glibc/elf/dl-deps.c

/* Load the dependencies of a mapped object.
Copyright (C) 1996 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 Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <link.h>
#include <errno.h>
#include <dlfcn.h>
#include <stdlib.h>

void
_dl_map_object_deps (struct link_map *map,
		     struct link_map **preloads, unsigned int npreloads)
{
  struct list
    {
      struct link_map *map;
      struct list *next;
    };
  struct list head[1 + npreloads], *tailp, *scanp;
  unsigned int nlist;

  /* Start the search list with one element: MAP itself.  */
  head[0].map = map;

  /* Add the preloaded items after MAP but before any of its dependencies.  */
  for (nlist = 0; nlist < npreloads; ++nlist)
    {
      head[nlist].next = &head[nlist + 1];
      head[nlist + 1].map = preloads[nlist];
    }

  /* Terminate the list.  */
  head[nlist].next = NULL;

  /* Start here for adding dependencies to the list.  */
  tailp = &head[nlist++];

  /* We use `l_reserved' as a mark bit to detect objects we have already
     put in the search list and avoid adding duplicate elements later in
     the list.  */
  map->l_reserved = 1;

  /* Process each element of the search list, loading each of its immediate
     dependencies and appending them to the list as we step through it.
     This produces a flat, ordered list that represents a breadth-first
     search of the dependency tree.  */
  for (scanp = head; scanp; scanp = scanp->next)
    {
      struct link_map *l = scanp->map;

      if (l->l_info[DT_NEEDED])
	{
	  const char *strtab
	    = ((void *) l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr);
	  const ElfW(Dyn) *d;
	  for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
	    if (d->d_tag == DT_NEEDED)
	      {
		/* Map in the needed object.  */
		struct link_map *dep
		  = _dl_map_object (l, strtab + d->d_un.d_val,
				    l->l_type == lt_executable ? lt_library :
				    l->l_type);

		if (dep->l_reserved)
		  /* This object is already in the search list we are
                     building.  Don't add a duplicate pointer.  Release the
                     reference just added by _dl_map_object.  */
		  --dep->l_opencount;
		else
		  {
		    /* Append DEP to the search list.  */
		    tailp->next = alloca (sizeof *tailp);
		    tailp = tailp->next;
		    tailp->map = dep;
		    tailp->next = NULL;
		    ++nlist;
		    /* Set the mark bit that says it's already in the list.  */
		    dep->l_reserved = 1;
		  }
	      }
	}
    }

  /* Store the search list we built in the object.  It will be used for
     searches in the scope of this object.  */
  map->l_searchlist = malloc (nlist * sizeof (struct link_map *));
  map->l_nsearchlist = nlist;

  nlist = 0;
  for (scanp = head; scanp; scanp = scanp->next)
    {
      map->l_searchlist[nlist++] = scanp->map;

      /* Now clear all the mark bits we set in the objects on the search list
	 to avoid duplicates, so the next call starts fresh.  */
      scanp->map->l_reserved = 0;
    }
}