1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//
8// This file implements the "Exception Handling APIs"
9// https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html
10//
11//===----------------------------------------------------------------------===//
12
13#include "cxxabi.h"
14
15#include <exception> // for std::terminate
16#include <string.h> // for memset
17#include "cxa_exception.h"
18#include "cxa_handlers.h"
19#include "fallback_malloc.h"
20#include "include/atomic_support.h" // from libc++
21
22#if __has_feature(address_sanitizer)
23#include <sanitizer/asan_interface.h>
24#endif
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
37namespace __cxxabiv1 {
38
39// Utility routines
40static
41inline
42__cxa_exception*
43cxa_exception_from_thrown_object(void* thrown_object)
44{
45 return static_cast<__cxa_exception*>(thrown_object) - 1;
46}
47
48// Note: This is never called when exception_header is masquerading as a
49// __cxa_dependent_exception.
50static
51inline
52void*
53thrown_object_from_cxa_exception(__cxa_exception* exception_header)
54{
55 return static_cast<void*>(exception_header + 1);
56}
57
58// Get the exception object from the unwind pointer.
59// Relies on the structure layout, where the unwind pointer is right in
60// front of the user's exception object
61static
62inline
63__cxa_exception*
64cxa_exception_from_exception_unwind_exception(_Unwind_Exception* unwind_exception)
65{
66 return cxa_exception_from_thrown_object(thrown_object: unwind_exception + 1 );
67}
68
69// Round s up to next multiple of a.
70static inline
71size_t aligned_allocation_size(size_t s, size_t a) {
72 return (s + a - 1) & ~(a - 1);
73}
74
75static inline
76size_t cxa_exception_size_from_exception_thrown_size(size_t size) {
77 return aligned_allocation_size(size + sizeof (__cxa_exception),
78 alignof(__cxa_exception));
79}
80
81void __setExceptionClass(_Unwind_Exception* unwind_exception, uint64_t newValue) {
82 ::memcpy(&unwind_exception->exception_class, &newValue, sizeof(newValue));
83}
84
85
86static void setOurExceptionClass(_Unwind_Exception* unwind_exception) {
87 __setExceptionClass(unwind_exception, kOurExceptionClass);
88}
89
90static void setDependentExceptionClass(_Unwind_Exception* unwind_exception) {
91 __setExceptionClass(unwind_exception, kOurDependentExceptionClass);
92}
93
94// Is it one of ours?
95uint64_t __getExceptionClass(const _Unwind_Exception* unwind_exception) {
96 // On x86 and some ARM unwinders, unwind_exception->exception_class is
97 // a uint64_t. On other ARM unwinders, it is a char[8].
98 // See: http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
99 // So we just copy it into a uint64_t to be sure.
100 uint64_t exClass;
101 ::memcpy(&exClass, &unwind_exception->exception_class, sizeof(exClass));
102 return exClass;
103}
104
105bool __isOurExceptionClass(const _Unwind_Exception* unwind_exception) {
106 return (__getExceptionClass(unwind_exception) & get_vendor_and_language) ==
107 (kOurExceptionClass & get_vendor_and_language);
108}
109
110static bool isDependentException(_Unwind_Exception* unwind_exception) {
111 return (__getExceptionClass(unwind_exception) & 0xFF) == 0x01;
112}
113
114// This does not need to be atomic
115static inline int incrementHandlerCount(__cxa_exception *exception) {
116 return ++exception->handlerCount;
117}
118
119// This does not need to be atomic
120static inline int decrementHandlerCount(__cxa_exception *exception) {
121 return --exception->handlerCount;
122}
123
124/*
125 If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
126 stored in exc is called. Otherwise the exceptionDestructor stored in
127 exc is called, and then the memory for the exception is deallocated.
128
129 This is never called for a __cxa_dependent_exception.
130*/
131static
132void
133exception_cleanup_func(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
134{
135 __cxa_exception* exception_header = cxa_exception_from_exception_unwind_exception(unwind_exception);
136 if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
137 std::__terminate(func: exception_header->terminateHandler);
138 // Just in case there exists a dependent exception that is pointing to this,
139 // check the reference count and only destroy this if that count goes to zero.
