libitm/eh_cpp.cc

   1 /* Copyright (C) 2009-2018 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU Transactional Memory Library (libitm).
   5
   6    Libitm is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14    more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #include "libitm_i.h"
  26
  27 using namespace GTM;
  28
  29 /* Exceptions can exist in three phases: (1) after having been allocated by
  30    __cxa_allocate_exception but before being handed off to __cxa_throw,
  31    (2) when they are in flight, so between __cxa_throw and __cxa_begin_catch,
  32    and (3) when they are being handled (between __cxa_begin_catch and
  33    __cxa_end_catch).  Note that when an exception is re-thrown in (3), it is
  34    not moving back to (2) but handled as a special case of (3) by the EH
  35    runtime.
  36
  37    We can get aborts in all three phases, for example in (1) during
  38    construction of the exception object, or in (2) in destructors called
  39    while unwinding the stack.  The transaction that created an exception
  40    object can only commit in phase (3) by re-throwing the exception; it cannot
  41    commit in other phases because throw expressions and catch clauses are
  42    properly nested wrt transactions and because the compiler wraps
  43    transaction bodies in a try/catch-all construct.
  44
  45    We handle phase (1) by dealing with exception objects similar to how we
  46    deal with other (de)allocations, which also ensures that we can have more
  47    than one exception object allocated at the same time (e.g., if the
  48    throw expression itself throws an exception and thus calls
  49    __cxa_allocate_exception).  However, on the call to __cxa_begin_catch
  50    we hand off the exception to the special handling of phase (3) and
  51    remove the undo log entry of the allocation.  Note that if the allocation
  52    happened outside of this transaction, we do not need to do anything.
  53
  54    When an exception reaches phase (2) due to a call to __cxa_throw, the count
  55    of uncaught exceptions is incremented.  We roll back this effect by saving
  56    and restoring this number in the structure returned from __cxa_get_globals.
  57    This also takes care of increments of this count when re-throwing an
  58    exception.
  59
  60    For phase (3), we keep track of the number of times __cxa_begin_catch
  61    has been called without a matching call to __cxa_end_catch.  This count
  62    is then used by __cxa_tm_cleanup to roll back the exception handling state
  63    by calling __cxa_end_catch for the exceptions that have not been finished
  64    yet (without running destructors though because we roll back the memory
  65    anyway).
  66    Once an exception that was allocated in this transaction enters phase (3),
  67    it does not need to be deallocated on abort anymore because the calls to
  68    __cxa_end_catch will take care of that.
  69
  70    We require all code executed by the transaction to be transaction_safe (or
  71    transaction_pure, or to have wrappers) if the transaction is to be rolled
  72    back.  However, we take care to not require this for transactions that
  73    just commit; this way, transactions that enter serial mode and then call
  74    uninstrumented code continue to work.
  75    */
  76
  77 /* Everything from libstdc++ is weak, to avoid requiring that library
  78    to be linked into plain C applications using libitm.so.  */
  79
  80 #define WEAK  __attribute__((weak))
  81
  82 extern "C" {
  83
  84 struct __cxa_eh_globals
  85 {
  86   void *        caughtExceptions;
  87   unsigned int  uncaughtExceptions;
  88 };
  89
  90 extern void *__cxa_allocate_exception (size_t) WEAK;
  91 extern void __cxa_free_exception (void *) WEAK;
  92 extern void __cxa_throw (void *, void *, void *) WEAK;
  93 extern void *__cxa_begin_catch (void *) WEAK;
  94 extern void __cxa_end_catch (void) WEAK;
  95 extern void __cxa_tm_cleanup (void *, void *, unsigned int) WEAK;
  96 extern __cxa_eh_globals *__cxa_get_globals (void) WEAK;
  97
  98 #if !defined (HAVE_ELF_STYLE_WEAKREF)
  99 void *__cxa_allocate_exception (size_t) { return NULL; }
 100 void __cxa_free_exception (void *) { return; }
 101 void __cxa_throw (void *, void *, void *) { return; }
 102 void *__cxa_begin_catch (void *) { return NULL; }
 103 void __cxa_end_catch (void) { return; }
 104 void __cxa_tm_cleanup (void *, void *, unsigned int) { return; }
 105 void _Unwind_DeleteException (_Unwind_Exception *) { return; }
 106 __cxa_eh_globals *__cxa_get_globals (void) { return NULL; }
 107 #endif /* HAVE_ELF_STYLE_WEAKREF */
 108
 109 }
 110
 111 static void
 112 free_any_exception (void *exc_ptr)
 113 {
 114   // The exception could be in phase (2) and thus calling just
 115   // _cxa_free_exception might not be sufficient.
