1 /*-
2 * Copyright (c) 2016 Mahdi Mokhtari <[email protected]>
3 * Copyright (c) 2016, 2017 The FreeBSD Foundation
4 * All rights reserved.
5 *
6 * Portions of this software were developed by Konstantin Belousov
7 * under sponsorship from the FreeBSD Foundation.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
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.
17 *
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
28 * SUCH DAMAGE.
29 */
30
31 #include <sys/cdefs.h>
32 __FBSDID("$FreeBSD$");
33
34 #include <sys/queue.h>
35 #include "namespace.h"
36 #include <errno.h>
37 #include <link.h>
38 #include <pthread.h>
39 #include <stddef.h>
40 #include <stdlib.h>
41 #include <stdio.h>
42 #include "un-namespace.h"
43 #include "libc_private.h"
44
45 /*
46 * C++11 introduces the thread_local scope (like __thread with some
47 * additions). As a key-feature it should support non-trivial
48 * destructors, registered with __cxa_thread_atexit() to be executed
49 * at the thread termination.
50 *
51 * The implemention keeps a _Thread_local list of destructors per each
52 * thread, and calls __cxa_thread_call_dtors() on each thread's exit
53 * to do cleanup. For a thread calling exit(3), in particular, for
54 * the initial thread returning from main(), we call
55 * __cxa_thread_call_dtors() inside exit().
56 *
57 * It could be possible that a dynamically loaded library, use
58 * thread_local variable but is dlclose()'d before thread exit. The
59 * destructor of this variable will then try to access the address,
60 * for calling it but it's unloaded, so it'll crash. We're using
61 * __elf_phdr_match_addr() to detect and prevent such cases and so
62 * prevent the crash.
63 */
64
65 #define CXA_DTORS_ITERATIONS 4
66
67 struct cxa_thread_dtor {
68 void *obj;
69 void (*func)(void *);
70 void *dso;
71 LIST_ENTRY(cxa_thread_dtor) entry;
72 };
73 static _Thread_local LIST_HEAD(dtor_list, cxa_thread_dtor) dtors =
74 LIST_HEAD_INITIALIZER(dtors);
75
76 int
__cxa_thread_atexit_impl(void (* dtor_func)(void *),void * obj,void * dso_symbol)77 __cxa_thread_atexit_impl(void (*dtor_func)(void *), void *obj,
78 void *dso_symbol)
79 {
80
81 return (__cxa_thread_atexit_hidden(dtor_func, obj, dso_symbol));
82 }
83
84 int
__cxa_thread_atexit_hidden(void (* dtor_func)(void *),void * obj,void * dso_symbol)85 __cxa_thread_atexit_hidden(void (*dtor_func)(void *), void *obj,
86 void *dso_symbol)
87 {
88 struct cxa_thread_dtor *new_dtor;
89
90 new_dtor = malloc(sizeof(*new_dtor));
91 if (new_dtor == NULL) {
92 errno = ENOMEM; /* forcibly override malloc(3) error */
93 return (-1);
94 }
95
96 new_dtor->obj = obj;
97 new_dtor->func = dtor_func;
98 new_dtor->dso = dso_symbol;
99 LIST_INSERT_HEAD(&dtors, new_dtor, entry);
100 return (0);
101 }
102
103 static void
walk_cb_call(struct cxa_thread_dtor * dtor)104 walk_cb_call(struct cxa_thread_dtor *dtor)
105 {
106 struct dl_phdr_info phdr_info;
107
108 if (_rtld_addr_phdr(dtor->dso, &phdr_info) &&
109 __elf_phdr_match_addr(&phdr_info, dtor->func))
110 dtor->func(dtor->obj);
111 else
112 fprintf(stderr, "__cxa_thread_call_dtors: dtr %p from "
113 "unloaded dso, skipping\n", (void *)(dtor->func));
114 }
115
116 static void
walk_cb_nocall(struct cxa_thread_dtor * dtor __unused)117 walk_cb_nocall(struct cxa_thread_dtor *dtor __unused)
118 {
119 }
120
121 static void
cxa_thread_walk(void (* cb)(struct cxa_thread_dtor *))122 cxa_thread_walk(void (*cb)(struct cxa_thread_dtor *))
123 {
124 struct cxa_thread_dtor *dtor, *tdtor;
125
126 LIST_FOREACH_SAFE(dtor, &dtors, entry, tdtor) {
127 LIST_REMOVE(dtor, entry);
128 cb(dtor);
129 free(dtor);
130 }
131 }
132
133 /*
134 * This is the callback function we use to call destructors, once for
135 * each thread. It is called in exit(3) in libc/stdlib/exit.c and
136 * before exit_thread() in libthr/thread/thr_exit.c.
137 */
138 void
__cxa_thread_call_dtors(void)139 __cxa_thread_call_dtors(void)
140 {
141 int i;
142
143 for (i = 0; i < CXA_DTORS_ITERATIONS && !LIST_EMPTY(&dtors); i++)
144 cxa_thread_walk(walk_cb_call);
145
146 if (!LIST_EMPTY(&dtors)) {
147 fprintf(stderr, "Thread %p is exiting with more "
148 "thread-specific dtors created after %d iterations "
149 "of destructor calls\n",
150 _pthread_self(), i);
151 cxa_thread_walk(walk_cb_nocall);
152 }
153 }
154