glibc/elf/dl-load.c

/* Map in a shared object's segments from the file.
   Copyright (C) 1995, 1996, 1997, 1998 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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <elf/ldsodefs.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include "dynamic-link.h"
#include <stdio-common/_itoa.h>

#include <dl-origin.h>


/* On some systems, no flag bits are given to specify file mapping.  */
#ifndef MAP_FILE
#define MAP_FILE	0
#endif

/* The right way to map in the shared library files is MAP_COPY, which
   makes a virtual copy of the data at the time of the mmap call; this
   guarantees the mapped pages will be consistent even if the file is
   overwritten.  Some losing VM systems like Linux's lack MAP_COPY.  All we
   get is MAP_PRIVATE, which copies each page when it is modified; this
   means if the file is overwritten, we may at some point get some pages
   from the new version after starting with pages from the old version.  */
#ifndef MAP_COPY
#define MAP_COPY	MAP_PRIVATE
#endif

/* Some systems link their relocatable objects for another base address
   than 0.  We want to know the base address for these such that we can
   subtract this address from the segment addresses during mapping.
   This results in a more efficient address space usage.  Defaults to
   zero for almost all systems.  */
#ifndef MAP_BASE_ADDR
#define MAP_BASE_ADDR(l)	0
#endif


#include <endian.h>
#if BYTE_ORDER == BIG_ENDIAN
#define byteorder ELFDATA2MSB
#define byteorder_name "big-endian"
#elif BYTE_ORDER == LITTLE_ENDIAN
#define byteorder ELFDATA2LSB
#define byteorder_name "little-endian"
#else
#error "Unknown BYTE_ORDER " BYTE_ORDER
#define byteorder ELFDATANONE
#endif

#define STRING(x) __STRING (x)

#ifdef MAP_ANON
/* The fd is not examined when using MAP_ANON.  */
#define ANONFD -1
#else
int _dl_zerofd = -1;
#define ANONFD _dl_zerofd
#endif

/* Handle situations where we have a preferred location in memory for
   the shared objects.  */
#ifdef ELF_PREFERRED_ADDRESS_DATA
ELF_PREFERRED_ADDRESS_DATA;
#endif
#ifndef ELF_PREFERRED_ADDRESS
#define ELF_PREFERRED_ADDRESS(loader, maplength, mapstartpref) (mapstartpref)
#endif
#ifndef ELF_FIXED_ADDRESS
#define ELF_FIXED_ADDRESS(loader, mapstart) ((void) 0)
#endif

size_t _dl_pagesize;

extern const char *_dl_platform;
extern size_t _dl_platformlen;

/* This is the decomposed LD_LIBRARY_PATH search path.  */
static struct r_search_path_elem **env_path_list;

/* List of the hardware capabilities we might end up using.  */
static const struct r_strlenpair *capstr;
static size_t ncapstr;
static size_t max_capstrlen;


/* This function has no public prototype.  */
extern ssize_t __libc_read (int, void *, size_t);


/* Local version of `strdup' function.  */
static inline char *
local_strdup (const char *s)
{
  size_t len = strlen (s) + 1;
  void *new = malloc (len);

  if (new == NULL)
    return NULL;

  return (char *) memcpy (new, s, len);
}

/* Return copy of argument with all recognized dynamic string tokens
   ($ORIGIN and $PLATFORM for now) replaced.  On some platforms it
   might not be possible to determine the path from which the object
   belonging to the map is loaded.  In this case the path element
   containing $ORIGIN is left out.  */
static char *
expand_dynamic_string_token (struct link_map *l, const char *s)
{
  /* We make two runs over the string.  First we determine how large the
     resulting string is and then we copy it over.  Since this is now
     frequently executed operation we are looking here not for performance
     but rather for code size.  */
  const char *st, *sf;
  size_t cnt = 0;
  size_t origin_len;
  size_t total;
  char *result, *last_elem, *wp;

  st = s;
  sf = strchr (s, '$');
  while (sf != NULL)
    {
      size_t len = 1;

      if (((strncmp (&sf[1], "ORIGIN", 6) == 0 && (len = 7) != 0)
	   || (strncmp (&sf[1], "PLATFORM", 8) == 0 && (len = 9) != 0))
	  && (s[len] == '\0' || s[len] == '/' || s[len] == ':'))
	++cnt;

      st = sf + len;
      sf = strchr (st, '$');
    }

  /* If we do not have to replace anything simply copy the string.  */
  if (cnt == 0)
    return local_strdup (s);

  /* Now we make a guess how many extra characters on top of the length
     of S we need to represent the result.  We know that we have CNT
     replacements.  Each at most can use
	MAX (strlen (ORIGIN), strlen (_dl_platform))
     minus 7 (which is the length of "$ORIGIN").

