1 /* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <assert.h>
20 #include <dlfcn.h>
21 #include <inttypes.h>
22 #include <search.h>
23 #include <stdlib.h>
24 #include <string.h>
25 #include <libc-lock.h>
26 #include <sys/param.h>
27
28 #include <gconv_int.h>
29 #include <pointer_guard.h>
30
31
32 #ifdef DEBUG
33 /* For debugging purposes. */
34 static void print_all (void);
35 #endif
36
37
38 /* This is a tuning parameter. If a transformation module is not used
39 anymore it gets not immediately unloaded. Instead we wait a certain
40 number of load attempts for further modules. If none of the
41 subsequent load attempts name the same object it finally gets unloaded.
42 Otherwise it is still available which hopefully is the frequent case.
43 The following number is the number of unloading attempts we wait
44 before unloading. */
45 #define TRIES_BEFORE_UNLOAD 2
46
47 /* Array of loaded objects. This is shared by all threads so we have
48 to use semaphores to access it. */
49 static void *loaded;
50
51 /* Comparison function for searching `loaded_object' tree. */
52 static int
53 known_compare (const void *p1, const void *p2)
54 {
55 const struct __gconv_loaded_object *s1 =
56 (const struct __gconv_loaded_object *) p1;
57 const struct __gconv_loaded_object *s2 =
58 (const struct __gconv_loaded_object *) p2;
59
60 return strcmp (s1->name, s2->name);
61 }
62
63 /* Open the gconv database if necessary. A non-negative return value
64 means success. */
65 struct __gconv_loaded_object *
66 __gconv_find_shlib (const char *name)
67 {
68 struct __gconv_loaded_object *found;
69 void *keyp;
70
71 /* Search the tree of shared objects previously requested. Data in
72 the tree are `loaded_object' structures, whose first member is a
73 `const char *', the lookup key. The search returns a pointer to
74 the tree node structure; the first member of the is a pointer to
75 our structure (i.e. what will be a `loaded_object'); since the
76 first member of that is the lookup key string, &FCT_NAME is close
77 enough to a pointer to our structure to use as a lookup key that
78 will be passed to `known_compare' (above). */
79
80 keyp = __tfind (&name, &loaded, known_compare);
81 if (keyp == NULL)
82 {
83 /* This name was not known before. */
84 size_t namelen = strlen (name) + 1;
85
86 found = malloc (sizeof (struct __gconv_loaded_object) + namelen);
87 if (found != NULL)
88 {
89 /* Point the tree node at this new structure. */
90 found->name = (char *) memcpy (found + 1, name, namelen);
91 found->counter = -TRIES_BEFORE_UNLOAD - 1;
92 found->handle = NULL;
93
94 if (__builtin_expect (__tsearch (found, &loaded, known_compare)
95 == NULL, 0))
96 {
97 /* Something went wrong while inserting the entry. */
98 free (found);
99 found = NULL;
100 }
101 }
102 }
103 else
104 found = *(struct __gconv_loaded_object **) keyp;
105
106 /* Try to load the shared object if the usage count is 0. This
107 implies that if the shared object is not loadable, the handle is
108 NULL and the usage count > 0. */
109 if (found != NULL)
110 {
111 if (found->counter < -TRIES_BEFORE_UNLOAD)
112 {
113 assert (found->handle == NULL);
114 found->handle = __libc_dlopen (found->name);
115 if (found->handle != NULL)
116 {
117 found->fct = __libc_dlsym (found->handle, "gconv");
118 if (found->fct == NULL)
119 {
120 /* Argh, no conversion function. There is something
121 wrong here. */
122 __gconv_release_shlib (found);
123 found = NULL;
124 }
125 else
126 {
127 found->init_fct = __libc_dlsym (found->handle, "gconv_init");
128 found->end_fct = __libc_dlsym (found->handle, "gconv_end");
129
130 PTR_MANGLE (found->fct);
131 PTR_MANGLE (found->init_fct);
132 PTR_MANGLE (found->end_fct);
133
134 /* We have succeeded in loading the shared object. */
135 found->counter = 1;
136 }
137 }
138 else
139 /* Error while loading the shared object. */
140 found = NULL;
141 }
142 else if (found->handle != NULL)
143 found->counter = MAX (found->counter + 1, 1);
144 }
145
146 return found;
147 }
148
149 static void
150 do_release_shlib (const void *nodep, VISIT value, void *closure)
151 {
152 struct __gconv_loaded_object *release_handle = closure;
153 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
154
155 if (value != preorder && value != leaf)
156 return;
157
158 if (obj == release_handle)
159 {
160 /* This is the object we want to unload. Now decrement the
161 reference counter. */
162 assert (obj->counter > 0);
163 --obj->counter;
164 }
165 else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
166 && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
167 {
168 /* Unload the shared object. */
169 __libc_dlclose (obj->handle);
170 obj->handle = NULL;
171 }
172 }
173
174
175 /* Notify system that a shared object is not longer needed. */
176 void
177 __gconv_release_shlib (struct __gconv_loaded_object *handle)
178 {
179 /* Process all entries. Please note that we also visit entries
180 with release counts <= 0. This way we can finally unload them
181 if necessary. */
182 __twalk_r (loaded, do_release_shlib, handle);
183 }
184
185
186 /* We run this if we debug the memory allocation. */
187 static void
188 do_release_all (void *nodep)
189 {
190 struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
191
192 /* Unload the shared object. */
193 if (obj->handle != NULL)
194 __libc_dlclose (obj->handle);
195
196 free (obj);
197 }
198
199 void
200 __gconv_dl_freemem (void)
201 {
202 __tdestroy (loaded, do_release_all);
203 loaded = NULL;
204 }
205
206
207 #ifdef DEBUG
208
209 #include <stdio.h>
210
211 static void
212 do_print (const void *nodep, VISIT value, int level)
213 {
214 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
215
216 printf ("%10s: \"%s\", %d\n",
217 value == leaf ? "leaf"
218 : value == preorder ? "preorder"
219 : value == postorder ? "postorder" : "endorder",
220 obj->name, obj->counter);
221 }
222
223 static void __attribute__ ((used))
224 print_all (void)
225 {
226 __twalk (loaded, do_print);
227 }
228 #endif