smatch_helper.c

   1 /*
   2  * Copyright (C) 2006 Dan Carpenter.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * Miscellaneous helper functions.
  20  */
  21
  22 #include <stdlib.h>
  23 #include <stdio.h>
  24 #include "allocate.h"
  25 #include "smatch.h"
  26 #include "smatch_extra.h"
  27
  28 #define VAR_LEN 512
  29
  30 char *alloc_string(const char *str)
  31 {
  32         char *tmp;
  33
  34         if (!str)
  35                 return NULL;
  36         tmp = malloc(strlen(str) + 1);
  37         strcpy(tmp, str);
  38         return tmp;
  39 }
  40
  41 void free_string(char *str)
  42 {
  43         free(str);
  44 }
  45
  46 void remove_parens(char *str)
  47 {
  48         char *src, *dst;
  49
  50         dst = src = str;
  51         while (*src != '\0') {
  52                 if (*src == '(' || *src == ')') {
  53                         src++;
  54                         continue;
  55                 }
  56                 *dst++ = *src++;
  57         }
  58         *dst = *src;
  59 }
  60
  61 struct smatch_state *alloc_state_num(int num)
  62 {
  63         struct smatch_state *state;
  64         static char buff[256];
  65
  66         state = __alloc_smatch_state(0);
  67         snprintf(buff, 255, "%d", num);
  68         buff[255] = '\0';
  69         state->name = alloc_string(buff);
  70         state->data = INT_PTR(num);
  71         return state;
  72 }
  73
  74 struct smatch_state *alloc_state_str(const char *name)
  75 {
  76         struct smatch_state *state;
  77
  78         state = __alloc_smatch_state(0);
  79         state->name = alloc_string(name);
  80         return state;
  81 }
  82
  83 void append(char *dest, const char *data, int buff_len)
  84 {
  85         strncat(dest, data, buff_len - strlen(dest) - 1);
  86 }
  87
  88 /*
  89  * If you have "foo(a, b, 1);" then use
  90  * get_argument_from_call_expr(expr, 0) to return the expression for
  91  * a.  Yes, it does start counting from 0.
  92  */
  93 struct expression *get_argument_from_call_expr(struct expression_list *args,
  94                                                int num)
  95 {
  96         struct expression *expr;
  97         int i = 0;
  98
  99         if (!args)
 100                 return NULL;
 101
 102         FOR_EACH_PTR(args, expr) {
 103                 if (i == num)
 104                         return expr;
 105                 i++;
 106         } END_FOR_EACH_PTR(expr);
 107         return NULL;
 108 }
 109
 110 static struct expression *get_array_expr(struct expression *expr)
 111 {
 112         struct symbol *type;
 113
 114         if (expr->type != EXPR_BINOP || expr->op != '+')
 115                 return NULL;
 116
 117         type = get_type(expr->left);
 118         if (!type || type->type != SYM_ARRAY)
 119                 return NULL;
 120         return expr->left;
 121 }
 122
 123 static void __get_variable_from_expr(struct symbol **sym_ptr, char *buf,
 124                                      struct expression *expr, int len,
 125                                      int *complicated, int no_parens)
 126 {
 127         switch (expr->type) {
 128         case EXPR_DEREF: {
 129                 struct expression *deref;
 130                 int op;
 131
 132                 deref = expr->deref;
 133                 op = deref->op;
 134                 if (op == '*') {
 135                         struct expression *unop = strip_expr(deref->unop);
 136
 137                         if (unop->type == EXPR_PREOP && unop->op == '&') {
 138                                 deref = unop->unop;
 139                                 op = '.';
 140                         } else {
 141                                 deref = deref->unop;
 142                         }
 143                 }
 144
 145                 __get_variable_from_expr(sym_ptr, buf, deref, len, complicated, no_parens);
 146
 147                 if (op == '*')
 148                         append(buf, "->", len);
 149                 else
 150                         append(buf, ".", len);
 151
 152                 if (expr->member)
 153                         append(buf, expr->member->name, len);
 154                 else
 155                         append(buf, "unknown_member", len);
 156
 157                 return;
 158         }
 159         case EXPR_SYMBOL:
 160                 if (expr->symbol_name)
 161                         append(buf, expr->symbol_name->name, len);
 162                 if (sym_ptr) {
 163                         if (*sym_ptr)
 164                                 *complicated = 1;
 165                         *sym_ptr = expr->symbol;
 166                 }
 167                 return;
 168         case EXPR_PREOP: {
 169                 const char *tmp;
 170
 171                 if (get_expression_statement(expr)) {
 172                         *complicated = 2;
 173                         return;
