libelf/elf32_updatefile.c

/* Write changed data structures.
   Copyright (C) 2000-2010, 2014 Red Hat, Inc.
   This file is part of elfutils.
   Written by Ulrich Drepper <drepper@redhat.com>, 2000.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at
       your option) any later version

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <assert.h>
#include <errno.h>
#include <libelf.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/param.h>

#include <system.h>
#include "libelfP.h"


#ifndef LIBELFBITS
# define LIBELFBITS 32
#endif


static int
compare_sections (const void *a, const void *b)
{
  const Elf_Scn **scna = (const Elf_Scn **) a;
  const Elf_Scn **scnb = (const Elf_Scn **) b;

  if ((*scna)->shdr.ELFW(e,LIBELFBITS)->sh_offset
      < (*scnb)->shdr.ELFW(e,LIBELFBITS)->sh_offset)
    return -1;

  if ((*scna)->shdr.ELFW(e,LIBELFBITS)->sh_offset
      > (*scnb)->shdr.ELFW(e,LIBELFBITS)->sh_offset)
    return 1;

  if ((*scna)->shdr.ELFW(e,LIBELFBITS)->sh_size
      < (*scnb)->shdr.ELFW(e,LIBELFBITS)->sh_size)
    return -1;

  if ((*scna)->shdr.ELFW(e,LIBELFBITS)->sh_size
      > (*scnb)->shdr.ELFW(e,LIBELFBITS)->sh_size)
    return 1;

  if ((*scna)->index < (*scnb)->index)
    return -1;

  if ((*scna)->index > (*scnb)->index)
    return 1;

  return 0;
}


/* Insert the sections in the list into the provided array and sort
   them according to their start offsets.  For sections with equal
   start offsets, the size is used; for sections with equal start
   offsets and sizes, the section index is used.  Sorting by size
   ensures that zero-length sections are processed first, which
   is what we want since they do not advance our file writing position.  */
static void
sort_sections (Elf_Scn **scns, Elf_ScnList *list)
{
  Elf_Scn **scnp = scns;
  do
    for (size_t cnt = 0; cnt < list->cnt; ++cnt)
      *scnp++ = &list->data[cnt];
  while ((list = list->next) != NULL);

  qsort (scns, scnp - scns, sizeof (*scns), compare_sections);
}


int
internal_function
__elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
{
  bool previous_scn_changed = false;

  /* We need the ELF header several times.  */
  ElfW2(LIBELFBITS,Ehdr) *ehdr = elf->state.ELFW(elf,LIBELFBITS).ehdr;

  /* Write out the ELF header.  */
  if ((elf->state.ELFW(elf,LIBELFBITS).ehdr_flags | elf->flags) & ELF_F_DIRTY)
    {
      /* If the type sizes should be different at some time we have to
	 rewrite this code.  */
      assert (sizeof (ElfW2(LIBELFBITS,Ehdr))
	      == elf_typesize (LIBELFBITS, ELF_T_EHDR, 1));

      if (unlikely (change_bo))
	{
	  /* Today there is only one version of the ELF header.  */
#if EV_NUM != 2
	  xfct_t fctp;
	  fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_EHDR];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_EHDR]
#endif

	  /* Do the real work.  */
	  (*fctp) ((char *) elf->map_address + elf->start_offset, ehdr,
		   sizeof (ElfW2(LIBELFBITS,Ehdr)), 1);
	}
      else if (elf->map_address + elf->start_offset != ehdr)
	memcpy (elf->map_address + elf->start_offset, ehdr,
		sizeof (ElfW2(LIBELFBITS,Ehdr)));

      elf->state.ELFW(elf,LIBELFBITS).ehdr_flags &= ~ELF_F_DIRTY;

      /* We start writing sections after the ELF header only if there is
	 no program header.  */
      previous_scn_changed = elf->state.ELFW(elf,LIBELFBITS).phdr == NULL;
    }

  size_t phnum;
  if (unlikely (__elf_getphdrnum_rdlock (elf, &phnum) != 0))
    return -1;

  /* Write out the program header table.  */
  if (elf->state.ELFW(elf,LIBELFBITS).phdr != NULL
      && ((elf->state.ELFW(elf,LIBELFBITS).phdr_flags | elf->flags)
	  & ELF_F_DIRTY))
    {
      /* If the type sizes should be different at some time we have to
	 rewrite this code.  */
      assert (sizeof (ElfW2(LIBELFBITS,Phdr))
	      == elf_typesize (LIBELFBITS, ELF_T_PHDR, 1));

