/* Handle loading/unloading of shared object for transformation.

   Copyright (C) 1997-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <assert.h>

#include <dlfcn.h>

#include <inttypes.h>

#include <search.h>

#include <stdlib.h>

#include <string.h>

#include <libc-lock.h>

#include <sys/param.h>

#include <gconv_int.h>

#include <sysdep.h>

#ifdef DEBUG

/* For debugging purposes.  */

static void print_all (void);

#endif

/* This is a tuning parameter.  If a transformation module is not used

   anymore it gets not immediately unloaded.  Instead we wait a certain

   number of load attempts for further modules.  If none of the

   subsequent load attempts name the same object it finally gets unloaded.

   Otherwise it is still available which hopefully is the frequent case.

   The following number is the number of unloading attempts we wait

   before unloading.  */

#define TRIES_BEFORE_UNLOAD	2

/* Array of loaded objects.  This is shared by all threads so we have

   to use semaphores to access it.  */

static void *loaded;

/* Comparison function for searching `loaded_object' tree.  */

static int

known_compare (const void *p1, const void *p2)

{

  const struct __gconv_loaded_object *s1 =

    (const struct __gconv_loaded_object *) p1;

  const struct __gconv_loaded_object *s2 =

    (const struct __gconv_loaded_object *) p2;

  return strcmp (s1->name, s2->name);

}

/* Open the gconv database if necessary.  A non-negative return value

   means success.  */

struct __gconv_loaded_object *

__gconv_find_shlib (const char *name)

{

  struct __gconv_loaded_object *found;

  void *keyp;

  /* Search the tree of shared objects previously requested.  Data in

     the tree are `loaded_object' structures, whose first member is a

     `const char *', the lookup key.  The search returns a pointer to

     the tree node structure; the first member of the is a pointer to

     our structure (i.e. what will be a `loaded_object'); since the

     first member of that is the lookup key string, &FCT_NAME is close

     enough to a pointer to our structure to use as a lookup key that

     will be passed to `known_compare' (above).  */

  keyp = __tfind (&name, &loaded, known_compare);

  if (keyp == NULL)

    {

      /* This name was not known before.  */

      size_t namelen = strlen (name) + 1;

      found = malloc (sizeof (struct __gconv_loaded_object) + namelen);

      if (found != NULL)

	{

	  /* Point the tree node at this new structure.  */

	  found->name = (char *) memcpy (found + 1, name, namelen);

	  found->counter = -TRIES_BEFORE_UNLOAD - 1;

	  found->handle = NULL;

	  if (__builtin_expect (__tsearch (found, &loaded, known_compare)

				== NULL, 0))

	    {

	      /* Something went wrong while inserting the entry.  */

	      free (found);

	      found = NULL;

	    }

	}

    }

  else

    found = *(struct __gconv_loaded_object **) keyp;

  /* Try to load the shared object if the usage count is 0.  This

     implies that if the shared object is not loadable, the handle is

     NULL and the usage count > 0.  */

  if (found != NULL)

    {

      if (found->counter < -TRIES_BEFORE_UNLOAD)

	{

	  assert (found->handle == NULL);

	  found->handle = __libc_dlopen (found->name);

	  if (found->handle != NULL)

	    {

	      found->fct = __libc_dlsym (found->handle, "gconv");

	      if (found->fct == NULL)

		{

		  /* Argh, no conversion function.  There is something

                     wrong here.  */

		  __gconv_release_shlib (found);

		  found = NULL;

		}

	      else

		{

		  found->init_fct = __libc_dlsym (found->handle, "gconv_init");

		  found->end_fct = __libc_dlsym (found->handle, "gconv_end");

#ifdef PTR_MANGLE

		  PTR_MANGLE (found->fct);

		  PTR_MANGLE (found->init_fct);

		  PTR_MANGLE (found->end_fct);

#endif

		  /* We have succeeded in loading the shared object.  */

		  found->counter = 1;

		}

	    }

	  else

	    /* Error while loading the shared object.  */

	    found = NULL;

	}

      else if (found->handle != NULL)

	found->counter = MAX (found->counter + 1, 1);

    }

  return found;

}

/* This is very ugly but the tsearch functions provide no way to pass

   information to the walker function.  So we use a global variable.

   It is MT safe since we use a lock.  */

static struct __gconv_loaded_object *release_handle;

static void

do_release_shlib (void *nodep, VISIT value, int level)

{

  struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;

  if (value != preorder && value != leaf)

    return;

  if (obj == release_handle)

    {

      /* This is the object we want to unload.  Now decrement the

	 reference counter.  */

      assert (obj->counter > 0);

      --obj->counter;

    }

  else if (obj->counter <= 0 && obj->counter >= -TRIES_BEFORE_UNLOAD

	   && --obj->counter < -TRIES_BEFORE_UNLOAD && obj->handle != NULL)

    {

      /* Unload the shared object.  */

      __libc_dlclose (obj->handle);

      obj->handle = NULL;

    }

}

/* Notify system that a shared object is not longer needed.  */

void

__gconv_release_shlib (struct __gconv_loaded_object *handle)

{

  /* Urgh, this is ugly but we have no other possibility.  */

  release_handle = handle;

  /* Process all entries.  Please note that we also visit entries

     with release counts <= 0.  This way we can finally unload them

     if necessary.  */

  __twalk (loaded, (__action_fn_t) do_release_shlib);

}

/* We run this if we debug the memory allocation.  */

static void __libc_freeres_fn_section

do_release_all (void *nodep)

{

  struct __gconv_loaded_object *obj = (struct __gconv_loaded_object *) nodep;

  /* Unload the shared object.  */

  if (obj->handle != NULL)

    __libc_dlclose (obj->handle);

  free (obj);

}

libc_freeres_fn (free_mem)

{

  __tdestroy (loaded, do_release_all);

  loaded = NULL;

}

#ifdef DEBUG

#include <stdio.h>

static void

do_print (const void *nodep, VISIT value, int level)

{

  struct __gconv_loaded_object *obj = *(struct __gconv_loaded_object **) nodep;

  printf ("%10s: \"%s\", %d\n",

	  value == leaf ? "leaf" :

	  value == preorder ? "preorder" :

	  value == postorder ? "postorder" : "endorder",

	  obj->name, obj->counter);

}

static void __attribute__ ((used))

print_all (void)

{

  __twalk (loaded, do_print);

}

#endif