 116   __cxa_tm_cleanup (NULL, exc_ptr, 0);
 117 }
 118
 119 void *
 120 _ITM_cxa_allocate_exception (size_t size)
 121 {
 122   void *r = __cxa_allocate_exception (size);
 123   gtm_thr()->record_allocation (r, free_any_exception);
 124   return r;
 125 }
 126
 127 void
 128 _ITM_cxa_free_exception (void *exc_ptr)
 129 {
 130   // __cxa_free_exception can be called from user code directly if
 131   // construction of an exception object throws another exception, in which
 132   // case we need to roll back the initial exception.  We handle this similar
 133   // to dead allocations in that we deallocate the exception on both commit
 134   // and abort of an outermost transaction.
 135   gtm_thr()->forget_allocation (exc_ptr, free_any_exception);
 136 }
 137
 138 void
 139 _ITM_cxa_throw (void *obj, void *tinfo, void *dest)
 140 {
 141   // This used to be instrumented, but does not need to be anymore.
 142   __cxa_throw (obj, tinfo, dest);
 143 }
 144
 145 void *
 146 _ITM_cxa_begin_catch (void *exc_ptr)
 147 {
 148   // If this exception object has been allocated by this transaction, we
 149   // discard the undo log entry for the allocation; we are entering phase (3)
 150   // now and will handle this exception specially.
 151   // Note that this exception cannot have been allocated in a parent
 152   // transaction or enclosing nontransactional block because an atomic block
 153   // cannot contain just a catch clause but not the associated try clause.
 154   // The exception can have been allocated in a nested transaction, in which
 155   // case the commit of the nested transaction will have inserted the undo
 156   // log entry of the allocation in our undo log.
 157   // The exception can also have been allocated in a nested nontransactional
 158   // block, but then this transaction cannot abort anymore; functions that
 159   // are marked transaction_pure, for example, must not side-step the
 160   // transactional exception handling we implement here.
 161   gtm_thread *t = gtm_thr ();
 162   t->discard_allocation (exc_ptr);
 163   // Keep track of the number of unfinished catch handlers.
 164   t->cxa_catch_count++;
 165   return __cxa_begin_catch (exc_ptr);
 166 }
 167
 168 void
 169 _ITM_cxa_end_catch (void)
 170 {
 171   // Keep track of the number of unfinished catch handlers.
 172   gtm_thr()->cxa_catch_count--;
 173   __cxa_end_catch ();
 174 }
 175
 176 void
 177 GTM::gtm_thread::init_cpp_exceptions ()
 178 {
 179   // Only save and restore the number of uncaught exceptions if this is
 180   // actually used in the program.
 181   if (__cxa_get_globals != NULL && __cxa_get_globals () != 0)
 182     cxa_uncaught_count_ptr = &__cxa_get_globals ()->uncaughtExceptions;
 183   else
 184     cxa_uncaught_count_ptr = 0;
 185 }
 186
 187 void
 188 GTM::gtm_thread::revert_cpp_exceptions (gtm_transaction_cp *cp)
 189 {
 190   if (cp)
 191     {
 192       // If rolling back a nested transaction, only clean up incompletely
 193       // caught exceptions since the last checkpoint.
 194       assert (cxa_catch_count >= cp->cxa_catch_count);
 195       uint32_t catch_count = cxa_catch_count - cp->cxa_catch_count;
 196       if (catch_count)
 197         {
 198           __cxa_tm_cleanup (NULL, NULL, catch_count);
 199           cxa_catch_count = cp->cxa_catch_count;
 200         }
 201     }
 202   else
 203     {
 204       // Both cxa_catch_count and cxa_unthrown are maximal because EH regions
 205       // and transactions are properly nested.
 206       if (cxa_catch_count)
 207         {
 208           __cxa_tm_cleanup (NULL, NULL, cxa_catch_count);
 209           cxa_catch_count = 0;
 210         }
 211     }
 212   // Reset the number of uncaught exceptions.  Any allocations for these
 213   // exceptions have been rolled back already, if necessary.
 214   if (cxa_uncaught_count_ptr != 0)
 215     *cxa_uncaught_count_ptr = cxa_uncaught_count;
 216   // Always reset eh_in_flight because it just contains the argument provided
 217   // to _ITM_commitTransactionEH.
 218   eh_in_flight = NULL;
 219 }