1 /* 2 * Common code for probe-based Dynamic events. 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 * 8 * This program is distributed in the hope that it will be useful, 9 * but WITHOUT ANY WARRANTY; without even the implied warranty of 10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 11 * GNU General Public License for more details. 12 * 13 * You should have received a copy of the GNU General Public License 14 * along with this program; if not, write to the Free Software 15 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 16 * 17 * This code was copied from kernel/trace/trace_kprobe.c written by 18 * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> 19 * 20 * Updates to make this generic: 21 * Copyright (C) IBM Corporation, 2010-2011 22 * Author: Srikar Dronamraju 23 */ 24 #define pr_fmt(fmt) "trace_probe: " fmt 25 26 #include "trace_probe.h" 27 28 const char *reserved_field_names[] = { 29 "common_type", 30 "common_flags", 31 "common_preempt_count", 32 "common_pid", 33 "common_tgid", 34 FIELD_STRING_IP, 35 FIELD_STRING_RETIP, 36 FIELD_STRING_FUNC, 37 }; 38 39 /* Printing in basic type function template */ 40 #define DEFINE_BASIC_PRINT_TYPE_FUNC(tname, type, fmt) \ 41 int PRINT_TYPE_FUNC_NAME(tname)(struct trace_seq *s, const char *name, \ 42 void *data, void *ent) \ 43 { \ 44 trace_seq_printf(s, " %s=" fmt, name, *(type *)data); \ 45 return !trace_seq_has_overflowed(s); \ 46 } \ 47 const char PRINT_TYPE_FMT_NAME(tname)[] = fmt; \ 48 NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(tname)); 49 50 DEFINE_BASIC_PRINT_TYPE_FUNC(u8, u8, "%u") 51 DEFINE_BASIC_PRINT_TYPE_FUNC(u16, u16, "%u") 52 DEFINE_BASIC_PRINT_TYPE_FUNC(u32, u32, "%u") 53 DEFINE_BASIC_PRINT_TYPE_FUNC(u64, u64, "%Lu") 54 DEFINE_BASIC_PRINT_TYPE_FUNC(s8, s8, "%d") 55 DEFINE_BASIC_PRINT_TYPE_FUNC(s16, s16, "%d") 56 DEFINE_BASIC_PRINT_TYPE_FUNC(s32, s32, "%d") 57 DEFINE_BASIC_PRINT_TYPE_FUNC(s64, s64, "%Ld") 58 DEFINE_BASIC_PRINT_TYPE_FUNC(x8, u8, "0x%x") 59 DEFINE_BASIC_PRINT_TYPE_FUNC(x16, u16, "0x%x") 60 DEFINE_BASIC_PRINT_TYPE_FUNC(x32, u32, "0x%x") 61 DEFINE_BASIC_PRINT_TYPE_FUNC(x64, u64, "0x%Lx") 62 63 /* Print type function for string type */ 64 int PRINT_TYPE_FUNC_NAME(string)(struct trace_seq *s, const char *name, 65 void *data, void *ent) 66 { 67 int len = *(u32 *)data >> 16; 68 69 if (!len) 70 trace_seq_printf(s, " %s=(fault)", name); 71 else 72 trace_seq_printf(s, " %s=\"%s\"", name, 73 (const char *)get_loc_data(data, ent)); 74 return !trace_seq_has_overflowed(s); 75 } 76 NOKPROBE_SYMBOL(PRINT_TYPE_FUNC_NAME(string)); 77 78 const char PRINT_TYPE_FMT_NAME(string)[] = "\\\"%s\\\""; 79 80 #define CHECK_FETCH_FUNCS(method, fn) \ 81 (((FETCH_FUNC_NAME(method, u8) == fn) || \ 82 (FETCH_FUNC_NAME(method, u16) == fn) || \ 83 (FETCH_FUNC_NAME(method, u32) == fn) || \ 84 (FETCH_FUNC_NAME(method, u64) == fn) || \ 85 (FETCH_FUNC_NAME(method, string) == fn) || \ 86 (FETCH_FUNC_NAME(method, string_size) == fn)) \ 87 && (fn != NULL)) 88 89 /* Data fetch function templates */ 90 #define DEFINE_FETCH_reg(type) \ 91 void FETCH_FUNC_NAME(reg, type)(struct pt_regs *regs, void *offset, void *dest) \ 92 { \ 93 *(type *)dest = (type)regs_get_register(regs, \ 94 (unsigned int)((unsigned long)offset)); \ 95 } \ 96 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(reg, type)); 97 DEFINE_BASIC_FETCH_FUNCS(reg) 98 /* No string on the register */ 99 #define fetch_reg_string NULL 100 #define fetch_reg_string_size NULL 101 102 #define DEFINE_FETCH_retval(type) \ 103 void FETCH_FUNC_NAME(retval, type)(struct pt_regs *regs, \ 104 void *dummy, void *dest) \ 105 { \ 106 *(type *)dest = (type)regs_return_value(regs); \ 107 } \ 108 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(retval, type)); 109 DEFINE_BASIC_FETCH_FUNCS(retval) 110 /* No string on the retval */ 111 #define fetch_retval_string NULL 112 #define fetch_retval_string_size NULL 113 114 /* Dereference memory access function */ 115 struct deref_fetch_param { 116 struct fetch_param orig; 117 long offset; 118 fetch_func_t fetch; 119 fetch_func_t fetch_size; 120 }; 121 122 #define DEFINE_FETCH_deref(type) \ 123 void FETCH_FUNC_NAME(deref, type)(struct pt_regs *regs, \ 124 void *data, void *dest) \ 125 { \ 126 struct deref_fetch_param *dprm = data; \ 127 unsigned long addr; \ 128 call_fetch(&dprm->orig, regs, &addr); \ 129 if (addr) { \ 130 addr += dprm->offset; \ 131 dprm->fetch(regs, (void *)addr, dest); \ 132 } else \ 133 *(type *)dest = 0; \ 134 } \ 135 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, type)); 136 DEFINE_BASIC_FETCH_FUNCS(deref) 137 DEFINE_FETCH_deref(string) 138 139 void FETCH_FUNC_NAME(deref, string_size)(struct pt_regs *regs, 140 void *data, void *dest) 141 { 142 struct deref_fetch_param *dprm = data; 143 unsigned long addr; 144 145 call_fetch(&dprm->orig, regs, &addr); 146 if (addr && dprm->fetch_size) { 147 addr += dprm->offset; 148 dprm->fetch_size(regs, (void *)addr, dest); 149 } else 150 *(string_size *)dest = 0; 151 } 152 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(deref, string_size)); 153 154 static void update_deref_fetch_param(struct deref_fetch_param *data) 155 { 156 if (CHECK_FETCH_FUNCS(deref, data->orig.fn)) 157 update_deref_fetch_param(data->orig.data); 158 else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn)) 159 update_symbol_cache(data->orig.data); 160 } 161 NOKPROBE_SYMBOL(update_deref_fetch_param); 162 163 static void free_deref_fetch_param(struct deref_fetch_param *data) 164 { 165 if (CHECK_FETCH_FUNCS(deref, data->orig.fn)) 166 free_deref_fetch_param(data->orig.data); 167 else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn)) 168 free_symbol_cache(data->orig.data); 169 kfree(data); 170 } 171 NOKPROBE_SYMBOL(free_deref_fetch_param); 172 173 /* Bitfield fetch function */ 174 struct bitfield_fetch_param { 175 struct fetch_param orig; 176 unsigned char hi_shift; 177 unsigned char low_shift; 178 }; 179 180 #define DEFINE_FETCH_bitfield(type) \ 181 void FETCH_FUNC_NAME(bitfield, type)(struct pt_regs *regs, \ 182 void *data, void *dest) \ 183 { \ 184 struct bitfield_fetch_param *bprm = data; \ 185 type buf = 0; \ 186 call_fetch(&bprm->orig, regs, &buf); \ 187 if (buf) { \ 188 buf <<= bprm->hi_shift; \ 189 buf >>= bprm->low_shift; \ 190 } \ 191 *(type *)dest = buf; \ 192 } \ 193 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(bitfield, type)); 194 DEFINE_BASIC_FETCH_FUNCS(bitfield) 195 #define fetch_bitfield_string NULL 196 #define fetch_bitfield_string_size NULL 197 198 static void 199 update_bitfield_fetch_param(struct bitfield_fetch_param *data) 200 { 201 /* 202 * Don't check the bitfield itself, because this must be the 203 * last fetch function. 