     First get the origin string if it is not available yet.  This can
     only happen for the map of the executable.  */
  if (l->l_origin == NULL)
    {
      assert (l->l_name[0] == '\0');
      l->l_origin = get_origin ();
      origin_len = (l->l_origin && l->l_origin != (char *) -1
		    ? strlen (l->l_origin) : 0);
    }
  else
    origin_len = l->l_origin == (char *) -1 ? 0 : strlen (l->l_origin);

  total = strlen (s) + cnt * (MAX (origin_len, _dl_platformlen) - 7);
  result = (char *) malloc (total + 1);
  if (result == NULL)
    return NULL;

  /* Now fill the result path.  While copying over the string we keep
     track of the start of the last path element.  When we come accross
     a DST we copy over the value or (if the value is not available)
     leave the entire path element out.  */
  last_elem = wp = result;
  do
    {
      if (*s == '$')
	{
	  const char *repl;
	  size_t len;

	  if (((strncmp (&s[1], "ORIGIN", 6) == 0 && (len = 7) != 0)
	       || (strncmp (&s[1], "PLATFORM", 8) == 0 && (len = 9) != 0))
	      && (s[len] == '\0' || s[len] == '/' || s[len] == ':'))
	    {
	      if ((repl = len == 7 ? l->l_origin : _dl_platform) != NULL
		  && repl != (const char *) -1)
		{
		  wp = __stpcpy (wp, repl);
		  s += len;
		}
	      else
		{
		  /* We cannot use this path element, the value of the
		     replacement is unknown.  */
		  wp = last_elem;
		  s += len;
		  while (*s != '\0' && *s != ':')
		    ++s;
		}
	    }
	  else
	    /* No SDK we recognize.  */
	    *wp++ = *s++;
	}
      else if (*s == ':')
	{
	  *wp++ = *s++;
	  last_elem = wp;
	}
      else
	*wp++ = *s++;
    }
  while (*s != '\0');

  *wp = '\0';

  return result;
}

/* Add `name' to the list of names for a particular shared object.
   `name' is expected to have been allocated with malloc and will
   be freed if the shared object already has this name.
   Returns false if the object already had this name.  */
static void
internal_function
add_name_to_object (struct link_map *l, const char *name)
{
  struct libname_list *lnp, *lastp;
  struct libname_list *newname;
  size_t name_len;

  lastp = NULL;
  for (lnp = l->l_libname; lnp != NULL; lastp = lnp, lnp = lnp->next)
    if (strcmp (name, lnp->name) == 0)
      return;

  name_len = strlen (name) + 1;
  newname = malloc (sizeof *newname + name_len);
  if (newname == NULL)
    {
      /* No more memory.  */
      _dl_signal_error (ENOMEM, name, "cannot allocate name record");
      return;
    }
  /* The object should have a libname set from _dl_new_object.  */
  assert (lastp != NULL);

  newname->name = memcpy (newname + 1, name, name_len);
  newname->next = NULL;
  lastp->next = newname;
}

/* All known directories in sorted order.  */
static struct r_search_path_elem *all_dirs;

/* Standard search directories.  */
static struct r_search_path_elem **rtld_search_dirs;

static size_t max_dirnamelen;

static inline struct r_search_path_elem **
fillin_rpath (char *rpath, struct r_search_path_elem **result, const char *sep,
	      const char **trusted, const char *what, const char *where)
{
  char *cp;
  size_t nelems = 0;

  while ((cp = __strsep (&rpath, sep)) != NULL)
    {
      struct r_search_path_elem *dirp;
      size_t len = strlen (cp);

      /* `strsep' can pass an empty string.  This has to be
         interpreted as `use the current directory'. */
      if (len == 0)
	{
	  static char curwd[] = "./";
	  cp = curwd;
	}

      /* Remove trailing slashes (except for "/").  */
      while (len > 1 && cp[len - 1] == '/')
	--len;

      /* Make sure we don't use untrusted directories if we run SUID.  */
      if (trusted != NULL)
	{
	  const char **trun = trusted;

	  /* All trusted directories must be complete names.  */
	  if (cp[0] != '/')
	    continue;

	  while (*trun != NULL
		 && (memcmp (*trun, cp, len) != 0
		     || (*trun)[len] != '/'
		     || (*trun)[len + 1] != '\0'))
	    ++trun;

	  if (*trun == NULL)
	    /* It's no trusted directory, skip it.  */
	    continue;
	}

      /* Now add one if there is none so far.  */
      if (len > 0 && cp[len - 1] != '/')
	cp[len++] = '/';

      /* See if this directory is already known.  */
      for (dirp = all_dirs; dirp != NULL; dirp = dirp->next)
	if (dirp->dirnamelen == len && memcmp (cp, dirp->dirname, len) == 0)
	  break;

      if (dirp != NULL)
	{
	  /* It is available, see whether it's on our own list.  */
	  size_t cnt;
	  for (cnt = 0; cnt < nelems; ++cnt)
	    if (result[cnt] == dirp)
	      break;

	  if (cnt == nelems)
	    result[nelems++] = dirp;
	}
      else
	{
	  size_t cnt;

	  /* It's a new directory.  Create an entry and add it.  */
	  dirp = (struct r_search_path_elem *)
	    malloc (sizeof (*dirp) + ncapstr * sizeof (enum r_dir_status));
	  if (dirp == NULL)
	    _dl_signal_error (ENOMEM, NULL,
			      "cannot create cache for search path");

	  dirp->dirname = cp;
	  dirp->dirnamelen = len;

	  if (len > max_dirnamelen)
	    max_dirnamelen = len;

