path: root/elf/dl-open.c

/* Load a shared object at runtime, relocate it, and run its initializer.
   Copyright (C) 1996-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   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 <errno.h>
#include <libintl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>		/* Check whether MAP_COPY is defined.  */
#include <sys/param.h>
#include <libc-lock.h>
#include <ldsodefs.h>
#include <caller.h>
#include <sysdep-cancel.h>
#include <tls.h>
#include <stap-probe.h>
#include <atomic.h>

#include <dl-dst.h>


extern int __libc_multiple_libcs;	/* Defined in init-first.c.  */

/* We must be careful not to leave us in an inconsistent state.  Thus we
   catch any error and re-raise it after cleaning up.  */

struct dl_open_args
{
  const char *file;
  int mode;
  /* This is the caller of the dlopen() function.  */
  const void *caller_dlopen;
  /* This is the caller of _dl_open().  */
  const void *caller_dl_open;
  struct link_map *map;
  /* Namespace ID.  */
  Lmid_t nsid;
  /* Original parameters to the program and the current environment.  */
  int argc;
  char **argv;
  char **env;
};


static int
add_to_global (struct link_map *new)
{
  struct link_map **new_global;
  unsigned int to_add = 0;
  unsigned int cnt;

  /* Count the objects we have to put in the global scope.  */
  for (cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
    if (new->l_searchlist.r_list[cnt]->l_global == 0)
      ++to_add;

  /* The symbols of the new objects and its dependencies are to be
     introduced into the global scope that will be used to resolve
     references from other dynamically-loaded objects.

     The global scope is the searchlist in the main link map.  We
     extend this list if necessary.  There is one problem though:
     since this structure was allocated very early (before the libc
     is loaded) the memory it uses is allocated by the malloc()-stub
     in the ld.so.  When we come here these functions are not used
     anymore.  Instead the malloc() implementation of the libc is
     used.  But this means the block from the main map cannot be used
     in an realloc() call.  Therefore we allocate a completely new
     array the first time we have to add something to the locale scope.  */

  struct link_namespaces *ns = &GL(dl_ns)[new->l_ns];
  if (ns->_ns_global_scope_alloc == 0)
    {
      /* This is the first dynamic object given global scope.  */
      ns->_ns_global_scope_alloc
	= ns->_ns_main_searchlist->r_nlist + to_add + 8;
      new_global = (struct link_map **)
	malloc (ns->_ns_global_scope_alloc * sizeof (struct link_map *));
      if (new_global == NULL)
	{
	  ns->_ns_global_scope_alloc = 0;
	nomem:
	  _dl_signal_error (ENOMEM, new->l_libname->name, NULL,
			    N_("cannot extend global scope"));
	  return 1;
	}

      /* Copy over the old entries.  */
      ns->_ns_main_searchlist->r_list
	= memcpy (new_global, ns->_ns_main_searchlist->r_list,
		  (ns->_ns_main_searchlist->r_nlist
		   * sizeof (struct link_map *)));
    }
  else if (ns->_ns_main_searchlist->r_nlist + to_add
	   > ns->_ns_global_scope_alloc)
    {
      /* We have to extend the existing array of link maps in the
	 main map.  */
      struct link_map **old_global
	= GL(dl_ns)[new->l_ns]._ns_main_searchlist->r_list;
      size_t new_nalloc = ((ns->_ns_global_scope_alloc + to_add) * 2);

      new_global = (struct link_map **)
	malloc (new_nalloc * sizeof (struct link_map *));
      if (new_global == NULL)
	goto nomem;

      memcpy (new_global, old_global,
	      ns->_ns_global_scope_alloc * sizeof (struct link_map *));

      ns->_ns_global_scope_alloc = new_nalloc;
      ns->_ns_main_searchlist->r_list = new_global;

      if (!RTLD_SINGLE_THREAD_P)
	THREAD_GSCOPE_WAIT ();

      free (old_global);
    }

  /* Now add the new entries.  */
  unsigned int new_nlist = ns->_ns_main_searchlist->r_nlist;
  for (cnt = 0; cnt < new->l_searchlist.r_nlist; ++cnt)
    {
      struct link_map *map = new->l_searchlist.r_list[cnt];

      if (map->l_global == 0)
	{
	  map->l_global = 1;
	  ns->_ns_main_searchlist->r_list[new_nlist++] = map;

