smatch_implied.c

   1 /*
   2  * sparse/smatch_implied.c
   3  *
   4  * Copyright (C) 2008 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * Imagine we have this code:
  12  * foo = 1;
  13  * if (bar)
  14  *         foo = 99;
  15  * else
  16  *         frob();
  17  *                   //  <-- point #1
  18  * if (foo == 99)    //  <-- point #2
  19  *         bar->baz; //  <-- point #3
  20  *
  21  *
  22  * At point #3 bar is non null and can be dereferenced.
  23  *
  24  * It's smatch_implied.c which sets bar to non null at point #2.
  25  *
  26  * At point #1 merge_slist() stores the list of states from both
  27  * the true and false paths.  On the true path foo == 99 and on
  28  * the false path foo == 1.  merge_slist() sets their my_pools
  29  * list to show the other states which were there when foo == 99.
  30  *
  31  * When it comes to the if (foo == 99) the smatch implied hook
  32  * looks for all the pools where foo was not 99.  It makes a list
  33  * of those.
  34  *
  35  * Then for bar (and all the other states) it says, ok bar is a
  36  * merged state that came from these previous states.  We'll
  37  * chop out all the states where it came from a pool where
  38  * foo != 99 and merge it all back together.
  39  *
  40  * That is the implied state of bar.
  41  *
  42  * merge_slist() sets up ->my_pools.
  43  * merge_sm_state() sets ->pre_merge.
  44  * If an sm_state is not the same on both sides of a merge, it
  45  *    gets a ->my_pool set for both sides.  The result is a merged
  46  *    state that has it's ->pre_merge pointers set.  Merged states
  47  *    do not immediately have any my_pools set, but maybe will later
  48  *    when they themselves are merged.
  49  * A pool is a list of all the states that were set at the time.
  50  */
  51
  52 #include "smatch.h"
  53 #include "smatch_slist.h"
  54 #include "smatch_extra.h"
  55
  56 int debug_implied_states = 0;
  57 int option_no_implied = 0;
  58
  59 static int pools_overlap(struct state_list_stack *pools1,
  60                         struct state_list_stack *pools2)
  61 {
  62         struct state_list *one;
  63         struct state_list *two;
  64
  65         PREPARE_PTR_LIST(pools1, one);
  66         PREPARE_PTR_LIST(pools2, two);
  67         for (;;) {
  68                 if (!one || !two)
  69                         return 0;
  70
  71                 if (one < two) {
  72                         NEXT_PTR_LIST(one);
  73                 } else if (one == two) {
  74                         return 1;
  75                 } else {
  76                         NEXT_PTR_LIST(two);
  77                 }
  78         }
  79         FINISH_PTR_LIST(two);
  80         FINISH_PTR_LIST(one);
  81         return 0;
  82 }
  83
  84 struct sm_state *remove_my_pools(struct sm_state *sm,
  85                                 struct state_list_stack *pools, int *modified)
  86 {
  87         struct sm_state *ret = NULL;
  88         struct sm_state *pre;
  89         struct sm_state *tmp_keep;
  90         struct state_list *keep = NULL;
  91
  92         if (pools_overlap(sm->my_pools, pools)) {
  93                 DIMPLIED("removed %s = %s from %d\n", sm->name,
  94                         show_state(sm->state), sm->line);
  95                 *modified = 1;
  96                 return NULL;
  97         }
  98
  99         if (is_merged(sm)) {
 100                 int removed = 0;
 101
 102                 DIMPLIED("checking %s = %s from %d\n", sm->name,
 103                         show_state(sm->state), sm->line);
 104                 FOR_EACH_PTR(sm->pre_merge, pre) {
 105                         tmp_keep = remove_my_pools(pre, pools, &removed);
 106                         if (tmp_keep)
 107                                 add_ptr_list(&keep, tmp_keep);
 108                 } END_FOR_EACH_PTR(pre);
 109                 if (!removed) {
 110                         DIMPLIED("kept %s = %s from %d\n", sm->name, show_state(sm->state), sm->line);
 111                         return sm;
 112                 }
 113                 *modified = 1;
 114                 if (!keep) {
