libstdc++-v3/libsupc++/tinfo.cc

   1 // Methods for type_info for -*- C++ -*- Run Time Type Identification.
   2 // Copyright (C) 1994, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004
   3 // Free Software Foundation
   4 //
   5 // This file is part of GCC.
   6 //
   7 // GCC is free software; you can redistribute it and/or modify
   8 // it under the terms of the GNU General Public License as published by
   9 // the Free Software Foundation; either version 2, or (at your option)
  10 // any later version.
  11
  12 // GCC is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // You should have received a copy of the GNU General Public License
  18 // along with GCC; see the file COPYING.  If not, write to
  19 // the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  20 // Boston, MA 02110-1301, USA.
  21
  22 // As a special exception, you may use this file as part of a free software
  23 // library without restriction.  Specifically, if other files instantiate
  24 // templates or use macros or inline functions from this file, or you compile
  25 // this file and link it with other files to produce an executable, this
  26 // file does not by itself cause the resulting executable to be covered by
  27 // the GNU General Public License.  This exception does not however
  28 // invalidate any other reasons why the executable file might be covered by
  29 // the GNU General Public License.
  30
  31 #include <bits/c++config.h>
  32 #include <cstddef>
  33 #include "tinfo.h"
  34 #include "new"                  // for placement new
  35
  36 // This file contains the minimal working set necessary to link with code
  37 // that uses virtual functions and -frtti but does not actually use RTTI
  38 // functionality.
  39
  40 std::type_info::
  41 ~type_info ()
  42 { }
  43
  44 std::bad_cast::~bad_cast() throw() { }
  45 std::bad_typeid::~bad_typeid() throw() { }
  46
  47 #if !__GXX_MERGED_TYPEINFO_NAMES
  48
  49 // We can't rely on common symbols being shared between shared objects.
  50 bool std::type_info::
  51 operator== (const std::type_info& arg) const
  52 {
  53   return (&arg == this) || (__builtin_strcmp (name (), arg.name ()) == 0);
  54 }
  55
  56 #endif
  57
  58 namespace std {
  59
  60 // return true if this is a type_info for a pointer type
  61 bool type_info::
  62 __is_pointer_p () const
  63 {
  64   return false;
  65 }
  66
  67 // return true if this is a type_info for a function type
  68 bool type_info::
  69 __is_function_p () const
  70 {
  71   return false;
  72 }
  73
  74 // try and catch a thrown object.
  75 bool type_info::
  76 __do_catch (const type_info *thr_type, void **, unsigned) const
  77 {
  78   return *this == *thr_type;
  79 }
  80
  81 // upcast from this type to the target. __class_type_info will override
  82 bool type_info::
  83 __do_upcast (const abi::__class_type_info *, void **) const
  84 {
  85   return false;
  86 }
  87
  88 }
  89
  90 namespace {
  91
  92 using namespace std;
  93 using namespace abi;
  94
  95 // Initial part of a vtable, this structure is used with offsetof, so we don't
  96 // have to keep alignments consistent manually.
  97 struct vtable_prefix
  98 {
  99   // Offset to most derived object.
 100   ptrdiff_t whole_object;
 101
 102   // Additional padding if necessary.
 103 #ifdef _GLIBCXX_VTABLE_PADDING
 104   ptrdiff_t padding1;
 105 #endif
 106
 107   // Pointer to most derived type_info.
 108   const __class_type_info *whole_type;
 109
 110   // Additional padding if necessary.
 111 #ifdef _GLIBCXX_VTABLE_PADDING
 112   ptrdiff_t padding2;
 113 #endif
 114
 115   // What a class's vptr points to.
 116   const void *origin;
 117 };
 118
 119 template <typename T>
 120 inline const T *
 121 adjust_pointer (const void *base, ptrdiff_t offset)
 122 {
 123   return reinterpret_cast <const T *>
 124     (reinterpret_cast <const char *> (base) + offset);
 125 }
 126
 127 // ADDR is a pointer to an object.  Convert it to a pointer to a base,
 128 // using OFFSET. IS_VIRTUAL is true, if we are getting a virtual base.
