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 = 0;
  13  * if (bar)
  14  *         foo = 1;
  15  *                   //  <-- point #1
  16  * else
  17  *         frob();
  18  *                   //  <-- point #2
  19  * if (foo == 1)     //  <-- point #3
  20  *         bar->baz; //  <-- point #4
  21  *
  22  * Currently (Oct 2008) in smatch when we merge bar states
  23  * null and nonnull, at point #2, the state becomes undefined.
  24  * As a result we get an error at point #3.
  25  *
  26  * The idea behind "implied state pools" is to fix that.
  27  *
  28  * The implied pools get created in merge_slist().  Whatever
  29  * is unique to one slist being merged gets put into a pool.
  30  *
  31  * If we set a state that removes it from all pools.
  32  *
  33  * When we come to an if statement where "foo" has some pools
  34  * associated we take all the pools where "foo == 1" and keep
  35  * all the states that are consistent across those pools.
  36  *
  37  * The point of doing this is to turn an undefined state into
  38  * a defined state.  This hopefully gets rid of some false positives.
  39  * What it doesn't do is find new errors that were
  40  * missed before.
  41  *
  42  * There are quite a few implementation details I haven't figured
  43  * out.  How do you create implied state pools inside a
  44  * complex condition?  How do you determine what is implied
  45  * from a complex condition?  The initial patch is extremely rudimentary...
  46  */
  47
  48 #include "smatch.h"
  49 #include "smatch_slist.h"
  50 #include "smatch_extra.h"
  51
  52 #define EQUALS 0
  53 #define NOTEQUALS 1
  54
  55 int debug_implied_states = 0;
  56 int option_no_implied = 0;
  57
  58 static int pool_in_pools(struct state_list_stack *pools,
  59                         struct state_list *pool)
  60 {
  61         struct state_list *tmp;
  62
  63         FOR_EACH_PTR(pools, tmp) {
  64                 if (tmp == pool)
  65                         return 1;
  66         } END_FOR_EACH_PTR(tmp);
  67         return 0;
  68 }
  69
  70 static struct state_list *clone_states_in_pool(struct state_list *pool,
  71                                                struct state_list *cur_slist)
  72 {
  73         struct sm_state *state;
  74         struct sm_state *cur_state;
  75         struct sm_state *tmp;
  76         struct state_list *to_slist = NULL;
  77
  78         FOR_EACH_PTR(pool, state) {
  79                 cur_state = get_sm_state_slist(cur_slist, state->name,
  80                                         state->owner, state->sym);
  81                 if (!cur_state)
  82                         continue;
  83                 if (state == cur_state)
  84                         continue;
  85                 if (pool_in_pools(cur_state->all_pools, pool)) {
  86                         tmp = clone_state(state);
  87                         add_ptr_list(&to_slist, tmp);
  88                 }
  89         } END_FOR_EACH_PTR(state);
  90         return to_slist;
  91 }
  92
  93 /*
  94  * merge_implied() takes an implied state and another possibly implied state
  95  * from another pool.  It checks that the second pool is reachable from
  96  * cur_slist then merges the two states and returns the result.
  97  */
  98 static struct sm_state *merge_implied(struct sm_state *one,
  99                                       struct sm_state *two,
 100                                       struct state_list *pool,
 101                                       struct state_list *cur_slist)
 102 {
 103         struct sm_state *cur_state;
 104
 105         cur_state = get_sm_state_slist(cur_slist, two->name, two->owner,
 106                                 two->sym);
 107         if (!cur_state)
 108                 return NULL;  /* this can't actually happen */
 109         if (!pool_in_pools(cur_state->all_pools, pool))
 110                 return NULL;
 111         return merge_sm_states(one, two);
 112 }
 113
 114 /*
 115  * filter() is used to find what states are the same across
 116  * a series of slists.
 117  * It takes a **slist and a *filter.
 118  * It removes everything from **slist that isn't in *filter.
