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1 // Copyright (C) 1994-2020 Free Software Foundation, Inc.
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111
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2 //
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3 // This file is part of GCC.
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4 //
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5 // GCC is free software; you can redistribute it and/or modify
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6 // it under the terms of the GNU General Public License as published by
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7 // the Free Software Foundation; either version 3, or (at your option)
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8 // any later version.
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9
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10 // GCC is distributed in the hope that it will be useful,
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11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 // GNU General Public License for more details.
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14
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15 // Under Section 7 of GPL version 3, you are granted additional
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16 // permissions described in the GCC Runtime Library Exception, version
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17 // 3.1, as published by the Free Software Foundation.
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18
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19 // You should have received a copy of the GNU General Public License and
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20 // a copy of the GCC Runtime Library Exception along with this program;
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21 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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22 // <http://www.gnu.org/licenses/>.
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23
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24 #include "tinfo.h"
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25
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26 namespace __cxxabiv1 {
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27
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28
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29 // this is the external interface to the dynamic cast machinery
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30 /* sub: source address to be adjusted; nonnull, and since the
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31 * source object is polymorphic, *(void**)sub is a virtual pointer.
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32 * src: static type of the source object.
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33 * dst: destination type (the "T" in "dynamic_cast<T>(v)").
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34 * src2dst_offset: a static hint about the location of the
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35 * source subobject with respect to the complete object;
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36 * special negative values are:
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37 * -1: no hint
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38 * -2: src is not a public base of dst
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39 * -3: src is a multiple public base type but never a
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40 * virtual base type
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41 * otherwise, the src type is a unique public nonvirtual
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42 * base type of dst at offset src2dst_offset from the
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43 * origin of dst. */
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44 extern "C" void *
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45 __dynamic_cast (const void *src_ptr, // object started from
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46 const __class_type_info *src_type, // type of the starting object
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47 const __class_type_info *dst_type, // desired target type
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48 ptrdiff_t src2dst) // how src and dst are related
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49 {
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50 const void *vtable = *static_cast <const void *const *> (src_ptr);
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51 const vtable_prefix *prefix =
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52 adjust_pointer <vtable_prefix> (vtable,
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53 -offsetof (vtable_prefix, origin));
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54 const void *whole_ptr =
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55 adjust_pointer <void> (src_ptr, prefix->whole_object);
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56 const __class_type_info *whole_type = prefix->whole_type;
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57 __class_type_info::__dyncast_result result;
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58
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59 // If the whole object vptr doesn't refer to the whole object type, we're
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60 // in the middle of constructing a primary base, and src is a separate
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61 // base. This has undefined behavior and we can't find anything outside
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62 // of the base we're actually constructing, so fail now rather than
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63 // segfault later trying to use a vbase offset that doesn't exist.
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64 const void *whole_vtable = *static_cast <const void *const *> (whole_ptr);
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65 const vtable_prefix *whole_prefix =
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66 adjust_pointer <vtable_prefix> (whole_vtable,
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67 -offsetof (vtable_prefix, origin));
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68 if (whole_prefix->whole_type != whole_type)
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69 return NULL;
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70
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71 whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
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72 dst_type, whole_ptr, src_type, src_ptr, result);
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73 if (!result.dst_ptr)
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74 return NULL;
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75 if (contained_public_p (result.dst2src))
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76 // Src is known to be a public base of dst.
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77 return const_cast <void *> (result.dst_ptr);
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78 if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
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79 // Both src and dst are known to be public bases of whole. Found a valid
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80 // cross cast.
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81 return const_cast <void *> (result.dst_ptr);
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82 if (contained_nonvirtual_p (result.whole2src))
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83 // Src is known to be a non-public nonvirtual base of whole, and not a
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84 // base of dst. Found an invalid cross cast, which cannot also be a down
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85 // cast
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86 return NULL;
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87 if (result.dst2src == __class_type_info::__unknown)
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88 result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
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89 src_type, src_ptr);
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90 if (contained_public_p (result.dst2src))
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91 // Found a valid down cast
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92 return const_cast <void *> (result.dst_ptr);
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93 // Must be an invalid down cast, or the cross cast wasn't bettered
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94 return NULL;
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95 }
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96
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97 }
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