unexelf.c

早期freebsd实现

2           0x60874     0x80a9874   0           
0x80        0           7           0           


 */

#include <sys/types.h>
#include <stdio.h>
#include <sys/stat.h>
#include <memory.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <elf.h>
#include <sys/mman.h>

#ifndef emacs
#define fatal(a, b, c) fprintf(stderr, a, b, c), exit(1)
#else
extern void fatal(char *, ...);
#endif

/* Get the address of a particular section or program header entry,
 * accounting for the size of the entries.
 */

#define OLD_SECTION_H(n) \
     (*(Elf32_Shdr *) ((byte *) old_section_h + old_file_h->e_shentsize * (n)))
#define NEW_SECTION_H(n) \
     (*(Elf32_Shdr *) ((byte *) new_section_h + new_file_h->e_shentsize * (n)))
#define OLD_PROGRAM_H(n) \
     (*(Elf32_Phdr *) ((byte *) old_program_h + old_file_h->e_phentsize * (n)))
#define NEW_PROGRAM_H(n) \
     (*(Elf32_Phdr *) ((byte *) new_program_h + new_file_h->e_phentsize * (n)))

typedef unsigned char byte;

/* ****************************************************************
 * unexec
 *
 * driving logic.
 *
 * In ELF, this works by replacing the old .bss section with a new
 * .data section, and inserting an empty .bss immediately afterwards.
 *
 */
void
unexec (new_name, old_name, data_start, bss_start, entry_address)
     char *new_name, *old_name;
     unsigned data_start, bss_start, entry_address;
{
  extern unsigned int bss_end;
  int new_file, old_file, new_file_size;

  /* Pointers to the base of the image of the two files. */
  caddr_t old_base, new_base;

  /* Pointers to the file, program and section headers for the old and new
   * files.
   */
  Elf32_Ehdr *old_file_h, *new_file_h;
  Elf32_Phdr *old_program_h, *new_program_h;
  Elf32_Shdr *old_section_h, *new_section_h;

  /* Point to the section name table in the old file */
  char *old_section_names;

  Elf32_Addr old_bss_addr, new_bss_addr;
  Elf32_Word old_bss_size, new_data2_size;
  Elf32_Off  new_data2_offset;
  Elf32_Addr new_data2_addr;

  int n, old_bss_index, old_data_index, new_data2_index;
  struct stat stat_buf;

  /* Open the old file & map it into the address space. */

  old_file = open (old_name, O_RDONLY);

  if (old_file < 0)
    fatal ("Can't open %s for reading: errno %d\n", old_name, errno);

  if (fstat (old_file, &stat_buf) == -1)
    fatal ("Can't fstat(%s): errno %d\n", old_name, errno);

  old_base = mmap (0, stat_buf.st_size, PROT_READ, MAP_SHARED, old_file, 0);

  if (old_base == (caddr_t) -1)
    fatal ("Can't mmap(%s): errno %d\n", old_name, errno);

#ifdef DEBUG
  fprintf (stderr, "mmap(%s, %x) -> %x\n", old_name, stat_buf.st_size,
	   old_base);
#endif

  /* Get pointers to headers & section names */

  old_file_h = (Elf32_Ehdr *) old_base;
  old_program_h = (Elf32_Phdr *) ((byte *) old_base + old_file_h->e_phoff);
  old_section_h = (Elf32_Shdr *) ((byte *) old_base + old_file_h->e_shoff);
  old_section_names = (char *) old_base
    + OLD_SECTION_H(old_file_h->e_shstrndx).sh_offset;

  /* Find the old .bss section.  Figure out parameters of the new
   * data2 and bss sections.
   */

  for (old_bss_index = 1; old_bss_index < old_file_h->e_shnum; old_bss_index++)
    {
#ifdef DEBUG
      fprintf (stderr, "Looking for .bss - found %s\n",
	       old_section_names + OLD_SECTION_H(old_bss_index).sh_name);
#endif
      if (!strcmp (old_section_names + OLD_SECTION_H(old_bss_index).sh_name,
		   ".bss"))
	break;
    }
  if (old_bss_index == old_file_h->e_shnum)
    fatal ("Can't find .bss in %s.\n", old_name, 0);

  old_bss_addr = OLD_SECTION_H(old_bss_index).sh_addr;
  old_bss_size = OLD_SECTION_H(old_bss_index).sh_size;
#if defined(emacs) || !defined(DEBUG)
  bss_end = (unsigned int) sbrk (0);
  new_bss_addr = (Elf32_Addr) bss_end;
#else
  new_bss_addr = old_bss_addr + old_bss_size + 0x1234;
#endif
  new_data2_addr = old_bss_addr;
  new_data2_size = new_bss_addr - old_bss_addr;
  new_data2_offset = OLD_SECTION_H(old_bss_index).sh_offset;