	  /* We have to make sure all the relative directories are never
	     ignored.  The current directory might change and all our
	     saved information would be void.  */
	  if (cp[0] != '/')
	    for (cnt = 0; cnt < ncapstr; ++cnt)
	      dirp->status[cnt] = existing;
	  else
	    for (cnt = 0; cnt < ncapstr; ++cnt)
	      dirp->status[cnt] = unknown;

	  dirp->what = what;
	  dirp->where = where;

	  dirp->next = all_dirs;
	  all_dirs = dirp;

	  /* Put it in the result array.  */
	  result[nelems++] = dirp;
	}
    }

  /* Terminate the array.  */
  result[nelems] = NULL;

  return result;
}


static struct r_search_path_elem **
internal_function
decompose_rpath (const char *rpath, struct link_map *l)
{
  /* Make a copy we can work with.  */
  const char *where = l->l_name;
  char *copy;
  char *cp;
  struct r_search_path_elem **result;
  size_t nelems;

  /* First see whether we must forget the RPATH from this object.  */
  if (_dl_inhibit_rpath != NULL && !__libc_enable_secure)
    {
      const char *found = strstr (_dl_inhibit_rpath, where);
      if (found != NULL)
	{
	  size_t len = strlen (where);
	  if ((found == _dl_inhibit_rpath || found[-1] == ':')
	      && (found[len] == '\0' || found[len] == ':'))
	    {
	      /* This object is on the list of objects for which the RPATH
		 must not be used.  */
	      result = (struct r_search_path_elem **)
		malloc (sizeof (*result));
	      if (result == NULL)
		_dl_signal_error (ENOMEM, NULL,
				  "cannot create cache for search path");
	      result[0] = NULL;

	      return result;
	    }
	}
    }

  /* Make a writable copy.  At the same time expand possible dynamic
     string tokens.  */
  copy = expand_dynamic_string_token (l, rpath);
  if (copy == NULL)
    _dl_signal_error (ENOMEM, NULL, "cannot create RPATH copy");

  /* Count the number of necessary elements in the result array.  */
  nelems = 0;
  for (cp = copy; *cp != '\0'; ++cp)
    if (*cp == ':')
      ++nelems;

  /* Allocate room for the result.  NELEMS + 1 is an upper limit for the
     number of necessary entries.  */
  result = (struct r_search_path_elem **) malloc ((nelems + 1 + 1)
						  * sizeof (*result));
  if (result == NULL)
    _dl_signal_error (ENOMEM, NULL, "cannot create cache for search path");

  return fillin_rpath (copy, result, ":", NULL, "RPATH", where);
}


void
internal_function
_dl_init_paths (const char *llp)
{
  static const char *system_dirs[] =
  {
#include "trusted-dirs.h"
    NULL
  };
  const char **strp;
  struct r_search_path_elem *pelem, **aelem;
  size_t round_size;

  /* Fill in the information about the application's RPATH and the
     directories addressed by the LD_LIBRARY_PATH environment variable.  */
  struct link_map *l;

  /* Get the capabilities.  */
  capstr = _dl_important_hwcaps (_dl_platform, _dl_platformlen,
				 &ncapstr, &max_capstrlen);

  /* First set up the rest of the default search directory entries.  */
  aelem = rtld_search_dirs = (struct r_search_path_elem **)
    malloc ((ncapstr + 1) * sizeof (struct r_search_path_elem *));

  round_size = ((2 * sizeof (struct r_search_path_elem) - 1
		 + ncapstr * sizeof (enum r_dir_status))
		/ sizeof (struct r_search_path_elem));

  rtld_search_dirs[0] = (struct r_search_path_elem *)
    malloc ((sizeof (system_dirs) / sizeof (system_dirs[0]) - 1)
	    * round_size * sizeof (struct r_search_path_elem));
  if (rtld_search_dirs[0] == NULL)
    _dl_signal_error (ENOMEM, NULL, "cannot create cache for search path");

  pelem = all_dirs = rtld_search_dirs[0];
  for (strp = system_dirs; *strp != NULL; ++strp, pelem += round_size)
    {
      size_t cnt;

      *aelem++ = pelem;

      pelem->next = *(strp + 1) == NULL ? NULL : (pelem + round_size);

      pelem->what = "system search path";
      pelem->where = NULL;

      pelem->dirnamelen = strlen (pelem->dirname = *strp);
      if (pelem->dirnamelen > max_dirnamelen)
	max_dirnamelen = pelem->dirnamelen;

      if (pelem->dirname[0] != '/')
	for (cnt = 0; cnt < ncapstr; ++cnt)
	  pelem->status[cnt] = existing;
      else
	for (cnt = 0; cnt < ncapstr; ++cnt)
	  pelem->status[cnt] = unknown;
    }
  *aelem = NULL;

#ifdef PIC
  /* This points to the map of the main object.  */
  l = _dl_loaded;
  if (l != NULL)
    {
      assert (l->l_type != lt_loaded);

      if (l->l_info[DT_RPATH])
	/* Allocate room for the search path and fill in information
	   from RPATH.  */
	l->l_rpath_dirs =
	  decompose_rpath ((const char *)
			   (l->l_addr + l->l_info[DT_STRTAB]->d_un.d_ptr
			    + l->l_info[DT_RPATH]->d_un.d_val), l);
      else
	l->l_rpath_dirs = NULL;
    }
#endif	/* PIC */

  if (llp != NULL && *llp != '\0')
    {
      size_t nllp;
      const char *cp = llp;

