check_signed.c

   1 /*
   2  * Copyright (C) 2009 Dan Carpenter.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * Check for things which are signed but probably should be unsigned.
  20  *
  21  * Hm...  It seems like at this point in the processing, sparse makes all
  22  * bitfields unsigned.  Which is logical but not what GCC does.
  23  *
  24  */
  25
  26 #include "smatch.h"
  27 #include "smatch_extra.h"
  28
  29 static int my_id;
  30
  31 #define VAR_ON_RIGHT 0
  32 #define VAR_ON_LEFT 1
  33
  34 static void match_assign(struct expression *expr)
  35 {
  36         struct symbol *sym;
  37         sval_t sval;
  38         sval_t max;
  39         sval_t min;
  40         char *left_name, *right_name;
  41
  42         if (expr->op == SPECIAL_AND_ASSIGN || expr->op == SPECIAL_OR_ASSIGN)
  43                 return;
  44
  45         sym = get_type(expr->left);
  46         if (!sym || sym->type != SYM_BASETYPE) {
  47                 //sm_msg("could not get type");
  48                 return;
  49         }
  50         if (type_bits(sym) < 0 || type_bits(sym) >= 32) /* max_val limits this */
  51                 return;
  52         if (!get_implied_value(expr->right, &sval))
  53                 return;
  54         max = sval_type_max(sym);
  55         if (sym != &bool_ctype && sval_cmp(max, sval) < 0 &&
  56             !(sval.value < 256 && max.value == 127)) {
  57                 left_name = expr_to_str(expr->left);
  58                 right_name = expr_to_str(expr->right);
  59                 sm_msg("warn: '%s' %s can't fit into %s '%s'",
  60                        right_name, sval_to_numstr(sval), sval_to_numstr(max), left_name);
  61                 free_string(left_name);
  62         }
  63         min = sval_type_min(sym);
  64         if (sval_cmp_t(&llong_ctype, min, sval) > 0) {
  65                 if (min.value == 0 && sval.value == -1) /* assigning -1 to unsigned variables is idiomatic */
  66                         return;
  67                 if (expr->right->type == EXPR_PREOP && expr->right->op == '~')
  68                         return;
  69                 if (expr->op == SPECIAL_SUB_ASSIGN || expr->op == SPECIAL_ADD_ASSIGN)
  70                         return;
  71                 if (sval_positive_bits(sval) == 7)
  72                         return;
  73                 left_name = expr_to_str(expr->left);
  74                 if (min.value == 0) {
  75                         sm_msg("warn: assigning %s to unsigned variable '%s'",
  76                                sval_to_str(sval), left_name);
  77                 } else {
  78                         sm_msg("warn: value %s can't fit into %s '%s'",
  79                                sval_to_str(sval), sval_to_str(min), left_name);
  80                 }
  81                 free_string(left_name);
  82         }
  83 }
  84
  85 static int cap_gt_zero_and_lt(struct expression *expr)
  86 {
  87
  88         struct expression *var = expr->left;
  89         struct expression *tmp;
  90         char *name1 = NULL;
  91         char *name2 = NULL;
  92         sval_t known;
  93         int ret = 0;
  94         int i;
  95
  96         if (!get_value(expr->right, &known) || known.value != 0)
  97                 return 0;
  98
  99         i = 0;
 100         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 101                 if (!i++)
 102                         continue;
 103                 if (tmp->op == SPECIAL_LOGICAL_AND) {
 104                         struct expression *right = strip_expr(tmp->right);
 105
 106                         if (right->op != '<' &&
 107                             right->op != SPECIAL_UNSIGNED_LT &&
 108                             right->op != SPECIAL_LTE &&
 109                             right->op != SPECIAL_UNSIGNED_LTE)
 110                                 return 0;
 111
 112                         name1 = expr_to_str(var);
 113                         if (!name1)
 114                                 goto free;
 115
 116                         name2 = expr_to_str(right->left);
 117                         if (!name2)
 118                                 goto free;
 119                         if (!strcmp(name1, name2))
 120                                 ret = 1;
 121                         goto free;
 122
 123                 }
 124                 return 0;
 125         } END_FOR_EACH_PTR_REVERSE(tmp);
 126
 127 free:
 128         free_string(name1);
 129         free_string(name2);
 130         return ret;
 131 }
 132
 133 static int cap_lt_zero_or_gt(struct expression *expr)
 134 {
 135
 136         struct expression *var = expr->left;
 137         struct expression *tmp;
 138         char *name1 = NULL;
 139         char *name2 = NULL;
 140         sval_t known;
 141         int ret = 0;
 142         int i;
 143
 144         if (!get_value(expr->right, &known) || known.value != 0)
 145                 return 0;
 146
 147         i = 0;
 148         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 149                 if (!i++)
 150                         continue;
 151                 if (tmp->op == SPECIAL_LOGICAL_OR) {
 152                         struct expression *right = strip_expr(tmp->right);
 153
 154                         if (right->op != '>' &&
 155                             right->op != SPECIAL_UNSIGNED_GT &&
 156                             right->op != SPECIAL_GTE &&