 174                 }
 175
 176                 if (expr->op == '(') {
 177                         if (!no_parens)
 178                                 append(buf, "(", len);
 179                 } else if (expr->op != '*' || !get_array_expr(expr->unop)) {
 180                         tmp = show_special(expr->op);
 181                         append(buf, tmp, len);
 182                 }
 183                 __get_variable_from_expr(sym_ptr, buf, expr->unop,
 184                                                  len, complicated, no_parens);
 185
 186                 if (expr->op == '(' && !no_parens)
 187                         append(buf, ")", len);
 188
 189                 if (expr->op == SPECIAL_DECREMENT ||
 190                                 expr->op == SPECIAL_INCREMENT)
 191                         *complicated = 1;
 192
 193                 return;
 194         }
 195         case EXPR_POSTOP: {
 196                 const char *tmp;
 197
 198                 __get_variable_from_expr(sym_ptr, buf, expr->unop,
 199                                                  len, complicated, no_parens);
 200                 tmp = show_special(expr->op);
 201                 append(buf, tmp, len);
 202
 203                 if (expr->op == SPECIAL_DECREMENT || expr->op == SPECIAL_INCREMENT)
 204                         *complicated = 1;
 205                 return;
 206         }
 207         case EXPR_ASSIGNMENT:
 208         case EXPR_COMPARE:
 209         case EXPR_LOGICAL:
 210         case EXPR_BINOP: {
 211                 char tmp[10];
 212                 struct expression *array_expr;
 213
 214                 *complicated = 1;
 215                 array_expr = get_array_expr(expr);
 216                 if (array_expr) {
 217                         __get_variable_from_expr(sym_ptr, buf, array_expr, len, complicated, no_parens);
 218                         append(buf, "[", len);
 219                 } else {
 220                         __get_variable_from_expr(sym_ptr, buf, expr->left, len, complicated, no_parens);
 221                         snprintf(tmp, sizeof(tmp), " %s ", show_special(expr->op));
 222                         append(buf, tmp, len);
 223                 }
 224                 __get_variable_from_expr(NULL, buf, expr->right, len, complicated, no_parens);
 225                 if (array_expr)
 226                         append(buf, "]", len);
 227                 return;
 228         }
 229         case EXPR_VALUE: {
 230                 char tmp[25];
 231
 232                 *complicated = 1;
 233                 snprintf(tmp, 25, "%lld", expr->value);
 234                 append(buf, tmp, len);
 235                 return;
 236         }
 237         case EXPR_STRING:
 238                 append(buf, "\"", len);
 239                 if (expr->string)
 240                         append(buf, expr->string->data, len);
 241                 append(buf, "\"", len);
 242                 return;
 243         case EXPR_CALL: {
 244                 struct expression *tmp;
 245                 int i;
 246
 247                 *complicated = 1;
 248                 __get_variable_from_expr(NULL, buf, expr->fn, len, complicated, no_parens);
 249                 append(buf, "(", len);
 250                 i = 0;
 251                 FOR_EACH_PTR(expr->args, tmp) {
 252                         if (i++)
 253                                 append(buf, ", ", len);
 254                         __get_variable_from_expr(NULL, buf, tmp, len, complicated, no_parens);
 255                 } END_FOR_EACH_PTR(tmp);
 256                 append(buf, ")", len);
 257                 return;
 258         }
 259         case EXPR_CAST:
 260         case EXPR_FORCE_CAST:
 261                 __get_variable_from_expr(sym_ptr, buf,
 262                                          expr->cast_expression, len,
 263                                          complicated, no_parens);
 264                 return;
 265         case EXPR_SIZEOF: {
 266                 int size;
 267                 char tmp[25];
 268
 269                 if (expr->cast_type && get_base_type(expr->cast_type)) {
 270                         size = type_bytes(get_base_type(expr->cast_type));
 271                         snprintf(tmp, 25, "%d", size);
 272                         append(buf, tmp, len);
 273                 }
 274                 return;
 275         }
 276         case EXPR_IDENTIFIER:
 277                 *complicated = 1;
 278                 if (expr->expr_ident)
 279                         append(buf, expr->expr_ident->name, len);
 280                 return;
 281         default:
 282                 *complicated = 1;
 283                 //printf("unknown type = %d\n", expr->type);
 284                 return;
 285         }
 286 }
 287
 288 /*
 289  * This is returns a stylized "c looking" representation of the
 290  * variable name.
