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1 | /* Copyright (C) 1999-2019 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. */ | |
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 | #ifdef UNREGISTER_ATFORK | |
106 | if (d != NULL) | |
107 | UNREGISTER_ATFORK (d); | |
108 | #endif | |
109 | __libc_lock_unlock (__exit_funcs_lock); | |
110 | } |