 129 inline void const *
 130 convert_to_base (void const *addr, bool is_virtual, ptrdiff_t offset)
 131 {
 132   if (is_virtual)
 133     {
 134       const void *vtable = *static_cast <const void *const *> (addr);
 135
 136       offset = *adjust_pointer<ptrdiff_t> (vtable, offset);
 137     }
 138
 139   return adjust_pointer<void> (addr, offset);
 140 }
 141
 142 // some predicate functions for __class_type_info::__sub_kind
 143 inline bool contained_p (__class_type_info::__sub_kind access_path)
 144 {
 145   return access_path >= __class_type_info::__contained_mask;
 146 }
 147 inline bool public_p (__class_type_info::__sub_kind access_path)
 148 {
 149   return access_path & __class_type_info::__contained_public_mask;
 150 }
 151 inline bool virtual_p (__class_type_info::__sub_kind access_path)
 152 {
 153   return (access_path & __class_type_info::__contained_virtual_mask);
 154 }
 155 inline bool contained_public_p (__class_type_info::__sub_kind access_path)
 156 {
 157   return ((access_path & __class_type_info::__contained_public)
 158           == __class_type_info::__contained_public);
 159 }
 160 inline bool contained_nonpublic_p (__class_type_info::__sub_kind access_path)
 161 {
 162   return ((access_path & __class_type_info::__contained_public)
 163           == __class_type_info::__contained_mask);
 164 }
 165 inline bool contained_nonvirtual_p (__class_type_info::__sub_kind access_path)
 166 {
 167   return ((access_path & (__class_type_info::__contained_mask
 168                           | __class_type_info::__contained_virtual_mask))
 169           == __class_type_info::__contained_mask);
 170 }
 171
 172 static const __class_type_info *const nonvirtual_base_type =
 173     static_cast <const __class_type_info *> (0) + 1;
 174
 175 } // namespace
 176
 177 namespace __cxxabiv1
 178 {
 179
 180 __class_type_info::
 181 ~__class_type_info ()
 182 {}
 183
 184 __si_class_type_info::
 185 ~__si_class_type_info ()
 186 {}
 187
 188 __vmi_class_type_info::
 189 ~__vmi_class_type_info ()
 190 {}
 191
 192 // __upcast_result is used to hold information during traversal of a class
 193 // hierarchy when catch matching.
 194 struct __class_type_info::__upcast_result
 195 {
 196   const void *dst_ptr;        // pointer to caught object
 197   __sub_kind part2dst;        // path from current base to target
 198   int src_details;            // hints about the source type hierarchy
 199   const __class_type_info *base_type; // where we found the target,
 200                               // if in vbase the __class_type_info of vbase
 201                               // if a non-virtual base then 1
 202                               // else NULL
 203   __upcast_result (int d)
 204     :dst_ptr (NULL), part2dst (__unknown), src_details (d), base_type (NULL)
 205     {}
 206 };
 207
 208 // __dyncast_result is used to hold information during traversal of a class
 209 // hierarchy when dynamic casting.
 210 struct __class_type_info::__dyncast_result
 211 {
 212   const void *dst_ptr;        // pointer to target object or NULL
 213   __sub_kind whole2dst;       // path from most derived object to target
 214   __sub_kind whole2src;       // path from most derived object to sub object
 215   __sub_kind dst2src;         // path from target to sub object
 216   int whole_details;          // details of the whole class hierarchy
 217
 218   __dyncast_result (int details_ = __vmi_class_type_info::__flags_unknown_mask)
 219     :dst_ptr (NULL), whole2dst (__unknown),
 220      whole2src (__unknown), dst2src (__unknown),
 221      whole_details (details_)
 222     {}
 223
 224 protected:
 225   __dyncast_result(const __dyncast_result&);
 226
 227   __dyncast_result&
 228   operator=(const __dyncast_result&);
 229 };
 230
 231 bool __class_type_info::
 232 __do_catch (const type_info *thr_type,
 233             void **thr_obj,
 234             unsigned outer) const
 235 {
 236   if (*this == *thr_type)
 237     return true;
 238   if (outer >= 4)
 239     // Neither `A' nor `A *'.
