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Support __cxa_free_exception and fix exception handling.

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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.

From-SVN: r230634
This commit is contained in:
Torvald Riegel 2015-11-20 00:10:08 +00:00 • committed by Torvald Riegel
parent 9afebea2d5
commit 258c1d0722
10 changed files with 243 additions and 30 deletions
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4
gcc/cp/ChangeLog
View file

@ -1,3 +1,7 @@
2015-11-19 Torvald Riegel <triegel@redhat.com>
* except.c (do_free_exception): Use transactional wrapper.
2015-11-19 Jason Merrill <jason@redhat.com>
PR c++/68422

10
gcc/cp/except.c
View file

@ -662,6 +662,16 @@ do_free_exception (tree ptr)
/* Declare void __cxa_free_exception (void *) throw(). */
fn = declare_library_fn (fn, void_type_node, ptr_type_node,
ECF_NOTHROW | ECF_LEAF);
if (flag_tm)
{
tree fn2 = get_identifier ("_ITM_cxa_free_exception");
if (!get_global_value_if_present (fn2, &fn2))
fn2 = declare_library_fn (fn2, void_type_node,
ptr_type_node,
ECF_NOTHROW | ECF_LEAF | ECF_TM_PURE);
record_tm_replacement (fn, fn2);
}
}
return cp_build_function_call_nary (fn, tf_warning_or_error, ptr, NULL_TREE);

26
libitm/ChangeLog
View file

@ -1,3 +1,29 @@
2015-11-19 Torvald Riegel <triegel@redhat.com>
* 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.
2015-11-09 Torvald Riegel <triegel@redhat.com>
* alloc_cpp.cc (_ZdlPvX, _ZdlPvXRKSt9nothrow_t, _ZGTtdlPvX,

10
libitm/beginend.cc
View file

@ -132,6 +132,8 @@ GTM::gtm_thread::gtm_thread ()
number_of_threads_changed(number_of_threads - 1, number_of_threads);
serial_lock.write_unlock ();
init_cpp_exceptions ();
if (pthread_once(&thr_release_once, thread_exit_init))
GTM_fatal("Initializing thread release TLS key failed.");
// Any non-null value is sufficient to trigger destruction of this
@ -383,6 +385,11 @@ GTM::gtm_thread::begin_transaction (uint32_t prop, const gtm_jmpbuf *jb)
#endif
}
// Log the number of uncaught exceptions if we might have to roll back this
// state.
if (tx->cxa_uncaught_count_ptr != 0)
tx->cxa_uncaught_count = *tx->cxa_uncaught_count_ptr;
// Run dispatch-specific restart code. Retry until we succeed.
GTM::gtm_restart_reason rr;
while ((rr = disp->begin_or_restart()) != NO_RESTART)
@ -411,7 +418,7 @@ GTM::gtm_transaction_cp::save(gtm_thread* tx)
id = tx->id;
prop = tx->prop;
cxa_catch_count = tx->cxa_catch_count;
cxa_unthrown = tx->cxa_unthrown;
cxa_uncaught_count = tx->cxa_uncaught_count;
disp = abi_disp();
nesting = tx->nesting;
}
@ -583,7 +590,6 @@ GTM::gtm_thread::trycommit ()
undolog.commit ();
// Reset further transaction state.
cxa_catch_count = 0;
cxa_unthrown = NULL;
restart_total = 0;
// Ensure privatization safety, if necessary.

140
libitm/eh_cpp.cc
View file

@ -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;
}

1
libitm/libitm.h
View file

@ -283,6 +283,7 @@ extern void _ITM_registerTMCloneTable (void *, size_t);
extern void _ITM_deregisterTMCloneTable (void *);
extern void *_ITM_cxa_allocate_exception (size_t);
extern void _ITM_cxa_free_exception (void *exc_ptr);
extern void _ITM_cxa_throw (void *obj, void *tinfo, void *dest);
extern void *_ITM_cxa_begin_catch (void *exc_ptr);
extern void _ITM_cxa_end_catch (void);

1
libitm/libitm.map
View file

@ -186,4 +186,5 @@ LIBITM_1.1 {
global:
_ZGTtdlPv?;
_ZGTtdlPv?RKSt9nothrow_t;
_ITM_cxa_free_exception;
} LIBITM_1.0;

