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 (__in_fake_assign)
  43                 return;
  44         if (expr->op == SPECIAL_AND_ASSIGN || expr->op == SPECIAL_OR_ASSIGN)
  45                 return;
  46
  47         sym = get_type(expr->left);
  48         if (!sym || sym->type != SYM_BASETYPE) {
  49                 //sm_msg("could not get type");
  50                 return;
  51         }
  52         if (type_bits(sym) < 0 || type_bits(sym) >= 32) /* max_val limits this */
  53                 return;
  54         if (!get_implied_value(expr->right, &sval))
  55                 return;
  56         max = sval_type_max(sym);
  57         if (sym != &bool_ctype && sym != &uchar_ctype &&
  58             sval_cmp(max, sval) < 0 &&
  59             !(sval.value < 256 && max.value == 127)) {
  60                 left_name = expr_to_str(expr->left);
  61                 right_name = expr_to_str(expr->right);
  62                 sm_msg("warn: '%s' %s can't fit into %s '%s'",
  63                        right_name, sval_to_numstr(sval), sval_to_numstr(max), left_name);
  64                 free_string(left_name);
  65         }
  66         min = sval_type_min(sym);
  67         if (sval_cmp_t(&llong_ctype, min, sval) > 0) {
  68                 if (min.value == 0 && sval.value == -1) /* assigning -1 to unsigned variables is idiomatic */
  69                         return;
  70                 if (expr->right->type == EXPR_PREOP && expr->right->op == '~')
  71                         return;
  72                 if (expr->op == SPECIAL_SUB_ASSIGN || expr->op == SPECIAL_ADD_ASSIGN)
  73                         return;
  74                 if (sval_positive_bits(sval) == 7)
  75                         return;
  76                 left_name = expr_to_str(expr->left);
  77                 if (min.value == 0) {
  78                         sm_msg("warn: assigning %s to unsigned variable '%s'",
  79                                sval_to_str(sval), left_name);
  80                 } else {
  81                         sm_msg("warn: value %s can't fit into %s '%s'",
  82                                sval_to_str(sval), sval_to_str(min), left_name);
  83                 }
  84                 free_string(left_name);
  85         }
  86 }
  87
  88 static int cap_gt_zero_and_lt(struct expression *expr)
  89 {
  90
  91         struct expression *var = expr->left;
  92         struct expression *tmp;
  93         char *name1 = NULL;
  94         char *name2 = NULL;
  95         sval_t known;
  96         int ret = 0;
  97         int i;
  98
  99         if (!get_value(expr->right, &known) || known.value != 0)
 100                 return 0;
 101
 102         i = 0;
 103         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 104                 if (!i++)
 105                         continue;
 106                 if (tmp->op == SPECIAL_LOGICAL_AND) {
 107                         struct expression *right = strip_expr(tmp->right);
 108
 109                         if (right->op != '<' &&
 110                             right->op != SPECIAL_UNSIGNED_LT &&
 111                             right->op != SPECIAL_LTE &&
 112                             right->op != SPECIAL_UNSIGNED_LTE)
 113                                 return 0;
 114
 115                         name1 = expr_to_str(var);
 116                         if (!name1)
 117                                 goto free;
 118
 119                         name2 = expr_to_str(right->left);
 120                         if (!name2)
 121                                 goto free;
 122                         if (!strcmp(name1, name2))
 123                                 ret = 1;
 124                         goto free;
 125
 126                 }
 127                 return 0;
 128         } END_FOR_EACH_PTR_REVERSE(tmp);
 129
 130 free:
 131         free_string(name1);
 132         free_string(name2);
 133         return ret;
 134 }
 135
 136 static int cap_lt_zero_or_gt(struct expression *expr)
 137 {
 138
 139         struct expression *var = expr->left;
 140         struct expression *tmp;
 141         char *name1 = NULL;
 142         char *name2 = NULL;
 143         sval_t known;
 144         int ret = 0;
 145         int i;
 146
 147         if (!get_value(expr->right, &known) || known.value != 0)
 148                 return 0;
 149
 150         i = 0;
 151         FOR_EACH_PTR_REVERSE(big_expression_stack, tmp) {
 152                 if (!i++)
 153                         continue;
 154                 if (tmp->op == SPECIAL_LOGICAL_OR) {
 155                         struct expression *right = strip_expr(tmp->right);
 156
 157                         if (right->op != '>' &&
 158                             right->op != SPECIAL_UNSIGNED_GT &&
 159                             right->op != SPECIAL_GTE &&
 160                             right->op != SPECIAL_UNSIGNED_GTE)
 161                                 return 0;
 162
 163                         name1 = expr_to_str(var);
 164                         if (!name1)
 165                                 goto free;
 166
