1 // ABI Support -*- C++ -*-
2 
3 // Copyright (C) 2000-2019 Free Software Foundation, Inc.
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 3, 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 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
20 
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
24 // <http://www.gnu.org/licenses/>.
25 
26 // Written by Nathan Sidwell, Codesourcery LLC, <nathan@codesourcery.com>
27 
28 /* This file declares the new abi entry points into the runtime. It is not
29    normally necessary for user programs to include this header, or use the
30    entry points directly. However, this header is available should that be
31    needed.
32 
33    Some of the entry points are intended for both C and C++, thus this header
34    is includable from both C and C++. Though the C++ specific parts are not
35    available in C, naturally enough.  */
36 
37 /** @file cxxabi.h
38  *  The header provides an interface to the C++ ABI.
39  */
40 
41 #ifndef _CXXABI_H
42 #define _CXXABI_H 1
43 
44 #pragma GCC system_header
45 
46 #pragma GCC visibility push(default)
47 
48 #include <stddef.h>
49 #include <bits/c++config.h>
50 #include <bits/cxxabi_tweaks.h>
51 #include <bits/cxxabi_forced.h>
52 #include <bits/cxxabi_init_exception.h>
53 
54 #ifdef __cplusplus
55 namespace __cxxabiv1
56 {
57   extern "C"
58   {
59 #endif
60 
61   typedef __cxa_cdtor_return_type (*__cxa_cdtor_type)(void *);
62 
63   // Allocate array.
64   void*
65   __cxa_vec_new(size_t __element_count, size_t __element_size,
66 		size_t __padding_size, __cxa_cdtor_type __constructor,
67 		__cxa_cdtor_type __destructor);
68 
69   void*
70   __cxa_vec_new2(size_t __element_count, size_t __element_size,
71 		 size_t __padding_size, __cxa_cdtor_type __constructor,
72 		 __cxa_cdtor_type __destructor, void *(*__alloc) (size_t),
73 		 void (*__dealloc) (void*));
74 
75   void*
76   __cxa_vec_new3(size_t __element_count, size_t __element_size,
77 		 size_t __padding_size, __cxa_cdtor_type __constructor,
78 		 __cxa_cdtor_type __destructor, void *(*__alloc) (size_t),
79 		 void (*__dealloc) (void*, size_t));
80 
81   // Construct array.
82   __cxa_vec_ctor_return_type
83   __cxa_vec_ctor(void* __array_address, size_t __element_count,
84 		 size_t __element_size, __cxa_cdtor_type __constructor,
85 		 __cxa_cdtor_type __destructor);
86 
87   __cxa_vec_ctor_return_type
88   __cxa_vec_cctor(void* __dest_array, void* __src_array,
89 		  size_t __element_count, size_t __element_size,
90 		  __cxa_cdtor_return_type (*__constructor) (void*, void*),
91 		  __cxa_cdtor_type __destructor);
92 
93   // Destruct array.
94   void
95   __cxa_vec_dtor(void* __array_address, size_t __element_count,
96 		 size_t __element_size, __cxa_cdtor_type __destructor);
97 
98   void
99   __cxa_vec_cleanup(void* __array_address, size_t __element_count, size_t __s,
100 		    __cxa_cdtor_type __destructor) _GLIBCXX_NOTHROW;
101 
102   // Destruct and release array.
103   void
104   __cxa_vec_delete(void* __array_address, size_t __element_size,
105 		   size_t __padding_size, __cxa_cdtor_type __destructor);
106 
107   void
108   __cxa_vec_delete2(void* __array_address, size_t __element_size,
109 		    size_t __padding_size, __cxa_cdtor_type __destructor,
110 		    void (*__dealloc) (void*));
111 
112   void
113   __cxa_vec_delete3(void* __array_address, size_t __element_size,
114 		    size_t __padding_size, __cxa_cdtor_type __destructor,
115 		    void (*__dealloc) (void*, size_t));
116 
117   int
118   __cxa_guard_acquire(__guard*);
119 
120   void
121   __cxa_guard_release(__guard*) _GLIBCXX_NOTHROW;
122 
123   void
124   __cxa_guard_abort(__guard*) _GLIBCXX_NOTHROW;
125 
126   // DSO destruction.
