1/* Copyright (C) 1999-2021 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 <fork.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. */
28void
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#ifdef UNREGISTER_ATFORK
106 if (d != NULL)
107 UNREGISTER_ATFORK (d);
108#endif
109 __libc_lock_unlock (__exit_funcs_lock);
110}
111