204 */ 205 if (CHECK_FETCH_FUNCS(deref, data->orig.fn)) 206 update_deref_fetch_param(data->orig.data); 207 else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn)) 208 update_symbol_cache(data->orig.data); 209 } 210 211 static void 212 free_bitfield_fetch_param(struct bitfield_fetch_param *data) 213 { 214 /* 215 * Don't check the bitfield itself, because this must be the 216 * last fetch function. 217 */ 218 if (CHECK_FETCH_FUNCS(deref, data->orig.fn)) 219 free_deref_fetch_param(data->orig.data); 220 else if (CHECK_FETCH_FUNCS(symbol, data->orig.fn)) 221 free_symbol_cache(data->orig.data); 222 223 kfree(data); 224 } 225 226 void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs, 227 void *data, void *dest) 228 { 229 int maxlen = get_rloc_len(*(u32 *)dest); 230 u8 *dst = get_rloc_data(dest); 231 long ret; 232 233 if (!maxlen) 234 return; 235 236 ret = strlcpy(dst, current->comm, maxlen); 237 *(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest)); 238 } 239 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string)); 240 241 void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs, 242 void *data, void *dest) 243 { 244 *(u32 *)dest = strlen(current->comm) + 1; 245 } 246 NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size)); 247 248 static const struct fetch_type *find_fetch_type(const char *type, 249 const struct fetch_type *ftbl) 250 { 251 int i; 252 253 if (!type) 254 type = DEFAULT_FETCH_TYPE_STR; 255 256 /* Special case: bitfield */ 257 if (*type == 'b') { 258 unsigned long bs; 259 260 type = strchr(type, '/'); 261 if (!type) 262 goto fail; 263 264 type++; 265 if (kstrtoul(type, 0, &bs)) 266 goto fail; 267 268 switch (bs) { 269 case 8: 270 return find_fetch_type("u8", ftbl); 271 case 16: 272 return find_fetch_type("u16", ftbl); 273 case 32: 274 return find_fetch_type("u32", ftbl); 275 case 64: 276 return find_fetch_type("u64", ftbl); 277 default: 278 goto fail; 279 } 280 } 281 282 for (i = 0; ftbl[i].name; i++) { 283 if (strcmp(type, ftbl[i].name) == 0) 284 return &ftbl[i]; 285 } 286 287 fail: 288 return NULL; 289 } 290 291 /* Special function : only accept unsigned long */ 292 static void fetch_kernel_stack_address(struct pt_regs *regs, void *dummy, void *dest) 293 { 294 *(unsigned long *)dest = kernel_stack_pointer(regs); 295 } 296 NOKPROBE_SYMBOL(fetch_kernel_stack_address); 297 298 static void fetch_user_stack_address(struct pt_regs *regs, void *dummy, void *dest) 299 { 300 *(unsigned long *)dest = user_stack_pointer(regs); 301 } 302 NOKPROBE_SYMBOL(fetch_user_stack_address); 303 304 static fetch_func_t get_fetch_size_function(const struct fetch_type *type, 305 fetch_func_t orig_fn, 306 const struct fetch_type *ftbl) 307 { 308 int i; 309 310 if (type != &ftbl[FETCH_TYPE_STRING]) 311 return