127   int
128   __cxa_atexit(void (*)(void*), void*, void*) _GLIBCXX_NOTHROW;
129 
130   int
131   __cxa_finalize(void*);
132 
133   // TLS destruction.
134   int
135   __cxa_thread_atexit(void (*)(void*), void*, void *) _GLIBCXX_NOTHROW;
136 
137   // Pure virtual functions.
138   void
139   __cxa_pure_virtual(void) __attribute__ ((__noreturn__));
140 
141   void
142   __cxa_deleted_virtual(void) __attribute__ ((__noreturn__));
143 
144   // Exception handling auxiliary.
145   void
146   __cxa_bad_cast() __attribute__((__noreturn__));
147 
148   void
149   __cxa_bad_typeid() __attribute__((__noreturn__));
150 
151   void
152   __cxa_throw_bad_array_new_length() __attribute__((__noreturn__));
153 
154   /**
155    *  @brief Demangling routine.
156    *  ABI-mandated entry point in the C++ runtime library for demangling.
157    *
158    *  @param __mangled_name A NUL-terminated character string
159    *  containing the name to be demangled.
160    *
161    *  @param __output_buffer A region of memory, allocated with
162    *  malloc, of @a *__length bytes, into which the demangled name is
163    *  stored.  If @a __output_buffer is not long enough, it is
164    *  expanded using realloc.  @a __output_buffer may instead be NULL;
165    *  in that case, the demangled name is placed in a region of memory
166    *  allocated with malloc.
167    *
168    *  @param __length If @a __length is non-null, the length of the
169    *  buffer containing the demangled name is placed in @a *__length.
170    *
171    *  @param __status If @a __status is non-null, @a *__status is set to
172    *  one of the following values:
173    *   0: The demangling operation succeeded.
174    *  -1: A memory allocation failure occurred.
175    *  -2: @a mangled_name is not a valid name under the C++ ABI mangling rules.
176    *  -3: One of the arguments is invalid.
177    *
178    *  @return A pointer to the start of the NUL-terminated demangled
179    *  name, or NULL if the demangling fails.  The caller is
180    *  responsible for deallocating this memory using @c free.
181    *
182    *  The demangling is performed using the C++ ABI mangling rules,
183    *  with GNU extensions. For example, this function is used in
184    *  __gnu_cxx::__verbose_terminate_handler.
185    *
186    *  See https://gcc.gnu.org/onlinedocs/libstdc++/manual/ext_demangling.html
187    *  for other examples of use.
188    *
189    *  @note The same demangling functionality is available via
190    *  libiberty (@c <libiberty/demangle.h> and @c libiberty.a) in GCC
191    *  3.1 and later, but that requires explicit installation (@c
192    *  --enable-install-libiberty) and uses a different API, although
193    *  the ABI is unchanged.
194    */
195   char*
196   __cxa_demangle(const char* __mangled_name, char* __output_buffer,
197 		 size_t* __length, int* __status);
198 
199 #ifdef __cplusplus
200   }
201 } // namespace __cxxabiv1
202 #endif
203 
204 #ifdef __cplusplus
205 
206 #include <typeinfo>
207 
208 namespace __cxxabiv1
209 {
210   // Type information for int, float etc.
211   class __fundamental_type_info : public std::type_info
212   {
213   public:
214     explicit
__fundamental_type_info(const char * __n)215     __fundamental_type_info(const char* __n) : std::type_info(__n) { }
216 
217     virtual
218     ~__fundamental_type_info();
219   };
220 
221   // Type information for array objects.
222   class __array_type_info : public std::type_info
223   {
224   public:
225     explicit
__array_type_info(const char * __n)226     __array_type_info(const char* __n) : std::type_info(__n) { }
227 
228     virtual
229     ~__array_type_info();
230   };
231 
232   // Type information for functions (both member and non-member).
233   class __function_type_info : public std::type_info
234   {
235   public:
236     explicit
__function_type_info(const char * __n)237     __function_type_info(const char* __n) : std::type_info(__n) { }
238 
239     virtual
240     ~__function_type_info();
241 
242   protected:
243     // Implementation defined member function.
244     virtual bool
245     __is_function_p() const;
246   };
247 
248   // Type information for enumerations.
