Differential D19566 Diff 55005 contrib/libcxxabi/src/cxa_exception.cpp

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contrib/libcxxabi/src/cxa_exception.cpp

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				//===------------------------- cxa_exception.cpp --------------------------===//
				//
				// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
				// See https://llvm.org/LICENSE.txt for license information.
				// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
				//
				//
				// This file implements the "Exception Handling APIs"
				// http://mentorembedded.github.io/cxx-abi/abi-eh.html
				//
				//===----------------------------------------------------------------------===//

				#include "cxxabi.h"

				#include <exception> // for std::terminate
				#include <cstring> // for memset
				#include "cxa_exception.hpp"
				#include "cxa_handlers.hpp"
				#include "fallback_malloc.h"
				#include "include/atomic_support.h"

				#if __has_feature(address_sanitizer)
				extern "C" void __asan_handle_no_return(void);
				#endif

				// +---------------------------+-----------------------------+---------------+
				// \| __cxa_exception \| _Unwind_Exception CLNGC++\0 \| thrown object \|
				// +---------------------------+-----------------------------+---------------+
				// ^
				// \|
				// +-------------------------------------------------------+
				// \|
				// +---------------------------+-----------------------------+
				// \| __cxa_dependent_exception \| _Unwind_Exception CLNGC++\1 \|
				// +---------------------------+-----------------------------+

				namespace __cxxabiv1 {

				// Utility routines
				static
				inline
				__cxa_exception*
				cxa_exception_from_thrown_object(void* thrown_object)
				{
				return static_cast<__cxa_exception*>(thrown_object) - 1;
				}

				// Note: This is never called when exception_header is masquerading as a
				// __cxa_dependent_exception.
				static
				inline
				void*
				thrown_object_from_cxa_exception(__cxa_exception* exception_header)
				{
				return static_cast<void*>(exception_header + 1);
				}

				// Get the exception object from the unwind pointer.
				// Relies on the structure layout, where the unwind pointer is right in
				// front of the user's exception object
				static
				inline
				__cxa_exception*
				cxa_exception_from_exception_unwind_exception(_Unwind_Exception* unwind_exception)
				{
				return cxa_exception_from_thrown_object(unwind_exception + 1 );
				}

				// Round s up to next multiple of a.
				static inline
				size_t aligned_allocation_size(size_t s, size_t a) {
				return (s + a - 1) & ~(a - 1);
				}

				static inline
				size_t cxa_exception_size_from_exception_thrown_size(size_t size) {
				return aligned_allocation_size(size + sizeof (__cxa_exception),
				alignof(__cxa_exception));
				}

				void __setExceptionClass(_Unwind_Exception* unwind_exception, uint64_t newValue) {
				::memcpy(&unwind_exception->exception_class, &newValue, sizeof(newValue));
				}


				static void setOurExceptionClass(_Unwind_Exception* unwind_exception) {
				__setExceptionClass(unwind_exception, kOurExceptionClass);
				}

				static void setDependentExceptionClass(_Unwind_Exception* unwind_exception) {
				__setExceptionClass(unwind_exception, kOurDependentExceptionClass);
				}

				// Is it one of ours?
				uint64_t __getExceptionClass(const _Unwind_Exception* unwind_exception) {
				// On x86 and some ARM unwinders, unwind_exception->exception_class is
				// a uint64_t. On other ARM unwinders, it is a char[8]
				// See: http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
				// So we just copy it into a uint64_t to be sure.
				uint64_t exClass;
				::memcpy(&exClass, &unwind_exception->exception_class, sizeof(exClass));
				return exClass;
				}

				bool __isOurExceptionClass(const _Unwind_Exception* unwind_exception) {
				return (__getExceptionClass(unwind_exception) & get_vendor_and_language) ==
				(kOurExceptionClass & get_vendor_and_language);
				}

				static bool isDependentException(_Unwind_Exception* unwind_exception) {
				return (__getExceptionClass(unwind_exception) & 0xFF) == 0x01;
				}

				// This does not need to be atomic
				static inline int incrementHandlerCount(__cxa_exception *exception) {
				return ++exception->handlerCount;
				}

				// This does not need to be atomic
				static inline int decrementHandlerCount(__cxa_exception *exception) {
				return --exception->handlerCount;
				}

				/*
				If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
				stored in exc is called. Otherwise the exceptionDestructor stored in
				exc is called, and then the memory for the exception is deallocated.

