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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 <cstdlib>          // for malloc, free
19 #include <cstring>          // for memset
20 #if !LIBCXXABI_SINGLE_THREADED
21 #  include <pthread.h>      // for fallback_malloc.ipp's mutexes
22 #endif
23 #include "cxa_exception.hpp"
24 #include "cxa_handlers.hpp"
25 
26 // +---------------------------+-----------------------------+---------------+
27 // | __cxa_exception           | _Unwind_Exception CLNGC++\0 | thrown object |
28 // +---------------------------+-----------------------------+---------------+
29 //                                                           ^
30 //                                                           |
31 //   +-------------------------------------------------------+
32 //   |
33 // +---------------------------+-----------------------------+
34 // | __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 |
35 // +---------------------------+-----------------------------+
36 
37 namespace __cxxabiv1 {
38 
39 #pragma GCC visibility push(default)
40 
41 //  Utility routines
42 static
43 inline
44 __cxa_exception*
cxa_exception_from_thrown_object(void * thrown_object)45 cxa_exception_from_thrown_object(void* thrown_object)
46 {
47     return static_cast<__cxa_exception*>(thrown_object) - 1;
48 }
49 
50 // Note:  This is never called when exception_header is masquerading as a
51 //        __cxa_dependent_exception.
52 static
53 inline
54 void*
thrown_object_from_cxa_exception(__cxa_exception * exception_header)55 thrown_object_from_cxa_exception(__cxa_exception* exception_header)
56 {
57     return static_cast<void*>(exception_header + 1);
58 }
59 
60 //  Get the exception object from the unwind pointer.
61 //  Relies on the structure layout, where the unwind pointer is right in
62 //  front of the user's exception object
63 static
64 inline
65 __cxa_exception*
cxa_exception_from_exception_unwind_exception(_Unwind_Exception * unwind_exception)66 cxa_exception_from_exception_unwind_exception(_Unwind_Exception* unwind_exception)
67 {
68     return cxa_exception_from_thrown_object(unwind_exception + 1 );
69 }
70 
71 static
72 inline
73 size_t
cxa_exception_size_from_exception_thrown_size(size_t size)74 cxa_exception_size_from_exception_thrown_size(size_t size)
75 {
76     return size + sizeof (__cxa_exception);
77 }
78 
setExceptionClass(_Unwind_Exception * unwind_exception)79 static void setExceptionClass(_Unwind_Exception* unwind_exception) {
80     unwind_exception->exception_class = kOurExceptionClass;
81 }
82 
setDependentExceptionClass(_Unwind_Exception * unwind_exception)83 static void setDependentExceptionClass(_Unwind_Exception* unwind_exception) {
84     unwind_exception->exception_class = kOurDependentExceptionClass;
85 }
86 
87 //  Is it one of ours?
isOurExceptionClass(const _Unwind_Exception * unwind_exception)88 static bool isOurExceptionClass(const _Unwind_Exception* unwind_exception) {
89     return (unwind_exception->exception_class & get_vendor_and_language) ==
90            (kOurExceptionClass                & get_vendor_and_language);
91 }
92 
isDependentException(_Unwind_Exception * unwind_exception)93 static bool isDependentException(_Unwind_Exception* unwind_exception) {
94     return (unwind_exception->exception_class & 0xFF) == 0x01;
95 }
96 
97 //  This does not need to be atomic
incrementHandlerCount(__cxa_exception * exception)98 static inline int incrementHandlerCount(__cxa_exception *exception) {
99     return ++exception->handlerCount;
100 }
101 
102 //  This does not need to be atomic
decrementHandlerCount(__cxa_exception * exception)103 static inline  int decrementHandlerCount(__cxa_exception *exception) {
104     return --exception->handlerCount;
105 }
106 
107 #include "fallback_malloc.ipp"
108 
109 //  Allocate some memory from _somewhere_
do_malloc(size_t size)110 static void *do_malloc(size_t size) {
111     void *ptr = std::malloc(size);
112     if (NULL == ptr) // if malloc fails, fall back to emergency stash
113         ptr = fallback_malloc(size);
114     return ptr;
115 }
116 
do_free(void * ptr)117 static void do_free(void *ptr) {
118     is_fallback_ptr(ptr) ? fallback_free(ptr) : std::free(ptr);
119 }
120 
121 /*
122     If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
123     stored in exc is called.  Otherwise the exceptionDestructor stored in
124     exc is called, and then the memory for the exception is deallocated.