      /* Decompose the LD_LIBRARY_PATH contents.  First determine how many
	 elements it has.  */
      nllp = 1;
      while (*cp)
	{
	  if (*cp == ':' || *cp == ';')
	    ++nllp;
	  ++cp;
	}

      env_path_list = (struct r_search_path_elem **)
	malloc ((nllp + 1) * sizeof (struct r_search_path_elem *));
      if (env_path_list == NULL)
	_dl_signal_error (ENOMEM, NULL,
			  "cannot create cache for search path");

      (void) fillin_rpath (local_strdup (llp), env_path_list, ":;",
			   __libc_enable_secure ? system_dirs : NULL,
			   "LD_LIBRARY_PATH", NULL);
    }
}


/* Map in the shared object NAME, actually located in REALNAME, and already
   opened on FD.  */

#ifndef EXTERNAL_MAP_FROM_FD
static
#endif
struct link_map *
_dl_map_object_from_fd (const char *name, int fd, char *realname,
			struct link_map *loader, int l_type)
{
  struct link_map *l = NULL;

#define LOSE(s) lose (0, (s))
  void lose (int code, const char *msg)
    {
      (void) __close (fd);
      if (l)
	{
	  /* Remove the stillborn object from the list and free it.  */
	  if (l->l_prev)
	    l->l_prev->l_next = l->l_next;
	  if (l->l_next)
	    l->l_next->l_prev = l->l_prev;
	  free (l);
	}
      free (realname);
      _dl_signal_error (code, name, msg);
    }

  inline caddr_t map_segment (ElfW(Addr) mapstart, size_t len,
			      int prot, int fixed, off_t offset)
    {
      caddr_t mapat = __mmap ((caddr_t) mapstart, len, prot,
			      fixed|MAP_COPY|MAP_FILE,
			      fd, offset);
      if (mapat == MAP_FAILED)
	lose (errno, "failed to map segment from shared object");
      return mapat;
    }

  const ElfW(Ehdr) *header;
  const ElfW(Phdr) *phdr;
  const ElfW(Phdr) *ph;
  size_t maplength;
  int type;
  char *readbuf;
  ssize_t readlength;

  /* Look again to see if the real name matched another already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (realname, l->l_name))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	__close (fd);

	/* If the name is not in the list of names for this object add
	   it.  */
	free (realname);
	add_name_to_object (l, name);
	++l->l_opencount;
	return l;
      }

  /* Print debugging message.  */
  if (_dl_debug_files)
    _dl_debug_message (1, "file=", name, ";  generating link map\n", NULL);

  /* Read the header directly.  */
  readbuf = alloca (_dl_pagesize);
  readlength = __libc_read (fd, readbuf, _dl_pagesize);
  if (readlength < (ssize_t) sizeof(*header))
    lose (errno, "cannot read file data");
  header = (void *) readbuf;

  /* Check the header for basic validity.  */
  if (*(Elf32_Word *) &header->e_ident !=
#if BYTE_ORDER == LITTLE_ENDIAN
      ((ELFMAG0 << (EI_MAG0 * 8)) |
       (ELFMAG1 << (EI_MAG1 * 8)) |
       (ELFMAG2 << (EI_MAG2 * 8)) |
       (ELFMAG3 << (EI_MAG3 * 8)))
#else
      ((ELFMAG0 << (EI_MAG3 * 8)) |
       (ELFMAG1 << (EI_MAG2 * 8)) |
       (ELFMAG2 << (EI_MAG1 * 8)) |
       (ELFMAG3 << (EI_MAG0 * 8)))
#endif
      )
    LOSE ("invalid ELF header");
#define ELF32_CLASS ELFCLASS32
#define ELF64_CLASS ELFCLASS64
  if (header->e_ident[EI_CLASS] != ELFW(CLASS))
    LOSE ("ELF file class not " STRING(__ELF_NATIVE_CLASS) "-bit");
  if (header->e_ident[EI_DATA] != byteorder)
    LOSE ("ELF file data encoding not " byteorder_name);
  if (header->e_ident[EI_VERSION] != EV_CURRENT)
    LOSE ("ELF file version ident not " STRING(EV_CURRENT));
  /* XXX We should be able so set system specific versions which are
     allowed here.  */
  if (header->e_ident[EI_OSABI] != ELFOSABI_SYSV)
    LOSE ("ELF file OS ABI not " STRING(ELFOSABI_SYSV));
  if (header->e_ident[EI_ABIVERSION] != 0)
    LOSE ("ELF file ABI version not 0");
  if (header->e_version != EV_CURRENT)
    LOSE ("ELF file version not " STRING(EV_CURRENT));
  if (! elf_machine_matches_host (header->e_machine))
    LOSE ("ELF file machine architecture not " ELF_MACHINE_NAME);
  if (header->e_phentsize != sizeof (ElfW(Phdr)))
    LOSE ("ELF file's phentsize not the expected size");

#ifndef MAP_ANON
#define MAP_ANON 0
  if (_dl_zerofd == -1)
    {
      _dl_zerofd = _dl_sysdep_open_zero_fill ();
      if (_dl_zerofd == -1)
	{
	  __close (fd);
	  _dl_signal_error (errno, NULL, "cannot open zero fill device");
	}
    }
#endif

