1 //===------------------------- cxa_exception.cpp --------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
7 //
8 //
9 //  This file implements the "Exception Handling APIs"
10 //  http://mentorembedded.github.io/cxx-abi/abi-eh.html
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "config.h"
15 #include "cxxabi.h"
16 
17 #include <exception>        // for std::terminate
18 #include <cstring>          // for memset
19 #include "cxa_exception.hpp"
20 #include "cxa_handlers.hpp"
21 #include "fallback_malloc.h"
22 
23 // +---------------------------+-----------------------------+---------------+
24 // | __cxa_exception           | _Unwind_Exception CLNGC++\0 | thrown object |
25 // +---------------------------+-----------------------------+---------------+
26 //                                                           ^
27 //                                                           |
28 //   +-------------------------------------------------------+
29 //   |
30 // +---------------------------+-----------------------------+
31 // | __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 |
32 // +---------------------------+-----------------------------+
33 
34 namespace __cxxabiv1 {
35 
36 #pragma GCC visibility push(default)
37 
38 //  Utility routines
39 static
40 inline
41 __cxa_exception*
cxa_exception_from_thrown_object(void * thrown_object)42 cxa_exception_from_thrown_object(void* thrown_object)
43 {
44     return static_cast<__cxa_exception*>(thrown_object) - 1;
45 }
46 
47 // Note:  This is never called when exception_header is masquerading as a
48 //        __cxa_dependent_exception.
49 static
50 inline
51 void*
thrown_object_from_cxa_exception(__cxa_exception * exception_header)52 thrown_object_from_cxa_exception(__cxa_exception* exception_header)
53 {
54     return static_cast<void*>(exception_header + 1);
55 }
56 
57 //  Get the exception object from the unwind pointer.
58 //  Relies on the structure layout, where the unwind pointer is right in
59 //  front of the user's exception object
60 static
61 inline
62 __cxa_exception*
cxa_exception_from_exception_unwind_exception(_Unwind_Exception * unwind_exception)63 cxa_exception_from_exception_unwind_exception(_Unwind_Exception* unwind_exception)
64 {
65     return cxa_exception_from_thrown_object(unwind_exception + 1 );
66 }
67 
68 static
69 inline
70 size_t
cxa_exception_size_from_exception_thrown_size(size_t size)71 cxa_exception_size_from_exception_thrown_size(size_t size)
72 {
73     return size + sizeof (__cxa_exception);
74 }
75 
setExceptionClass(_Unwind_Exception * unwind_exception)76 static void setExceptionClass(_Unwind_Exception* unwind_exception) {
77     unwind_exception->exception_class = kOurExceptionClass;
78 }
79 
setDependentExceptionClass(_Unwind_Exception * unwind_exception)80 static void setDependentExceptionClass(_Unwind_Exception* unwind_exception) {
81     unwind_exception->exception_class = kOurDependentExceptionClass;
82 }
83 
84 //  Is it one of ours?
isOurExceptionClass(const _Unwind_Exception * unwind_exception)85 static bool isOurExceptionClass(const _Unwind_Exception* unwind_exception) {
86     return (unwind_exception->exception_class & get_vendor_and_language) ==
87            (kOurExceptionClass                & get_vendor_and_language);
88 }
89 
isDependentException(_Unwind_Exception * unwind_exception)90 static bool isDependentException(_Unwind_Exception* unwind_exception) {
91     return (unwind_exception->exception_class & 0xFF) == 0x01;
92 }
93 
94 //  This does not need to be atomic
incrementHandlerCount(__cxa_exception * exception)95 static inline int incrementHandlerCount(__cxa_exception *exception) {
96     return ++exception->handlerCount;
97 }
98 
99 //  This does not need to be atomic
decrementHandlerCount(__cxa_exception * exception)100 static inline  int decrementHandlerCount(__cxa_exception *exception) {
101     return --exception->handlerCount;
102 }
103 
104 /*
105     If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
106     stored in exc is called.  Otherwise the exceptionDestructor stored in
107     exc is called, and then the memory for the exception is deallocated.