      /* Maybe the user wants a gap between the ELF header and the program
	 header.  */
      if (ehdr->e_phoff > ehdr->e_ehsize)
	memset (elf->map_address + elf->start_offset + ehdr->e_ehsize,
		__libelf_fill_byte, ehdr->e_phoff - ehdr->e_ehsize);

      if (unlikely (change_bo))
	{
	  /* Today there is only one version of the ELF header.  */
#if EV_NUM != 2
	  xfct_t fctp;
	  fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_PHDR];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_PHDR]
#endif

	  /* Do the real work.  */
	  (*fctp) (elf->map_address + elf->start_offset + ehdr->e_phoff,
		   elf->state.ELFW(elf,LIBELFBITS).phdr,
		   sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum, 1);
	}
      else
	memcpy (elf->map_address + elf->start_offset + ehdr->e_phoff,
		elf->state.ELFW(elf,LIBELFBITS).phdr,
		sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum);

      elf->state.ELFW(elf,LIBELFBITS).phdr_flags &= ~ELF_F_DIRTY;

      /* We modified the program header.  Maybe this created a gap so
	 we have to write fill bytes, if necessary.  */
      previous_scn_changed = true;
    }

  /* From now on we have to keep track of the last position to eventually
     fill the gaps with the prescribed fill byte.  */
  char *last_position = ((char *) elf->map_address + elf->start_offset
			 + MAX (elf_typesize (LIBELFBITS, ELF_T_EHDR, 1),
				ehdr->e_phoff)
			 + elf_typesize (LIBELFBITS, ELF_T_PHDR, phnum));

  /* Write all the sections.  Well, only those which are modified.  */
  if (shnum > 0)
    {
      if (unlikely (shnum > SIZE_MAX / sizeof (Elf_Scn *)))
	return 1;

      Elf_ScnList *list = &elf->state.ELFW(elf,LIBELFBITS).scns;
      Elf_Scn **scns = (Elf_Scn **) alloca (shnum * sizeof (Elf_Scn *));
      char *const shdr_start = ((char *) elf->map_address + elf->start_offset
				+ ehdr->e_shoff);
      char *const shdr_end = shdr_start + ehdr->e_shnum * ehdr->e_shentsize;

#if EV_NUM != 2
      xfct_t shdr_fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_SHDR];
#else
# undef shdr_fctp
# define shdr_fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_SHDR]
#endif
#define shdr_dest ((ElfW2(LIBELFBITS,Shdr) *) shdr_start)

      /* Get all sections into the array and sort them.  */
      sort_sections (scns, list);

      /* We possibly have to copy the section header data because moving
	 the sections might overwrite the data.  */
      for (size_t cnt = 0; cnt < shnum; ++cnt)
	{
	  Elf_Scn *scn = scns[cnt];

	  if (!elf->state.ELFW(elf,LIBELFBITS).shdr_malloced
	      && (scn->shdr_flags & ELF_F_MALLOCED) == 0
	      && scn->shdr.ELFW(e,LIBELFBITS) != &shdr_dest[scn->index])
	    {
	      assert ((char *) elf->map_address + elf->start_offset
		      < (char *) scn->shdr.ELFW(e,LIBELFBITS));
	      assert ((char *) scn->shdr.ELFW(e,LIBELFBITS)
		      < ((char *) elf->map_address + elf->start_offset
			 + elf->maximum_size));

	      void *p = alloca (sizeof (ElfW2(LIBELFBITS,Shdr)));
	      scn->shdr.ELFW(e,LIBELFBITS)
		= memcpy (p, scn->shdr.ELFW(e,LIBELFBITS),
			  sizeof (ElfW2(LIBELFBITS,Shdr)));
	    }

	  /* If the file is mmaped and the original position of the
	     section in the file is lower than the new position we
	     need to save the section content since otherwise it is
	     overwritten before it can be copied.  If there are
	     multiple data segments in the list only the first can be
	     from the file.  */
	  if (((char *) elf->map_address + elf->start_offset
	       <= (char  *) scn->data_list.data.d.d_buf)
	      && ((char *) scn->data_list.data.d.d_buf
		  < ((char *) elf->map_address + elf->start_offset
		     + elf->maximum_size))
	      && (((char *) elf->map_address + elf->start_offset
		   + scn->shdr.ELFW(e,LIBELFBITS)->sh_offset)
		  > (char *) scn->data_list.data.d.d_buf))
	    {
	      void *p = malloc (scn->data_list.data.d.d_size);
	      if (p == NULL)
		{
		  __libelf_seterrno (ELF_E_NOMEM);
		  return -1;
		}
	      scn->data_list.data.d.d_buf = scn->data_base
		= memcpy (p, scn->data_list.data.d.d_buf,
			  scn->data_list.data.d.d_size);
	    }
	}

      /* Iterate over all the section in the order in which they
	 appear in the output file.  */
      for (size_t cnt = 0; cnt < shnum; ++cnt)
	{
	  Elf_Scn *scn = scns[cnt];
	  if (scn->index == 0)
	    {
	      /* The dummy section header entry.  It should not be
		 possible to mark this "section" as dirty.  */
	      assert ((scn->flags & ELF_F_DIRTY) == 0);
	      continue;
	    }