	  /* We modify the global scope.  Report this.  */
	  if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_SCOPES))
	    _dl_debug_printf ("\nadd %s [%lu] to global scope\n",
			      map->l_name, map->l_ns);
	}
    }
  atomic_write_barrier ();
  ns->_ns_main_searchlist->r_nlist = new_nlist;

  return 0;
}

/* Search link maps in all namespaces for the DSO that contains the object at
   address ADDR.  Returns the pointer to the link map of the matching DSO, or
   NULL if a match is not found.  */
struct link_map *
internal_function
_dl_find_dso_for_object (const ElfW(Addr) addr)
{
  struct link_map *l;

  /* Find the highest-addressed object that ADDR is not below.  */
  for (Lmid_t ns = 0; ns < GL(dl_nns); ++ns)
    for (l = GL(dl_ns)[ns]._ns_loaded; l != NULL; l = l->l_next)
      if (addr >= l->l_map_start && addr < l->l_map_end
	  && (l->l_contiguous
	      || _dl_addr_inside_object (l, (ElfW(Addr)) addr)))
	{
	  assert (ns == l->l_ns);
	  return l;
	}
  return NULL;
}
rtld_hidden_def (_dl_find_dso_for_object);

static void
dl_open_worker (void *a)
{
  struct dl_open_args *args = a;
  const char *file = args->file;
  int mode = args->mode;
  struct link_map *call_map = NULL;

  /* Check whether _dl_open() has been called from a valid DSO.  */
  if (__check_caller (args->caller_dl_open,
		      allow_libc|allow_libdl|allow_ldso) != 0)
    _dl_signal_error (0, "dlopen", NULL, N_("invalid caller"));

  /* Determine the caller's map if necessary.  This is needed in case
     we have a DST, when we don't know the namespace ID we have to put
     the new object in, or when the file name has no path in which
     case we need to look along the RUNPATH/RPATH of the caller.  */
  const char *dst = strchr (file, '$');
  if (dst != NULL || args->nsid == __LM_ID_CALLER
      || strchr (file, '/') == NULL)
    {
      const void *caller_dlopen = args->caller_dlopen;

      /* We have to find out from which object the caller is calling.
	 By default we assume this is the main application.  */
      call_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;

      struct link_map *l = _dl_find_dso_for_object ((ElfW(Addr)) caller_dlopen);

      if (l)
	call_map = l;

      if (args->nsid == __LM_ID_CALLER)
	args->nsid = call_map->l_ns;
    }

  /* One might be tempted to assert that we are RT_CONSISTENT at this point, but that
     may not be true if this is a recursive call to dlopen.  */
  _dl_debug_initialize (0, args->nsid);

  /* Load the named object.  */
  struct link_map *new;
  args->map = new = _dl_map_object (call_map, file, lt_loaded, 0,
				    mode | __RTLD_CALLMAP, args->nsid);

  /* If the pointer returned is NULL this means the RTLD_NOLOAD flag is
     set and the object is not already loaded.  */
  if (new == NULL)
    {
      assert (mode & RTLD_NOLOAD);
      return;
    }

  /* Mark the object as not deletable if the RTLD_NODELETE flags was passed.
     Do this early so that we don't skip marking the object if it was
     already loaded.  */
  if (__glibc_unlikely (mode & RTLD_NODELETE))
    new->l_flags_1 |= DF_1_NODELETE;

  if (__glibc_unlikely (mode & __RTLD_SPROF))
    /* This happens only if we load a DSO for 'sprof'.  */
    return;

  /* This object is directly loaded.  */
  ++new->l_direct_opencount;