108 
109     This is never called for a __cxa_dependent_exception.
110 */
111 static
112 void
exception_cleanup_func(_Unwind_Reason_Code reason,_Unwind_Exception * unwind_exception)113 exception_cleanup_func(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
114 {
115     __cxa_exception* exception_header = cxa_exception_from_exception_unwind_exception(unwind_exception);
116     if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
117         std::__terminate(exception_header->terminateHandler);
118     // Just in case there exists a dependent exception that is pointing to this,
119     //    check the reference count and only destroy this if that count goes to zero.
120     __cxa_decrement_exception_refcount(unwind_exception + 1);
121 }
122 
failed_throw(__cxa_exception * exception_header)123 static LIBCXXABI_NORETURN void failed_throw(__cxa_exception* exception_header) {
124 //  Section 2.5.3 says:
125 //      * For purposes of this ABI, several things are considered exception handlers:
126 //      ** A terminate() call due to a throw.
127 //  and
128 //      * Upon entry, Following initialization of the catch parameter,
129 //          a handler must call:
130 //      * void *__cxa_begin_catch(void *exceptionObject );
131     (void) __cxa_begin_catch(&exception_header->unwindHeader);
132     std::__terminate(exception_header->terminateHandler);
133 }
134 
135 extern "C" {
136 
137 //  Allocate a __cxa_exception object, and zero-fill it.
138 //  Reserve "thrown_size" bytes on the end for the user's exception
139 //  object. Zero-fill the object. If memory can't be allocated, call
140 //  std::terminate. Return a pointer to the memory to be used for the
141 //  user's exception object.
__cxa_allocate_exception(size_t thrown_size)142 _LIBCXXABI_FUNC_VIS void *__cxa_allocate_exception(size_t thrown_size) throw() {
143     size_t actual_size = cxa_exception_size_from_exception_thrown_size(thrown_size);
144     __cxa_exception *exception_header =
145         static_cast<__cxa_exception *>(__malloc_with_fallback(actual_size));
146     if (NULL == exception_header)
147         std::terminate();
148     std::memset(exception_header, 0, actual_size);
149     return thrown_object_from_cxa_exception(exception_header);
150 }
151 
152 
153 //  Free a __cxa_exception object allocated with __cxa_allocate_exception.
__cxa_free_exception(void * thrown_object)154 _LIBCXXABI_FUNC_VIS void __cxa_free_exception(void *thrown_object) throw() {
155     __free_with_fallback(cxa_exception_from_thrown_object(thrown_object));
156 }
157 
158 
159 //  This function shall allocate a __cxa_dependent_exception and
160 //  return a pointer to it. (Really to the object, not past its' end).
161 //  Otherwise, it will work like __cxa_allocate_exception.
__cxa_allocate_dependent_exception()162 void * __cxa_allocate_dependent_exception () {
163     size_t actual_size = sizeof(__cxa_dependent_exception);
164     void *ptr = __malloc_with_fallback(actual_size);
165     if (NULL == ptr)
166         std::terminate();
167     std::memset(ptr, 0, actual_size);
168     return ptr;
169 }
170 
171 
172 //  This function shall free a dependent_exception.
173 //  It does not affect the reference count of the primary exception.
__cxa_free_dependent_exception(void * dependent_exception)174 void __cxa_free_dependent_exception (void * dependent_exception) {
175     __free_with_fallback(dependent_exception);
176 }
177 
178 
179 // 2.4.3 Throwing the Exception Object
180 /*
181 After constructing the exception object with the throw argument value,
182 the generated code calls the __cxa_throw runtime library routine. This
183 routine never returns.
