check_signed.c

   1 /*
   2  * sparse/check_signed.c
   3  *
   4  * Copyright (C) 2009 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * Check for things which are signed but probably should be unsigned.
  12  *
  13  * Hm...  It seems like at this point in the processing, sparse makes all
  14  * bitfields unsigned.  Which is logical but not what GCC does.
  15  *
  16  */
  17
  18 #include "smatch.h"
  19
  20 static int my_id;
  21
  22 #define VAR_ON_RIGHT 0
  23 #define VAR_ON_LEFT 1
  24
  25 static long long eqneq_max(struct symbol *base_type)
  26 {
  27         long long ret = whole_range.max;
  28         int bits;
  29
  30         if (!base_type || !base_type->bit_size)
  31                 return ret;
  32         bits = base_type->bit_size;
  33         if (bits == 64)
  34                 return ret;
  35         if (bits < 32)
  36                 return type_max(base_type);
  37         ret >>= (63 - bits);
  38         return ret;
  39 }
  40
  41 static long long eqneq_min(struct symbol *base_type)
  42 {
  43         long long ret = whole_range.min;
  44         int bits;
  45
  46         if (!base_type || !base_type->bit_size)
  47                 return ret;
  48         if (base_type->bit_size < 32)
  49                 return type_min(base_type);
  50         ret = whole_range.max;
  51         bits = base_type->bit_size - 1;
  52         ret >>= (63 - bits);
  53         return -(ret + 1);
  54 }
  55
  56 static void match_assign(struct expression *expr)
  57 {
  58         struct symbol *sym;
  59         long long val;
  60         long long max;
  61         long long min;
  62         char *name;
  63
  64         if (expr->op == SPECIAL_AND_ASSIGN || expr->op == SPECIAL_OR_ASSIGN)
  65                 return;
  66
  67         sym = get_type(expr->left);
  68         if (!sym) {
  69                 //sm_msg("could not get type");
  70                 return;
  71         }
  72         if (sym->bit_size >= 32) /* max_val limits this */
  73                 return;
  74         if (!get_implied_value(expr->right, &val))
  75                 return;
  76         max = type_max(sym);
  77         if (max < val && !(val < 256 && max == 127)) {
  78                 name = get_variable_from_expr_complex(expr->left, NULL);
  79                 sm_msg("warn: value %lld can't fit into %lld '%s'", val, max, name);
  80                 free_string(name);
  81         }
  82         min = type_min(sym);
  83         if (min > val) {
  84                 if (min == 0 && val == -1) /* assigning -1 to unsigned variables is idiomatic */
  85                         return;
  86                 if (expr->right->type == EXPR_PREOP && expr->right->op == '~')
  87                         return;
  88                 if (expr->op == SPECIAL_SUB_ASSIGN || expr->op == SPECIAL_ADD_ASSIGN)
  89                         return;
  90                 name = get_variable_from_expr_complex(expr->left, NULL);
  91                 if (min == 0)
  92                         sm_msg("warn: assigning %lld to unsigned variable '%s'", val, name);
  93                 else
  94                         sm_msg("warn: value %lld can't fit into %lld '%s'", val, min, name);
  95                 free_string(name);
  96         }
  97
  98 }
  99
 100 static const char *get_tf(long long variable, long long known, int var_pos, int op)
 101 {
 102         if (op == SPECIAL_EQUAL)
 103                 return "false";
 104         if (op == SPECIAL_NOTEQUAL)
 105                 return "true";
 106         if (var_pos == VAR_ON_LEFT) {
 107                 if (variable > known && (op == '<' || op == SPECIAL_LTE))
 108                         return "false";
 109                 if (variable > known && (op == '>' || op == SPECIAL_GTE))
 110                         return "true";
 111                 if (variable < known && (op == '<' || op == SPECIAL_LTE))
 112                         return "true";
 113                 if (variable < known && (op == '>' || op == SPECIAL_GTE))
 114                         return "false";
 115         }
 116         if (var_pos == VAR_ON_RIGHT) {
 117                 if (known > variable && (op == '<' || op == SPECIAL_LTE))
 118                         return "false";
 119                 if (known > variable && (op == '>' || op == SPECIAL_GTE))
 120                         return "true";
 121                 if (known < variable && (op == '<' || op == SPECIAL_LTE))
 122                         return "true";
 123                 if (known < variable && (op == '>' || op == SPECIAL_GTE))
 124                         return "false";
 125         }
 126         return "the same";
 127 }
 128
 129 static void match_condition(struct expression *expr)
 130 {
 131         long long known;
 132         struct expression *var = NULL;
 133         struct symbol *var_type = NULL;
 134         struct symbol *known_type = NULL;
 135         long long max;
 136         long long min;
 137         int lr;
 138         char *name;
 139
 140         if (expr->type != EXPR_COMPARE)
 141                 return;
 142
 143         if (get_value(expr->left, &known)) {
 144                 if (get_value(expr->right, &max))
 145                         return; /* both sides known */
 146                 lr = VAR_ON_RIGHT;
 147                 var = expr->right;
 148                 known_type = get_type(expr->left);
 149         } else if (get_value(expr->right, &known)) {
 150                 lr = VAR_ON_LEFT;
 151                 var = expr->left;
 152                 known_type = get_type(expr->right);
 153         } else {
 154                 return;
 155         }
 156
 157         var_type = get_type(var);
 158         if (!var_type)
 159                 return;
 160         if (var_type->bit_size >= 32 && !option_spammy)
 161                 return;
 162
 163         name = get_variable_from_expr_complex(var, NULL);
 164
 165         if (expr->op == SPECIAL_EQUAL || expr->op == SPECIAL_NOTEQUAL) {
 166                 if (eqneq_max(var_type) < known || eqneq_min(var_type) > known)
 167                         sm_msg("error: %s is never equal to %lld (wrong type %lld - %lld).",
 168                                 name, known, eqneq_min(var_type), eqneq_max(var_type));
 169                 goto free;
 170         }
 171
 172         max = type_max(var_type);
 173         min = type_min(var_type);
 174
 175         if (max < known) {
 176                 const char *tf = get_tf(max, known, lr, expr->op);
 177
 178                 sm_msg("warn: %lld is more than %lld (max '%s' can be) so this is always %s.",
 179                         known, max, name, tf);
 180         }
 181
 182         if (known == 0 && type_unsigned(var_type)) {
 183                 if ((lr && expr->op == '<') || (!lr && expr->op == '>'))
 184                         sm_msg("warn: unsigned '%s' is never less than zero.", name);
 185                 goto free;
 186         }
 187
 188         if (type_unsigned(var_type) && known_type && !type_unsigned(known_type) && known < 0) {
 189                 sm_msg("warn: unsigned '%s' is never less than zero (%lld).", name, known);
 190                 goto free;
 191         }
 192
 193         if (min < 0 && min > known) {
 194                 const char *tf = get_tf(min, known, lr, expr->op);
 195
 196                 sm_msg("warn: %lld is less than %lld (min '%s' can be) so this is always %s.",
 197                         known, min, name, tf);
 198         }
 199 free:
 200         free_string(name);
 201 }
 202
 203 void check_signed(int id)
 204 {
 205         my_id = id;
 206
 207         add_hook(&match_assign, ASSIGNMENT_HOOK);
 208         add_hook(&match_condition, CONDITION_HOOK);
 209 }