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
 166         if (!is_logical_and(expr))
 167                 __use_cond_false_states();
 168
 169         __push_cond_stacks();
 170
 171         __save_pre_cond_states();
 172         split_conditions(expr->right);
 173         __discard_pre_cond_states();
 174
 175         if (is_logical_and(expr))
 176                 __and_cond_states();
 177         else
 178                 __or_cond_states();
 179
 180         __use_cond_true_states();
 181 }
 182
 183 static struct state_list *combine(struct state_list *orig, struct state_list *fake,
 184                                 struct state_list *new)
 185 {
 186         struct state_list *ret = NULL;
 187
 188         overwrite_slist(orig, &ret);
 189         overwrite_slist(fake, &ret);
 190         overwrite_slist(new, &ret);
 191         free_slist(&new);
 192
 193         return ret;
 194 }
 195
 196 /*
 197  * handle_select()
 198  * if ((aaa()?bbb():ccc())) { ...
 199  *
 200  * This is almost the same as:
 201  * if ((aaa() && bbb()) || (!aaa() && ccc())) { ...
 202  *
 203  * It's a bit complicated because we shouldn't pass aaa()
 204  * to the clients more than once.
 205  */
 206
 207 static void handle_select(struct expression *expr)
 208 {
 209         struct state_list *a_T = NULL;
 210         struct state_list *a_F = NULL;
 211         struct state_list *a_T_b_T = NULL;
 212         struct state_list *a_T_b_F = NULL;
 213         struct state_list *a_T_b_fake = NULL;
 214         struct state_list *a_F_c_T = NULL;
 215         struct state_list *a_F_c_F = NULL;
 216         struct state_list *a_F_c_fake = NULL;
 217         struct sm_state *sm;
 218
 219         /*
 220          * Imagine we have this:  if (a ? b : c) { ...
 221          *
 222          * The condition is true if "a" is true and "b" is true or
 223          * "a" is false and "c" is true.  It's false if "a" is true
 224          * and "b" is false or "a" is false and "c" is false.
 225          *
 226          * The variable name "a_T_b_T" stands for "a true b true" etc.
 227          *
 228          * But if we know "b" is true then we can simpilify things.
 229          * The condition is true if "a" is true or if "a" is false and
 230          * "c" is true.  The only way the condition can be false is if
 231          * "a" is false and "c" is false.
 232          *
 233          * The remaining thing is the "a_T_b_fake".  When we simplify
 234          * the equations we have to take into consideration that other
 235          * states may have changed that don't play into the true false
 236          * equation.  Take the following example:
 237          * if ({
 238          *         (flags) = __raw_local_irq_save();
 239          *         _spin_trylock(lock) ? 1 :
 240          *                 ({ raw_local_irq_restore(flags);  0; });
 241          *    })
 242          * Smatch has to record that the irq flags were restored on the
 243          * false path.
 244          *
 245          */
 246
 247         __save_pre_cond_states();
 248
 249         split_conditions(expr->conditional);
 250
 251         a_T = __copy_cond_true_states();
 252         a_F = __copy_cond_false_states();
 253
 254         __push_cond_stacks();
 255         __push_fake_cur_slist();
 256         split_conditions(expr->cond_true);
 257         a_T_b_fake = __pop_fake_cur_slist();
 258         a_T_b_T = combine(a_T, a_T_b_fake, __pop_cond_true_stack());
 259         a_T_b_F = combine(a_T, a_T_b_fake, __pop_cond_false_stack());
 260
 261         __use_cond_false_states();
 262
 263         __push_cond_stacks();
 264         __push_fake_cur_slist();
 265         split_conditions(expr->cond_false);
 266         a_F_c_fake = __pop_fake_cur_slist();
 267         a_F_c_T = combine(a_F, a_F_c_fake, __pop_cond_true_stack());
 268         a_F_c_F = combine(a_F, a_F_c_fake, __pop_cond_false_stack());
 269
 270         /* We have to restore the pre condition states so that
 271            implied_condition_true() will use the right cur_slist */
 272         __use_pre_cond_states();