  /* Enter the new object in the list of loaded objects.  */
  l = _dl_new_object (realname, name, l_type, loader);
  if (! l)
    lose (ENOMEM, "cannot create shared object descriptor");
  l->l_opencount = 1;

  /* Extract the remaining details we need from the ELF header
     and then read in the program header table.  */
  l->l_entry = header->e_entry;
  type = header->e_type;
  l->l_phnum = header->e_phnum;

  maplength = header->e_phnum * sizeof (ElfW(Phdr));
  if (header->e_phoff + maplength <= readlength)
    phdr = (void *) (readbuf + header->e_phoff);
  else
    {
      phdr = alloca (maplength);
      __lseek (fd, SEEK_SET, header->e_phoff);
      if (__libc_read (fd, (void *) phdr, maplength) != maplength)
        lose (errno, "cannot read file data");
    }

  {
    /* Scan the program header table, collecting its load commands.  */
    struct loadcmd
      {
	ElfW(Addr) mapstart, mapend, dataend, allocend;
	off_t mapoff;
	int prot;
      } loadcmds[l->l_phnum], *c;
    size_t nloadcmds = 0;

    l->l_ld = 0;
    l->l_phdr = 0;
    l->l_addr = 0;
    for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
      switch (ph->p_type)
	{
	  /* These entries tell us where to find things once the file's
	     segments are mapped in.  We record the addresses it says
	     verbatim, and later correct for the run-time load address.  */
	case PT_DYNAMIC:
	  l->l_ld = (void *) ph->p_vaddr;
	  break;
	case PT_PHDR:
	  l->l_phdr = (void *) ph->p_vaddr;
	  break;

	case PT_LOAD:
	  /* A load command tells us to map in part of the file.
	     We record the load commands and process them all later.  */
	  if (ph->p_align % _dl_pagesize != 0)
	    LOSE ("ELF load command alignment not page-aligned");
	  if ((ph->p_vaddr - ph->p_offset) % ph->p_align)
	    LOSE ("ELF load command address/offset not properly aligned");
	  {
	    struct loadcmd *c = &loadcmds[nloadcmds++];
	    c->mapstart = ph->p_vaddr & ~(ph->p_align - 1);
	    c->mapend = ((ph->p_vaddr + ph->p_filesz + _dl_pagesize - 1)
			 & ~(_dl_pagesize - 1));
	    c->dataend = ph->p_vaddr + ph->p_filesz;
	    c->allocend = ph->p_vaddr + ph->p_memsz;
	    c->mapoff = ph->p_offset & ~(ph->p_align - 1);
	    c->prot = 0;
	    if (ph->p_flags & PF_R)
	      c->prot |= PROT_READ;
	    if (ph->p_flags & PF_W)
	      c->prot |= PROT_WRITE;
	    if (ph->p_flags & PF_X)
	      c->prot |= PROT_EXEC;
	    break;
	  }
	}

    /* Now process the load commands and map segments into memory.  */
    c = loadcmds;

    /* Length of the sections to be loaded.  */
    maplength = loadcmds[nloadcmds - 1].allocend - c->mapstart;

    if (type == ET_DYN || type == ET_REL)
      {
	/* This is a position-independent shared object.  We can let the
	   kernel map it anywhere it likes, but we must have space for all
	   the segments in their specified positions relative to the first.
	   So we map the first segment without MAP_FIXED, but with its
	   extent increased to cover all the segments.  Then we remove
	   access from excess portion, and there is known sufficient space
	   there to remap from the later segments.

	   As a refinement, sometimes we have an address that we would
	   prefer to map such objects at; but this is only a preference,
	   the OS can do whatever it likes. */
 	caddr_t mapat;
	ElfW(Addr) mappref;
	mappref = (ELF_PREFERRED_ADDRESS (loader, maplength, c->mapstart)
		   - MAP_BASE_ADDR (l));
	mapat = map_segment (mappref, maplength, c->prot, 0, c->mapoff);
	l->l_addr = (ElfW(Addr)) mapat - c->mapstart;

	/* Change protection on the excess portion to disallow all access;
	   the portions we do not remap later will be inaccessible as if
	   unallocated.  Then jump into the normal segment-mapping loop to
	   handle the portion of the segment past the end of the file
	   mapping.  */
	__mprotect ((caddr_t) (l->l_addr + c->mapend),
		    loadcmds[nloadcmds - 1].allocend - c->mapend,
		    0);

	/* Remember which part of the address space this object uses.  */
	l->l_map_start = c->mapstart + l->l_addr;
	l->l_map_end = l->l_map_start + maplength;

	goto postmap;
      }
    else
      {
	/* Notify ELF_PREFERRED_ADDRESS that we have to load this one
	   fixed.  */
	ELF_FIXED_ADDRESS (loader, c->mapstart);
      }