140 __cxa_decrement_exception_refcount(unwind_exception + 1);
141}
142
143static _LIBCXXABI_NORETURN void failed_throw(__cxa_exception* exception_header) {
144// Section 2.5.3 says:
145// * For purposes of this ABI, several things are considered exception handlers:
146// ** A terminate() call due to a throw.
147// and
148// * Upon entry, Following initialization of the catch parameter,
149// a handler must call:
150// * void *__cxa_begin_catch(void *exceptionObject );
151 (void) __cxa_begin_catch(&exception_header->unwindHeader);
152 std::__terminate(func: exception_header->terminateHandler);
153}
154
155// Return the offset of the __cxa_exception header from the start of the
156// allocated buffer. If __cxa_exception's alignment is smaller than the maximum
157// useful alignment for the target machine, padding has to be inserted before
158// the header to ensure the thrown object that follows the header is
159// sufficiently aligned. This happens if _Unwind_exception isn't double-word
160// aligned (on Darwin, for example).
161static size_t get_cxa_exception_offset() {
162 struct S {
163 } __attribute__((aligned));
164
165 // Compute the maximum alignment for the target machine.
166 constexpr size_t alignment = alignof(S);
167 constexpr size_t excp_size = sizeof(__cxa_exception);
168 constexpr size_t aligned_size =
169 (excp_size + alignment - 1) / alignment * alignment;
170 constexpr size_t offset = aligned_size - excp_size;
171 static_assert((offset == 0 || alignof(_Unwind_Exception) < alignment),
172 "offset is non-zero only if _Unwind_Exception isn't aligned");
173 return offset;
174}
175
176extern "C" {
177
178// Allocate a __cxa_exception object, and zero-fill it.
179// Reserve "thrown_size" bytes on the end for the user's exception
180// object. Zero-fill the object. If memory can't be allocated, call
181// std::terminate. Return a pointer to the memory to be used for the
182// user's exception object.
183void *__cxa_allocate_exception(size_t thrown_size) throw() {
184 size_t actual_size = cxa_exception_size_from_exception_thrown_size(size: thrown_size);
185
186 // Allocate extra space before the __cxa_exception header to ensure the
187 // start of the thrown object is sufficiently aligned.
188 size_t header_offset = get_cxa_exception_offset();
189 char *raw_buffer =
190 (char *)__aligned_malloc_with_fallback(size: header_offset + actual_size);
191 if (NULL == raw_buffer)
192 std::terminate();
193 __cxa_exception *exception_header =
194 static_cast<__cxa_exception *>((void *)(raw_buffer + header_offset));
195 ::memset(exception_header, 0, actual_size);
196 return thrown_object_from_cxa_exception(exception_header);
197}
198
199
200// Free a __cxa_exception object allocated with __cxa_allocate_exception.
201void __cxa_free_exception(void *thrown_object) throw() {
202 // Compute the size of the padding before the header.
203 size_t header_offset = get_cxa_exception_offset();
204 char *raw_buffer =
205 ((char *)cxa_exception_from_thrown_object(thrown_object)) - header_offset;
206 __aligned_free_with_fallback((void *)raw_buffer);
207}
208
209__cxa_exception* __cxa_init_primary_exception(void* object, std::type_info* tinfo,
210 void(_LIBCXXABI_DTOR_FUNC* dest)(void*)) throw() {
211 __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object: object);
212 exception_header->referenceCount = 0;
213 exception_header->unexpectedHandler = std::get_unexpected();
214 exception_header->terminateHandler = std::get_terminate();
215 exception_header->exceptionType = tinfo;
216 exception_header->exceptionDestructor = dest;
217 setOurExceptionClass(&exception_header->unwindHeader);
218 exception_header->unwindHeader.exception_cleanup = exception_cleanup_func;
219
220 return exception_header;
221}
222
223// This function shall allocate a __cxa_dependent_exception and
224// return a pointer to it. (Really to the object, not past its' end).