 291  *
 292  * It uses the same buffer every time so you have to save the result
 293  * yourself if you want to keep it.
 294  *
 295  */
 296
 297 char *expr_to_str_sym(struct expression *expr, struct symbol **sym_ptr)
 298 {
 299         static char var_name[VAR_LEN];
 300         int complicated = 0;
 301
 302         if (sym_ptr)
 303                 *sym_ptr = NULL;
 304         var_name[0] = '\0';
 305
 306         if (!expr)
 307                 return NULL;
 308         __get_variable_from_expr(sym_ptr, var_name, expr, sizeof(var_name),
 309                                  &complicated, 0);
 310         if (complicated < 2)
 311                 return alloc_string(var_name);
 312         else
 313                 return NULL;
 314 }
 315
 316 char *expr_to_str(struct expression *expr)
 317 {
 318         return expr_to_str_sym(expr, NULL);
 319 }
 320
 321 /*
 322  * get_variable_from_expr_simple() only returns simple variables.
 323  * If it's a complicated variable like a->foo[x] instead of just 'a->foo'
 324  * then it returns NULL.
 325  */
 326 char *expr_to_var_sym(struct expression *expr,
 327                                     struct symbol **sym_ptr)
 328 {
 329         static char var_name[VAR_LEN];
 330         int complicated = 0;
 331
 332         if (sym_ptr)
 333                 *sym_ptr = NULL;
 334         var_name[0] = '\0';
 335
 336         if (!expr)
 337                 return NULL;
 338         expr = strip_expr(expr);
 339         __get_variable_from_expr(sym_ptr, var_name, expr, sizeof(var_name),
 340                                  &complicated, 1);
 341
 342         if (complicated) {
 343                 if (sym_ptr)
 344                         *sym_ptr = NULL;
 345                 return NULL;
 346         }
 347         return alloc_string(var_name);
 348 }
 349
 350 char *expr_to_var(struct expression *expr)
 351 {
 352         return expr_to_var_sym(expr, NULL);
 353 }
 354
 355 struct symbol *expr_to_sym(struct expression *expr)
 356 {
 357         struct symbol *sym;
 358         char *name;
 359
 360         name = expr_to_var_sym(expr, &sym);
 361         free_string(name);
 362         return sym;
 363 }
 364
 365 char *expr_to_chunk_sym(struct expression *expr, struct symbol **sym)
 366 {
 367         char *name, *left_name, *right_name;
 368         struct symbol *tmp, *left_sym, *right_sym;
 369         char buf[128];
 370
 371         expr = strip_parens(expr);
 372         if (!expr)
 373                 return NULL;
 374         if (sym)
 375                 *sym = NULL;
 376
 377         name = expr_to_var_sym(expr, &tmp);
 378         if (name && tmp) {
 379                 if (sym)
 380                         *sym = tmp;
 381                 return name;
 382         }
 383         free_string(name);
 384
 385         if (expr->type != EXPR_BINOP)
 386                 return NULL;
 387         if (expr->op != '-' && expr->op != '+')
 388                 return NULL;
 389
 390         left_name = expr_to_var_sym(expr->left, &left_sym);
 391         if (!left_name || !left_sym)
 392                 return NULL;
 393         right_name = expr_to_var_sym(expr->right, &right_sym);
 394         if (!right_name || !right_sym) {
 395                 free_string(left_name);
 396                 return NULL;
 397         }
 398
 399         if (expr->op == '+') {
 400                 if (strcmp(left_name, right_name) > 0) {
 401                         char *tmp_name;
 402
 403                         tmp = left_sym;
 404                         left_sym = right_sym;
 405                         right_sym = tmp;
 406
 407                         tmp_name = left_name;
 408                         left_name = right_name;
 409                         right_name = tmp_name;
 410                 }
 411         }
 412
 413         snprintf(buf, sizeof(buf), "%s %s %s", left_name, show_special(expr->op), right_name);
 414         *sym = left_sym;
 415         free_string(left_name);
 416         free_string(right_name);
 417         return alloc_string(buf);
 418 }
 419
 420 int sym_name_is(const char *name, struct expression *expr)
 421 {
 422         if (!expr)
