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