	  ElfW2(LIBELFBITS,Shdr) *shdr = scn->shdr.ELFW(e,LIBELFBITS);
	  if (shdr->sh_type == SHT_NOBITS)
	    goto next;

	  char *scn_start = ((char *) elf->map_address
			     + elf->start_offset + shdr->sh_offset);
	  Elf_Data_List *dl = &scn->data_list;
	  bool scn_changed = false;

	  void fill_mmap (size_t offset)
	  {
	    size_t written = 0;

	    if (last_position < shdr_start)
	      {
		written = MIN (scn_start + offset - last_position,
			       shdr_start - last_position);

		memset (last_position, __libelf_fill_byte, written);
	      }

	    if (last_position + written != scn_start + offset
		&& shdr_end < scn_start + offset)
	      {
		char *fill_start = MAX (shdr_end, scn_start);
		memset (fill_start, __libelf_fill_byte,
			scn_start + offset - fill_start);
	      }
	  }

	  if (scn->data_list_rear != NULL)
	    do
	      {
		assert (dl->data.d.d_off >= 0);
		assert ((GElf_Off) dl->data.d.d_off <= shdr->sh_size);
		assert (dl->data.d.d_size <= (shdr->sh_size
					      - (GElf_Off) dl->data.d.d_off));

		/* If there is a gap, fill it.  */
		if (scn_start + dl->data.d.d_off > last_position
		    && (dl->data.d.d_off == 0
			|| ((scn->flags | dl->flags | elf->flags)
			    & ELF_F_DIRTY) != 0))
		  {
		    fill_mmap (dl->data.d.d_off);
		    last_position = scn_start + dl->data.d.d_off;
		  }

		if ((scn->flags | dl->flags | elf->flags) & ELF_F_DIRTY)
		  {
		    /* Let it go backward if the sections use a bogus
		       layout with overlaps.  We'll overwrite the stupid
		       user's section data with the latest one, rather than
		       crashing.  */

		    last_position = scn_start + dl->data.d.d_off;

		    if (unlikely (change_bo))
		      {
#if EV_NUM != 2
			xfct_t fctp;
			fctp = __elf_xfctstom[__libelf_version - 1][dl->data.d.d_version - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][dl->data.d.d_type];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][dl->data.d.d_type]
#endif

			/* Do the real work.  */
			(*fctp) (last_position, dl->data.d.d_buf,
				 dl->data.d.d_size, 1);

			last_position += dl->data.d.d_size;
		      }
		    else
		      last_position = mempcpy (last_position,
					       dl->data.d.d_buf,
					       dl->data.d.d_size);

		    scn_changed = true;
		  }
		else
		  last_position += dl->data.d.d_size;

		assert (scn_start + dl->data.d.d_off + dl->data.d.d_size
			== last_position);

		dl->flags &= ~ELF_F_DIRTY;

		dl = dl->next;
	      }
	    while (dl != NULL);
	  else
	    {
	      /* If the previous section (or the ELF/program
		 header) changed we might have to fill the gap.  */
	      if (scn_start > last_position && previous_scn_changed)
		fill_mmap (0);

	      /* We have to trust the existing section header information.  */
	      last_position = scn_start + shdr->sh_size;
	    }


	  previous_scn_changed = scn_changed;
	next:
	  scn->flags &= ~ELF_F_DIRTY;
	}

      /* Fill the gap between last section and section header table if
	 necessary.  */
      if ((elf->flags & ELF_F_DIRTY)
	  && last_position < ((char *) elf->map_address + elf->start_offset
			      + ehdr->e_shoff))
	memset (last_position, __libelf_fill_byte,
		(char *) elf->map_address + elf->start_offset + ehdr->e_shoff
		- last_position);

      /* Write the section header table entry if necessary.  */
      for (size_t cnt = 0; cnt < shnum; ++cnt)
	{
	  Elf_Scn *scn = scns[cnt];

	  if ((scn->shdr_flags | elf->flags) & ELF_F_DIRTY)
	    {
	      if (unlikely (change_bo))
		(*shdr_fctp) (&shdr_dest[scn->index],
			      scn->shdr.ELFW(e,LIBELFBITS),
			      sizeof (ElfW2(LIBELFBITS,Shdr)), 1);
	      else
		memcpy (&shdr_dest[scn->index],
			scn->shdr.ELFW(e,LIBELFBITS),
			sizeof (ElfW2(LIBELFBITS,Shdr)));