125 
126     This is never called for a __cxa_dependent_exception.
127 */
128 static
129 void
exception_cleanup_func(_Unwind_Reason_Code reason,_Unwind_Exception * unwind_exception)130 exception_cleanup_func(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
131 {
132     __cxa_exception* exception_header = cxa_exception_from_exception_unwind_exception(unwind_exception);
133     if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
134         std::__terminate(exception_header->terminateHandler);
135     // Just in case there exists a dependent exception that is pointing to this,
136     //    check the reference count and only destroy this if that count goes to zero.
137     __cxa_decrement_exception_refcount(unwind_exception + 1);
138 }
139 
failed_throw(__cxa_exception * exception_header)140 static LIBCXXABI_NORETURN void failed_throw(__cxa_exception* exception_header) {
141 //  Section 2.5.3 says:
142 //      * For purposes of this ABI, several things are considered exception handlers:
143 //      ** A terminate() call due to a throw.
144 //  and
145 //      * Upon entry, Following initialization of the catch parameter,
146 //          a handler must call:
147 //      * void *__cxa_begin_catch(void *exceptionObject );
148     (void) __cxa_begin_catch(&exception_header->unwindHeader);
149     std::__terminate(exception_header->terminateHandler);
150 }
151 
152 extern "C" {
153 
154 //  Allocate a __cxa_exception object, and zero-fill it.
155 //  Reserve "thrown_size" bytes on the end for the user's exception
156 //  object. Zero-fill the object. If memory can't be allocated, call
157 //  std::terminate. Return a pointer to the memory to be used for the
158 //  user's exception object.
__cxa_allocate_exception(size_t thrown_size)159 void * __cxa_allocate_exception (size_t thrown_size) throw() {
160     size_t actual_size = cxa_exception_size_from_exception_thrown_size(thrown_size);
161     __cxa_exception* exception_header = static_cast<__cxa_exception*>(do_malloc(actual_size));
162     if (NULL == exception_header)
163         std::terminate();
164     std::memset(exception_header, 0, actual_size);
165     return thrown_object_from_cxa_exception(exception_header);
166 }
167 
168 
169 //  Free a __cxa_exception object allocated with __cxa_allocate_exception.
__cxa_free_exception(void * thrown_object)170 void __cxa_free_exception (void * thrown_object) throw() {
171     do_free(cxa_exception_from_thrown_object(thrown_object));
172 }
173 
174 
175 //  This function shall allocate a __cxa_dependent_exception and
176 //  return a pointer to it. (Really to the object, not past its' end).
177 //  Otherwise, it will work like __cxa_allocate_exception.
__cxa_allocate_dependent_exception()178 void * __cxa_allocate_dependent_exception () {
179     size_t actual_size = sizeof(__cxa_dependent_exception);
180     void *ptr = do_malloc(actual_size);
181     if (NULL == ptr)
182         std::terminate();
183     std::memset(ptr, 0, actual_size);
184     return ptr;
185 }
186 
187 
188 //  This function shall free a dependent_exception.
189 //  It does not affect the reference count of the primary exception.
__cxa_free_dependent_exception(void * dependent_exception)190 void __cxa_free_dependent_exception (void * dependent_exception) {
191     do_free(dependent_exception);
192 }
193 
194 
195 // 2.4.3 Throwing the Exception Object
196 /*
197 After constructing the exception object with the throw argument value,
198 the generated code calls the __cxa_throw runtime library routine. This
199 routine never returns.
200 
201 The __cxa_throw routine will do the following:
202 
203 * Obtain the __cxa_exception header from the thrown exception object address,
204 which can be computed as follows:
205  __cxa_exception *header = ((__cxa_exception *) thrown_exception - 1);
206 * Save the current unexpected_handler and terminate_handler in the __cxa_exception header.
207 * Save the tinfo and dest arguments in the __cxa_exception header.
208 * Set the exception_class field in the unwind header. This is a 64-bit value
209 representing the ASCII string "XXXXC++\0", where "XXXX" is a
210 vendor-dependent string. That is, for implementations conforming to this
211 ABI, the low-order 4 bytes of this 64-bit value will be "C++\0".
212 * Increment the uncaught_exception flag.
213 * Call _Unwind_RaiseException in the system unwind library, Its argument is the
214 pointer to the thrown exception, which __cxa_throw itself received as an argument.