 115                         DIMPLIED("removed %s = %s from %d\n", sm->name, show_state(sm->state), sm->line);
 116                         return NULL;
 117                 }
 118
 119                 FOR_EACH_PTR(keep, tmp_keep) {
 120                         if (!ret)
 121                                 ret = tmp_keep;
 122                         else
 123                                 ret = merge_sm_states(ret, tmp_keep);
 124                 } END_FOR_EACH_PTR(tmp_keep);
 125                 merge_pools(&ret->my_pools, sm->my_pools);
 126                 DIMPLIED("partial %s = %s from %d\n", sm->name, show_state(sm->state), sm->line);
 127                 return ret;
 128         }
 129         DIMPLIED("kept %s = %s from %d\n", sm->name, show_state(sm->state),
 130                 sm->line);
 131         return sm;
 132 }
 133
 134 static struct state_list *filter_stack(struct state_list *pre_list,
 135                                 struct state_list_stack *stack)
 136 {
 137         struct state_list *ret = NULL;
 138         struct sm_state *tmp;
 139         struct sm_state *filtered_state;
 140         int modified = 0;
 141
 142         if (!stack)
 143                 return NULL;
 144
 145         FOR_EACH_PTR(pre_list, tmp) {
 146                 filtered_state = remove_my_pools(tmp, stack, &modified);
 147                 if (filtered_state && modified)
 148                         add_ptr_list(&ret, filtered_state);
 149         } END_FOR_EACH_PTR(tmp);
 150         return ret;
 151 }
 152
 153 static void separate_pools(struct sm_state *sm_state, int comparison, int num,
 154                 int left,
 155                 struct state_list_stack **true_stack,
 156                 struct state_list_stack **false_stack)
 157 {
 158         struct state_list *list;
 159         struct sm_state *s;
 160         int istrue, isfalse;
 161
 162         FOR_EACH_PTR(sm_state->my_pools, list) {
 163                 s = get_sm_state_slist(list, sm_state->name, sm_state->owner,
 164                                     sm_state->sym);
 165                 istrue = !possibly_false(comparison,
 166                                        (struct data_info *)s->state->data, num,
 167                                        left);
 168                 isfalse = !possibly_true(comparison,
 169                                          (struct data_info *)s->state->data,
 170                                          num, left);
 171                 if (debug_implied_states || debug_states) {
 172                         if (istrue && isfalse) {
 173                                 printf("'%s = %s' from %d does not exist.\n",
 174                                          s->name, show_state(s->state),
 175                                          s->line);
 176                         } else if (istrue) {
 177                                 printf("'%s = %s' from %d is true. %p\n",
 178                                         s->name, show_state(s->state),
 179                                         s->line, list);
 180                         } else if (isfalse) {
 181                                 printf("'%s = %s' from %d is false. %p\n",
 182                                         s->name, show_state(s->state),
 183                                         s->line, list);
 184                         } else {
 185                                 printf("'%s = %s' from %d could be true or "
 186                                          "false.\n", s->name,
 187                                          show_state(s->state), s->line);
 188                         }
 189                 }
 190                 if (istrue) {
 191                         add_pool(true_stack, list);
 192                 }
 193                 if (isfalse) {
 194                         add_pool(false_stack, list);
 195                 }
 196         } END_FOR_EACH_PTR(list);
 197         FOR_EACH_PTR(sm_state->pre_merge, s) {
 198                 separate_pools(s, comparison, num, left, true_stack, false_stack);
 199         } END_FOR_EACH_PTR(s);
 200 }
 201
 202 static void get_eq_neq(struct sm_state *sm_state, int comparison, int num,
