smatch_struct_assignment.c

   1 /*
   2  * Copyright (C) 2014 Oracle.
   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  * This file started out by saying that if you have:
  20  *
  21  *      struct foo one, two;
  22  *      ...
  23  *      one = two;
  24  *
  25  * That's equivalent to saying:
  26  *
  27  *      one.x = two.x;
  28  *      one.y = two.y;
  29  *
  30  * Turning an assignment like that into a bunch of small fake assignments is
  31  * really useful.
  32  *
  33  * The call to memcpy(&one, &two, sizeof(foo)); is the same as "one = two;" so
  34  * we can re-use the code.  And we may as well use it for memset() too.
  35  * Assigning pointers is almost the same:
  36  *
  37  *      p1 = p2;
  38  *
  39  * Is the same as:
  40  *
  41  *      p1->x = p2->x;
  42  *      p1->y = p2->y;
  43  *
  44  * The problem is that you can go a bit crazy with pointers to pointers.
  45  *
  46  *      p1->x->y->z->one->two->three = p2->x->y->z->one->two->three;
  47  *
  48  * We probably want to distinguish between between shallow and deep copies so
  49  * that if we memset(p1, 0, sizeof(*p1)) then it just sets p1->x to zero and not
  50  * p1->x->y.
  51  *
  52  * I don't have a proper solution for this problem right now.  I just copy one
  53  * level and don't nest.  It should handle limitted nesting but intelligently.
  54  *
  55  * The other thing is that you end up with a lot of garbage assignments where
  56  * we record "x could be anything. x->y could be anything. x->y->z->a->b->c
  57  * could *also* be anything!".  There should be a better way to filter this
  58  * useless information.
  59  *
  60  */
  61
  62 #include "smatch.h"
  63 #include "smatch_slist.h"
  64 #include "smatch_extra.h"
  65
  66 static int my_id;
  67
  68 enum {
  69         COPY_NORMAL,
  70         COPY_UNKNOWN,
  71         COPY_ZERO,
  72 };
  73
  74 static struct symbol *get_struct_type(struct expression *expr)
  75 {
  76         struct symbol *type;
  77
  78         type = get_type(expr);
  79         if (!type)
  80                 return NULL;
  81         if (type->type == SYM_PTR) {
  82                 type = get_real_base_type(type);
  83                 if (!type)
  84                         return NULL;
  85         }
  86         if (type->type == SYM_STRUCT)
  87                 return type;
  88         if (type->type == SYM_UNION)
  89                 return type;
  90         return NULL;
  91 }
  92
  93 static struct expression *get_right_base_expr(struct symbol *left_type, struct expression *right)
  94 {
  95         struct symbol *struct_type;
  96
  97         if (!right)
  98                 return NULL;
  99
 100         struct_type = get_struct_type(right);
 101         if (!struct_type)
 102                 return NULL;
 103         if (struct_type != left_type)
 104                 return NULL;
 105
 106         if (right->type == EXPR_PREOP && right->op == '&')
 107                 right = strip_expr(right->unop);
 108
 109         if (right->type == EXPR_CALL)
 110                 return NULL;
 111
 112         return right;
 113 }
 114
 115 static struct expression *add_dereference(struct expression *expr)
 116 {
 117         struct symbol *type;
 118
 119         /*
 120          * We want to re-write "memcpy(foo, bar, sizeof(*foo));" as
 121          * "*foo = *bar;".