    /* Remember which part of the address space this object uses.  */
    l->l_map_start = c->mapstart + l->l_addr;
    l->l_map_end = l->l_map_start + maplength;

    while (c < &loadcmds[nloadcmds])
      {
	if (c->mapend > c->mapstart)
	  /* Map the segment contents from the file.  */
	  map_segment (l->l_addr + c->mapstart, c->mapend - c->mapstart,
		       c->prot, MAP_FIXED, c->mapoff);

      postmap:
	if (c->allocend > c->dataend)
	  {
	    /* Extra zero pages should appear at the end of this segment,
	       after the data mapped from the file.   */
	    ElfW(Addr) zero, zeroend, zeropage;

	    zero = l->l_addr + c->dataend;
	    zeroend = l->l_addr + c->allocend;
	    zeropage = (zero + _dl_pagesize - 1) & ~(_dl_pagesize - 1);

	    if (zeroend < zeropage)
	      /* All the extra data is in the last page of the segment.
		 We can just zero it.  */
	      zeropage = zeroend;

	    if (zeropage > zero)
	      {
		/* Zero the final part of the last page of the segment.  */
		if ((c->prot & PROT_WRITE) == 0)
		  {
		    /* Dag nab it.  */
		    if (__mprotect ((caddr_t) (zero & ~(_dl_pagesize - 1)),
				    _dl_pagesize, c->prot|PROT_WRITE) < 0)
		      lose (errno, "cannot change memory protections");
		  }
		memset ((void *) zero, 0, zeropage - zero);
		if ((c->prot & PROT_WRITE) == 0)
		  __mprotect ((caddr_t) (zero & ~(_dl_pagesize - 1)),
			      _dl_pagesize, c->prot);
	      }

	    if (zeroend > zeropage)
	      {
		/* Map the remaining zero pages in from the zero fill FD.  */
		caddr_t mapat;
		mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
				c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
				ANONFD, 0);
		if (mapat == MAP_FAILED)
		  lose (errno, "cannot map zero-fill pages");
	      }
	  }

	++c;
      }

    if (l->l_phdr == 0)
      {
	/* There was no PT_PHDR specified.  We need to find the phdr in the
           load image ourselves.  We assume it is in fact in the load image
           somewhere, and that the first load command starts at the
           beginning of the file and thus contains the ELF file header.  */
	ElfW(Addr) bof = l->l_addr + loadcmds[0].mapstart;
	assert (loadcmds[0].mapoff == 0);
	l->l_phdr = (void *) (bof + ((const ElfW(Ehdr) *) bof)->e_phoff);
      }
    else
      /* Adjust the PT_PHDR value by the runtime load address.  */
      (ElfW(Addr)) l->l_phdr += l->l_addr;
  }

  /* We are done mapping in the file.  We no longer need the descriptor.  */
  __close (fd);

  if (l->l_type == lt_library && type == ET_EXEC)
    l->l_type = lt_executable;

  if (l->l_ld == 0)
    {
      if (type == ET_DYN)
	LOSE ("object file has no dynamic section");
    }
  else
    (ElfW(Addr)) l->l_ld += l->l_addr;

  l->l_entry += l->l_addr;

  if (_dl_debug_files)
    {
      const size_t nibbles = sizeof (void *) * 2;
      char buf1[nibbles + 1];
      char buf2[nibbles + 1];
      char buf3[nibbles + 1];

      buf1[nibbles] = '\0';
      buf2[nibbles] = '\0';
      buf3[nibbles] = '\0';

      memset (buf1, '0', nibbles);
      memset (buf2, '0', nibbles);
      memset (buf3, '0', nibbles);
      _itoa_word ((unsigned long int) l->l_ld, &buf1[nibbles], 16, 0);
      _itoa_word ((unsigned long int) l->l_addr, &buf2[nibbles], 16, 0);
      _itoa_word (maplength, &buf3[nibbles], 16, 0);

      _dl_debug_message (1, "  dynamic: 0x", buf1, "  base: 0x", buf2,
			 "   size: 0x", buf3, "\n", NULL);
      memset (buf1, '0', nibbles);
      memset (buf2, '0', nibbles);
      memset (buf3, ' ', nibbles);
      _itoa_word ((unsigned long int) l->l_entry, &buf1[nibbles], 16, 0);
      _itoa_word ((unsigned long int) l->l_phdr, &buf2[nibbles], 16, 0);
      _itoa_word (l->l_phnum, &buf3[nibbles], 10, 0);
      _dl_debug_message (1, "    entry: 0x", buf1, "  phdr: 0x", buf2,
			 "  phnum:   ", buf3, "\n\n", NULL);
    }

  elf_get_dynamic_info (l->l_ld, l->l_info);
  if (l->l_info[DT_HASH])
    _dl_setup_hash (l);

  /* If this object has DT_SYMBOLIC set modify now its scope.  We don't
     have to do this for the main map.  */
  if (l->l_info[DT_SYMBOLIC] && &l->l_searchlist != l->l_scope[0])
    {
      /* Create an appropriate searchlist.  It contains only this map.

