smatch_conditions.c

   1 /*
   2  * sparse/smatch_conditions.c
   3  *
   4  * Copyright (C) 2006,2008 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * The simplest type of condition is
  12  * if (a) { ...
  13  *
  14  * The next simplest kind of conditions is
  15  * if (a && b) { c;
  16  * In that case 'a' is true when we get to 'b' and both are true
  17  * when we get to c.
  18  *
  19  * Or's are a little more complicated.
  20  * if (a || b) { c;
  21  * We know 'a' is not true when we get to 'b' but it may be true
  22  * when we get to c.
  23  *
  24  * If we mix and's and or's that's even more complicated.
  25  * if (a && b && c || a && d) { d ;
  26  * 'a' is true when we evaluate 'b', and 'd'.
  27  * 'b' is true when we evaluate 'c' but otherwise we don't.
  28  *
  29  * The other thing that complicates matters is if we negate
  30  * some if conditions.
  31  * if (!a) { ...
  32  * Smatch has passes the un-negated version to the client and flip
  33  * the true and false values internally.  This makes it easier
  34  * to write checks.
  35  *
  36  * And negations can be part of a compound.
  37  * if (a && !(b || c)) { d;
  38  * In that situation we multiply the negative through to simplify
  39  * stuff so that we can remove the parens like this:
  40  * if (a && !b && !c) { d;
  41  *
  42  * One other thing is that:
  43  * if ((a) != 0){ ...
  44  * that's basically the same as testing for just 'a' and we simplify
  45  * comparisons with zero before passing it to the script.
  46  *
  47  */
  48
  49 #include "smatch.h"
  50 #include "smatch_slist.h"
  51 #include "smatch_extra.h"
  52 #include "smatch_expression_stacks.h"
  53
  54 extern int __expr_stmt_count;
  55
  56 static void split_conditions(struct expression *expr);
  57
  58 static int is_logical_and(struct expression *expr)
  59 {
  60         if (expr->op == SPECIAL_LOGICAL_AND)
  61                 return 1;
  62         return 0;
  63 }
  64
  65 static int handle_zero_comparisons(struct expression *expr)
  66 {
  67         struct expression *tmp = NULL;
  68
  69         // if left is zero or right is zero
  70         if (is_zero(expr->left))
  71                 tmp = expr->right;
  72         else if (is_zero(expr->right))
  73                 tmp = expr->left;
  74         else
  75                 return 0;
  76
  77         // "if (foo != 0)" is the same as "if (foo)"
  78         if (expr->op == SPECIAL_NOTEQUAL) {
  79                 split_conditions(tmp);
  80                 return 1;
  81         }
  82
  83         // "if (foo == 0)" is the same as "if (!foo)"
  84         if (expr->op == SPECIAL_EQUAL) {
  85                 split_conditions(tmp);
  86                 __negate_cond_stacks();
  87                 return 1;
  88         }
  89
  90         return 0;
  91 }
  92
  93 /*
  94  * This function is for handling calls to likely/unlikely
  95  */
  96
  97 static int ignore_builtin_expect(struct expression *expr)
  98 {
  99         if (sym_name_is("__builtin_expect", expr->fn)) {
 100                 split_conditions(first_ptr_list((struct ptr_list *) expr->args));
 101                 return 1;
 102         }
 103         return 0;
 104 }
 105
 106 /*
 107  * handle_compound_stmt() is for: foo = ({blah; blah; blah; 1})
 108  */
 109
 110 static void handle_compound_stmt(struct statement *stmt)
 111 {
 112         struct expression *expr = NULL;
 113         struct statement *last;
 114         struct statement *s;
 115
 116         last = last_ptr_list((struct ptr_list *)stmt->stmts);
 117         if (last->type != STMT_EXPRESSION)
 118                 last = NULL;
 119         else
 120                 expr = last->expression;
 121
 122         FOR_EACH_PTR(stmt->stmts, s) {
 123                 if (s != last)
 124                         __split_stmt(s);
 125         } END_FOR_EACH_PTR(s);
 126         split_conditions(expr);
 127         return;
 128 }
 129
 130 static int handle_preop(struct expression *expr)
 131 {
 132         struct statement *stmt;
 133
 134         if (expr->op == '!') {
 135                 split_conditions(expr->unop);
 136                 __negate_cond_stacks();
 137                 return 1;
 138         }
 139         stmt = get_expression_statement(expr);
 140         if (stmt) {
 141                 handle_compound_stmt(stmt);
 142                 return 1;
 143         }
 144         return 0;
 145 }
 146
 147 static void handle_logical(struct expression *expr)
 148 {
 149         /*
 150          * If we come to an "and" expr then:
 151          * We split the left side.