 240     return false;
 241   return thr_type->__do_upcast (this, thr_obj);
 242 }
 243
 244 bool __class_type_info::
 245 __do_upcast (const __class_type_info *dst_type,
 246              void **obj_ptr) const
 247 {
 248   __upcast_result result (__vmi_class_type_info::__flags_unknown_mask);
 249
 250   __do_upcast (dst_type, *obj_ptr, result);
 251   if (!contained_public_p (result.part2dst))
 252     return false;
 253   *obj_ptr = const_cast <void *> (result.dst_ptr);
 254   return true;
 255 }
 256
 257 inline __class_type_info::__sub_kind __class_type_info::
 258 __find_public_src (ptrdiff_t src2dst,
 259                    const void *obj_ptr,
 260                    const __class_type_info *src_type,
 261                    const void *src_ptr) const
 262 {
 263   if (src2dst >= 0)
 264     return adjust_pointer <void> (obj_ptr, src2dst) == src_ptr
 265             ? __contained_public : __not_contained;
 266   if (src2dst == -2)
 267     return __not_contained;
 268   return __do_find_public_src (src2dst, obj_ptr, src_type, src_ptr);
 269 }
 270
 271 __class_type_info::__sub_kind __class_type_info::
 272 __do_find_public_src (ptrdiff_t,
 273                       const void *obj_ptr,
 274                       const __class_type_info *,
 275                       const void *src_ptr) const
 276 {
 277   if (src_ptr == obj_ptr)
 278     // Must be our type, as the pointers match.
 279     return __contained_public;
 280   return __not_contained;
 281 }
 282
 283 __class_type_info::__sub_kind __si_class_type_info::
 284 __do_find_public_src (ptrdiff_t src2dst,
 285                       const void *obj_ptr,
 286                       const __class_type_info *src_type,
 287                       const void *src_ptr) const
 288 {
 289   if (src_ptr == obj_ptr && *this == *src_type)
 290     return __contained_public;
 291   return __base_type->__do_find_public_src (src2dst, obj_ptr, src_type, src_ptr);
 292 }
 293
 294 __class_type_info::__sub_kind __vmi_class_type_info::
 295 __do_find_public_src (ptrdiff_t src2dst,
 296                       const void *obj_ptr,
 297                       const __class_type_info *src_type,
 298                       const void *src_ptr) const
 299 {
 300   if (obj_ptr == src_ptr && *this == *src_type)
 301     return __contained_public;
 302
 303   for (std::size_t i = __base_count; i--;)
 304     {
 305       if (!__base_info[i].__is_public_p ())
 306         continue; // Not public, can't be here.
 307
 308       const void *base = obj_ptr;
 309       ptrdiff_t offset = __base_info[i].__offset ();
 310       bool is_virtual = __base_info[i].__is_virtual_p ();
 311
 312       if (is_virtual)
 313         {
 314           if (src2dst == -3)
 315             continue; // Not a virtual base, so can't be here.
 316         }
 317       base = convert_to_base (base, is_virtual, offset);
 318
 319       __sub_kind base_kind = __base_info[i].__base_type->__do_find_public_src
 320                               (src2dst, base, src_type, src_ptr);
 321       if (contained_p (base_kind))
 322         {
 323           if (is_virtual)
 324             base_kind = __sub_kind (base_kind | __contained_virtual_mask);
 325           return base_kind;
 326         }
 327     }
 328
 329   return __not_contained;
 330 }
 331
 332 bool __class_type_info::
 333 __do_dyncast (ptrdiff_t,
 334               __sub_kind access_path,
 335               const __class_type_info *dst_type,
 336               const void *obj_ptr,
 337               const __class_type_info *src_type,
 338               const void *src_ptr,
 339               __dyncast_result &__restrict result) const
 340 {
 341   if (obj_ptr == src_ptr && *this == *src_type)
 342     {
 343       // The src object we started from. Indicate how we are accessible from
 344       // the most derived object.