225// Otherwise, it will work like __cxa_allocate_exception.
226void * __cxa_allocate_dependent_exception () {
227 size_t actual_size = sizeof(__cxa_dependent_exception);
228 void *ptr = __aligned_malloc_with_fallback(size: actual_size);
229 if (NULL == ptr)
230 std::terminate();
231 ::memset(ptr, 0, actual_size);
232 return ptr;
233}
234
235
236// This function shall free a dependent_exception.
237// It does not affect the reference count of the primary exception.
238void __cxa_free_dependent_exception (void * dependent_exception) {
239 __aligned_free_with_fallback(dependent_exception);
240}
241
242
243// 2.4.3 Throwing the Exception Object
244/*
245After constructing the exception object with the throw argument value,
246the generated code calls the __cxa_throw runtime library routine. This
247routine never returns.
248
249The __cxa_throw routine will do the following:
250
251* Obtain the __cxa_exception header from the thrown exception object address,
252which can be computed as follows:
253 __cxa_exception *header = ((__cxa_exception *) thrown_exception - 1);
254* Save the current unexpected_handler and terminate_handler in the __cxa_exception header.
255* Save the tinfo and dest arguments in the __cxa_exception header.
256* Set the exception_class field in the unwind header. This is a 64-bit value
257representing the ASCII string "XXXXC++\0", where "XXXX" is a
258vendor-dependent string. That is, for implementations conforming to this
259ABI, the low-order 4 bytes of this 64-bit value will be "C++\0".
260* Increment the uncaught_exception flag.
261* Call _Unwind_RaiseException in the system unwind library, Its argument is the
262pointer to the thrown exception, which __cxa_throw itself received as an argument.
263__Unwind_RaiseException begins the process of stack unwinding, described
264in Section 2.5. In special cases, such as an inability to find a
265handler, _Unwind_RaiseException may return. In that case, __cxa_throw
266will call terminate, assuming that there was no handler for the
267exception.
268*/
269void
270#ifdef __USING_WASM_EXCEPTIONS__
271// In Wasm, a destructor returns its argument
272__cxa_throw(void *thrown_object, std::type_info *tinfo, void *(_LIBCXXABI_DTOR_FUNC *dest)(void *)) {
273#else
274__cxa_throw(void *thrown_object, std::type_info *tinfo, void (_LIBCXXABI_DTOR_FUNC *dest)(void *)) {
275#endif
276 __cxa_eh_globals* globals = __cxa_get_globals();
277 globals->uncaughtExceptions += 1; // Not atomically, since globals are thread-local
278
279 __cxa_exception* exception_header = __cxa_init_primary_exception(thrown_object, tinfo, dest);
280 exception_header->referenceCount = 1; // This is a newly allocated exception, no need for thread safety.
281
282#if __has_feature(address_sanitizer)
283 // Inform the ASan runtime that now might be a good time to clean stuff up.
284 __asan_handle_no_return();
285#endif
286
287#ifdef __USING_SJLJ_EXCEPTIONS__
288 _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
289#else
290 _Unwind_RaiseException(&exception_header->unwindHeader);
291#endif
292 // This only happens when there is no handler, or some unexpected unwinding
293 // error happens.
294 failed_throw(exception_header);
295}
296
297
298// 2.5.3 Exception Handlers
299/*
300The adjusted pointer is computed by the personality routine during phase 1
301 and saved in the exception header (either __cxa_exception or
302 __cxa_dependent_exception).
303
304 Requires: exception is native
305*/
306void *__cxa_get_exception_ptr(void *unwind_exception) throw() {
307#if defined(_LIBCXXABI_ARM_EHABI)
308 return reinterpret_cast<void*>(
309 static_cast<_Unwind_Control_Block*>(unwind_exception)->barrier_cache.bitpattern[0]);
310#else
311 return cxa_exception_from_exception_unwind_exception(
312 unwind_exception: static_cast<_Unwind_Exception*>(unwind_exception))->adjustedPtr;
313#endif
314}
315
316#if defined(_LIBCXXABI_ARM_EHABI)
317/*
318The routine to be called before the cleanup. This will save __cxa_exception in
319__cxa_eh_globals, so that __cxa_end_cleanup() can recover later.