 152          * We keep all the current states.
 153          * We split the right side.
 154          * We keep all the states from both true sides.
 155          *
 156          * If it's an "or" expr then:
 157          * We save the current slist.
 158          * We split the left side.
 159          * We use the false states for the right side.
 160          * We split the right side.
 161          * We save all the states that are the same on both sides.
 162          */
 163
 164         split_conditions(expr->left);
 165         __process_post_op_stack();
 166
 167         if (!is_logical_and(expr))
 168                 __use_cond_false_states();
 169
 170         __push_cond_stacks();
 171
 172         __save_pre_cond_states();
 173         split_conditions(expr->right);
 174         __process_post_op_stack();
 175         __discard_pre_cond_states();
 176
 177         if (is_logical_and(expr))
 178                 __and_cond_states();
 179         else
 180                 __or_cond_states();
 181
 182         __use_cond_true_states();
 183 }
 184
 185 static struct state_list *combine(struct state_list *orig, struct state_list *fake,
 186                                 struct state_list *new)
 187 {
 188         struct state_list *ret = NULL;
 189
 190         overwrite_slist(orig, &ret);
 191         overwrite_slist(fake, &ret);
 192         overwrite_slist(new, &ret);
 193         free_slist(&new);
 194
 195         return ret;
 196 }
 197
 198 /*
 199  * handle_select()
 200  * if ((aaa()?bbb():ccc())) { ...
 201  *
 202  * This is almost the same as:
 203  * if ((aaa() && bbb()) || (!aaa() && ccc())) { ...
 204  *
 205  * It's a bit complicated because we shouldn't pass aaa()
 206  * to the clients more than once.
 207  */
 208
 209 static void handle_select(struct expression *expr)
 210 {
 211         struct state_list *a_T = NULL;
 212         struct state_list *a_F = NULL;
 213         struct state_list *a_T_b_T = NULL;
 214         struct state_list *a_T_b_F = NULL;
 215         struct state_list *a_T_b_fake = NULL;
 216         struct state_list *a_F_c_T = NULL;
 217         struct state_list *a_F_c_F = NULL;
 218         struct state_list *a_F_c_fake = NULL;
 219         struct sm_state *sm;
 220
 221         /*
 222          * Imagine we have this:  if (a ? b : c) { ...
 223          *
 224          * The condition is true if "a" is true and "b" is true or
 225          * "a" is false and "c" is true.  It's false if "a" is true
 226          * and "b" is false or "a" is false and "c" is false.
 227          *
 228          * The variable name "a_T_b_T" stands for "a true b true" etc.
 229          *
 230          * But if we know "b" is true then we can simpilify things.
 231          * The condition is true if "a" is true or if "a" is false and
 232          * "c" is true.  The only way the condition can be false is if
 233          * "a" is false and "c" is false.
 234          *
 235          * The remaining thing is the "a_T_b_fake".  When we simplify
 236          * the equations we have to take into consideration that other
 237          * states may have changed that don't play into the true false
 238          * equation.  Take the following example:
 239          * if ({
 240          *         (flags) = __raw_local_irq_save();
 241          *         _spin_trylock(lock) ? 1 :
 242          *                 ({ raw_local_irq_restore(flags);  0; });
 243          *    })
 244          * Smatch has to record that the irq flags were restored on the
 245          * false path.