NULL; /* Only string type needs size function */ 312 313 for (i = 0; i < FETCH_MTD_END; i++) 314 if (type->fetch[i] == orig_fn) 315 return ftbl[FETCH_TYPE_STRSIZE].fetch[i]; 316 317 WARN_ON(1); /* This should not happen */ 318 319 return NULL; 320 } 321 322 /* Split symbol and offset. */ 323 int traceprobe_split_symbol_offset(char *symbol, long *offset) 324 { 325 char *tmp; 326 int ret; 327 328 if (!offset) 329 return -EINVAL; 330 331 tmp = strpbrk(symbol, "+-"); 332 if (tmp) { 333 ret = kstrtol(tmp, 0, offset); 334 if (ret) 335 return ret; 336 *tmp = '\0'; 337 } else 338 *offset = 0; 339 340 return 0; 341 } 342 343 #define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long)) 344 345 static int parse_probe_vars(char *arg, const struct fetch_type *t, 346 struct fetch_param *f, bool is_return, 347 bool is_kprobe) 348 { 349 int ret = 0; 350 unsigned long param; 351 352 if (strcmp(arg, "retval") == 0) { 353 if (is_return) 354 f->fn = t->fetch[FETCH_MTD_retval]; 355 else 356 ret = -EINVAL; 357 } else if (strncmp(arg, "stack", 5) == 0) { 358 if (arg[5] == '\0') { 359 if (strcmp(t->name, DEFAULT_FETCH_TYPE_STR)) 360 return -EINVAL; 361 362 if (is_kprobe) 363 f->fn = fetch_kernel_stack_address; 364 else 365 f->fn = fetch_user_stack_address; 366 } else if (isdigit(arg[5])) { 367 ret = kstrtoul(arg + 5, 10, ¶m); 368 if (ret || (is_kprobe && param > PARAM_MAX_STACK)) 369 ret = -EINVAL; 370 else { 371 f->fn = t->fetch[FETCH_MTD_stack]; 372 f->data = (void *)param; 373 } 374 } else 375 ret = -EINVAL; 376 } else if (strcmp(arg, "comm") == 0) { 377 if (strcmp(t->name, "string") != 0 && 378 strcmp(t->name, "string_size") != 0) 379 return -EINVAL; 380 f->fn = t->fetch[FETCH_MTD_comm]; 381 } else 382 ret = -EINVAL; 383 384 return ret; 385 } 386 387 /* Recursive argument parser */ 388 static int parse_probe_arg(char *arg, const struct fetch_type *t, 389 struct fetch_param *f, bool is_return, bool is_kprobe, 390 const struct fetch_type *ftbl) 391 { 392 unsigned long param; 393 long offset; 394 char *tmp; 395 int ret = 0; 396 397 switch (arg[0]) { 398 case '$': 399 ret = parse_probe_vars(arg + 1, t, f, is_return, is_kprobe); 400 break; 401 402 case '%': /* named register */ 403 ret = regs_query_register_offset(arg + 1); 404 if (ret >= 0) { 405 f->fn = t->fetch[FETCH_MTD_reg]; 406 f->data = (void *)(unsigned long)ret; 407 ret = 0; 408 } 409 break; 410 411 case '@': /* memory, file-offset or symbol */ 412 if (isdigit(arg[1])) { 413 ret = kstrtoul(arg + 1, 0, ¶m); 414 if (ret) 415 break; 416 417 f->fn = t->fetch[FETCH_MTD_memory]; 418 f->data = (void *)param; 419 } else if (arg[1] == '+') { 420 /* kprobes don't support file offsets */ 421 if (is_kprobe) 422 return -EINVAL; 423 424 ret = kstrtol(arg + 2, 0, &offset); 425 if (ret) 426 break; 427 428 f->fn = t->fetch[FETCH_MTD_file_offset]; 429 f->data = (void *)offset; 430 } else { 431 /* uprobes don't support symbols */ 432 if (!is_kprobe) 433 return -EINVAL; 434 435 ret = traceprobe_split_symbol_offset(arg + 1, &offset); 436 if (ret) 437 break; 438 439 f->data = alloc_symbol_cache(arg + 1, offset); 440 if (f->data) 441 f->fn = t->fetch[FETCH_MTD_symbol]; 442 } 443 