iconv/gconv_dl.c

   1 /* Handle loading/unloading of shared object for transformation.
   2    Copyright (C) 1997, 1998 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 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.
  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    Library General Public License for more details.
  15
  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.  */
  20
  21 #include <dlfcn.h>
  22 #include <gconv.h>
  23 #include <inttypes.h>
  24 #include <link.h>
  25 #include <search.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <bits/libc-lock.h>
  29 #include <sys/param.h>
  30
  31
  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
  38    before unloading.  */
  39 #define TRIES_BEFORE_UNLOAD     2
  40
  41
  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.  */
  45 struct loaded_object
  46 {
  47   /* Name of the object.  */
  48   const char *name;
  49
  50   /* Reference counter for the db functionality.  If no conversion is
  51      needed we unload the db library.  */
  52   int counter;
  53
  54   /* The handle for the shared object.  */
  55   void *handle;
  56 };
  57
  58
  59 /* Array of loaded objects.  This is shared by all threads so we have
  60    to use semaphores to access it.  */
  61 static void *loaded;
  62 __libc_lock_define_initialized (static, lock)
  63
  64
  65
  66 /* Comparison function for searching `loaded_object' tree.  */
  67 static int
  68 known_compare (const void *p1, const void *p2)
  69 {
  70   const struct loaded_object *s1 = (const struct loaded_object *) p1;
  71   const struct loaded_object *s2 = (const struct loaded_object *) p2;
  72
  73   return (intptr_t) s1->handle - (intptr_t) s2->handle;
  74 }
  75
  76
  77 static void
  78 do_open (void *a)
  79 {
  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);
  83 }
  84
  85
  86 static int
  87 internal_function
  88 dlerror_run (void (*operate) (void *), void *args)
  89 {
  90   char *last_errstring = NULL;
  91   int result;
  92
  93   (void) _dl_catch_error (&last_errstring, operate, args);
  94
  95   result = last_errstring != NULL;
  96   if (result)
  97     free (last_errstring);
  98
  99   return result;
 100 }
 101
 102
 103 struct get_sym_args
 104 {
 105   /* Arguments to get_sym.  */
 106   struct link_map *map;
 107   const char *name;
 108
 109   /* Return values of get_sym.  */
 110   ElfW(Addr) loadbase;
 111   const ElfW(Sym) *ref;
 112 };
 113
 114 static void
 115 get_sym (void *a)
 116 {
 117   struct get_sym_args *args = (struct get_sym_args *) a;
 118   struct link_map *scope[2] = { args->map, NULL };
 119   args->ref = NULL;
 120   args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
 121                                       scope, args->map->l_name, 0);
 122 }
 123
 124
 125 void *
 126 __gconv_find_func (void *handle, const char *name)
 127 {
 128   struct get_sym_args args;
 129
 130   args.map = handle;
 131   args.name = name;
 132
 133   return (dlerror_run (get_sym, &args) ? NULL
 134           : (void *) (args.loadbase + args.ref->st_value));
 135 }
 136
 137
 138
 139 /* Open the gconv database if necessary.  A non-negative return value
 140    means success.  */
 141 void *
 142 __gconv_find_shlib (const char *name)
 143 {
 144   void *result = NULL;
 145   struct loaded_object *found;
 146
 147   /* Acquire the lock.  */
 148   __libc_lock_lock (lock);
 149
 150   /* Search the tree of shared objects previously requested.  Data in
 151      the tree are `loaded_object' structures, whose first member is a
 152      `const char *', the lookup key.  The search returns a pointer to
 153      the tree node structure; the first member of the is a pointer to
 154      our structure (i.e. what will be a `loaded_object'); since the
 155      first member of that is the lookup key string, &FCT_NAME is close
 156      enough to a pointer to our structure to use as a lookup key that
 157      will be passed to `known_compare' (above).  */
 158
 159   found = __tfind (&name, &loaded, known_compare);
 160   if (found == NULL)
 161     {
 162       /* This name was not known before.  */
 163       found = malloc (sizeof (struct loaded_object));
 164       if (found != NULL)
 165         {
 166           /* Point the tree node at this new structure.  */
 167           found->name = name;
 168           found->counter = -TRIES_BEFORE_UNLOAD - 1;
 169           found->handle = NULL;
 170
 171           if (__tsearch (found, &loaded, known_compare) == NULL)
 172             {
 173               /* Something went wrong while inserting the entry.  */
 174               free (found);
 175               found = NULL;
 176             }
 177         }
 178     }
 179
 180   /* Try to load the shared object if the usage count is 0.  This
 181      implies that if the shared object is not loadable, the handle is
 182      NULL and the usage count > 0.  */
 183   if (found != NULL)
 184     {
 185       if (found->counter < -TRIES_BEFORE_UNLOAD)
 186         {
 187           if (dlerror_run (do_open, found) == 0)
 188             found->counter = 1;
 189         }
 190       else if (found->handle != NULL)
 191         found->counter = MAX (found->counter + 1, 1);
 192
 193       result = found->handle;
 194     }
 195
 196   /* Release the lock.  */
 197   __libc_lock_unlock (lock);
 198
 199   return result;
 200 }
 201
 202
 203 /* This is very ugly but the tsearch functions provide no way to pass
 204    information to the walker function.  So we use a global variable.
 205    It is MT safe since we use a lock.  */
 206 static void *release_handle;
 207
 208 static void
 209 do_release_shlib (const void *nodep, VISIT value, int level)
 210 {
 211   struct loaded_object *obj = *(struct loaded_object **) nodep;
 212
 213   if (value != preorder && value != leaf)
 214     return;
 215
 216   if (obj->handle == release_handle)
 217     /* This is the object we want to unload.  Now set the release
 218        counter to zero.  */
 219     obj->counter = 0;
 220   else if (obj->counter <= 0)
 221     {
 222       if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
 223         {
 224           /* Unload the shared object.  We don't use the trick to
 225              catch errors since in the case an error is signalled
 226              something is really wrong.  */
 227           _dl_close ((struct link_map *) obj->handle);
 228
 229           obj->handle = NULL;
 230         }
 231     }
 232 }
 233
 234
 235 /* Notify system that a shared object is not longer needed.  */
 236 int
 237 __gconv_release_shlib (void *handle)
 238 {
 239   /* Acquire the lock.  */
 240   __libc_lock_lock (lock);
 241
 242   /* Urgh, this is ugly but we have no other possibility.  */
 243   release_handle = handle;
 244
 245   /* Process all entries.  Please note that we also visit entries
 246      with release counts <= 0.  This way we can finally unload them
 247      if necessary.  */
 248   __twalk (loaded, do_release_shlib);
 249
 250   /* Release the lock.  */
 251   __libc_lock_unlock (lock);
 252
 253   return GCONV_OK;
 254 }