215 __Unwind_RaiseException begins the process of stack unwinding, described
216 in Section 2.5. In special cases, such as an inability to find a
217 handler, _Unwind_RaiseException may return. In that case, __cxa_throw
218 will call terminate, assuming that there was no handler for the
219 exception.
220 */
221 LIBCXXABI_NORETURN
222 void
__cxa_throw(void * thrown_object,std::type_info * tinfo,void (* dest)(void *))223 __cxa_throw(void* thrown_object, std::type_info* tinfo, void (*dest)(void*))
224 {
225     __cxa_eh_globals *globals = __cxa_get_globals();
226     __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
227 
228     exception_header->unexpectedHandler = std::get_unexpected();
229     exception_header->terminateHandler  = std::get_terminate();
230     exception_header->exceptionType = tinfo;
231     exception_header->exceptionDestructor = dest;
232     setExceptionClass(&exception_header->unwindHeader);
233     exception_header->referenceCount = 1;  // This is a newly allocated exception, no need for thread safety.
234     globals->uncaughtExceptions += 1;   // Not atomically, since globals are thread-local
235 
236     exception_header->unwindHeader.exception_cleanup = exception_cleanup_func;
237 #if __USING_SJLJ_EXCEPTIONS__
238     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
239 #else
240     _Unwind_RaiseException(&exception_header->unwindHeader);
241 #endif
242     //  This only happens when there is no handler, or some unexpected unwinding
243     //     error happens.
244     failed_throw(exception_header);
245 }
246 
247 
248 // 2.5.3 Exception Handlers
249 /*
250 The adjusted pointer is computed by the personality routine during phase 1
251   and saved in the exception header (either __cxa_exception or
252   __cxa_dependent_exception).
253 
254   Requires:  exception is native
255 */
256 void*
__cxa_get_exception_ptr(void * unwind_exception)257 __cxa_get_exception_ptr(void* unwind_exception) throw()
258 {
259 #if LIBCXXABI_ARM_EHABI
260     return reinterpret_cast<void*>(
261            static_cast<_Unwind_Control_Block*>(unwind_exception)->barrier_cache.bitpattern[0]);
262 #else
263     return cxa_exception_from_exception_unwind_exception
264            (
265                static_cast<_Unwind_Exception*>(unwind_exception)
266            )->adjustedPtr;
267 #endif
268 }
269 
270 #if LIBCXXABI_ARM_EHABI
271 /*
272 The routine to be called before the cleanup.  This will save __cxa_exception in
273 __cxa_eh_globals, so that __cxa_end_cleanup() can recover later.
274 */
275 bool
__cxa_begin_cleanup(void * unwind_arg)276 __cxa_begin_cleanup(void* unwind_arg) throw ()
277 {
278     _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
279     __cxa_eh_globals* globals = __cxa_get_globals();
280     __cxa_exception* exception_header =
281         cxa_exception_from_exception_unwind_exception(unwind_exception);
282 
283     if (isOurExceptionClass(unwind_exception))
284     {
285         if (0 == exception_header->propagationCount)
286         {
287             exception_header->nextPropagatingException = globals->propagatingExceptions;
288             globals->propagatingExceptions = exception_header;
289         }
290         ++exception_header->propagationCount;
291     }
292     else
293     {
294         // If the propagatingExceptions stack is not empty, since we can't
295         // chain the foreign exception, terminate it.
296         if (NULL != globals->propagatingExceptions)
297             std::terminate();
298         globals->propagatingExceptions = exception_header;
299     }
300     return true;
301 }
302 
303 /*
304 The routine to be called after the cleanup has been performed.  It will get the
305 propagating __cxa_exception from __cxa_eh_globals, and continue the stack
306 unwinding with _Unwind_Resume.
307 
308 According to ARM EHABI 8.4.1, __cxa_end_cleanup() should not clobber any
309 register, thus we have to write this function in assembly so that we can save
310 {r1, r2, r3}.  We don't have to save r0 because it is the return value and the
311 first argument to _Unwind_Resume().  In addition, we are saving r4 in order to
312 align the stack to 16 bytes, even though it is a callee-save register.
313 */
314 __attribute__((used)) static _Unwind_Exception *
__cxa_end_cleanup_impl()315 __cxa_end_cleanup_impl()
316 {
317     __cxa_eh_globals* globals = __cxa_get_globals();
318     __cxa_exception* exception_header = globals->propagatingExceptions;
319     if (NULL == exception_header)
320     {
321         // It seems that __cxa_begin_cleanup() is not called properly.
