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 static void split_conditions(struct expression *expr);
  55
  56 static int is_logical_and(struct expression *expr)
  57 {
  58         if (expr->op == SPECIAL_LOGICAL_AND)
  59                 return 1;
  60         return 0;
  61 }
  62
  63 static int handle_zero_comparisons(struct expression *expr)
  64 {
  65         struct expression *tmp = NULL;
  66
  67         // if left is zero or right is zero
  68         if (is_zero(expr->left))
  69                 tmp = expr->right;
  70         else if (is_zero(expr->right))
  71                 tmp = expr->left;
  72         else
  73                 return 0;
  74
  75         // "if (foo != 0)" is the same as "if (foo)"
  76         if (expr->op == SPECIAL_NOTEQUAL) {
  77                 split_conditions(tmp);
  78                 return 1;
  79         }
  80
  81         // "if (foo == 0)" is the same as "if (!foo)"
  82         if (expr->op == SPECIAL_EQUAL) {
  83                 split_conditions(tmp);
  84                 __negate_cond_stacks();
  85                 return 1;
  86         }
  87
  88         return 0;
  89 }
  90
  91 /*
  92  * This function is for handling calls to likely/unlikely
  93  */
  94
  95 static int ignore_builtin_expect(struct expression *expr)
  96 {
  97         if (sym_name_is("__builtin_expect", expr->fn)) {
  98                 split_conditions(first_ptr_list((struct ptr_list *) expr->args));
  99                 return 1;
 100         }
 101         if (sym_name_is("__builtin_constant_p", expr->fn)) {
 102                 split_conditions(first_ptr_list((struct ptr_list *) expr->args));
 103                 return 1;
 104         }
 105         return 0;
 106 }
 107
 108 /*
 109  * handle_compound_stmt() is for: foo = ({blah; blah; blah; 1})
 110  */
 111
 112 static void handle_compound_stmt(struct statement *stmt)
 113 {
 114         struct expression *expr = NULL;
 115         struct statement *last;
 116         struct statement *s;
 117
 118         last = last_ptr_list((struct ptr_list *)stmt->stmts);
 119         if (last->type != STMT_EXPRESSION) {
 120                 last = NULL;
 121         } else {
 122                 expr = last->expression;
 123         }
 124         FOR_EACH_PTR(stmt->stmts, s) {
 125                 if (s != last)
 126                         __split_statements(s);
 127         } END_FOR_EACH_PTR(s);
 128         split_conditions(expr);
 129         return;
 130 }
 131
 132 static int handle_preop(struct expression *expr)
 133 {
 134         struct statement *stmt;
 135
 136         if (expr->op == '!') {
 137                 split_conditions(expr->unop);
 138                 __negate_cond_stacks();
 139                 return 1;
 140         }
 141         stmt = get_block_thing(expr);
 142         if (stmt) {
 143                 handle_compound_stmt(stmt);
 144                 return 1;
 145         }
 146         return 0;
 147 }
 148
 149 static void handle_logical(struct expression *expr)
 150 {
 151         /*
 152          * If we come to an "and" expr then:
 153          * We split the left side.
 154          * We keep all the current states.
 155          * We split the right side.
 156          * We keep all the states from both true sides.
 157          *
 158          * If it's an "or" expr then:
 159          * We save the current slist.
 160          * We split the left side.
 161          * We use the false states for the right side.
 162          * We split the right side.
 163          * We save all the states that are the same on both sides.
 164          */
 165
 166         split_conditions(expr->left);
 167
 168         if (!is_logical_and(expr))
 169                 __use_cond_false_states();
 170
 171         __push_cond_stacks();
 172
 173         __save_pre_cond_states();
 174         split_conditions(expr->right);
 175         __pop_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 void move_cur_to_tf(int tf)
 186 {
 187         struct sm_state *sm;
 188
 189         FOR_EACH_PTR(__fake_cur_slist, sm) {
 190                 if (tf)
 191                         __set_true_false_sm(sm, NULL);
 192                 else
 193                         __set_true_false_sm(NULL, sm);
 194         } END_FOR_EACH_PTR(sm);
 195         free_slist(&__fake_cur_slist);
 196 }
 197
 198
 199 /*
 200  * handle_select()
 201  * if ((aaa()?bbb():ccc())) { ...
 202  *
 203  * This is almost the same as:
 204  * if ((aaa() && bbb()) || (!aaa() && ccc())) { ...
 205  *
 206  * It's a bit complicated because we shouldn't pass aaa()
 207  * to the clients more than once.
