iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997-2017 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    <http://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.  */
  35 static 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.  */
  50 static void *loaded;
  51
  52 /* Comparison function for searching `loaded_object' tree.  */
  53 static int
  54 known_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.  */
  66 struct __gconv_loaded_object *
  67 internal_function
  68 __gconv_find_shlib (const char *name)
  69 {
  70   struct __gconv_loaded_object *found;
  71   void *keyp;
  72
  73   /* Search the tree of shared objects previously requested.  Data in
  74      the tree are `loaded_object' structures, whose first member is a
  75      `const char *', the lookup key.  The search returns a pointer to
  76      the tree node structure; the first member of the is a pointer to
  77      our structure (i.e. what will be a `loaded_object'); since the
  78      first member of that is the lookup key string, &FCT_NAME is close
  79      enough to a pointer to our structure to use as a lookup key that
  80      will be passed to `known_compare' (above).  */
  81
  82   keyp = __tfind (&name, &loaded, known_compare);
  83   if (keyp == NULL)
  84     {
  85       /* This name was not known before.  */
  86       size_t namelen = strlen (name) + 1;
  87
  88       found = malloc (sizeof (struct __gconv_loaded_object) + namelen);
  89       if (found != NULL)
  90         {
  91           /* Point the tree node at this new structure.  */
  92           found->name = (char *) memcpy (found + 1, name, namelen);
  93           found->counter = -TRIES_BEFORE_UNLOAD - 1;
  94           found->handle = NULL;
  95
  96           if (__builtin_expect (__tsearch (found, &loaded, known_compare)
  97                                 == NULL, 0))
  98             {
  99               /* Something went wrong while inserting the entry.  */
 100               free (found);
 101               found = NULL;
 102             }
 103         }
 104     }
 105   else
 106     found = *(struct __gconv_loaded_object **) keyp;
 107
 108   /* Try to load the shared object if the usage count is 0.  This
 109      implies that if the shared object is not loadable, the handle is
 110      NULL and the usage count > 0.  */
 111   if (found != NULL)
 112     {
 113       if (found->counter < -TRIES_BEFORE_UNLOAD)
 114         {
 115           assert (found->handle == NULL);
 116           found->handle = __libc_dlopen (found->name);
 117           if (found->handle != NULL)
 118             {
 119               found->fct = __libc_dlsym (found->handle, "gconv");
 120               if (found->fct == NULL)
 121                 {
 122                   /* Argh, no conversion function.  There is something
 123                      wrong here.  */
 124                   __gconv_release_shlib (found);
 125                   found = NULL;
 126                 }
 127               else
 128                 {
 129                   found->init_fct = __libc_dlsym (found->handle, "gconv_init");
 130                   found->end_fct = __libc_dlsym (found->handle, "gconv_end");
 131
 132 #ifdef PTR_MANGLE
 133                   PTR_MANGLE (found->fct);
 134                   PTR_MANGLE (found->init_fct);
 135                   PTR_MANGLE (found->end_fct);
 136 #endif
 137
 138                   /* We have succeeded in loading the shared object.  */
 139                   found->counter = 1;
 140                 }
 141             }
 142           else
 143             /* Error while loading the shared object.  */
 144             found = NULL;
 145         }
 146       else if (found->handle != NULL)
 147         found->counter = MAX (found->counter + 1, 1);
 148     }
 149
 150   return found;
 151 }
 152
 153
 154 /* This is very ugly but the tsearch functions provide no way to pass
 155    information to the walker function.  So we use a global variable.
 156    It is MT safe since we use a lock.  */
 157 static struct __gconv_loaded_object *release_handle;
 158
 159 static void
 160 do_release_shlib (void *nodep, VISIT value, int level)
 161 {
 162   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 163
 164   if (value != preorder && value != leaf)
 165     return;
 166
 167   if (obj == release_handle)
 168     {
 169       /* This is the object we want to unload.  Now decrement the
 170          reference counter.  */
 171       assert (obj->counter > 0);
 172       --obj->counter;
 173     }
 174   else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
 175            && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 176     {
 177       /* Unload the shared object.  */
 178       __libc_dlclose (obj->handle);
 179       obj->handle = NULL;
 180     }
 181 }
 182
 183
 184 /* Notify system that a shared object is not longer needed.  */
 185 void
 186 internal_function
 187 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 188 {
 189   /* Urgh, this is ugly but we have no other possibility.  */
 190   release_handle = handle;
 191
 192   /* Process all entries.  Please note that we also visit entries
 193      with release counts <= 0.  This way we can finally unload them
 194      if necessary.  */
 195   __twalk (loaded, (__action_fn_t) do_release_shlib);
 196 }
 197
 198
 199 /* We run this if we debug the memory allocation.  */
 200 static void __libc_freeres_fn_section
 201 do_release_all (void *nodep)
 202 {
 203   struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
 204
 205   /* Unload the shared object.  */
 206   if (obj->handle != NULL)
 207     __libc_dlclose (obj->handle);
 208
 209   free (obj);
 210 }
 211
 212 libc_freeres_fn (free_mem)
 213 {
 214   __tdestroy (loaded, do_release_all);
 215   loaded = NULL;
 216 }
 217
 218
 219 #ifdef DEBUG
 220
 221 #include <stdio.h>
 222
 223 static void
 224 do_print (const void *nodep, VISIT value, int level)
 225 {
 226   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 227
 228   printf ("%10s: \"%s\", %d\n",
 229           value == leaf ? "leaf" :
 230           value == preorder ? "preorder" :
 231           value == postorder ? "postorder" : "endorder",
 232           obj->name, obj->counter);
 233 }
 234
 235 static void __attribute__ ((used))
 236 print_all (void)
 237 {
 238   __twalk (loaded, do_print);
 239 }
 240 #endif