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