				This is never called for a __cxa_dependent_exception.
				*/
				static
				void
				exception_cleanup_func(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
				{
				__cxa_exception* exception_header = cxa_exception_from_exception_unwind_exception(unwind_exception);
				if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
				std::__terminate(exception_header->terminateHandler);
				// Just in case there exists a dependent exception that is pointing to this,
				// check the reference count and only destroy this if that count goes to zero.
				__cxa_decrement_exception_refcount(unwind_exception + 1);
				}

				static _LIBCXXABI_NORETURN void failed_throw(__cxa_exception* exception_header) {
				// Section 2.5.3 says:
				// * For purposes of this ABI, several things are considered exception handlers:
				// ** A terminate() call due to a throw.
				// and
				// * Upon entry, Following initialization of the catch parameter,
				// a handler must call:
				// * void __cxa_begin_catch(void exceptionObject );
				(void) __cxa_begin_catch(&exception_header->unwindHeader);
				std::__terminate(exception_header->terminateHandler);
				}

				// Return the offset of the __cxa_exception header from the start of the
				// allocated buffer. If __cxa_exception's alignment is smaller than the maximum
				// useful alignment for the target machine, padding has to be inserted before
				// the header to ensure the thrown object that follows the header is
				// sufficiently aligned. This happens if _Unwind_exception isn't double-word
				// aligned (on Darwin, for example).
				static size_t get_cxa_exception_offset() {
				struct S {
				} __attribute__((aligned));

				// Compute the maximum alignment for the target machine.
				constexpr size_t alignment = std::alignment_of<S>::value;
				constexpr size_t excp_size = sizeof(__cxa_exception);
				constexpr size_t aligned_size =
				(excp_size + alignment - 1) / alignment * alignment;
				constexpr size_t offset = aligned_size - excp_size;
				static_assert((offset == 0 \|\|
				std::alignment_of<_Unwind_Exception>::value < alignment),
				"offset is non-zero only if _Unwind_Exception isn't aligned");
				return offset;
				}

				extern "C" {

				// Allocate a __cxa_exception object, and zero-fill it.
				// Reserve "thrown_size" bytes on the end for the user's exception
				// object. Zero-fill the object. If memory can't be allocated, call
				// std::terminate. Return a pointer to the memory to be used for the
				// user's exception object.
				void *__cxa_allocate_exception(size_t thrown_size) throw() {
				size_t actual_size = cxa_exception_size_from_exception_thrown_size(thrown_size);

				// Allocate extra space before the __cxa_exception header to ensure the
				// start of the thrown object is sufficiently aligned.
				size_t header_offset = get_cxa_exception_offset();
				char *raw_buffer =
				(char *)__aligned_malloc_with_fallback(header_offset + actual_size);
				if (NULL == raw_buffer)
				std::terminate();
				__cxa_exception *exception_header =
				static_cast<__cxa_exception >((void )(raw_buffer + header_offset));
				std::memset(exception_header, 0, actual_size);
				return thrown_object_from_cxa_exception(exception_header);
				}


				// Free a __cxa_exception object allocated with __cxa_allocate_exception.
				void __cxa_free_exception(void *thrown_object) throw() {
				// Compute the size of the padding before the header.
				size_t header_offset = get_cxa_exception_offset();
				char *raw_buffer =
				((char *)cxa_exception_from_thrown_object(thrown_object)) - header_offset;
				__aligned_free_with_fallback((void *)raw_buffer);
				}


				// This function shall allocate a __cxa_dependent_exception and
				// return a pointer to it. (Really to the object, not past its' end).
				// Otherwise, it will work like __cxa_allocate_exception.
				void * __cxa_allocate_dependent_exception () {
				size_t actual_size = sizeof(__cxa_dependent_exception);
				void *ptr = __aligned_malloc_with_fallback(actual_size);
				if (NULL == ptr)
				std::terminate();
				std::memset(ptr, 0, actual_size);
				return ptr;
				}


				// This function shall free a dependent_exception.
				// It does not affect the reference count of the primary exception.
				void __cxa_free_dependent_exception (void * dependent_exception) {
				__aligned_free_with_fallback(dependent_exception);
				}


				// 2.4.3 Throwing the Exception Object
				/*
				After constructing the exception object with the throw argument value,
				the generated code calls the __cxa_throw runtime library routine. This
				routine never returns.