 423                 return 0;
 424         if (expr->type != EXPR_SYMBOL)
 425                 return 0;
 426         if (!strcmp(expr->symbol_name->name, name))
 427                 return 1;
 428         return 0;
 429 }
 430
 431 int is_zero(struct expression *expr)
 432 {
 433         sval_t sval;
 434
 435         if (get_value(expr, &sval) && sval.value == 0)
 436                 return 1;
 437         return 0;
 438 }
 439
 440 int is_array(struct expression *expr)
 441 {
 442         struct symbol *type;
 443
 444         expr = strip_expr(expr);
 445         if (!expr)
 446                 return 0;
 447
 448         if (expr->type == EXPR_PREOP && expr->op == '*') {
 449                 expr = strip_expr(expr->unop);
 450                 if (expr->type == EXPR_BINOP && expr->op == '+')
 451                         return 1;
 452         }
 453
 454         if (expr->type != EXPR_BINOP || expr->op != '+')
 455                 return 0;
 456
 457         type = get_type(expr->left);
 458         if (!type || type->type != SYM_ARRAY)
 459                 return 0;
 460
 461         return 1;
 462 }
 463
 464 struct expression *get_array_base(struct expression *expr)
 465 {
 466         if (!is_array(expr))
 467                 return NULL;
 468         expr = strip_expr(expr);
 469         if (expr->type == EXPR_PREOP && expr->op == '*')
 470                 expr = strip_expr(expr->unop);
 471         if (expr->type != EXPR_BINOP || expr->op != '+')
 472                 return NULL;
 473         return strip_parens(expr->left);
 474 }
 475
 476 struct expression *get_array_offset(struct expression *expr)
 477 {
 478         if (!is_array(expr))
 479                 return NULL;
 480         expr = strip_expr(expr);
 481         if (expr->type == EXPR_PREOP && expr->op == '*')
 482                 expr = strip_expr(expr->unop);
 483         if (expr->type != EXPR_BINOP || expr->op != '+')
 484                 return NULL;
 485         return strip_parens(expr->right);
 486 }
 487
 488 const char *show_state(struct smatch_state *state)
 489 {
 490         if (!state)
 491                 return NULL;
 492         return state->name;
 493 }
 494
 495 struct statement *get_expression_statement(struct expression *expr)
 496 {
 497         /* What are those things called? if (({....; ret;})) { ...*/
 498
 499         if (expr->type != EXPR_PREOP)
 500                 return NULL;
 501         if (expr->op != '(')
 502                 return NULL;
 503         if (expr->unop->type != EXPR_STATEMENT)
 504                 return NULL;
 505         if (expr->unop->statement->type != STMT_COMPOUND)
 506                 return NULL;
 507         return expr->unop->statement;
 508 }
 509
 510 struct expression *strip_parens(struct expression *expr)
 511 {
 512         if (!expr)
 513                 return NULL;
 514
 515         if (expr->type == EXPR_PREOP) {
 516                 if (expr->op == '(' && expr->unop->type == EXPR_STATEMENT &&
 517                         expr->unop->statement->type == STMT_COMPOUND)
 518                         return expr;
 519                 if (expr->op == '(')
 520                         return strip_parens(expr->unop);
 521         }
 522         return expr;
 523 }
 524
 525 struct expression *strip_expr(struct expression *expr)
 526 {
 527         if (!expr)
 528                 return NULL;
 529
 530         switch (expr->type) {
 531         case EXPR_FORCE_CAST:
 532         case EXPR_CAST:
 533                 return strip_expr(expr->cast_expression);
 534         case EXPR_PREOP: {
 535                 struct expression *unop;
 536
 537                 if (expr->op == '(' && expr->unop->type == EXPR_STATEMENT &&
 538                         expr->unop->statement->type == STMT_COMPOUND)
 539                         return expr;
 540
 541                 unop = strip_expr(expr->unop);
 542
 543                 if (expr->op == '*' &&
 544                     unop->type == EXPR_PREOP && unop->op == '&') {
 545                         struct symbol *type = get_type(unop->unop);
 546
 547                         if (type && type->type == SYM_ARRAY)
 548                                 return expr;
