path: root/src/unexcoff.c

/* Copyright (C) 1985-1988, 1992-1994, 2001-2023 Free Software
 * Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

GNU Emacs 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */


/*
 * unexcoff.c - Convert a running program into an a.out or COFF file.
 *
 * ==================================================================
 * Note: This file is currently used only by the MSDOS (a.k.a. DJGPP)
 * build of Emacs.  If you are not interested in the MSDOS build, you
 * are looking at the wrong version of unexec!
 * ==================================================================
 *
 * Author:	Spencer W. Thomas
 * 		Computer Science Dept.
 * 		University of Utah
 * Date:	Tue Mar  2 1982
 * Originally under the name unexec.c.
 * Modified heavily since then.
 *
 * Synopsis:
 *	unexec (const char *new_name, const char *old_name);
 *
 * Takes a snapshot of the program and makes an a.out format file in the
 * file named by the string argument new_name.
 * If a_name is non-NULL, the symbol table will be taken from the given file.
 * On some machines, an existing a_name file is required.
 *
 * If you make improvements I'd like to get them too.
 * harpo!utah-cs!thomas, thomas@Utah-20
 *
 */

/* Modified to support SysVr3 shared libraries by James Van Artsdalen
 * of Dell Computer Corporation.  james@bigtex.cactus.org.
 */

#include <config.h>
#include "unexec.h"
#include "lisp.h"

#define PERROR(file) report_error (file, new)

#ifdef HAVE_UNEXEC  /* all rest of file!  */

#ifdef HAVE_COFF_H
#include <coff.h>
#ifdef MSDOS
#include <fcntl.h>  /* for O_RDONLY, O_RDWR */
#include <crt0.h>   /* for _crt0_startup_flags and its bits */
#include <sys/exceptn.h>
static int save_djgpp_startup_flags;
#include <libc/atexit.h>
static struct __atexit *save_atexit_ptr;
#define filehdr external_filehdr
#define scnhdr external_scnhdr
#define syment external_syment
#define auxent external_auxent
#define n_numaux e_numaux
#define n_type e_type
struct aouthdr
{
  unsigned short	magic;	/* type of file				*/
  unsigned short	vstamp;	/* version stamp			*/
  unsigned long		tsize;	/* text size in bytes, padded to FW bdry*/
  unsigned long		dsize;	/* initialized data "  "		*/
  unsigned long		bsize;	/* uninitialized data "   "		*/
  unsigned long		entry;	/* entry pt.				*/
  unsigned long	 	text_start;/* base of text used for this file */
  unsigned long	 	data_start;/* base of data used for this file */
};
#endif /* MSDOS */
#else  /* not HAVE_COFF_H */
#include <a.out.h>
#endif /* not HAVE_COFF_H */

/* Define getpagesize if the system does not.
   Note that this may depend on symbols defined in a.out.h.  */
#include "getpagesize.h"

#ifndef makedev			/* Try to detect types.h already loaded */
#include <sys/types.h>
#endif /* makedev */
#include <errno.h>

#include <sys/file.h>

extern int etext;

static long block_copy_start;		/* Old executable start point */
static struct filehdr f_hdr;		/* File header */
static struct aouthdr f_ohdr;		/* Optional file header (a.out) */
long bias;			/* Bias to add for growth */
long lnnoptr;			/* Pointer to line-number info within file */
#define SYMS_START block_copy_start

static long text_scnptr;
static long data_scnptr;

static long coff_offset;

static int pagemask;

/* Correct an int which is the bit pattern of a pointer to a byte
   into an int which is the number of a byte.
   This is a no-op on ordinary machines, but not on all.  */

#define ADDR_CORRECT(x) ((char *) (x) - (char *) 0)

#include "lisp.h"

static void
report_error (const char *file, int fd)
{
  int err = errno;
  if (fd)
    emacs_close (fd);
  report_file_errno ("Cannot unexec", build_string (file), err);
}

#define ERROR0(msg) report_error_1 (new, msg, 0, 0); return -1
#define ERROR1(msg,x) report_error_1 (new, msg, x, 0); return -1
#define ERROR2(msg,x,y) report_error_1 (new, msg, x, y); return -1

static void
report_error_1 (int fd, const char *msg, int a1, int a2)
{
  emacs_close (fd);
  error (msg, a1, a2);
}

static int make_hdr (int, int, const char *, const char *);
static int copy_text_and_data (int, int);
static int copy_sym (int, int, const char *, const char *);
static void mark_x (const char *);

