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 void match_assign(struct expression *expr)
  26 {
  27         struct symbol *sym;
  28         sval_t sval;
  29         sval_t max;
  30         sval_t min;
  31         char *name;
  32
  33         if (expr->op == SPECIAL_AND_ASSIGN || expr->op == SPECIAL_OR_ASSIGN)
  34                 return;
  35
  36         sym = get_type(expr->left);
  37         if (!sym) {
  38                 //sm_msg("could not get type");
  39                 return;
  40         }
  41         if (sym->bit_size >= 32) /* max_val limits this */
  42                 return;
  43         if (!get_implied_value_sval(expr->right, &sval))
  44                 return;
  45         max = sval_type_max(sym);
  46         if (sval_cmp(max, sval) < 0 && !(sval.value < 256 && max.value == 127)) {
  47                 name = get_variable_from_expr_complex(expr->left, NULL);
  48                 sm_msg("warn: value %s can't fit into %s '%s'",
  49                        sval_to_str(sval), sval_to_str(max), name);
  50                 free_string(name);
  51         }
  52         min = sval_type_min(sym);
  53         if (sval_cmp(min, sval) > 0) {
  54                 if (min.value == 0 && sval.value == -1) /* assigning -1 to unsigned variables is idiomatic */
  55                         return;
  56                 if (expr->right->type == EXPR_PREOP && expr->right->op == '~')
  57                         return;
  58                 if (expr->op == SPECIAL_SUB_ASSIGN || expr->op == SPECIAL_ADD_ASSIGN)
  59                         return;
  60                 name = get_variable_from_expr_complex(expr->left, NULL);
  61                 if (min.value == 0) {
  62                         sm_msg("warn: assigning %s to unsigned variable '%s'",
  63                                sval_to_str(sval), name);
  64                 } else {
  65                         sm_msg("warn: value %s can't fit into %s '%s'",
  66                                sval_to_str(sval), sval_to_str(min), name);
  67                 }
  68                 free_string(name);
  69         }
  70 }
  71
  72 static const char *get_tf(sval_t variable, sval_t known, int var_pos, int op)
  73 {
  74         if (op == SPECIAL_EQUAL)
  75                 return "false";
  76         if (op == SPECIAL_NOTEQUAL)
  77                 return "true";
  78         if (var_pos == VAR_ON_LEFT) {
  79                 if (sval_cmp(variable, known) > 0 && (op == '<' || op == SPECIAL_LTE))
  80                         return "false";
  81                 if (sval_cmp(variable, known) > 0 && (op == '>' || op == SPECIAL_GTE))
  82                         return "true";
  83                 if (sval_cmp(variable, known) < 0 && (op == '<' || op == SPECIAL_LTE))
  84                         return "true";
  85                 if (sval_cmp(variable, known) < 0 && (op == '>' || op == SPECIAL_GTE))
  86                         return "false";
  87         }
  88         if (var_pos == VAR_ON_RIGHT) {
  89                 if (sval_cmp(known, variable) > 0 && (op == '<' || op == SPECIAL_LTE))
  90                         return "false";
  91                 if (sval_cmp(known, variable) > 0 && (op == '>' || op == SPECIAL_GTE))
  92                         return "true";
  93                 if (sval_cmp(known, variable) < 0 && (op == '<' || op == SPECIAL_LTE))
  94                         return "true";
  95                 if (sval_cmp(known, variable) < 0 && (op == '>' || op == SPECIAL_GTE))
  96                         return "false";
  97         }
  98         return "the same";
  99 }
 100
 101 static int compare_against_macro(int lr, struct expression *expr)
 102 {
 103         struct expression *known = expr->left;
 104
 105         if (lr == VAR_ON_LEFT)
 106                 known = expr->right;
 107
 108         return !!get_macro_name(known->pos);
 109 }
 110
 111 static int cap_both_size(int lr, struct expression *expr)
 112 {
 113
 114         struct expression *var = expr->left;
 115         struct expression *tmp;
 116         char *name1 = NULL;
 117         char *name2 = NULL;
 118         int ret = 0;
 119         int i;
 120
 121         /* screw it.  I am writing this to mark yoda code as buggy.
 122          * Valid comparisons between an unsigned and zero are:
 123          * 1) inside a macro.
 124          * 2) foo < LOWER_BOUND where LOWER_BOUND is a macro.
 125          * 3) foo < 0 || foo > X in exactly this format.  No Yoda.
