gcc/c-family/c-ubsan.c

   1 /* UndefinedBehaviorSanitizer, undefined behavior detector.
   2    Copyright (C) 2013 Free Software Foundation, Inc.
   3    Contributed by Marek Polacek <polacek@redhat.com>
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tree.h"
  25 #include "alloc-pool.h"
  26 #include "cgraph.h"
  27 #include "output.h"
  28 #include "toplev.h"
  29 #include "ubsan.h"
  30 #include "c-family/c-common.h"
  31 #include "c-family/c-ubsan.h"
  32
  33 /* Instrument division by zero and INT_MIN / -1.  If not instrumenting,
  34    return NULL_TREE.  */
  35
  36 tree
  37 ubsan_instrument_division (location_t loc, tree op0, tree op1)
  38 {
  39   tree t, tt;
  40   tree type = TREE_TYPE (op0);
  41
  42   /* At this point both operands should have the same type,
  43      because they are already converted to RESULT_TYPE.
  44      Use TYPE_MAIN_VARIANT since typedefs can confuse us.  */
  45   gcc_assert (TYPE_MAIN_VARIANT (TREE_TYPE (op0))
  46               == TYPE_MAIN_VARIANT (TREE_TYPE (op1)));
  47
  48   /* TODO: REAL_TYPE is not supported yet.  */
  49   if (TREE_CODE (type) != INTEGER_TYPE)
  50     return NULL_TREE;
  51
  52   t = fold_build2 (EQ_EXPR, boolean_type_node,
  53                     op1, build_int_cst (type, 0));
  54
  55   /* We check INT_MIN / -1 only for signed types.  */
  56   if (!TYPE_UNSIGNED (type))
  57     {
  58       tree x;
  59       tt = fold_build2 (EQ_EXPR, boolean_type_node, op1,
  60                         build_int_cst (type, -1));
  61       x = fold_build2 (EQ_EXPR, boolean_type_node, op0,
  62                        TYPE_MIN_VALUE (type));
  63       x = fold_build2 (TRUTH_AND_EXPR, boolean_type_node, x, tt);
  64       t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t, x);
  65     }
  66
  67   /* If the condition was folded to 0, no need to instrument
  68      this expression.  */
  69   if (integer_zerop (t))
  70     return NULL_TREE;
  71
  72   /* In case we have a SAVE_EXPR in a conditional context, we need to
  73      make sure it gets evaluated before the condition.  */
  74   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), op0, t);
  75   tree data = ubsan_create_data ("__ubsan_overflow_data",
  76                                  loc, NULL,
  77                                  ubsan_type_descriptor (type, false),
  78                                  NULL_TREE);
  79   data = build_fold_addr_expr_loc (loc, data);
  80   tt = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_DIVREM_OVERFLOW);
  81   tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
  82                             ubsan_encode_value (op1));
  83   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_zero_node);
  84
  85   return t;
  86 }
  87
  88 /* Instrument left and right shifts.  */
  89
  90 tree
  91 ubsan_instrument_shift (location_t loc, enum tree_code code,
  92                         tree op0, tree op1)
  93 {
  94   tree t, tt = NULL_TREE;
  95   tree type0 = TREE_TYPE (op0);
  96   tree type1 = TREE_TYPE (op1);
  97   tree op1_utype = unsigned_type_for (type1);
  98   HOST_WIDE_INT op0_prec = TYPE_PRECISION (type0);
  99   tree uprecm1 = build_int_cst (op1_utype, op0_prec - 1);
 100   tree precm1 = build_int_cst (type1, op0_prec - 1);
 101
 102   t = fold_convert_loc (loc, op1_utype, op1);
 103   t = fold_build2 (GT_EXPR, boolean_type_node, t, uprecm1);
 104
 105   /* For signed x << y, in C99/C11, the following:
 106      (unsigned) x >> (precm1 - y)
 107      if non-zero, is undefined.  */
 108   if (code == LSHIFT_EXPR
 109       && !TYPE_UNSIGNED (type0)
 110       && flag_isoc99)
 111     {