break; 444 445 case '+': /* deref memory */ 446 arg++; /* Skip '+', because kstrtol() rejects it. */ 447 case '-': 448 tmp = strchr(arg, '('); 449 if (!tmp) 450 break; 451 452 *tmp = '\0'; 453 ret = kstrtol(arg, 0, &offset); 454 455 if (ret) 456 break; 457 458 arg = tmp + 1; 459 tmp = strrchr(arg, ')'); 460 461 if (tmp) { 462 struct deref_fetch_param *dprm; 463 const struct fetch_type *t2; 464 465 t2 = find_fetch_type(NULL, ftbl); 466 *tmp = '\0'; 467 dprm = kzalloc(sizeof(struct deref_fetch_param), GFP_KERNEL); 468 469 if (!dprm) 470 return -ENOMEM; 471 472 dprm->offset = offset; 473 dprm->fetch = t->fetch[FETCH_MTD_memory]; 474 dprm->fetch_size = get_fetch_size_function(t, 475 dprm->fetch, ftbl); 476 ret = parse_probe_arg(arg, t2, &dprm->orig, is_return, 477 is_kprobe, ftbl); 478 if (ret) 479 kfree(dprm); 480 else { 481 f->fn = t->fetch[FETCH_MTD_deref]; 482 f->data = (void *)dprm; 483 } 484 } 485 break; 486 } 487 if (!ret && !f->fn) { /* Parsed, but do not find fetch method */ 488 pr_info("%s type has no corresponding fetch method.\n", t->name); 489 ret = -EINVAL; 490 } 491 492 return ret; 493 } 494 495 #define BYTES_TO_BITS(nb) ((BITS_PER_LONG * (nb)) / sizeof(long)) 496 497 /* Bitfield type needs to be parsed into a fetch function */ 498 static int __parse_bitfield_probe_arg(const char *bf, 499 const struct fetch_type *t, 500 struct fetch_param *f) 501 { 502 struct bitfield_fetch_param *bprm; 503 unsigned long bw, bo; 504 char *tail; 505 506 if (*bf != 'b') 507 return 0; 508 509 bprm = kzalloc(sizeof(*bprm), GFP_KERNEL); 510 if (!bprm) 511 return -ENOMEM; 512 513 bprm->orig = *f; 514 f->fn = t->fetch[FETCH_MTD_bitfield]; 515 f->data = (void *)bprm; 516 bw = simple_strtoul(bf + 1, &tail, 0); /* Use simple one */ 517 518 if (bw == 0 || *tail != '@') 519 return -EINVAL; 520 521 bf = tail + 1; 522 bo = simple_strtoul(bf, &tail, 0); 523 524 if (tail == bf || *tail != '/') 525 return -EINVAL; 526 527 bprm->hi_shift = BYTES_TO_BITS(t->size) - (bw + bo); 528 bprm->low_shift = bprm->hi_shift + bo; 529 530 return (BYTES_TO_BITS(t->size) < (bw + bo)) ? -EINVAL : 0; 531 } 532 533 /* String length checking wrapper */ 534 int traceprobe_parse_probe_arg(char *arg, ssize_t *size, 535 struct probe_arg *parg, bool is_return, bool is_kprobe, 536 const struct fetch_type *ftbl) 537 { 538 const char *t; 539 int ret; 540 541 if (strlen(arg) > MAX_ARGSTR_LEN) { 542 pr_info("Argument is too long.: %s\n", arg); 543 return -ENOSPC; 544 } 545 parg->comm = kstrdup(arg, GFP_KERNEL); 546 if (!parg->comm) { 547 pr_info("Failed to allocate memory for command '%s'.\n", arg); 548 return -ENOMEM; 549 } 550 t = strchr(parg->comm, ':'); 551 if (t) { 552 arg[t - parg->comm] = '\0'; 553 t++; 554 } 555 /* 556 * The default type of $comm should be "string", and it can't be 557 * dereferenced. 