 549                         return strip_expr(unop->unop);
 550                 }
 551
 552                 if (expr->op == '(')
 553                         return unop;
 554
 555                 return expr;
 556         }
 557         case EXPR_CONDITIONAL:
 558                 if (known_condition_true(expr->conditional)) {
 559                         if (expr->cond_true)
 560                                 return strip_expr(expr->cond_true);
 561                         return strip_expr(expr->conditional);
 562                 }
 563                 if (known_condition_false(expr->conditional))
 564                         return strip_expr(expr->cond_false);
 565                 return expr;
 566         case EXPR_CALL:
 567                 if (sym_name_is("__builtin_expect", expr->fn)) {
 568                         expr = get_argument_from_call_expr(expr->args, 0);
 569                         return strip_expr(expr);
 570                 }
 571                 return expr;
 572         }
 573         return expr;
 574 }
 575
 576 static void delete_state_tracker(struct tracker *t)
 577 {
 578         delete_state(t->owner, t->name, t->sym);
 579         __free_tracker(t);
 580 }
 581
 582 void scoped_state(int my_id, const char *name, struct symbol *sym)
 583 {
 584         struct tracker *t;
 585
 586         t = alloc_tracker(my_id, name, sym);
 587         add_scope_hook((scope_hook *)&delete_state_tracker, t);
 588 }
 589
 590 int is_error_return(struct expression *expr)
 591 {
 592         struct symbol *cur_func = cur_func_sym;
 593         sval_t sval;
 594
 595         if (!expr)
 596                 return 0;
 597         if (cur_func->type != SYM_NODE)
 598                 return 0;
 599         cur_func = get_base_type(cur_func);
 600         if (cur_func->type != SYM_FN)
 601                 return 0;
 602         cur_func = get_base_type(cur_func);
 603         if (cur_func == &void_ctype)
 604                 return 0;
 605         if (!get_implied_value(expr, &sval))
 606                 return 0;
 607         if (sval.value < 0)
 608                 return 1;
 609         if (cur_func->type == SYM_PTR && sval.value == 0)
 610                 return 1;
 611         return 0;
 612 }
 613
 614 int getting_address(void)
 615 {
 616         struct expression *tmp;
 617         int i = 0;
 618         int dot_ops = 0;
 619
 620         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 621                 if (!i++)
 622                         continue;
 623                 if (tmp->type == EXPR_PREOP && tmp->op == '(')
 624                         continue;
 625                 if (tmp->op == '.' && !dot_ops++)
 626                         continue;
 627                 if (tmp->op == '&')
 628                         return 1;
 629                 return 0;
 630         } END_FOR_EACH_PTR_REVERSE(tmp);
 631         return 0;
 632 }
 633
 634 char *get_member_name(struct expression *expr)
 635 {
 636         char buf[256];
 637         struct symbol *sym;
 638
 639         expr = strip_expr(expr);
 640         if (expr->type != EXPR_DEREF)
 641                 return NULL;
 642         if (!expr->member)
 643                 return NULL;
 644
 645         sym = get_type(expr->deref);
 646         if (!sym)
 647                 return NULL;
 648         if (sym->type == SYM_UNION) {
 649                 sym = expr_to_sym(expr->deref);
 650                 sym = get_real_base_type(sym);
 651                 if (sym && sym->type == SYM_PTR)
 652                         sym = get_real_base_type(sym);
 653                 if (!sym || !sym->ident) {
 654                         snprintf(buf, sizeof(buf), "(union hack)->%s", expr->member->name);
 655                         return alloc_string(buf);
 656                 }
 657         }
 658         if (!sym->ident)
 659                 return NULL;
 660         snprintf(buf, sizeof(buf), "(struct %s)->%s", sym->ident->name, expr->member->name);
 661         return alloc_string(buf);
 662 }
 663
 664 int cmp_pos(struct position pos1, struct position pos2)
 665 {
 666         /* the stream position is ... */
 667         if (pos1.stream > pos2.stream)
