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 RIGHT 0
  23 #define LEFT 1
  24
  25 static int is_unsigned(struct symbol *base_type)
  26 {
  27         if (base_type->ctype.modifiers & MOD_UNSIGNED)
  28                 return 1;
  29         return 0;
  30 }
  31
  32 static void match_assign(struct expression *expr)
  33 {
  34         struct symbol *sym;
  35         long long val;
  36         long long max;
  37         long long min;
  38         char *name;
  39
  40         sym = get_type(expr->left);
  41         if (!sym) {
  42                 //sm_msg("could not get type");
  43                 return;
  44         }
  45         if (sym->bit_size >= 32) /* max_val limits this */
  46                 return;
  47         if (!get_implied_value(expr->right, &val))
  48                 return;
  49         max = type_max(sym);
  50         if (max && max < val) {
  51                 name = get_variable_from_expr_complex(expr->left, NULL);
  52                 sm_msg("warn: value %lld can't fit into %lld '%s'", val, max, name);
  53                 free_string(name);
  54         }
  55         min = type_min(sym);
  56         if (min > val) {
  57                 name = get_variable_from_expr_complex(expr->left, NULL);
  58                 sm_msg("warn: value %lld can't fit into %lld '%s'", val, min, name);
  59                 free_string(name);
  60         }
  61
  62 }
  63
  64 static void match_condition(struct expression *expr)
  65 {
  66         long long known;
  67         struct expression *var = NULL;
  68         struct symbol *type = NULL;
  69         long long max;
  70         int lr;
  71         char *name;
  72
  73         if (expr->type != EXPR_COMPARE)
  74                 return;
  75
  76         if (get_value(expr->left, &known)) {
  77                 lr = RIGHT;
  78                 var = expr->right;
  79         } else if (get_value(expr->right, &known)) {
  80                 lr = LEFT;
  81                 var = expr->left;
  82         } else {
  83                 return;
  84         }
  85
  86         type = get_type(var);
  87         if (!type || type->bit_size >= 32)
  88                 return;
  89
  90         max = type_max(type);
  91         if (!max)
  92                 return;
  93
  94         name = get_variable_from_expr_complex(var, NULL);
  95
  96         if (known < 0) {
  97                 if (is_unsigned(type))
  98                         sm_msg("error: comparing unsigned '%s' to negative", name);
  99                 goto free;
 100         }
 101
 102         if (known == 0) {
 103                 if (!is_unsigned(type))
 104                         goto free;
 105                 if (lr == LEFT) {
 106                         if (expr->op == '<')
 107                                 sm_msg("error: unsigned '%s' cannot be less than 0", name);
 108                         if (expr->op == SPECIAL_LTE)
 109                                 sm_msg("warn: unsigned '%s' cannot be less than 0", name);
 110                 }
 111                 if (lr == RIGHT) {
 112                         if (expr->op == '>')
 113                                 sm_msg("error: unsigned '%s' cannot be less than 0", name);
 114                         if (expr->op == SPECIAL_GTE)
 115                                 sm_msg("warn: unsigned '%s' cannot be less than 0", name);
 116                 }
 117                 goto free;
 118         }
 119
 120         if (max < known) {
 121                 const char *tf = "the same";
 122
 123                 if (expr->op == SPECIAL_EQUAL)
 124                         tf = "false";
 125                 if (expr->op == SPECIAL_NOTEQUAL)
 126                         tf = "true";
 127                 if (lr == LEFT && (expr->op == '<' || expr->op == SPECIAL_LTE))
 128                         tf = "true";
 129                 if (lr == RIGHT && (expr->op == '>' || expr->op == SPECIAL_GTE))
 130                         tf = "false";
 131                 sm_msg("warn: %lld is higher than %lld (max '%s' can be) so this is always %s.",
 132                         known, max, name, tf);
 133         }
 134 free:
 135         free_string(name);
 136 }
 137
 138 void check_signed(int id)
 139 {
 140         my_id = id;
 141
 142         add_hook(&match_assign, ASSIGNMENT_HOOK);
 143         add_hook(&match_condition, CONDITION_HOOK);
 144 }