				The __cxa_throw routine will do the following:

				* Obtain the __cxa_exception header from the thrown exception object address,
				which can be computed as follows:
				__cxa_exception header = ((__cxa_exception ) thrown_exception - 1);
				* Save the current unexpected_handler and terminate_handler in the __cxa_exception header.
				* Save the tinfo and dest arguments in the __cxa_exception header.
				* Set the exception_class field in the unwind header. This is a 64-bit value
				representing the ASCII string "XXXXC++\0", where "XXXX" is a
				vendor-dependent string. That is, for implementations conforming to this
				ABI, the low-order 4 bytes of this 64-bit value will be "C++\0".
				* Increment the uncaught_exception flag.
				* Call _Unwind_RaiseException in the system unwind library, Its argument is the
				pointer to the thrown exception, which __cxa_throw itself received as an argument.
				__Unwind_RaiseException begins the process of stack unwinding, described
				in Section 2.5. In special cases, such as an inability to find a
				handler, _Unwind_RaiseException may return. In that case, __cxa_throw
				will call terminate, assuming that there was no handler for the
				exception.
				*/
				void
				__cxa_throw(void thrown_object, std::type_info tinfo, void (dest)(void )) {
				__cxa_eh_globals *globals = __cxa_get_globals();
				__cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);

				exception_header->unexpectedHandler = std::get_unexpected();
				exception_header->terminateHandler = std::get_terminate();
				exception_header->exceptionType = tinfo;
				exception_header->exceptionDestructor = dest;
				setOurExceptionClass(&exception_header->unwindHeader);
				exception_header->referenceCount = 1; // This is a newly allocated exception, no need for thread safety.
				globals->uncaughtExceptions += 1; // Not atomically, since globals are thread-local

				exception_header->unwindHeader.exception_cleanup = exception_cleanup_func;

				#if __has_feature(address_sanitizer)
				// Inform the ASan runtime that now might be a good time to clean stuff up.
				__asan_handle_no_return();
				#endif

				#ifdef __USING_SJLJ_EXCEPTIONS__
				_Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
				#else
				_Unwind_RaiseException(&exception_header->unwindHeader);
				#endif
				// This only happens when there is no handler, or some unexpected unwinding
				// error happens.
				failed_throw(exception_header);
				}


				// 2.5.3 Exception Handlers
				/*
				The adjusted pointer is computed by the personality routine during phase 1
				and saved in the exception header (either __cxa_exception or
				__cxa_dependent_exception).

				Requires: exception is native
				*/
				void __cxa_get_exception_ptr(void unwind_exception) throw() {
				#if defined(_LIBCXXABI_ARM_EHABI)
				return reinterpret_cast<void*>(
				static_cast<_Unwind_Control_Block*>(unwind_exception)->barrier_cache.bitpattern[0]);
				#else
				return cxa_exception_from_exception_unwind_exception(
				static_cast<_Unwind_Exception*>(unwind_exception))->adjustedPtr;
				#endif
				}

				#if defined(_LIBCXXABI_ARM_EHABI)
				/*
				The routine to be called before the cleanup. This will save __cxa_exception in
				__cxa_eh_globals, so that __cxa_end_cleanup() can recover later.
				*/
				bool __cxa_begin_cleanup(void *unwind_arg) throw() {
				_Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
				__cxa_eh_globals* globals = __cxa_get_globals();
				__cxa_exception* exception_header =
				cxa_exception_from_exception_unwind_exception(unwind_exception);

				if (__isOurExceptionClass(unwind_exception))
				{
				if (0 == exception_header->propagationCount)
				{
				exception_header->nextPropagatingException = globals->propagatingExceptions;
				globals->propagatingExceptions = exception_header;
				}
				++exception_header->propagationCount;
				}
				else
				{
				// If the propagatingExceptions stack is not empty, since we can't
				// chain the foreign exception, terminate it.
				if (NULL != globals->propagatingExceptions)
				std::terminate();
				globals->propagatingExceptions = exception_header;
				}
				return true;
				}

				/*
				The routine to be called after the cleanup has been performed. It will get the
				propagating __cxa_exception from __cxa_eh_globals, and continue the stack
				unwinding with _Unwind_Resume.

