external/bsd/libc++/dist/libcxxrt/src/dynamic_cast.cc

   1 /*
   2  * Copyright 2010-2011 PathScale, Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are met:
   6  *
   7  * 1. Redistributions of source code must retain the above copyright notice,
   8  *    this list of conditions and the following disclaimer.
   9  *
  10  * 2. Redistributions in binary form must reproduce the above copyright notice,
  11  *    this list of conditions and the following disclaimer in the documentation
  12  *    and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
  15  * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  16  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  17  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
  18  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  19  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  20  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
  21  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  22  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  23  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  24  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "typeinfo.h"
  28 #include <stdio.h>
  29
  30 using namespace ABI_NAMESPACE;
  31
  32 /**
  33  * Vtable header.
  34  */
  35 struct vtable_header
  36 {
  37         /** Offset of the leaf object. */
  38         ptrdiff_t leaf_offset;
  39         /** Type of the object. */
  40         const __class_type_info *type;
  41 };
  42
  43 /**
  44  * Simple macro that does pointer arithmetic in bytes but returns a value of
  45  * the same type as the original.
  46  */
  47 #define ADD_TO_PTR(x, off) reinterpret_cast<__typeof__(x)>(reinterpret_cast<char*>(x) + off)
  48
  49 bool std::type_info::__do_catch(std::type_info const *ex_type,
  50                                 void **exception_object,
  51                                 unsigned int outer) const
  52 {
  53         const type_info *type = this;
  54
  55         if (type == ex_type)
  56         {
  57                 return true;
  58         }
  59         if (const __class_type_info *cti = dynamic_cast<const __class_type_info *>(type))
  60         {
  61                 return ex_type->__do_upcast(cti, exception_object);
  62         }
  63         return false;
  64 }
  65
  66 bool __pbase_type_info::__do_catch(std::type_info const *ex_type,
  67                                    void **exception_object,
  68                                    unsigned int outer) const
  69 {
  70         if (ex_type == this)
  71         {
  72                 return true;
  73         }
  74         if (!ex_type->__is_pointer_p())
  75         {
  76                 // Can't catch a non-pointer type in a pointer catch
  77                 return false;
  78         }
  79
  80         if (!(outer & 1))
  81         {
  82                 // If the low bit is cleared on this means that we've gone
  83                 // through a pointer that is not const qualified.
  84                 return false;
  85         }
  86         // Clear the low bit on outer if we're not const qualified.
  87         if (!(__flags & __const_mask))
  88         {
  89                 outer &= ~1;
  90         }
  91
  92         const __pbase_type_info *ptr_type =
  93                 static_cast<const __pbase_type_info*>(ex_type);
  94
  95         if (ptr_type->__flags & ~__flags)
  96         {
  97                 // Handler pointer is less qualified
  98                 return false;
  99         }
 100
 101         // Special case for void* handler.
 102         if(*__pointee == typeid(void))
 103         {
 104                 return true;
 105         }
 106
 107         return __pointee->__do_catch(ptr_type->__pointee, exception_object, outer);
 108 }
 109
 110 void *__class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
 111 {
 112         if (this == other)
 113         {
 114                 return obj;
 115         }
 116         return 0;
 117 }
 118
 119 void *__si_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
 120 {
 121         if (this == other)
 122         {
 123                 return obj;
 124         }
 125         return __base_type->cast_to(obj, other);
 126 }
 127 bool __si_class_type_info::__do_upcast(const __class_type_info *target,
 128                                      void **thrown_object) const
 129 {
 130         if (this == target)
 131         {
 132                 return true;
 133         }
 134         return __base_type->__do_upcast(target, thrown_object);
 135 }
 136
 137 void *__vmi_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
 138 {
 139         if (__do_upcast(other, &obj))
 140         {
 141                 return obj;
 142         }
 143         return 0;
 144 }
 145
 146 bool __vmi_class_type_info::__do_upcast(const __class_type_info *target,
 147                                       void **thrown_object) const
 148 {
 149         if (this == target)
 150         {
 151                 return true;
 152         }
 153         for (unsigned int i=0 ; i<__base_count ; i++)
 154         {
 155                 const __base_class_type_info *info = &__base_info[i];
 156                 ptrdiff_t offset = info->offset();
 157                 // If this is a virtual superclass, the offset is stored in the
 158                 // object's vtable at the offset requested; 2.9.5.6.c:
 159                 //
 160                 // 'For a non-virtual base, this is the offset in the object of the
 161                 // base subobject. For a virtual base, this is the offset in the
 162                 // virtual table of the virtual base offset for the virtual base
 163                 // referenced (negative).'
 164
 165                 void *obj = *thrown_object;
 166                 if (info->isVirtual())
 167                 {
 168                         // Object's vtable
 169                         ptrdiff_t *off = *static_cast<ptrdiff_t**>(obj);
 170                         // Offset location in vtable
 171                         off = ADD_TO_PTR(off, offset);
 172                         offset = *off;
 173                 }
 174                 void *cast = ADD_TO_PTR(obj, offset);
 175
 176                 if (info->__base_type == target ||
 177                     (info->__base_type->__do_upcast(target, &cast)))
 178                 {
 179                         *thrown_object = cast;
 180                         return true;
 181                 }
 182         }
 183         return 0;
 184 }
 185
 186
 187 /**
 188  * ABI function used to implement the dynamic_cast<> operator.  Some cases of
 189  * this operator are implemented entirely in the compiler (e.g. to void*).
 190  * This function implements the dynamic casts of the form dynamic_cast<T>(v).
 191  * This will be translated to a call to this function with the value v as the
 192  * first argument.  The type id of the static type of v is the second argument
 193  * and the type id of the destination type (T) is the third argument.
 194  *
 195  * The third argument is a hint about the compiler's guess at the correct
 196  * pointer offset.  If this value is negative, then -1 indicates no hint, -2
 197  * that src is not a public base of dst, and -3 that src is a multiple public
 198  * base type but never a virtual base type
 199  */
 200 extern "C" void* __dynamic_cast(const void *sub,
 201                                 const __class_type_info *src,
 202                                 const __class_type_info *dst,
 203                                 ptrdiff_t src2dst_offset)
 204 {
 205         const char *vtable_location = *static_cast<const char * const *>(sub);
 206         const vtable_header *header =
 207                 reinterpret_cast<const vtable_header*>(vtable_location - sizeof(vtable_header));
 208         void *leaf = ADD_TO_PTR(const_cast<void *>(sub), header->leaf_offset);
 209         return header->type->cast_to(leaf, dst);
 210 }