  /* It was already open.  */
  if (__glibc_unlikely (new->l_searchlist.r_list != NULL))
    {
      /* Let the user know about the opencount.  */
      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
	_dl_debug_printf ("opening file=%s [%lu]; direct_opencount=%u\n\n",
			  new->l_name, new->l_ns, new->l_direct_opencount);

      /* If the user requested the object to be in the global namespace
	 but it is not so far, add it now.  */
      if ((mode & RTLD_GLOBAL) && new->l_global == 0)
	(void) add_to_global (new);

      assert (_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT);

      return;
    }

  /* Load that object's dependencies.  */
  _dl_map_object_deps (new, NULL, 0, 0,
		       mode & (__RTLD_DLOPEN | RTLD_DEEPBIND | __RTLD_AUDIT));

  /* So far, so good.  Now check the versions.  */
  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
    if (new->l_searchlist.r_list[i]->l_real->l_versions == NULL)
      (void) _dl_check_map_versions (new->l_searchlist.r_list[i]->l_real,
				     0, 0);

#ifdef SHARED
  /* Auditing checkpoint: we have added all objects.  */
  if (__glibc_unlikely (GLRO(dl_naudit) > 0))
    {
      struct link_map *head = GL(dl_ns)[new->l_ns]._ns_loaded;
      /* Do not call the functions for any auditing object.  */
      if (head->l_auditing == 0)
	{
	  struct audit_ifaces *afct = GLRO(dl_audit);
	  for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
	    {
	      if (afct->activity != NULL)
		afct->activity (&head->l_audit[cnt].cookie, LA_ACT_CONSISTENT);

	      afct = afct->next;
	    }
	}
    }
#endif

  /* Notify the debugger all new objects are now ready to go.  */
  struct r_debug *r = _dl_debug_initialize (0, args->nsid);
  r->r_state = RT_CONSISTENT;
  _dl_debug_state ();
  LIBC_PROBE (map_complete, 3, args->nsid, r, new);

  /* Print scope information.  */
  if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_SCOPES))
    _dl_show_scope (new, 0);

  /* Only do lazy relocation if `LD_BIND_NOW' is not set.  */
  int reloc_mode = mode & __RTLD_AUDIT;
  if (GLRO(dl_lazy))
    reloc_mode |= mode & RTLD_LAZY;

  /* Sort the objects by dependency for the relocation process.  This
     allows IFUNC relocations to work and it also means copy
     relocation of dependencies are if necessary overwritten.  */
  size_t nmaps = 0;
  struct link_map *l = new;
  do
    {
      if (! l->l_real->l_relocated)
	++nmaps;
      l = l->l_next;
    }
  while (l != NULL);
  struct link_map *maps[nmaps];
  nmaps = 0;
  l = new;
  do
    {
      if (! l->l_real->l_relocated)
	maps[nmaps++] = l;
      l = l->l_next;
    }
  while (l != NULL);
  if (nmaps > 1)
    {
      uint16_t seen[nmaps];
      memset (seen, '\0', sizeof (seen));
      size_t i = 0;
      while (1)
	{
	  ++seen[i];
	  struct link_map *thisp = maps[i];

	  /* Find the last object in the list for which the current one is
	     a dependency and move the current object behind the object
	     with the dependency.  */
	  size_t k = nmaps - 1;
	  while (k > i)
	    {
	      struct link_map **runp = maps[k]->l_initfini;
	      if (runp != NULL)
		/* Look through the dependencies of the object.  */
		while (*runp != NULL)
		  if (__glibc_unlikely (*runp++ == thisp))
		    {
		      /* Move the current object to the back past the last
			 object with it as the dependency.  */
		      memmove (&maps[i], &maps[i + 1],
			       (k - i) * sizeof (maps[0]));
		      maps[k] = thisp;

		      if (seen[i + 1] > nmaps - i)
			{
			  ++i;
			  goto next_clear;
			}

		      uint16_t this_seen = seen[i];
		      memmove (&seen[i], &seen[i + 1],
			       (k - i) * sizeof (seen[0]));
		      seen[k] = this_seen;

