kernel/trace/trace_functions.c

   1 /*
   2  * ring buffer based function tracer
   3  *
   4  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   5  * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
   6  *
   7  * Based on code from the latency_tracer, that is:
   8  *
   9  *  Copyright (C) 2004-2006 Ingo Molnar
  10  *  Copyright (C) 2004 Nadia Yvette Chambers
  11  */
  12 #include <linux/ring_buffer.h>
  13 #include <linux/debugfs.h>
  14 #include <linux/uaccess.h>
  15 #include <linux/ftrace.h>
  16 #include <linux/slab.h>
  17 #include <linux/fs.h>
  18
  19 #include "trace.h"
  20
  21 static void tracing_start_function_trace(struct trace_array *tr);
  22 static void tracing_stop_function_trace(struct trace_array *tr);
  23 static void
  24 function_trace_call(unsigned long ip, unsigned long parent_ip,
  25                     struct ftrace_ops *op, struct pt_regs *pt_regs);
  26 static void
  27 function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
  28                           struct ftrace_ops *op, struct pt_regs *pt_regs);
  29 static struct tracer_flags func_flags;
  30
  31 /* Our option */
  32 enum {
  33         TRACE_FUNC_OPT_STACK    = 0x1,
  34 };
  35
  36 static int allocate_ftrace_ops(struct trace_array *tr)
  37 {
  38         struct ftrace_ops *ops;
  39
  40         ops = kzalloc(sizeof(*ops), GFP_KERNEL);
  41         if (!ops)
  42                 return -ENOMEM;
  43
  44         /* Currently only the non stack verision is supported */
  45         ops->func = function_trace_call;
  46         ops->flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_PID;
  47
  48         tr->ops = ops;
  49         ops->private = tr;
  50         return 0;
  51 }
  52
  53
  54 int ftrace_create_function_files(struct trace_array *tr,
  55                                  struct dentry *parent)
  56 {
  57         int ret;
  58
  59         /*
  60          * The top level array uses the "global_ops", and the files are
  61          * created on boot up.
  62          */
  63         if (tr->flags & TRACE_ARRAY_FL_GLOBAL)
  64                 return 0;
  65
  66         ret = allocate_ftrace_ops(tr);
  67         if (ret)
  68                 return ret;
  69
  70         ftrace_create_filter_files(tr->ops, parent);
  71
  72         return 0;
  73 }
  74
  75 void ftrace_destroy_function_files(struct trace_array *tr)
  76 {
  77         ftrace_destroy_filter_files(tr->ops);
  78         kfree(tr->ops);
  79         tr->ops = NULL;
  80 }
  81
  82 static int function_trace_init(struct trace_array *tr)
  83 {
  84         ftrace_func_t func;
  85
  86         /*
  87          * Instance trace_arrays get their ops allocated
  88          * at instance creation. Unless it failed
  89          * the allocation.
  90          */
  91         if (!tr->ops)
  92                 return -ENOMEM;
  93
  94         /* Currently only the global instance can do stack tracing */
  95         if (tr->flags & TRACE_ARRAY_FL_GLOBAL &&
  96             func_flags.val & TRACE_FUNC_OPT_STACK)
  97                 func = function_stack_trace_call;
  98         else
  99                 func = function_trace_call;
 100
 101         ftrace_init_array_ops(tr, func);
 102
 103         tr->trace_buffer.cpu = get_cpu();
 104         put_cpu();
 105
 106         tracing_start_cmdline_record();
 107         tracing_start_function_trace(tr);
 108         return 0;
 109 }
 110
 111 static void function_trace_reset(struct trace_array *tr)
 112 {
 113         tracing_stop_function_trace(tr);
 114         tracing_stop_cmdline_record();
 115         ftrace_reset_array_ops(tr);
 116 }
 117
 118 static void function_trace_start(struct trace_array *tr)
 119 {
 120         tracing_reset_online_cpus(&tr->trace_buffer);
 121 }
 122
 123 static void
 124 function_trace_call(unsigned long ip, unsigned long parent_ip,
 125                     struct ftrace_ops *op, struct pt_regs *pt_regs)
 126 {
 127         struct trace_array *tr = op->private;
 128         struct trace_array_cpu *data;
 129         unsigned long flags;
 130         int bit;
 131         int cpu;
 132         int pc;
 133
 134         if (unlikely(!tr->function_enabled))
 135                 return;
 136
 137         pc = preempt_count();
 138         preempt_disable_notrace();
 139
 140         bit = trace_test_and_set_recursion(TRACE_FTRACE_START, TRACE_FTRACE_MAX);
 141         if (bit < 0)
 142                 goto out;
 143
 144         cpu = smp_processor_id();
 145         data = per_cpu_ptr(tr->trace_buffer.data, cpu);