#ifdef DEBUG
  fprintf (stderr, "old_bss_index %d\n", old_bss_index);
  fprintf (stderr, "old_bss_addr %x\n", old_bss_addr);
  fprintf (stderr, "old_bss_size %x\n", old_bss_size);
  fprintf (stderr, "new_bss_addr %x\n", new_bss_addr);
  fprintf (stderr, "new_data2_addr %x\n", new_data2_addr);
  fprintf (stderr, "new_data2_size %x\n", new_data2_size);
  fprintf (stderr, "new_data2_offset %x\n", new_data2_offset);
#endif

  if ((unsigned) new_bss_addr < (unsigned) old_bss_addr + old_bss_size)
    fatal (".bss shrank when undumping???\n", 0, 0);

  /* Set the output file to the right size and mmap(2) it.  Set
   * pointers to various interesting objects.  stat_buf still has
   * old_file data.
   */

  new_file = open (new_name, O_RDWR | O_CREAT, 0666);
  if (new_file < 0)
    fatal ("Can't creat(%s): errno %d\n", new_name, errno);

  new_file_size = stat_buf.st_size + old_file_h->e_shentsize + new_data2_size;

  if (ftruncate (new_file, new_file_size))
    fatal ("Can't ftruncate(%s): errno %d\n", new_name, errno);

  new_base = mmap (0, new_file_size, PROT_READ | PROT_WRITE, MAP_SHARED,
		   new_file, 0);

  if (new_base == (caddr_t) -1)
    fatal ("Can't mmap(%s): errno %d\n", new_name, errno);

  new_file_h = (Elf32_Ehdr *) new_base;
  new_program_h = (Elf32_Phdr *) ((byte *) new_base + old_file_h->e_phoff);
  new_section_h = (Elf32_Shdr *)
    ((byte *) new_base + old_file_h->e_shoff + new_data2_size);

  /* Make our new file, program and section headers as copies of the
   * originals.
   */

  memcpy (new_file_h, old_file_h, old_file_h->e_ehsize);
  memcpy (new_program_h, old_program_h,
	  old_file_h->e_phnum * old_file_h->e_phentsize);
  memcpy (new_section_h, old_section_h,
	  old_file_h->e_shnum * old_file_h->e_shentsize);

  /* Fix up file header.  We'll add one section.  Section header is
   * further away now.
   */

  new_file_h->e_shoff += new_data2_size;
  new_file_h->e_shnum += 1;

#ifdef DEBUG
  fprintf (stderr, "Old section offset %x\n", old_file_h->e_shoff);
  fprintf (stderr, "Old section count %d\n", old_file_h->e_shnum);
  fprintf (stderr, "New section offset %x\n", new_file_h->e_shoff);
  fprintf (stderr, "New section count %d\n", new_file_h->e_shnum);
#endif

  /* Fix up a new program header.  Extend the writable data segment so
   * that the bss area is covered too. Find that segment by looking
   * for a segment that ends just before the .bss area.  Make sure
   * that no segments are above the new .data2.  Put a loop at the end
   * to adjust the offset and address of any segment that is above
   * data2, just in case we decide to allow this later.
   */

  for (n = new_file_h->e_phnum - 1; n >= 0; n--)
    {
      if (NEW_PROGRAM_H(n).p_vaddr + NEW_PROGRAM_H(n).p_filesz > old_bss_addr)
	fatal ("Program segment above .bss in %s\n", old_name, 0);

      if (NEW_PROGRAM_H(n).p_type == PT_LOAD
	  && (NEW_PROGRAM_H(n).p_vaddr + NEW_PROGRAM_H(n).p_filesz
	      == old_bss_addr))
	break;
    }
  if (n < 0)
    fatal ("Couldn't find segment next to .bss in %s\n", old_name, 0);

