1 /*- 2 * Copyright (c) 2016 Mahdi Mokhtari <mokhi64@gmail.com> 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 #include <sys/queue.h> 33 #include "namespace.h" 34 #include <errno.h> 35 #include <link.h> 36 #include <pthread.h> 37 #include <stddef.h> 38 #include <stdlib.h> 39 #include <stdio.h> 40 #include "un-namespace.h" 41 #include "libc_private.h" 42 43 /* 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. 48 * 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(). 54 * 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 60 * prevent the crash. 61 */ 62 63 #define CXA_DTORS_ITERATIONS 4 64 65 struct cxa_thread_dtor { 66 void *obj; 67 void (*func)(void *); 68 void *dso; 69 LIST_ENTRY(cxa_thread_dtor) entry; 70 }; 71 static _Thread_local LIST_HEAD(dtor_list, cxa_thread_dtor) dtors = 72 LIST_HEAD_INITIALIZER(dtors); 73 74 int 75 __cxa_thread_atexit_impl(void (*dtor_func)(void *), void *obj, 76 void *dso_symbol) 77 { 78 79 return (__cxa_thread_atexit_hidden(dtor_func, obj, dso_symbol)); 80 } 81 82 int 83 __cxa_thread_atexit_hidden(void (*dtor_func)(void *), void *obj, 84 void *dso_symbol) 85 { 86 struct cxa_thread_dtor *new_dtor; 87 88 new_dtor = malloc(sizeof(*new_dtor)); 89 if (new_dtor == NULL) { 90 errno = ENOMEM; /* forcibly override malloc(3) error */ 91 return (-1); 92 } 93 94 new_dtor->obj = obj; 95 new_dtor->func = dtor_func; 96 new_dtor->dso = dso_symbol; 97 LIST_INSERT_HEAD(&dtors, new_dtor, entry); 98 return (0); 99 } 100 101 static void 102 walk_cb_call(struct cxa_thread_dtor *dtor) 103 { 104 struct dl_phdr_info phdr_info; 105 106 if (_rtld_addr_phdr(dtor->dso, &phdr_info) && 107 __elf_phdr_match_addr(&phdr_info, dtor->func)) 108 dtor->func(dtor->obj); 109 else 110 fprintf(stderr, 111 "__cxa_thread_call_dtors: dtr %p from unloaded dso, skipping\n", 112 (void *)(dtor->func)); 113 } 114 115 static void 116 walk_cb_nocall(struct cxa_thread_dtor *dtor __unused) 117 { 118 } 119 120 static void 121 cxa_thread_walk(void (*cb)(struct cxa_thread_dtor *)) 122 { 123 struct cxa_thread_dtor *dtor, *tdtor; 124 125 LIST_FOREACH_SAFE(dtor, &dtors, entry, tdtor) { 126 LIST_REMOVE(dtor, entry); 127 cb(dtor); 128 free(dtor); 129 } 130 } 131 132 /* 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. 136 */ 137 void 138 __cxa_thread_call_dtors(void) 139 { 140 int i; 141 142 for (i = 0; i < CXA_DTORS_ITERATIONS && !LIST_EMPTY(&dtors); i++) 143 cxa_thread_walk(walk_cb_call); 144 145 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", 149 _pthread_self(), i); 150 cxa_thread_walk(walk_cb_nocall); 151 } 152 } 153