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- /* 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;
- }
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