 112       tree x = fold_build2 (MINUS_EXPR, integer_type_node, precm1, op1);
 113       tt = fold_convert_loc (loc, unsigned_type_for (type0), op0);
 114       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 115       tt = fold_build2 (NE_EXPR, boolean_type_node, tt,
 116                         build_int_cst (TREE_TYPE (tt), 0));
 117     }
 118
 119   /* For signed x << y, in C++11/C++14, the following:
 120      x < 0 || ((unsigned) x >> (precm1 - y))
 121      if > 1, is undefined.  */
 122   if (code == LSHIFT_EXPR
 123       && !TYPE_UNSIGNED (TREE_TYPE (op0))
 124       && (cxx_dialect == cxx11 || cxx_dialect == cxx1y))
 125     {
 126       tree x = fold_build2 (MINUS_EXPR, integer_type_node, precm1, op1);
 127       tt = fold_convert_loc (loc, unsigned_type_for (type0), op0);
 128       tt = fold_build2 (RSHIFT_EXPR, TREE_TYPE (tt), tt, x);
 129       tt = fold_build2 (GT_EXPR, boolean_type_node, tt,
 130                         build_int_cst (TREE_TYPE (tt), 1));
 131       x = fold_build2 (LT_EXPR, boolean_type_node, op0,
 132                        build_int_cst (type0, 0));
 133       tt = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, x, tt);
 134     }
 135
 136   /* If the condition was folded to 0, no need to instrument
 137      this expression.  */
 138   if (integer_zerop (t) && (tt == NULL_TREE || integer_zerop (tt)))
 139     return NULL_TREE;
 140
 141   /* In case we have a SAVE_EXPR in a conditional context, we need to
 142      make sure it gets evaluated before the condition.  */
 143   t = fold_build2 (COMPOUND_EXPR, TREE_TYPE (t), op0, t);
 144   tree data = ubsan_create_data ("__ubsan_shift_data",
 145                                  loc, NULL,
 146                                  ubsan_type_descriptor (type0, false),
 147                                  ubsan_type_descriptor (type1, false),
 148                                  NULL_TREE);
 149
 150   data = build_fold_addr_expr_loc (loc, data);
 151
 152   t = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, t,
 153                    tt ? tt : integer_zero_node);
 154   tt = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_SHIFT_OUT_OF_BOUNDS);
 155   tt = build_call_expr_loc (loc, tt, 3, data, ubsan_encode_value (op0),
 156                             ubsan_encode_value (op1));
 157   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_zero_node);
 158
 159   return t;
 160 }
 161
 162 /* Instrument variable length array bound.  */
 163
 164 tree
 165 ubsan_instrument_vla (location_t loc, tree size)
 166 {
 167   tree type = TREE_TYPE (size);
 168   tree t, tt;
 169
 170   t = fold_build2 (LE_EXPR, boolean_type_node, size, build_int_cst (type, 0));
 171   tree data = ubsan_create_data ("__ubsan_vla_data",
 172                                  loc, NULL,
 173                                  ubsan_type_descriptor (type, false),
 174                                  NULL_TREE);
 175   data = build_fold_addr_expr_loc (loc, data);
 176   tt = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_VLA_BOUND_NOT_POSITIVE);
 177   tt = build_call_expr_loc (loc, tt, 2, data, ubsan_encode_value (size));
 178   t = fold_build3 (COND_EXPR, void_type_node, t, tt, void_zero_node);
 179
 180   return t;
 181 }
 182
 183 /* Instrument missing return in C++ functions returning non-void.  */
 184
 185 tree
 186 ubsan_instrument_return (location_t loc)
 187 {
 188   tree data = ubsan_create_data ("__ubsan_missing_return_data", loc,
 189                                  NULL, NULL_TREE);
 190   tree t = builtin_decl_explicit (BUILT_IN_UBSAN_HANDLE_MISSING_RETURN);
 191   return build_call_expr_loc (loc, t, 1, build_fold_addr_expr_loc (loc, data));
 192 }