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         long long val;
  29         long long max;
  30         long long min;
  31         char *name;
  32
  33         sym = get_type(expr->left);
  34         if (!sym) {
  35                 //sm_msg("could not get type");
  36                 return;
  37         }
  38         if (sym->bit_size >= 32) /* max_val limits this */
  39                 return;
  40         if (!get_implied_value(expr->right, &val))
  41                 return;
  42         max = type_max(sym);
  43         if (max && max < val) {
  44                 name = get_variable_from_expr_complex(expr->left, NULL);
  45                 sm_msg("warn: value %lld can't fit into %lld '%s'", val, max, name);
  46                 free_string(name);
  47         }
  48         min = type_min(sym);
  49         if (min > val) {
  50                 name = get_variable_from_expr_complex(expr->left, NULL);
  51                 sm_msg("warn: value %lld can't fit into %lld '%s'", val, min, name);
  52                 free_string(name);
  53         }
  54
  55 }
  56
  57 static const char *get_tf(long long variable, long long known, int var_pos, char op)
  58 {
  59         if (op == SPECIAL_EQUAL)
  60                 return "false";
  61         if (op == SPECIAL_NOTEQUAL)
  62                 return "true";
  63         if (var_pos == VAR_ON_LEFT) {
  64                 if (variable > known && (op == '<' || op == SPECIAL_LTE))
  65                         return "false";
  66                 if (variable > known && (op == '>' || op == SPECIAL_GTE))
  67                         return "true";
  68                 if (variable < known && (op == '<' || op == SPECIAL_LTE))
  69                         return "true";
  70                 if (variable < known && (op == '>' || op == SPECIAL_GTE))
  71                         return "false";
  72         }
  73         if (var_pos == VAR_ON_RIGHT) {
  74                 if (known > variable && (op == '<' || op == SPECIAL_LTE))
  75                         return "false";
  76                 if (known > variable && (op == '>' || op == SPECIAL_GTE))
  77                         return "true";
  78                 if (known < variable && (op == '<' || op == SPECIAL_LTE))
  79                         return "true";
  80                 if (known < variable && (op == '>' || op == SPECIAL_GTE))
  81                         return "false";
  82         }
  83         return "the same";
  84 }
  85
  86 static void match_condition(struct expression *expr)
  87 {
  88         long long known;
  89         struct expression *var = NULL;
  90         struct symbol *type = NULL;
  91         long long max;
  92         long long min;
  93         int lr;
  94         char *name;
  95
  96         if (expr->type != EXPR_COMPARE)
  97                 return;
  98
  99         if (get_value(expr->left, &known)) {
 100                 lr = VAR_ON_RIGHT;
 101                 var = expr->right;
 102         } else if (get_value(expr->right, &known)) {
 103                 lr = VAR_ON_LEFT;
 104                 var = expr->left;
 105         } else {
 106                 return;
 107         }
 108
 109         type = get_type(var);
 110         if (!type || type->bit_size >= 32)
 111                 return;
 112
 113         max = type_max(type);
 114         if (!max)
 115                 return;
 116         min = type_min(type);
 117
 118         name = get_variable_from_expr_complex(var, NULL);
 119
 120         if (known < 0 && type_unsigned(type)) {
 121                 sm_msg("error: comparing unsigned '%s' to negative", name);
 122                 goto free;
 123         }
 124
 125         if (known == 0) {
 126                 if (!type_unsigned(type))
 127                         goto free;
 128                 if (lr == VAR_ON_LEFT) {
 129                         if (expr->op == '<')
 130                                 sm_msg("error: unsigned '%s' cannot be less than 0", name);
 131                         if (expr->op == SPECIAL_LTE)
 132                                 sm_msg("warn: unsigned '%s' cannot be less than 0", name);
 133                 }
 134                 if (lr == VAR_ON_RIGHT) {
 135                         if (expr->op == '>')
 136                                 sm_msg("error: unsigned '%s' cannot be less than 0", name);
 137                         if (expr->op == SPECIAL_GTE)
 138                                 sm_msg("warn: unsigned '%s' cannot be less than 0", name);
 139                 }
 140                 goto free;
 141         }
 142
 143         if (max < known) {
 144                 const char *tf = get_tf(max, known, lr, expr->op);
 145
 146                 sm_msg("warn: %lld is more than %lld (max '%s' can be) so this is always %s.",
 147                         known, max, name, tf);
 148         }
 149
 150         if (min > known) {
 151                 const char *tf = get_tf(max, known, lr, expr->op);
 152
 153                 sm_msg("warn: %lld is less than %lld (min '%s' can be) so this is always %s.",
 154                         known, min, name, tf);
 155         }
 156 free:
 157         free_string(name);
 158 }
 159
 160 void check_signed(int id)
 161 {
 162         my_id = id;
 163
 164         add_hook(&match_assign, ASSIGNMENT_HOOK);
 165         add_hook(&match_condition, CONDITION_HOOK);
 166 }