				According to ARM EHABI 8.4.1, __cxa_end_cleanup() should not clobber any
				register, thus we have to write this function in assembly so that we can save
				{r1, r2, r3}. We don't have to save r0 because it is the return value and the
				first argument to _Unwind_Resume(). In addition, we are saving r4 in order to
				align the stack to 16 bytes, even though it is a callee-save register.
				*/
				__attribute__((used)) static _Unwind_Exception *
				__cxa_end_cleanup_impl()
				{
				__cxa_eh_globals* globals = __cxa_get_globals();
				__cxa_exception* exception_header = globals->propagatingExceptions;
				if (NULL == exception_header)
				{
				// It seems that __cxa_begin_cleanup() is not called properly.
				// We have no choice but terminate the program now.
				std::terminate();
				}

				if (__isOurExceptionClass(&exception_header->unwindHeader))
				{
				--exception_header->propagationCount;
				if (0 == exception_header->propagationCount)
				{
				globals->propagatingExceptions = exception_header->nextPropagatingException;
				exception_header->nextPropagatingException = NULL;
				}
				}
				else
				{
				globals->propagatingExceptions = NULL;
				}
				return &exception_header->unwindHeader;
				}

				asm (
				" .pushsection .text.__cxa_end_cleanup,\"ax\",%progbits\n"
				" .globl __cxa_end_cleanup\n"
				" .type __cxa_end_cleanup,%function\n"
				"__cxa_end_cleanup:\n"
				" push {r1, r2, r3, r4}\n"
				" bl __cxa_end_cleanup_impl\n"
				" pop {r1, r2, r3, r4}\n"
				" bl _Unwind_Resume\n"
				" bl abort\n"
				" .popsection"
				);
				#endif // defined(_LIBCXXABI_ARM_EHABI)

				/*
				This routine can catch foreign or native exceptions. If native, the exception
				can be a primary or dependent variety. This routine may remain blissfully
				ignorant of whether the native exception is primary or dependent.

				If the exception is native:
				* Increment's the exception's handler count.
				* Push the exception on the stack of currently-caught exceptions if it is not
				already there (from a rethrow).
				* Decrements the uncaught_exception count.
				* Returns the adjusted pointer to the exception object, which is stored in
				the __cxa_exception by the personality routine.

				If the exception is foreign, this means it did not originate from one of throw
				routines. The foreign exception does not necessarily have a __cxa_exception
				header. However we can catch it here with a catch (...), or with a call
				to terminate or unexpected during unwinding.
				* Do not try to increment the exception's handler count, we don't know where
				it is.
				* Push the exception on the stack of currently-caught exceptions only if the
				stack is empty. The foreign exception has no way to link to the current
				top of stack. If the stack is not empty, call terminate. Even with an
				empty stack, this is hacked in by pushing a pointer to an imaginary
				__cxa_exception block in front of the foreign exception. It would be better
				if the __cxa_eh_globals structure had a stack of _Unwind_Exception, but it
				doesn't. It has a stack of __cxa_exception (which has a next* in it).
				* Do not decrement the uncaught_exception count because we didn't increment it
				in __cxa_throw (or one of our rethrow functions).
				* If we haven't terminated, assume the exception object is just past the
				_Unwind_Exception and return a pointer to that.
				*/
				void*
				__cxa_begin_catch(void* unwind_arg) throw()
				{
				_Unwind_Exception* unwind_exception = static_cast<_Unwind_Exception*>(unwind_arg);
				bool native_exception = __isOurExceptionClass(unwind_exception);
				__cxa_eh_globals* globals = __cxa_get_globals();
				// exception_header is a hackish offset from a foreign exception, but it
				// works as long as we're careful not to try to access any __cxa_exception
				// parts.
				__cxa_exception* exception_header =
				cxa_exception_from_exception_unwind_exception
				(
				static_cast<_Unwind_Exception*>(unwind_exception)
				);
				if (native_exception)
				{
				// Increment the handler count, removing the flag about being rethrown
				exception_header->handlerCount = exception_header->handlerCount < 0 ?
				-exception_header->handlerCount + 1 : exception_header->handlerCount + 1;
				// place the exception on the top of the stack if it's not already
				// there by a previous rethrow
				if (exception_header != globals->caughtExceptions)
				{
				exception_header->nextException = globals->caughtExceptions;
				globals->caughtExceptions = exception_header;
				}
				globals->uncaughtExceptions -= 1; // Not atomically, since globals are thread-local
				#if defined(_LIBCXXABI_ARM_EHABI)
				return reinterpret_cast<void*>(exception_header->unwindHeader.barrier_cache.bitpattern[0]);
				#else
				return exception_header->adjustedPtr;
				#endif
				}
				// Else this is a foreign exception
				// If the caughtExceptions stack is not empty, terminate
				if (globals->caughtExceptions != 0)
				std::terminate();
				// Push the foreign exception on to the stack
				globals->caughtExceptions = exception_header;
				return unwind_exception + 1;
				}