		      goto next;
		    }

	      --k;
	    }

	  if (++i == nmaps)
	    break;
	next_clear:
	  memset (&seen[i], 0, (nmaps - i) * sizeof (seen[0]));
	next:;
	}
    }

  int relocation_in_progress = 0;

  for (size_t i = nmaps; i-- > 0; )
    {
      l = maps[i];

      if (! relocation_in_progress)
	{
	  /* Notify the debugger that relocations are about to happen.  */
	  LIBC_PROBE (reloc_start, 2, args->nsid, r);
	  relocation_in_progress = 1;
	}

#ifdef SHARED
      if (__glibc_unlikely (GLRO(dl_profile) != NULL))
	{
	  /* If this here is the shared object which we want to profile
	     make sure the profile is started.  We can find out whether
	     this is necessary or not by observing the `_dl_profile_map'
	     variable.  If it was NULL but is not NULL afterwards we must
	     start the profiling.  */
	  struct link_map *old_profile_map = GL(dl_profile_map);

	  _dl_relocate_object (l, l->l_scope, reloc_mode | RTLD_LAZY, 1);

	  if (old_profile_map == NULL && GL(dl_profile_map) != NULL)
	    {
	      /* We must prepare the profiling.  */
	      _dl_start_profile ();

	      /* Prevent unloading the object.  */
	      GL(dl_profile_map)->l_flags_1 |= DF_1_NODELETE;
	    }
	}
      else
#endif
	_dl_relocate_object (l, l->l_scope, reloc_mode, 0);
    }

  /* If the file is not loaded now as a dependency, add the search
     list of the newly loaded object to the scope.  */
  bool any_tls = false;
  unsigned int first_static_tls = new->l_searchlist.r_nlist;
  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
    {
      struct link_map *imap = new->l_searchlist.r_list[i];
      int from_scope = 0;

      /* If the initializer has been called already, the object has
	 not been loaded here and now.  */
      if (imap->l_init_called && imap->l_type == lt_loaded)
	{
	  struct r_scope_elem **runp = imap->l_scope;
	  size_t cnt = 0;

	  while (*runp != NULL)
	    {
	      if (*runp == &new->l_searchlist)
		break;
	      ++cnt;
	      ++runp;
	    }

	  if (*runp != NULL)
	    /* Avoid duplicates.  */
	    continue;

	  if (__glibc_unlikely (cnt + 1 >= imap->l_scope_max))
	    {
	      /* The 'r_scope' array is too small.  Allocate a new one
		 dynamically.  */
	      size_t new_size;
	      struct r_scope_elem **newp;

#define SCOPE_ELEMS(imap) \
  (sizeof (imap->l_scope_mem) / sizeof (imap->l_scope_mem[0]))

	      if (imap->l_scope != imap->l_scope_mem
		  && imap->l_scope_max < SCOPE_ELEMS (imap))
		{
		  new_size = SCOPE_ELEMS (imap);
		  newp = imap->l_scope_mem;
		}
	      else
		{
		  new_size = imap->l_scope_max * 2;
		  newp = (struct r_scope_elem **)
		    malloc (new_size * sizeof (struct r_scope_elem *));
		  if (newp == NULL)
		    _dl_signal_error (ENOMEM, "dlopen", NULL,
				      N_("cannot create scope list"));
		}

	      memcpy (newp, imap->l_scope, cnt * sizeof (imap->l_scope[0]));
	      struct r_scope_elem **old = imap->l_scope;

	      imap->l_scope = newp;

	      if (old != imap->l_scope_mem)
		_dl_scope_free (old);

	      imap->l_scope_max = new_size;
	    }

	  /* First terminate the extended list.  Otherwise a thread
	     might use the new last element and then use the garbage
	     at offset IDX+1.  */
	  imap->l_scope[cnt + 1] = NULL;
	  atomic_write_barrier ();
	  imap->l_scope[cnt] = &new->l_searchlist;