 668                 return -1;
 669         if (pos1.stream < pos2.stream)
 670                 return 1;
 671
 672         if (pos1.line < pos2.line)
 673                 return -1;
 674         if (pos1.line > pos2.line)
 675                 return 1;
 676
 677         if (pos1.pos < pos2.pos)
 678                 return -1;
 679         if (pos1.pos > pos2.pos)
 680                 return 1;
 681
 682         return 0;
 683 }
 684
 685 int positions_eq(struct position pos1, struct position pos2)
 686 {
 687         if (pos1.line != pos2.line)
 688                 return 0;
 689         if (pos1.pos != pos2.pos)
 690                 return 0;
 691         if (pos1.stream != pos2.stream)
 692                 return 0;
 693         return 1;
 694 }
 695
 696 struct statement *get_current_statement(void)
 697 {
 698         struct statement *prev, *tmp;
 699
 700         prev = last_ptr_list((struct ptr_list *)big_statement_stack);
 701
 702         if (!prev || !get_macro_name(prev->pos))
 703                 return prev;
 704
 705         FOR_EACH_PTR_REVERSE(big_statement_stack, tmp) {
 706                 if (positions_eq(tmp->pos, prev->pos))
 707                         continue;
 708                 if (prev->pos.line > tmp->pos.line)
 709                         return prev;
 710                 return tmp;
 711         } END_FOR_EACH_PTR_REVERSE(tmp);
 712         return prev;
 713 }
 714
 715 struct statement *get_prev_statement(void)
 716 {
 717         struct statement *tmp;
 718         int i;
 719
 720         i = 0;
 721         FOR_EACH_PTR_REVERSE(big_statement_stack, tmp) {
 722                 if (i++ == 1)
 723                         return tmp;
 724         } END_FOR_EACH_PTR_REVERSE(tmp);
 725         return NULL;
 726 }
 727
 728 int get_param_num_from_sym(struct symbol *sym)
 729 {
 730         struct symbol *tmp;
 731         int i;
 732
 733         if (!cur_func_sym)
 734                 return -1;
 735
 736         i = 0;
 737         FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, tmp) {
 738                 if (tmp == sym)
 739                         return i;
 740                 i++;
 741         } END_FOR_EACH_PTR(tmp);
 742         return -1;
 743 }
 744
 745 int get_param_num(struct expression *expr)
 746 {
 747         struct symbol *sym;
 748         char *name;
 749
 750         if (!cur_func_sym)
 751                 return -1;
 752         name = expr_to_var_sym(expr, &sym);
 753         free_string(name);
 754         if (!sym)
 755                 return -1;
 756         return get_param_num_from_sym(sym);
 757 }
 758
 759 int ms_since(struct timeval *start)
 760 {
 761         struct timeval end;
 762         double diff;
 763
 764         gettimeofday(&end, NULL);
 765         diff = (end.tv_sec - start->tv_sec) * 1000.0;
 766         diff += (end.tv_usec - start->tv_usec) / 1000.0;
 767         return (int)diff;
 768 }
 769
 770 int parent_is_gone_var_sym(const char *name, struct symbol *sym)
 771 {
 772         if (!name || !sym)
 773                 return 0;
 774
 775         if (parent_is_null_var_sym(name, sym) ||
 776             parent_is_free_var_sym(name, sym))
 777                 return 1;
 778         return 0;
 779 }
 780
 781 int parent_is_gone(struct expression *expr)
 782 {
 783         struct symbol *sym;
 784         char *var;
 785         int ret = 0;
 786
 787         expr = strip_expr(expr);
 788         var = expr_to_var_sym(expr, &sym);
 789         if (!var || !sym)
 790                 goto free;
 791         ret = parent_is_gone_var_sym(var, sym);
 792 free:
 793         free_string(var);
 794         return ret;
 795 }
 796
 797 int invert_op(int op)
 798 {
 799         switch (op) {
 800         case '*':
 801                 return '/';
 802         case '/':
 803                 return '*';
 804         case '+':
 805                 return '-';
 806         case '-':
 807                 return '+';
 808         case SPECIAL_LEFTSHIFT:
 809                 return SPECIAL_RIGHTSHIFT;
 810         case SPECIAL_RIGHTSHIFT:
 811                 return SPECIAL_LEFTSHIFT;
 812         }
 813         return 0;
 814 }