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 split_conditions(struct expression *expr)
 314 {
 315         if (option_debug) {
 316                 char *cond = get_variable_from_expr_complex(expr, NULL);
 317
 318                 sm_debug("%d in split_conditions (%s)\n", get_lineno(), cond);
 319                 free_string(cond);
 320         }
 321
 322         expr = strip_expr(expr);
 323         if (!expr)
 324                 return;
 325
 326         switch (expr->type) {
 327         case EXPR_LOGICAL:
 328                 __pass_to_client(expr, LOGIC_HOOK);
 329                 handle_logical(expr);
 330                 return;
 331         case EXPR_COMPARE:
 332                 if (handle_zero_comparisons(expr))
 333                         return;
 334                 break;
 335         case EXPR_CALL:
 336                 if (ignore_builtin_expect(expr))
 337                         return;
 338                 break;
 339         case EXPR_PREOP:
 340                 if (handle_preop(expr))
 341                         return;
 342                 break;
 343         case EXPR_CONDITIONAL:
 344         case EXPR_SELECT:
 345                 handle_select(expr);
 346                 return;
 347         }
 348
 349         /* fixme: this should be in smatch_flow.c
 350            but because of the funny stuff we do with conditions
 351            it's awkward to put it there.  We would need to
 352            call CONDITION_HOOK in smatch_flow as well.
 353         */
 354         push_expression(&big_expression_stack, expr);
 355         if (expr->type == EXPR_COMPARE) {
 356                 if (expr->left->type != EXPR_POSTOP)
 357                         __split_expr(expr->left);
 358                 if (expr->right->type != EXPR_POSTOP)
 359                         __split_expr(expr->right);
 360         } else if (expr->type != EXPR_POSTOP) {
 361                 __split_expr(expr);
 362         }
 363         __pass_to_client(expr, CONDITION_HOOK);
 364         if (expr->type == EXPR_COMPARE) {
 365                 if (expr->left->type == EXPR_POSTOP)
 366                         __split_expr(expr->left);
 367                 if (expr->right->type == EXPR_POSTOP)
 368                         __split_expr(expr->right);
 369         } else if (expr->type == EXPR_POSTOP) {
 370                 __split_expr(expr);
 371         }
 372         pop_expression(&big_expression_stack);
 373 }
 374
 375 static int inside_condition;
 376 void __split_whole_condition(struct expression *expr)
 377 {
 378         sm_debug("%d in __split_whole_condition\n", get_lineno());
 379         inside_condition++;
 380         __save_pre_cond_states();
 381         __push_cond_stacks();
 382         /* it's a hack, but it's sometimes handy to have this stuff
 383            on the big_expression_stack.  */
 384         push_expression(&big_expression_stack, expr);
 385         if (expr)
 386                 split_conditions(expr);
 387         __use_cond_states();
 388         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 389         pop_expression(&big_expression_stack);
 390         inside_condition--;
 391         sm_debug("%d done __split_whole_condition\n", get_lineno());
 392 }
 393
 394 void __handle_logic(struct expression *expr)
 395 {
 396         sm_debug("%d in __handle_logic\n", get_lineno());
 397         inside_condition++;
 398         __save_pre_cond_states();
 399         __push_cond_stacks();
 400         /* it's a hack, but it's sometimes handy to have this stuff
 401            on the big_expression_stack.  */
 402         push_expression(&big_expression_stack, expr);
 403         if (expr)
 404                 split_conditions(expr);
 405         __use_cond_states();
 406         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 407         pop_expression(&big_expression_stack);
 408         __merge_false_states();
 409         inside_condition--;
 410         sm_debug("%d done __handle_logic\n", get_lineno());
 411 }
 412
 413 int __is_condition_assign(struct expression *expr)
 414 {
 415         struct expression *right;
 416
 417         right = strip_expr(expr->right);
 418         switch (right->type) {
 419         case EXPR_LOGICAL:
 420         case EXPR_COMPARE:
 421                 break;
 422         case EXPR_PREOP:
 423                 if (right->op == '!')
