2 * Copyright (c) 2016 Mahdi Mokhtari <mokhi64@gmail.com>
3 * Copyright (c) 2016, 2017 The FreeBSD Foundation
6 * Portions of this software were developed by Konstantin Belousov
7 * under sponsorship from the FreeBSD Foundation.
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 #include <sys/cdefs.h>
32 #include <sys/queue.h>
33 #include "namespace.h"
40 #include "un-namespace.h"
41 #include "libc_private.h"
44 * C++11 introduces the thread_local scope (like __thread with some
45 * additions). As a key-feature it should support non-trivial
46 * destructors, registered with __cxa_thread_atexit() to be executed
47 * at the thread termination.
49 * The implemention keeps a _Thread_local list of destructors per each
50 * thread, and calls __cxa_thread_call_dtors() on each thread's exit
51 * to do cleanup. For a thread calling exit(3), in particular, for
52 * the initial thread returning from main(), we call
53 * __cxa_thread_call_dtors() inside exit().
55 * It could be possible that a dynamically loaded library, use
56 * thread_local variable but is dlclose()'d before thread exit. The
57 * destructor of this variable will then try to access the address,
58 * for calling it but it's unloaded, so it'll crash. We're using
59 * __elf_phdr_match_addr() to detect and prevent such cases and so
63 #define CXA_DTORS_ITERATIONS 4
65 struct cxa_thread_dtor {
69 LIST_ENTRY(cxa_thread_dtor) entry;
71 static _Thread_local LIST_HEAD(dtor_list, cxa_thread_dtor) dtors =
72 LIST_HEAD_INITIALIZER(dtors);
75 __cxa_thread_atexit_impl(void (*dtor_func)(void *), void *obj,
79 return (__cxa_thread_atexit_hidden(dtor_func, obj, dso_symbol));
83 __cxa_thread_atexit_hidden(void (*dtor_func)(void *), void *obj,
86 struct cxa_thread_dtor *new_dtor;
88 new_dtor = malloc(sizeof(*new_dtor));
89 if (new_dtor == NULL) {
90 errno = ENOMEM; /* forcibly override malloc(3) error */
95 new_dtor->func = dtor_func;
96 new_dtor->dso = dso_symbol;
97 LIST_INSERT_HEAD(&dtors, new_dtor, entry);
102 walk_cb_call(struct cxa_thread_dtor *dtor)
104 struct dl_phdr_info phdr_info;
106 if (_rtld_addr_phdr(dtor->dso, &phdr_info) &&
107 __elf_phdr_match_addr(&phdr_info, dtor->func))
108 dtor->func(dtor->obj);
111 "__cxa_thread_call_dtors: dtr %p from unloaded dso, skipping\n",
112 (void *)(dtor->func));
116 walk_cb_nocall(struct cxa_thread_dtor *dtor __unused)
121 cxa_thread_walk(void (*cb)(struct cxa_thread_dtor *))
123 struct cxa_thread_dtor *dtor, *tdtor;
125 LIST_FOREACH_SAFE(dtor, &dtors, entry, tdtor) {
126 LIST_REMOVE(dtor, entry);
133 * This is the callback function we use to call destructors, once for
134 * each thread. It is called in exit(3) in libc/stdlib/exit.c and
135 * before exit_thread() in libthr/thread/thr_exit.c.
138 __cxa_thread_call_dtors(void)
142 for (i = 0; i < CXA_DTORS_ITERATIONS && !LIST_EMPTY(&dtors); i++)
143 cxa_thread_walk(walk_cb_call);
145 if (!LIST_EMPTY(&dtors)) {
146 fprintf(stderr, "Thread %p is exiting with more "
147 "thread-specific dtors created after %d iterations "
148 "of destructor calls\n",
150 cxa_thread_walk(walk_cb_nocall);