1/* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997-2020 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 <https://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 *
67__gconv_find_shlib (const char *name)
68{
69 struct __gconv_loaded_object *found;
70 void *keyp;
71
72 /* Search the tree of shared objects previously requested. Data in
73 the tree are `loaded_object' structures, whose first member is a
74 `const char *', the lookup key. The search returns a pointer to
75 the tree node structure; the first member of the is a pointer to
76 our structure (i.e. what will be a `loaded_object'); since the
77 first member of that is the lookup key string, &FCT_NAME is close
78 enough to a pointer to our structure to use as a lookup key that
79 will be passed to `known_compare' (above). */
80
81 keyp = __tfind (&name, &loaded, known_compare);
82 if (keyp == NULL)
83 {
84 /* This name was not known before. */
85 size_t namelen = strlen (name) + 1;
86
87 found = malloc (sizeof (struct __gconv_loaded_object) + namelen);
88 if (found != NULL)
89 {
90 /* Point the tree node at this new structure. */
91 found->name = (char *) memcpy (found + 1, name, namelen);
92 found->counter = -TRIES_BEFORE_UNLOAD - 1;
93 found->handle = NULL;
94
95 if (__builtin_expect (__tsearch (found, &loaded, known_compare)
96 == NULL, 0))
97 {
98 /* Something went wrong while inserting the entry. */
99 free (found);
100 found = NULL;
101 }
102 }
103 }
104 else
105 found = *(struct __gconv_loaded_object **) keyp;
106
107 /* Try to load the shared object if the usage count is 0. This
108 implies that if the shared object is not loadable, the handle is
109 NULL and the usage count > 0. */
110 if (found != NULL)
111 {
112 if (found->counter < -TRIES_BEFORE_UNLOAD)
113 {
114 assert (found->handle == NULL);
115 found->handle = __libc_dlopen (found->name);
116 if (found->handle != NULL)
117 {
118 found->fct = __libc_dlsym (found->handle, "gconv");
119 if (found->fct == NULL)
120 {
121 /* Argh, no conversion function. There is something
122 wrong here. */
123 __gconv_release_shlib (found);
124 found = NULL;
125 }
126 else
127 {
128 found->init_fct = __libc_dlsym (found->handle, "gconv_init");
129 found->end_fct = __libc_dlsym (found->handle, "gconv_end");
130
131#ifdef PTR_MANGLE
132 PTR_MANGLE (found->fct);
133 PTR_MANGLE (found->init_fct);
134 PTR_MANGLE (found->end_fct);
135#endif
136
137 /* We have succeeded in loading the shared object. */
138 found->counter = 1;
139 }
140 }
141 else
142 /* Error while loading the shared object. */
143 found = NULL;
144 }
145 else if (found->handle != NULL)
146 found->counter = MAX (found->counter + 1, 1);
147 }
148
149 return found;
150}
151
152static void
153do_release_shlib (const void *nodep, VISIT value, void *closure)
154{
155 struct __gconv_loaded_object *release_handle = closure;
156 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
157
158 if (value != preorder && value != leaf)
159 return;
160
161 if (obj == release_handle)
162 {
163 /* This is the object we want to unload. Now decrement the
164 reference counter. */
165 assert (obj->counter > 0);
166 --obj->counter;
167 }
168 else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
169 && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
170 {
171 /* Unload the shared object. */
172 __libc_dlclose (obj->handle);
173 obj->handle = NULL;
174 }
175}
176
177
178/* Notify system that a shared object is not longer needed. */
179void
180__gconv_release_shlib (struct __gconv_loaded_object *handle)
181{
182 /* Process all entries. Please note that we also visit entries
183 with release counts <= 0. This way we can finally unload them
184 if necessary. */
185 __twalk_r (loaded, do_release_shlib, handle);
186}
187
188
189/* We run this if we debug the memory allocation. */
190static void __libc_freeres_fn_section
191do_release_all (void *nodep)
192{
193 struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
194
195 /* Unload the shared object. */
196 if (obj->handle != NULL)
197 __libc_dlclose (obj->handle);
198
199 free (obj);
200}
201
202libc_freeres_fn (free_mem)
203{
204 __tdestroy (loaded, do_release_all);
205 loaded = NULL;
206}
207
208
209#ifdef DEBUG
210
211#include <stdio.h>
212
213static void
214do_print (const void *nodep, VISIT value, int level)
215{
216 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
217
218 printf ("%10s: \"%s\", %d\n",
219 value == leaf ? "leaf"
220 : value == preorder ? "preorder"
221 : value == postorder ? "postorder" : "endorder",
222 obj->name, obj->counter);
223}
224
225static void __attribute__ ((used))
226print_all (void)
227{
228 __twalk (loaded, do_print);
229}
230#endif
231