/* ****************************************************************
 * make_hdr
 *
 * Make the header in the new a.out from the header in core.
 * Modify the text and data sizes.
 */
static int
make_hdr (int new, int a_out,
	  const char *a_name, const char *new_name)
{
  auto struct scnhdr f_thdr;		/* Text section header */
  auto struct scnhdr f_dhdr;		/* Data section header */
  auto struct scnhdr f_bhdr;		/* Bss section header */
  auto struct scnhdr scntemp;		/* Temporary section header */
  register int scns;
  unsigned int bss_start;
  unsigned int data_start;

  pagemask = getpagesize () - 1;

  /* Adjust text/data boundary. */
  data_start = (int) DATA_START;
  data_start = ADDR_CORRECT (data_start);
  data_start = data_start & ~pagemask; /* (Down) to page boundary. */

  bss_start = ADDR_CORRECT (sbrk (0)) + pagemask;
  bss_start &= ~ pagemask;

  if (data_start > bss_start)	/* Can't have negative data size. */
    {
      ERROR2 ("unexec: data_start (%u) can't be greater than bss_start (%u)",
	      data_start, bss_start);
    }

  coff_offset = 0L;		/* stays zero, except in DJGPP */

  /* Salvage as much info from the existing file as possible */
  if (a_out >= 0)
    {
#ifdef MSDOS
      /* Support the coff-go32-exe format with a prepended stub, since
	 this is what GCC 2.8.0 and later generates by default in DJGPP.  */
      unsigned short mz_header[3];

      if (read (a_out, &mz_header, sizeof (mz_header)) != sizeof (mz_header))
	{
	  PERROR (a_name);
	}
      if (mz_header[0] == 0x5a4d || mz_header[0] == 0x4d5a) /* "MZ" or "ZM" */
	{
	  coff_offset = (long)mz_header[2] * 512L;
	  if (mz_header[1])
	    coff_offset += (long)mz_header[1] - 512L;
	  lseek (a_out, coff_offset, 0);
	}
      else
	lseek (a_out, 0L, 0);
#endif /* MSDOS */
      if (read (a_out, &f_hdr, sizeof (f_hdr)) != sizeof (f_hdr))
	{
	  PERROR (a_name);
	}
      block_copy_start += sizeof (f_hdr);
      if (f_hdr.f_opthdr > 0)
	{
	  if (read (a_out, &f_ohdr, sizeof (f_ohdr)) != sizeof (f_ohdr))
	    {
	      PERROR (a_name);
	    }
	  block_copy_start += sizeof (f_ohdr);
	}
      /* Loop through section headers, copying them in */
      lseek (a_out, coff_offset + sizeof (f_hdr) + f_hdr.f_opthdr, 0);
      for (scns = f_hdr.f_nscns; scns > 0; scns--) {
	if (read (a_out, &scntemp, sizeof (scntemp)) != sizeof (scntemp))
	  {
	    PERROR (a_name);
	  }
	if (scntemp.s_scnptr > 0L)
	  {
            if (block_copy_start < scntemp.s_scnptr + scntemp.s_size)
	      block_copy_start = scntemp.s_scnptr + scntemp.s_size;
	  }
	if (strcmp (scntemp.s_name, ".text") == 0)
	  {
	    f_thdr = scntemp;
	  }
	else if (strcmp (scntemp.s_name, ".data") == 0)
	  {
	    f_dhdr = scntemp;
	  }
	else if (strcmp (scntemp.s_name, ".bss") == 0)
	  {
	    f_bhdr = scntemp;
	  }
      }
    }
  else
    {
      ERROR0 ("can't build a COFF file from scratch yet");
    }