320*/
321bool __cxa_begin_cleanup(void *unwind_arg) throw() {
322 _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
323 __cxa_eh_globals* globals = __cxa_get_globals();
324 __cxa_exception* exception_header =
325 cxa_exception_from_exception_unwind_exception(unwind_exception);
326
327 if (__isOurExceptionClass(unwind_exception))
328 {
329 if (0 == exception_header->propagationCount)
330 {
331 exception_header->nextPropagatingException = globals->propagatingExceptions;
332 globals->propagatingExceptions = exception_header;
333 }
334 ++exception_header->propagationCount;
335 }
336 else
337 {
338 // If the propagatingExceptions stack is not empty, since we can't
339 // chain the foreign exception, terminate it.
340 if (NULL != globals->propagatingExceptions)
341 std::terminate();
342 globals->propagatingExceptions = exception_header;
343 }
344 return true;
345}
346
347/*
348The routine to be called after the cleanup has been performed. It will get the
349propagating __cxa_exception from __cxa_eh_globals, and continue the stack
350unwinding with _Unwind_Resume.
351
352According to ARM EHABI 8.4.1, __cxa_end_cleanup() should not clobber any
353register, thus we have to write this function in assembly so that we can save
354{r1, r2, r3}. We don't have to save r0 because it is the return value and the
355first argument to _Unwind_Resume(). The function also saves/restores r4 to
356keep the stack aligned and to provide a temp register. _Unwind_Resume never
357returns and we need to keep the original lr so just branch to it. When
358targeting bare metal, the function also clobbers ip/r12 to hold the address of
359_Unwind_Resume, which may be too far away for an ordinary branch.
360*/
361__attribute__((used)) static _Unwind_Exception *
362__cxa_end_cleanup_impl()
363{
364 __cxa_eh_globals* globals = __cxa_get_globals();
365 __cxa_exception* exception_header = globals->propagatingExceptions;
366 if (NULL == exception_header)
367 {
368 // It seems that __cxa_begin_cleanup() is not called properly.
369 // We have no choice but terminate the program now.
370 std::terminate();
371 }
372
373 if (__isOurExceptionClass(&exception_header->unwindHeader))
374 {
375 --exception_header->propagationCount;
376 if (0 == exception_header->propagationCount)
377 {
378 globals->propagatingExceptions = exception_header->nextPropagatingException;
379 exception_header->nextPropagatingException = NULL;
380 }
381 }
382 else
383 {
384 globals->propagatingExceptions = NULL;
385 }
386 return &exception_header->unwindHeader;
387}
388
389asm(" .pushsection .text.__cxa_end_cleanup,\"ax\",%progbits\n"
390 " .globl __cxa_end_cleanup\n"
391 " .type __cxa_end_cleanup,%function\n"
392 "__cxa_end_cleanup:\n"
393#if defined(__ARM_FEATURE_BTI_DEFAULT)
394 " bti\n"
395#endif
396 " push {r1, r2, r3, r4}\n"
397 " mov r4, lr\n"
398 " bl __cxa_end_cleanup_impl\n"
399 " mov lr, r4\n"
400#if defined(LIBCXXABI_BAREMETAL)
401 " ldr r4, =_Unwind_Resume\n"
402 " mov ip, r4\n"
403#endif
404 " pop {r1, r2, r3, r4}\n"
405#if defined(LIBCXXABI_BAREMETAL)
406 " bx ip\n"
407#else
408 " b _Unwind_Resume\n"
409#endif
410 " .popsection");
411#endif // defined(_LIBCXXABI_ARM_EHABI)
412
413/*
414This routine can catch foreign or native exceptions. If native, the exception
415can be a primary or dependent variety. This routine may remain blissfully
416ignorant of whether the native exception is primary or dependent.
