cxa_thread_atexit.c revision 304527 
1/*-
2 * Copyright (c) 2016 Mahdi Mokhtari <mokhi64@gmail.com>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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.
13 *
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
24 * SUCH DAMAGE.
25 */
26
27#include <sys/cdefs.h>
28__FBSDID("$FreeBSD: stable/10/lib/libc/stdlib/cxa_thread_atexit.c 304527 2016-08-20 12:26:44Z kib $");
29
30#include <sys/queue.h>
31#include "namespace.h"
32#include <errno.h>
33#include <link.h>
34#include <pthread.h>
35#include <stddef.h>
36#include <stdlib.h>
37#include <stdio.h>
38#include "un-namespace.h"
39#include "libc_private.h"
40
41/*
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.
46 *
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().
52 *
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
58 * prevent the crash.
59 */
60
61#define CXA_DTORS_ITERATIONS 4
62
63struct cxa_thread_dtor {
64	void *obj;
65	void (*func)(void *);
66	void *dso;
67	LIST_ENTRY(cxa_thread_dtor) entry;
68};
69static _Thread_local LIST_HEAD(dtor_list, cxa_thread_dtor) dtors =
70    LIST_HEAD_INITIALIZER(dtors);
71
72int
73__cxa_thread_atexit(void (*dtor_func)(void *), void *obj, void *dso_symbol)
74{
75	struct cxa_thread_dtor *new_dtor;
76
77	new_dtor = malloc(sizeof(*new_dtor));
78	if (new_dtor == NULL) {
79		errno = ENOMEM; /* forcibly override malloc(3) error */
80		return (-1);
81	}
82
83	new_dtor->obj = obj;
84	new_dtor->func = dtor_func;
85	new_dtor->dso = dso_symbol;
86	LIST_INSERT_HEAD(&dtors, new_dtor, entry);
87	return (0);
88}
89
90static void
91walk_cb_call(struct cxa_thread_dtor *dtor)
92{
93	struct dl_phdr_info phdr_info;
94
95	if (_rtld_addr_phdr(dtor->dso, &phdr_info) &&
96	    __elf_phdr_match_addr(&phdr_info, dtor->func))
97		dtor->func(dtor->obj);
98	else
99		fprintf(stderr, "__cxa_thread_call_dtors: dtr %p from "
100		    "unloaded dso, skipping\n", (void *)(dtor->func));
101}
102
103static void
104walk_cb_nocall(struct cxa_thread_dtor *dtor __unused)
105{
106}
107
108static void
109cxa_thread_walk(void (*cb)(struct cxa_thread_dtor *))
110{
111	struct cxa_thread_dtor *dtor, *tdtor;
112
113	LIST_FOREACH_SAFE(dtor, &dtors, entry, tdtor) {
114		LIST_REMOVE(dtor, entry);
115		cb(dtor);
116		free(dtor);
117	}
118}
119
120/*
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.
124 */
125void
126__cxa_thread_call_dtors(void)
127{
128	int i;
129
130	for (i = 0; i < CXA_DTORS_ITERATIONS && !LIST_EMPTY(&dtors); i++)
131		cxa_thread_walk(walk_cb_call);
132
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",
137		    _pthread_self(), i);
138		cxa_thread_walk(walk_cb_nocall);
139	}
140}
141