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[glibc.git] / iconv / gconv_dl.c
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1 /* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997, 1998 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Library General Public License as
8 published by the Free Software Foundation; either version 2 of the
9 License, or (at your option) any later version.
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 Library General Public License for more details.
16 You should have received a copy of the GNU Library General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If not,
18 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
21 #include <dlfcn.h>
22 #include <inttypes.h>
23 #include <search.h>
24 #include <stdlib.h>
25 #include <string.h>
26 #include <bits/libc-lock.h>
27 #include <elf/ldsodefs.h>
28 #include <sys/param.h>
30 #include <gconv_int.h>
33 /* This is a tuning parameter. If a transformation module is not used
34 anymore it gets not immediately unloaded. Instead we wait a certain
35 number of load attempts for further modules. If none of the
36 subsequent load attempts name the same object it finally gets unloaded.
37 Otherwise it is still available which hopefully is the frequent case.
38 The following number is the number of unloading attempts we wait
39 before unloading. */
40 #define TRIES_BEFORE_UNLOAD 2
43 /* Array of loaded objects. This is shared by all threads so we have
44 to use semaphores to access it. */
45 static void *loaded;
49 /* Comparison function for searching `loaded_object' tree. */
50 static int
51 known_compare (const void *p1, const void *p2)
53 const struct gconv_loaded_object *s1 =
54 (const struct gconv_loaded_object *) p1;
55 const struct gconv_loaded_object *s2 =
56 (const struct gconv_loaded_object *) p2;
58 return (intptr_t) s1->handle - (intptr_t) s2->handle;
62 static void
63 do_open (void *a)
65 struct gconv_loaded_object *args = (struct gconv_loaded_object *) a;
66 /* Open and relocate the shared object. */
67 args->handle = _dl_open (args->name, RTLD_LAZY);
71 static int
72 internal_function
73 dlerror_run (void (*operate) (void *), void *args)
75 char *last_errstring = NULL;
76 int result;
78 (void) _dl_catch_error (&last_errstring, operate, args);
80 result = last_errstring != NULL;
81 if (result)
82 free (last_errstring);
84 return result;
88 struct get_sym_args
90 /* Arguments to get_sym. */
91 struct link_map *map;
92 const char *name;
94 /* Return values of get_sym. */
95 ElfW(Addr) loadbase;
96 const ElfW(Sym) *ref;
99 static void
100 get_sym (void *a)
102 struct get_sym_args *args = (struct get_sym_args *) a;
103 struct link_map *scope[2] = { args->map, NULL };
104 args->ref = NULL;
105 args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
106 scope, args->map->l_name, 0);
110 void *
111 internal_function
112 __gconv_find_func (void *handle, const char *name)
114 struct get_sym_args args;
116 args.map = handle;
117 args.name = name;
119 return (dlerror_run (get_sym, &args) ? NULL
120 : (void *) (args.loadbase + args.ref->st_value));
125 /* Open the gconv database if necessary. A non-negative return value
126 means success. */
127 struct gconv_loaded_object *
128 internal_function
129 __gconv_find_shlib (const char *name)
131 struct gconv_loaded_object *found;
132 void *keyp;
134 /* Search the tree of shared objects previously requested. Data in
135 the tree are `loaded_object' structures, whose first member is a
136 `const char *', the lookup key. The search returns a pointer to
137 the tree node structure; the first member of the is a pointer to
138 our structure (i.e. what will be a `loaded_object'); since the
139 first member of that is the lookup key string, &FCT_NAME is close
140 enough to a pointer to our structure to use as a lookup key that
141 will be passed to `known_compare' (above). */
143 keyp = __tfind (&name, &loaded, known_compare);
144 if (keyp == NULL)
146 /* This name was not known before. */
147 found = malloc (sizeof (struct gconv_loaded_object));
148 if (found != NULL)
150 /* Point the tree node at this new structure. */
151 found->name = name;
152 found->counter = -TRIES_BEFORE_UNLOAD - 1;
153 found->handle = NULL;
155 if (__tsearch (found, &loaded, known_compare) == NULL)
157 /* Something went wrong while inserting the entry. */
158 free (found);
159 found = NULL;
163 else
164 found = *(struct gconv_loaded_object **) keyp;
166 /* Try to load the shared object if the usage count is 0. This
167 implies that if the shared object is not loadable, the handle is
168 NULL and the usage count > 0. */
169 if (found != NULL)
171 if (found->counter < -TRIES_BEFORE_UNLOAD)
173 if (dlerror_run (do_open, found) == 0)
175 found->fct = __gconv_find_func (found->handle, "gconv");
176 if (found->fct == NULL)
178 /* Argh, no conversion function. There is something
179 wrong here. */
180 __gconv_release_shlib (found);
181 found = NULL;
183 else
185 found->init_fct = __gconv_find_func (found->handle,
186 "gconv_init");
187 found->end_fct = __gconv_find_func (found->handle,
188 "gconv_end");
190 /* We have succeeded in loading the shared object. */
191 found->counter = 1;
194 else
195 /* Error while loading the shared object. */
196 found = NULL;
198 else if (found->handle != NULL)
199 found->counter = MAX (found->counter + 1, 1);
202 return found;
206 /* This is very ugly but the tsearch functions provide no way to pass
207 information to the walker function. So we use a global variable.
208 It is MT safe since we use a lock. */
209 static struct gconv_loaded_object *release_handle;
211 static void
212 do_release_shlib (const void *nodep, VISIT value, int level)
214 struct gconv_loaded_object *obj = *(struct gconv_loaded_object **) nodep;
216 if (value != preorder && value != leaf)
217 return;
219 if (obj == release_handle)
220 /* This is the object we want to unload. Now set the release
221 counter to zero. */
222 obj->counter = 0;
223 else if (obj->counter <= 0)
225 if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
227 /* Unload the shared object. We don't use the trick to
228 catch errors since in the case an error is signalled
229 something is really wrong. */
230 _dl_close (obj->handle);
232 obj->handle = NULL;
238 /* Notify system that a shared object is not longer needed. */
240 internal_function
241 __gconv_release_shlib (struct gconv_loaded_object *handle)
243 /* Urgh, this is ugly but we have no other possibility. */
244 release_handle = handle;
246 /* Process all entries. Please note that we also visit entries
247 with release counts <= 0. This way we can finally unload them
248 if necessary. */
249 __twalk (loaded, do_release_shlib);
251 return GCONV_OK;