	 XXX This is the definition of DT_SYMBOLIC in SysVr4.  The old
	 GNU ld.so implementation had a different interpretation which
	 is more reasonable.  We are prepared to add this possibility
	 back as part of a GNU extension of the ELF format.  */
      l->l_symbolic_searchlist.r_list =
	(struct link_map **) malloc (sizeof (struct link_map *));

      if (l->l_symbolic_searchlist.r_list == NULL)
	lose (ENOMEM, "cannot create searchlist");

      l->l_symbolic_searchlist.r_list[0] = l;
      l->l_symbolic_searchlist.r_nlist = 1;
      l->l_symbolic_searchlist.r_duplist = l->l_symbolic_searchlist.r_list;
      l->l_symbolic_searchlist.r_nduplist = 1;

      /* Now move the existing entries one back.  */
      memmove (&l->l_scope[1], &l->l_scope[0],
	       3 * sizeof (struct r_scope_elem *));

      /* Now add the new entry.  */
      l->l_scope[0] = &l->l_symbolic_searchlist;
    }

  return l;
}

/* Print search path.  */
static void
print_search_path (struct r_search_path_elem **list,
                   const char *what, const char *name)
{
  char buf[max_dirnamelen + max_capstrlen];
  int first = 1;

  _dl_debug_message (1, " search path=", NULL);

  while (*list != NULL && (*list)->what == what) /* Yes, ==.  */
    {
      char *endp = __mempcpy (buf, (*list)->dirname, (*list)->dirnamelen);
      size_t cnt;

      for (cnt = 0; cnt < ncapstr; ++cnt)
	if ((*list)->status[cnt] != nonexisting)
	  {
	    char *cp = __mempcpy (endp, capstr[cnt].str, capstr[cnt].len);
	    if (cp == buf || (cp == buf + 1 && buf[0] == '/'))
	      cp[0] = '\0';
	    else
	      cp[-1] = '\0';
	    _dl_debug_message (0, first ? "" : ":", buf, NULL);
	    first = 0;
	  }

      ++list;
    }

  if (name != NULL)
    _dl_debug_message (0, "\t\t(", what, " from file ",
			name[0] ? name : _dl_argv[0], ")\n", NULL);
  else
    _dl_debug_message (0, "\t\t(", what, ")\n", NULL);
}

/* Try to open NAME in one of the directories in DIRS.
   Return the fd, or -1.  If successful, fill in *REALNAME
   with the malloc'd full directory name.  */

static int
open_path (const char *name, size_t namelen, int preloaded,
	   struct r_search_path_elem **dirs,
	   char **realname)
{
  char *buf;
  int fd = -1;
  const char *current_what = NULL;

  if (dirs == NULL || *dirs == NULL)
    {
      __set_errno (ENOENT);
      return -1;
    }

  buf = __alloca (max_dirnamelen + max_capstrlen + namelen);
  do
    {
      struct r_search_path_elem *this_dir = *dirs;
      size_t buflen = 0;
      size_t cnt;
      char *edp;

      /* If we are debugging the search for libraries print the path
	 now if it hasn't happened now.  */
      if (_dl_debug_libs && current_what != this_dir->what)
	{
	  current_what = this_dir->what;
	  print_search_path (dirs, current_what, this_dir->where);
	}

      edp = (char *) __mempcpy (buf, this_dir->dirname, this_dir->dirnamelen);
      for (cnt = 0; fd == -1 && cnt < ncapstr; ++cnt)
	{
	  /* Skip this directory if we know it does not exist.  */
	  if (this_dir->status[cnt] == nonexisting)
	    continue;

	  buflen =
	    ((char *) __mempcpy (__mempcpy (edp,
					    capstr[cnt].str, capstr[cnt].len),
				 name, namelen)
	     - buf);

	  /* Print name we try if this is wanted.  */
	  if (_dl_debug_libs)
	    _dl_debug_message (1, "  trying file=", buf, "\n", NULL);

	  fd = __open (buf, O_RDONLY);
	  if (this_dir->status[cnt] == unknown)
	    {
	      if (fd != -1)
		this_dir->status[cnt] = existing;
	      else
		{
		  /* We failed to open machine dependent library.  Let's
		     test whether there is any directory at all.  */
		  struct stat st;

		  buf[buflen - namelen - 1] = '\0';

		  if (__xstat (_STAT_VER, buf, &st) != 0
		      || ! S_ISDIR (st.st_mode))
		    /* The directory does not exist or it is no directory.  */
		    this_dir->status[cnt] = nonexisting;
		  else
		    this_dir->status[cnt] = existing;
		}
	    }

	  if (fd != -1 && preloaded && __libc_enable_secure)
	    {
	      /* This is an extra security effort to make sure nobody can
		 preload broken shared objects which are in the trusted
		 directories and so exploit the bugs.  */
	      struct stat st;

	      if (__fxstat (_STAT_VER, fd, &st) != 0
		  || (st.st_mode & S_ISUID) == 0)
		{
		  /* The shared object cannot be tested for being SUID
		     or this bit is not set.  In this case we must not
		     use this object.  */
		  __close (fd);
		  fd = -1;
		  /* We simply ignore the file, signal this by setting
		     the error value which would have been set by `open'.  */
		  errno = ENOENT;
		}
	    }
	}

      if (fd != -1)
	{
	  *realname = malloc (buflen);
	  if (*realname != NULL)
	    {
	      memcpy (*realname, buf, buflen);
	      return fd;
	    }
	  else
	    {
	      /* No memory for the name, we certainly won't be able
		 to load and link it.  */
	      __close (fd);
	      return -1;
	    }
	}
      if (errno != ENOENT && errno != EACCES)
	/* The file exists and is readable, but something went wrong.  */
	return -1;
    }
  while (*++dirs != NULL);

  return -1;
}

/* Map in the shared object file NAME.  */

struct link_map *
internal_function
_dl_map_object (struct link_map *loader, const char *name, int preloaded,
		int type, int trace_mode)
{
  int fd;
  char *realname;
  char *name_copy;
  struct link_map *l;

