1 // Copyright (C) 1994-2022 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
26 namespace __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. */
44 extern "C" void *
__dynamic_cast(const void * src_ptr,const __class_type_info * src_type,const __class_type_info * dst_type,ptrdiff_t src2dst)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 if (__builtin_expect(!src_ptr, 0))
51 return NULL; // Handle precondition violations gracefully.
52
53 const void *vtable = *static_cast <const void *const *> (src_ptr);
54 const vtable_prefix *prefix =
55 (adjust_pointer <vtable_prefix>
56 (vtable, -ptrdiff_t (offsetof (vtable_prefix, origin))));
57 const void *whole_ptr =
58 adjust_pointer <void> (src_ptr, prefix->whole_object);
59 const __class_type_info *whole_type = prefix->whole_type;
60 __class_type_info::__dyncast_result result;
61
62 // If the whole object vptr doesn't refer to the whole object type, we're
63 // in the middle of constructing a primary base, and src is a separate
64 // base. This has undefined behavior and we can't find anything outside
65 // of the base we're actually constructing, so fail now rather than
66 // segfault later trying to use a vbase offset that doesn't exist.
67 const void *whole_vtable = *static_cast <const void *const *> (whole_ptr);
68 const vtable_prefix *whole_prefix =
69 (adjust_pointer <vtable_prefix>
70 (whole_vtable, -ptrdiff_t (offsetof (vtable_prefix, origin))));
71 if (whole_prefix->whole_type != whole_type)
72 return NULL;
73
74 whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
75 dst_type, whole_ptr, src_type, src_ptr, result);
76 if (!result.dst_ptr)
77 return NULL;
78 if (contained_public_p (result.dst2src))
79 // Src is known to be a public base of dst.
80 return const_cast <void *> (result.dst_ptr);
81 if (contained_public_p (__class_type_info::__sub_kind
82 (result.whole2src & result.whole2dst)))
83 // Both src and dst are known to be public bases of whole. Found a valid
84 // cross cast.
85 return const_cast <void *> (result.dst_ptr);
86 if (contained_nonvirtual_p (result.whole2src))
87 // Src is known to be a non-public nonvirtual base of whole, and not a
88 // base of dst. Found an invalid cross cast, which cannot also be a down
89 // cast
90 return NULL;
91 if (result.dst2src == __class_type_info::__unknown)
92 result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
93 src_type, src_ptr);
94 if (contained_public_p (result.dst2src))
95 // Found a valid down cast
96 return const_cast <void *> (result.dst_ptr);
97 // Must be an invalid down cast, or the cross cast wasn't bettered
98 return NULL;
99 }
100
101 }
102