322         // We have no choice but terminate the program now.
323         std::terminate();
324     }
325 
326     if (isOurExceptionClass(&exception_header->unwindHeader))
327     {
328         --exception_header->propagationCount;
329         if (0 == exception_header->propagationCount)
330         {
331             globals->propagatingExceptions = exception_header->nextPropagatingException;
332             exception_header->nextPropagatingException = NULL;
333         }
334     }
335     else
336     {
337         globals->propagatingExceptions = NULL;
338     }
339     return &exception_header->unwindHeader;
340 }
341 
342 asm (
343     "	.pushsection	.text.__cxa_end_cleanup\n"
344     "	.globl	__cxa_end_cleanup\n"
345     "	.type	__cxa_end_cleanup,%function\n"
346     "__cxa_end_cleanup:\n"
347     "	push	{r1, r2, r3, r4}\n"
348     "	bl	__cxa_end_cleanup_impl\n"
349     "	pop	{r1, r2, r3, r4}\n"
350     "	bl	_Unwind_Resume\n"
351     "	bl	abort\n"
352     "	.popsection"
353 );
354 #endif  // LIBCXXABI_ARM_EHABI
355 
356 /*
357 This routine can catch foreign or native exceptions.  If native, the exception
358 can be a primary or dependent variety.  This routine may remain blissfully
359 ignorant of whether the native exception is primary or dependent.
360 
361 If the exception is native:
362 * Increment's the exception's handler count.
363 * Push the exception on the stack of currently-caught exceptions if it is not
364   already there (from a rethrow).
365 * Decrements the uncaught_exception count.
366 * Returns the adjusted pointer to the exception object, which is stored in
367   the __cxa_exception by the personality routine.
368 
369 If the exception is foreign, this means it did not originate from one of throw
370 routines.  The foreign exception does not necessarily have a __cxa_exception
371 header.  However we can catch it here with a catch (...), or with a call
372 to terminate or unexpected during unwinding.
373 * Do not try to increment the exception's handler count, we don't know where
374   it is.
375 * Push the exception on the stack of currently-caught exceptions only if the
376   stack is empty.  The foreign exception has no way to link to the current
377   top of stack.  If the stack is not empty, call terminate.  Even with an
378   empty stack, this is hacked in by pushing a pointer to an imaginary
379   __cxa_exception block in front of the foreign exception.  It would be better
380   if the __cxa_eh_globals structure had a stack of _Unwind_Exception, but it
381   doesn't.  It has a stack of __cxa_exception (which has a next* in it).
382 * Do not decrement the uncaught_exception count because we didn't increment it
383   in __cxa_throw (or one of our rethrow functions).
384 * If we haven't terminated, assume the exception object is just past the
385   _Unwind_Exception and return a pointer to that.
386 */
387 void*
__cxa_begin_catch(void * unwind_arg)388 __cxa_begin_catch(void* unwind_arg) throw()
389 {
390     _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
391     bool native_exception = isOurExceptionClass(unwind_exception);
392     __cxa_eh_globals* globals = __cxa_get_globals();
393     // exception_header is a hackish offset from a foreign exception, but it
394     //   works as long as we're careful not to try to access any __cxa_exception
395     //   parts.
396     __cxa_exception* exception_header =
397             cxa_exception_from_exception_unwind_exception
398             (
399                 static_cast<_Unwind_Exception*>(unwind_exception)
400             );
401     if (native_exception)
402     {
403         // Increment the handler count, removing the flag about being rethrown
404         exception_header->handlerCount = exception_header->handlerCount < 0 ?
405             -exception_header->handlerCount + 1 : exception_header->handlerCount + 1;
406         //  place the exception on the top of the stack if it's not already
407         //    there by a previous rethrow
408         if (exception_header != globals->caughtExceptions)
409         {
410             exception_header->nextException = globals->caughtExceptions;
411             globals->caughtExceptions = exception_header;
412         }
413         globals->uncaughtExceptions -= 1;   // Not atomically, since globals are thread-local
414 #if LIBCXXABI_ARM_EHABI
415         return reinterpret_cast<void*>(exception_header->unwindHeader.barrier_cache.bitpattern[0]);
416 #else
417         return exception_header->adjustedPtr;
418 #endif
419     }
420     // Else this is a foreign exception
421     // If the caughtExceptions stack is not empty, terminate
422     if (globals->caughtExceptions != 0)
423         std::terminate();
424     // Push the foreign exception on to the stack
425     globals->caughtExceptions = exception_header;
426     return unwind_exception + 1;
427 }
428 
429 
430 /*
431 Upon exit for any reason, a handler must call:
432     void __cxa_end_catch ();
433 
434 This routine can be called for either a native or foreign exception.
435 For a native exception:
436 * Locates the most recently caught exception and decrements its handler count.