 146         if (!atomic_read(&data->disabled)) {
 147                 local_save_flags(flags);
 148                 trace_function(tr, ip, parent_ip, flags, pc);
 149         }
 150         trace_clear_recursion(bit);
 151
 152  out:
 153         preempt_enable_notrace();
 154 }
 155
 156 static void
 157 function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
 158                           struct ftrace_ops *op, struct pt_regs *pt_regs)
 159 {
 160         struct trace_array *tr = op->private;
 161         struct trace_array_cpu *data;
 162         unsigned long flags;
 163         long disabled;
 164         int cpu;
 165         int pc;
 166
 167         if (unlikely(!tr->function_enabled))
 168                 return;
 169
 170         /*
 171          * Need to use raw, since this must be called before the
 172          * recursive protection is performed.
 173          */
 174         local_irq_save(flags);
 175         cpu = raw_smp_processor_id();
 176         data = per_cpu_ptr(tr->trace_buffer.data, cpu);
 177         disabled = atomic_inc_return(&data->disabled);
 178
 179         if (likely(disabled == 1)) {
 180                 pc = preempt_count();
 181                 trace_function(tr, ip, parent_ip, flags, pc);
 182                 /*
 183                  * skip over 5 funcs:
 184                  *    __ftrace_trace_stack,
 185                  *    __trace_stack,
 186                  *    function_stack_trace_call
 187                  *    ftrace_list_func
 188                  *    ftrace_call
 189                  */
 190                 __trace_stack(tr, flags, 5, pc);
 191         }
 192
 193         atomic_dec(&data->disabled);
 194         local_irq_restore(flags);
 195 }
 196
 197 static struct tracer_opt func_opts[] = {
 198 #ifdef CONFIG_STACKTRACE
 199         { TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
 200 #endif
 201         { } /* Always set a last empty entry */
 202 };
 203
 204 static struct tracer_flags func_flags = {
 205         .val = 0, /* By default: all flags disabled */
 206         .opts = func_opts
 207 };
 208
 209 static void tracing_start_function_trace(struct trace_array *tr)
 210 {
 211         tr->function_enabled = 0;
 212         register_ftrace_function(tr->ops);
 213         tr->function_enabled = 1;
 214 }
 215
 216 static void tracing_stop_function_trace(struct trace_array *tr)
 217 {
 218         tr->function_enabled = 0;
 219         unregister_ftrace_function(tr->ops);
 220 }
 221
 222 static struct tracer function_trace;
 223
 224 static int
 225 func_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
 226 {
 227         switch (bit) {
 228         case TRACE_FUNC_OPT_STACK:
 229                 /* do nothing if already set */
 230                 if (!!set == !!(func_flags.val & TRACE_FUNC_OPT_STACK))
 231                         break;
 232
 233                 /* We can change this flag when not running. */
 234                 if (tr->current_trace != &function_trace)
 235                         break;
 236
 237                 unregister_ftrace_function(tr->ops);
 238
 239                 if (set) {
 240                         tr->ops->func = function_stack_trace_call;
 241                         register_ftrace_function(tr->ops);
 242                 } else {
 243                         tr->ops->func = function_trace_call;
 244                         register_ftrace_function(tr->ops);
 245                 }
 246
 247                 break;
 248         default:
 249                 return -EINVAL;
 250         }
 251
 252         return 0;
 253 }
 254
 255 static struct tracer function_trace __tracer_data =
 256 {
 257         .name           = "function",
 258         .init           = function_trace_init,
 259         .reset          = function_trace_reset,
 260         .start          = function_trace_start,
 261         .flags          = &func_flags,
 262         .set_flag       = func_set_flag,
 263         .allow_instances = true,
 264 #ifdef CONFIG_FTRACE_SELFTEST
 265         .selftest       = trace_selftest_startup_function,
 266 #endif
 267 };
 268
 269 #ifdef CONFIG_DYNAMIC_FTRACE
 270 static void update_traceon_count(struct ftrace_probe_ops *ops,
 271                                  unsigned long ip, bool on)
 272 {
 273         struct ftrace_func_mapper *mapper = ops->private_data;
 274         long *count;
 275         long old_count;
 276
 277         /*
 278          * Tracing gets disabled (or enabled) once per count.
