iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997-2021 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.  */
  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 __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
 152 static void
 153 do_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.  */
 179 void
 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.  */
 190 static void __libc_freeres_fn_section
 191 do_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
 202 libc_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
 213 static void
 214 do_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
 225 static void __attribute__ ((used))
 226 print_all (void)
 227 {
 228   __twalk (loaded, do_print);
 229 }
 230 #endif