From c06f419b283d713f5dadfb3a8612381f1cec738e Mon Sep 17 00:00:00 2001 From: torvald Date: Fri, 20 Nov 2015 00:10:08 +0000 Subject: Support __cxa_free_exception and fix exception handling. gcc/cp/ * except.c (do_free_exception): Use transactional wrapper. libitm/ * testsuite/libitm.c++/eh-5.C: New. * libitm.h (_ITM_cxa_free_exception): New. * libitm.map (_ITM_cxa_free_exception): Add it. * libitm.texi: Update ABI docs. * libitm_i.h (gtm_transaction_cp::cxa_unthrown): Remove. (gtm_transaction_cp::cxa_uncaught_count): Add. (gtm_thread::cxa_unthrown): Remove. (gtm_thread::cxa_uncaught_count_ptr): Add. (gtm_thread::cxa_uncaught_count): Add. (gtm_thread::drop_references_allocations): Rename to... (gtm_thread::discard_allocation): ... this and adapt. (gtm_thread::init_cpp_exceptions): New. * beginend.cc (gtm_thread::gtm_thread): Adapt EH handling. (gtm_thread::begin_transaction): Likewise. (gtm_transaction_cp::save): Likewise. (gtm_thread::trycommit): Likewise. * eh_cpp.cc: Add overview comments. (__cxa_eh_globals, __cxa_get_globals, __cxa_free_exception): Declare. (free_any_exception, _ITM_cxa_free_exception): New. (gtm_thread::init_cpp_exceptions): Define. (_ITM_cxa_allocate_exception, _ITM_cxa_throw): Adapt. (_ITM_cxa_begin_catch, _ITM_cxa_end_catch): Likewise. (gtm_thread::revert_cpp_exceptions): Likewise. git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@230634 138bc75d-0d04-0410-961f-82ee72b054a4 --- libitm/eh_cpp.cc | 140 +++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 121 insertions(+), 19 deletions(-) (limited to 'libitm/eh_cpp.cc') diff --git a/libitm/eh_cpp.cc b/libitm/eh_cpp.cc index a86dbf164ddc..1fe1c909339c 100644 --- a/libitm/eh_cpp.cc +++ b/libitm/eh_cpp.cc @@ -26,6 +26,54 @@ 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. */ @@ -33,85 +81,139 @@ using namespace GTM; extern "C" { +struct __cxa_eh_globals +{ + void * caughtExceptions; + unsigned int uncaughtExceptions; +}; + extern void *__cxa_allocate_exception (size_t) WEAK; +extern void __cxa_free_exception (void *) WEAK; extern void __cxa_throw (void *, void *, void *) WEAK; extern void *__cxa_begin_catch (void *) WEAK; extern void __cxa_end_catch (void) WEAK; extern void __cxa_tm_cleanup (void *, void *, unsigned int) WEAK; +extern __cxa_eh_globals *__cxa_get_globals (void) WEAK; #if !defined (HAVE_ELF_STYLE_WEAKREF) void *__cxa_allocate_exception (size_t) { return NULL; } +void __cxa_free_exception (void *) { return; } void __cxa_throw (void *, void *, void *) { return; } void *__cxa_begin_catch (void *) { return NULL; } void __cxa_end_catch (void) { return; } void __cxa_tm_cleanup (void *, void *, unsigned int) { return; } void _Unwind_DeleteException (_Unwind_Exception *) { return; } +__cxa_eh_globals *__cxa_get_globals (void) { 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) { void *r = __cxa_allocate_exception (size); - gtm_thr()->cxa_unthrown = r; + gtm_thr()->record_allocation (r, free_any_exception); return r; } +void +_ITM_cxa_free_exception (void *exc_ptr) +{ + // __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) { - gtm_thr()->cxa_unthrown = NULL; + // 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) { - gtm_thr()->cxa_catch_count++; + // 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 (__cxa_get_globals != NULL && __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 unthrown - // exceptions since the last checkpoint. Always reset eh_in_flight - // because it just contains the argument provided to - // _ITM_commitTransactionEH - void *unthrown = - (cxa_unthrown != cp->cxa_unthrown ? cxa_unthrown : NULL); + // 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 (unthrown || catch_count) + if (catch_count) { - __cxa_tm_cleanup (unthrown, this->eh_in_flight, catch_count); + __cxa_tm_cleanup (NULL, NULL, catch_count); cxa_catch_count = cp->cxa_catch_count; - cxa_unthrown = cp->cxa_unthrown; - this->eh_in_flight = NULL; } } else { // Both cxa_catch_count and cxa_unthrown are maximal because EH regions // and transactions are properly nested. - if (this->cxa_unthrown || this->cxa_catch_count) + if (cxa_catch_count) { - __cxa_tm_cleanup (this->cxa_unthrown, this->eh_in_flight, - this->cxa_catch_count); - this->cxa_catch_count = 0; - this->cxa_unthrown = NULL; - this->eh_in_flight = NULL; + __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; } -- cgit v1.2.3