 279          * This function can be called at the same time on multiple CPUs.
 280          * It is fine if both disable (or enable) tracing, as disabling
 281          * (or enabling) the second time doesn't do anything as the
 282          * state of the tracer is already disabled (or enabled).
 283          * What needs to be synchronized in this case is that the count
 284          * only gets decremented once, even if the tracer is disabled
 285          * (or enabled) twice, as the second one is really a nop.
 286          *
 287          * The memory barriers guarantee that we only decrement the
 288          * counter once. First the count is read to a local variable
 289          * and a read barrier is used to make sure that it is loaded
 290          * before checking if the tracer is in the state we want.
 291          * If the tracer is not in the state we want, then the count
 292          * is guaranteed to be the old count.
 293          *
 294          * Next the tracer is set to the state we want (disabled or enabled)
 295          * then a write memory barrier is used to make sure that
 296          * the new state is visible before changing the counter by
 297          * one minus the old counter. This guarantees that another CPU
 298          * executing this code will see the new state before seeing
 299          * the new counter value, and would not do anything if the new
 300          * counter is seen.
 301          *
 302          * Note, there is no synchronization between this and a user
 303          * setting the tracing_on file. But we currently don't care
 304          * about that.
 305          */
 306         count = (long *)ftrace_func_mapper_find_ip(mapper, ip);
 307         old_count = *count;
 308
 309         if (old_count <= 0)
 310                 return;
 311
 312         /* Make sure we see count before checking tracing state */
 313         smp_rmb();
 314
 315         if (on == !!tracing_is_on())
 316                 return;
 317
 318         if (on)
 319                 tracing_on();
 320         else
 321                 tracing_off();
 322
 323         /* Make sure tracing state is visible before updating count */
 324         smp_wmb();
 325
 326         *count = old_count - 1;
 327 }
 328
 329 static void
 330 ftrace_traceon_count(unsigned long ip, unsigned long parent_ip,
 331                      struct ftrace_probe_ops *ops, void **data)
 332 {
 333         update_traceon_count(ops, ip, 1);
 334 }
 335
 336 static void
 337 ftrace_traceoff_count(unsigned long ip, unsigned long parent_ip,
 338                       struct ftrace_probe_ops *ops, void **data)
 339 {
 340         update_traceon_count(ops, ip, 0);
 341 }
 342
 343 static void
 344 ftrace_traceon(unsigned long ip, unsigned long parent_ip,
 345                struct ftrace_probe_ops *ops, void **data)
 346 {
 347         if (tracing_is_on())
 348                 return;
 349
 350         tracing_on();
 351 }
 352
 353 static void
 354 ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
 355                 struct ftrace_probe_ops *ops, void **data)
 356 {
 357         if (!tracing_is_on())
 358                 return;
 359
 360         tracing_off();
 361 }
 362
 363 /*
 364  * Skip 4:
 365  *   ftrace_stacktrace()
 366  *   function_trace_probe_call()
 367  *   ftrace_ops_list_func()
 368  *   ftrace_call()
 369  */
 370 #define STACK_SKIP 4
 371
 372 static void
 373 ftrace_stacktrace(unsigned long ip, unsigned long parent_ip,
 374                   struct ftrace_probe_ops *ops, void **data)
 375 {
 376         trace_dump_stack(STACK_SKIP);
 377 }
 378
 379 static void
 380 ftrace_stacktrace_count(unsigned long ip, unsigned long parent_ip,
 381                         struct ftrace_probe_ops *ops, void **data)
 382 {
 383         struct ftrace_func_mapper *mapper = ops->private_data;
 384         long *count;
 385         long old_count;
 386         long new_count;
 387
 388         if (!tracing_is_on())
 389                 return;
 390
 391         /* unlimited? */
 392         if (!mapper) {
 393                 trace_dump_stack(STACK_SKIP);
 394                 return;
 395         }
 396
 397         count = (long *)ftrace_func_mapper_find_ip(mapper, ip);
 398
 399         /*
 400          * Stack traces should only execute the number of times the
 401          * user specified in the counter.
