check_shift_to_zero.c

   1 /*
   2  * Copyright (C) 2014 Oracle.
   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
  20 static int my_id;
  21
  22 static void match_binop(struct expression *expr)
  23 {
  24         struct symbol *type;
  25         sval_t bits;
  26
  27         if (expr->op != SPECIAL_RIGHTSHIFT)
  28                 return;
  29
  30         if (!get_implied_value(expr->right, &bits))
  31                 return;
  32
  33         type = get_type(expr->left);
  34         if (!type)
  35                 return;
  36         if (type_bits(type) == -1 || type_bits(type) > bits.value)
  37                 return;
  38         if (is_ignored_expr(my_id, expr))
  39                 return;
  40         sm_warning("right shifting more than type allows %d vs %lld", type_bits(type), bits.value);
  41 }
  42
  43 static void match_binop2(struct expression *expr)
  44 {
  45         struct expression *left;
  46         struct expression *tmp;
  47         sval_t mask, shift;
  48         char *macro, *inner;
  49
  50         if (expr->op != SPECIAL_RIGHTSHIFT)
  51                 return;
  52
  53         left = strip_expr(expr->left);
  54         tmp = get_assigned_expr(left);
  55         if (tmp)
  56                 left = tmp;
  57         if (left->type != EXPR_BINOP || left->op != '&')
  58                 return;
  59
  60         if (!get_value(expr->right, &shift))
  61                 return;
  62         if (!get_value(left->right, &mask))
  63                 return;
  64
  65         if (mask.uvalue >> shift.uvalue)
  66                 return;
  67
  68         macro = get_macro_name(expr->pos);
  69         inner = get_inner_macro(expr->pos);
  70         if (macro && inner) {
  71                 if (strcmp(macro, "unlikely") == 0)
  72                         goto warn;
  73                 if (strcmp(inner, "unlikely") == 0 ||
  74                     strcmp(inner, "__const_hweight8") == 0 ||
  75                     strcmp(inner, "BITS_PER_LONG") == 0 ||
  76                     strcmp(inner, "CORDIC_PRECISION_SHIFT") == 0)
  77                         return;
  78         }
  79
  80 warn:
  81         sm_warning("mask and shift to zero: expr='%s'", expr_to_str(expr));
  82 }
  83
  84 static void match_assign(struct expression *expr)
  85 {
  86         struct symbol *type;
  87         sval_t bits;
  88
  89         if (expr->op != SPECIAL_SHR_ASSIGN)
  90                 return;
  91
  92         if (!get_implied_value(expr->right, &bits))
  93                 return;
  94         type = get_type(expr->left);
  95         if (!type)
  96                 return;
  97         if (type_bits(type) > bits.value)
  98                 return;
  99         sm_warning("right shift assign to zero");
 100 }
 101
 102 void check_shift_to_zero(int id)
 103 {
 104         my_id = id;
 105
 106         add_hook(&match_binop, BINOP_HOOK);
 107         add_hook(&match_binop2, BINOP_HOOK);
 108
 109         add_hook(&match_assign, ASSIGNMENT_HOOK);
 110
 111 }