  /* Now we alter the contents of all the f_*hdr variables
     to correspond to what we want to dump.  */

  f_hdr.f_flags |= (F_RELFLG | F_EXEC);
  f_ohdr.dsize = bss_start - f_ohdr.data_start;
  f_ohdr.bsize = 0;
  f_thdr.s_size = f_ohdr.tsize;
  f_thdr.s_scnptr = sizeof (f_hdr) + sizeof (f_ohdr);
  f_thdr.s_scnptr += (f_hdr.f_nscns) * (sizeof (f_thdr));
  lnnoptr = f_thdr.s_lnnoptr;
  text_scnptr = f_thdr.s_scnptr;
  f_dhdr.s_paddr = f_ohdr.data_start;
  f_dhdr.s_vaddr = f_ohdr.data_start;
  f_dhdr.s_size = f_ohdr.dsize;
  f_dhdr.s_scnptr = f_thdr.s_scnptr + f_thdr.s_size;
  data_scnptr = f_dhdr.s_scnptr;
  f_bhdr.s_paddr = f_ohdr.data_start + f_ohdr.dsize;
  f_bhdr.s_vaddr = f_ohdr.data_start + f_ohdr.dsize;
  f_bhdr.s_size = f_ohdr.bsize;
  f_bhdr.s_scnptr = 0L;
  bias = f_dhdr.s_scnptr + f_dhdr.s_size - block_copy_start;

  if (f_hdr.f_symptr > 0L)
    {
      f_hdr.f_symptr += bias;
    }

  if (f_thdr.s_lnnoptr > 0L)
    {
      f_thdr.s_lnnoptr += bias;
    }

  if (write (new, &f_hdr, sizeof (f_hdr)) != sizeof (f_hdr))
    {
      PERROR (new_name);
    }

  if (write (new, &f_ohdr, sizeof (f_ohdr)) != sizeof (f_ohdr))
    {
      PERROR (new_name);
    }

  if (write (new, &f_thdr, sizeof (f_thdr)) != sizeof (f_thdr))
    {
      PERROR (new_name);
    }

  if (write (new, &f_dhdr, sizeof (f_dhdr)) != sizeof (f_dhdr))
    {
      PERROR (new_name);
    }

  if (write (new, &f_bhdr, sizeof (f_bhdr)) != sizeof (f_bhdr))
    {
      PERROR (new_name);
    }

  return (0);

}

void
write_segment (int new, const char *ptr, const char *end)
{
  register int i, nwrite, ret;
  /* This is the normal amount to write at once.
     It is the size of block that NFS uses.  */
  int writesize = 1 << 13;
  int pagesize = getpagesize ();
  char zeros[1 << 13];

  memset (zeros, 0, sizeof (zeros));

  for (i = 0; ptr < end;)
    {
      /* Distance to next multiple of writesize.  */
      nwrite = (((int) ptr + writesize) & -writesize) - (int) ptr;
      /* But not beyond specified end.  */
      if (nwrite > end - ptr) nwrite = end - ptr;
      ret = write (new, ptr, nwrite);
      /* If write gets a page fault, it means we reached
	 a gap between the old text segment and the old data segment.
	 This gap has probably been remapped into part of the text segment.
	 So write zeros for it.  */
      if (ret == -1 && errno == EFAULT)
	{
	  /* Write only a page of zeros at once,
	     so that we don't overshoot the start
	     of the valid memory in the old data segment.  */
	  if (nwrite > pagesize)
	    nwrite = pagesize;
	  write (new, zeros, nwrite);
	}
      i += nwrite;
      ptr += nwrite;
    }
}
/* ****************************************************************
 * copy_text_and_data
 *
 * Copy the text and data segments from memory to the new a.out
 */
static int
copy_text_and_data (int new, int a_out)
{
  register char *end;
  register char *ptr;

#ifdef MSDOS
  /* Dump the original table of exception handlers, not the one
     where our exception hooks are registered.  */
  __djgpp_exception_toggle ();

  /* Switch off startup flags that might have been set at runtime
     and which might change the way that dumped Emacs works.  */
  save_djgpp_startup_flags = _crt0_startup_flags;
  _crt0_startup_flags &= ~(_CRT0_FLAG_NO_LFN | _CRT0_FLAG_NEARPTR);

  /* Zero out the 'atexit' chain in the dumped executable, to avoid
     calling the atexit functions twice.  (emacs.c:main installs an
     atexit function.)  */
  save_atexit_ptr = __atexit_ptr;
  __atexit_ptr = NULL;
#endif

  lseek (new, (long) text_scnptr, 0);
  ptr = (char *) f_ohdr.text_start;
  end = ptr + f_ohdr.tsize;
  write_segment (new, ptr, end);

  lseek (new, (long) data_scnptr, 0);
  ptr = (char *) f_ohdr.data_start;
  end = ptr + f_ohdr.dsize;
  write_segment (new, ptr, end);