 402          */
 403         do {
 404                 old_count = *count;
 405
 406                 if (!old_count)
 407                         return;
 408
 409                 new_count = old_count - 1;
 410                 new_count = cmpxchg(count, old_count, new_count);
 411                 if (new_count == old_count)
 412                         trace_dump_stack(STACK_SKIP);
 413
 414                 if (!tracing_is_on())
 415                         return;
 416
 417         } while (new_count != old_count);
 418 }
 419
 420 static int update_count(struct ftrace_probe_ops *ops, unsigned long ip)
 421 {
 422         struct ftrace_func_mapper *mapper = ops->private_data;
 423         long *count = NULL;
 424
 425         if (mapper)
 426                 count = (long *)ftrace_func_mapper_find_ip(mapper, ip);
 427
 428         if (count) {
 429                 if (*count <= 0)
 430                         return 0;
 431                 (*count)--;
 432         }
 433
 434         return 1;
 435 }
 436
 437 static void
 438 ftrace_dump_probe(unsigned long ip, unsigned long parent_ip,
 439         struct ftrace_probe_ops *ops, void **data)
 440 {
 441         if (update_count(ops, ip))
 442                 ftrace_dump(DUMP_ALL);
 443 }
 444
 445 /* Only dump the current CPU buffer. */
 446 static void
 447 ftrace_cpudump_probe(unsigned long ip, unsigned long parent_ip,
 448         struct ftrace_probe_ops *ops, void **data)
 449 {
 450         if (update_count(ops, ip))
 451                 ftrace_dump(DUMP_ORIG);
 452 }
 453
 454 static int
 455 ftrace_probe_print(const char *name, struct seq_file *m,
 456                    unsigned long ip, struct ftrace_probe_ops *ops)
 457 {
 458         struct ftrace_func_mapper *mapper = ops->private_data;
 459         long *count = NULL;
 460
 461         seq_printf(m, "%ps:%s", (void *)ip, name);
 462
 463         if (mapper)
 464                 count = (long *)ftrace_func_mapper_find_ip(mapper, ip);
 465
 466         if (count)
 467                 seq_printf(m, ":count=%ld\n", *count);
 468         else
 469                 seq_puts(m, ":unlimited\n");
 470
 471         return 0;
 472 }
 473
 474 static int
 475 ftrace_traceon_print(struct seq_file *m, unsigned long ip,
 476                          struct ftrace_probe_ops *ops, void *data)
 477 {
 478         return ftrace_probe_print("traceon", m, ip, ops);
 479 }
 480
 481 static int
 482 ftrace_traceoff_print(struct seq_file *m, unsigned long ip,
 483                          struct ftrace_probe_ops *ops, void *data)
 484 {
 485         return ftrace_probe_print("traceoff", m, ip, ops);
 486 }
 487
 488 static int
 489 ftrace_stacktrace_print(struct seq_file *m, unsigned long ip,
 490                         struct ftrace_probe_ops *ops, void *data)
 491 {
 492         return ftrace_probe_print("stacktrace", m, ip, ops);
 493 }
 494
 495 static int
 496 ftrace_dump_print(struct seq_file *m, unsigned long ip,
 497                         struct ftrace_probe_ops *ops, void *data)
 498 {
 499         return ftrace_probe_print("dump", m, ip, ops);
 500 }
 501
 502 static int
 503 ftrace_cpudump_print(struct seq_file *m, unsigned long ip,
 504                         struct ftrace_probe_ops *ops, void *data)
 505 {
 506         return ftrace_probe_print("cpudump", m, ip, ops);
 507 }
 508
 509
 510 static int
 511 ftrace_count_init(struct ftrace_probe_ops *ops, unsigned long ip,
 512                      void *data)
 513 {
 514         struct ftrace_func_mapper *mapper = ops->private_data;