 122          */
 123
 124         expr = strip_expr(expr);
 125         if (!expr)
 126                 return NULL;
 127
 128         if (expr->type == EXPR_PREOP && expr->op == '&')
 129                 return strip_expr(expr->unop);
 130         type = get_type(expr);
 131         if (!type)
 132                 return NULL;
 133         if (type->type != SYM_PTR && type->type != SYM_ARRAY)
 134                 return NULL;
 135
 136         return deref_expression(expr);
 137 }
 138
 139 static struct expression *faked_expression;
 140 struct expression *get_faked_expression(void)
 141 {
 142         if (!__in_fake_assign)
 143                 return NULL;
 144         return faked_expression;
 145 }
 146
 147 static void split_fake_expr(struct expression *expr, void *unused)
 148 {
 149         __in_fake_assign++;
 150         __in_fake_struct_assign++;
 151         __split_expr(expr);
 152         __in_fake_struct_assign--;
 153         __in_fake_assign--;
 154 }
 155
 156 static void handle_non_struct_assignments(struct expression *left, struct expression *right,
 157                         void (*assign_handler)(struct expression *expr, void *data),
 158                         void *data)
 159 {
 160         struct symbol *left_type, *right_type;
 161         struct expression *assign;
 162
 163         while (right && right->type == EXPR_ASSIGNMENT)
 164                 right = strip_parens(right->left);
 165
 166         if (!right)
 167                 right = unknown_value_expression(left);
 168
 169         left_type = get_type(left);
 170         right_type = get_type(right);
 171         if (!left_type || !right_type)
 172                 return;
 173
 174         if (right_type->type == SYM_ARRAY)
 175                 right = unknown_value_expression(left);
 176
 177         if (left_type->type == SYM_PTR) {
 178                 left = deref_expression(left);
 179                 assign = assign_expression(left, '=', right);
 180                 assign_handler(assign, data);
 181                 return;
 182         }
 183         if (left_type->type != SYM_BASETYPE)
 184                 return;
 185         assign = assign_expression(left, '=', right);
 186         assign_handler(assign, data);
 187 }
 188
 189 static bool dont_care(int mode, struct stree *left_care, struct stree *right_care,
 190                       struct expression *left, struct expression *right)
 191 {
 192         struct symbol *left_sym, *right_sym;
 193         int left_len = 0, right_len = 0;
 194         char *left_name = NULL;
 195         char *right_name = NULL;
 196         struct sm_state *sm;
 197         int ret = false;
 198         int len;
 199
 200         if (mode == COPY_ZERO)
 201                 return false;
 202
 203         left_name = expr_to_str_sym(left, &left_sym);
 204         if (left_name && !strstr(left_name, "->"))
 205                 goto free;
 206         if (left_name)
 207                 left_len = strlen(left_name);
 208
 209         ret = true;
 210         FOR_EACH_SM(left_care, sm) {
 211                 len = strlen(sm->name);
 212                 if (left_name && left_sym == sm->sym &&
 213                     len >= left_len &&
 214                     strncmp(sm->name, left_name, len)) {
 215                         ret = false;
 216                         goto free;
 217                 }
 218         } END_FOR_EACH_SM(sm);
 219
 220         right_name = expr_to_str_sym(right, &right_sym);
 221         if (right_name)
 222                 right_len = strlen(right_name);
 223         if (!right_sym || left_sym == right_sym)
 224                 goto free;
 225
 226         FOR_EACH_SM(right_care, sm) {
 227                 len = strlen(sm->name);
 228                 if (right_name && right_sym == sm->sym &&
 229                     len >= right_len &&
 230                     strncmp(sm->name, right_name, len)) {
 231                         ret = false;
 232                         goto free;
 233                 }
 234         } END_FOR_EACH_SM(sm);
 235
 236 free:
 237         free_string(left_name);
 238         free_string(right_name);
 239         return ret;
 240 }
 241
 242 static void set_inner_struct_members(int mode, struct expression *faked,
 243                 struct expression *left, struct expression *right, struct symbol *member,
 244                 struct stree *care_left, struct stree *care_right,
 245                 void (*assign_handler)(struct expression *expr, void *data),
 246                 void *data)
 247 {
