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