 157                             right->op != SPECIAL_UNSIGNED_GTE)
 158                                 return 0;
 159
 160                         name1 = expr_to_str(var);
 161                         if (!name1)
 162                                 goto free;
 163
 164                         name2 = expr_to_str(right->left);
 165                         if (!name2)
 166                                 goto free;
 167                         if (!strcmp(name1, name2))
 168                                 ret = 1;
 169                         goto free;
 170
 171                 }
 172                 return 0;
 173         } END_FOR_EACH_PTR_REVERSE(tmp);
 174
 175 free:
 176         free_string(name1);
 177         free_string(name2);
 178         return ret;
 179 }
 180
 181 static int cap_both_sides(struct expression *expr)
 182 {
 183         switch (expr->op) {
 184         case '<':
 185         case SPECIAL_UNSIGNED_LT:
 186         case SPECIAL_LTE:
 187         case SPECIAL_UNSIGNED_LTE:
 188                 return cap_lt_zero_or_gt(expr);
 189         case '>':
 190         case SPECIAL_UNSIGNED_GT:
 191         case SPECIAL_GTE:
 192         case SPECIAL_UNSIGNED_GTE:
 193                 return cap_gt_zero_and_lt(expr);
 194         }
 195         return 0;
 196 }
 197
 198 static int compare_against_macro(struct expression *expr)
 199 {
 200         sval_t known;
 201
 202         if (expr->op != SPECIAL_UNSIGNED_LT)
 203                 return 0;
 204
 205         if (!get_value(expr->right, &known) || known.value != 0)
 206                 return 0;
 207         return !!get_macro_name(expr->right->pos);
 208 }
 209
 210 static int print_unsigned_never_less_than_zero(struct expression *expr)
 211 {
 212         sval_t known;
 213         char *name;
 214
 215         if (expr->op != SPECIAL_UNSIGNED_LT)
 216                 return 0;
 217
 218         if (!get_value(expr->right, &known) || known.value != 0)
 219                 return 0;
 220
 221         name = expr_to_str(expr->left);
 222         sm_msg("warn: unsigned '%s' is never less than zero.", name);
 223         free_string(name);
 224         return 1;
 225 }
 226
 227 static void match_condition(struct expression *expr)
 228 {
 229         struct symbol *type;
 230         sval_t known;
 231         sval_t min, max;
 232         struct range_list *rl_left_orig, *rl_right_orig;
 233         struct range_list *rl_left, *rl_right;
 234
 235         if (expr->type != EXPR_COMPARE)
 236                 return;
 237
 238         type = get_type(expr);
 239         if (!type)
 240                 return;
 241
 242         /* screw it.  I am writing this to mark yoda code as buggy.
 243          * Valid comparisons between an unsigned and zero are:
 244          * 1) inside a macro.
 245          * 2) foo < LOWER_BOUND where LOWER_BOUND is a macro.
 246          * 3) foo < 0 || foo > X in exactly this format.  No Yoda.
 247          * 4) foo >= 0 && foo < X
 248          */
 249         if (get_macro_name(expr->pos))
 250                 return;
 251         if (compare_against_macro(expr))
 252                 return;
 253         if (cap_both_sides(expr))
 254                 return;
 255
 256         /* This is a special case for the common error */
 257         if (print_unsigned_never_less_than_zero(expr))
 258                 return;
 259
 260         /* check that one and only one side is known */
 261         if (get_value(expr->left, &known)) {
 262                 if (get_value(expr->right, &known))
 263                         return;
 264                 rl_left_orig = alloc_rl(known, known);
 265                 rl_left = cast_rl(type, rl_left_orig);
 266
 267                 min = sval_type_min(get_type(expr->right));
 268                 max = sval_type_max(get_type(expr->right));
 269                 rl_right_orig = alloc_rl(min, max);
 270                 rl_right = cast_rl(type, rl_right_orig);
 271         } else if (get_value(expr->right, &known)) {
 272                 rl_right_orig = alloc_rl(known, known);
 273                 rl_right = cast_rl(type, rl_right_orig);
 274
 275                 min = sval_type_min(get_type(expr->left));
 276                 max = sval_type_max(get_type(expr->left));
 277                 rl_left_orig = alloc_rl(min, max);
 278                 rl_left = cast_rl(type, rl_left_orig);
 279         } else {
 280                 return;
 281         }
 282
 283         if (!possibly_true_rl(rl_left, expr->op, rl_right)) {
 284                 char *name = expr_to_str(expr);
 285
 286                 sm_msg("warn: impossible condition '(%s) => (%s %s %s)'", name,
 287                        show_rl(rl_left), show_special(expr->op),
 288                        show_rl(rl_right));
 289                 free_string(name);
 290         }
 291
 292         if (!possibly_false_rl(rl_left, expr->op, rl_right)) {
 293                 char *name = expr_to_str(expr);
 294
 295                 sm_msg("warn: always true condition '(%s) => (%s %s %s)'", name,
 296                        show_rl(rl_left_orig), show_special(expr->op),
 297                        show_rl(rl_right_orig));
 298                 free_string(name);
 299         }
 300 }
 301
 302 void check_signed(int id)
 303 {
 304         my_id = id;
 305
 306         add_hook(&match_assign, ASSIGNMENT_HOOK);
 307         add_hook(&match_condition, CONDITION_HOOK);
 308 }