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 int __ors = 0;
  52 int __ands = 0;
  53
  54 static int negative = 0;
  55 int __negate()
  56 {
  57         return negative;
  58 }
  59
  60 static void split_conditions(struct expression *expr);
  61
  62 static int is_logical_and(struct expression *expr)
  63 {
  64         /* If you have if (!(a && b)) smatch translates that to
  65          * if (!a || !b).  Logically those are the same.
  66          */
  67
  68         if ((!__negate() && expr->op == SPECIAL_LOGICAL_AND) ||
  69             (__negate() && expr->op == SPECIAL_LOGICAL_OR))
  70                 return 1;
  71         return 0;
  72 }
  73
  74 static int is_logical_or(struct expression *expr)
  75 {
  76         if ((!__negate() && expr->op == SPECIAL_LOGICAL_OR) ||
  77              (__negate() && expr->op == SPECIAL_LOGICAL_AND))
  78                 return 1;
  79         return 0;
  80 }
  81
  82 static void inc_ands_ors(struct expression *expr)
  83 {
  84         if (is_logical_and(expr))
  85                 __ands++;
  86         else if (is_logical_or(expr))
  87                 __ors++;
  88 }
  89
  90 static void dec_ands_ors(struct expression *expr)
  91 {
  92         if (is_logical_and(expr))
  93                 __ands--;
  94         else if (is_logical_or(expr))
  95                 __ors--;
  96 }
  97
  98 static void special_kernel_macros(struct expression *expr)
  99 {
 100 #ifdef KERNEL
 101         struct expression *tmp;
 102
 103         tmp = first_ptr_list((struct ptr_list *) expr->args);
 104         if (tmp->op == '!' && tmp->unop->op == '!'
 105             && tmp->unop->unop->op == '(') {
 106                 split_conditions(tmp->unop->unop->unop);
 107         } else {
 108                 __pass_to_client(expr, CONDITION_HOOK);
 109                 __split_expr(expr);
 110                 return;
 111         }
 112
 113 #endif
 114 }
 115
 116 static int is_zero(struct expression *expr)
 117 {
 118         if (expr->type == EXPR_VALUE && expr->value == 0)
 119                 return 1;
 120         if (expr->op == '(')
 121                 return is_zero(expr->unop);
 122         if (expr->type == EXPR_CAST)
 123                 return is_zero(expr->cast_expression);
 124         return 0;
 125 }
 126
 127 static int handle_zero_comparisons(struct expression *expr)
 128 {
 129         struct expression *tmp = NULL;
 130
 131         // if left is zero or right is zero
 132         if (is_zero(expr->left))
 133                 tmp = expr->right;
 134         else if (is_zero(expr->right))
 135                 tmp = expr->left;
 136         else
 137                 return 0;
 138
 139         // "if (foo != 0)" is the same as "if (foo)"
 140         if (expr->op == SPECIAL_NOTEQUAL) {
 141                 split_conditions(tmp);
 142                 return 1;
 143         }
 144
 145         // "if (foo == 0)" is the same as "if (!foo)"
 146         if (expr->op == SPECIAL_EQUAL) {
 147                 negative = (negative +  1)%2;
 148                 split_conditions(tmp);
 149                 negative = (negative +  1)%2;
 150                 return 1;
 151         }
 152
 153         return 0;
 154 }
 155
 156 static void split_conditions(struct expression *expr)
 157 {
 158         static int __ors_reached;
 159
 160         SM_DEBUG("%d in split_conditions type=%d\n", get_lineno(), expr->type);
 161
 162         if (expr->type == EXPR_COMPARE)
 163                 if (handle_zero_comparisons(expr))
 164                         return;
 165
 166         if (expr->type == EXPR_LOGICAL) {
 167                 inc_ands_ors(expr);
 168                 __split_false_states_mini();
 169
 170                 split_conditions(expr->left);
 171
 172                 if (is_logical_and(expr)) {
 173                         __pop_false_states_mini();
 174                         split_conditions(expr->right);
 175                 } else if (is_logical_or(expr)) {
 176                         if (!__ors_reached) {
 177                                 __ors_reached = 1;
 178                                 __first_and_clump();
 179                         } else {
 180                                 __merge_and_clump();
 181                         }
 182                         __use_false_states_mini();
 183                         split_conditions(expr->right);
 184                 }
 185                 dec_ands_ors(expr);
 186
 187                 if (__ands + __ors == 0) {
 188                         __merge_and_clump();
 189                         __use_and_clumps();
 190                         __ors_reached = 0;
 191                 }
 192
 193                 return;
 194         } else if (expr->type == EXPR_PREOP && expr->op == '!') {
 195                 negative = (negative +  1)%2;
 196                 split_conditions(expr->unop);
 197                 negative = (negative +  1)%2;
 198                 return;
 199         } else if (expr->type == EXPR_PREOP && expr->op == '(') {
 200                 split_conditions(expr->unop);
 201         } else if (expr->type == EXPR_CALL) {
 202
 203                 if (expr->fn->type != EXPR_SYMBOL ||
 204                     strcmp("__builtin_expect", expr->fn->symbol_name->name)) {
 205                         __pass_to_client(expr, CONDITION_HOOK);
 206                         __split_expr(expr);
 207                         return;
 208                 }
 209                 special_kernel_macros(expr);
 210         } else {
 211                 __pass_to_client(expr, CONDITION_HOOK);
 212                 __split_expr(expr);
 213         }
 214 }
 215
 216 void __split_whole_condition(struct expression *expr)
 217 {
 218
 219         __pass_to_client(expr, WHOLE_CONDITION_HOOK);
 220         split_conditions(expr);
 221         SM_DEBUG("%d __ands = %d __ors = %d __negate() = %d\n", get_lineno(),
 222                  __ands, __ors, __negate());
 223 }