  /* Look for this name among those already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    {
      /* If the requested name matches the soname of a loaded object,
	 use that object.  Elide this check for names that have not
	 yet been opened.  */
      if (l->l_opencount <= 0)
	continue;
      if (!_dl_name_match_p (name, l))
	{
	  const char *soname;

	  if (l->l_info[DT_SONAME] == NULL)
	    continue;

	  soname = (const char *) (l->l_addr
				   + l->l_info[DT_STRTAB]->d_un.d_ptr
				   + l->l_info[DT_SONAME]->d_un.d_val);
	  if (strcmp (name, soname) != 0)
	    continue;

	  /* We have a match on a new name -- cache it.  */
	  add_name_to_object (l, soname);
	}

      /* We have a match -- bump the reference count and return it.  */
      ++l->l_opencount;
      return l;
    }

  /* Display information if we are debugging.  */
  if (_dl_debug_files && loader != NULL)
    _dl_debug_message (1, "\nfile=", name, ";  needed by ",
		       loader->l_name[0] ? loader->l_name : _dl_argv[0],
		       "\n", NULL);

  if (strchr (name, '/') == NULL)
    {
      /* Search for NAME in several places.  */

      size_t namelen = strlen (name) + 1;

      if (_dl_debug_libs)
	_dl_debug_message (1, "find library=", name, "; searching\n", NULL);

      fd = -1;

      /* First try the DT_RPATH of the dependent object that caused NAME
	 to be loaded.  Then that object's dependent, and on up.  */
      for (l = loader; fd == -1 && l; l = l->l_loader)
	if (l && l->l_info[DT_RPATH])
	  {
	    /* Make sure the cache information is available.  */
	    if (l->l_rpath_dirs == NULL)
	      {
		size_t ptrval = (l->l_addr
				 + l->l_info[DT_STRTAB]->d_un.d_ptr
				 + l->l_info[DT_RPATH]->d_un.d_val);
		l->l_rpath_dirs =
		  decompose_rpath ((const char *) ptrval, l);
	      }

	    if (l->l_rpath_dirs != NULL)
	      fd = open_path (name, namelen, preloaded, l->l_rpath_dirs,
			      &realname);
	  }

      /* If dynamically linked, try the DT_RPATH of the executable itself.  */
      l = _dl_loaded;
      if (fd == -1 && l && l->l_type != lt_loaded && l != loader
	  && l->l_rpath_dirs != NULL)
	fd = open_path (name, namelen, preloaded, l->l_rpath_dirs, &realname);

      /* Try the LD_LIBRARY_PATH environment variable.  */
      if (fd == -1 && env_path_list != NULL)
	fd = open_path (name, namelen, preloaded, env_path_list, &realname);

      if (fd == -1)
	{
	  /* Check the list of libraries in the file /etc/ld.so.cache,
	     for compatibility with Linux's ldconfig program.  */
	  extern const char *_dl_load_cache_lookup (const char *name);
	  const char *cached = _dl_load_cache_lookup (name);
	  if (cached)
	    {
	      fd = __open (cached, O_RDONLY);
	      if (fd != -1)
		{
		  realname = local_strdup (cached);
		  if (realname == NULL)
		    {
		      __close (fd);
		      fd = -1;
		    }
		}
	    }
	}

      /* Finally, try the default path.  */
      if (fd == -1)
	fd = open_path (name, namelen, preloaded, rtld_search_dirs, &realname);

      /* Add another newline when we a tracing the library loading.  */
      if (_dl_debug_libs)
        _dl_debug_message (1, "\n", NULL);
    }
  else
    {
      /* The path may contain dynamic string tokens.  */
      realname = (loader
		  ? expand_dynamic_string_token (loader, name)
		  : local_strdup (name));
      if (realname == NULL)
	fd = -1;
      else
	{
	  fd = __open (realname, O_RDONLY);
	  if (fd == -1)
	    free (realname);
	}
    }

  if (fd == -1)
    {
      if (trace_mode)
	{
	  /* We haven't found an appropriate library.  But since we
	     are only interested in the list of libraries this isn't
	     so severe.  Fake an entry with all the information we
	     have.  */
	  static const ElfW(Symndx) dummy_bucket = STN_UNDEF;

	  /* Enter the new object in the list of loaded objects.  */
	  if ((name_copy = local_strdup (name)) == NULL
	      || (l = _dl_new_object (name_copy, name, type, loader)) == NULL)
	    _dl_signal_error (ENOMEM, name,
			      "cannot create shared object descriptor");
	  /* We use an opencount of 0 as a sign for the faked entry.  */
	  l->l_opencount = 0;
	  l->l_reserved = 0;
	  l->l_buckets = &dummy_bucket;
	  l->l_nbuckets = 1;
	  l->l_relocated = 1;

	  return l;
	}
      else
	_dl_signal_error (errno, name, "cannot open shared object file");
    }

  return _dl_map_object_from_fd (name, fd, realname, loader, type);
}