 208  */
 209
 210 static void handle_select(struct expression *expr)
 211 {
 212         split_conditions(expr->conditional);
 213
 214         __save_false_states_for_later();
 215
 216         __fake_cur++;
 217         if (implied_condition_true(expr->cond_true)) {
 218                 __split_expr(expr->cond_true);
 219         } else {
 220                 __push_cond_stacks();
 221                 split_conditions(expr->cond_true);
 222                 __and_cond_states();
 223         }
 224         move_cur_to_tf(TRUE);
 225
 226         if (implied_condition_false(expr->cond_false)) {
 227                 __split_expr(expr->cond_false);
 228                 __pop_pre_cond_states();
 229                 move_cur_to_tf(FALSE);
 230                 __fake_cur--;
 231                 return;
 232         }
 233
 234         __use_previously_stored_false_states();
 235
 236         __save_pre_cond_states();
 237         __push_cond_stacks();
 238         split_conditions(expr->cond_false);
 239         move_cur_to_tf(FALSE);
 240         __fake_cur--;
 241         __or_cond_states();
 242         __pop_pre_cond_states();
 243
 244         __use_cond_true_states();
 245 }
 246
 247 static void split_conditions(struct expression *expr)
 248 {
 249
 250         sm_debug("%d in split_conditions type=%d\n", get_lineno(), expr->type);
 251
 252         expr = strip_expr(expr);
 253         if (!expr)
 254                 return;
 255
 256         switch (expr->type) {
 257         case EXPR_LOGICAL:
 258                 handle_logical(expr);
 259                 return;
 260         case EXPR_COMPARE:
 261                 if (handle_zero_comparisons(expr))
 262                         return;
 263                 break;
 264         case EXPR_CALL:
 265                 if (ignore_builtin_expect(expr))
 266                         return;
 267                 break;
 268         case EXPR_PREOP:
 269                 if (handle_preop(expr))
 270                         return;
 271                 break;
 272         case EXPR_CONDITIONAL:
 273         case EXPR_SELECT:
 274                 handle_select(expr);
 275                 return;
 276         }
 277
 278         /* fixme: this should be in smatch_flow.c
 279            but because of the funny stuff we do with conditions
 280            it's awkward to put it there.  We would need to
 281            call CONDITION_HOOK in smatch_flow as well.
 282         */
 283         push_expression(&big_expression_stack, expr);
 284         if (expr->type == EXPR_COMPARE) {
 285                 if (expr->left->type != EXPR_POSTOP)
 286                         __split_expr(expr->left);
 287                 if (expr->right->type != EXPR_POSTOP)
 288                         __split_expr(expr->right);
 289         } else {
 290                 __split_expr(expr);
 291         }
 292         __pass_to_client(expr, CONDITION_HOOK);
 293         if (expr->type == EXPR_COMPARE) {
 294                 if (expr->left->type == EXPR_POSTOP)
 295                         __split_expr(expr->left);
 296                 if (expr->right->type == EXPR_POSTOP)
 297                         __split_expr(expr->right);
 298         }
 299         pop_expression(&big_expression_stack);
 300 }
 301
 302 static int inside_condition;
 303 void __split_whole_condition(struct expression *expr)
 304 {
 305         sm_debug("%d in __split_whole_condition\n", get_lineno());
 306         inside_condition++;
 307         __save_pre_cond_states();
 308         __push_cond_stacks();
 309         /* it's a hack, but it's sometimes handy to have this stuff
 310            on the big_expression_stack.  */
 311         push_expression(&big_expression_stack, expr);
 312         if (expr)
 313                 split_conditions(expr);
 314         __use_cond_states();
 315         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 316         pop_expression(&big_expression_stack);
 317         inside_condition--;
 318 }
 319
 320 int __handle_condition_assigns(struct expression *expr)
 321 {
 322         struct expression *right;
 323
 324         right = strip_expr(expr->right);
 325         if (right->type != EXPR_PREOP)
 326                 return 0;
 327         if (right->op != '!')
 328                 return 0;
 329         sm_debug("%d in __handle_condition_assigns\n", get_lineno());
 330         inside_condition++;
 331         __save_pre_cond_states();
 332         __push_cond_stacks();
 333         /* it's a hack, but it's sometimes handy to have this stuff
 334            on the big_expression_stack.  */
 335         push_expression(&big_expression_stack, right);
 336         split_conditions(right);
 337         set_true_false_states_expr(SMATCH_EXTRA, expr->left, alloc_extra_state(1), alloc_extra_state(0));
 338         __use_cond_states();
 339         __pass_to_client(right, WHOLE_CONDITION_HOOK);
 340         pop_expression(&big_expression_stack);
 341         inside_condition--;
 342
 343         __push_true_states();
 344         __use_false_states();
 345         __merge_true_states();
 346         return 1;
 347 }
 348
 349 int in_condition(void)
 350 {
 351         return inside_condition;
 352 }