 126          */
 127
 128         if (lr != VAR_ON_LEFT)
 129                 return 0;
 130         if (expr->op != '<' && expr->op != SPECIAL_UNSIGNED_LT)
 131                 return 0;
 132
 133         i = 0;
 134         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 135                 if (!i++)
 136                         continue;
 137                 if (tmp->op == SPECIAL_LOGICAL_OR) {
 138                         struct expression *right = strip_expr(tmp->right);
 139
 140                         if (right->op != '>' &&
 141                             right->op != SPECIAL_UNSIGNED_GT &&
 142                             right->op != SPECIAL_GTE &&
 143                             right->op != SPECIAL_UNSIGNED_GTE)
 144                                 return 0;
 145
 146                         name1 = get_variable_from_expr_complex(var, NULL);
 147                         if (!name1)
 148                                 goto free;
 149
 150                         name2 = get_variable_from_expr_complex(right->left, NULL);
 151                         if (!name2)
 152                                 goto free;
 153                         if (!strcmp(name1, name2))
 154                                 ret = 1;
 155                         goto free;
 156
 157                 }
 158                 return 0;
 159         } END_FOR_EACH_PTR_REVERSE(tmp);
 160
 161 free:
 162         free_string(name1);
 163         free_string(name2);
 164         return ret;
 165 }
 166
 167 static void match_condition(struct expression *expr)
 168 {
 169         struct expression *var = NULL;
 170         struct symbol *var_type = NULL;
 171         struct symbol *known_type = NULL;
 172         sval_t known;
 173         sval_t max;
 174         sval_t min;
 175         int lr;
 176         char *name;
 177
 178         if (expr->type != EXPR_COMPARE)
 179                 return;
 180
 181         if (get_value_sval(expr->left, &known)) {
 182                 if (get_value_sval(expr->right, &max))
 183                         return; /* both sides known */
 184                 lr = VAR_ON_RIGHT;
 185                 var = expr->right;
 186                 known_type = get_type(expr->left);
 187         } else if (get_value_sval(expr->right, &known)) {
 188                 lr = VAR_ON_LEFT;
 189                 var = expr->left;
 190                 known_type = get_type(expr->right);
 191         } else {
 192                 return;
 193         }
 194
 195         var_type = get_type(var);
 196         if (!var_type)
 197                 return;
 198         if (var_type->bit_size >= 32 && !option_spammy)
 199                 return;
 200
 201         name = get_variable_from_expr_complex(var, NULL);
 202
 203         if (expr->op == SPECIAL_EQUAL || expr->op == SPECIAL_NOTEQUAL) {
 204                 sval_t sval_min, sval_max;
 205
 206                 sval_min = sval_type_min(var_type);
 207                 sval_max = sval_type_max(var_type);
 208
 209                 if (sval_cmp(sval_min, known) > 0 || sval_cmp(sval_max, known) < 0)
 210                         sm_msg("error: %s is never equal to %s (wrong type %s - %s).",
 211                                 name, sval_to_str(known), sval_to_str(sval_min), sval_to_str(sval_max));
 212                 goto free;
 213         }
 214
 215         max = sval_type_max(var_type);
 216         min = sval_type_min(var_type);
 217
 218         if (sval_cmp(max, known) < 0) {
 219                 const char *tf = get_tf(max, known, lr, expr->op);
 220
 221                 sm_msg("warn: %s is more than %s (max '%s' can be) so this is always %s.",
 222                         sval_to_str(known), sval_to_str(max), name, tf);
 223         }
 224
 225         if (known.value == 0 && type_unsigned(var_type)) {
 226                 if ((lr && expr->op == '<') ||
 227                     (lr && expr->op == SPECIAL_UNSIGNED_LT) ||
 228                     (!lr && expr->op == '>') ||
 229                     (!lr && expr->op == SPECIAL_UNSIGNED_GT)) {
 230                         if (!compare_against_macro(lr, expr) && !cap_both_size(lr, expr)) {
 231                                 sm_msg("warn: unsigned '%s' is never less than zero.", name);
 232                                 goto free;
 233                         }
 234                 }
 235         }
 236
 237         if (type_unsigned(var_type) && known_type && !type_unsigned(known_type) && known.value < 0) {
 238                 sm_msg("warn: unsigned '%s' is never less than zero %s.", name, sval_to_str(known));
 239                 goto free;
 240         }
 241
 242         if (sval_signed(min) && sval_cmp(min, known) > 0) {
 243                 const char *tf = get_tf(min, known, lr, expr->op);
 244
 245                 sm_msg("warn: %s is less than %s (min '%s' can be) so this is always %s.",
 246                         sval_to_str(known), sval_to_str(min), name, tf);
 247         }
 248 free:
 249         free_string(name);
 250 }
 251
 252 void check_signed(int id)
 253 {
 254         my_id = id;
 255
 256         add_hook(&match_assign, ASSIGNMENT_HOOK);
 257         add_hook(&match_condition, CONDITION_HOOK);
 258 }