255 lines
6.9 KiB
C
255 lines
6.9 KiB
C
/* Handle loading/unloading of shared object for transformation.
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Copyright (C) 1997 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <dlfcn.h>
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#include <gconv.h>
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#include <inttypes.h>
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#include <link.h>
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#include <search.h>
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#include <stdlib.h>
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#include <string.h>
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#include <bits/libc-lock.h>
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#include <sys/param.h>
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/* This is a tuning parameter. If a transformation module is not used
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anymore it gets not immediately unloaded. Instead we wait a certain
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number of load attempts for further modules. If none of the
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subsequent load attempts name the same object it finally gets unloaded.
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Otherwise it is still available which hopefully is the frequent case.
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The following number is the number of unloading attempts we wait
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before unloading. */
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#define TRIES_BEFORE_UNLOAD 2
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/* Structure describing one loaded shared object. This normally are
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objects to perform conversation but as a special case the db shared
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object is also handled. */
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struct loaded_object
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{
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/* Name of the object. */
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const char *name;
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/* Reference counter for the db functionality. If no conversion is
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needed we unload the db library. */
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int counter;
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/* The handle for the shared object. */
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void *handle;
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};
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/* Array of loaded objects. This is shared by all threads so we have
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to use semaphores to access it. */
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static void *loaded;
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__libc_lock_define_initialized (static, lock)
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/* Comparison function for searching `loaded_object' tree. */
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static int
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known_compare (const void *p1, const void *p2)
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{
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const struct loaded_object *s1 = (const struct loaded_object *) p1;
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const struct loaded_object *s2 = (const struct loaded_object *) p2;
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return (intptr_t) s1->handle - (intptr_t) s2->handle;
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}
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static void
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do_open (void *a)
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{
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struct loaded_object *args = (struct loaded_object *) a;
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/* Open and relocate the shared object. */
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args->handle = _dl_open (args->name, RTLD_LAZY);
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}
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static int
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dlerror_run (void (*operate) (void *), void *args)
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{
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char *last_errstring = NULL;
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const char *last_object_name = NULL;
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int result;
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(void) _dl_catch_error (&last_errstring, &last_object_name, operate, args);
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result = last_errstring != NULL;
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if (result)
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free (last_errstring);
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return result;
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}
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struct get_sym_args
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{
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/* Arguments to get_sym. */
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struct link_map *map;
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const char *name;
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/* Return values of get_sym. */
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ElfW(Addr) loadbase;
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const ElfW(Sym) *ref;
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};
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static void
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get_sym (void *a)
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{
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struct get_sym_args *args = (struct get_sym_args *) a;
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struct link_map *scope[2] = { args->map, NULL };
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args->ref = NULL;
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args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
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scope, args->map->l_name, 0);
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}
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void *
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__gconv_find_func (void *handle, const char *name)
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{
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struct get_sym_args args;
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args.map = handle;
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args.name = name;
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return (dlerror_run (get_sym, &args) ? NULL
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: (void *) (args.loadbase + args.ref->st_value));
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}
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/* Open the gconv database if necessary. A non-negative return value
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means success. */
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void *
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__gconv_find_shlib (const char *name)
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{
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void *result = NULL;
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struct loaded_object *found;
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/* Acquire the lock. */
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__libc_lock_lock (lock);
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/* Search the tree of shared objects previously requested. Data in
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the tree are `loaded_object' structures, whose first member is a
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`const char *', the lookup key. The search returns a pointer to
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the tree node structure; the first member of the is a pointer to
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our structure (i.e. what will be a `loaded_object'); since the
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first member of that is the lookup key string, &FCT_NAME is close
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enough to a pointer to our structure to use as a lookup key that
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will be passed to `known_compare' (above). */
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found = __tfind (&name, loaded, known_compare);
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if (found == NULL)
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{
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/* This name was not known before. */
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found = malloc (sizeof (struct loaded_object));
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if (found != NULL)
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{
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/* Point the tree node at this new structure. */
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found->name = name;
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found->counter = -TRIES_BEFORE_UNLOAD - 1;
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found->handle = NULL;
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if (__tsearch (found, &loaded, known_compare) == NULL)
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{
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/* Something went wrong while inserting the entry. */
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free (found);
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found = NULL;
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}
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}
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}
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/* Try to load the shared object if the usage count is 0. This
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implies that if the shared object is not loadable, the handle is
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NULL and the usage count > 0. */
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if (found != NULL)
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{
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if (found->counter < -TRIES_BEFORE_UNLOAD)
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{
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if (dlerror_run (do_open, found) == 0)
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found->counter = 1;
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}
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else if (found->handle != NULL)
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found->counter = MAX (found->counter + 1, 1);
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result = found->handle;
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}
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/* Release the lock. */
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__libc_lock_unlock (lock);
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return result;
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}
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/* This is very ugly but the tsearch functions provide no way to pass
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information to the walker function. So we use a global variable.
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It is MT safe since we use a lock. */
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static void *release_handle;
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static void
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do_release_shlib (const void *nodep, VISIT value, int level)
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{
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struct loaded_object *obj = (struct loaded_object *) nodep;
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if (value != preorder && value != leaf)
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return;
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if (obj->handle == release_handle)
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/* This is the object we want to unload. Now set the release
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counter to zero. */
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obj->counter = 0;
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else if (obj->counter <= 0)
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{
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if (--obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)
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{
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/* Unload the shared object. We don't use the trick to
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catch errors since in the case an error is signalled
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something is really wrong. */
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_dl_close ((struct link_map *) obj->handle);
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obj->handle = NULL;
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}
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}
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}
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/* Notify system that a shared object is not longer needed. */
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int
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__gconv_release_shlib (void *handle)
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{
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/* Acquire the lock. */
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__libc_lock_lock (lock);
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/* Urgh, this is ugly but we have no other possibility. */
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release_handle = handle;
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/* Process all entries. Please note that we also visit entries
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with release counts <= 0. This way we can finally unload them
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if necessary. */
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__twalk (loaded, do_release_shlib);
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/* Release the lock. */
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__libc_lock_unlock (lock);
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return GCONV_OK;
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}
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