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;
  const char *p;
  int fd;

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

  buf = alloca (strlen (dirpath) + 1 + namelen);
  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;
  struct link_map *l = NULL;
  char *realname;
  const size_t pagesize = getpagesize ();
  void *file_mapping = NULL;
  size_t mapping_size = 0;

  void lose (int code, const char *msg)
    {
      (void) close (fd);
      if (file_mapping)
	munmap (file_mapping, mapping_size);
      _dl_signal_error (code, l ? l->l_name : name, msg);
    }

  /* 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)
	    lose (errno, "cannot map file data");
	  file_mapping = result;
	}
      return file_mapping + location;
    }

  const Elf32_Ehdr *header;

  /* 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;

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

      fd = -1;
      if (loader && loader->l_info[DT_RPATH])
	trypath ((const char *) (loader->l_addr +
				 loader->l_info[DT_STRTAB]->d_un.d_ptr +
				 loader->l_info[DT_RPATH]->d_un.d_val));
      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)
    lose (errno, "cannot open shared object file");

  /* 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);

#undef LOSE
#define LOSE(s) lose (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, NULL, "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));
    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)
	      lose (errno, "failed to map segment 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.   */
		caddr_t zero, zeroend, zeropage;

		mapat += ph->p_vaddr - mapstart;
		zero = mapat + ph->p_filesz;
		zeroend = mapat + ph->p_memsz;
		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)
			  lose (errno, "cannot change memory protections");
		      }
		    memset (zero, 0, zeropage - 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|MAP_INHERIT,
				_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;
}