24
libitm/libitm.texi
View file

@ -268,17 +268,26 @@ transactions.
@example
void _ITM_commitTransactionEH(void *exc_ptr) ITM_REGPARM;
void *_ITM_cxa_allocate_exception (size_t);
void _ITM_cxa_free_exception (void *exc_ptr);
void _ITM_cxa_throw (void *obj, void *tinfo, void *dest);
void *_ITM_cxa_begin_catch (void *exc_ptr);
void _ITM_cxa_end_catch (void);
@end example
@code{_ITM_commitTransactionEH} must be called to commit a transaction if an
exception could be in flight at this position in the code. @code{exc_ptr} is
the current exception or zero if there is no current exception.
The EH scheme changed in version 6 of GCC. Previously, the compiler
added a call to @code{_ITM_commitTransactionEH} to commit a transaction if
an exception could be in flight at this position in the code; @code{exc_ptr} is
the address of the current exception and must be non-zero. Now, the
compiler must catch all exceptions that are about to be thrown out of a
transaction and call @code{_ITM_commitTransactionEH} from the catch clause,
with @code{exc_ptr} being zero.
Note that the old EH scheme never worked completely in GCC's implementation;
libitm currently does not try to be compatible with the old scheme.
The @code{_ITM_cxa...} functions are transactional wrappers for the respective
@code{__cxa...} functions and must be called instead of these in transactional
code.
code. @code{_ITM_cxa_free_exception} is new in GCC 6.
To support this EH scheme, libstdc++ needs to provide one additional function
(@code{_cxa_tm_cleanup}), which is used by the TM to clean up the exception
@ -289,7 +298,8 @@ void __cxa_tm_cleanup (void *unthrown_obj, void *cleanup_exc,
unsigned int caught_count);
@end example
@code{unthrown_obj} is non-null if the program called
Since GCC 6, @code{unthrown_obj} is not used anymore and always null;
prior to that, @code{unthrown_obj} is non-null if the program called
@code{__cxa_allocate_exception} for this exception but did not yet called
@code{__cxa_throw} for it. @code{cleanup_exc} is non-null if the program is
currently processing a cleanup along an exception path but has not caught this
@ -406,6 +416,10 @@ These functions are essentially transactional wrappers for @code{malloc},
@code{calloc}, and @code{free}. Within transactions, the compiler should
replace calls to the original functions with calls to the wrapper functions.
libitm also provides transactional clones of C++ memory management functions
such as global operator new and delete. They are part of libitm for historic
reasons but do not need to be part of this ABI.
@section [No changes] Future Enhancements to the ABI

11
libitm/libitm_i.h
View file

@ -132,7 +132,7 @@ struct gtm_transaction_cp
_ITM_transactionId_t id;
uint32_t prop;
uint32_t cxa_catch_count;
void *cxa_unthrown;
unsigned int cxa_uncaught_count;
// We might want to use a different but compatible dispatch method for
// a nested transaction.
abi_dispatch *disp;
@ -242,7 +242,9 @@ struct gtm_thread
// Data used by eh_cpp.c for managing exceptions within the transaction.
uint32_t cxa_catch_count;
void *cxa_unthrown;
// If cxa_uncaught_count_ptr is 0, we don't need to roll back exceptions.
unsigned int *cxa_uncaught_count_ptr;
unsigned int cxa_uncaught_count;
void *eh_in_flight;
// Checkpoints for closed nesting.
@ -284,9 +286,9 @@ struct gtm_thread
void record_allocation (void *, void (*)(void *));
void forget_allocation (void *, void (*)(void *));
void forget_allocation (void *, size_t, void (*)(void *, size_t));
void drop_references_allocations (const void *ptr)
void discard_allocation (const void *ptr)
{
this->alloc_actions.erase((uintptr_t) ptr);
alloc_actions.erase((uintptr_t) ptr);
}
// In beginend.cc
@ -306,6 +308,7 @@ struct gtm_thread
static uint32_t begin_transaction(uint32_t, const gtm_jmpbuf *)
__asm__(UPFX "GTM_begin_transaction") ITM_REGPARM;
// In eh_cpp.cc
void init_cpp_exceptions ();
void revert_cpp_exceptions (gtm_transaction_cp *cp = 0);
// In retry.cc

46
libitm/testsuite/libitm.c++/eh-5.C Normal file
View file

@ -0,0 +1,46 @@
// Test throwing an exception whose constructor might throw. This tests that
// _cxa_free_exception is instrumented.
// { dg-do run }
// { dg-options "-fgnu-tm" }
void __attribute__ ((transaction_pure,noinline)) dontoptimize (int *i)
{ }
struct test
{
int* data;
test (int i)
{
// new may throw
data = new int[1];
data[0] = i;
dontoptimize (data);
}
test (const test& t) : test (t.data[0])
{ }
~test ()
{
delete data;
}
bool operator !=(const test& other)
{
return data[0] != other.data[0];
}
};
int main()
{
try
{
atomic_commit
{
throw test(23);
}
}
catch (test ex)
{
if (ex.data[0] != 23) __builtin_abort ();
}
return 0;
}