184 
185 The __cxa_throw routine will do the following:
186 
187 * Obtain the __cxa_exception header from the thrown exception object address,
188 which can be computed as follows:
189  __cxa_exception *header = ((__cxa_exception *) thrown_exception - 1);
190 * Save the current unexpected_handler and terminate_handler in the __cxa_exception header.
191 * Save the tinfo and dest arguments in the __cxa_exception header.
192 * Set the exception_class field in the unwind header. This is a 64-bit value
193 representing the ASCII string "XXXXC++\0", where "XXXX" is a
194 vendor-dependent string. That is, for implementations conforming to this
195 ABI, the low-order 4 bytes of this 64-bit value will be "C++\0".
196 * Increment the uncaught_exception flag.
197 * Call _Unwind_RaiseException in the system unwind library, Its argument is the
198 pointer to the thrown exception, which __cxa_throw itself received as an argument.
199 __Unwind_RaiseException begins the process of stack unwinding, described
200 in Section 2.5. In special cases, such as an inability to find a
201 handler, _Unwind_RaiseException may return. In that case, __cxa_throw
202 will call terminate, assuming that there was no handler for the
203 exception.
204 */
205 _LIBCXXABI_FUNC_VIS LIBCXXABI_NORETURN void
__cxa_throw(void * thrown_object,std::type_info * tinfo,void (* dest)(void *))206 __cxa_throw(void *thrown_object, std::type_info *tinfo, void (*dest)(void *)) {
207     __cxa_eh_globals *globals = __cxa_get_globals();
208     __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
209 
210     exception_header->unexpectedHandler = std::get_unexpected();
211     exception_header->terminateHandler  = std::get_terminate();
212     exception_header->exceptionType = tinfo;
213     exception_header->exceptionDestructor = dest;
214     setExceptionClass(&exception_header->unwindHeader);
215     exception_header->referenceCount = 1;  // This is a newly allocated exception, no need for thread safety.
216     globals->uncaughtExceptions += 1;   // Not atomically, since globals are thread-local
217 
218     exception_header->unwindHeader.exception_cleanup = exception_cleanup_func;
219 #ifdef __USING_SJLJ_EXCEPTIONS__
220     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
221 #else
222     _Unwind_RaiseException(&exception_header->unwindHeader);
223 #endif
224     //  This only happens when there is no handler, or some unexpected unwinding
225     //     error happens.
226     failed_throw(exception_header);
227 }
228 
229 
230 // 2.5.3 Exception Handlers
231 /*
232 The adjusted pointer is computed by the personality routine during phase 1
233   and saved in the exception header (either __cxa_exception or
234   __cxa_dependent_exception).
235 
236   Requires:  exception is native
237 */
238 _LIBCXXABI_FUNC_VIS
__cxa_get_exception_ptr(void * unwind_exception)239 void *__cxa_get_exception_ptr(void *unwind_exception) throw() {
240 #if LIBCXXABI_ARM_EHABI
241     return reinterpret_cast<void*>(
242         static_cast<_Unwind_Control_Block*>(unwind_exception)->barrier_cache.bitpattern[0]);
243 #else
244     return cxa_exception_from_exception_unwind_exception(
245         static_cast<_Unwind_Exception*>(unwind_exception))->adjustedPtr;
246 #endif
247 }
248 
249 #if LIBCXXABI_ARM_EHABI
250 /*
251 The routine to be called before the cleanup.  This will save __cxa_exception in
252 __cxa_eh_globals, so that __cxa_end_cleanup() can recover later.
253 */
254 _LIBCXXABI_FUNC_VIS
__cxa_begin_cleanup(void * unwind_arg)255 bool __cxa_begin_cleanup(void *unwind_arg) throw() {
256     _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
257     __cxa_eh_globals* globals = __cxa_get_globals();
258     __cxa_exception* exception_header =
259         cxa_exception_from_exception_unwind_exception(unwind_exception);
260 
261     if (isOurExceptionClass(unwind_exception))
262     {
263         if (0 == exception_header->propagationCount)
264         {
265             exception_header->nextPropagatingException = globals->propagatingExceptions;
266             globals->propagatingExceptions = exception_header;
267         }
268         ++exception_header->propagationCount;
269     }
270     else
271     {
272         // If the propagatingExceptions stack is not empty, since we can't
273         // chain the foreign exception, terminate it.