				/*
				Upon exit for any reason, a handler must call:
				void __cxa_end_catch ();

				This routine can be called for either a native or foreign exception.
				For a native exception:
				* Locates the most recently caught exception and decrements its handler count.
				* Removes the exception from the caught exception stack, if the handler count goes to zero.
				* If the handler count goes down to zero, and the exception was not re-thrown
				by throw, it locates the primary exception (which may be the same as the one
				it's handling) and decrements its reference count. If that reference count
				goes to zero, the function destroys the exception. In any case, if the current
				exception is a dependent exception, it destroys that.

				For a foreign exception:
				* If it has been rethrown, there is nothing to do.
				* Otherwise delete the exception and pop the catch stack to empty.
				*/
				void __cxa_end_catch() {
				static_assert(sizeof(__cxa_exception) == sizeof(__cxa_dependent_exception),
				"sizeof(__cxa_exception) must be equal to "
				"sizeof(__cxa_dependent_exception)");
				static_assert(__builtin_offsetof(__cxa_exception, referenceCount) ==
				__builtin_offsetof(__cxa_dependent_exception,
				primaryException),
				"the layout of __cxa_exception must match the layout of "
				"__cxa_dependent_exception");
				static_assert(__builtin_offsetof(__cxa_exception, handlerCount) ==
				__builtin_offsetof(__cxa_dependent_exception, handlerCount),
				"the layout of __cxa_exception must match the layout of "
				"__cxa_dependent_exception");
				__cxa_eh_globals* globals = __cxa_get_globals_fast(); // __cxa_get_globals called in __cxa_begin_catch
				__cxa_exception* exception_header = globals->caughtExceptions;
				// If we've rethrown a foreign exception, then globals->caughtExceptions
				// will have been made an empty stack by __cxa_rethrow() and there is
				// nothing more to be done. Do nothing!
				if (NULL != exception_header)
				{
				bool native_exception = __isOurExceptionClass(&exception_header->unwindHeader);
				if (native_exception)
				{
				// This is a native exception
				if (exception_header->handlerCount < 0)
				{
				// The exception has been rethrown by __cxa_rethrow, so don't delete it
				if (0 == incrementHandlerCount(exception_header))
				{
				// Remove from the chain of uncaught exceptions
				globals->caughtExceptions = exception_header->nextException;
				// but don't destroy
				}
				// Keep handlerCount negative in case there are nested catch's
				// that need to be told that this exception is rethrown. Don't
				// erase this rethrow flag until the exception is recaught.
				}
				else
				{
				// The native exception has not been rethrown
				if (0 == decrementHandlerCount(exception_header))
				{
				// Remove from the chain of uncaught exceptions
				globals->caughtExceptions = exception_header->nextException;
				// Destroy this exception, being careful to distinguish
				// between dependent and primary exceptions
				if (isDependentException(&exception_header->unwindHeader))
				{
				// Reset exception_header to primaryException and deallocate the dependent exception
				__cxa_dependent_exception* dep_exception_header =
				reinterpret_cast<__cxa_dependent_exception*>(exception_header);
				exception_header =
				cxa_exception_from_thrown_object(dep_exception_header->primaryException);
				__cxa_free_dependent_exception(dep_exception_header);
				}
				// Destroy the primary exception only if its referenceCount goes to 0
				// (this decrement must be atomic)
				__cxa_decrement_exception_refcount(thrown_object_from_cxa_exception(exception_header));
				}
				}
				}
				else
				{
				// The foreign exception has not been rethrown. Pop the stack
				// and delete it. If there are nested catch's and they try
				// to touch a foreign exception in any way, that is undefined
				// behavior. They likely can't since the only way to catch
				// a foreign exception is with catch (...)!
				_Unwind_DeleteException(&globals->caughtExceptions->unwindHeader);
				globals->caughtExceptions = 0;
				}
				}
				}