 246          *
 247          */
 248
 249         __save_pre_cond_states();
 250
 251         split_conditions(expr->conditional);
 252
 253         a_T = __copy_cond_true_states();
 254         a_F = __copy_cond_false_states();
 255
 256         __push_cond_stacks();
 257         __push_fake_cur_slist();
 258         split_conditions(expr->cond_true);
 259         __process_post_op_stack();
 260         a_T_b_fake = __pop_fake_cur_slist();
 261         a_T_b_T = combine(a_T, a_T_b_fake, __pop_cond_true_stack());
 262         a_T_b_F = combine(a_T, a_T_b_fake, __pop_cond_false_stack());
 263
 264         __use_cond_false_states();
 265
 266         __push_cond_stacks();
 267         __push_fake_cur_slist();
 268         split_conditions(expr->cond_false);
 269         a_F_c_fake = __pop_fake_cur_slist();
 270         a_F_c_T = combine(a_F, a_F_c_fake, __pop_cond_true_stack());
 271         a_F_c_F = combine(a_F, a_F_c_fake, __pop_cond_false_stack());
 272
 273         /* We have to restore the pre condition states so that
 274            implied_condition_true() will use the right cur_slist */
 275         __use_pre_cond_states();
 276
 277         if (implied_condition_true(expr->cond_true)) {
 278                 free_slist(&a_T_b_T);
 279                 free_slist(&a_T_b_F);
 280                 a_T_b_T = clone_slist(a_T);
 281                 overwrite_slist(a_T_b_fake, &a_T_b_T);
 282         }
 283         if (implied_condition_false(expr->cond_true)) {
 284                 free_slist(&a_T_b_T);
 285                 free_slist(&a_T_b_F);
 286                 a_T_b_F = clone_slist(a_T);
 287                 overwrite_slist(a_T_b_fake, &a_T_b_F);
 288         }
 289         if (implied_condition_true(expr->cond_false)) {
 290                 free_slist(&a_F_c_T);
 291                 free_slist(&a_F_c_F);
 292                 a_F_c_T = clone_slist(a_F);
 293                 overwrite_slist(a_F_c_fake, &a_F_c_T);
 294         }
 295         if (implied_condition_false(expr->cond_false)) {
 296                 free_slist(&a_F_c_T);
 297                 free_slist(&a_F_c_F);
 298                 a_F_c_F = clone_slist(a_F);
 299                 overwrite_slist(a_F_c_fake, &a_F_c_F);
 300         }
 301
 302         merge_slist(&a_T_b_T, a_F_c_T);
 303         merge_slist(&a_T_b_F, a_F_c_F);
 304
 305         __pop_cond_true_stack();
 306         __pop_cond_false_stack();
 307         __push_cond_stacks();
 308         FOR_EACH_PTR(a_T_b_T, sm) {
 309                 __set_true_false_sm(sm, NULL);
 310         } END_FOR_EACH_PTR(sm);
 311         FOR_EACH_PTR(a_T_b_F, sm) {
 312                 __set_true_false_sm(NULL, sm);
 313         } END_FOR_EACH_PTR(sm);
 314 }
 315
 316 static int make_op_unsigned(int op)
 317 {
 318         switch (op) {
 319         case '<':
 320                 return SPECIAL_UNSIGNED_LT;
 321         case SPECIAL_LTE:
 322                 return SPECIAL_UNSIGNED_LTE;
 323         case '>':
 324                 return SPECIAL_UNSIGNED_GT;
 325         case SPECIAL_GTE:
 326                 return SPECIAL_UNSIGNED_GTE;
 327         }
 328         return op;
 329 }
 330
 331 static void hackup_unsigned_compares(struct expression *expr)
 332 {
 333         if (expr->type != EXPR_COMPARE)
 334                 return;
 335
 336         if (type_unsigned(get_type(expr)))
 337                 expr->op = make_op_unsigned(expr->op);
 338 }
 339
 340 static void split_conditions(struct expression *expr)
 341 {
 342         if (option_debug) {
 343                 char *cond = expr_to_str(expr);
 344
 345                 sm_debug("%d in split_conditions (%s)\n", get_lineno(), cond);
 346                 free_string(cond);
 347         }
 348
 349         expr = strip_expr(expr);
 350         if (!expr)
 351                 return;
 352
 353         switch (expr->type) {
 354         case EXPR_LOGICAL:
 355                 __pass_to_client(expr, LOGIC_HOOK);
 356                 handle_logical(expr);
 357                 return;
 358         case EXPR_COMPARE:
 359                 hackup_unsigned_compares(expr);
 360                 if (handle_zero_comparisons(expr))
 361                         return;
 362                 break;
 363         case EXPR_CALL:
 364                 if (ignore_builtin_expect(expr))
 365                         return;
 366                 break;
 367         case EXPR_PREOP:
 368                 if (handle_preop(expr))
 369                         return;
 370                 break;
 371         case EXPR_CONDITIONAL:
 372         case EXPR_SELECT:
 373                 handle_select(expr);
 374                 return;
 375         }
 376
 377         /* fixme: this should be in smatch_flow.c
 378            but because of the funny stuff we do with conditions
 379            it's awkward to put it there.  We would need to
 380            call CONDITION_HOOK in smatch_flow as well.
