init(void)
  67 {
  68         return register_ftrace_direct((unsigned long)wake_up_process,
  69                                      (unsigned long)my_tramp);
  70 }
  71
  72 static void __exit ftrace_direct_exit(void)
  73 {
  74         unregister_ftrace_direct((unsigned long)wake_up_process,
  75                                  (unsigned long)my_tramp);
  76 }
  77
  78 module_init(ftrace_direct_init);
  79 module_exit(ftrace_direct_exit);
  80
  81 MODULE_AUTHOR("Steven Rostedt");
  82 MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
  83 MODULE_LICENSE("GPL");