	  /* Print only new scope information.  */
	  from_scope = cnt;
	}
      /* Only add TLS memory if this object is loaded now and
	 therefore is not yet initialized.  */
      else if (! imap->l_init_called
	       /* Only if the module defines thread local data.  */
	       && __builtin_expect (imap->l_tls_blocksize > 0, 0))
	{
	  /* Now that we know the object is loaded successfully add
	     modules containing TLS data to the slot info table.  We
	     might have to increase its size.  */
	  _dl_add_to_slotinfo (imap);

	  if (imap->l_need_tls_init
	      && first_static_tls == new->l_searchlist.r_nlist)
	    first_static_tls = i;

	  /* We have to bump the generation counter.  */
	  any_tls = true;
	}

      /* Print scope information.  */
      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_SCOPES))
	_dl_show_scope (imap, from_scope);
    }

  /* Bump the generation number if necessary.  */
  if (any_tls && __builtin_expect (++GL(dl_tls_generation) == 0, 0))
    _dl_fatal_printf (N_("\
TLS generation counter wrapped!  Please report this."));

  /* We need a second pass for static tls data, because _dl_update_slotinfo
     must not be run while calls to _dl_add_to_slotinfo are still pending.  */
  for (unsigned int i = first_static_tls; i < new->l_searchlist.r_nlist; ++i)
    {
      struct link_map *imap = new->l_searchlist.r_list[i];

      if (imap->l_need_tls_init
	  && ! imap->l_init_called
	  && imap->l_tls_blocksize > 0)
	{
	  /* For static TLS we have to allocate the memory here and
	     now, but we can delay updating the DTV.  */
	  imap->l_need_tls_init = 0;
#ifdef SHARED
	  /* Update the slot information data for at least the
	     generation of the DSO we are allocating data for.  */
	  _dl_update_slotinfo (imap->l_tls_modid);
#endif

	  GL(dl_init_static_tls) (imap);
	  assert (imap->l_need_tls_init == 0);
	}
    }

  /* Notify the debugger all new objects have been relocated.  */
  if (relocation_in_progress)
    LIBC_PROBE (reloc_complete, 3, args->nsid, r, new);

#ifndef SHARED
  DL_STATIC_INIT (new);
#endif

  /* Run the initializer functions of new objects.  */
  _dl_init (new, args->argc, args->argv, args->env);

  /* Now we can make the new map available in the global scope.  */
  if (mode & RTLD_GLOBAL)
    /* Move the object in the global namespace.  */
    if (add_to_global (new) != 0)
      /* It failed.  */
      return;

#ifndef SHARED
  /* We must be the static _dl_open in libc.a.  A static program that
     has loaded a dynamic object now has competition.  */
  __libc_multiple_libcs = 1;
#endif

  /* Let the user know about the opencount.  */
  if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
    _dl_debug_printf ("opening file=%s [%lu]; direct_opencount=%u\n\n",
		      new->l_name, new->l_ns, new->l_direct_opencount);
}


void *
_dl_open (const char *file, int mode, const void *caller_dlopen, Lmid_t nsid,
	  int argc, char *argv[], char *env[])
{
  if ((mode & RTLD_BINDING_MASK) == 0)
    /* One of the flags must be set.  */
    _dl_signal_error (EINVAL, file, NULL, N_("invalid mode for dlopen()"));

  /* Make sure we are alone.  */
  __rtld_lock_lock_recursive (GL(dl_load_lock));

  if (__glibc_unlikely (nsid == LM_ID_NEWLM))
    {
      /* Find a new namespace.  */
      for (nsid = 1; DL_NNS > 1 && nsid < GL(dl_nns); ++nsid)
	if (GL(dl_ns)[nsid]._ns_loaded == NULL)
	  break;

      if (__glibc_unlikely (nsid == DL_NNS))
	{
	  /* No more namespace available.  */
	  __rtld_lock_unlock_recursive (GL(dl_load_lock));