437 * Removes the exception from the caught exception stack, if the handler count goes to zero.
438 * If the handler count goes down to zero, and the exception was not re-thrown
439   by throw, it locates the primary exception (which may be the same as the one
440   it's handling) and decrements its reference count. If that reference count
441   goes to zero, the function destroys the exception. In any case, if the current
442   exception is a dependent exception, it destroys that.
443 
444 For a foreign exception:
445 * If it has been rethrown, there is nothing to do.
446 * Otherwise delete the exception and pop the catch stack to empty.
447 */
__cxa_end_catch()448 void __cxa_end_catch()
449 {
450     static_assert(sizeof(__cxa_exception) == sizeof(__cxa_dependent_exception),
451                   "sizeof(__cxa_exception) must be equal to sizeof(__cxa_dependent_exception)");
452     static_assert(offsetof(__cxa_exception, referenceCount) == offsetof(__cxa_dependent_exception, primaryException),
453                   "the layout of __cxa_exception must match the layout of __cxa_dependent_exception");
454     static_assert(offsetof(__cxa_exception, handlerCount) == offsetof(__cxa_dependent_exception, handlerCount),
455                   "the layout of __cxa_exception must match the layout of __cxa_dependent_exception");
456     __cxa_eh_globals* globals = __cxa_get_globals_fast(); // __cxa_get_globals called in __cxa_begin_catch
457     __cxa_exception* exception_header = globals->caughtExceptions;
458     // If we've rethrown a foreign exception, then globals->caughtExceptions
459     //    will have been made an empty stack by __cxa_rethrow() and there is
460     //    nothing more to be done.  Do nothing!
461     if (NULL != exception_header)
462     {
463         bool native_exception = isOurExceptionClass(&exception_header->unwindHeader);
464         if (native_exception)
465         {
466             // This is a native exception
467             if (exception_header->handlerCount < 0)
468             {
469                 //  The exception has been rethrown by __cxa_rethrow, so don't delete it
470                 if (0 == incrementHandlerCount(exception_header))
471                 {
472                     //  Remove from the chain of uncaught exceptions
473                     globals->caughtExceptions = exception_header->nextException;
474                     // but don't destroy
475                 }
476                 // Keep handlerCount negative in case there are nested catch's
477                 //   that need to be told that this exception is rethrown.  Don't
478                 //   erase this rethrow flag until the exception is recaught.
479             }
480             else
481             {
482                 // The native exception has not been rethrown
483                 if (0 == decrementHandlerCount(exception_header))
484                 {
485                     //  Remove from the chain of uncaught exceptions
486                     globals->caughtExceptions = exception_header->nextException;
487                     // Destroy this exception, being careful to distinguish
488                     //    between dependent and primary exceptions
489                     if (isDependentException(&exception_header->unwindHeader))
490                     {
491                         // Reset exception_header to primaryException and deallocate the dependent exception
492                         __cxa_dependent_exception* dep_exception_header =
493                             reinterpret_cast<__cxa_dependent_exception*>(exception_header);
494                         exception_header =
495                             cxa_exception_from_thrown_object(dep_exception_header->primaryException);
496                         __cxa_free_dependent_exception(dep_exception_header);
497                     }
498                     // Destroy the primary exception only if its referenceCount goes to 0
499                     //    (this decrement must be atomic)
500                     __cxa_decrement_exception_refcount(thrown_object_from_cxa_exception(exception_header));
501                 }
502             }
503         }
504         else
505         {
506             // The foreign exception has not been rethrown.  Pop the stack
507             //    and delete it.  If there are nested catch's and they try
508             //    to touch a foreign exception in any way, that is undefined
509             //     behavior.  They likely can't since the only way to catch
510             //     a foreign exception is with catch (...)!
511             _Unwind_DeleteException(&globals->caughtExceptions->unwindHeader);
512             globals->caughtExceptions = 0;
513         }
514     }
515 }
516 
517 // Note:  exception_header may be masquerading as a __cxa_dependent_exception
518 //        and that's ok.  exceptionType is there too.