417
418If the exception is native:
419* Increment's the exception's handler count.
420* Push the exception on the stack of currently-caught exceptions if it is not
421 already there (from a rethrow).
422* Decrements the uncaught_exception count.
423* Returns the adjusted pointer to the exception object, which is stored in
424 the __cxa_exception by the personality routine.
425
426If the exception is foreign, this means it did not originate from one of throw
427routines. The foreign exception does not necessarily have a __cxa_exception
428header. However we can catch it here with a catch (...), or with a call
429to terminate or unexpected during unwinding.
430* Do not try to increment the exception's handler count, we don't know where
431 it is.
432* Push the exception on the stack of currently-caught exceptions only if the
433 stack is empty. The foreign exception has no way to link to the current
434 top of stack. If the stack is not empty, call terminate. Even with an
435 empty stack, this is hacked in by pushing a pointer to an imaginary
436 __cxa_exception block in front of the foreign exception. It would be better
437 if the __cxa_eh_globals structure had a stack of _Unwind_Exception, but it
438 doesn't. It has a stack of __cxa_exception (which has a next* in it).
439* Do not decrement the uncaught_exception count because we didn't increment it
440 in __cxa_throw (or one of our rethrow functions).
441* If we haven't terminated, assume the exception object is just past the
442 _Unwind_Exception and return a pointer to that.
443*/
444void*
445__cxa_begin_catch(void* unwind_arg) throw()
446{
447 _Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
448 bool native_exception = __isOurExceptionClass(unwind_exception);
449 __cxa_eh_globals* globals = __cxa_get_globals();
450 // exception_header is a hackish offset from a foreign exception, but it
451 // works as long as we're careful not to try to access any __cxa_exception
452 // parts.
453 __cxa_exception* exception_header =
454 cxa_exception_from_exception_unwind_exception
455 (
456 unwind_exception: static_cast<_Unwind_Exception*>(unwind_exception)
457 );
458
459#if defined(__MVS__)
460 // Remove the exception object from the linked list of exceptions that the z/OS unwinder
461 // maintains before adding it to the libc++abi list of caught exceptions.
462 // The libc++abi will manage the lifetime of the exception from this point forward.
463 _UnwindZOS_PopException();
464#endif
465
466 if (native_exception)
467 {
468 // Increment the handler count, removing the flag about being rethrown
469 exception_header->handlerCount = exception_header->handlerCount < 0 ?
470 -exception_header->handlerCount + 1 : exception_header->handlerCount + 1;
471 // place the exception on the top of the stack if it's not already
472 // there by a previous rethrow
473 if (exception_header != globals->caughtExceptions)
474 {
475 exception_header->nextException = globals->caughtExceptions;
476 globals->caughtExceptions = exception_header;
477 }
478 globals->uncaughtExceptions -= 1; // Not atomically, since globals are thread-local
479#if defined(_LIBCXXABI_ARM_EHABI)
480 return reinterpret_cast<void*>(exception_header->unwindHeader.barrier_cache.bitpattern[0]);
481#else
482 return exception_header->adjustedPtr;
483#endif
484 }
485 // Else this is a foreign exception
486 // If the caughtExceptions stack is not empty, terminate
487 if (globals->caughtExceptions != 0)
488 std::terminate();
489 // Push the foreign exception on to the stack
490 globals->caughtExceptions = exception_header;
491 return unwind_exception + 1;
492}
493
494
495/*
496Upon exit for any reason, a handler must call:
497 void __cxa_end_catch ();
498
499This routine can be called for either a native or foreign exception.
500For a native exception:
501* Locates the most recently caught exception and decrements its handler count.
502* Removes the exception from the caught exception stack, if the handler count goes to zero.