 345       result.whole2src = access_path;
 346       return false;
 347     }
 348   if (*this == *dst_type)
 349     {
 350       result.dst_ptr = obj_ptr;
 351       result.whole2dst = access_path;
 352       result.dst2src = __not_contained;
 353       return false;
 354     }
 355   return false;
 356 }
 357
 358 bool __si_class_type_info::
 359 __do_dyncast (ptrdiff_t src2dst,
 360               __sub_kind access_path,
 361               const __class_type_info *dst_type,
 362               const void *obj_ptr,
 363               const __class_type_info *src_type,
 364               const void *src_ptr,
 365               __dyncast_result &__restrict result) const
 366 {
 367   if (*this == *dst_type)
 368     {
 369       result.dst_ptr = obj_ptr;
 370       result.whole2dst = access_path;
 371       if (src2dst >= 0)
 372         result.dst2src = adjust_pointer <void> (obj_ptr, src2dst) == src_ptr
 373               ? __contained_public : __not_contained;
 374       else if (src2dst == -2)
 375         result.dst2src = __not_contained;
 376       return false;
 377     }
 378   if (obj_ptr == src_ptr && *this == *src_type)
 379     {
 380       // The src object we started from. Indicate how we are accessible from
 381       // the most derived object.
 382       result.whole2src = access_path;
 383       return false;
 384     }
 385   return __base_type->__do_dyncast (src2dst, access_path, dst_type, obj_ptr,
 386                              src_type, src_ptr, result);
 387 }
 388
 389 // This is a big hairy function. Although the run-time behaviour of
 390 // dynamic_cast is simple to describe, it gives rise to some non-obvious
 391 // behaviour. We also desire to determine as early as possible any definite
 392 // answer we can get. Because it is unknown what the run-time ratio of
 393 // succeeding to failing dynamic casts is, we do not know in which direction
 394 // to bias any optimizations. To that end we make no particular effort towards
 395 // early fail answers or early success answers. Instead we try to minimize
 396 // work by filling in things lazily (when we know we need the information),
 397 // and opportunisticly take early success or failure results.
 398 bool __vmi_class_type_info::
 399 __do_dyncast (ptrdiff_t src2dst,
 400               __sub_kind access_path,
 401               const __class_type_info *dst_type,
 402               const void *obj_ptr,
 403               const __class_type_info *src_type,
 404               const void *src_ptr,
 405               __dyncast_result &__restrict result) const
 406 {
 407   if (result.whole_details & __flags_unknown_mask)
 408     result.whole_details = __flags;
 409
 410   if (obj_ptr == src_ptr && *this == *src_type)
 411     {
 412       // The src object we started from. Indicate how we are accessible from
 413       // the most derived object.
 414       result.whole2src = access_path;
 415       return false;
 416     }
 417   if (*this == *dst_type)
 418     {
 419       result.dst_ptr = obj_ptr;
 420       result.whole2dst = access_path;
 421       if (src2dst >= 0)
 422         result.dst2src = adjust_pointer <void> (obj_ptr, src2dst) == src_ptr
 423               ? __contained_public : __not_contained;
 424       else if (src2dst == -2)
 425         result.dst2src = __not_contained;
 426       return false;
 427     }
 428
 429   bool result_ambig = false;
 430   for (std::size_t i = __base_count; i--;)
 431     {
 432       __dyncast_result result2 (result.whole_details);
 433       void const *base = obj_ptr;
 434       __sub_kind base_access = access_path;
 435       ptrdiff_t offset = __base_info[i].__offset ();
 436       bool is_virtual = __base_info[i].__is_virtual_p ();
 437
 438       if (is_virtual)
 439         base_access = __sub_kind (base_access | __contained_virtual_mask);
 440       base = convert_to_base (base, is_virtual, offset);
 441
 442       if (!__base_info[i].__is_public_p ())
 443         {
 444           if (src2dst == -2 &&
 445               !(result.whole_details
 446                 & (__non_diamond_repeat_mask | __diamond_shaped_mask)))
 447             // The hierarchy has no duplicate bases (which might ambiguate
 448             // things) and where we started is not a public base of what we
 449             // want (so it cannot be a downcast). There is nothing of interest
 450             // hiding in a non-public base.
