223 lines
8.8 KiB
C++
223 lines
8.8 KiB
C++
/* Copyright (C) 2009-2022 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Transactional Memory Library (libitm).
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Libitm is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "libitm_i.h"
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using namespace GTM;
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/* Exceptions can exist in three phases: (1) after having been allocated by
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__cxa_allocate_exception but before being handed off to __cxa_throw,
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(2) when they are in flight, so between __cxa_throw and __cxa_begin_catch,
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and (3) when they are being handled (between __cxa_begin_catch and
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__cxa_end_catch). Note that when an exception is re-thrown in (3), it is
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not moving back to (2) but handled as a special case of (3) by the EH
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runtime.
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We can get aborts in all three phases, for example in (1) during
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construction of the exception object, or in (2) in destructors called
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while unwinding the stack. The transaction that created an exception
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object can only commit in phase (3) by re-throwing the exception; it cannot
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commit in other phases because throw expressions and catch clauses are
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properly nested wrt transactions and because the compiler wraps
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transaction bodies in a try/catch-all construct.
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We handle phase (1) by dealing with exception objects similar to how we
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deal with other (de)allocations, which also ensures that we can have more
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than one exception object allocated at the same time (e.g., if the
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throw expression itself throws an exception and thus calls
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__cxa_allocate_exception). However, on the call to __cxa_begin_catch
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we hand off the exception to the special handling of phase (3) and
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remove the undo log entry of the allocation. Note that if the allocation
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happened outside of this transaction, we do not need to do anything.
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When an exception reaches phase (2) due to a call to __cxa_throw, the count
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of uncaught exceptions is incremented. We roll back this effect by saving
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and restoring this number in the structure returned from __cxa_get_globals.
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This also takes care of increments of this count when re-throwing an
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exception.
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For phase (3), we keep track of the number of times __cxa_begin_catch
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has been called without a matching call to __cxa_end_catch. This count
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is then used by __cxa_tm_cleanup to roll back the exception handling state
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by calling __cxa_end_catch for the exceptions that have not been finished
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yet (without running destructors though because we roll back the memory
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anyway).
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Once an exception that was allocated in this transaction enters phase (3),
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it does not need to be deallocated on abort anymore because the calls to
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__cxa_end_catch will take care of that.
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We require all code executed by the transaction to be transaction_safe (or
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transaction_pure, or to have wrappers) if the transaction is to be rolled
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back. However, we take care to not require this for transactions that
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just commit; this way, transactions that enter serial mode and then call
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uninstrumented code continue to work.
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*/
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/* Everything from libstdc++ is weak, to avoid requiring that library
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to be linked into plain C applications using libitm.so. */
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#define WEAK __attribute__((weak))
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extern "C" {
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struct __cxa_eh_globals
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{
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void * caughtExceptions;
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unsigned int uncaughtExceptions;
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};
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extern void *__cxa_allocate_exception (size_t) _ITM_NOTHROW WEAK;
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extern void __cxa_free_exception (void *) _ITM_NOTHROW WEAK;
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extern void __cxa_throw (void *, void *, void (*) (void *)) WEAK;
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extern void *__cxa_begin_catch (void *) _ITM_NOTHROW WEAK;
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extern void __cxa_end_catch (void) WEAK;
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extern void __cxa_tm_cleanup (void *, void *, unsigned int) throw () WEAK;
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extern __cxa_eh_globals *__cxa_get_globals (void) _ITM_NOTHROW WEAK;
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#if !defined (HAVE_ELF_STYLE_WEAKREF)
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void *__cxa_allocate_exception (size_t) _ITM_NOTHROW { return NULL; }
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void __cxa_free_exception (void *) _ITM_NOTHROW { return; }
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void __cxa_throw (void *, void *, void (*) (void *)) { return; }
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void *__cxa_begin_catch (void *) _ITM_NOTHROW { return NULL; }
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void __cxa_end_catch (void) { return; }
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void __cxa_tm_cleanup (void *, void *, unsigned int) throw () { return; }
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void _Unwind_DeleteException (_Unwind_Exception *) { return; }
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__cxa_eh_globals *__cxa_get_globals (void) _ITM_NOTHROW { return NULL; }
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#endif /* HAVE_ELF_STYLE_WEAKREF */
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}
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static void
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free_any_exception (void *exc_ptr)
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{
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// The exception could be in phase (2) and thus calling just
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// _cxa_free_exception might not be sufficient.
