dynamic_cast.cc revision 278017
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 30using namespace ABI_NAMESPACE; 31 32/** 33 * Vtable header. 34 */ 35struct 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 49bool 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 66bool __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 110void *__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 119void *__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} 127bool __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 137void *__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 146bool __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 */ 200extern "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} 211