1/* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997-2016 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
5
6 The GNU C 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 The GNU C 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 the GNU C Library; if not, see
18 <http://www.gnu.org/licenses/>. */
19
20#include <assert.h>
21#include <dlfcn.h>
22#include <inttypes.h>
23#include <search.h>
24#include <stdlib.h>
25#include <string.h>
26#include <libc-lock.h>
27#include <sys/param.h>
28
29#include <gconv_int.h>
30#include <sysdep.h>
31
32
33#ifdef DEBUG
34/* For debugging purposes. */
35static void print_all (void);
36#endif
37
38
39/* This is a tuning parameter. If a transformation module is not used
40 anymore it gets not immediately unloaded. Instead we wait a certain
41 number of load attempts for further modules. If none of the
42 subsequent load attempts name the same object it finally gets unloaded.
43 Otherwise it is still available which hopefully is the frequent case.
44 The following number is the number of unloading attempts we wait
45 before unloading. */
46#define TRIES_BEFORE_UNLOAD 2
47
48/* Array of loaded objects. This is shared by all threads so we have
49 to use semaphores to access it. */
50static void *loaded;
51
52/* Comparison function for searching `loaded_object' tree. */
53static int
54known_compare (const void *p1, const void *p2)
55{
56 const struct __gconv_loaded_object *s1 =
57 (const struct __gconv_loaded_object *) p1;
58 const struct __gconv_loaded_object *s2 =
59 (const struct __gconv_loaded_object *) p2;
60
61 return strcmp (s1->name, s2->name);
62}
63
64/* Open the gconv database if necessary. A non-negative return value
65 means success. */
66struct __gconv_loaded_object *
67internal_function
68__gconv_find_shlib (const char *name)
69{
70 struct __gconv_loaded_object *found;
71 void *keyp;
72
73 /* Search the tree of shared objects previously requested. Data in
74 the tree are `loaded_object' structures, whose first member is a
75 `const char *', the lookup key. The search returns a pointer to
76 the tree node structure; the first member of the is a pointer to
77 our structure (i.e. what will be a `loaded_object'); since the
78 first member of that is the lookup key string, &FCT_NAME is close
79 enough to a pointer to our structure to use as a lookup key that
80 will be passed to `known_compare' (above). */
81
82 keyp = __tfind (&name, &loaded, known_compare);
83 if (keyp == NULL)
84 {
85 /* This name was not known before. */
86 size_t namelen = strlen (name) + 1;
87
88 found = malloc (sizeof (struct __gconv_loaded_object) + namelen);
89 if (found != NULL)
90 {
91 /* Point the tree node at this new structure. */
92 found->name = (char *) memcpy (found + 1, name, namelen);
93 found->counter = -TRIES_BEFORE_UNLOAD - 1;
94 found->handle = NULL;
95
96 if (__builtin_expect (__tsearch (found, &loaded, known_compare)
97 == NULL, 0))
98 {
99 /* Something went wrong while inserting the entry. */
100 free (found);
101 found = NULL;
102 }
103 }
104 }
105 else
106 found = *(struct __gconv_loaded_object **) keyp;
107
108 /* Try to load the shared object if the usage count is 0. This
109 implies that if the shared object is not loadable, the handle is
110 NULL and the usage count > 0. */
111 if (found != NULL)
112 {
113 if (found->counter < -TRIES_BEFORE_UNLOAD)
114 {
115 assert (found->handle == NULL);
116 found->handle = __libc_dlopen (found->name);
117 if (found->handle != NULL)
118 {
119 found->fct = __libc_dlsym (found->handle, "gconv");
120 if (found->fct == NULL)
121 {
122 /* Argh, no conversion function. There is something
123 wrong here. */
124 __gconv_release_shlib (found);
125 found = NULL;
126 }
127 else
128 {
129 found->init_fct = __libc_dlsym (found->handle, "gconv_init");
130 found->end_fct = __libc_dlsym (found->handle, "gconv_end");
131
132#ifdef PTR_MANGLE
133 PTR_MANGLE (found->fct);
134 if (found->init_fct != NULL)
135 PTR_MANGLE (found->init_fct);
136 if (found->end_fct != NULL)
137 PTR_MANGLE (found->end_fct);
138#endif
139
140 /* We have succeeded in loading the shared object. */
141 found->counter = 1;
142 }
143 }
144 else
145 /* Error while loading the shared object. */
146 found = NULL;
147 }
148 else if (found->handle != NULL)
149 found->counter = MAX (found->counter + 1, 1);
150 }
151
152 return found;
153}
154
155
156/* This is very ugly but the tsearch functions provide no way to pass
157 information to the walker function. So we use a global variable.
158 It is MT safe since we use a lock. */
159static struct __gconv_loaded_object *release_handle;
160
161static void
162do_release_shlib (void *nodep, VISIT value, int level)
163{
164 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
165
166 if (value != preorder && value != leaf)
167 return;
168
169 if (obj == release_handle)
170 {
171 /* This is the object we want to unload. Now decrement the
172 reference counter. */
173 assert (obj->counter > 0);
174 --obj->counter;
175 }
176 else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
177 && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
178 {
179 /* Unload the shared object. */
180 __libc_dlclose (obj->handle);
181 obj->handle = NULL;
182 }
183}
184
185
186/* Notify system that a shared object is not longer needed. */
187void
188internal_function
189__gconv_release_shlib (struct __gconv_loaded_object *handle)
190{
191 /* Urgh, this is ugly but we have no other possibility. */
192 release_handle = handle;
193
194 /* Process all entries. Please note that we also visit entries
195 with release counts <= 0. This way we can finally unload them
196 if necessary. */
197 __twalk (loaded, (__action_fn_t) do_release_shlib);
198}
199
200
201/* We run this if we debug the memory allocation. */
202static void __libc_freeres_fn_section
203do_release_all (void *nodep)
204{
205 struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
206
207 /* Unload the shared object. */
208 if (obj->handle != NULL)
209 __libc_dlclose (obj->handle);
210
211 free (obj);
212}
213
214libc_freeres_fn (free_mem)
215{
216 __tdestroy (loaded, do_release_all);
217 loaded = NULL;
218}
219
220
221#ifdef DEBUG
222
223#include <stdio.h>
224
225static void
226do_print (const void *nodep, VISIT value, int level)
227{
228 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
229
230 printf ("%10s: \"%s\", %d\n",
231 value == leaf ? "leaf" :
232 value == preorder ? "preorder" :
233 value == postorder ? "postorder" : "endorder",
234 obj->name, obj->counter);
235}
236
237static void __attribute__ ((used))
238print_all (void)
239{
240 __twalk (loaded, do_print);
241}
242#endif
243