1 /* Handle loading/unloading of shared object for transformation.
2 Copyright (C) 1997 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. */
28 #include <bits/libc-lock.h>
29 #include <sys/param.h>
32 /* This is a tuning parameter. If a transformation module is not used
33 anymore it gets not immediately unloaded. Instead we wait a certain
34 number of load attempts for further modules. If none of the
35 subsequent load attempts name the same object it finally gets unloaded.
36 Otherwise it is still available which hopefully is the frequent case.
37 The following number is the number of unloading attempts we wait
39 #define TRIES_BEFORE_UNLOAD 2
42 /* Structure describing one loaded shared object. This normally are
43 objects to perform conversation but as a special case the db shared
44 object is also handled. */
47 /* Name of the object. */
50 /* Reference counter for the db functionality. If no conversion is
51 needed we unload the db library. */
54 /* The handle for the shared object. */
59 /* Array of loaded objects. This is shared by all threads so we have
60 to use semaphores to access it. */
62 __libc_lock_define_initialized (static, lock)
66 /* Comparison function for searching `loaded_object' tree. */
68 known_compare (const void *p1, const void *p2)
70 const struct loaded_object *s1 = (const struct loaded_object *) p1;
71 const struct loaded_object *s2 = (const struct loaded_object *) p2;
73 return (intptr_t) s1->handle - (intptr_t) s2->handle;
80 struct loaded_object *args = (struct loaded_object *) a;
81 /* Open and relocate the shared object. */
82 args->handle = _dl_open (args->name, RTLD_LAZY);
88 dlerror_run (void (*operate) (void *), void *args)
90 char *last_errstring = NULL;
91 const char *last_object_name = NULL;
94 (void) _dl_catch_error (&last_errstring, &last_object_name, operate, args);
96 result = last_errstring != NULL;
98 free (last_errstring);
106 /* Arguments to get_sym. */
107 struct link_map *map;
110 /* Return values of get_sym. */
112 const ElfW(Sym) *ref;
118 struct get_sym_args *args = (struct get_sym_args *) a;
119 struct link_map *scope[2] = { args->map, NULL };
121 args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
122 scope, args->map->l_name, 0);
127 __gconv_find_func (void *handle, const char *name)
129 struct get_sym_args args;
134 return (dlerror_run (get_sym, &args) ? NULL
135 : (void *) (args.loadbase + args.ref->st_value));
140 /* Open the gconv database if necessary. A non-negative return value
143 __gconv_find_shlib (const char *name)
146 struct loaded_object *found;
148 /* Acquire the lock. */
149 __libc_lock_lock (lock);
151 /* Search the tree of shared objects previously requested. Data in
152 the tree are `loaded_object' structures, whose first member is a
153 `const char *', the lookup key. The search returns a pointer to
154 the tree node structure; the first member of the is a pointer to
155 our structure (i.e. what will be a `loaded_object'); since the
156 first member of that is the lookup key string, &FCT_NAME is close
157 enough to a pointer to our structure to use as a lookup key that
158 will be passed to `known_compare' (above). */
160 found = __tfind (&name, &loaded, known_compare);
163 /* This name was not known before. */
164 found = malloc (sizeof (struct loaded_object));
167 /* Point the tree node at this new structure. */
169 found->counter = -TRIES_BEFORE_UNLOAD - 1;
170 found->handle = NULL;
172 if (__tsearch (found, &loaded, known_compare) == NULL)
174 /* Something went wrong while inserting the entry. */
181 /* Try to load the shared object if the usage count is 0. This
182 implies that if the shared object is not loadable, the handle is
183 NULL and the usage count > 0. */
186 if (found->counter < -TRIES_BEFORE_UNLOAD)
188 if (dlerror_run (do_open, found) == 0)
191 else if (found->handle != NULL)
192 found->counter = MAX (found->counter + 1, 1);
194 result = found->handle;
197 /* Release the lock. */
198 __libc_lock_unlock (lock);
204 /* This is very ugly but the tsearch functions provide no way to pass
205 information to the walker function. So we use a global variable.
206 It is MT safe since we use a lock. */
207 static void *release_handle;
210 do_release_shlib (const void *nodep, VISIT value, int level)
212 struct loaded_object *obj = *(struct loaded_object **) nodep;
214 if (value != preorder && value != leaf)
217 if (obj->handle == release_handle)
218 /* This is the object we want to unload. Now set the release
221 else if (obj->counter <= 0)
223 if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
225 /* Unload the shared object. We don't use the trick to
226 catch errors since in the case an error is signalled
227 something is really wrong. */
228 _dl_close ((struct link_map *) obj->handle);
236 /* Notify system that a shared object is not longer needed. */
238 __gconv_release_shlib (void *handle)
240 /* Acquire the lock. */
241 __libc_lock_lock (lock);
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
249 __twalk (loaded, do_release_shlib);
251 /* Release the lock. */
252 __libc_lock_unlock (lock);