				// Note: exception_header may be masquerading as a __cxa_dependent_exception
				// and that's ok. exceptionType is there too.
				// However watch out for foreign exceptions. Return null for them.
				std::type_info *__cxa_current_exception_type() {
				// get the current exception
				__cxa_eh_globals *globals = __cxa_get_globals_fast();
				if (NULL == globals)
				return NULL; // If there have never been any exceptions, there are none now.
				__cxa_exception *exception_header = globals->caughtExceptions;
				if (NULL == exception_header)
				return NULL; // No current exception
				if (!__isOurExceptionClass(&exception_header->unwindHeader))
				return NULL;
				return exception_header->exceptionType;
				}

				// 2.5.4 Rethrowing Exceptions
				/* This routine can rethrow native or foreign exceptions.
				If the exception is native:
				* marks the exception object on top of the caughtExceptions stack
				(in an implementation-defined way) as being rethrown.
				* If the caughtExceptions stack is empty, it calls terminate()
				(see [C++FDIS] [except.throw], 15.1.8).
				* It then calls _Unwind_RaiseException which should not return
				(terminate if it does).
				Note: exception_header may be masquerading as a __cxa_dependent_exception
				and that's ok.
				*/
				void __cxa_rethrow() {
				__cxa_eh_globals* globals = __cxa_get_globals();
				__cxa_exception* exception_header = globals->caughtExceptions;
				if (NULL == exception_header)
				std::terminate(); // throw; called outside of a exception handler
				bool native_exception = __isOurExceptionClass(&exception_header->unwindHeader);
				if (native_exception)
				{
				// Mark the exception as being rethrown (reverse the effects of __cxa_begin_catch)
				exception_header->handlerCount = -exception_header->handlerCount;
				globals->uncaughtExceptions += 1;
				// __cxa_end_catch will remove this exception from the caughtExceptions stack if necessary
				}
				else // this is a foreign exception
				{
				// The only way to communicate to __cxa_end_catch that we've rethrown
				// a foreign exception, so don't delete us, is to pop the stack here
				// which must be empty afterwards. Then __cxa_end_catch will do
				// nothing
				globals->caughtExceptions = 0;
				}
				#ifdef __USING_SJLJ_EXCEPTIONS__
				_Unwind_SjLj_RaiseException(&exception_header->unwindHeader);
				#else
				_Unwind_RaiseException(&exception_header->unwindHeader);
				#endif

				// If we get here, some kind of unwinding error has occurred.
				// There is some weird code generation bug happening with
				// Apple clang version 4.0 (tags/Apple/clang-418.0.2) (based on LLVM 3.1svn)
				// If we call failed_throw here. Turns up with -O2 or higher, and -Os.
				__cxa_begin_catch(&exception_header->unwindHeader);
				if (native_exception)
				std::__terminate(exception_header->terminateHandler);
				// Foreign exception: can't get exception_header->terminateHandler
				std::terminate();
				}

				/*
				If thrown_object is not null, atomically increment the referenceCount field
				of the __cxa_exception header associated with the thrown object referred to
				by thrown_object.

				Requires: If thrown_object is not NULL, it is a native exception.
				*/
				void
				__cxa_increment_exception_refcount(void *thrown_object) throw() {
				if (thrown_object != NULL )
				{
				__cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
				std::__libcpp_atomic_add(&exception_header->referenceCount, size_t(1));
				}
				}

				/*
				If thrown_object is not null, atomically decrement the referenceCount field
				of the __cxa_exception header associated with the thrown object referred to
				by thrown_object. If the referenceCount drops to zero, destroy and
				deallocate the exception.

				Requires: If thrown_object is not NULL, it is a native exception.
				*/
				_LIBCXXABI_NO_CFI
				void __cxa_decrement_exception_refcount(void *thrown_object) throw() {
				if (thrown_object != NULL )
				{
				__cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
				if (std::__libcpp_atomic_add(&exception_header->referenceCount, size_t(-1)) == 0)
				{
				if (NULL != exception_header->exceptionDestructor)
				exception_header->exceptionDestructor(thrown_object);
				__cxa_free_exception(thrown_object);
				}
				}
				}

				/*
				Returns a pointer to the thrown object (if any) at the top of the
				caughtExceptions stack. Atomically increment the exception's referenceCount.
				If there is no such thrown object or if the thrown object is foreign,
				returns null.