558 */ 559 if (!t && strcmp(arg, "$comm") == 0) 560 t = "string"; 561 parg->type = find_fetch_type(t, ftbl); 562 if (!parg->type) { 563 pr_info("Unsupported type: %s\n", t); 564 return -EINVAL; 565 } 566 parg->offset = *size; 567 *size += parg->type->size; 568 ret = parse_probe_arg(arg, parg->type, &parg->fetch, is_return, 569 is_kprobe, ftbl); 570 571 if (ret >= 0 && t != NULL) 572 ret = __parse_bitfield_probe_arg(t, parg->type, &parg->fetch); 573 574 if (ret >= 0) { 575 parg->fetch_size.fn = get_fetch_size_function(parg->type, 576 parg->fetch.fn, 577 ftbl); 578 parg->fetch_size.data = parg->fetch.data; 579 } 580 581 return ret; 582 } 583 584 /* Return 1 if name is reserved or already used by another argument */ 585 int traceprobe_conflict_field_name(const char *name, 586 struct probe_arg *args, int narg) 587 { 588 int i; 589 590 for (i = 0; i < ARRAY_SIZE(reserved_field_names); i++) 591 if (strcmp(reserved_field_names[i], name) == 0) 592 return 1; 593 594 for (i = 0; i < narg; i++) 595 if (strcmp(args[i].name, name) == 0) 596 return 1; 597 598 return 0; 599 } 600 601 void traceprobe_update_arg(struct probe_arg *arg) 602 { 603 if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn)) 604 update_bitfield_fetch_param(arg->fetch.data); 605 else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn)) 606 update_deref_fetch_param(arg->fetch.data); 607 else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn)) 608 update_symbol_cache(arg->fetch.data); 609 } 610 611 void traceprobe_free_probe_arg(struct probe_arg *arg) 612 { 613 if (CHECK_FETCH_FUNCS(bitfield, arg->fetch.fn)) 614 free_bitfield_fetch_param(arg->fetch.data); 615 else if (CHECK_FETCH_FUNCS(deref, arg->fetch.fn)) 616 free_deref_fetch_param(arg->fetch.data); 617 else if (CHECK_FETCH_FUNCS(symbol, arg->fetch.fn)) 618 free_symbol_cache(arg->fetch.data); 619 620 kfree(arg->name); 621 kfree(arg->comm); 622 } 623 624 static int __set_print_fmt(struct trace_probe *tp, char *buf, int len, 625 bool is_return) 626 { 627 int i; 628 int pos = 0; 629 630 const char *fmt, *arg; 631 632 if (!is_return) { 633 fmt = "(%lx)"; 634 arg = "REC->" FIELD_STRING_IP; 635 } else { 636 fmt = "(%lx <- %lx)"; 637 arg = "REC->" FIELD_STRING_FUNC ", REC->" FIELD_STRING_RETIP; 638 } 639 640 /* When len=0, we just calculate the needed length */ 641 #define LEN_OR_ZERO (len ? len - pos : 0) 642 643 pos += snprintf(buf + pos, LEN_OR_ZERO, "\"%s", fmt); 644 645 for (i = 0; i < tp->nr_args; i++) { 646 pos += snprintf(buf + pos, LEN_OR_ZERO, " %s=%s", 647 tp->args[i].name, tp->args[i].type->fmt); 648 } 649 650 pos += snprintf(buf + pos, LEN_OR_ZERO, "\", %s", arg); 651 652 for (i = 0; i < tp->nr_args; i++) { 653 if (strcmp(tp->args[i].type->name, "string") == 0) 654 pos += snprintf(buf + pos, LEN_OR_ZERO, 655 ", __get_str(%s)", 656 tp->args[i].name); 657 else 658 pos += snprintf(buf + pos, LEN_OR_ZERO, ", REC->%s", 659 tp->args[i].name); 660 } 661 662 #undef LEN_OR_ZERO 663 664 /* return the length of print_fmt */ 665 return pos; 666 } 667 668 int set_print_fmt(struct trace_probe *tp, bool is_return) 669 { 670 int len; 671 char *print_fmt; 672 673 /* First: called with 0 length to calculate the needed length */ 674 len = __set_print_fmt(tp, NULL, 0, is_return); 675 print_fmt = kmalloc(len + 1, GFP_KERNEL); 676 if (!print_fmt) 677 return -ENOMEM; 678 679 /* Second: actually write the @print_fmt */ 680 __set_print_fmt(tp, print_fmt, len + 1, is_return); 681 tp->call.print_fmt = print_fmt; 682 683 return 0; 684 } 685