1// Copyright (C) 1994-2017 Free Software Foundation, Inc.
2//
3// This file is part of GCC.
4//
5// GCC is free software; you can redistribute it and/or modify
6// it under the terms of the GNU General Public License as published by
7// the Free Software Foundation; either version 3, or (at your option)
8// any later version.
9
10// GCC is distributed in the hope that it will be useful,
11// but WITHOUT ANY WARRANTY; without even the implied warranty of
12// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13// GNU General Public License for more details.
14
15// Under Section 7 of GPL version 3, you are granted additional
16// permissions described in the GCC Runtime Library Exception, version
17// 3.1, as published by the Free Software Foundation.
18
19// You should have received a copy of the GNU General Public License and
20// a copy of the GCC Runtime Library Exception along with this program;
21// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
22// <http://www.gnu.org/licenses/>.
23
24#include "tinfo.h"
25
26namespace __cxxabiv1 {
27
28
29// this is the external interface to the dynamic cast machinery
30/* sub: source address to be adjusted; nonnull, and since the
31 * source object is polymorphic, *(void**)sub is a virtual pointer.
32 * src: static type of the source object.
33 * dst: destination type (the "T" in "dynamic_cast<T>(v)").
34 * src2dst_offset: a static hint about the location of the
35 * source subobject with respect to the complete object;
36 * special negative values are:
37 * -1: no hint
38 * -2: src is not a public base of dst
39 * -3: src is a multiple public base type but never a
40 * virtual base type
41 * otherwise, the src type is a unique public nonvirtual
42 * base type of dst at offset src2dst_offset from the
43 * origin of dst. */
44extern "C" void *
45__dynamic_cast (const void *src_ptr, // object started from
46 const __class_type_info *src_type, // type of the starting object
47 const __class_type_info *dst_type, // desired target type
48 ptrdiff_t src2dst) // how src and dst are related
49 {
50 const void *vtable = *static_cast <const void *const *> (src_ptr);
51 const vtable_prefix *prefix =
52 adjust_pointer <vtable_prefix> (vtable,
53 -offsetof (vtable_prefix, origin));
54 const void *whole_ptr =
55 adjust_pointer <void> (src_ptr, prefix->whole_object);
56 const __class_type_info *whole_type = prefix->whole_type;
57 __class_type_info::__dyncast_result result;
58
59 // If the whole object vptr doesn't refer to the whole object type, we're
60 // in the middle of constructing a primary base, and src is a separate
61 // base. This has undefined behavior and we can't find anything outside
62 // of the base we're actually constructing, so fail now rather than
63 // segfault later trying to use a vbase offset that doesn't exist.
64 const void *whole_vtable = *static_cast <const void *const *> (whole_ptr);
65 const vtable_prefix *whole_prefix =
66 adjust_pointer <vtable_prefix> (whole_vtable,
67 -offsetof (vtable_prefix, origin));
68 if (whole_prefix->whole_type != whole_type)
69 return NULL;
70
71 whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
72 dst_type, whole_ptr, src_type, src_ptr, result);
73 if (!result.dst_ptr)
74 return NULL;
75 if (contained_public_p (result.dst2src))
76 // Src is known to be a public base of dst.
77 return const_cast <void *> (result.dst_ptr);
78 if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
79 // Both src and dst are known to be public bases of whole. Found a valid
80 // cross cast.
81 return const_cast <void *> (result.dst_ptr);
82 if (contained_nonvirtual_p (result.whole2src))
83 // Src is known to be a non-public nonvirtual base of whole, and not a
84 // base of dst. Found an invalid cross cast, which cannot also be a down
85 // cast
86 return NULL;
87 if (result.dst2src == __class_type_info::__unknown)
88 result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
89 src_type, src_ptr);
90 if (contained_public_p (result.dst2src))
91 // Found a valid down cast
92 return const_cast <void *> (result.dst_ptr);
93 // Must be an invalid down cast, or the cross cast wasn't bettered
94 return NULL;
95}
96
97}
98