head[nlist++].next = NULL;
head[nlist].next = NULL;   tailp = &head[nlist++];
_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;  /* 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 = tailp = 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;    }}