503* If the handler count goes down to zero, and the exception was not re-thrown
504 by throw, it locates the primary exception (which may be the same as the one
505 it's handling) and decrements its reference count. If that reference count
506 goes to zero, the function destroys the exception. In any case, if the current
507 exception is a dependent exception, it destroys that.
508
509For a foreign exception:
510* If it has been rethrown, there is nothing to do.
511* Otherwise delete the exception and pop the catch stack to empty.
512*/
513void __cxa_end_catch() {
514 static_assert(sizeof(__cxa_exception) == sizeof(__cxa_dependent_exception),
515 "sizeof(__cxa_exception) must be equal to "
516 "sizeof(__cxa_dependent_exception)");
517 static_assert(__builtin_offsetof(__cxa_exception, referenceCount) ==
518 __builtin_offsetof(__cxa_dependent_exception,
519 primaryException),
520 "the layout of __cxa_exception must match the layout of "
521 "__cxa_dependent_exception");
522 static_assert(__builtin_offsetof(__cxa_exception, handlerCount) ==
523 __builtin_offsetof(__cxa_dependent_exception, handlerCount),
524 "the layout of __cxa_exception must match the layout of "
525 "__cxa_dependent_exception");
526 __cxa_eh_globals* globals = __cxa_get_globals_fast(); // __cxa_get_globals called in __cxa_begin_catch
527 __cxa_exception* exception_header = globals->caughtExceptions;
528 // If we've rethrown a foreign exception, then globals->caughtExceptions
529 // will have been made an empty stack by __cxa_rethrow() and there is
530 // nothing more to be done. Do nothing!
531 if (NULL != exception_header)
532 {
533 bool native_exception = __isOurExceptionClass(&exception_header->unwindHeader);
534 if (native_exception)
535 {
536 // This is a native exception
537 if (exception_header->handlerCount < 0)
538 {
539 // The exception has been rethrown by __cxa_rethrow, so don't delete it
540 if (0 == incrementHandlerCount(exception: exception_header))
541 {
542 // Remove from the chain of uncaught exceptions
543 globals->caughtExceptions = exception_header->nextException;
544 // but don't destroy
545 }
546 // Keep handlerCount negative in case there are nested catch's
547 // that need to be told that this exception is rethrown. Don't
548 // erase this rethrow flag until the exception is recaught.
549 }
550 else
551 {
552 // The native exception has not been rethrown
553 if (0 == decrementHandlerCount(exception: exception_header))
554 {
555 // Remove from the chain of uncaught exceptions
556 globals->caughtExceptions = exception_header->nextException;
557 // Destroy this exception, being careful to distinguish
558 // between dependent and primary exceptions
559 if (isDependentException(&exception_header->unwindHeader))
560 {
561 // Reset exception_header to primaryException and deallocate the dependent exception
562 __cxa_dependent_exception* dep_exception_header =
563 reinterpret_cast<__cxa_dependent_exception*>(exception_header);
564 exception_header =
565 cxa_exception_from_thrown_object(dep_exception_header->primaryException);
566 __cxa_free_dependent_exception(dep_exception_header);
567 }
568 // Destroy the primary exception only if its referenceCount goes to 0
569 // (this decrement must be atomic)
570 __cxa_decrement_exception_refcount(thrown_object_from_cxa_exception(exception_header));
571 }
572 }
573 }
574 else
575 {
576 // The foreign exception has not been rethrown. Pop the stack
577 // and delete it. If there are nested catch's and they try
578 // to touch a foreign exception in any way, that is undefined
579 // behavior. They likely can't since the only way to catch
580 // a foreign exception is with catch (...)!
581 _Unwind_DeleteException(&globals->caughtExceptions->unwindHeader);
582 globals->caughtExceptions = 0;
583 }
584 }
585}
586
587// Note: exception_header may be masquerading as a __cxa_dependent_exception
588// and that's ok. exceptionType is there too.
589// However watch out for foreign exceptions. Return null for them.
590std::type_info *__cxa_current_exception_type() {
591// get the current exception
592 __cxa_eh_globals *globals = __cxa_get_globals_fast();
593 if (NULL == globals)
594 return NULL; // If there have never been any exceptions, there are none now.