519 //        However watch out for foreign exceptions.  Return null for them.
__cxa_current_exception_type()520 std::type_info * __cxa_current_exception_type() {
521 //  get the current exception
522     __cxa_eh_globals *globals = __cxa_get_globals_fast();
523     if (NULL == globals)
524         return NULL;     //  If there have never been any exceptions, there are none now.
525     __cxa_exception *exception_header = globals->caughtExceptions;
526     if (NULL == exception_header)
527         return NULL;        //  No current exception
528     if (!isOurExceptionClass(&exception_header->unwindHeader))
529         return NULL;
530     return exception_header->exceptionType;
531 }
532 
533 // 2.5.4 Rethrowing Exceptions
534 /*  This routine can rethrow native or foreign exceptions.
535 If the exception is native:
536 * marks the exception object on top of the caughtExceptions stack
537   (in an implementation-defined way) as being rethrown.
538 * If the caughtExceptions stack is empty, it calls terminate()
539   (see [C++FDIS] [except.throw], 15.1.8).
540 * It then calls _Unwind_RaiseException which should not return
541    (terminate if it does).
542   Note:  exception_header may be masquerading as a __cxa_dependent_exception
543          and that's ok.
544 */
545 LIBCXXABI_NORETURN
546 void
__cxa_rethrow()547 __cxa_rethrow()
548 {
549     __cxa_eh_globals* globals = __cxa_get_globals();
550     __cxa_exception* exception_header = globals->caughtExceptions;
551     if (NULL == exception_header)
552         std::terminate();      // throw; called outside of a exception handler
553     bool native_exception = isOurExceptionClass(&exception_header->unwindHeader);
554     if (native_exception)
555     {
556         //  Mark the exception as being rethrown (reverse the effects of __cxa_begin_catch)
557         exception_header->handlerCount = -exception_header->handlerCount;
558         globals->uncaughtExceptions += 1;
559         //  __cxa_end_catch will remove this exception from the caughtExceptions stack if necessary
560     }
561     else  // this is a foreign exception
562     {
563         // The only way to communicate to __cxa_end_catch that we've rethrown
564         //   a foreign exception, so don't delete us, is to pop the stack here
565         //   which must be empty afterwards.  Then __cxa_end_catch will do
566         //   nothing
567         globals->caughtExceptions = 0;
568     }
569 #if __USING_SJLJ_EXCEPTIONS__
570     _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
571 #else
572     _Unwind_RaiseException(&exception_header->unwindHeader);
573 #endif
574 
575     //  If we get here, some kind of unwinding error has occurred.
576     //  There is some weird code generation bug happening with
577     //     Apple clang version 4.0 (tags/Apple/clang-418.0.2) (based on LLVM 3.1svn)
578     //     If we call failed_throw here.  Turns up with -O2 or higher, and -Os.
579     __cxa_begin_catch(&exception_header->unwindHeader);
580     if (native_exception)
581         std::__terminate(exception_header->terminateHandler);
582     // Foreign exception: can't get exception_header->terminateHandler
583     std::terminate();
584 }
585 
586 /*
587     If thrown_object is not null, atomically increment the referenceCount field
588     of the __cxa_exception header associated with the thrown object referred to
589     by thrown_object.
590 
591     Requires:  If thrown_object is not NULL, it is a native exception.
592 */
593 void
__cxa_increment_exception_refcount(void * thrown_object)594 __cxa_increment_exception_refcount(void* thrown_object) throw()
595 {
596     if (thrown_object != NULL )
597     {
598         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
599         __sync_add_and_fetch(&exception_header->referenceCount, 1);
600     }
601 }
602 
603 /*
604     If thrown_object is not null, atomically decrement the referenceCount field
605     of the __cxa_exception header associated with the thrown object referred to
606     by thrown_object.  If the referenceCount drops to zero, destroy and
607     deallocate the exception.
608 
609     Requires:  If thrown_object is not NULL, it is a native exception.
610 */
611 void
__cxa_decrement_exception_refcount(void * thrown_object)612 __cxa_decrement_exception_refcount(void* thrown_object) throw()
613 {
614     if (thrown_object != NULL )
615     {
616         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
617         if (__sync_sub_and_fetch(&exception_header->referenceCount, size_t(1)) == 0)
618         {
619             if (NULL != exception_header->exceptionDestructor)
620                 exception_header->exceptionDestructor(thrown_object);
621             __cxa_free_exception(thrown_object);
622         }
623     }
624 }
625 
626 /*
627     Returns a pointer to the thrown object (if any) at the top of the
628     caughtExceptions stack.  Atomically increment the exception's referenceCount.
