1/* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997-2022 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 <sysdep.h>
30
31
32#ifdef DEBUG
33/* For debugging purposes. */
34static 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. */
49static void *loaded;
50
51/* Comparison function for searching `loaded_object' tree. */
52static int
53known_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. */
65struct __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 (size: 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 (ptr: 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 (map: found->handle, name: "gconv");
118 if (found->fct == NULL)
119 {
120 /* Argh, no conversion function. There is something
121 wrong here. */
122 __gconv_release_shlib (handle: found);
123 found = NULL;
124 }
125 else
126 {
127 found->init_fct = __libc_dlsym (map: found->handle, name: "gconv_init");
128 found->end_fct = __libc_dlsym (map: found->handle, name: "gconv_end");
129
130#ifdef PTR_MANGLE
131 PTR_MANGLE (found->fct);
132 PTR_MANGLE (found->init_fct);
133 PTR_MANGLE (found->end_fct);
134#endif
135
136 /* We have succeeded in loading the shared object. */
137 found->counter = 1;
138 }
139 }
140 else
141 /* Error while loading the shared object. */
142 found = NULL;
143 }
144 else if (found->handle != NULL)
145 found->counter = MAX (found->counter + 1, 1);
146 }
147
148 return found;
149}
150
151static void
152do_release_shlib (const void *nodep, VISIT value, void *closure)
153{
154 struct __gconv_loaded_object *release_handle = closure;
155 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
156
157 if (value != preorder && value != leaf)
158 return;
159
160 if (obj == release_handle)
161 {
162 /* This is the object we want to unload. Now decrement the
163 reference counter. */
164 assert (obj->counter > 0);
165 --obj->counter;
166 }
167 else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
168 && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
169 {
170 /* Unload the shared object. */
171 __libc_dlclose (map: obj->handle);
172 obj->handle = NULL;
173 }
174}
175
176
177/* Notify system that a shared object is not longer needed. */
178void
179__gconv_release_shlib (struct __gconv_loaded_object *handle)
180{
181 /* Process all entries. Please note that we also visit entries
182 with release counts <= 0. This way we can finally unload them
183 if necessary. */
184 __twalk_r (loaded, do_release_shlib, handle);
185}
186
187
188/* We run this if we debug the memory allocation. */
189static void __libc_freeres_fn_section
190do_release_all (void *nodep)
191{
192 struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
193
194 /* Unload the shared object. */
195 if (obj->handle != NULL)
196 __libc_dlclose (map: obj->handle);
197
198 free (ptr: obj);
199}
200
201libc_freeres_fn (free_mem)
202{
203 __tdestroy (loaded, do_release_all);
204 loaded = NULL;
205}
206
207
208#ifdef DEBUG
209
210#include <stdio.h>
211
212static void
213do_print (const void *nodep, VISIT value, int level)
214{
215 struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
216
217 printf ("%10s: \"%s\", %d\n",
218 value == leaf ? "leaf"
219 : value == preorder ? "preorder"
220 : value == postorder ? "postorder" : "endorder",
221 obj->name, obj->counter);
222}
223
224static void __attribute__ ((used))
225print_all (void)
226{
227 __twalk (loaded, do_print);
228}
229#endif
230

source code of glibc/iconv/gconv_dl.c