1 /* GMODULE - GLIB wrapper code for dynamic module loading
2 * Copyright (C) 1998, 2000 Tim Janik
3 *
4 * SPDX-License-Identifier: LGPL-2.1-or-later
5 *
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
10 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
18 */
19
20 /*
21 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
22 * file for a list of people on the GLib Team. See the ChangeLog
23 * files for a list of changes. These files are distributed with
24 * GLib at ftp://ftp.gtk.org/pub/gtk/.
25 */
26
27 /*
28 * MT safe
29 */
30 #include "config.h"
31
32 #include <dlfcn.h>
33 #include <glib.h>
34
35 /* Perl includes <nlist.h> and <link.h> instead of <dlfcn.h> on some systems? */
36
37
38 /* dlerror() is not implemented on all systems
39 */
40 #ifndef G_MODULE_HAVE_DLERROR
41 # ifdef __NetBSD__
42 # define dlerror() g_strerror (errno)
43 # else /* !__NetBSD__ */
44 /* could we rely on errno's state here? */
45 # define dlerror() "unknown dl-error"
46 # endif /* !__NetBSD__ */
47 #endif /* G_MODULE_HAVE_DLERROR */
48
49 /* some flags are missing on some systems, so we provide
50 * harmless defaults.
51 * The Perl sources say, RTLD_LAZY needs to be defined as (1),
52 * at least for Solaris 1.
53 *
54 * Mandatory:
55 * RTLD_LAZY - resolve undefined symbols as code from the dynamic library
56 * is executed.
57 * RTLD_NOW - resolve all undefined symbols before dlopen returns, and fail
58 * if this cannot be done.
59 * Optionally:
60 * RTLD_GLOBAL - the external symbols defined in the library will be made
61 * available to subsequently loaded libraries.
62 */
63 #ifndef HAVE_RTLD_LAZY
64 #define RTLD_LAZY 1
65 #endif /* RTLD_LAZY */
66 #ifndef HAVE_RTLD_NOW
67 #define RTLD_NOW 0
68 #endif /* RTLD_NOW */
69 /* some systems (OSF1 V5.0) have broken RTLD_GLOBAL linkage */
70 #ifdef G_MODULE_BROKEN_RTLD_GLOBAL
71 #undef RTLD_GLOBAL
72 #undef HAVE_RTLD_GLOBAL
73 #endif /* G_MODULE_BROKEN_RTLD_GLOBAL */
74 #ifndef HAVE_RTLD_GLOBAL
75 #define RTLD_GLOBAL 0
76 #endif /* RTLD_GLOBAL */
77
78
79 /* According to POSIX.1-2001, dlerror() is not necessarily thread-safe
80 * (see https://pubs.opengroup.org/onlinepubs/009695399/), and so must be
81 * called within the same locked section as the dlopen()/dlsym() call which
82 * may have caused an error.
83 *
84 * However, some libc implementations, such as glibc, implement dlerror() using
85 * thread-local storage, so are thread-safe. As of early 2021:
86 * - glibc is thread-safe: https://github.com/bminor/glibc/blob/HEAD/dlfcn/libc_dlerror_result.c
87 * - uclibc-ng is not thread-safe: https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/ldso/libdl/libdl.c?id=132decd2a043d0ccf799f42bf89f3ae0c11e95d5#n1075
88 * - Other libc implementations have not been checked, and no problems have
89 * been reported with them in 10 years, so default to assuming that they
90 * don’t need additional thread-safety from GLib
91 */
92 #if defined(__UCLIBC__)
93 G_LOCK_DEFINE_STATIC (errors);
94 #else
95 #define DLERROR_IS_THREADSAFE 1
96 #endif
97
98 static void
99 lock_dlerror (void)
100 {
101 #ifndef DLERROR_IS_THREADSAFE
102 G_LOCK (errors);
103 #endif
104 }
105
106 static void
107 unlock_dlerror (void)
108 {
109 #ifndef DLERROR_IS_THREADSAFE
110 G_UNLOCK (errors);
111 #endif
112 }
113
114 /* This should be called with lock_dlerror() held */
115 static const gchar *
116 fetch_dlerror (gboolean replace_null)
117 {
118 const gchar *msg = dlerror ();
119
120 /* make sure we always return an error message != NULL, if
121 * expected to do so. */
122
123 if (!msg && replace_null)
124 return "unknown dl-error";
125
126 return msg;
127 }
128
129 static gpointer
130 _g_module_open (const gchar *file_name,
131 gboolean bind_lazy,
132 gboolean bind_local,
133 GError **error)
134 {
135 gpointer handle;
136
137 lock_dlerror ();
138 handle = dlopen (file_name,
139 (bind_local ? 0 : RTLD_GLOBAL) | (bind_lazy ? RTLD_LAZY : RTLD_NOW));
140 if (!handle)
141 {
142 const gchar *message = fetch_dlerror (TRUE);
143
144 g_module_set_error (message);
145 g_set_error_literal (error, G_MODULE_ERROR, G_MODULE_ERROR_FAILED, message);
146 }
147
148 unlock_dlerror ();
149
150 return handle;
151 }
152
153 static gpointer
154 _g_module_self (void)
155 {
156 gpointer handle;
157
158 /* to query symbols from the program itself, special link options
159 * are required on some systems.
160 */
161
162 /* On Android 32 bit (i.e. not __LP64__), dlopen(NULL)
163 * does not work reliable and generally no symbols are found
164 * at all. RTLD_DEFAULT works though.
165 * On Android 64 bit, dlopen(NULL) seems to work but dlsym(handle)
166 * always returns 'undefined symbol'. Only if RTLD_DEFAULT or
167 * NULL is given, dlsym returns an appropriate pointer.
168 */
169 lock_dlerror ();
170 #if defined(__BIONIC__) || defined(__NetBSD__) || defined(__FreeBSD__)
171 handle = RTLD_DEFAULT;
172 #else
173 handle = dlopen (NULL, RTLD_GLOBAL | RTLD_LAZY);
174 #endif
175 if (!handle)
176 g_module_set_error (fetch_dlerror (TRUE));
177 unlock_dlerror ();
178
179 return handle;
180 }
181
182 static void
183 _g_module_close (gpointer handle)
184 {
185 #if defined(__BIONIC__) || defined(__NetBSD__) || defined(__FreeBSD__)
186 if (handle != RTLD_DEFAULT)
187 #endif
188 {
189 lock_dlerror ();
190 if (dlclose (handle) != 0)
191 g_module_set_error (fetch_dlerror (TRUE));
192 unlock_dlerror ();
193 }
194 }
195
196 static gpointer
197 _g_module_symbol (gpointer handle,
198 const gchar *symbol_name)
199 {
200 gpointer p;
201 const gchar *msg;
202
203 lock_dlerror ();
204 fetch_dlerror (FALSE);
205 p = dlsym (handle, symbol_name);
206 msg = fetch_dlerror (FALSE);
207 if (msg)
208 g_module_set_error (msg);
209 unlock_dlerror ();
210
211 return p;
212 }