 451             continue;
 452           base_access = __sub_kind (base_access & ~__contained_public_mask);
 453         }
 454
 455       bool result2_ambig
 456           = __base_info[i].__base_type->__do_dyncast (src2dst, base_access,
 457                                              dst_type, base,
 458                                              src_type, src_ptr, result2);
 459       result.whole2src = __sub_kind (result.whole2src | result2.whole2src);
 460       if (result2.dst2src == __contained_public
 461           || result2.dst2src == __contained_ambig)
 462         {
 463           result.dst_ptr = result2.dst_ptr;
 464           result.whole2dst = result2.whole2dst;
 465           result.dst2src = result2.dst2src;
 466           // Found a downcast which can't be bettered or an ambiguous downcast
 467           // which can't be disambiguated
 468           return result2_ambig;
 469         }
 470
 471       if (!result_ambig && !result.dst_ptr)
 472         {
 473           // Not found anything yet.
 474           result.dst_ptr = result2.dst_ptr;
 475           result.whole2dst = result2.whole2dst;
 476           result_ambig = result2_ambig;
 477           if (result.dst_ptr && result.whole2src != __unknown
 478               && !(__flags & __non_diamond_repeat_mask))
 479             // Found dst and src and we don't have repeated bases.
 480             return result_ambig;
 481         }
 482       else if (result.dst_ptr && result.dst_ptr == result2.dst_ptr)
 483         {
 484           // Found at same address, must be via virtual.  Pick the most
 485           // accessible path.
 486           result.whole2dst =
 487               __sub_kind (result.whole2dst | result2.whole2dst);
 488         }
 489       else if ((result.dst_ptr != 0 & result2.dst_ptr != 0)
 490                || (result.dst_ptr != 0 & result2_ambig)
 491                || (result2.dst_ptr != 0 & result_ambig))
 492         {
 493           // Found two different DST_TYPE bases, or a valid one and a set of
 494           // ambiguous ones, must disambiguate. See whether SRC_PTR is
 495           // contained publicly within one of the non-ambiguous choices. If it
 496           // is in only one, then that's the choice. If it is in both, then
 497           // we're ambiguous and fail. If it is in neither, we're ambiguous,
 498           // but don't yet fail as we might later find a third base which does
 499           // contain SRC_PTR.
 500
 501           __sub_kind new_sub_kind = result2.dst2src;
 502           __sub_kind old_sub_kind = result.dst2src;
 503
 504           if (contained_p (result.whole2src)
 505               && (!virtual_p (result.whole2src)
 506                   || !(result.whole_details & __diamond_shaped_mask)))
 507             {
 508               // We already found SRC_PTR as a base of most derived, and
 509               // either it was non-virtual, or the whole hierarchy is
 510               // not-diamond shaped. Therefore if it is in either choice, it
 511               // can only be in one of them, and we will already know.
 512               if (old_sub_kind == __unknown)
 513                 old_sub_kind = __not_contained;
 514               if (new_sub_kind == __unknown)
 515                 new_sub_kind = __not_contained;
 516             }
 517           else
 518             {
 519               if (old_sub_kind >= __not_contained)
 520                 ;// already calculated
 521               else if (contained_p (new_sub_kind)
 522                        && (!virtual_p (new_sub_kind)
 523                            || !(__flags & __diamond_shaped_mask)))
 524                 // Already found inside the other choice, and it was
 525                 // non-virtual or we are not diamond shaped.
 526                 old_sub_kind = __not_contained;
 527               else
 528                 old_sub_kind = dst_type->__find_public_src
 529                                 (src2dst, result.dst_ptr, src_type, src_ptr);
 530
 531               if (new_sub_kind >= __not_contained)
 532                 ;// already calculated
 533               else if (contained_p (old_sub_kind)
 534                        && (!virtual_p (old_sub_kind)
 535                            || !(__flags & __diamond_shaped_mask)))
 536                 // Already found inside the other choice, and it was
 537                 // non-virtual or we are not diamond shaped.