 119  * The reason you would want to do this is if you want to
 120  * know what other states are true if one state is true.  (smatch_implied).
 121  */
 122 static void filter(struct state_list **slist, struct state_list *filter,
 123                    struct state_list *cur_slist)
 124 {
 125         struct sm_state *s_one, *s_two;
 126         struct state_list *results = NULL;
 127         struct sm_state *tmp;
 128
 129         PREPARE_PTR_LIST(*slist, s_one);
 130         PREPARE_PTR_LIST(filter, s_two);
 131         for (;;) {
 132                 if (!s_one || !s_two)
 133                         break;
 134                 if (cmp_tracker(s_one, s_two) < 0) {
 135                         DIMPLIED("removed %s\n", s_one->name);
 136                         NEXT_PTR_LIST(s_one);
 137                 } else if (cmp_tracker(s_one, s_two) == 0) {
 138                         tmp = merge_implied(s_one, s_two, filter, cur_slist);
 139                         if (tmp)
 140                                 add_ptr_list(&results, tmp);
 141                         else
 142                                 DIMPLIED("removed %s\n", s_one->name);
 143                         NEXT_PTR_LIST(s_one);
 144                         NEXT_PTR_LIST(s_two);
 145                 } else {
 146                         NEXT_PTR_LIST(s_two);
 147                 }
 148         }
 149         FINISH_PTR_LIST(s_two);
 150         FINISH_PTR_LIST(s_one);
 151
 152         free_slist(slist);
 153         *slist = results;
 154 }
 155
 156 static struct state_list *filter_stack(struct state_list_stack *stack)
 157 {
 158         struct state_list *tmp;
 159         struct state_list *ret = NULL;
 160         int i = 0;
 161
 162         FOR_EACH_PTR(stack, tmp) {
 163                 if (!i++) {
 164                         ret = clone_states_in_pool(tmp, __get_cur_slist());
 165                         if (debug_implied_states) {
 166                                 printf("The first implied pool is:\n");
 167                                 __print_slist(ret);
 168                         }
 169                 } else {
 170                         filter(&ret, tmp, __get_cur_slist());
 171                         DIMPLIED("filtered\n");
 172                 }
 173         } END_FOR_EACH_PTR(tmp);
 174         return ret;
 175 }
 176
 177 static void get_eq_neq(struct sm_state *sm_state, int comparison, int num,
 178                        int left, struct state_list **true_states,
 179                        struct state_list **false_states)
 180 {
 181         struct state_list *list;
 182         struct sm_state *s;
 183         struct state_list_stack *true_stack = NULL;
 184         struct state_list_stack *false_stack = NULL;
 185
 186         if (left)
 187                 DIMPLIED("%d checking implications: (%s %s %d)\n", get_lineno(),
 188                          sm_state->name, show_special(comparison), num);
 189         else
 190                 DIMPLIED("%d checking implications: (%d %s %s)\n", get_lineno(),
 191                          num, show_special(comparison), sm_state->name);
 192
 193         FOR_EACH_PTR(sm_state->my_pools, list) {
 194                 s = get_sm_state_slist(list, sm_state->name, sm_state->owner,
 195                                     sm_state->sym);
 196                 if (possibly_true(comparison,
 197                                   (struct data_info *)s->state->data, num,
 198                                   left)) {
 199                         DIMPLIED("'%s' from %d is true.\n", s->name, s->line);
 200                         push_slist(&true_stack, list);
 201                 }
 202                 if (possibly_false(comparison,
 203                                    (struct data_info *)s->state->data, num,
 204                                    left)) {
 205                         DIMPLIED("'%s' from %d is false.\n", s->name, s->line);
 206                         push_slist(&false_stack, list);
 207                 }
 208         } END_FOR_EACH_PTR(list);
 209         DIMPLIED("filtering true stack.\n");
 210         *true_states = filter_stack(true_stack);
 211         DIMPLIED("filtering false stack.\n");