 248         struct expression *left_member;
 249         struct expression *right_expr;
 250         struct expression *assign;
 251         struct symbol *base = get_real_base_type(member);
 252         struct symbol *tmp;
 253
 254         if (member->ident) {
 255                 left = member_expression(left, '.', member->ident);
 256                 if (mode == COPY_NORMAL && right)
 257                         right = member_expression(right, '.', member->ident);
 258         }
 259
 260         if (dont_care(mode, care_left, care_right, left, right))
 261                 return;
 262
 263         FOR_EACH_PTR(base->symbol_list, tmp) {
 264                 struct symbol *type;
 265
 266                 type = get_real_base_type(tmp);
 267                 if (!type)
 268                         continue;
 269
 270                 if (type->type == SYM_ARRAY)
 271                         continue;
 272                 if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
 273                         set_inner_struct_members(mode, faked, left, right, tmp, care_left, care_right, assign_handler, data);
 274                         continue;
 275                 }
 276                 if (!tmp->ident)
 277                         continue;
 278
 279                 left_member = member_expression(left, '.', tmp->ident);
 280
 281                 right_expr = NULL;
 282                 if (mode == COPY_NORMAL && right)
 283                         right_expr = member_expression(right, '.', tmp->ident);
 284                 if (mode == COPY_ZERO)
 285                         right_expr = zero_expr();
 286                 if (!right_expr)
 287                         right_expr = unknown_value_expression(left_member);
 288
 289                 assign = assign_expression(left_member, '=', right_expr);
 290                 assign_handler(assign, data);
 291         } END_FOR_EACH_PTR(tmp);
 292 }
 293
 294 static void get_care_stree(struct expression *left, struct stree **left_care,
 295                            struct expression *right, struct stree **right_care)
 296 {
 297         struct symbol *left_sym, *right_sym;
 298         struct sm_state *sm;
 299
 300         *left_care = NULL;
 301         *right_care = NULL;
 302
 303         left_sym = expr_to_sym(left);
 304         right_sym = expr_to_sym(right);
 305
 306         FOR_EACH_SM(__get_cur_stree(), sm) {
 307                 if (!sm->sym)
 308                         continue;
 309                 if (sm->sym == left_sym)
 310                         overwrite_sm_state_stree(left_care, sm);
 311         } END_FOR_EACH_SM(sm);
 312
 313         if (!right_sym || left_sym == right_sym)
 314                 return;
 315
 316         FOR_EACH_SM(__get_cur_stree(), sm) {
 317                 if (!sm->sym)
 318                         continue;
 319                 if (sm->sym == right_sym)
 320                         overwrite_sm_state_stree(right_care, sm);
 321         } END_FOR_EACH_SM(sm);
 322 }
 323
 324 static void __struct_members_copy(int mode, struct expression *faked,
 325                                   struct expression *left,
 326                                   struct expression *right,
 327                                   void (*assign_handler)(struct expression *expr, void *data),
 328                                   void *data)
 329 {
 330         struct symbol *struct_type, *tmp, *type;
 331         struct stree *care_left = NULL;
 332         struct stree *care_right = NULL;
 333         struct expression *left_member;
 334         struct expression *right_expr;
 335         struct expression *assign;
 336
 337         if (__in_fake_assign || !left)
 338                 return;
 339
 340         faked_expression = faked;
 341
 342         left = strip_expr(left);
 343         right = strip_expr(right);
 344
 345         if (left->type == EXPR_PREOP && left->op == '*' && is_pointer(left))
 346                 left = preop_expression(left, '(');
 347
 348         struct_type = get_struct_type(left);
 349         if (!struct_type) {
 350                 /*
 351                  * This is not a struct assignment obviously.  But this is where
 352                  * memcpy() is handled so it feels like a good place to add this
 353                  * code.
 354                  */
 355                 handle_non_struct_assignments(left, right, assign_handler, data);
 356                 goto done;
 357         }
 358
 359         if (mode == COPY_NORMAL)
 360                 right = get_right_base_expr(struct_type, right);