	  _dl_signal_error (EINVAL, file, NULL, N_("\
no more namespaces available for dlmopen()"));
	}
      else if (nsid == GL(dl_nns))
	{
	  __rtld_lock_initialize (GL(dl_ns)[nsid]._ns_unique_sym_table.lock);
	  ++GL(dl_nns);
	}

      _dl_debug_initialize (0, nsid)->r_state = RT_CONSISTENT;
    }
  /* Never allow loading a DSO in a namespace which is empty.  Such
     direct placements is only causing problems.  Also don't allow
     loading into a namespace used for auditing.  */
  else if (__glibc_unlikely (nsid != LM_ID_BASE && nsid != __LM_ID_CALLER)
	   && (__glibc_unlikely (nsid < 0 || nsid >= GL(dl_nns))
	       /* This prevents the [NSID] index expressions from being
		  evaluated, so the compiler won't think that we are
		  accessing an invalid index here in the !SHARED case where
		  DL_NNS is 1 and so any NSID != 0 is invalid.  */
	       || DL_NNS == 1
	       || GL(dl_ns)[nsid]._ns_nloaded == 0
	       || GL(dl_ns)[nsid]._ns_loaded->l_auditing))
    _dl_signal_error (EINVAL, file, NULL,
		      N_("invalid target namespace in dlmopen()"));

  struct dl_open_args args;
  args.file = file;
  args.mode = mode;
  args.caller_dlopen = caller_dlopen;
  args.caller_dl_open = RETURN_ADDRESS (0);
  args.map = NULL;
  args.nsid = nsid;
  args.argc = argc;
  args.argv = argv;
  args.env = env;

  struct dl_exception exception;
  int errcode = _dl_catch_exception (&exception, dl_open_worker, &args);

#if defined USE_LDCONFIG && !defined MAP_COPY
  /* We must unmap the cache file.  */
  _dl_unload_cache ();
#endif

  /* See if an error occurred during loading.  */
  if (__glibc_unlikely (exception.errstring != NULL))
    {
      /* Remove the object from memory.  It may be in an inconsistent
	 state if relocation failed, for example.  */
      if (args.map)
	{
	  /* Maybe some of the modules which were loaded use TLS.
	     Since it will be removed in the following _dl_close call
	     we have to mark the dtv array as having gaps to fill the
	     holes.  This is a pessimistic assumption which won't hurt
	     if not true.  There is no need to do this when we are
	     loading the auditing DSOs since TLS has not yet been set
	     up.  */
	  if ((mode & __RTLD_AUDIT) == 0)
	    GL(dl_tls_dtv_gaps) = true;

	  _dl_close_worker (args.map, true);
	}

      assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);

      /* Release the lock.  */
      __rtld_lock_unlock_recursive (GL(dl_load_lock));

      /* Reraise the error.  */
      _dl_signal_exception (errcode, &exception, NULL);
    }

  assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);

  /* Release the lock.  */
  __rtld_lock_unlock_recursive (GL(dl_load_lock));

  return args.map;
}


void
_dl_show_scope (struct link_map *l, int from)
{
  _dl_debug_printf ("object=%s [%lu]\n",
		    DSO_FILENAME (l->l_name), l->l_ns);
  if (l->l_scope != NULL)
    for (int scope_cnt = from; l->l_scope[scope_cnt] != NULL; ++scope_cnt)
      {
	_dl_debug_printf (" scope %u:", scope_cnt);

	for (unsigned int cnt = 0; cnt < l->l_scope[scope_cnt]->r_nlist; ++cnt)
	  if (*l->l_scope[scope_cnt]->r_list[cnt]->l_name)
	    _dl_debug_printf_c (" %s",
				l->l_scope[scope_cnt]->r_list[cnt]->l_name);
	  else
	    _dl_debug_printf_c (" %s", RTLD_PROGNAME);

	_dl_debug_printf_c ("\n");
      }
  else
    _dl_debug_printf (" no scope\n");
  _dl_debug_printf ("\n");
}