iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997-2023 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 <pointer_guard.h>
  30
  31
  32 #ifdef DEBUG
  33 /* For debugging purposes.  */
  34 static 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.  */
  49 static void *loaded;
  50
  51 /* Comparison function for searching `loaded_object' tree.  */
  52 static int
  53 known_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.  */
  65 struct __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 (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 (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 (found->handle, "gconv");
 118               if (found->fct == NULL)
 119                 {
 120                   /* Argh, no conversion function.  There is something
 121                      wrong here.  */
 122                   __gconv_release_shlib (found);
 123                   found = NULL;
 124                 }
 125               else
 126                 {
 127                   found->init_fct = __libc_dlsym (found->handle, "gconv_init");
 128                   found->end_fct = __libc_dlsym (found->handle, "gconv_end");
 129
 130                   PTR_MANGLE (found->fct);
 131                   PTR_MANGLE (found->init_fct);
 132                   PTR_MANGLE (found->end_fct);
 133
 134                   /* We have succeeded in loading the shared object.  */
 135                   found->counter = 1;
 136                 }
 137             }
 138           else
 139             /* Error while loading the shared object.  */
 140             found = NULL;
 141         }
 142       else if (found->handle != NULL)
 143         found->counter = MAX (found->counter + 1, 1);
 144     }
 145
 146   return found;
 147 }
 148
 149 static void
 150 do_release_shlib (const void *nodep, VISIT value, void *closure)
 151 {
 152   struct __gconv_loaded_object *release_handle = closure;
 153   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 154
 155   if (value != preorder && value != leaf)
 156     return;
 157
 158   if (obj == release_handle)
 159     {
 160       /* This is the object we want to unload.  Now decrement the
 161          reference counter.  */
 162       assert (obj->counter > 0);
 163       --obj->counter;
 164     }
 165   else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
 166            && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 167     {
 168       /* Unload the shared object.  */
 169       __libc_dlclose (obj->handle);
 170       obj->handle = NULL;
 171     }
 172 }
 173
 174
 175 /* Notify system that a shared object is not longer needed.  */
 176 void
 177 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 178 {
 179   /* Process all entries.  Please note that we also visit entries
 180      with release counts <= 0.  This way we can finally unload them
 181      if necessary.  */
 182   __twalk_r (loaded, do_release_shlib, handle);
 183 }
 184
 185
 186 /* We run this if we debug the memory allocation.  */
 187 static void __libc_freeres_fn_section
 188 do_release_all (void *nodep)
 189 {
 190   struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
 191
 192   /* Unload the shared object.  */
 193   if (obj->handle != NULL)
 194     __libc_dlclose (obj->handle);
 195
 196   free (obj);
 197 }
 198
 199 libc_freeres_fn (free_mem)
 200 {
 201   __tdestroy (loaded, do_release_all);
 202   loaded = NULL;
 203 }
 204
 205
 206 #ifdef DEBUG
 207
 208 #include <stdio.h>
 209
 210 static void
 211 do_print (const void *nodep, VISIT value, int level)
 212 {
 213   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 214
 215   printf ("%10s: \"%s\", %d\n",
 216           value == leaf ? "leaf"
 217           : value == preorder ? "preorder"
 218           : value == postorder ? "postorder" : "endorder",
 219           obj->name, obj->counter);
 220 }
 221
 222 static void __attribute__ ((used))
 223 print_all (void)
 224 {
 225   __twalk (loaded, do_print);
 226 }
 227 #endif