 167                         name2 = expr_to_str(right->left);
 168                         if (!name2)
 169                                 goto free;
 170                         if (!strcmp(name1, name2))
 171                                 ret = 1;
 172                         goto free;
 173
 174                 }
 175                 return 0;
 176         } END_FOR_EACH_PTR_REVERSE(tmp);
 177
 178 free:
 179         free_string(name1);
 180         free_string(name2);
 181         return ret;
 182 }
 183
 184 static int cap_both_sides(struct expression *expr)
 185 {
 186         switch (expr->op) {
 187         case '<':
 188         case SPECIAL_UNSIGNED_LT:
 189         case SPECIAL_LTE:
 190         case SPECIAL_UNSIGNED_LTE:
 191                 return cap_lt_zero_or_gt(expr);
 192         case '>':
 193         case SPECIAL_UNSIGNED_GT:
 194         case SPECIAL_GTE:
 195         case SPECIAL_UNSIGNED_GTE:
 196                 return cap_gt_zero_and_lt(expr);
 197         }
 198         return 0;
 199 }
 200
 201 static int compare_against_macro(struct expression *expr)
 202 {
 203         sval_t known;
 204
 205         if (expr->op != SPECIAL_UNSIGNED_LT)
 206                 return 0;
 207
 208         if (!get_value(expr->right, &known) || known.value != 0)
 209                 return 0;
 210         return !!get_macro_name(expr->right->pos);
 211 }
 212
 213 static int print_unsigned_never_less_than_zero(struct expression *expr)
 214 {
 215         sval_t known;
 216         char *name;
 217
 218         if (expr->op != SPECIAL_UNSIGNED_LT)
 219                 return 0;
 220
 221         if (!get_value(expr->right, &known) || known.value != 0)
 222                 return 0;
 223
 224         name = expr_to_str(expr->left);
 225         sm_msg("warn: unsigned '%s' is never less than zero.", name);
 226         free_string(name);
 227         return 1;
 228 }
 229
 230 static void match_condition(struct expression *expr)
 231 {
 232         struct symbol *type;
 233         sval_t known;
 234         sval_t min, max;
 235         struct range_list *rl_left_orig, *rl_right_orig;
 236         struct range_list *rl_left, *rl_right;
 237
 238         if (expr->type != EXPR_COMPARE)
 239                 return;
 240
 241         type = get_type(expr);
 242         if (!type)
 243                 return;
 244
 245         /* screw it.  I am writing this to mark yoda code as buggy.
 246          * Valid comparisons between an unsigned and zero are:
 247          * 1) inside a macro.
 248          * 2) foo < LOWER_BOUND where LOWER_BOUND is a macro.
 249          * 3) foo < 0 || foo > X in exactly this format.  No Yoda.
 250          * 4) foo >= 0 && foo < X
 251          */
 252         if (get_macro_name(expr->pos))
 253                 return;
 254         if (compare_against_macro(expr))
 255                 return;
 256         if (cap_both_sides(expr))
 257                 return;
 258
 259         /* This is a special case for the common error */
 260         if (print_unsigned_never_less_than_zero(expr))
 261                 return;
 262
 263         /* check that one and only one side is known */
 264         if (get_value(expr->left, &known)) {
 265                 if (get_value(expr->right, &known))
 266                         return;
 267                 rl_left_orig = alloc_rl(known, known);
 268                 rl_left = cast_rl(type, rl_left_orig);
 269
 270                 min = sval_type_min(get_type(expr->right));
 271                 max = sval_type_max(get_type(expr->right));
 272                 rl_right_orig = alloc_rl(min, max);
 273                 rl_right = cast_rl(type, rl_right_orig);
 274         } else if (get_value(expr->right, &known)) {
 275                 rl_right_orig = alloc_rl(known, known);
 276                 rl_right = cast_rl(type, rl_right_orig);
 277
 278                 min = sval_type_min(get_type(expr->left));
 279                 max = sval_type_max(get_type(expr->left));
 280                 rl_left_orig = alloc_rl(min, max);
 281                 rl_left = cast_rl(type, rl_left_orig);
 282         } else {
 283                 return;
 284         }
 285
 286         if (!possibly_true_rl(rl_left, expr->op, rl_right)) {
 287                 char *name = expr_to_str(expr);
 288
 289                 sm_msg("warn: impossible condition '(%s) => (%s %s %s)'", name,
 290                        show_rl(rl_left), show_special(expr->op),
 291                        show_rl(rl_right));
 292                 free_string(name);
 293         }
 294
 295         if (!possibly_false_rl(rl_left, expr->op, rl_right)) {
 296                 char *name = expr_to_str(expr);
 297
 298                 sm_msg("warn: always true condition '(%s) => (%s %s %s)'", name,
 299                        show_rl(rl_left_orig), show_special(expr->op),
 300                        show_rl(rl_right_orig));
 301                 free_string(name);
 302         }
 303 }
 304
 305 void check_signed(int id)
 306 {
 307         my_id = id;
 308
 309         add_hook(&match_assign, ASSIGNMENT_HOOK);
 310         add_hook(&match_condition, CONDITION_HOOK);
 311 }