 361
 362         if (mode != COPY_ZERO)
 363                 get_care_stree(left, &care_left, right, &care_right);
 364         FOR_EACH_PTR(struct_type->symbol_list, tmp) {
 365                 type = get_real_base_type(tmp);
 366                 if (!type)
 367                         continue;
 368                 if (type->type == SYM_ARRAY)
 369                         continue;
 370
 371                 if (type->type == SYM_UNION || type->type == SYM_STRUCT) {
 372                         set_inner_struct_members(mode, faked, left, right, tmp,
 373                                                  care_left, care_right,
 374                                                  assign_handler, data);
 375                         continue;
 376                 }
 377
 378                 if (!tmp->ident)
 379                         continue;
 380
 381                 left_member = member_expression(left, '.', tmp->ident);
 382                 right_expr = NULL;
 383
 384                 if (mode == COPY_NORMAL && right)
 385                         right_expr = member_expression(right, '.', tmp->ident);
 386                 if (mode == COPY_ZERO)
 387                         right_expr = zero_expr();
 388                 if (!right_expr)
 389                         right_expr = unknown_value_expression(left_member);
 390
 391                 assign = assign_expression(left_member, '=', right_expr);
 392                 assign_handler(assign, data);
 393         } END_FOR_EACH_PTR(tmp);
 394
 395         free_stree(&care_left);
 396         free_stree(&care_right);
 397 done:
 398         faked_expression = NULL;
 399 }
 400
 401 static int returns_zeroed_mem(struct expression *expr)
 402 {
 403         struct expression *tmp;
 404         char *fn;
 405
 406         if (expr->type != EXPR_CALL || expr->fn->type != EXPR_SYMBOL)
 407                 return 0;
 408
 409         if (is_fake_call(expr)) {
 410                 tmp = get_faked_expression();
 411                 if (!tmp || tmp->type != EXPR_ASSIGNMENT || tmp->op != '=')
 412                         return 0;
 413                 expr = tmp->right;
 414                 if (expr->type != EXPR_CALL || expr->fn->type != EXPR_SYMBOL)
 415                         return 0;
 416         }
 417
 418         fn = expr_to_var(expr->fn);
 419         if (!fn)
 420                 return 0;
 421         if (strcmp(fn, "kcalloc") == 0)
 422                 return 1;
 423         if (option_project == PROJ_KERNEL && strstr(fn, "zalloc"))
 424                 return 1;
 425         return 0;
 426 }
 427
 428 static int copy_containter_states(struct expression *left, struct expression *right, int offset)
 429 {
 430         char *left_name = NULL, *right_name = NULL;
 431         struct symbol *left_sym, *right_sym;
 432         struct sm_state *sm, *new_sm;
 433         int ret = 0;
 434         int len;
 435         char buf[64];
 436         char new_name[128];
 437
 438         right_name = expr_to_var_sym(right, &right_sym);
 439         if (!right_name || !right_sym)
 440                 goto free;
 441         left_name = expr_to_var_sym(left, &left_sym);
 442         if (!left_name || !left_sym)
 443                 goto free;
 444
 445         len = snprintf(buf, sizeof(buf), "%s(-%d)", right_name, offset);
 446         if (len >= sizeof(buf))
 447                 goto free;
 448
 449         FOR_EACH_SM_SAFE(__get_cur_stree(), sm) {
 450                 if (sm->sym != right_sym)
 451                         continue;
 452                 if (strncmp(sm->name, buf, len) != 0)
 453                         continue;
 454                 snprintf(new_name, sizeof(new_name), "%s%s", left_name, sm->name + len);
 455                 new_sm = clone_sm(sm);
 456                 new_sm->name = alloc_sname(new_name);
 457                 new_sm->sym = left_sym;
 458                 __set_sm(new_sm);
 459                 ret = 1;
 460         } END_FOR_EACH_SM_SAFE(sm);
 461 free:
 462         free_string(left_name);
 463         free_string(right_name);
 464         return ret;
 465 }
 466
 467 static int handle_param_offsets(struct expression *expr)
 468 {
 469         struct expression *right;
 470         sval_t sval;
 471
 472         right = strip_expr(expr->right);
 473
 474         if (right->type != EXPR_BINOP || right->op != '-')
 475                 return 0;
 476
 477         if (!get_value(right->right, &sval))
 478                 return 0;
 479
 480         right = get_assigned_expr(right->left);
 481         if (!right)