 273
 274         if (implied_condition_true(expr->cond_true)) {
 275                 free_slist(&a_T_b_T);
 276                 free_slist(&a_T_b_F);
 277                 a_T_b_T = clone_slist(a_T);
 278                 overwrite_slist(a_T_b_fake, &a_T_b_T);
 279         }
 280         if (implied_condition_false(expr->cond_true)) {
 281                 free_slist(&a_T_b_T);
 282                 free_slist(&a_T_b_F);
 283                 a_T_b_F = clone_slist(a_T);
 284                 overwrite_slist(a_T_b_fake, &a_T_b_F);
 285         }
 286         if (implied_condition_true(expr->cond_false)) {
 287                 free_slist(&a_F_c_T);
 288                 free_slist(&a_F_c_F);
 289                 a_F_c_T = clone_slist(a_F);
 290                 overwrite_slist(a_F_c_fake, &a_F_c_T);
 291         }
 292         if (implied_condition_false(expr->cond_false)) {
 293                 free_slist(&a_F_c_T);
 294                 free_slist(&a_F_c_F);
 295                 a_F_c_F = clone_slist(a_F);
 296                 overwrite_slist(a_F_c_fake, &a_F_c_F);
 297         }
 298
 299         merge_slist(&a_T_b_T, a_F_c_T);
 300         merge_slist(&a_T_b_F, a_F_c_F);
 301
 302         __pop_cond_true_stack();
 303         __pop_cond_false_stack();
 304         __push_cond_stacks();
 305         FOR_EACH_PTR(a_T_b_T, sm) {
 306                 __set_true_false_sm(sm, NULL);
 307         } END_FOR_EACH_PTR(sm);
 308         FOR_EACH_PTR(a_T_b_F, sm) {
 309                 __set_true_false_sm(NULL, sm);
 310         } END_FOR_EACH_PTR(sm);
 311 }
 312
 313 static void hackup_unsigned_compares(struct expression *expr)
 314 {
 315         if (expr->type != EXPR_COMPARE)
 316                 return;
 317
 318         switch (expr->op) {
 319         case '<':
 320                 if (expr_unsigned(expr->left) || expr_unsigned(expr->right))
 321                         expr->op = SPECIAL_UNSIGNED_LT;
 322                 break;
 323         case SPECIAL_LTE:
 324                 if (expr_unsigned(expr->left) || expr_unsigned(expr->right))
 325                         expr->op = SPECIAL_UNSIGNED_LTE;
 326                 break;
 327         case '>':
 328                 if (expr_unsigned(expr->left) || expr_unsigned(expr->right))
 329                         expr->op = SPECIAL_UNSIGNED_GT;
 330                 break;
 331         case SPECIAL_GTE:
 332                 if (expr_unsigned(expr->left) || expr_unsigned(expr->right))
 333                         expr->op = SPECIAL_UNSIGNED_GTE;
 334                 break;
 335         }
 336 }
 337
 338 static void split_conditions(struct expression *expr)
 339 {
 340         if (option_debug) {
 341                 char *cond = get_variable_from_expr_complex(expr, NULL);
 342
 343                 sm_debug("%d in split_conditions (%s)\n", get_lineno(), cond);
 344                 free_string(cond);
 345         }
 346
 347         expr = strip_expr(expr);
 348         if (!expr)
 349                 return;
 350
 351         switch (expr->type) {
 352         case EXPR_LOGICAL:
 353                 __pass_to_client(expr, LOGIC_HOOK);
 354                 handle_logical(expr);
 355                 return;
 356         case EXPR_COMPARE:
 357                 hackup_unsigned_compares(expr);
 358                 if (handle_zero_comparisons(expr))
 359                         return;
 360                 break;
 361         case EXPR_CALL:
 362                 if (ignore_builtin_expect(expr))
 363                         return;
 364                 break;
 365         case EXPR_PREOP:
 366                 if (handle_preop(expr))
 367                         return;
 368                 break;
 369         case EXPR_CONDITIONAL:
 370         case EXPR_SELECT:
 371                 handle_select(expr);
 372                 return;
 373         }
 374
 375         /* fixme: this should be in smatch_flow.c
 376            but because of the funny stuff we do with conditions
 377            it's awkward to put it there.  We would need to
 378            call CONDITION_HOOK in smatch_flow as well.