 538                 new_sub_kind = __not_contained;
 539               else
 540                 new_sub_kind = dst_type->__find_public_src
 541                                 (src2dst, result2.dst_ptr, src_type, src_ptr);
 542             }
 543
 544           // Neither sub_kind can be contained_ambig -- we bail out early
 545           // when we find those.
 546           if (contained_p (__sub_kind (new_sub_kind ^ old_sub_kind)))
 547             {
 548               // Only on one choice, not ambiguous.
 549               if (contained_p (new_sub_kind))
 550                 {
 551                   // Only in new.
 552                   result.dst_ptr = result2.dst_ptr;
 553                   result.whole2dst = result2.whole2dst;
 554                   result_ambig = false;
 555                   old_sub_kind = new_sub_kind;
 556                 }
 557               result.dst2src = old_sub_kind;
 558               if (public_p (result.dst2src))
 559                 return false; // Can't be an ambiguating downcast for later discovery.
 560               if (!virtual_p (result.dst2src))
 561                 return false; // Found non-virtually can't be bettered
 562             }
 563           else if (contained_p (__sub_kind (new_sub_kind & old_sub_kind)))
 564             {
 565               // In both.
 566               result.dst_ptr = NULL;
 567               result.dst2src = __contained_ambig;
 568               return true;  // Fail.
 569             }
 570           else
 571             {
 572               // In neither publicly, ambiguous for the moment, but keep
 573               // looking. It is possible that it was private in one or
 574               // both and therefore we should fail, but that's just tough.
 575               result.dst_ptr = NULL;
 576               result.dst2src = __not_contained;
 577               result_ambig = true;
 578             }
 579         }
 580
 581       if (result.whole2src == __contained_private)
 582         // We found SRC_PTR as a private non-virtual base, therefore all
 583         // cross casts will fail. We have already found a down cast, if
 584         // there is one.
 585         return result_ambig;
 586     }
 587
 588   return result_ambig;
 589 }
 590
 591 bool __class_type_info::
 592 __do_upcast (const __class_type_info *dst, const void *obj,
 593              __upcast_result &__restrict result) const
 594 {
 595   if (*this == *dst)
 596     {
 597       result.dst_ptr = obj;
 598       result.base_type = nonvirtual_base_type;
 599       result.part2dst = __contained_public;
 600       return true;
 601     }
 602   return false;
 603 }
 604
 605 bool __si_class_type_info::
 606 __do_upcast (const __class_type_info *dst, const void *obj_ptr,
 607              __upcast_result &__restrict result) const
 608 {
 609   if (__class_type_info::__do_upcast (dst, obj_ptr, result))
 610     return true;
 611
 612   return __base_type->__do_upcast (dst, obj_ptr, result);
 613 }
 614
 615 bool __vmi_class_type_info::
 616 __do_upcast (const __class_type_info *dst, const void *obj_ptr,
 617              __upcast_result &__restrict result) const
 618 {
 619   if (__class_type_info::__do_upcast (dst, obj_ptr, result))
 620     return true;
 621
 622   int src_details = result.src_details;
 623   if (src_details & __flags_unknown_mask)
 624     src_details = __flags;
 625
 626   for (std::size_t i = __base_count; i--;)
 627     {
 628       __upcast_result result2 (src_details);
 629       const void *base = obj_ptr;
 630       ptrdiff_t offset = __base_info[i].__offset ();
 631       bool is_virtual = __base_info[i].__is_virtual_p ();
 632       bool is_public = __base_info[i].__is_public_p ();
 633
 634       if (!is_public && !(src_details & __non_diamond_repeat_mask))
 635         // original cannot have an ambiguous base, so skip private bases
 636         continue;
 637
 638       if (base)
 639         base = convert_to_base (base, is_virtual, offset);
 640
 641       if (__base_info[i].__base_type->__do_upcast (dst, base, result2))
 642         {
 643           if (result2.base_type == nonvirtual_base_type && is_virtual)
 644             result2.base_type = __base_info[i].__base_type;
 645           if (contained_p (result2.part2dst) && !is_public)
 646             result2.part2dst = __sub_kind (result2.part2dst & ~__contained_public_mask);
 647
 648           if (!result.base_type)
 649             {
 650               result = result2;
 651               if (!contained_p (result.part2dst))
 652                 return true; // found ambiguously
 653
 654               if (result.part2dst & __contained_public_mask)
 655                 {
 656                   if (!(__flags & __non_diamond_repeat_mask))
 657                     return true;  // cannot have an ambiguous other base
 658                 }
 659               else
 660                 {
 661                   if (!virtual_p (result.part2dst))
 662                     return true; // cannot have another path
 663                   if (!(__flags & __diamond_shaped_mask))
 664                     return true; // cannot have a more accessible path
 665                 }
 666             }
 667           else if (result.dst_ptr != result2.dst_ptr)
 668             {
 669               // Found an ambiguity.