 515
 516         return ftrace_func_mapper_add_ip(mapper, ip, data);
 517 }
 518
 519 static void
 520 ftrace_count_free(struct ftrace_probe_ops *ops, unsigned long ip,
 521                   void **_data)
 522 {
 523         struct ftrace_func_mapper *mapper = ops->private_data;
 524
 525         ftrace_func_mapper_remove_ip(mapper, ip);
 526 }
 527
 528 static struct ftrace_probe_ops traceon_count_probe_ops = {
 529         .func                   = ftrace_traceon_count,
 530         .print                  = ftrace_traceon_print,
 531         .init                   = ftrace_count_init,
 532         .free                   = ftrace_count_free,
 533 };
 534
 535 static struct ftrace_probe_ops traceoff_count_probe_ops = {
 536         .func                   = ftrace_traceoff_count,
 537         .print                  = ftrace_traceoff_print,
 538         .init                   = ftrace_count_init,
 539         .free                   = ftrace_count_free,
 540 };
 541
 542 static struct ftrace_probe_ops stacktrace_count_probe_ops = {
 543         .func                   = ftrace_stacktrace_count,
 544         .print                  = ftrace_stacktrace_print,
 545         .init                   = ftrace_count_init,
 546         .free                   = ftrace_count_free,
 547 };
 548
 549 static struct ftrace_probe_ops dump_probe_ops = {
 550         .func                   = ftrace_dump_probe,
 551         .print                  = ftrace_dump_print,
 552         .init                   = ftrace_count_init,
 553         .free                   = ftrace_count_free,
 554 };
 555
 556 static struct ftrace_probe_ops cpudump_probe_ops = {
 557         .func                   = ftrace_cpudump_probe,
 558         .print                  = ftrace_cpudump_print,
 559 };
 560
 561 static struct ftrace_probe_ops traceon_probe_ops = {
 562         .func                   = ftrace_traceon,
 563         .print                  = ftrace_traceon_print,
 564 };
 565
 566 static struct ftrace_probe_ops traceoff_probe_ops = {
 567         .func                   = ftrace_traceoff,
 568         .print                  = ftrace_traceoff_print,
 569 };
 570
 571 static struct ftrace_probe_ops stacktrace_probe_ops = {
 572         .func                   = ftrace_stacktrace,
 573         .print                  = ftrace_stacktrace_print,
 574 };
 575
 576 static int
 577 ftrace_trace_probe_callback(struct trace_array *tr,
 578                             struct ftrace_probe_ops *ops,
 579                             struct ftrace_hash *hash, char *glob,
 580                             char *cmd, char *param, int enable)
 581 {
 582         void *count = (void *)-1;
 583         char *number;
 584         int ret;
 585
 586         /* hash funcs only work with set_ftrace_filter */
 587         if (!enable)
 588                 return -EINVAL;
 589
 590         if (glob[0] == '!')
 591                 return unregister_ftrace_function_probe_func(glob+1, ops);
 592
 593         if (!param)
 594                 goto out_reg;
 595
 596         number = strsep(&param, ":");
 597
 598         if (!strlen(number))
 599                 goto out_reg;
 600
 601         if (!ops->private_data) {
 602                 ops->private_data = allocate_ftrace_func_mapper();
 603                 if (!ops->private_data)
 604                         return -ENOMEM;
 605         }
 606
 607         /*
 608          * We use the callback data field (which is a pointer)
 609          * as our counter.