249   class __enum_type_info : public std::type_info
250   {
251   public:
252     explicit
__enum_type_info(const char * __n)253     __enum_type_info(const char* __n) : std::type_info(__n) { }
254 
255     virtual
256     ~__enum_type_info();
257   };
258 
259   // Common type information for simple pointers and pointers to member.
260   class __pbase_type_info : public std::type_info
261   {
262   public:
263     unsigned int 		__flags; // Qualification of the target object.
264     const std::type_info* 	__pointee; // Type of pointed to object.
265 
266     explicit
__pbase_type_info(const char * __n,int __quals,const std::type_info * __type)267     __pbase_type_info(const char* __n, int __quals,
268 		      const std::type_info* __type)
269     : std::type_info(__n), __flags(__quals), __pointee(__type)
270     { }
271 
272     virtual
273     ~__pbase_type_info();
274 
275     // Implementation defined type.
276     enum __masks
277       {
278 	__const_mask = 0x1,
279 	__volatile_mask = 0x2,
280 	__restrict_mask = 0x4,
281 	__incomplete_mask = 0x8,
282 	__incomplete_class_mask = 0x10,
283 	__transaction_safe_mask = 0x20,
284 	__noexcept_mask = 0x40
285       };
286 
287   protected:
288     __pbase_type_info(const __pbase_type_info&);
289 
290     __pbase_type_info&
291     operator=(const __pbase_type_info&);
292 
293     // Implementation defined member functions.
294     virtual bool
295     __do_catch(const std::type_info* __thr_type, void** __thr_obj,
296 	       unsigned int __outer) const;
297 
298     inline virtual bool
299     __pointer_catch(const __pbase_type_info* __thr_type, void** __thr_obj,
300 		    unsigned __outer) const;
301   };
302 
303   inline bool __pbase_type_info::
__pointer_catch(const __pbase_type_info * thrown_type,void ** thr_obj,unsigned outer)304   __pointer_catch (const __pbase_type_info *thrown_type,
305 		   void **thr_obj,
306 		   unsigned outer) const
307   {
308     return __pointee->__do_catch (thrown_type->__pointee, thr_obj, outer + 2);
309   }
310 
311   // Type information for simple pointers.
312   class __pointer_type_info : public __pbase_type_info
313   {
314   public:
315     explicit
__pointer_type_info(const char * __n,int __quals,const std::type_info * __type)316     __pointer_type_info(const char* __n, int __quals,
317 			const std::type_info* __type)
318     : __pbase_type_info (__n, __quals, __type) { }
319 
320 
321     virtual
322     ~__pointer_type_info();
323 
324   protected:
325     // Implementation defined member functions.
326     virtual bool
327     __is_pointer_p() const;
328 
329     virtual bool
330     __pointer_catch(const __pbase_type_info* __thr_type, void** __thr_obj,
331 		    unsigned __outer) const;
332   };
333 
334   class __class_type_info;
335 
336   // Type information for a pointer to member variable.
337   class __pointer_to_member_type_info : public __pbase_type_info
338   {
339   public:
340     __class_type_info* __context;   // Class of the member.
341 
342     explicit
__pointer_to_member_type_info(const char * __n,int __quals,const std::type_info * __type,__class_type_info * __klass)343     __pointer_to_member_type_info(const char* __n, int __quals,
344 				  const std::type_info* __type,
345 				  __class_type_info* __klass)
346     : __pbase_type_info(__n, __quals, __type), __context(__klass) { }
347 
348     virtual
349     ~__pointer_to_member_type_info();
350 
351   protected:
352     __pointer_to_member_type_info(const __pointer_to_member_type_info&);
353 
354     __pointer_to_member_type_info&
355     operator=(const __pointer_to_member_type_info&);
356 
357     // Implementation defined member function.
358     virtual bool
359     __pointer_catch(const __pbase_type_info* __thr_type, void** __thr_obj,
360 		    unsigned __outer) const;
361   };
362 
363   // Helper class for __vmi_class_type.
364   class __base_class_type_info
365   {
366   public:
367     const __class_type_info* 	__base_type;  // Base class type.
368 #ifdef _GLIBCXX_LLP64
369     long long			__offset_flags;  // Offset and info.
370 #else
371     long 			__offset_flags;  // Offset and info.
372 #endif
373 
374     enum __offset_flags_masks
375       {
376 	__virtual_mask = 0x1,
377 	__public_mask = 0x2,
378 	__hwm_bit = 2,
379 	__offset_shift = 8          // Bits to shift offset.
