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 <inttypes.h>
  23 #include <search.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <bits/libc-lock.h>
  27 #include <elf/ldsodefs.h>
  28 #include <sys/param.h>
  29
  30 #include <gconv_int.h>
  31
  32
  33 /* This is a tuning parameter.  If a transformation module is not used
  34    anymore it gets not immediately unloaded.  Instead we wait a certain
  35    number of load attempts for further modules.  If none of the
  36    subsequent load attempts name the same object it finally gets unloaded.
  37    Otherwise it is still available which hopefully is the frequent case.
  38    The following number is the number of unloading attempts we wait
  39    before unloading.  */
  40 #define TRIES_BEFORE_UNLOAD     2
  41
  42
  43 /* Array of loaded objects.  This is shared by all threads so we have
  44    to use semaphores to access it.  */
  45 static void *loaded;
  46
  47
  48
  49 /* Comparison function for searching `loaded_object' tree.  */
  50 static int
  51 known_compare (const void *p1, const void *p2)
  52 {
  53   const struct gconv_loaded_object *s1 =
  54     (const struct gconv_loaded_object *) p1;
  55   const struct gconv_loaded_object *s2 =
  56     (const struct gconv_loaded_object *) p2;
  57
  58   return (intptr_t) s1->handle - (intptr_t) s2->handle;
  59 }
  60
  61
  62 static void
  63 do_open (void *a)
  64 {
  65   struct gconv_loaded_object *args = (struct gconv_loaded_object *) a;
  66   /* Open and relocate the shared object.  */
  67   args->handle = _dl_open (args->name, RTLD_LAZY);
  68 }
  69
  70
  71 static int
  72 internal_function
  73 dlerror_run (void (*operate) (void *), void *args)
  74 {
  75   char *last_errstring = NULL;
  76   int result;
  77
  78   (void) _dl_catch_error (&last_errstring, operate, args);
  79
  80   result = last_errstring != NULL;
  81   if (result)
  82     free (last_errstring);
  83
  84   return result;
  85 }
  86
  87
  88 struct get_sym_args
  89 {
  90   /* Arguments to get_sym.  */
  91   struct link_map *map;
  92   const char *name;
  93
  94   /* Return values of get_sym.  */
  95   ElfW(Addr) loadbase;
  96   const ElfW(Sym) *ref;
  97 };
  98
  99 static void
 100 get_sym (void *a)
 101 {
 102   struct get_sym_args *args = (struct get_sym_args *) a;
 103   struct link_map *scope[2] = { args->map, NULL };
 104   args->ref = NULL;
 105   args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
 106                                       scope, args->map->l_name, 0);
 107 }
 108
 109
 110 void *
 111 internal_function
 112 __gconv_find_func (void *handle, const char *name)
 113 {
 114   struct get_sym_args args;
 115
 116   args.map = handle;
 117   args.name = name;
 118
 119   return (dlerror_run (get_sym, &args) ? NULL
 120           : (void *) (args.loadbase + args.ref->st_value));
 121 }
 122
 123
 124
 125 /* Open the gconv database if necessary.  A non-negative return value
 126    means success.  */
 127 struct gconv_loaded_object *
 128 internal_function
 129 __gconv_find_shlib (const char *name)
 130 {
 131   struct gconv_loaded_object *found;
 132
 133   /* Search the tree of shared objects previously requested.  Data in
 134      the tree are `loaded_object' structures, whose first member is a
 135      `const char *', the lookup key.  The search returns a pointer to
 136      the tree node structure; the first member of the is a pointer to
 137      our structure (i.e. what will be a `loaded_object'); since the
 138      first member of that is the lookup key string, &FCT_NAME is close
 139      enough to a pointer to our structure to use as a lookup key that
 140      will be passed to `known_compare' (above).  */
 141
 142   found = __tfind (&name, &loaded, known_compare);
 143   if (found == NULL)
 144     {
 145       /* This name was not known before.  */
 146       found = malloc (sizeof (struct gconv_loaded_object));
 147       if (found != NULL)
 148         {
 149           /* Point the tree node at this new structure.  */
 150           found->name = name;
 151           found->counter = -TRIES_BEFORE_UNLOAD - 1;
 152           found->handle = NULL;
 153
 154           if (__tsearch (found, &loaded, known_compare) == NULL)
 155             {
 156               /* Something went wrong while inserting the entry.  */
 157               free (found);
 158               found = NULL;
 159             }
 160         }
 161     }
 162
 163   /* Try to load the shared object if the usage count is 0.  This
 164      implies that if the shared object is not loadable, the handle is
 165      NULL and the usage count > 0.  */
 166   if (found != NULL)
 167     {
 168       if (found->counter < -TRIES_BEFORE_UNLOAD)
 169         {
 170           if (dlerror_run (do_open, found) == 0)
 171             {
 172               found->fct = __gconv_find_func (found->handle, "gconv");
 173               if (found->fct == NULL)
 174                 {
 175                   /* Argh, no conversion function.  There is something
 176                      wrong here.  */
 177                   __gconv_release_shlib (found);
 178                   found = NULL;
 179                 }
 180               else
 181                 {
 182                   found->init_fct = __gconv_find_func (found->handle,
 183                                                        "gconv_init");
 184                   found->end_fct = __gconv_find_func (found->handle,
 185                                                       "gconv_end");
 186
 187                   /* We have succeeded in loading the shared object.  */
 188                   found->counter = 1;
 189                 }
 190             }
 191           else
 192             /* Error while loading the shared object.  */
 193             found = NULL;
 194         }
 195       else if (found->handle != NULL)
 196         found->counter = MAX (found->counter + 1, 1);
 197     }
 198
 199   return found;
 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 struct gconv_loaded_object *release_handle;
 207
 208 static void
 209 do_release_shlib (const void *nodep, VISIT value, int level)
 210 {
 211   struct gconv_loaded_object *obj = *(struct gconv_loaded_object **) nodep;
 212
 213   if (value != preorder && value != leaf)
 214     return;
 215
 216   if (obj == 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 (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 internal_function
 238 __gconv_release_shlib (struct gconv_loaded_object *handle)
 239 {
 240   /* Urgh, this is ugly but we have no other possibility.  */
 241   release_handle = handle;
 242
 243   /* Process all entries.  Please note that we also visit entries
 244      with release counts <= 0.  This way we can finally unload them
 245      if necessary.  */
 246   __twalk (loaded, do_release_shlib);
 247
 248   return GCONV_OK;
 249 }