274         if (NULL != globals->propagatingExceptions)
275             std::terminate();
276         globals->propagatingExceptions = exception_header;
277     }
278     return true;
279 }
280 
281 /*
282 The routine to be called after the cleanup has been performed.  It will get the
283 propagating __cxa_exception from __cxa_eh_globals, and continue the stack
284 unwinding with _Unwind_Resume.
285 
286 According to ARM EHABI 8.4.1, __cxa_end_cleanup() should not clobber any
287 register, thus we have to write this function in assembly so that we can save
288 {r1, r2, r3}.  We don't have to save r0 because it is the return value and the
289 first argument to _Unwind_Resume().  In addition, we are saving r4 in order to
290 align the stack to 16 bytes, even though it is a callee-save register.
291 */
292 __attribute__((used)) static _Unwind_Exception *
__cxa_end_cleanup_impl()293 __cxa_end_cleanup_impl()
294 {
295     __cxa_eh_globals* globals = __cxa_get_globals();
296     __cxa_exception* exception_header = globals->propagatingExceptions;
297     if (NULL == exception_header)
298     {
299         // It seems that __cxa_begin_cleanup() is not called properly.
300         // We have no choice but terminate the program now.
301         std::terminate();
302     }
303 
304     if (isOurExceptionClass(&exception_header->unwindHeader))
305     {
306         --exception_header->propagationCount;
307         if (0 == exception_header->propagationCount)
308         {
309             globals->propagatingExceptions = exception_header->nextPropagatingException;
310             exception_header->nextPropagatingException = NULL;
311         }
312     }
313     else
314     {
315         globals->propagatingExceptions = NULL;
316     }
317     return &exception_header->unwindHeader;
318 }
319 
320 asm (
321     "	.pushsection	.text.__cxa_end_cleanup,\"ax\",%progbits\n"
322     "	.globl	__cxa_end_cleanup\n"
323     "	.type	__cxa_end_cleanup,%function\n"
324     "__cxa_end_cleanup:\n"
325     "	push	{r1, r2, r3, r4}\n"
326     "	bl	__cxa_end_cleanup_impl\n"
327     "	pop	{r1, r2, r3, r4}\n"
328     "	bl	_Unwind_Resume\n"
329     "	bl	abort\n"
330     "	.popsection"
331 );
332 #endif  // LIBCXXABI_ARM_EHABI
333 
334 /*
335 This routine can catch foreign or native exceptions.  If native, the exception
336 can be a primary or dependent variety.  This routine may remain blissfully
337 ignorant of whether the native exception is primary or dependent.
338 
339 If the exception is native:
340 * Increment's the exception's handler count.
341 * Push the exception on the stack of currently-caught exceptions if it is not
342   already there (from a rethrow).
343 * Decrements the uncaught_exception count.
344 * Returns the adjusted pointer to the exception object, which is stored in
345   the __cxa_exception by the personality routine.
346 
347 If the exception is foreign, this means it did not originate from one of throw
348 routines.  The foreign exception does not necessarily have a __cxa_exception
349 header.  However we can catch it here with a catch (...), or with a call
350 to terminate or unexpected during unwinding.
351 * Do not try to increment the exception's handler count, we don't know where
352   it is.
353 * Push the exception on the stack of currently-caught exceptions only if the
354   stack is empty.  The foreign exception has no way to link to the current
355   top of stack.  If the stack is not empty, call terminate.  Even with an
356   empty stack, this is hacked in by pushing a pointer to an imaginary
357   __cxa_exception block in front of the foreign exception.  It would be better
358   if the __cxa_eh_globals structure had a stack of _Unwind_Exception, but it
359   doesn't.  It has a stack of __cxa_exception (which has a next* in it).
