glibc/elf/dl-load.c

/* _dl_map_object -- Map in a shared object's segments from the file.
Copyright (C) 1995 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 <sys/types.h>
#include <sys/mman.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include "dynamic-link.h"


#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) #x

int _dl_zerofd = -1;


/* Try to open NAME in one of the directories in DIRPATH.
   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,
	   const char *dirpath,
	   char **realname)
{
  char buf[strlen (dirpath) + 1 + namelen];
  const char *p;
  int fd;

  p = dirpath;
  if (p == NULL || *p == '\0')
    {
      errno = ENOENT;
      return -1;
    }

  do
    {
      dirpath = p;
      p = strpbrk (dirpath, ":;");
      if (p == NULL)
	p = strchr (dirpath, '\0');

      if (p == dirpath)
	/* Two adjacent colons, or a colon at the beginning or the end of
	   the path means to search the current directory.  */
	(void) memcpy (buf, name, namelen);
      else
	{
	  /* Construct the pathname to try.  */
	  (void) memcpy (buf, dirpath, p - dirpath);
	  buf[p - dirpath] = '/';
	  (void) memcpy (&buf[(p - dirpath) + 1], name, namelen);
	}

      fd = open (buf, O_RDONLY);
      if (fd != -1)
	{
	  *realname = strdup (buf);
	  return fd;
	}
      if (errno != ENOENT && errno != EACCES)
	/* The file exists and is readable, but something went wrong.  */
	return -1;
    }
  while (*p++ != '\0');

  return -1;
}


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

struct link_map *
_dl_map_object (struct link_map *loader, const char *name,
		Elf32_Addr *entry_point)
{
  int fd;
  char *realname;
  const size_t pagesize = getpagesize ();
  void *file_mapping = NULL;
  size_t mapping_size = 0;
  /* Make sure LOCATION is mapped in.  */
  void *map (off_t location, size_t size)
    {
      if ((off_t) mapping_size <= location + (off_t) size)
	{
	  void *result;
	  if (file_mapping)
	    munmap (file_mapping, mapping_size);
	  mapping_size = (location + size + 1 + pagesize - 1);
	  mapping_size &= ~(pagesize - 1);
	  result = mmap (file_mapping, mapping_size, PROT_READ,
			 MAP_COPY|MAP_FILE, fd, 0);
	  if (result == (void *) -1)
	    return NULL;
	  file_mapping = result;
	}
      return file_mapping + location;
    }

  const Elf32_Ehdr *header;
  struct link_map *l;

  /* Look for this name among those already loaded.  */
  for (l = _dl_loaded; l; l = l->l_next)
    if (! strcmp (name, l->l_libname))
      {
	/* The object is already loaded.
	   Just bump its reference count and return it.  */
	++l->l_opencount;
	return l;
      }

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

      size_t namelen = strlen (name) + 1;

      void trypath (const char *dirpath)
	{
	  fd = open_path (name, namelen, dirpath, &realname);
	}

      if (loader && loader->l_info[DT_RPATH])
	trypath ((const char *) (loader->l_addr +
				 loader->l_info[DT_RPATH]->d_un.d_ptr));
      if (fd == -1 && ! _dl_secure)
	trypath (getenv ("LD_LIBRARY_PATH"));
      if (fd == -1)
	trypath ("/lib:/usr/lib");
    }
  else
    {
      fd = open (name, O_RDONLY);
      if (fd != -1)
	realname = strdup (name);
    }

  if (fd == -1)
    return NULL;

  /* 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);
	++l->l_opencount;
	return l;
      }


  /* Map in the first page to read the header.  */
  header = map (0, sizeof *header);
  if (! header)
    {
    lose:
      (void) close (fd);
      if (file_mapping)
	munmap (file_mapping, mapping_size);
      return NULL;
    }

#undef LOSE
#define LOSE(s) _dl_signal_error (0, s)
  /* Check the header for basic validity.  */
  if (*(Elf32_Word *) &header->e_ident != ((ELFMAG0 << (EI_MAG0 * 8)) |
					   (ELFMAG1 << (EI_MAG1 * 8)) |
					   (ELFMAG2 << (EI_MAG2 * 8)) |
					   (ELFMAG3 << (EI_MAG3 * 8))))
    LOSE ("invalid ELF header");
  if (header->e_ident[EI_CLASS] != ELFCLASS32)
    LOSE ("ELF file class not 32-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));
  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 (Elf32_Phdr))
    LOSE ("ELF file's phentsize not the expected size");

  /* Enter the new object in the list of loaded objects.  */
  l = _dl_new_object (realname, name, lt_loaded);
  l->l_opencount = 1;

  if (_dl_zerofd == -1)
    {
      _dl_zerofd = _dl_sysdep_open_zero_fill ();
      if (_dl_zerofd == -1)
	_dl_signal_error (errno, "cannot open zero fill device");
    }