380       };
381 
382     // Implementation defined member functions.
383     bool
__is_virtual_p()384     __is_virtual_p() const
385     { return __offset_flags & __virtual_mask; }
386 
387     bool
__is_public_p()388     __is_public_p() const
389     { return __offset_flags & __public_mask; }
390 
391     ptrdiff_t
__offset()392     __offset() const
393     {
394       // This shift, being of a signed type, is implementation
395       // defined. GCC implements such shifts as arithmetic, which is
396       // what we want.
397       return static_cast<ptrdiff_t>(__offset_flags) >> __offset_shift;
398     }
399   };
400 
401   // Type information for a class.
402   class __class_type_info : public std::type_info
403   {
404   public:
405     explicit
__class_type_info(const char * __n)406     __class_type_info (const char *__n) : type_info(__n) { }
407 
408     virtual
409     ~__class_type_info ();
410 
411     // Implementation defined types.
412     // The type sub_kind tells us about how a base object is contained
413     // within a derived object. We often do this lazily, hence the
414     // UNKNOWN value. At other times we may use NOT_CONTAINED to mean
415     // not publicly contained.
416     enum __sub_kind
417       {
418 	// We have no idea.
419 	__unknown = 0,
420 
421 	// Not contained within us (in some circumstances this might
422 	// mean not contained publicly)
423 	__not_contained,
424 
425 	// Contained ambiguously.
426 	__contained_ambig,
427 
428 	// Via a virtual path.
429 	__contained_virtual_mask = __base_class_type_info::__virtual_mask,
430 
431 	// Via a public path.
432 	__contained_public_mask = __base_class_type_info::__public_mask,
433 
434 	// Contained within us.
435 	__contained_mask = 1 << __base_class_type_info::__hwm_bit,
436 
437 	__contained_private = __contained_mask,
438 	__contained_public = __contained_mask | __contained_public_mask
439       };
440 
441     struct __upcast_result;
442     struct __dyncast_result;
443 
444   protected:
445     // Implementation defined member functions.
446     virtual bool
447     __do_upcast(const __class_type_info* __dst_type, void**__obj_ptr) const;
448 
449     virtual bool
450     __do_catch(const type_info* __thr_type, void** __thr_obj,
451 	       unsigned __outer) const;
452 
453   public:
454     // Helper for upcast. See if DST is us, or one of our bases.
455     // Return false if not found, true if found.
456     virtual bool
457     __do_upcast(const __class_type_info* __dst, const void* __obj,
458 		__upcast_result& __restrict __result) const;
459 
460     // Indicate whether SRC_PTR of type SRC_TYPE is contained publicly
461     // within OBJ_PTR. OBJ_PTR points to a base object of our type,
462     // which is the destination type. SRC2DST indicates how SRC
463     // objects might be contained within this type.  If SRC_PTR is one
464     // of our SRC_TYPE bases, indicate the virtuality. Returns
465     // not_contained for non containment or private containment.
466     inline __sub_kind
467     __find_public_src(ptrdiff_t __src2dst, const void* __obj_ptr,
468 		      const __class_type_info* __src_type,
469 		      const void* __src_ptr) const;
470 
471     // Helper for dynamic cast. ACCESS_PATH gives the access from the
472     // most derived object to this base. DST_TYPE indicates the
473     // desired type we want. OBJ_PTR points to a base of our type
474     // within the complete object. SRC_TYPE indicates the static type
475     // started from and SRC_PTR points to that base within the most
476     // derived object. Fill in RESULT with what we find. Return true
477     // if we have located an ambiguous match.
478     virtual bool
479     __do_dyncast(ptrdiff_t __src2dst, __sub_kind __access_path,
480 		 const __class_type_info* __dst_type, const void* __obj_ptr,
481 		 const __class_type_info* __src_type, const void* __src_ptr,
482 		 __dyncast_result& __result) const;
483 
484     // Helper for find_public_subobj. SRC2DST indicates how SRC_TYPE
485     // bases are inherited by the type started from -- which is not
486     // necessarily the current type. The current type will be a base
487     // of the destination type.  OBJ_PTR points to the current base.