 203                 int left,
 204                 struct state_list *pre_list,
 205                 struct state_list **true_states,
 206                 struct state_list **false_states)
 207 {
 208         struct state_list_stack *true_stack = NULL;
 209         struct state_list_stack *false_stack = NULL;
 210
 211         if (debug_implied_states || debug_states) {
 212                 if (left)
 213                         smatch_msg("checking implications: (%s %s %d)",
 214                                 sm_state->name, show_special(comparison), num);
 215                 else
 216                         smatch_msg("checking implications: (%d %s %s)",
 217                                 num, show_special(comparison), sm_state->name);
 218         }
 219
 220         separate_pools(sm_state, comparison, num, left, &true_stack, &false_stack);
 221
 222         DIMPLIED("filtering true stack.\n");
 223         *true_states = filter_stack(pre_list, false_stack);
 224         DIMPLIED("filtering false stack.\n");
 225         *false_states = filter_stack(pre_list, true_stack);
 226         free_stack(&true_stack);
 227         free_stack(&false_stack);
 228         if (debug_implied_states || debug_states) {
 229                 printf("These are the implied states for the true path:\n");
 230                 __print_slist(*true_states);
 231                 printf("These are the implied states for the false path:\n");
 232                 __print_slist(*false_states);
 233         }
 234 }
 235
 236 static char *get_implication_variable(struct expression *expr, struct symbol **symp)
 237 {
 238         expr = strip_expr(expr);
 239         if (expr->type == EXPR_ASSIGNMENT)
 240                 return get_implication_variable(expr->left, symp);
 241         return get_variable_from_expr(expr, symp);
 242 }
 243
 244 static void handle_comparison(struct expression *expr,
 245                               struct state_list **implied_true,
 246                               struct state_list **implied_false)
 247 {
 248         struct symbol *sym;
 249         char *name;
 250         struct sm_state *state;
 251         int value;
 252         int left = 0;
 253
 254         value = get_value(expr->left);
 255         if (value == UNDEFINED) {
 256                 value = get_value(expr->right);
 257                 if (value == UNDEFINED)
 258                         return;
 259                 left = 1;
 260         }
 261         if (left)
 262                 name = get_implication_variable(expr->left, &sym);
 263         else
 264                 name = get_implication_variable(expr->right, &sym);
 265         if (!name || !sym)
 266                 goto free;
 267         state = get_sm_state(name, SMATCH_EXTRA, sym);
 268         if (!state)
 269                 goto free;
 270         if (!is_merged(state)) {
 271                 DIMPLIED("%d '%s' is not merged.\n", get_lineno(), state->name);
 272                 goto free;
 273         }
 274         get_eq_neq(state, expr->op, value, left, __get_cur_slist(), implied_true, implied_false);
 275         delete_state_slist(implied_true, name, SMATCH_EXTRA, sym);
 276         delete_state_slist(implied_false, name, SMATCH_EXTRA, sym);
 277 free:
 278         free_string(name);
 279 }
 280
 281 static void get_tf_states(struct expression *expr,
 282                           struct state_list **implied_true,
 283                           struct state_list **implied_false)
 284 {
 285         struct symbol *sym;
 286         char *name;
 287         struct sm_state *state;
 288
 289         if (expr->type == EXPR_COMPARE) {
 290                 handle_comparison(expr, implied_true, implied_false);
 291                 return;
 292         }
 293         if (expr->type == EXPR_ASSIGNMENT) {
 294                 /* most of the time ->my_pools will be empty here because we
 295                    just set the state, but if have assigned a conditional
 296                    function there are implications. */
 297                 expr = expr->left;
 298         }
 299
 300         name = get_variable_from_expr(expr, &sym);