360 * Do not decrement the uncaught_exception count because we didn't increment it
361   in __cxa_throw (or one of our rethrow functions).
362 * If we haven't terminated, assume the exception object is just past the
363   _Unwind_Exception and return a pointer to that.
364 */
365 void*
__cxa_begin_catch(void * unwind_arg)366 __cxa_begin_catch(void* unwind_arg) throw()
367 {
368     _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
369     bool native_exception = isOurExceptionClass(unwind_exception);
370     __cxa_eh_globals* globals = __cxa_get_globals();
371     // exception_header is a hackish offset from a foreign exception, but it
372     //   works as long as we're careful not to try to access any __cxa_exception
373     //   parts.
374     __cxa_exception* exception_header =
375             cxa_exception_from_exception_unwind_exception
376             (
377                 static_cast<_Unwind_Exception*>(unwind_exception)
378             );
379     if (native_exception)
380     {
381         // Increment the handler count, removing the flag about being rethrown
382         exception_header->handlerCount = exception_header->handlerCount < 0 ?
383             -exception_header->handlerCount + 1 : exception_header->handlerCount + 1;
384         //  place the exception on the top of the stack if it's not already
385         //    there by a previous rethrow
386         if (exception_header != globals->caughtExceptions)
387         {
388             exception_header->nextException = globals->caughtExceptions;
389             globals->caughtExceptions = exception_header;
390         }
391         globals->uncaughtExceptions -= 1;   // Not atomically, since globals are thread-local
392 #if LIBCXXABI_ARM_EHABI
393         return reinterpret_cast<void*>(exception_header->unwindHeader.barrier_cache.bitpattern[0]);
394 #else
395         return exception_header->adjustedPtr;
396 #endif
397     }
398     // Else this is a foreign exception
399     // If the caughtExceptions stack is not empty, terminate
400     if (globals->caughtExceptions != 0)
401         std::terminate();
402     // Push the foreign exception on to the stack
403     globals->caughtExceptions = exception_header;
404     return unwind_exception + 1;
405 }
406 
407 
408 /*
409 Upon exit for any reason, a handler must call:
410     void __cxa_end_catch ();
411 
412 This routine can be called for either a native or foreign exception.
413 For a native exception:
414 * Locates the most recently caught exception and decrements its handler count.
415 * Removes the exception from the caught exception stack, if the handler count goes to zero.
416 * If the handler count goes down to zero, and the exception was not re-thrown
417   by throw, it locates the primary exception (which may be the same as the one
418   it's handling) and decrements its reference count. If that reference count
419   goes to zero, the function destroys the exception. In any case, if the current
420   exception is a dependent exception, it destroys that.
421 
422 For a foreign exception:
423 * If it has been rethrown, there is nothing to do.
424 * Otherwise delete the exception and pop the catch stack to empty.
425 */
__cxa_end_catch()426 _LIBCXXABI_FUNC_VIS void __cxa_end_catch() {
427   static_assert(sizeof(__cxa_exception) == sizeof(__cxa_dependent_exception),
428                 "sizeof(__cxa_exception) must be equal to "
429                 "sizeof(__cxa_dependent_exception)");
430   static_assert(__builtin_offsetof(__cxa_exception, referenceCount) ==
431                     __builtin_offsetof(__cxa_dependent_exception,
432                                        primaryException),
433                 "the layout of __cxa_exception must match the layout of "
434                 "__cxa_dependent_exception");
435   static_assert(__builtin_offsetof(__cxa_exception, handlerCount) ==
436                     __builtin_offsetof(__cxa_dependent_exception, handlerCount),
437                 "the layout of __cxa_exception must match the layout of "
438                 "__cxa_dependent_exception");
439     __cxa_eh_globals* globals = __cxa_get_globals_fast(); // __cxa_get_globals called in __cxa_begin_catch
440     __cxa_exception* exception_header = globals->caughtExceptions;
441     // If we've rethrown a foreign exception, then globals->caughtExceptions
442     //    will have been made an empty stack by __cxa_rethrow() and there is
443     //    nothing more to be done.  Do nothing!
