stdlib/cxa_finalize.c

   1 /* Copyright (C) 1999-2022 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <stdlib.h>
  20 #include "exit.h"
  21 #include <register-atfork.h>
  22 #include <sysdep.h>
  23 #include <stdint.h>
  24
  25 /* If D is non-NULL, call all functions registered with `__cxa_atexit'
  26    with the same dso handle.  Otherwise, if D is NULL, call all of the
  27    registered handlers.  */
  28 void
  29 __cxa_finalize (void *d)
  30 {
  31   struct exit_function_list *funcs;
  32
  33   __libc_lock_lock (__exit_funcs_lock);
  34
  35  restart:
  36   for (funcs = __exit_funcs; funcs; funcs = funcs->next)
  37     {
  38       struct exit_function *f;
  39
  40       for (f = &funcs->fns[funcs->idx - 1]; f >= &funcs->fns[0]; --f)
  41         if ((d == NULL || d == f->func.cxa.dso_handle) && f->flavor == ef_cxa)
  42           {
  43             const uint64_t check = __new_exitfn_called;
  44             void (*cxafn) (void *arg, int status) = f->func.cxa.fn;
  45             void *cxaarg = f->func.cxa.arg;
  46
  47             /* We don't want to run this cleanup more than once.  The Itanium
  48                C++ ABI requires that multiple calls to __cxa_finalize not
  49                result in calling termination functions more than once.  One
  50                potential scenario where that could happen is with a concurrent
  51                dlclose and exit, where the running dlclose must at some point
  52                release the list lock, an exiting thread may acquire it, and
  53                without setting flavor to ef_free, might re-run this destructor
  54                which could result in undefined behaviour.  Therefore we must
  55                set flavor to ef_free to avoid calling this destructor again.
  56                Note that the concurrent exit must also take the dynamic loader
  57                lock (for library finalizer processing) and therefore will
  58                block while dlclose completes the processing of any in-progress
  59                exit functions. Lastly, once we release the list lock for the
  60                entry marked ef_free, we must not read from that entry again
  61                since it may have been reused by the time we take the list lock
  62                again.  Lastly the detection of new registered exit functions is
  63                based on a monotonically incrementing counter, and there is an
  64                ABA if between the unlock to run the exit function and the
  65                re-lock after completion the user registers 2^64 exit functions,
  66                the implementation will not detect this and continue without
  67                executing any more functions.
  68
  69                One minor issue remains: A registered exit function that is in
  70                progress by a call to dlclose() may not completely finish before
  71                the next registered exit function is run. This may, according to
  72                some readings of POSIX violate the requirement that functions
  73                run in effective LIFO order.  This should probably be fixed in a
  74                future implementation to ensure the functions do not run in
  75                parallel.  */
  76             f->flavor = ef_free;
  77
  78 #ifdef PTR_DEMANGLE
  79             PTR_DEMANGLE (cxafn);
  80 #endif
  81             /* Unlock the list while we call a foreign function.  */
  82             __libc_lock_unlock (__exit_funcs_lock);
  83             cxafn (cxaarg, 0);
  84             __libc_lock_lock (__exit_funcs_lock);
  85
  86             /* It is possible that that last exit function registered
  87                more exit functions.  Start the loop over.  */
  88             if (__glibc_unlikely (check != __new_exitfn_called))
  89               goto restart;
  90           }
  91     }
  92
  93   /* Also remove the quick_exit handlers, but do not call them.  */
  94   for (funcs = __quick_exit_funcs; funcs; funcs = funcs->next)
  95     {
  96       struct exit_function *f;
  97
  98       for (f = &funcs->fns[funcs->idx - 1]; f >= &funcs->fns[0]; --f)
  99         if (d == NULL || d == f->func.cxa.dso_handle)
 100           f->flavor = ef_free;
 101     }
 102
 103   /* Remove the registered fork handlers.  We do not have to
 104      unregister anything if the program is going to terminate anyway.  */
 105   if (d != NULL)
 106     UNREGISTER_ATFORK (d);
 107   __libc_lock_unlock (__exit_funcs_lock);
 108 }