629     If there is no such thrown object or if the thrown object is foreign,
630     returns null.
631 
632     We can use __cxa_get_globals_fast here to get the globals because if there have
633     been no exceptions thrown, ever, on this thread, we can return NULL without
634     the need to allocate the exception-handling globals.
635 */
636 void*
__cxa_current_primary_exception()637 __cxa_current_primary_exception() throw()
638 {
639 //  get the current exception
640     __cxa_eh_globals* globals = __cxa_get_globals_fast();
641     if (NULL == globals)
642         return NULL;        //  If there are no globals, there is no exception
643     __cxa_exception* exception_header = globals->caughtExceptions;
644     if (NULL == exception_header)
645         return NULL;        //  No current exception
646     if (!isOurExceptionClass(&exception_header->unwindHeader))
647         return NULL;        // Can't capture a foreign exception (no way to refcount it)
648     if (isDependentException(&exception_header->unwindHeader)) {
649         __cxa_dependent_exception* dep_exception_header =
650             reinterpret_cast<__cxa_dependent_exception*>(exception_header);
651         exception_header = cxa_exception_from_thrown_object(dep_exception_header->primaryException);
652     }
653     void* thrown_object = thrown_object_from_cxa_exception(exception_header);
654     __cxa_increment_exception_refcount(thrown_object);
655     return thrown_object;
656 }
657 
658 /*
659     If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
660     stored in exc is called.  Otherwise the referenceCount stored in the
661     primary exception is decremented, destroying the primary if necessary.
662     Finally the dependent exception is destroyed.
663 */
664 static
665 void
dependent_exception_cleanup(_Unwind_Reason_Code reason,_Unwind_Exception * unwind_exception)666 dependent_exception_cleanup(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
667 {
668     __cxa_dependent_exception* dep_exception_header =
669                       reinterpret_cast<__cxa_dependent_exception*>(unwind_exception + 1) - 1;
670     if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
671         std::__terminate(dep_exception_header->terminateHandler);
672     __cxa_decrement_exception_refcount(dep_exception_header->primaryException);
673     __cxa_free_dependent_exception(dep_exception_header);
674 }
675 
676 /*
677     If thrown_object is not null, allocate, initialize and throw a dependent
678     exception.
679 */
680 void
__cxa_rethrow_primary_exception(void * thrown_object)681 __cxa_rethrow_primary_exception(void* thrown_object)
682 {
683     if ( thrown_object != NULL )
684     {
685         // thrown_object guaranteed to be native because
686         //   __cxa_current_primary_exception returns NULL for foreign exceptions
687         __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
688         __cxa_dependent_exception* dep_exception_header =
689             static_cast<__cxa_dependent_exception*>(__cxa_allocate_dependent_exception());
690         dep_exception_header->primaryException = thrown_object;
691         __cxa_increment_exception_refcount(thrown_object);
692         dep_exception_header->exceptionType = exception_header->exceptionType;
693         dep_exception_header->unexpectedHandler = std::get_unexpected();
694         dep_exception_header->terminateHandler = std::get_terminate();
695         setDependentExceptionClass(&dep_exception_header->unwindHeader);
696         __cxa_get_globals()->uncaughtExceptions += 1;
697         dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup;
698 #if __USING_SJLJ_EXCEPTIONS__
699         _Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader);
700 #else
701         _Unwind_RaiseException(&dep_exception_header->unwindHeader);
702 #endif
703         // Some sort of unwinding error.  Note that terminate is a handler.
704         __cxa_begin_catch(&dep_exception_header->unwindHeader);
705     }
706     // If we return client will call terminate()
707 }
708 
709 bool
__cxa_uncaught_exception()710 __cxa_uncaught_exception() throw()
711 {
712     // This does not report foreign exceptions in flight
713     __cxa_eh_globals* globals = __cxa_get_globals_fast();
714     if (globals == 0)
715         return false;
716     return globals->uncaughtExceptions != 0;
717 }
718 
719 }  // extern "C"
720 
721 #pragma GCC visibility pop
722 
723 }  // abi
724