 381         */
 382         push_expression(&big_expression_stack, expr);
 383         if (expr->type == EXPR_COMPARE) {
 384                 if (expr->left->type != EXPR_POSTOP)
 385                         __split_expr(expr->left);
 386                 if (expr->right->type != EXPR_POSTOP)
 387                         __split_expr(expr->right);
 388         } else if (expr->type != EXPR_POSTOP) {
 389                 __split_expr(expr);
 390         }
 391         __pass_to_client(expr, CONDITION_HOOK);
 392         if (expr->type == EXPR_COMPARE) {
 393                 if (expr->left->type == EXPR_POSTOP)
 394                         __split_expr(expr->left);
 395                 if (expr->right->type == EXPR_POSTOP)
 396                         __split_expr(expr->right);
 397         } else if (expr->type == EXPR_POSTOP) {
 398                 __split_expr(expr);
 399         }
 400         __process_post_op_stack();
 401         pop_expression(&big_expression_stack);
 402 }
 403
 404 static int inside_condition;
 405 void __split_whole_condition(struct expression *expr)
 406 {
 407         sm_debug("%d in __split_whole_condition\n", get_lineno());
 408         inside_condition++;
 409         __save_pre_cond_states();
 410         __push_cond_stacks();
 411         /* it's a hack, but it's sometimes handy to have this stuff
 412            on the big_expression_stack.  */
 413         push_expression(&big_expression_stack, expr);
 414         if (expr)
 415                 split_conditions(expr);
 416         __use_cond_states();
 417         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 418         pop_expression(&big_expression_stack);
 419         inside_condition--;
 420         sm_debug("%d done __split_whole_condition\n", get_lineno());
 421 }
 422
 423 void __handle_logic(struct expression *expr)
 424 {
 425         sm_debug("%d in __handle_logic\n", get_lineno());
 426         inside_condition++;
 427         __save_pre_cond_states();
 428         __push_cond_stacks();
 429         /* it's a hack, but it's sometimes handy to have this stuff
 430            on the big_expression_stack.  */
 431         push_expression(&big_expression_stack, expr);
 432         if (expr)
 433                 split_conditions(expr);
 434         __use_cond_states();
 435         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 436         pop_expression(&big_expression_stack);
 437         __merge_false_states();
 438         inside_condition--;
 439         sm_debug("%d done __handle_logic\n", get_lineno());
 440 }
 441
 442 int is_condition(struct expression *expr)
 443 {
 444
 445         expr = strip_expr(expr);
 446         if (!expr)
 447                 return 0;
 448
 449         switch (expr->type) {
 450         case EXPR_LOGICAL:
 451         case EXPR_COMPARE:
 452                 return 1;
 453         case EXPR_PREOP:
 454                 if (expr->op == '!')
 455                         return 1;
 456         }
 457         return 0;
 458 }
 459
 460 int __handle_condition_assigns(struct expression *expr)
 461 {
 462         struct expression *right;
 463
 464         right = strip_expr(expr->right);
 465         if (!is_condition(expr->right))
 466                 return 0;
 467
 468         sm_debug("%d in __handle_condition_assigns\n", get_lineno());
 469         inside_condition++;
 470         __save_pre_cond_states();
 471         __push_cond_stacks();
 472         /* it's a hack, but it's sometimes handy to have this stuff
 473            on the big_expression_stack.  */
 474         push_expression(&big_expression_stack, right);
 475         split_conditions(right);
 476         __use_cond_states();
 477         set_extra_expr_mod(expr->left, alloc_estate_sval(sval_type_val(get_type(expr->left), 1)));
 478         __pass_to_client(right, WHOLE_CONDITION_HOOK);
 479         pop_expression(&big_expression_stack);
 480         inside_condition--;
 481         sm_debug("%d done __handle_condition_assigns\n", get_lineno());
 482
 483         __push_true_states();
 484         __use_false_states();
 485         set_extra_expr_mod(expr->left, alloc_estate_sval(sval_type_val(get_type(expr->left), 0)));
 486         __merge_true_states();
 487         __pass_to_client(expr, ASSIGNMENT_HOOK);
 488         return 1;
 489 }
 490
 491 static int is_select_assign(struct expression *expr)
 492 {
 493         struct expression *right;
 494
 495         if (expr->op != '=')
 496                 return 0;
 497         right = strip_expr(expr->right);
 498         if (right->type == EXPR_CONDITIONAL)
 499                 return 1;
 500         if (right->type == EXPR_SELECT)
 501                 return 1;
 502         return 0;
 503 }
 504
 505 static void set_fake_assign(struct expression *new,