444     if (NULL != exception_header)
445     {
446         bool native_exception = isOurExceptionClass(&exception_header->unwindHeader);
447         if (native_exception)
448         {
449             // This is a native exception
450             if (exception_header->handlerCount < 0)
451             {
452                 //  The exception has been rethrown by __cxa_rethrow, so don't delete it
453                 if (0 == incrementHandlerCount(exception_header))
454                 {
455                     //  Remove from the chain of uncaught exceptions
456                     globals->caughtExceptions = exception_header->nextException;
457                     // but don't destroy
458                 }
459                 // Keep handlerCount negative in case there are nested catch's
460                 //   that need to be told that this exception is rethrown.  Don't
461                 //   erase this rethrow flag until the exception is recaught.
462             }
463             else
464             {
465                 // The native exception has not been rethrown
466                 if (0 == decrementHandlerCount(exception_header))
467                 {
468                     //  Remove from the chain of uncaught exceptions
469                     globals->caughtExceptions = exception_header->nextException;
470                     // Destroy this exception, being careful to distinguish
471                     //    between dependent and primary exceptions
472                     if (isDependentException(&exception_header->unwindHeader))
473                     {
474                         // Reset exception_header to primaryException and deallocate the dependent exception
475                         __cxa_dependent_exception* dep_exception_header =
476                             reinterpret_cast<__cxa_dependent_exception*>(exception_header);
477                         exception_header =
478                             cxa_exception_from_thrown_object(dep_exception_header->primaryException);
479                         __cxa_free_dependent_exception(dep_exception_header);
480                     }
481                     // Destroy the primary exception only if its referenceCount goes to 0
482                     //    (this decrement must be atomic)
483                     __cxa_decrement_exception_refcount(thrown_object_from_cxa_exception(exception_header));
484                 }
485             }
486         }
487         else
488         {
489             // The foreign exception has not been rethrown.  Pop the stack
490             //    and delete it.  If there are nested catch's and they try
491             //    to touch a foreign exception in any way, that is undefined
492             //     behavior.  They likely can't since the only way to catch
493             //     a foreign exception is with catch (...)!
494             _Unwind_DeleteException(&globals->caughtExceptions->unwindHeader);
495             globals->caughtExceptions = 0;
496         }
497     }
498 }
499 
500 // Note:  exception_header may be masquerading as a __cxa_dependent_exception
501 //        and that's ok.  exceptionType is there too.
502 //        However watch out for foreign exceptions.  Return null for them.
__cxa_current_exception_type()503 _LIBCXXABI_FUNC_VIS std::type_info *__cxa_current_exception_type() {
504 //  get the current exception
505     __cxa_eh_globals *globals = __cxa_get_globals_fast();
506     if (NULL == globals)
507         return NULL;     //  If there have never been any exceptions, there are none now.
508     __cxa_exception *exception_header = globals->caughtExceptions;
509     if (NULL == exception_header)
510         return NULL;        //  No current exception
511     if (!isOurExceptionClass(&exception_header->unwindHeader))
512         return NULL;
513     return exception_header->exceptionType;
514 }
515 
516 // 2.5.4 Rethrowing Exceptions
517 /*  This routine can rethrow native or foreign exceptions.
518 If the exception is native:
519 * marks the exception object on top of the caughtExceptions stack
520   (in an implementation-defined way) as being rethrown.
521 * If the caughtExceptions stack is empty, it calls terminate()
522   (see [C++FDIS] [except.throw], 15.1.8).
523 * It then calls _Unwind_RaiseException which should not return
524    (terminate if it does).
525   Note:  exception_header may be masquerading as a __cxa_dependent_exception
526          and that's ok.
