/* Copyright (C) 1999-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <assert.h>

#include <stdlib.h>

#include "exit.h"

#include <fork.h>

#include <sysdep.h>

#include <stdint.h>

/* If D is non-NULL, call all functions registered with `__cxa_atexit'

   with the same dso handle.  Otherwise, if D is NULL, call all of the

   registered handlers.  */

void

__cxa_finalize (void *d)

{

  struct exit_function_list *funcs;

  __libc_lock_lock (__exit_funcs_lock);

 restart:

  for (funcs = __exit_funcs; funcs; funcs = funcs->next)

    {

      struct exit_function *f;

      for (f = &funcs->fns[funcs->idx - 1]; f >= &funcs->fns[0]; --f)

	if ((d == NULL || d == f->func.cxa.dso_handle) && f->flavor == ef_cxa)

	  {

	    const uint64_t check = __new_exitfn_called;

	    void (*cxafn) (void *arg, int status) = f->func.cxa.fn;

	    void *cxaarg = f->func.cxa.arg;

	    /* We don't want to run this cleanup more than once.  The Itanium

	       C++ ABI requires that multiple calls to __cxa_finalize not

	       result in calling termination functions more than once.  One

	       potential scenario where that could happen is with a concurrent

	       dlclose and exit, where the running dlclose must at some point

	       release the list lock, an exiting thread may acquire it, and

	       without setting flavor to ef_free, might re-run this destructor

	       which could result in undefined behaviour.  Therefore we must

	       set flavor to ef_free to avoid calling this destructor again.

	       Note that the concurrent exit must also take the dynamic loader

	       lock (for library finalizer processing) and therefore will

	       block while dlclose completes the processing of any in-progress

	       exit functions. Lastly, once we release the list lock for the

	       entry marked ef_free, we must not read from that entry again

	       since it may have been reused by the time we take the list lock

	       again.  Lastly the detection of new registered exit functions is

	       based on a monotonically incrementing counter, and there is an

	       ABA if between the unlock to run the exit function and the

	       re-lock after completion the user registers 2^64 exit functions,

	       the implementation will not detect this and continue without

	       executing any more functions.

	       One minor issue remains: A registered exit function that is in

	       progress by a call to dlclose() may not completely finish before

	       the next registered exit function is run. This may, according to

	       some readings of POSIX violate the requirement that functions

	       run in effective LIFO order.  This should probably be fixed in a

	       future implementation to ensure the functions do not run in

	       parallel.  */

	    f->flavor = ef_free;

#ifdef PTR_DEMANGLE

	    PTR_DEMANGLE (cxafn);

#endif

	    /* Unlock the list while we call a foreign function.  */

	    __libc_lock_unlock (__exit_funcs_lock);

	    cxafn (cxaarg, 0);

	    __libc_lock_lock (__exit_funcs_lock);

	    /* It is possible that that last exit function registered

	       more exit functions.  Start the loop over.  */

	    if (__glibc_unlikely (check != __new_exitfn_called))

	      goto restart;

	  }

    }

  /* Also remove the quick_exit handlers, but do not call them.  */

  for (funcs = __quick_exit_funcs; funcs; funcs = funcs->next)

    {

      struct exit_function *f;

      for (f = &funcs->fns[funcs->idx - 1]; f >= &funcs->fns[0]; --f)

	if (d == NULL || d == f->func.cxa.dso_handle)

	  f->flavor = ef_free;

    }

  /* Remove the registered fork handlers.  We do not have to

     unregister anything if the program is going to terminate anyway.  */

#ifdef UNREGISTER_ATFORK

  if (d != NULL)

    UNREGISTER_ATFORK (d);

#endif

  __libc_lock_unlock (__exit_funcs_lock);

}