 379         */
 380         push_expression(&big_expression_stack, expr);
 381         if (expr->type == EXPR_COMPARE) {
 382                 if (expr->left->type != EXPR_POSTOP)
 383                         __split_expr(expr->left);
 384                 if (expr->right->type != EXPR_POSTOP)
 385                         __split_expr(expr->right);
 386         } else if (expr->type != EXPR_POSTOP) {
 387                 __split_expr(expr);
 388         }
 389         __pass_to_client(expr, CONDITION_HOOK);
 390         if (expr->type == EXPR_COMPARE) {
 391                 if (expr->left->type == EXPR_POSTOP)
 392                         __split_expr(expr->left);
 393                 if (expr->right->type == EXPR_POSTOP)
 394                         __split_expr(expr->right);
 395         } else if (expr->type == EXPR_POSTOP) {
 396                 __split_expr(expr);
 397         }
 398         pop_expression(&big_expression_stack);
 399 }
 400
 401 static int inside_condition;
 402 void __split_whole_condition(struct expression *expr)
 403 {
 404         sm_debug("%d in __split_whole_condition\n", get_lineno());
 405         inside_condition++;
 406         __save_pre_cond_states();
 407         __push_cond_stacks();
 408         /* it's a hack, but it's sometimes handy to have this stuff
 409            on the big_expression_stack.  */
 410         push_expression(&big_expression_stack, expr);
 411         if (expr)
 412                 split_conditions(expr);
 413         __use_cond_states();
 414         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 415         pop_expression(&big_expression_stack);
 416         inside_condition--;
 417         sm_debug("%d done __split_whole_condition\n", get_lineno());
 418 }
 419
 420 void __handle_logic(struct expression *expr)
 421 {
 422         sm_debug("%d in __handle_logic\n", get_lineno());
 423         inside_condition++;
 424         __save_pre_cond_states();
 425         __push_cond_stacks();
 426         /* it's a hack, but it's sometimes handy to have this stuff
 427            on the big_expression_stack.  */
 428         push_expression(&big_expression_stack, expr);
 429         if (expr)
 430                 split_conditions(expr);
 431         __use_cond_states();
 432         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 433         pop_expression(&big_expression_stack);
 434         __merge_false_states();
 435         inside_condition--;
 436         sm_debug("%d done __handle_logic\n", get_lineno());
 437 }
 438
 439 int __is_condition_assign(struct expression *expr)
 440 {
 441         struct expression *right;
 442
 443         right = strip_expr(expr->right);
 444         switch (right->type) {
 445         case EXPR_LOGICAL:
 446         case EXPR_COMPARE:
 447                 break;
 448         case EXPR_PREOP:
 449                 if (right->op == '!')
 450                         break;
 451                 return 0;
 452         default:
 453                 return 0;
 454         }
 455         return 1;
 456 }
 457
 458 int __handle_condition_assigns(struct expression *expr)
 459 {
 460         struct expression *right;
 461
 462         right = strip_expr(expr->right);
 463         if (!__is_condition_assign(expr))
 464                 return 0;
 465
 466         sm_debug("%d in __handle_condition_assigns\n", get_lineno());
 467         inside_condition++;
 468         __save_pre_cond_states();
 469         __push_cond_stacks();
 470         /* it's a hack, but it's sometimes handy to have this stuff
 471            on the big_expression_stack.  */
 472         push_expression(&big_expression_stack, right);
 473         split_conditions(right);
 474         set_true_false_states_expr(SMATCH_EXTRA, expr->left, alloc_estate(1), alloc_estate(0));
 475         __use_cond_states();
 476         __pass_to_client(right, WHOLE_CONDITION_HOOK);
 477         pop_expression(&big_expression_stack);
 478         inside_condition--;
 479         sm_debug("%d done __handle_condition_assigns\n", get_lineno());
 480
 481         __push_true_states();
 482         __use_false_states();
 483         __merge_true_states();
 484         __pass_to_client(expr, ASSIGNMENT_HOOK);
 485         return 1;
 486 }
 487
 488 static int is_select_assign(struct expression *expr)
 489 {
 490         struct expression *right;
 491
 492         if (expr->op != '=')
 493                 return 0;
 494         right = strip_expr(expr->right);
 495         if (right->type == EXPR_CONDITIONAL)
 496                 return 1;
 497         if (right->type == EXPR_SELECT)
 498                 return 1;
 499         return 0;
 500 }
 501
 502 static void set_fake_assign(struct expression *new,
 503                         struct expression *left, int op, struct expression *right)