527 */
__cxa_rethrow()528 _LIBCXXABI_FUNC_VIS LIBCXXABI_NORETURN void __cxa_rethrow() {
529     __cxa_eh_globals* globals = __cxa_get_globals();
530     __cxa_exception* exception_header = globals->caughtExceptions;
531     if (NULL == exception_header)
532         std::terminate();      // throw; called outside of a exception handler
533     bool native_exception = isOurExceptionClass(&exception_header->unwindHeader);
534     if (native_exception)
535     {
536         //  Mark the exception as being rethrown (reverse the effects of __cxa_begin_catch)
537         exception_header->handlerCount = -exception_header->handlerCount;
538         globals->uncaughtExceptions += 1;
539         //  __cxa_end_catch will remove this exception from the caughtExceptions stack if necessary
540     }
541     else  // this is a foreign exception
542     {
543         // The only way to communicate to __cxa_end_catch that we've rethrown
544         //   a foreign exception, so don't delete us, is to pop the stack here
545         //   which must be empty afterwards.  Then __cxa_end_catch will do
546         //   nothing
547         globals->caughtExceptions = 0;
548     }
549 #ifdef __USING_SJLJ_EXCEPTIONS__
550     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
551 #else
552     _Unwind_RaiseException(&exception_header->unwindHeader);
553 #endif
554 
555     //  If we get here, some kind of unwinding error has occurred.
556     //  There is some weird code generation bug happening with
557     //     Apple clang version 4.0 (tags/Apple/clang-418.0.2) (based on LLVM 3.1svn)
558     //     If we call failed_throw here.  Turns up with -O2 or higher, and -Os.
559     __cxa_begin_catch(&exception_header->unwindHeader);
560     if (native_exception)
561         std::__terminate(exception_header->terminateHandler);
562     // Foreign exception: can't get exception_header->terminateHandler
563     std::terminate();
564 }
565 
566 /*
567     If thrown_object is not null, atomically increment the referenceCount field
568     of the __cxa_exception header associated with the thrown object referred to
569     by thrown_object.
570 
571     Requires:  If thrown_object is not NULL, it is a native exception.
572 */
573 _LIBCXXABI_FUNC_VIS void
__cxa_increment_exception_refcount(void * thrown_object)574 __cxa_increment_exception_refcount(void *thrown_object) throw() {
575     if (thrown_object != NULL )
576     {
577         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
578         __sync_add_and_fetch(&exception_header->referenceCount, 1);
579     }
580 }
581 
582 /*
583     If thrown_object is not null, atomically decrement the referenceCount field
584     of the __cxa_exception header associated with the thrown object referred to
585     by thrown_object.  If the referenceCount drops to zero, destroy and
586     deallocate the exception.
587 
588     Requires:  If thrown_object is not NULL, it is a native exception.
589 */
590 _LIBCXXABI_FUNC_VIS void
__cxa_decrement_exception_refcount(void * thrown_object)591 __cxa_decrement_exception_refcount(void *thrown_object) throw() {
592     if (thrown_object != NULL )
593     {
594         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
595         if (__sync_sub_and_fetch(&exception_header->referenceCount, size_t(1)) == 0)
596         {
597             if (NULL != exception_header->exceptionDestructor)
598                 exception_header->exceptionDestructor(thrown_object);
599             __cxa_free_exception(thrown_object);
600         }
601     }
602 }
603 
604 /*
605     Returns a pointer to the thrown object (if any) at the top of the
606     caughtExceptions stack.  Atomically increment the exception's referenceCount.
607     If there is no such thrown object or if the thrown object is foreign,
608     returns null.
609 
610     We can use __cxa_get_globals_fast here to get the globals because if there have
611     been no exceptions thrown, ever, on this thread, we can return NULL without
612     the need to allocate the exception-handling globals.