  {
    /* Copy the program header table into stack space so we can then unmap
       the headers.  */
    Elf32_Phdr phdr[header->e_phnum];
    const Elf32_Phdr *ph;
    int anywhere;

    ph = map (header->e_phoff, header->e_phnum * sizeof (Elf32_Phdr));
    if (! ph)
      goto lose;
    memcpy (phdr, ph, sizeof phdr);
    l->l_phnum = header->e_phnum;

    anywhere = header->e_type == ET_DYN || header->e_type == ET_REL;

    if (entry_point)
      *entry_point = header->e_entry;

    /* We are done reading the file's headers now.  Unmap them.  */
    munmap (file_mapping, mapping_size);

    /* Scan the program header table, processing its load commands.  */
    l->l_addr = 0;
    l->l_ld = 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.  */
	  if (ph->p_align % 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");
	  {
	    Elf32_Addr mapstart = ph->p_vaddr & ~(ph->p_align - 1);
	    Elf32_Addr mapend = ((ph->p_vaddr + ph->p_filesz + ph->p_align - 1)
				 & ~(ph->p_align - 1));
	    off_t mapoff = ph->p_offset & ~(ph->p_align - 1);
	    caddr_t mapat;
	    int prot = 0;
	    if (ph->p_flags & PF_R)
	      prot |= PROT_READ;
	    if (ph->p_flags & PF_W)
	      prot |= PROT_WRITE;
	    if (ph->p_flags & PF_X)
	      prot |= PROT_EXEC;

	    if (anywhere)
	      {
		/* XXX this loses if the first segment mmap call puts
		   it someplace where the later segments cannot fit.  */
		mapat = mmap ((caddr_t) l->l_addr + mapstart, mapend - mapstart,
			      prot, MAP_COPY|MAP_FILE|MAP_INHERIT |
			      /* Let the system choose any convenient
				 location if this is the first segment.
				 Following segments must be contiguous in
				 virtual space with the first.  */
			      (l->l_addr == 0 ? 0 : MAP_FIXED),
			      fd, mapoff);
		if (l->l_addr == 0)
		  /* This was the first segment mapped, so MAPAT is
		     the address the system chose for us.  Record it.  */
		  l->l_addr = (Elf32_Addr) mapat - mapstart;
	      }
	    else
	      {
		mapat = mmap ((caddr_t) mapstart, mapend - mapstart,
			      prot, MAP_COPY|MAP_FILE|MAP_INHERIT|MAP_FIXED,
			      fd, mapoff);
		/* This file refers to absolute addresses.  So consider its
		   "load base" to be zero, since that is what we add to the
		   file's addresses to find them in our memory.  */
		l->l_addr = 0;
	      }
	    if (mapat == (caddr_t) -1)
	      _dl_signal_error (errno,
				"failed to map region from shared object");

	    if (ph->p_memsz > ph->p_filesz)
	      {
		/* Extra zero pages should appear at the end of this segment,
		   after the data mapped from the file.  Adjust MAPEND to map
		   only the data from the file.  We will later allocate zero
		   pages following the data mapping.  */
		caddr_t zero = mapat - mapstart + ph->p_filesz;
		caddr_t zeroend = mapat - mapstart + ph->p_memsz;
		caddr_t zeropage
		  = (caddr_t) ((Elf32_Addr) (zero + pagesize - 1)
			       & ~(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 ((prot & PROT_WRITE) == 0)
		      {
			/* Dag nab it.  */
			if (mprotect ((caddr_t) ((Elf32_Addr) zero
						 & ~(pagesize - 1)),
				      pagesize,
				      prot|PROT_WRITE) < 0)
			  _dl_signal_error (errno,
					    "cannot change protections");
		      }
		    memset (zero, 0, zeroend - zero);
		    if ((prot & PROT_WRITE) == 0)
		      mprotect ((caddr_t) ((Elf32_Addr) zero
					   & ~(pagesize - 1)),
				pagesize, prot);
		  }

		if (zeroend > zeropage)
		  /* Map the remaining zero pages in from the zero fill FD.  */
		  mapat = mmap (zeropage, zeroend - zeropage,
				prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
				_dl_zerofd, 0);
	      }
	  }
	}

    if (l->l_ld == 0)
      LOSE ("object file has no dynamic section");
    (Elf32_Addr) l->l_ld += l->l_addr;

    if (l->l_phdr == 0)
      l->l_phdr = (void *) ((const Elf32_Ehdr *) l->l_addr)->e_phoff;
    (Elf32_Addr) l->l_phdr += l->l_addr;
  }

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

  return l;
}