#ifdef MSDOS
  /* Restore our exception hooks.  */
  __djgpp_exception_toggle ();

  /* Restore the startup flags.  */
  _crt0_startup_flags = save_djgpp_startup_flags;

  /* Restore the atexit chain.  */
  __atexit_ptr = save_atexit_ptr;
#endif


  return 0;
}

/* ****************************************************************
 * copy_sym
 *
 * Copy the relocation information and symbol table from the a.out to the new
 */
static int
copy_sym (int new, int a_out, const char *a_name, const char *new_name)
{
  char page[1024];
  int n;

  if (a_out < 0)
    return 0;

  if (SYMS_START == 0L)
    return 0;

  if (lnnoptr)			/* if there is line number info */
    lseek (a_out, coff_offset + lnnoptr, 0);	/* start copying from there */
  else
    lseek (a_out, coff_offset + SYMS_START, 0);	/* Position a.out to symtab. */

  while ((n = read (a_out, page, sizeof page)) > 0)
    {
      if (write (new, page, n) != n)
	{
	  PERROR (new_name);
	}
    }
  if (n < 0)
    {
      PERROR (a_name);
    }
  return 0;
}


/*
 *	If the COFF file contains a symbol table and a line number section,
 *	then any auxiliary entries that have values for x_lnnoptr must
 *	be adjusted by the amount that the line number section has moved
 *	in the file (bias computed in make_hdr).  The #@$%&* designers of
 *	the auxiliary entry structures used the absolute file offsets for
 *	the line number entry rather than an offset from the start of the
 *	line number section!
 *
 *	When I figure out how to scan through the symbol table and pick out
 *	the auxiliary entries that need adjustment, this routine will
 *	be fixed.  As it is now, all such entries are wrong and sdb
 *	will complain.   Fred Fish, UniSoft Systems Inc.
 */

/* This function is probably very slow.  Instead of reopening the new
   file for input and output it should copy from the old to the new
   using the two descriptors already open (WRITEDESC and READDESC).
   Instead of reading one small structure at a time it should use
   a reasonable size buffer.  But I don't have time to work on such
   things, so I am installing it as submitted to me.  -- RMS.  */

int
adjust_lnnoptrs (int writedesc, int readdesc, const char *new_name)
{
  register int nsyms;
  register int new;
  struct syment symentry;
  union auxent auxentry;

  if (!lnnoptr || !f_hdr.f_symptr)
    return 0;

#ifdef MSDOS
  if ((new = writedesc) < 0)
#else
  if ((new = emacs_open (new_name, O_RDWR, 0)) < 0)
#endif
    {
      PERROR (new_name);
      return -1;
    }

  lseek (new, f_hdr.f_symptr, 0);
  for (nsyms = 0; nsyms < f_hdr.f_nsyms; nsyms++)
    {
      read (new, &symentry, SYMESZ);
      if (symentry.n_numaux)
	{
	  read (new, &auxentry, AUXESZ);
	  nsyms++;
	  if (ISFCN (symentry.n_type) || symentry.n_type == 0x2400)
	    {
	      auxentry.x_sym.x_fcnary.x_fcn.x_lnnoptr += bias;
	      lseek (new, -AUXESZ, 1);
	      write (new, &auxentry, AUXESZ);
	    }
	}
    }
#ifndef MSDOS
  emacs_close (new);
#endif
  return 0;
}

/* ****************************************************************
 * unexec
 *
 * driving logic.
 */
void
unexec (const char *new_name, const char *a_name)
{
  int new = -1, a_out = -1;

  if (a_name && (a_out = emacs_open (a_name, O_RDONLY, 0)) < 0)
    {
      PERROR (a_name);
    }
  if ((new = emacs_open (new_name, O_WRONLY | O_CREAT | O_TRUNC, 0777)) < 0)
    {
      PERROR (new_name);
    }

  if (make_hdr (new, a_out, a_name, new_name) < 0
      || copy_text_and_data (new, a_out) < 0
      || copy_sym (new, a_out, a_name, new_name) < 0
      || adjust_lnnoptrs (new, a_out, new_name) < 0
      )
    {
      emacs_close (new);
      return;
    }

  emacs_close (new);
  if (a_out >= 0)
    emacs_close (a_out);
}

#endif /* HAVE_UNEXEC */