 424                         break;
 425                 return 0;
 426         default:
 427                 return 0;
 428         }
 429         return 1;
 430 }
 431
 432 int __handle_condition_assigns(struct expression *expr)
 433 {
 434         struct expression *right;
 435
 436         right = strip_expr(expr->right);
 437         if (!__is_condition_assign(expr))
 438                 return 0;
 439
 440         sm_debug("%d in __handle_condition_assigns\n", get_lineno());
 441         inside_condition++;
 442         __save_pre_cond_states();
 443         __push_cond_stacks();
 444         /* it's a hack, but it's sometimes handy to have this stuff
 445            on the big_expression_stack.  */
 446         push_expression(&big_expression_stack, right);
 447         split_conditions(right);
 448         set_true_false_states_expr(SMATCH_EXTRA, expr->left, alloc_estate(1), alloc_estate(0));
 449         __use_cond_states();
 450         __pass_to_client(right, WHOLE_CONDITION_HOOK);
 451         pop_expression(&big_expression_stack);
 452         inside_condition--;
 453         sm_debug("%d done __handle_condition_assigns\n", get_lineno());
 454
 455         __push_true_states();
 456         __use_false_states();
 457         __merge_true_states();
 458         __pass_to_client(expr, ASSIGNMENT_HOOK);
 459         return 1;
 460 }
 461
 462 static int is_select_assign(struct expression *expr)
 463 {
 464         struct expression *right;
 465
 466         if (expr->op != '=')
 467                 return 0;
 468         right = strip_expr(expr->right);
 469         if (right->type == EXPR_CONDITIONAL)
 470                 return 1;
 471         if (right->type == EXPR_SELECT)
 472                 return 1;
 473         return 0;
 474 }
 475
 476 static void set_fake_assign(struct expression *new,
 477                         struct expression *left, struct expression *right)
 478 {
 479
 480         new->pos = left->pos;
 481         new->op = (int)'=';
 482         new->type = EXPR_ASSIGNMENT;
 483         new->left = left;
 484         new->right = right;
 485 }
 486
 487 int __handle_select_assigns(struct expression *expr)
 488 {
 489         struct expression *right;
 490         struct state_list *final_states = NULL;
 491         struct sm_state *sm;
 492         int is_true;
 493         int is_false;
 494
 495         if (!is_select_assign(expr))
 496                 return 0;
 497         sm_debug("%d in __handle_ternary_assigns\n", get_lineno());
 498         right = strip_expr(expr->right);
 499
 500         is_true = implied_condition_true(right->conditional);
 501         is_false = implied_condition_false(right->conditional);
 502
 503         /* hah hah.  the ultra fake out */
 504         __save_pre_cond_states();
 505         __split_whole_condition(right->conditional);
 506
 507         if (!is_false) {
 508                 struct expression fake_expr;
 509
 510                 if (right->cond_true)
 511                         set_fake_assign(&fake_expr, expr->left, right->cond_true);
 512                 else
 513                         set_fake_assign(&fake_expr, expr->left, right->conditional);
 514                 __split_expr(&fake_expr);
 515                 final_states = clone_slist(__get_cur_slist());
 516         }
 517
 518         __use_false_states();
 519         if (!is_true) {
 520                 struct expression fake_expr;
 521
 522                 set_fake_assign(&fake_expr, expr->left, right->cond_false);
 523                 __split_expr(&fake_expr);
 524                 merge_slist(&final_states, __get_cur_slist());
 525         }
 526
 527         __use_pre_cond_states();
 528
 529         FOR_EACH_PTR(final_states, sm) {
 530                 __set_sm(sm);
 531         } END_FOR_EACH_PTR(sm);
 532
 533         free_slist(&final_states);
 534
 535         sm_debug("%d done __handle_ternary_assigns\n", get_lineno());
 536
 537         return 1;
 538 }
 539
 540 static struct statement *split_then_return_last(struct statement *stmt)
 541 {
 542         struct statement *tmp;
 543         struct statement *last_stmt;
 544
 545         last_stmt = last_ptr_list((struct ptr_list *)stmt->stmts);
 546         if (!last_stmt)
 547                 return NULL;
 548
 549         __push_scope_hooks();
 550         FOR_EACH_PTR(stmt->stmts, tmp) {
 551                 if (tmp == last_stmt)
 552                         return last_stmt;
 553                 __split_stmt(tmp);
 554         } END_FOR_EACH_PTR(tmp);
 555         return NULL;
 556 }
 557
 558 int __handle_expr_statement_assigns(struct expression *expr)
 559 {
 560         struct expression *right;
 561         struct statement *stmt;
 562
 563         right = expr->right;
 564         if (right->type == EXPR_PREOP && right->op == '(')
 565                 right = right->unop;
 566         if (right->type != EXPR_STATEMENT)
 567                 return 0;
 568
 569         __expr_stmt_count++;
 570         stmt = right->statement;
 571         if (stmt->type == STMT_COMPOUND) {
 572                 struct statement *last_stmt;
 573                 struct expression fake_assign;
 574                 struct expression fake_expr_stmt;
 575
 576                 last_stmt = split_then_return_last(stmt);
 577                 if (!last_stmt) {
 578                         __expr_stmt_count--;
 579                         return 0;
 580                 }
 581
 582                 fake_expr_stmt.pos = last_stmt->pos;
 583                 fake_expr_stmt.type = EXPR_STATEMENT;
 584                 fake_expr_stmt.statement = last_stmt;
 585
 586                 fake_assign.pos = last_stmt->pos;
 587                 fake_assign.op = (int)'=';
 588                 fake_assign.type = EXPR_ASSIGNMENT;
 589                 fake_assign.left = expr->left;
 590                 fake_assign.right = &fake_expr_stmt;
 591
 592                 __split_expr(&fake_assign);
 593
 594                 __call_scope_hooks();
 595         } else if (stmt->type == STMT_EXPRESSION) {
 596                 struct expression fake_assign;
 597
 598                 fake_assign.pos = stmt->pos;
 599                 fake_assign.op = (int)'=';
 600                 fake_assign.type = EXPR_ASSIGNMENT;
 601                 fake_assign.left = expr->left;
 602                 fake_assign.right = stmt->expression;
 603
 604                 __split_expr(&fake_assign);
 605         } else {
 606                 __split_stmt(stmt);
 607         }
 608         __expr_stmt_count--;
 609         return 1;
 610 }
 611
 612 int in_condition(void)
 613 {
 614         return inside_condition;
 615 }