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 get to 'b', 'c' and 'd'.
  27  * 'b' is true when we reach 'c' but otherwise we don't know.
  28  *
  29  * The other thing that complicates matters is if we negate
  30  * some if conditions.
  31  * if (!a) { ...
  32  * We pass the un-negated version to the client and flip the true
  33  * and false values internally.
  34  *
  35  * And negations can be part of a compound.
  36  * if (a && !(b || c)) { d;
  37  * In that situation we multiply the negative through to simplify
  38  * stuff so that we can remove the parens like this:
  39  * if (a && !b && !c) { d;
  40  *
  41  * One other thing is that:
  42  * if ((a) != 0){ ...
  43  * that's basically the same as testing for just 'a' so we simplify
  44  * it before passing it to the script.
  45  */
  46
  47 #include "smatch.h"
  48
  49 #define KERNEL
  50
  51 static void split_conditions(struct expression *expr);
  52
  53 static int is_logical_and(struct expression *expr)
  54 {
  55         if (expr->op == SPECIAL_LOGICAL_AND)
  56                 return 1;
  57         return 0;
  58 }
  59
  60 static int handle_zero_comparisons(struct expression *expr)
  61 {
  62         struct expression *tmp = NULL;
  63
  64         // if left is zero or right is zero
  65         if (is_zero(expr->left))
  66                 tmp = expr->right;
  67         else if (is_zero(expr->right))
  68                 tmp = expr->left;
  69         else
  70                 return 0;
  71
  72         // "if (foo != 0)" is the same as "if (foo)"
  73         if (expr->op == SPECIAL_NOTEQUAL) {
  74                 split_conditions(tmp);
  75                 return 1;
  76         }
  77
  78         // "if (foo == 0)" is the same as "if (!foo)"
  79         if (expr->op == SPECIAL_EQUAL) {
  80                 split_conditions(tmp);
  81                 __negate_cond_stacks();
  82                 return 1;
  83         }
  84
  85         return 0;
  86 }
  87
  88 /*
  89  * This function is for handling calls to likely/unlikely
  90  */
  91
  92 static int ignore_builtin_expect(struct expression *expr)
  93 {
  94         if (sym_name_is("__builtin_expect", expr->fn)) {
  95                 split_conditions(first_ptr_list((struct ptr_list *) expr->args));
  96                 return 1;
  97         }
  98         if (sym_name_is("__builtin_constant_p", expr->fn)) {
  99                 split_conditions(first_ptr_list((struct ptr_list *) expr->args));
 100                 return 1;
 101         }
 102         return 0;
 103 }
 104
 105 static void handle_compound_stmt(struct statement *stmt)
 106 {
 107         struct expression *expr = NULL;
 108         struct statement *last;
 109         struct statement *s;
 110
 111         last = last_ptr_list((struct ptr_list *)stmt->stmts);
 112         if (last->type != STMT_EXPRESSION) {
 113                 last = NULL;
 114         } else {
 115                 expr = last->expression;
 116         }
 117         FOR_EACH_PTR(stmt->stmts, s) {
 118                 if (s != last)
 119                         __split_statements(s);
 120         } END_FOR_EACH_PTR(s);
 121         split_conditions(expr);
 122         return;
 123 }
 124
 125 static int handle_preop(struct expression *expr)
 126 {
 127         struct statement *stmt;
 128
 129         if (expr->op == '!') {
 130                 split_conditions(expr->unop);
 131                 __negate_cond_stacks();
 132                 return 1;
 133         }
 134         stmt = get_block_thing(expr);
 135         if (stmt) {
 136                 handle_compound_stmt(stmt);
 137                 return 1;
 138         }
 139         return 0;
 140 }
 141
 142 static void handle_logical(struct expression *expr)
 143 {
 144         /*
 145          * If we come to an "and" expr then:
 146          * We split the left side.
 147          * We keep all the current states.
 148          * We split the right side.
 149          * We keep all the states from both true sides.
 150          *
 151          * If it's an "or" expr then:
 152          * We save the current slist.
 153          * We split the left side.
 154          * We use the false states for the right side.
 155          * We split the right side.
 156          * We save all the states that are the same on both sides.
 157          */
 158
 159         split_conditions(expr->left);
 160
 161         if (is_logical_and(expr)) {
 162                 __use_cond_true_states();
 163         } else {
 164                 __use_cond_false_states();
 165         }
 166
 167         __save_pre_cond_states();
 168         __push_cond_stacks();
 169
 170         split_conditions(expr->right);
 171
 172         if (is_logical_and(expr)) {
 173                 __and_cond_states();
 174         } else {
 175                 __or_cond_states();
 176         }
 177
 178         __pop_pre_cond_states();
 179         __use_cond_true_states();
 180 }
 181
 182 static void handle_select(struct expression *expr)
 183 {
 184         /*
 185          * if ((aaa()?bbb():ccc())) { ...
 186          *
 187          * This is almost the same as:
 188          * if ((aaa() && bbb()) || (!aaa() && ccc())) { ...
 189          *
 190          * It's a bit complicated because we shouldn't pass aaa()
 191          * to the clients more than once.
 192          */
 193
 194         split_conditions(expr->conditional);
 195
 196         __save_false_states_for_later();
 197         __use_cond_true_states();
 198
 199         if (known_condition_true(expr->cond_true)) {
 200                 __split_expr(expr->cond_true);
 201         } else {
 202                 __push_cond_stacks();
 203                 split_conditions(expr->cond_true);
 204                 __and_cond_states();
 205         }
 206
 207         if (known_condition_false(expr->cond_false)) {
 208                 __pop_pre_cond_states();
 209                 __use_cond_true_states();
 210                 return;
 211         }
 212
 213         __use_previously_stored_false_states();
 214
 215         __save_pre_cond_states();
 216         __push_cond_stacks();
 217         split_conditions(expr->cond_false);
 218         __or_cond_states();
 219         __pop_pre_cond_states();
 220
 221         __use_cond_true_states();
 222 }
 223
 224 static void split_conditions(struct expression *expr)
 225 {
 226
 227         SM_DEBUG("%d in split_conditions type=%d\n", get_lineno(), expr->type);
 228
 229         expr = strip_expr(expr);
 230         if (!expr)
 231                 return;
 232
 233         switch(expr->type) {
 234         case EXPR_LOGICAL:
 235                 handle_logical(expr);
 236                 return;
 237         case EXPR_COMPARE:
 238                 if (handle_zero_comparisons(expr))
 239                         return;
 240                 break;
 241         case EXPR_CALL:
 242                 if (ignore_builtin_expect(expr))
 243                         return;
 244                 break;
 245         case EXPR_PREOP:
 246                 if (handle_preop(expr))
 247                         return;
 248                 break;
 249         case EXPR_CONDITIONAL:
 250         case EXPR_SELECT:
 251                 handle_select(expr);
 252                 return;
 253         }
 254
 255         __pass_to_client(expr, CONDITION_HOOK);
 256         __split_expr(expr);
 257 }
 258
 259 static int inside_condition;
 260 void __split_whole_condition(struct expression *expr)
 261 {
 262         SM_DEBUG("%d in __split_whole_condition\n", get_lineno());
 263         inside_condition++;
 264         __save_pre_cond_states();
 265         __push_cond_stacks();
 266         if (expr)
 267                 split_conditions(expr);
 268         __use_cond_states();
 269         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 270         inside_condition--;
 271 }
 272
 273 int in_condition()
 274 {
 275         return inside_condition;
 276 }