				We can use __cxa_get_globals_fast here to get the globals because if there have
				been no exceptions thrown, ever, on this thread, we can return NULL without
				the need to allocate the exception-handling globals.
				*/
				void *__cxa_current_primary_exception() throw() {
				// get the current exception
				__cxa_eh_globals* globals = __cxa_get_globals_fast();
				if (NULL == globals)
				return NULL; // If there are no globals, there is no exception
				__cxa_exception* exception_header = globals->caughtExceptions;
				if (NULL == exception_header)
				return NULL; // No current exception
				if (!__isOurExceptionClass(&exception_header->unwindHeader))
				return NULL; // Can't capture a foreign exception (no way to refcount it)
				if (isDependentException(&exception_header->unwindHeader)) {
				__cxa_dependent_exception* dep_exception_header =
				reinterpret_cast<__cxa_dependent_exception*>(exception_header);
				exception_header = cxa_exception_from_thrown_object(dep_exception_header->primaryException);
				}
				void* thrown_object = thrown_object_from_cxa_exception(exception_header);
				__cxa_increment_exception_refcount(thrown_object);
				return thrown_object;
				}

				/*
				If reason isn't _URC_FOREIGN_EXCEPTION_CAUGHT, then the terminateHandler
				stored in exc is called. Otherwise the referenceCount stored in the
				primary exception is decremented, destroying the primary if necessary.
				Finally the dependent exception is destroyed.
				*/
				static
				void
				dependent_exception_cleanup(_Unwind_Reason_Code reason, _Unwind_Exception* unwind_exception)
				{
				__cxa_dependent_exception* dep_exception_header =
				reinterpret_cast<__cxa_dependent_exception*>(unwind_exception + 1) - 1;
				if (_URC_FOREIGN_EXCEPTION_CAUGHT != reason)
				std::__terminate(dep_exception_header->terminateHandler);
				__cxa_decrement_exception_refcount(dep_exception_header->primaryException);
				__cxa_free_dependent_exception(dep_exception_header);
				}

				/*
				If thrown_object is not null, allocate, initialize and throw a dependent
				exception.
				*/
				void
				__cxa_rethrow_primary_exception(void* thrown_object)
				{
				if ( thrown_object != NULL )
				{
				// thrown_object guaranteed to be native because
				// __cxa_current_primary_exception returns NULL for foreign exceptions
				__cxa_exception* exception_header = cxa_exception_from_thrown_object(thrown_object);
				__cxa_dependent_exception* dep_exception_header =
				static_cast<__cxa_dependent_exception*>(__cxa_allocate_dependent_exception());
				dep_exception_header->primaryException = thrown_object;
				__cxa_increment_exception_refcount(thrown_object);
				dep_exception_header->exceptionType = exception_header->exceptionType;
				dep_exception_header->unexpectedHandler = std::get_unexpected();
				dep_exception_header->terminateHandler = std::get_terminate();
				setDependentExceptionClass(&dep_exception_header->unwindHeader);
				__cxa_get_globals()->uncaughtExceptions += 1;
				dep_exception_header->unwindHeader.exception_cleanup = dependent_exception_cleanup;
				#ifdef __USING_SJLJ_EXCEPTIONS__
				_Unwind_SjLj_RaiseException(&dep_exception_header->unwindHeader);
				#else
				_Unwind_RaiseException(&dep_exception_header->unwindHeader);
				#endif
				// Some sort of unwinding error. Note that terminate is a handler.
				__cxa_begin_catch(&dep_exception_header->unwindHeader);
				}
				// If we return client will call terminate()
				}

				bool
				__cxa_uncaught_exception() throw() { return __cxa_uncaught_exceptions() != 0; }

				unsigned int
				__cxa_uncaught_exceptions() throw()
				{
				// This does not report foreign exceptions in flight
				__cxa_eh_globals* globals = __cxa_get_globals_fast();
				if (globals == 0)
				return 0;
				return globals->uncaughtExceptions;
				}

				} // extern "C"

				} // abi