488     virtual __sub_kind
489     __do_find_public_src(ptrdiff_t __src2dst, const void* __obj_ptr,
490 			 const __class_type_info* __src_type,
491 			 const void* __src_ptr) const;
492   };
493 
494   // Type information for a class with a single non-virtual base.
495   class __si_class_type_info : public __class_type_info
496   {
497   public:
498     const __class_type_info* __base_type;
499 
500     explicit
__si_class_type_info(const char * __n,const __class_type_info * __base)501     __si_class_type_info(const char *__n, const __class_type_info *__base)
502     : __class_type_info(__n), __base_type(__base) { }
503 
504     virtual
505     ~__si_class_type_info();
506 
507   protected:
508     __si_class_type_info(const __si_class_type_info&);
509 
510     __si_class_type_info&
511     operator=(const __si_class_type_info&);
512 
513     // Implementation defined member functions.
514     virtual bool
515     __do_dyncast(ptrdiff_t __src2dst, __sub_kind __access_path,
516 		 const __class_type_info* __dst_type, const void* __obj_ptr,
517 		 const __class_type_info* __src_type, const void* __src_ptr,
518 		 __dyncast_result& __result) const;
519 
520     virtual __sub_kind
521     __do_find_public_src(ptrdiff_t __src2dst, const void* __obj_ptr,
522 			 const __class_type_info* __src_type,
523 			 const void* __sub_ptr) const;
524 
525     virtual bool
526     __do_upcast(const __class_type_info*__dst, const void*__obj,
527 		__upcast_result& __restrict __result) const;
528   };
529 
530   // Type information for a class with multiple and/or virtual bases.
531   class __vmi_class_type_info : public __class_type_info
532   {
533   public:
534     unsigned int 		__flags;  // Details about the class hierarchy.
535     unsigned int 		__base_count;  // Number of direct bases.
536 
537     // The array of bases uses the trailing array struct hack so this
538     // class is not constructable with a normal constructor. It is
539     // internally generated by the compiler.
540     __base_class_type_info 	__base_info[1];  // Array of bases.
541 
542     explicit
__vmi_class_type_info(const char * __n,int ___flags)543     __vmi_class_type_info(const char* __n, int ___flags)
544     : __class_type_info(__n), __flags(___flags), __base_count(0) { }
545 
546     virtual
547     ~__vmi_class_type_info();
548 
549     // Implementation defined types.
550     enum __flags_masks
551       {
552 	__non_diamond_repeat_mask = 0x1, // Distinct instance of repeated base.
553 	__diamond_shaped_mask = 0x2, // Diamond shaped multiple inheritance.
554 	__flags_unknown_mask = 0x10
555       };
556 
557   protected:
558     // Implementation defined member functions.
559     virtual bool
560     __do_dyncast(ptrdiff_t __src2dst, __sub_kind __access_path,
561 		 const __class_type_info* __dst_type, const void* __obj_ptr,
562 		 const __class_type_info* __src_type, const void* __src_ptr,
563 		 __dyncast_result& __result) const;
564 
565     virtual __sub_kind
566     __do_find_public_src(ptrdiff_t __src2dst, const void* __obj_ptr,
567 			 const __class_type_info* __src_type,
568 			 const void* __src_ptr) const;
569 
570     virtual bool
571     __do_upcast(const __class_type_info* __dst, const void* __obj,
572 		__upcast_result& __restrict __result) const;
573   };
574 
575   // Exception handling forward declarations.
576   struct __cxa_exception;
577   struct __cxa_refcounted_exception;
578   struct __cxa_dependent_exception;
579   struct __cxa_eh_globals;
580 
581   extern "C"
582   {
583   // Dynamic cast runtime.
584 
585   // src2dst has the following possible values
586   //  >-1: src_type is a unique public non-virtual base of dst_type
587   //       dst_ptr + src2dst == src_ptr
588   //   -1: unspecified relationship
589   //   -2: src_type is not a public base of dst_type
590   //   -3: src_type is a multiple public non-virtual base of dst_type
591   void*
592   __dynamic_cast(const void* __src_ptr, // Starting object.
593 		 const __class_type_info* __src_type, // Static type of object.
594 		 const __class_type_info* __dst_type, // Desired target type.
595 		 ptrdiff_t __src2dst); // How src and dst are related.
596 
597 
598   // Exception handling runtime.
