iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997-2022 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 <sysdep.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 #ifdef PTR_MANGLE
 131                   PTR_MANGLE (found->fct);
 132                   PTR_MANGLE (found->init_fct);
 133                   PTR_MANGLE (found->end_fct);
 134 #endif
 135
 136                   /* We have succeeded in loading the shared object.  */
 137                   found->counter = 1;
 138                 }
 139             }
 140           else
 141             /* Error while loading the shared object.  */
 142             found = NULL;
 143         }
 144       else if (found->handle != NULL)
 145         found->counter = MAX (found->counter + 1, 1);
 146     }
 147
 148   return found;
 149 }
 150
 151 static void
 152 do_release_shlib (const void *nodep, VISIT value, void *closure)
 153 {
 154   struct __gconv_loaded_object *release_handle = closure;
 155   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 156
 157   if (value != preorder && value != leaf)
 158     return;
 159
 160   if (obj == release_handle)
 161     {
 162       /* This is the object we want to unload.  Now decrement the
 163          reference counter.  */
 164       assert (obj->counter > 0);
 165       --obj->counter;
 166     }
 167   else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD
 168            && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 169     {
 170       /* Unload the shared object.  */
 171       __libc_dlclose (obj->handle);
 172       obj->handle = NULL;
 173     }
 174 }
 175
 176
 177 /* Notify system that a shared object is not longer needed.  */
 178 void
 179 __gconv_release_shlib (struct __gconv_loaded_object *handle)
 180 {
 181   /* Process all entries.  Please note that we also visit entries
 182      with release counts <= 0.  This way we can finally unload them
 183      if necessary.  */
 184   __twalk_r (loaded, do_release_shlib, handle);
 185 }
 186
 187
 188 /* We run this if we debug the memory allocation.  */
 189 static void __libc_freeres_fn_section
 190 do_release_all (void *nodep)
 191 {
 192   struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;
 193
 194   /* Unload the shared object.  */
 195   if (obj->handle != NULL)
 196     __libc_dlclose (obj->handle);
 197
 198   free (obj);
 199 }
 200
 201 libc_freeres_fn (free_mem)
 202 {
 203   __tdestroy (loaded, do_release_all);
 204   loaded = NULL;
 205 }
 206
 207
 208 #ifdef DEBUG
 209
 210 #include <stdio.h>
 211
 212 static void
 213 do_print (const void *nodep, VISIT value, int level)
 214 {
 215   struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;
 216
 217   printf ("%10s: \"%s\", %d\n",
 218           value == leaf ? "leaf"
 219           : value == preorder ? "preorder"
 220           : value == postorder ? "postorder" : "endorder",
 221           obj->name, obj->counter);
 222 }
 223
 224 static void __attribute__ ((used))
 225 print_all (void)
 226 {
 227   __twalk (loaded, do_print);
 228 }
 229 #endif