613 */
__cxa_current_primary_exception()614 _LIBCXXABI_FUNC_VIS void *__cxa_current_primary_exception() throw() {
615 //  get the current exception
616     __cxa_eh_globals* globals = __cxa_get_globals_fast();
617     if (NULL == globals)
618         return NULL;        //  If there are no globals, there is no exception
619     __cxa_exception* exception_header = globals->caughtExceptions;
620     if (NULL == exception_header)
621         return NULL;        //  No current exception
622     if (!isOurExceptionClass(&exception_header->unwindHeader))
623         return NULL;        // Can't capture a foreign exception (no way to refcount it)
624     if (isDependentException(&exception_header->unwindHeader)) {
625         __cxa_dependent_exception* dep_exception_header =
626             reinterpret_cast<__cxa_dependent_exception*>(exception_header);
627         exception_header = cxa_exception_from_thrown_object(dep_exception_header->primaryException);
628     }
629     void* thrown_object = thrown_object_from_cxa_exception(exception_header);
630     __cxa_increment_exception_refcount(thrown_object);
631     return thrown_object;
632 }
633 
634 /*
635     If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
636     stored in exc is called.  Otherwise the referenceCount stored in the
637     primary exception is decremented, destroying the primary if necessary.
638     Finally the dependent exception is destroyed.
639 */
640 static
641 void
dependent_exception_cleanup(_Unwind_Reason_Code reason,_Unwind_Exception * unwind_exception)642 dependent_exception_cleanup(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
643 {
644     __cxa_dependent_exception* dep_exception_header =
645                       reinterpret_cast<__cxa_dependent_exception*>(unwind_exception + 1) - 1;
646     if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
647         std::__terminate(dep_exception_header->terminateHandler);
648     __cxa_decrement_exception_refcount(dep_exception_header->primaryException);
649     __cxa_free_dependent_exception(dep_exception_header);
650 }
651 
652 /*
653     If thrown_object is not null, allocate, initialize and throw a dependent
654     exception.
655 */
656 void
__cxa_rethrow_primary_exception(void * thrown_object)657 __cxa_rethrow_primary_exception(void* thrown_object)
658 {
659     if ( thrown_object != NULL )
660     {
661         // thrown_object guaranteed to be native because
662         //   __cxa_current_primary_exception returns NULL for foreign exceptions
663         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
664         __cxa_dependent_exception* dep_exception_header =
665             static_cast<__cxa_dependent_exception*>(__cxa_allocate_dependent_exception());
666         dep_exception_header->primaryException = thrown_object;
667         __cxa_increment_exception_refcount(thrown_object);
668         dep_exception_header->exceptionType = exception_header->exceptionType;
669         dep_exception_header->unexpectedHandler = std::get_unexpected();
670         dep_exception_header->terminateHandler = std::get_terminate();
671         setDependentExceptionClass(&dep_exception_header->unwindHeader);
672         __cxa_get_globals()->uncaughtExceptions += 1;
673         dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup;
674 #ifdef __USING_SJLJ_EXCEPTIONS__
675         _Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader);
676 #else
677         _Unwind_RaiseException(&dep_exception_header->unwindHeader);
678 #endif
679         // Some sort of unwinding error.  Note that terminate is a handler.
680         __cxa_begin_catch(&dep_exception_header->unwindHeader);
681     }
682     // If we return client will call terminate()
683 }
684 
685 bool
__cxa_uncaught_exception()686 __cxa_uncaught_exception() throw() { return __cxa_uncaught_exceptions() != 0; }
687 
688 unsigned int
__cxa_uncaught_exceptions()689 __cxa_uncaught_exceptions() throw()
690 {
691     // This does not report foreign exceptions in flight
692     __cxa_eh_globals* globals = __cxa_get_globals_fast();
693     if (globals == 0)
694         return 0;
695     return globals->uncaughtExceptions;
696 }
697 
698 }  // extern "C"
699 
700 #pragma GCC visibility pop
701 
702 }  // abi
703