 506                         struct expression *left, int op, struct expression *right)
 507 {
 508
 509         new->pos = left->pos;
 510         new->op = op;
 511         new->type = EXPR_ASSIGNMENT;
 512         new->left = left;
 513         new->right = right;
 514 }
 515
 516 int __handle_select_assigns(struct expression *expr)
 517 {
 518         struct expression *right;
 519         struct state_list *final_states = NULL;
 520         struct sm_state *sm;
 521         int is_true;
 522         int is_false;
 523
 524         if (!is_select_assign(expr))
 525                 return 0;
 526         sm_debug("%d in __handle_ternary_assigns\n", get_lineno());
 527         right = strip_expr(expr->right);
 528
 529         is_true = implied_condition_true(right->conditional);
 530         is_false = implied_condition_false(right->conditional);
 531
 532         /* hah hah.  the ultra fake out */
 533         __save_pre_cond_states();
 534         __split_whole_condition(right->conditional);
 535
 536         if (!is_false) {
 537                 struct expression fake_expr;
 538
 539                 if (right->cond_true)
 540                         set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_true);
 541                 else
 542                         set_fake_assign(&fake_expr, expr->left, expr->op, right->conditional);
 543                 __split_expr(&fake_expr);
 544                 final_states = clone_slist(__get_cur_slist());
 545         }
 546
 547         __use_false_states();
 548         if (!is_true) {
 549                 struct expression fake_expr;
 550
 551                 set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_false);
 552                 __split_expr(&fake_expr);
 553                 merge_slist(&final_states, __get_cur_slist());
 554         }
 555
 556         __use_pre_cond_states();
 557
 558         FOR_EACH_PTR(final_states, sm) {
 559                 __set_sm(sm);
 560         } END_FOR_EACH_PTR(sm);
 561
 562         free_slist(&final_states);
 563
 564         sm_debug("%d done __handle_ternary_assigns\n", get_lineno());
 565
 566         return 1;
 567 }
 568
 569 static struct statement *split_then_return_last(struct statement *stmt)
 570 {
 571         struct statement *tmp;
 572         struct statement *last_stmt;
 573
 574         last_stmt = last_ptr_list((struct ptr_list *)stmt->stmts);
 575         if (!last_stmt)
 576                 return NULL;
 577
 578         __push_scope_hooks();
 579         FOR_EACH_PTR(stmt->stmts, tmp) {
 580                 if (tmp == last_stmt)
 581                         return last_stmt;
 582                 __split_stmt(tmp);
 583         } END_FOR_EACH_PTR(tmp);
 584         return NULL;
 585 }
 586
 587 int __handle_expr_statement_assigns(struct expression *expr)
 588 {
 589         struct expression *right;
 590         struct statement *stmt;
 591
 592         right = expr->right;
 593         if (right->type == EXPR_PREOP && right->op == '(')
 594                 right = right->unop;
 595         if (right->type != EXPR_STATEMENT)
 596                 return 0;
 597
 598         __expr_stmt_count++;
 599         stmt = right->statement;
 600         if (stmt->type == STMT_COMPOUND) {
 601                 struct statement *last_stmt;
 602                 struct expression fake_assign;
 603                 struct expression fake_expr_stmt;
 604
 605                 last_stmt = split_then_return_last(stmt);
 606                 if (!last_stmt) {
 607                         __expr_stmt_count--;
 608                         return 0;
 609                 }
 610
 611                 fake_expr_stmt.pos = last_stmt->pos;
 612                 fake_expr_stmt.type = EXPR_STATEMENT;
 613                 fake_expr_stmt.statement = last_stmt;
 614
 615                 fake_assign.pos = last_stmt->pos;
 616                 fake_assign.op = expr->op;
 617                 fake_assign.type = EXPR_ASSIGNMENT;
 618                 fake_assign.left = expr->left;
 619                 fake_assign.right = &fake_expr_stmt;
 620
 621                 __split_expr(&fake_assign);
 622
 623                 __call_scope_hooks();
 624         } else if (stmt->type == STMT_EXPRESSION) {
 625                 struct expression fake_assign;
 626
 627                 fake_assign.pos = stmt->pos;
 628                 fake_assign.op = expr->op;
 629                 fake_assign.type = EXPR_ASSIGNMENT;
 630                 fake_assign.left = expr->left;
 631                 fake_assign.right = stmt->expression;
 632
 633                 __split_expr(&fake_assign);
 634
 635         } else {
 636                 __split_stmt(stmt);
 637         }
 638         __expr_stmt_count--;
 639         return 1;
 640 }
 641
 642 int in_condition(void)
 643 {
 644         return inside_condition;
 645 }