 482                 return 0;
 483         return copy_containter_states(expr->left, right, sval.value);
 484 }
 485
 486 static void returns_container_of(struct expression *expr, int param, char *key, char *value)
 487 {
 488         struct expression *call, *arg;
 489         int offset;
 490
 491         if (expr->type != EXPR_ASSIGNMENT || expr->op != '=')
 492                 return;
 493         call = strip_expr(expr->right);
 494         if (call->type != EXPR_CALL)
 495                 return;
 496         if (param != -1)
 497                 return;
 498         param = atoi(key);
 499         offset = atoi(value);
 500
 501         arg = get_argument_from_call_expr(call->args, param);
 502         if (!arg)
 503                 return;
 504
 505         copy_containter_states(expr->left, arg, -offset);
 506 }
 507
 508 void __fake_struct_member_assignments(struct expression *expr)
 509 {
 510         struct expression *left, *right;
 511         struct symbol *type;
 512         int mode;
 513
 514         if (expr->op != '=')
 515                 return;
 516
 517         if (is_noderef_ptr(expr->right))
 518                 return;
 519
 520         type = get_type(expr->left);
 521         if (!type)
 522                 return;
 523         if (type->type != SYM_PTR && type->type != SYM_STRUCT)
 524                 return;
 525
 526         if (handle_param_offsets(expr))
 527                 return;
 528
 529         left = expr->left;
 530         right = expr->right;
 531
 532         if (type->type == SYM_PTR) {
 533                 /* Convert "p = q;" to "*p = *q;" */
 534                 left = add_dereference(left);
 535                 right = add_dereference(right);
 536         }
 537
 538         if (returns_zeroed_mem(expr->right))
 539                 mode = COPY_ZERO;
 540         else if (types_equiv(get_type(left), get_type(right)))
 541                 mode = COPY_NORMAL;
 542         else
 543                 mode = COPY_UNKNOWN;
 544
 545         __struct_members_copy(mode, expr, left, right, split_fake_expr, NULL);
 546 }
 547
 548 static void match_memset(const char *fn, struct expression *expr, void *_size_arg)
 549 {
 550         struct expression *buf;
 551         struct expression *val;
 552         int mode;
 553
 554         buf = get_argument_from_call_expr(expr->args, 0);
 555         val = get_argument_from_call_expr(expr->args, 1);
 556
 557         buf = strip_expr(buf);
 558         if (expr_is_zero(val))
 559                 mode = COPY_ZERO;
 560         else
 561                 mode = COPY_UNKNOWN;
 562         __struct_members_copy(mode, expr, add_dereference(buf), NULL, split_fake_expr, NULL);
 563 }
 564
 565 static void match_memcpy(const char *fn, struct expression *expr, void *_arg)
 566 {
 567         struct expression *dest;
 568         struct expression *src;
 569         int mode;
 570
 571         dest = get_argument_from_call_expr(expr->args, 0);
 572         src = get_argument_from_call_expr(expr->args, 1);
 573
 574         if (types_equiv(get_type(src), get_type(dest)))
 575                 mode = COPY_NORMAL;
 576         else
 577                 mode = COPY_UNKNOWN;
 578
 579         __struct_members_copy(mode, expr, add_dereference(dest), add_dereference(src), split_fake_expr, NULL);
 580 }
 581
 582 static void match_memdup(const char *fn, struct expression *call_expr,
 583                         struct expression *expr, void *_unused)
 584 {
 585         struct expression *left, *right, *arg;
 586         int mode;
 587
 588         if (!expr || expr->type != EXPR_ASSIGNMENT)
 589                 return;
 590
 591         left = strip_expr(expr->left);
 592         right = strip_expr(expr->right);
 593
 594         if (right->type != EXPR_CALL)
 595                 return;
 596         arg = get_argument_from_call_expr(right->args, 0);
 597
 598         if (types_equiv(get_type(left), get_type(right)))
 599                 mode = COPY_NORMAL;
 600         else
 601                 mode = COPY_UNKNOWN;
 602
 603         __struct_members_copy(mode, expr, add_dereference(left), add_dereference(arg), split_fake_expr, NULL);
 604 }
 605
 606 static void match_memcpy_unknown(const char *fn, struct expression *expr, void *_arg)
 607 {
 608         struct expression *dest;
 609
 610         dest = get_argument_from_call_expr(expr->args, 0);
 611         __struct_members_copy(COPY_UNKNOWN, expr, add_dereference(dest), NULL, split_fake_expr, NULL);
 612 }
 613
 614 static void match_sscanf(const char *fn, struct expression *expr, void *unused)