 301         if (!name || !sym)
 302                 goto free;
 303         state = get_sm_state(name, SMATCH_EXTRA, sym);
 304         if (!state)
 305                 goto free;
 306         if (!is_merged(state)) {
 307                 DIMPLIED("%d '%s' has no pools.\n", get_lineno(), state->name);
 308                 goto free;
 309         }
 310         get_eq_neq(state, SPECIAL_NOTEQUAL, 0, 1, __get_cur_slist(), implied_true, implied_false);
 311         delete_state_slist(implied_true, name, SMATCH_EXTRA, sym);
 312         delete_state_slist(implied_false, name, SMATCH_EXTRA, sym);
 313 free:
 314         free_string(name);
 315 }
 316
 317 static void implied_states_hook(struct expression *expr)
 318 {
 319         struct sm_state *state;
 320         struct sm_state *clone;
 321         struct state_list *implied_true = NULL;
 322         struct state_list *implied_false = NULL;
 323
 324         if (option_no_implied)
 325                 return;
 326
 327         get_tf_states(expr, &implied_true, &implied_false);
 328
 329         FOR_EACH_PTR(implied_true, state) {
 330                 clone = clone_state(state);
 331                 __set_true_false_sm(clone, NULL);
 332         } END_FOR_EACH_PTR(state);
 333         free_slist(&implied_true);
 334
 335         FOR_EACH_PTR(implied_false, state) {
 336                 clone = clone_state(state);
 337                 __set_true_false_sm(NULL, clone);
 338         } END_FOR_EACH_PTR(state);
 339         free_slist(&implied_false);
 340 }
 341
 342 void get_implications(char *name, struct symbol *sym, int comparison, int num,
 343                       struct state_list **true_states,
 344                       struct state_list **false_states)
 345 {
 346         struct sm_state *sm;
 347
 348         sm = get_sm_state(name, SMATCH_EXTRA, sym);
 349         if (!sm)
 350                 return;
 351         if (slist_has_state(sm->possible, &undefined))
 352                 return;
 353         get_eq_neq(sm, comparison, num, 1, __get_cur_slist(), true_states, false_states);
 354 }
 355
 356 struct state_list *__implied_case_slist(struct expression *switch_expr,
 357                                         struct expression *case_expr,
 358                                         struct state_list **raw_slist)
 359 {
 360         char *name = NULL;
 361         struct symbol *sym;
 362         struct sm_state *sm;
 363         struct sm_state *true_sm;
 364         struct sm_state *false_sm;
 365         struct state_list *true_states = NULL;
 366         struct state_list *false_states = NULL;
 367         struct state_list *ret = clone_slist(*raw_slist);
 368         long long val;
 369
 370         if (!case_expr)
 371                 return ret;
 372         name = get_variable_from_expr(switch_expr, &sym);
 373         if (!name || !sym)
 374                 goto free;
 375         sm = get_sm_state_slist(*raw_slist, name, SMATCH_EXTRA, sym);
 376         val = get_value(case_expr);
 377         if (val == UNDEFINED)
 378                 goto free;
 379         if (sm) {
 380                 get_eq_neq(sm, SPECIAL_EQUAL, val, 1, *raw_slist, &true_states, &false_states);
 381         }
 382
 383         true_sm = get_sm_state_slist(true_states, name, SMATCH_EXTRA, sym);
 384         if (!true_sm)
 385                 set_state_slist(&true_states, name, SMATCH_EXTRA, sym, alloc_extra_state(val));
 386         false_sm = get_sm_state_slist(false_states, name, SMATCH_EXTRA, sym);
 387         if (!false_sm)
 388                 set_state_slist(&false_states, name, SMATCH_EXTRA, sym, add_filter(sm?sm->state:NULL, val));
 389         overwrite_slist(false_states, raw_slist);
 390         overwrite_slist(true_states, &ret);
 391         free_slist(&true_states);
 392         free_slist(&false_states);
 393 free:
 394         free_string(name);
 395         return ret;
 396 }
 397
 398 void __extra_match_condition(struct expression *expr);
 399 void register_implications(int id)
 400 {
 401         add_hook(&implied_states_hook, CONDITION_HOOK);
 402         add_hook(&__extra_match_condition, CONDITION_HOOK);
 403 }