 504 {
 505
 506         new->pos = left->pos;
 507         new->op = op;
 508         new->type = EXPR_ASSIGNMENT;
 509         new->left = left;
 510         new->right = right;
 511 }
 512
 513 int __handle_select_assigns(struct expression *expr)
 514 {
 515         struct expression *right;
 516         struct state_list *final_states = NULL;
 517         struct sm_state *sm;
 518         int is_true;
 519         int is_false;
 520
 521         if (!is_select_assign(expr))
 522                 return 0;
 523         sm_debug("%d in __handle_ternary_assigns\n", get_lineno());
 524         right = strip_expr(expr->right);
 525
 526         is_true = implied_condition_true(right->conditional);
 527         is_false = implied_condition_false(right->conditional);
 528
 529         /* hah hah.  the ultra fake out */
 530         __save_pre_cond_states();
 531         __split_whole_condition(right->conditional);
 532
 533         if (!is_false) {
 534                 struct expression fake_expr;
 535
 536                 if (right->cond_true)
 537                         set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_true);
 538                 else
 539                         set_fake_assign(&fake_expr, expr->left, expr->op, right->conditional);
 540                 __split_expr(&fake_expr);
 541                 final_states = clone_slist(__get_cur_slist());
 542         }
 543
 544         __use_false_states();
 545         if (!is_true) {
 546                 struct expression fake_expr;
 547
 548                 set_fake_assign(&fake_expr, expr->left, expr->op, right->cond_false);
 549                 __split_expr(&fake_expr);
 550                 merge_slist(&final_states, __get_cur_slist());
 551         }
 552
 553         __use_pre_cond_states();
 554
 555         FOR_EACH_PTR(final_states, sm) {
 556                 __set_sm(sm);
 557         } END_FOR_EACH_PTR(sm);
 558
 559         free_slist(&final_states);
 560
 561         sm_debug("%d done __handle_ternary_assigns\n", get_lineno());
 562
 563         return 1;
 564 }
 565
 566 static struct statement *split_then_return_last(struct statement *stmt)
 567 {
 568         struct statement *tmp;
 569         struct statement *last_stmt;
 570
 571         last_stmt = last_ptr_list((struct ptr_list *)stmt->stmts);
 572         if (!last_stmt)
 573                 return NULL;
 574
 575         __push_scope_hooks();
 576         FOR_EACH_PTR(stmt->stmts, tmp) {
 577                 if (tmp == last_stmt)
 578                         return last_stmt;
 579                 __split_stmt(tmp);
 580         } END_FOR_EACH_PTR(tmp);
 581         return NULL;
 582 }
 583
 584 int __handle_expr_statement_assigns(struct expression *expr)
 585 {
 586         struct expression *right;
 587         struct statement *stmt;
 588
 589         right = expr->right;
 590         if (right->type == EXPR_PREOP && right->op == '(')
 591                 right = right->unop;
 592         if (right->type != EXPR_STATEMENT)
 593                 return 0;
 594
 595         __expr_stmt_count++;
 596         stmt = right->statement;
 597         if (stmt->type == STMT_COMPOUND) {
 598                 struct statement *last_stmt;
 599                 struct expression fake_assign;
 600                 struct expression fake_expr_stmt;
 601
 602                 last_stmt = split_then_return_last(stmt);
 603                 if (!last_stmt) {
 604                         __expr_stmt_count--;
 605                         return 0;
 606                 }
 607
 608                 fake_expr_stmt.pos = last_stmt->pos;
 609                 fake_expr_stmt.type = EXPR_STATEMENT;
 610                 fake_expr_stmt.statement = last_stmt;
 611
 612                 fake_assign.pos = last_stmt->pos;
 613                 fake_assign.op = expr->op;
 614                 fake_assign.type = EXPR_ASSIGNMENT;
 615                 fake_assign.left = expr->left;
 616                 fake_assign.right = &fake_expr_stmt;
 617
 618                 __split_expr(&fake_assign);
 619
 620                 __call_scope_hooks();
 621         } else if (stmt->type == STMT_EXPRESSION) {
 622                 struct expression fake_assign;
 623
 624                 fake_assign.pos = stmt->pos;
 625                 fake_assign.op = expr->op;
 626                 fake_assign.type = EXPR_ASSIGNMENT;
 627                 fake_assign.left = expr->left;
 628                 fake_assign.right = stmt->expression;
 629
 630                 __split_expr(&fake_assign);
 631
 632         } else {
 633                 __split_stmt(stmt);
 634         }
 635         __expr_stmt_count--;
 636         return 1;
 637 }
 638
 639 int in_condition(void)
 640 {
 641         return inside_condition;
 642 }