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__cxa_tm_cleanup (NULL, exc_ptr, 0);
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}
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void *
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_ITM_cxa_allocate_exception (size_t size) _ITM_NOTHROW
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{
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void *r = __cxa_allocate_exception (size);
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gtm_thr()->record_allocation (r, free_any_exception);
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return r;
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}
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void
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_ITM_cxa_free_exception (void *exc_ptr) _ITM_NOTHROW
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{
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// __cxa_free_exception can be called from user code directly if
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// construction of an exception object throws another exception, in which
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// case we need to roll back the initial exception. We handle this similar
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// to dead allocations in that we deallocate the exception on both commit
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// and abort of an outermost transaction.
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gtm_thr()->forget_allocation (exc_ptr, free_any_exception);
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}
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void
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_ITM_cxa_throw (void *obj, void *tinfo, void (*dest) (void *))
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{
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// This used to be instrumented, but does not need to be anymore.
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__cxa_throw (obj, tinfo, dest);
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}
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void *
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_ITM_cxa_begin_catch (void *exc_ptr) _ITM_NOTHROW
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{
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// If this exception object has been allocated by this transaction, we
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// discard the undo log entry for the allocation; we are entering phase (3)
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// now and will handle this exception specially.
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// Note that this exception cannot have been allocated in a parent
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// transaction or enclosing nontransactional block because an atomic block
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// cannot contain just a catch clause but not the associated try clause.
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// The exception can have been allocated in a nested transaction, in which
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// case the commit of the nested transaction will have inserted the undo
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// log entry of the allocation in our undo log.
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// The exception can also have been allocated in a nested nontransactional
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// block, but then this transaction cannot abort anymore; functions that
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// are marked transaction_pure, for example, must not side-step the
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// transactional exception handling we implement here.
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gtm_thread *t = gtm_thr ();
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t->discard_allocation (exc_ptr);
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// Keep track of the number of unfinished catch handlers.
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t->cxa_catch_count++;
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return __cxa_begin_catch (exc_ptr);
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}
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void
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_ITM_cxa_end_catch (void)
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{
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// Keep track of the number of unfinished catch handlers.
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gtm_thr()->cxa_catch_count--;
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__cxa_end_catch ();
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}
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void
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GTM::gtm_thread::init_cpp_exceptions ()
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{
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// Only save and restore the number of uncaught exceptions if this is
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// actually used in the program.
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if (
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#if HAVE_ELF_STYLE_WEAKREF
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__cxa_get_globals != NULL &&
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#endif
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__cxa_get_globals () != 0)
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cxa_uncaught_count_ptr = &__cxa_get_globals ()->uncaughtExceptions;
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else
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cxa_uncaught_count_ptr = 0;
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}
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void
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GTM::gtm_thread::revert_cpp_exceptions (gtm_transaction_cp *cp)
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{
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if (cp)
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{
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// If rolling back a nested transaction, only clean up incompletely
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// caught exceptions since the last checkpoint.
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assert (cxa_catch_count >= cp->cxa_catch_count);
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uint32_t catch_count = cxa_catch_count - cp->cxa_catch_count;
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if (catch_count)
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{
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__cxa_tm_cleanup (NULL, NULL, catch_count);
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cxa_catch_count = cp->cxa_catch_count;
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}
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}
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else
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{
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// Both cxa_catch_count and cxa_unthrown are maximal because EH regions
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// and transactions are properly nested.
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if (cxa_catch_count)
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{
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__cxa_tm_cleanup (NULL, NULL, cxa_catch_count);
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cxa_catch_count = 0;
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}
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}
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// Reset the number of uncaught exceptions. Any allocations for these
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// exceptions have been rolled back already, if necessary.
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if (cxa_uncaught_count_ptr != 0)
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*cxa_uncaught_count_ptr = cxa_uncaught_count;
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// Always reset eh_in_flight because it just contains the argument provided
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// to _ITM_commitTransactionEH.
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eh_in_flight = NULL;
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}
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