599 
600   // The __cxa_eh_globals for the current thread can be obtained by using
601   // either of the following functions.  The "fast" version assumes at least
602   // one prior call of __cxa_get_globals has been made from the current
603   // thread, so no initialization is necessary.
604   __cxa_eh_globals*
605   __cxa_get_globals() _GLIBCXX_NOTHROW __attribute__ ((__const__));
606 
607   __cxa_eh_globals*
608   __cxa_get_globals_fast() _GLIBCXX_NOTHROW __attribute__ ((__const__));
609 
610   // Free the space allocated for the primary exception.
611   void
612   __cxa_free_exception(void*) _GLIBCXX_NOTHROW;
613 
614   // Throw the exception.
615   void
616   __cxa_throw(void*, std::type_info*, void (_GLIBCXX_CDTOR_CALLABI *) (void *))
617   __attribute__((__noreturn__));
618 
619   // Used to implement exception handlers.
620   void*
621   __cxa_get_exception_ptr(void*) _GLIBCXX_NOTHROW __attribute__ ((__pure__));
622 
623   void*
624   __cxa_begin_catch(void*) _GLIBCXX_NOTHROW;
625 
626   void
627   __cxa_end_catch();
628 
629   void
630   __cxa_rethrow() __attribute__((__noreturn__));
631 
632   // Returns the type_info for the currently handled exception [15.3/8], or
633   // null if there is none.
634   std::type_info*
635   __cxa_current_exception_type() _GLIBCXX_NOTHROW __attribute__ ((__pure__));
636 
637   // GNU Extensions.
638 
639   // Allocate memory for a dependent exception.
640   __cxa_dependent_exception*
641   __cxa_allocate_dependent_exception() _GLIBCXX_NOTHROW;
642 
643   // Free the space allocated for the dependent exception.
644   void
645   __cxa_free_dependent_exception(__cxa_dependent_exception*) _GLIBCXX_NOTHROW;
646 
647   } // extern "C"
648 
649   // A magic placeholder class that can be caught by reference
650   // to recognize foreign exceptions.
651   class __foreign_exception
652   {
653     virtual ~__foreign_exception() throw();
654     virtual void __pure_dummy() = 0; // prevent catch by value
655   };
656 
657 } // namespace __cxxabiv1
658 
659 /** @namespace abi
660  *  @brief The cross-vendor C++ Application Binary Interface. A
661  *  namespace alias to __cxxabiv1, but user programs should use the
662  *  alias 'abi'.
663  *
664  *  A brief overview of an ABI is given in the libstdc++ FAQ, question
665  *  5.8 (you may have a copy of the FAQ locally, or you can view the online
666  *  version at http://gcc.gnu.org/onlinedocs/libstdc++/faq.html#5_8 ).
667  *
668  *  GCC subscribes to a cross-vendor ABI for C++, sometimes
669  *  called the IA64 ABI because it happens to be the native ABI for that
670  *  platform.  It is summarized at http://www.codesourcery.com/cxx-abi/
671  *  along with the current specification.
672  *
673  *  For users of GCC greater than or equal to 3.x, entry points are
674  *  available in <cxxabi.h>, which notes, <em>'It is not normally
675  *  necessary for user programs to include this header, or use the
676  *  entry points directly.  However, this header is available should
677  *  that be needed.'</em>
678 */
679 namespace abi = __cxxabiv1;
680 
681 namespace __gnu_cxx
682 {
683   /**
684    *  @brief Exception thrown by __cxa_guard_acquire.
685    *  @ingroup exceptions
686    *
687    *  C++ 2011 6.7 [stmt.dcl]/4: If control re-enters the declaration
688    *  recursively while the variable is being initialized, the behavior
689    *  is undefined.
690    *
691    *  Since we already have a library function to handle locking, we might
692    *  as well check for this situation and throw an exception.
693    *  We use the second byte of the guard variable to remember that we're
694    *  in the middle of an initialization.
695    */
696   class recursive_init_error: public std::exception
697   {
698   public:
699     recursive_init_error() _GLIBCXX_NOTHROW;
700     virtual ~recursive_init_error() _GLIBCXX_NOTHROW;
701   };
702 }
703 #endif // __cplusplus
704 
705 #pragma GCC visibility pop
706 
707 #endif // __CXXABI_H
708