595 __cxa_exception *exception_header = globals->caughtExceptions;
596 if (NULL == exception_header)
597 return NULL; // No current exception
598 if (!__isOurExceptionClass(&exception_header->unwindHeader))
599 return NULL;
600 return exception_header->exceptionType;
601}
602
603// 2.5.4 Rethrowing Exceptions
604/* This routine can rethrow native or foreign exceptions.
605If the exception is native:
606* marks the exception object on top of the caughtExceptions stack
607 (in an implementation-defined way) as being rethrown.
608* If the caughtExceptions stack is empty, it calls terminate()
609 (see [C++FDIS] [except.throw], 15.1.8).
610* It then calls _Unwind_RaiseException which should not return
611 (terminate if it does).
612 Note: exception_header may be masquerading as a __cxa_dependent_exception
613 and that's ok.
614*/
615void __cxa_rethrow() {
616 __cxa_eh_globals* globals = __cxa_get_globals();
617 __cxa_exception* exception_header = globals->caughtExceptions;
618 if (NULL == exception_header)
619 std::terminate(); // throw; called outside of a exception handler
620 bool native_exception = __isOurExceptionClass(&exception_header->unwindHeader);
621 if (native_exception)
622 {
623 // Mark the exception as being rethrown (reverse the effects of __cxa_begin_catch)
624 exception_header->handlerCount = -exception_header->handlerCount;
625 globals->uncaughtExceptions += 1;
626 // __cxa_end_catch will remove this exception from the caughtExceptions stack if necessary
627 }
628 else // this is a foreign exception
629 {
630 // The only way to communicate to __cxa_end_catch that we've rethrown
631 // a foreign exception, so don't delete us, is to pop the stack here
632 // which must be empty afterwards. Then __cxa_end_catch will do
633 // nothing
634 globals->caughtExceptions = 0;
635 }
636#ifdef __USING_SJLJ_EXCEPTIONS__
637 _Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
638#else
639 _Unwind_RaiseException(&exception_header->unwindHeader);
640#endif
641
642 // If we get here, some kind of unwinding error has occurred.
643 // There is some weird code generation bug happening with
644 // Apple clang version 4.0 (tags/Apple/clang-418.0.2) (based on LLVM 3.1svn)
645 // If we call failed_throw here. Turns up with -O2 or higher, and -Os.
646 __cxa_begin_catch(&exception_header->unwindHeader);
647 if (native_exception)
648 std::__terminate(func: exception_header->terminateHandler);
649 // Foreign exception: can't get exception_header->terminateHandler
650 std::terminate();
651}
652
653/*
654 If thrown_object is not null, atomically increment the referenceCount field
655 of the __cxa_exception header associated with the thrown object referred to
656 by thrown_object.
657
658 Requires: If thrown_object is not NULL, it is a native exception.
659*/
660void
661__cxa_increment_exception_refcount(void *thrown_object) throw() {
662 if (thrown_object != NULL )
663 {
664 __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
665 std::__libcpp_atomic_add(&exception_header->referenceCount, size_t(1));
666 }
667}
668
669/*
670 If thrown_object is not null, atomically decrement the referenceCount field
671 of the __cxa_exception header associated with the thrown object referred to
672 by thrown_object. If the referenceCount drops to zero, destroy and
673 deallocate the exception.
674
675 Requires: If thrown_object is not NULL, it is a native exception.
676*/
677_LIBCXXABI_NO_CFI
678void __cxa_decrement_exception_refcount(void *thrown_object) throw() {
679 if (thrown_object != NULL )
680 {
681 __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
682 if (std::__libcpp_atomic_add(&exception_header->referenceCount, size_t(-1)) == 0)
683 {
684 if (NULL != exception_header->exceptionDestructor)
685 exception_header->exceptionDestructor(thrown_object);
686 __cxa_free_exception(thrown_object);
687 }
688 }
689}
690
691/*
692 Returns a pointer to the thrown object (if any) at the top of the
693 caughtExceptions stack. Atomically increment the exception's referenceCount.