 610          */
 611         ret = kstrtoul(number, 0, (unsigned long *)&count);
 612         if (ret)
 613                 return ret;
 614
 615  out_reg:
 616         ret = register_ftrace_function_probe(glob, tr, ops, count);
 617
 618         return ret < 0 ? ret : 0;
 619 }
 620
 621 static int
 622 ftrace_trace_onoff_callback(struct trace_array *tr, struct ftrace_hash *hash,
 623                             char *glob, char *cmd, char *param, int enable)
 624 {
 625         struct ftrace_probe_ops *ops;
 626
 627         /* we register both traceon and traceoff to this callback */
 628         if (strcmp(cmd, "traceon") == 0)
 629                 ops = param ? &traceon_count_probe_ops : &traceon_probe_ops;
 630         else
 631                 ops = param ? &traceoff_count_probe_ops : &traceoff_probe_ops;
 632
 633         return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
 634                                            param, enable);
 635 }
 636
 637 static int
 638 ftrace_stacktrace_callback(struct trace_array *tr, struct ftrace_hash *hash,
 639                            char *glob, char *cmd, char *param, int enable)
 640 {
 641         struct ftrace_probe_ops *ops;
 642
 643         ops = param ? &stacktrace_count_probe_ops : &stacktrace_probe_ops;
 644
 645         return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
 646                                            param, enable);
 647 }
 648
 649 static int
 650 ftrace_dump_callback(struct trace_array *tr, struct ftrace_hash *hash,
 651                            char *glob, char *cmd, char *param, int enable)
 652 {
 653         struct ftrace_probe_ops *ops;
 654
 655         ops = &dump_probe_ops;
 656
 657         /* Only dump once. */
 658         return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
 659                                            "1", enable);
 660 }
 661
 662 static int
 663 ftrace_cpudump_callback(struct trace_array *tr, struct ftrace_hash *hash,
 664                            char *glob, char *cmd, char *param, int enable)
 665 {
 666         struct ftrace_probe_ops *ops;
 667
 668         ops = &cpudump_probe_ops;
 669
 670         /* Only dump once. */
 671         return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
 672                                            "1", enable);
 673 }
 674
 675 static struct ftrace_func_command ftrace_traceon_cmd = {
 676         .name                   = "traceon",
 677         .func                   = ftrace_trace_onoff_callback,
 678 };
 679
 680 static struct ftrace_func_command ftrace_traceoff_cmd = {
 681         .name                   = "traceoff",
 682         .func                   = ftrace_trace_onoff_callback,
 683 };
 684
 685 static struct ftrace_func_command ftrace_stacktrace_cmd = {
 686         .name                   = "stacktrace",
 687         .func                   = ftrace_stacktrace_callback,
 688 };
 689
 690 static struct ftrace_func_command ftrace_dump_cmd = {
 691         .name                   = "dump",
 692         .func                   = ftrace_dump_callback,
 693 };
 694
 695 static struct ftrace_func_command ftrace_cpudump_cmd = {
 696         .name                   = "cpudump",
 697         .func                   = ftrace_cpudump_callback,
 698 };
 699
 700 static int __init init_func_cmd_traceon(void)
 701 {
 702         int ret;
 703
 704         ret = register_ftrace_command(&ftrace_traceoff_cmd);
 705         if (ret)
 706                 return ret;
 707
 708         ret = register_ftrace_command(&ftrace_traceon_cmd);
 709         if (ret)
 710                 goto out_free_traceoff;
 711
 712         ret = register_ftrace_command(&ftrace_stacktrace_cmd);
 713         if (ret)
 714                 goto out_free_traceon;
 715
 716         ret = register_ftrace_command(&ftrace_dump_cmd);
 717         if (ret)
 718                 goto out_free_stacktrace;
 719
 720         ret = register_ftrace_command(&ftrace_cpudump_cmd);
 721         if (ret)
 722                 goto out_free_dump;
 723
 724         return 0;
 725
 726  out_free_dump:
 727         unregister_ftrace_command(&ftrace_dump_cmd);
 728  out_free_stacktrace:
 729         unregister_ftrace_command(&ftrace_stacktrace_cmd);
 730  out_free_traceon:
 731         unregister_ftrace_command(&ftrace_traceon_cmd);
 732  out_free_traceoff:
 733         unregister_ftrace_command(&ftrace_traceoff_cmd);
 734
 735         return ret;
 736 }
 737 #else
 738 static inline int init_func_cmd_traceon(void)
 739 {
 740         return 0;
 741 }
 742 #endif /* CONFIG_DYNAMIC_FTRACE */
 743
 744 __init int init_function_trace(void)
 745 {
 746         init_func_cmd_traceon();
 747         return register_tracer(&function_trace);
 748 }