 670               result.dst_ptr = NULL;
 671               result.part2dst = __contained_ambig;
 672               return true;
 673             }
 674           else if (result.dst_ptr)
 675             {
 676               // Ok, found real object via a virtual path.
 677               result.part2dst
 678                   = __sub_kind (result.part2dst | result2.part2dst);
 679             }
 680           else
 681             {
 682               // Dealing with a null pointer, need to check vbase
 683               // containing each of the two choices.
 684               if (result2.base_type == nonvirtual_base_type
 685                   || result.base_type == nonvirtual_base_type
 686                   || !(*result2.base_type == *result.base_type))
 687                 {
 688                   // Already ambiguous, not virtual or via different virtuals.
 689                   // Cannot match.
 690                   result.part2dst = __contained_ambig;
 691                   return true;
 692                 }
 693               result.part2dst
 694                   = __sub_kind (result.part2dst | result2.part2dst);
 695             }
 696         }
 697     }
 698   return result.part2dst != __unknown;
 699 }
 700
 701 // this is the external interface to the dynamic cast machinery
 702 extern "C" void *
 703 __dynamic_cast (const void *src_ptr,    // object started from
 704                 const __class_type_info *src_type, // type of the starting object
 705                 const __class_type_info *dst_type, // desired target type
 706                 ptrdiff_t src2dst) // how src and dst are related
 707 {
 708   const void *vtable = *static_cast <const void *const *> (src_ptr);
 709   const vtable_prefix *prefix =
 710       adjust_pointer <vtable_prefix> (vtable,
 711                                       -offsetof (vtable_prefix, origin));
 712   const void *whole_ptr =
 713       adjust_pointer <void> (src_ptr, prefix->whole_object);
 714   const __class_type_info *whole_type = prefix->whole_type;
 715   __class_type_info::__dyncast_result result;
 716
 717   whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public,
 718                             dst_type, whole_ptr, src_type, src_ptr, result);
 719   if (!result.dst_ptr)
 720     return NULL;
 721   if (contained_public_p (result.dst2src))
 722     // Src is known to be a public base of dst.
 723     return const_cast <void *> (result.dst_ptr);
 724   if (contained_public_p (__class_type_info::__sub_kind (result.whole2src & result.whole2dst)))
 725     // Both src and dst are known to be public bases of whole. Found a valid
 726     // cross cast.
 727     return const_cast <void *> (result.dst_ptr);
 728   if (contained_nonvirtual_p (result.whole2src))
 729     // Src is known to be a non-public nonvirtual base of whole, and not a
 730     // base of dst. Found an invalid cross cast, which cannot also be a down
 731     // cast
 732     return NULL;
 733   if (result.dst2src == __class_type_info::__unknown)
 734     result.dst2src = dst_type->__find_public_src (src2dst, result.dst_ptr,
 735                                                   src_type, src_ptr);
 736   if (contained_public_p (result.dst2src))
 737     // Found a valid down cast
 738     return const_cast <void *> (result.dst_ptr);
 739   // Must be an invalid down cast, or the cross cast wasn't bettered
 740   return NULL;
 741 }
 742
 743 } // namespace __cxxabiv1