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         return 0;
  99 }
 100
 101 static int handle_preop(struct expression *expr)
 102 {
 103         if (expr->op == '!') {
 104                 split_conditions(expr->unop);
 105                 __negate_cond_stacks();
 106                 return 1;
 107         }
 108         if (expr->op == '(') {
 109                 split_conditions(expr->unop);
 110                 return 1;
 111         }
 112         return 0;
 113 }
 114
 115 static void handle_logical(struct expression *expr)
 116 {
 117         /*
 118          * If we come to an "and" expr then:
 119          * We split the left side.
 120          * We keep all the current states.
 121          * We split the right side.
 122          * We keep all the states from both true sides.
 123          *
 124          * If it's an "or" expr then:
 125          * We save the current slist.
 126          * We split the left side.
 127          * We use the false states for the right side.
 128          * We split the right side.
 129          * We save all the states that are the same on both sides.
 130          */
 131
 132         split_conditions(expr->left);
 133
 134         if (is_logical_and(expr)) {
 135                 __use_cond_true_states();
 136         } else {
 137                 __use_cond_false_states();
 138         }
 139
 140         __save_pre_cond_states();
 141         __push_cond_stacks();
 142
 143         split_conditions(expr->right);
 144
 145         if (is_logical_and(expr)) {
 146                 __and_cond_states();
 147         } else {
 148                 __or_cond_states();
 149         }
 150
 151         __pop_pre_cond_states();
 152         __use_cond_true_states();
 153 }
 154
 155 static void split_conditions(struct expression *expr)
 156 {
 157
 158         SM_DEBUG("%d in split_conditions type=%d\n", get_lineno(), expr->type);
 159
 160         switch(expr->type) {
 161         case EXPR_LOGICAL:
 162                 handle_logical(expr);
 163                 return;
 164         case EXPR_COMPARE:
 165                 if (handle_zero_comparisons(expr))
 166                         return;
 167                 break;
 168         case EXPR_CALL:
 169                 if (ignore_builtin_expect(expr))
 170                         return;
 171                 break;
 172         case EXPR_PREOP:
 173                 if (handle_preop(expr))
 174                         return;
 175                 break;
 176         }
 177
 178         __pass_to_client(expr, CONDITION_HOOK);
 179         __split_expr(expr);
 180 }
 181
 182 void __split_whole_condition(struct expression *expr)
 183 {
 184         SM_DEBUG("%d in __split_whole_condition\n", get_lineno());
 185         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 186         __save_pre_cond_states();
 187         __push_cond_stacks();
 188         if (expr)
 189                 split_conditions(expr);
 190         __use_cond_states();
 191 }