  NEW_PROGRAM_H(n).p_filesz += new_data2_size;
  NEW_PROGRAM_H(n).p_memsz = NEW_PROGRAM_H(n).p_filesz;

#if 0 /* Maybe allow section after data2 - does this ever happen? */
  for (n = new_file_h->e_phnum - 1; n >= 0; n--)
    {
      if (NEW_PROGRAM_H(n).p_vaddr
	  && NEW_PROGRAM_H(n).p_vaddr >= new_data2_addr)
	NEW_PROGRAM_H(n).p_vaddr += new_data2_size - old_bss_size;

      if (NEW_PROGRAM_H(n).p_offset >= new_data2_offset)
	NEW_PROGRAM_H(n).p_offset += new_data2_size;
    }
#endif

  /* Fix up section headers based on new .data2 section.  Any section
   * whose offset or virtual address is after the new .data2 section
   * gets its value adjusted.  .bss size becomes zero and new address
   * is set.  data2 section header gets added by copying the existing
   * .data header and modifying the offset, address and size.
   */

  for (n = 1; n < new_file_h->e_shnum; n++)
    {
      if (NEW_SECTION_H(n).sh_offset >= new_data2_offset)
	NEW_SECTION_H(n).sh_offset += new_data2_size;

      if (NEW_SECTION_H(n).sh_addr
	  && NEW_SECTION_H(n).sh_addr >= new_data2_addr)
	NEW_SECTION_H(n).sh_addr += new_data2_size - old_bss_size;
    }

  new_data2_index = old_file_h->e_shnum;

  for (old_data_index = 1; old_data_index < old_file_h->e_shnum;
       old_data_index++)
    if (!strcmp (old_section_names + OLD_SECTION_H(old_data_index).sh_name,
		 ".data"))
      break;
  if (old_data_index == old_file_h->e_shnum)
    fatal ("Can't find .data in %s.\n", old_name, 0);

  memcpy (&NEW_SECTION_H(new_data2_index), &OLD_SECTION_H(old_data_index),
	  new_file_h->e_shentsize);

  NEW_SECTION_H(new_data2_index).sh_addr = new_data2_addr;
  NEW_SECTION_H(new_data2_index).sh_offset = new_data2_offset;
  NEW_SECTION_H(new_data2_index).sh_size = new_data2_size;

  NEW_SECTION_H(old_bss_index).sh_size = 0;
  NEW_SECTION_H(old_bss_index).sh_addr = new_data2_addr + new_data2_size;

  /* Write out the sections. .data and .data1 (and data2, called
   * ".data" in the strings table) get copied from the current process
   * instead of the old file.
   */

  for (n = new_file_h->e_shnum - 1; n; n--)
    {
      caddr_t src;

      if (NEW_SECTION_H(n).sh_type == SHT_NULL
	  || NEW_SECTION_H(n).sh_type == SHT_NOBITS)
	continue;

      if (!strcmp (old_section_names + NEW_SECTION_H(n).sh_name, ".data")
	  || !strcmp ((old_section_names + NEW_SECTION_H(n).sh_name),
		      ".data1"))
	src = (caddr_t) NEW_SECTION_H(n).sh_addr;
      else
	src = old_base + OLD_SECTION_H(n).sh_offset;

      memcpy (NEW_SECTION_H(n).sh_offset + new_base, src,
	      NEW_SECTION_H(n).sh_size);
    }

  /* Close the files and make the new file executable */

  if (close (old_file))
    fatal ("Can't close(%s): errno %d\n", old_name, errno);

  if (close (new_file))
    fatal ("Can't close(%s): errno %d\n", new_name, errno);

  if (stat (new_name, &stat_buf) == -1)
    fatal ("Can't stat(%s): errno %d\n", new_name, errno);

  n = umask (777);
  umask (n);
  stat_buf.st_mode |= 0111 & ~n;
  if (chmod (new_name, stat_buf.st_mode) == -1)
    fatal ("Can't chmod(%s): errno %d\n", new_name, errno);
}