 212         *false_states = filter_stack(false_stack);
 213         free_stack(&true_stack);
 214         free_stack(&false_stack);
 215         if (debug_implied_states || debug_states) {
 216                 printf("These are the implied states for the true path:\n");
 217                 __print_slist(*true_states);
 218                 printf("These are the implied states for the false path:\n");
 219                 __print_slist(*false_states);
 220         }
 221 }
 222
 223 static void handle_comparison(struct expression *expr,
 224                               struct state_list **implied_true,
 225                               struct state_list **implied_false)
 226 {
 227         struct symbol *sym;
 228         char *name;
 229         struct sm_state *state;
 230         int value;
 231         int left = 0;
 232
 233         value = get_value(expr->left);
 234         if (value == UNDEFINED) {
 235                 value = get_value(expr->right);
 236                 if (value == UNDEFINED)
 237                         return;
 238                 left = 1;
 239         }
 240         if (left)
 241                 name = get_variable_from_expr(expr->left, &sym);
 242         else
 243                 name = get_variable_from_expr(expr->right, &sym);
 244         if (!name || !sym) {
 245                 free_string(name);
 246                 return;
 247         }
 248         state = get_sm_state(name, SMATCH_EXTRA, sym);
 249         free_string(name);
 250         if (!state)
 251                 return;
 252         if (!state->my_pools) {
 253                 DIMPLIED("%d '%s' has no pools.\n", get_lineno(), state->name);
 254                 return;
 255         }
 256         get_eq_neq(state, expr->op, value, left, implied_true, implied_false);
 257 }
 258
 259 static void get_tf_states(struct expression *expr,
 260                           struct state_list **implied_true,
 261                           struct state_list **implied_false)
 262 {
 263         struct symbol *sym;
 264         char *name;
 265         struct sm_state *state;
 266
 267         if (expr->type == EXPR_COMPARE) {
 268                 handle_comparison(expr, implied_true, implied_false);
 269                 return;
 270         }
 271
 272         name = get_variable_from_expr(expr, &sym);
 273         if (!name || !sym) {
 274                 free_string(name);
 275                 return;
 276         }
 277         state = get_sm_state(name, SMATCH_EXTRA, sym);
 278         free_string(name);
 279         if (!state)
 280                 return;
 281         if (!state->my_pools) {
 282                 DIMPLIED("%d '%s' has no pools.\n", get_lineno(), state->name);
 283                 return;
 284         }
 285         get_eq_neq(state, SPECIAL_NOTEQUAL, 0, 1, implied_true, implied_false);
 286 }
 287
 288 static void implied_states_hook(struct expression *expr)
 289 {
 290         struct sm_state *state;
 291         struct state_list *implied_true = NULL;
 292         struct state_list *implied_false = NULL;
 293
 294         if (option_no_implied)
 295                 return;
 296
 297         get_tf_states(expr, &implied_true, &implied_false);
 298
 299         FOR_EACH_PTR(implied_true, state) {
 300                 __set_true_false_sm(state, NULL);
 301         } END_FOR_EACH_PTR(state);
 302         free_slist(&implied_true);
 303
 304         FOR_EACH_PTR(implied_false, state) {
 305                 __set_true_false_sm(NULL, state);
 306         } END_FOR_EACH_PTR(state);
 307         free_slist(&implied_false);
 308 }
 309
 310 void get_implications(char *name, struct symbol *sym, int comparison, int num,
 311                       struct state_list **true_states,
 312                       struct state_list **false_states)
 313 {
 314         struct sm_state *sm;
 315
 316         sm = get_sm_state(name, SMATCH_EXTRA, sym);
 317         if (!sm)
 318                 return;
 319         if (slist_has_state(sm->possible, &undefined))
 320                 return;
 321         get_eq_neq(sm, comparison, num, 1, true_states, false_states);
 322 }
 323
 324 void register_implications(int id)
 325 {
 326         add_hook(&implied_states_hook, CONDITION_HOOK);
 327 }