check_bogus_loop.c

   1 /*
   2  * Copyright (C) 2011 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 #include "smatch.h"
  19 #include "smatch_slist.h"
  20
  21 static int my_id;
  22
  23 static int right_side_changes(struct expression *expr)
  24 {
  25         sval_t dummy;
  26
  27         if (get_value(expr->right, &dummy))
  28                 return 0;
  29         return 1;
  30 }
  31
  32 static bool is_lt_ARRAY_SIZE(struct expression *expr)
  33 {
  34         char *macro;
  35
  36         /*
  37          * One cause of false positives is:
  38          * for (i = 0; i < ARRAY_SIZE(); i++) {
  39          * but the ARRAY_SIZE() is zero.  Silence these false positives.
  40          *
  41          */
  42         if (!expr || expr->type != EXPR_COMPARE)
  43                 return false;
  44         if (expr->op != '<' && expr->op != SPECIAL_UNSIGNED_LT)
  45                 return false;
  46         if (!expr_is_zero(expr->right))
  47                 return false;
  48         macro = get_macro_name(expr->right->pos);
  49         if (!macro || strcmp(macro, "ARRAY_SIZE") != 0)
  50                 return false;
  51
  52         return true;
  53 }
  54
  55 static struct expression *get_iterator_set(struct statement *stmt)
  56 {
  57         struct expression *expr;
  58
  59         if (!stmt)
  60                 return NULL;
  61         if (stmt->type != STMT_EXPRESSION)
  62                 return NULL;
  63         expr = stmt->expression;
  64         if (expr->type != EXPR_ASSIGNMENT)
  65                 return NULL;
  66         if (expr->op != '=')
  67                 return NULL;
  68         if (right_side_changes(expr))
  69                 return NULL;
  70         return expr->left;
  71 }
  72
  73 static struct expression *get_iterator_tested(struct expression *expr)
  74 {
  75         if (!expr)
  76                 return NULL;
  77         if (expr->type != EXPR_COMPARE)
  78                 return NULL;
  79         return expr->left;
  80 }
  81
  82 static void match_loop(struct statement *stmt)
  83 {
  84         struct expression *iterator;
  85         char *iter_set;
  86         char *iter_tested;
  87
  88         if (get_macro_name(stmt->pos))
  89                 return;
  90
  91         iterator = get_iterator_set(stmt->iterator_pre_statement);
  92         iter_set = expr_to_var(iterator);
  93         iterator = get_iterator_tested(stmt->iterator_pre_condition);
  94         iter_tested = expr_to_var(iterator);
  95         if (!iter_set || !iter_tested)
  96                 goto free;
  97         if (strcmp(iter_set, iter_tested))
  98                 goto free;
  99
 100         /* smatch doesn't handle loops correctly so this silences some
 101          * false positives.
 102          */
 103         if (right_side_changes(stmt->iterator_pre_condition))
 104                 goto free;
 105
 106         if (is_lt_ARRAY_SIZE(stmt->iterator_pre_condition))
 107                 goto free;
 108
 109         if (implied_condition_false(stmt->iterator_pre_condition))
 110                 sm_warning("we never enter this loop");
 111
 112 free:
 113         free_string(iter_set);
 114         free_string(iter_tested);
 115 }
 116
 117 void check_bogus_loop(int id)
 118 {
 119         my_id = id;
 120         add_hook(&match_loop, PRELOOP_HOOK);
 121 }