| // Copyright (C) 1994-2021 Free Software Foundation, Inc. |
| // |
| // This file is part of GCC. |
| // |
| // GCC is free software; you can redistribute it and/or modify |
| // it under the terms of the GNU General Public License as published by |
| // the Free Software Foundation; either version 3, or (at your option) |
| // any later version. |
| |
| // GCC is distributed in the hope that it will be useful, |
| // but WITHOUT ANY WARRANTY; without even the implied warranty of |
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| // GNU General Public License for more details. |
| |
| // Under Section 7 of GPL version 3, you are granted additional |
| // permissions described in the GCC Runtime Library Exception, version |
| // 3.1, as published by the Free Software Foundation. |
| |
| // You should have received a copy of the GNU General Public License and |
| // a copy of the GCC Runtime Library Exception along with this program; |
| // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
| // <http://www.gnu.org/licenses/>. |
| |
| #include "tinfo.h" |
| |
| namespace __cxxabiv1 { |
| |
| |
| // this is the external interface to the dynamic cast machinery |
| /* sub: source address to be adjusted; nonnull, and since the |
| * source object is polymorphic, *(void**)sub is a virtual pointer. |
| * src: static type of the source object. |
| * dst: destination type (the "T" in "dynamic_cast<T>(v)"). |
| * src2dst_offset: a static hint about the location of the |
| * source subobject with respect to the complete object; |
| * special negative values are: |
| * -1: no hint |
| * -2: src is not a public base of dst |
| * -3: src is a multiple public base type but never a |
| * virtual base type |
| * otherwise, the src type is a unique public nonvirtual |
| * base type of dst at offset src2dst_offset from the |
| * origin of dst. */ |
| extern "C" void * |
| __dynamic_cast (const void *src_ptr, // object started from |
| const __class_type_info *src_type, // type of the starting object |
| const __class_type_info *dst_type, // desired target type |
| ptrdiff_t src2dst) // how src and dst are related |
| { |
| if (__builtin_expect(!src_ptr, 0)) |
| return NULL; // Handle precondition violations gracefully. |
| |
| const void *vtable = *static_cast <const void *const *> (src_ptr); |
| const vtable_prefix *prefix = |
| (adjust_pointer <vtable_prefix> |
| (vtable, -ptrdiff_t (offsetof (vtable_prefix, origin)))); |
| const void *whole_ptr = |
| adjust_pointer <void> (src_ptr, prefix->whole_object); |
| const __class_type_info *whole_type = prefix->whole_type; |
| __class_type_info::__dyncast_result result; |
| |
| // If the whole object vptr doesn't refer to the whole object type, we're |
| // in the middle of constructing a primary base, and src is a separate |
| // base. This has undefined behavior and we can't find anything outside |
| // of the base we're actually constructing, so fail now rather than |
| // segfault later trying to use a vbase offset that doesn't exist. |
| const void *whole_vtable = *static_cast <const void *const *> (whole_ptr); |
| const vtable_prefix *whole_prefix = |
| (adjust_pointer <vtable_prefix> |
| (whole_vtable, -ptrdiff_t (offsetof (vtable_prefix, origin)))); |
| if (whole_prefix->whole_type != whole_type) |
| return NULL; |
| |
| whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public, |
| dst_type, whole_ptr, src_type, src_ptr, result); |
| if (!result.dst_ptr) |
| return NULL; |
| if (contained_public_p (result.dst2src)) |
| // Src is known to be a public base of dst. |
| return const_cast <void *> (result.dst_ptr); |
| if (contained_public_p (__class_type_info::__sub_kind |
| (result.whole2src & result.whole2dst))) |
| // Both src and dst are known to be public bases of whole. Found a valid |
| // cross cast. |
| return const_cast <void *> (result.dst_ptr); |
| if (contained_nonvirtual_p (result.whole2src)) |
| // Src is known to be a non-public nonvirtual base of whole, and not a |
| // base of dst. Found an invalid cross cast, which cannot also be a down |
| // cast |
| return NULL; |
| if (result.dst2src == __class_type_info::__unknown) |
| result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr, |
| src_type, src_ptr); |
| if (contained_public_p (result.dst2src)) |
| // Found a valid down cast |
| return const_cast <void *> (result.dst_ptr); |
| // Must be an invalid down cast, or the cross cast wasn't bettered |
| return NULL; |
| } |
| |
| } |