dynamic_cast.cc revision 232950 
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) (__typeof__(x))(((char*)x) + off)
48
49bool __class_type_info::can_cast_to(const struct __class_type_info *other) const
50{
51    return this == other;
52}
53
54void *__class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
55{
56	if (this == other)
57	{
58		return obj;
59	}
60	return 0;
61}
62
63
64bool __si_class_type_info::can_cast_to(const struct __class_type_info *other) const
65{
66    return this == other || __base_type->can_cast_to(other);
67}
68
69void *__si_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
70{
71	if (this == other)
72	{
73		return obj;
74	}
75	return __base_type->cast_to(obj, other);
76}
77
78
79bool __vmi_class_type_info::can_cast_to(const struct __class_type_info *other) const
80{
81	if (this == other)
82	{
83		return true;
84	}
85	for (unsigned int i=0 ; i<__base_count ; i++)
86	{
87		const __base_class_type_info *info = &__base_info[i];
88        if(info->isPublic() && info->__base_type->can_cast_to(other))
89        {
90            return true;
91        }
92	}
93	return false;
94}
95
96void *__vmi_class_type_info::cast_to(void *obj, const struct __class_type_info *other) const
97{
98	if (this == other)
99	{
100		return obj;
101	}
102	for (unsigned int i=0 ; i<__base_count ; i++)
103	{
104		const __base_class_type_info *info = &__base_info[i];
105		ptrdiff_t offset = info->offset();
106		// If this is a virtual superclass, the offset is stored in the
107		// object's vtable at the offset requested; 2.9.5.6.c:
108		//
109		// 'For a non-virtual base, this is the offset in the object of the
110		// base subobject. For a virtual base, this is the offset in the
111		// virtual table of the virtual base offset for the virtual base
112		// referenced (negative).'
113
114		if (info->isVirtual())
115		{
116			// Object's vtable
117			ptrdiff_t *off = *(ptrdiff_t**)obj;
118			// Offset location in vtable
119			off = ADD_TO_PTR(off, offset);
120			offset = *off;
121		}
122		void *cast = ADD_TO_PTR(obj, offset);
123
124		if (info->__base_type == other)
125		{
126			return cast;
127		}
128		if ((cast = info->__base_type->cast_to(cast, other)))
129		{
130			return cast;
131		}
132	}
133	return 0;
134}
135
136/**
137 * ABI function used to implement the dynamic_cast<> operator.  Some cases of
138 * this operator are implemented entirely in the compiler (e.g. to void*).
139 * This function implements the dynamic casts of the form dynamic_cast<T>(v).
140 * This will be translated to a call to this function with the value v as the
141 * first argument.  The type id of the static type of v is the second argument
142 * and the type id of the destination type (T) is the third argument.
143 *
144 * The third argument is a hint about the compiler's guess at the correct
145 * pointer offset.  If this value is negative, then -1 indicates no hint, -2
146 * that src is not a public base of dst, and -3 that src is a multiple public
147 * base type but never a virtual base type
148 */
149extern "C" void* __dynamic_cast(const void *sub,
150                                const __class_type_info *src,
151                                const __class_type_info *dst,
152                                ptrdiff_t src2dst_offset)
153{
154	char *vtable_location = *(char**)sub;
155	const vtable_header *header =
156		(const vtable_header*)(vtable_location - sizeof(vtable_header));
157	void *leaf = ADD_TO_PTR((void*)sub, header->leaf_offset);
158	return header->type->cast_to(leaf, dst);
159}
160