 615 {
 616         struct expression *arg;
 617         int i;
 618
 619         i = -1;
 620         FOR_EACH_PTR(expr->args, arg) {
 621                 if (++i < 2)
 622                         continue;
 623                 __struct_members_copy(COPY_UNKNOWN, expr, add_dereference(arg), NULL, split_fake_expr, NULL);
 624         } END_FOR_EACH_PTR(arg);
 625 }
 626
 627 static void unop_expr(struct expression *expr)
 628 {
 629         if (expr->op != SPECIAL_INCREMENT &&
 630             expr->op != SPECIAL_DECREMENT)
 631                 return;
 632
 633         if (!is_pointer(expr))
 634                 return;
 635         faked_expression = expr;
 636         __struct_members_copy(COPY_UNKNOWN, expr, expr->unop, NULL, split_fake_expr, NULL);
 637         faked_expression = NULL;
 638 }
 639
 640 static void register_clears_param(void)
 641 {
 642         struct token *token;
 643         char name[256];
 644         const char *function;
 645         int param;
 646
 647         if (option_project == PROJ_NONE)
 648                 return;
 649
 650         snprintf(name, 256, "%s.clears_argument", option_project_str);
 651
 652         token = get_tokens_file(name);
 653         if (!token)
 654                 return;
 655         if (token_type(token) != TOKEN_STREAMBEGIN)
 656                 return;
 657         token = token->next;
 658         while (token_type(token) != TOKEN_STREAMEND) {
 659                 if (token_type(token) != TOKEN_IDENT)
 660                         return;
 661                 function = show_ident(token->ident);
 662                 token = token->next;
 663                 if (token_type(token) != TOKEN_NUMBER)
 664                         return;
 665                 param = atoi(token->number);
 666                 add_function_hook(function, &match_memcpy_unknown, INT_PTR(param));
 667                 token = token->next;
 668         }
 669         clear_token_alloc();
 670 }
 671
 672 void create_recursive_fake_assignments(struct expression *expr,
 673                 void (*assign_handler)(struct expression *expr, void *data),
 674                 void *data)
 675 {
 676         __struct_members_copy(COPY_UNKNOWN, expr, expr, NULL, assign_handler, data);
 677 }
 678
 679 static void db_buf_cleared(struct expression *expr, int param, char *key, char *value)
 680 {
 681         struct expression *arg;
 682
 683         arg = gen_expr_from_param_key(expr, param, key);
 684         if (!arg)
 685                 return;
 686
 687         __in_buf_clear++;
 688         if (strcmp(value, "0") == 0)
 689                 __struct_members_copy(COPY_ZERO, expr, arg, NULL, split_fake_expr, NULL);
 690         else
 691                 __struct_members_copy(COPY_UNKNOWN, expr, arg, NULL, split_fake_expr, NULL);
 692         __in_buf_clear--;
 693 }
 694
 695 void register_struct_assignment(int id)
 696 {
 697         my_id = id;
 698
 699         add_function_data((unsigned long *)&faked_expression);
 700
 701         add_function_hook("memset", &match_memset, NULL);
 702         add_function_hook("__memset", &match_memset, NULL);
 703         add_function_hook("__builtin_memset", &match_memset, NULL);
 704
 705         add_function_hook("memcpy", &match_memcpy, INT_PTR(0));
 706         add_function_hook("memmove", &match_memcpy, INT_PTR(0));
 707         add_function_hook("__memcpy", &match_memcpy, INT_PTR(0));
 708         add_function_hook("__memmove", &match_memcpy, INT_PTR(0));
 709         add_function_hook("__builtin_memcpy", &match_memcpy, INT_PTR(0));
 710         add_function_hook("__builtin_memmove", &match_memcpy, INT_PTR(0));
 711
 712         if (option_project == PROJ_KERNEL) {
 713                 return_implies_state_sval("kmemdup", valid_ptr_min_sval, valid_ptr_max_sval, &match_memdup, NULL);
 714                 add_function_hook("copy_from_user", &match_memcpy, INT_PTR(0));
 715                 add_function_hook("_copy_from_user", &match_memcpy, INT_PTR(0));
 716                 add_function_hook("memcpy_fromio", &match_memcpy, INT_PTR(0));
 717                 add_function_hook("__memcpy_fromio", &match_memcpy, INT_PTR(0));
 718         }
 719
 720         add_function_hook("sscanf", &match_sscanf, NULL);
 721
 722         add_hook(&unop_expr, OP_HOOK);
 723         register_clears_param();
 724         select_return_states_hook(BUF_CLEARED, &db_buf_cleared);
 725         select_return_states_hook(BUF_ADD, &db_buf_cleared);
 726
 727         select_return_states_hook(CONTAINER, &returns_container_of);
 728 }