694 If there is no such thrown object or if the thrown object is foreign,
695 returns null.
696
697 We can use __cxa_get_globals_fast here to get the globals because if there have
698 been no exceptions thrown, ever, on this thread, we can return NULL without
699 the need to allocate the exception-handling globals.
700*/
701void *__cxa_current_primary_exception() throw() {
702// get the current exception
703 __cxa_eh_globals* globals = __cxa_get_globals_fast();
704 if (NULL == globals)
705 return NULL; // If there are no globals, there is no exception
706 __cxa_exception* exception_header = globals->caughtExceptions;
707 if (NULL == exception_header)
708 return NULL; // No current exception
709 if (!__isOurExceptionClass(&exception_header->unwindHeader))
710 return NULL; // Can't capture a foreign exception (no way to refcount it)
711 if (isDependentException(&exception_header->unwindHeader)) {
712 __cxa_dependent_exception* dep_exception_header =
713 reinterpret_cast<__cxa_dependent_exception*>(exception_header);
714 exception_header = cxa_exception_from_thrown_object(dep_exception_header->primaryException);
715 }
716 void* thrown_object = thrown_object_from_cxa_exception(exception_header);
717 __cxa_increment_exception_refcount(thrown_object);
718 return thrown_object;
719}
720
721/*
722 If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
723 stored in exc is called. Otherwise the referenceCount stored in the
724 primary exception is decremented, destroying the primary if necessary.
725 Finally the dependent exception is destroyed.
726*/
727static
728void
729dependent_exception_cleanup(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
730{
731 __cxa_dependent_exception* dep_exception_header =
732 reinterpret_cast<__cxa_dependent_exception*>(unwind_exception + 1) - 1;
733 if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
734 std::__terminate(func: dep_exception_header->terminateHandler);
735 __cxa_decrement_exception_refcount(dep_exception_header->primaryException);
736 __cxa_free_dependent_exception(dep_exception_header);
737}
738
739/*
740 If thrown_object is not null, allocate, initialize and throw a dependent
741 exception.
742*/
743void
744__cxa_rethrow_primary_exception(void* thrown_object)
745{
746 if ( thrown_object != NULL )
747 {
748 // thrown_object guaranteed to be native because
749 // __cxa_current_primary_exception returns NULL for foreign exceptions
750 __cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
751 __cxa_dependent_exception* dep_exception_header =
752 static_cast<__cxa_dependent_exception*>(__cxa_allocate_dependent_exception());
753 dep_exception_header->primaryException = thrown_object;
754 __cxa_increment_exception_refcount(thrown_object);
755 dep_exception_header->exceptionType = exception_header->exceptionType;
756 dep_exception_header->unexpectedHandler = std::get_unexpected();
757 dep_exception_header->terminateHandler = std::get_terminate();
758 setDependentExceptionClass(&dep_exception_header->unwindHeader);
759 __cxa_get_globals()->uncaughtExceptions += 1;
760 dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup;
761#ifdef __USING_SJLJ_EXCEPTIONS__
762 _Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader);
763#else
764 _Unwind_RaiseException(&dep_exception_header->unwindHeader);
765#endif
766 // Some sort of unwinding error. Note that terminate is a handler.
767 __cxa_begin_catch(&dep_exception_header->unwindHeader);
768 }
769 // If we return client will call terminate()
770}
771
772bool
773__cxa_uncaught_exception() throw() { return __cxa_uncaught_exceptions() != 0; }
774
775unsigned int
776__cxa_uncaught_exceptions() throw()
777{
778 // This does not report foreign exceptions in flight
779 __cxa_eh_globals* globals = __cxa_get_globals_fast();
780 if (globals == 0)
781 return 0;
782 return globals->uncaughtExceptions;
783}
784
785} // extern "C"
786
787} // abi
788

source code of libcxxabi/src/cxa_exception.cpp