	      /* If we previously made a copy of the section header
		 entry we now have to adjust the pointer again so
		 point to new place in the mapping.  */
	      if (!elf->state.ELFW(elf,LIBELFBITS).shdr_malloced
		  && (scn->shdr_flags & ELF_F_MALLOCED) == 0)
		scn->shdr.ELFW(e,LIBELFBITS) = &shdr_dest[scn->index];

	      scn->shdr_flags &= ~ELF_F_DIRTY;
	    }
	}
    }

  /* That was the last part.  Clear the overall flag.  */
  elf->flags &= ~ELF_F_DIRTY;

  /* Make sure the content hits the disk.  */
  char *msync_start = ((char *) elf->map_address
		       + (elf->start_offset & ~(sysconf (_SC_PAGESIZE) - 1)));
  char *msync_end = ((char *) elf->map_address
		     + elf->start_offset + ehdr->e_shoff
		     + ehdr->e_shentsize * shnum);
  (void) msync (msync_start, msync_end - msync_start, MS_SYNC);

  return 0;
}


/* Size of the buffer we use to generate the blocks of fill bytes.  */
#define FILLBUFSIZE	4096

/* If we have to convert the section buffer contents we have to use
   temporary buffer.  Only buffers up to MAX_TMPBUF bytes are allocated
   on the stack.  */
#define MAX_TMPBUF	32768


/* Helper function to write out fill bytes.  */
static int
fill (int fd, off_t pos, size_t len, char *fillbuf, size_t *filledp)
{
  size_t filled = *filledp;
  size_t fill_len = MIN (len, FILLBUFSIZE);

  if (unlikely (fill_len > filled) && filled < FILLBUFSIZE)
    {
      /* Initialize a few more bytes.  */
      memset (fillbuf + filled, __libelf_fill_byte, fill_len - filled);
      *filledp = filled = fill_len;
    }

  do
    {
      /* This many bytes we want to write in this round.  */
      size_t n = MIN (filled, len);

      if (unlikely ((size_t) pwrite_retry (fd, fillbuf, n, pos) != n))
	{
	  __libelf_seterrno (ELF_E_WRITE_ERROR);
	  return 1;
	}

      pos += n;
      len -= n;
    }
  while (len > 0);

  return 0;
}


int
internal_function
__elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
{
  char fillbuf[FILLBUFSIZE];
  size_t filled = 0;
  bool previous_scn_changed = false;

  /* We need the ELF header several times.  */
  ElfW2(LIBELFBITS,Ehdr) *ehdr = elf->state.ELFW(elf,LIBELFBITS).ehdr;

  /* Write out the ELF header.  */
  if ((elf->state.ELFW(elf,LIBELFBITS).ehdr_flags | elf->flags) & ELF_F_DIRTY)
    {
      ElfW2(LIBELFBITS,Ehdr) tmp_ehdr;
      ElfW2(LIBELFBITS,Ehdr) *out_ehdr = ehdr;

      /* If the type sizes should be different at some time we have to
	 rewrite this code.  */
      assert (sizeof (ElfW2(LIBELFBITS,Ehdr))
	      == elf_typesize (LIBELFBITS, ELF_T_EHDR, 1));

      if (unlikely (change_bo))
	{
	  /* Today there is only one version of the ELF header.  */
#if EV_NUM != 2
	  xfct_t fctp;
	  fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_EHDR];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_EHDR]
#endif

	  /* Write the converted ELF header in a temporary buffer.  */
	  (*fctp) (&tmp_ehdr, ehdr, sizeof (ElfW2(LIBELFBITS,Ehdr)), 1);

	  /* This is the buffer we want to write.  */
	  out_ehdr = &tmp_ehdr;
	}

      /* Write out the ELF header.  */
      if (unlikely (pwrite_retry (elf->fildes, out_ehdr,
				  sizeof (ElfW2(LIBELFBITS,Ehdr)), 0)
		    != sizeof (ElfW2(LIBELFBITS,Ehdr))))
	{
	  __libelf_seterrno (ELF_E_WRITE_ERROR);
	  return 1;
	}

      elf->state.ELFW(elf,LIBELFBITS).ehdr_flags &= ~ELF_F_DIRTY;

      /* We start writing sections after the ELF header only if there is
	 no program header.  */
      previous_scn_changed = elf->state.ELFW(elf,LIBELFBITS).phdr == NULL;
    }

  /* If the type sizes should be different at some time we have to
     rewrite this code.  */
  assert (sizeof (ElfW2(LIBELFBITS,Phdr))
	  == elf_typesize (LIBELFBITS, ELF_T_PHDR, 1));

  size_t phnum;
  if (unlikely (__elf_getphdrnum_rdlock (elf, &phnum) != 0))
    return -1;

  /* Write out the program header table.  */
  if (elf->state.ELFW(elf,LIBELFBITS).phdr != NULL
      && ((elf->state.ELFW(elf,LIBELFBITS).phdr_flags | elf->flags)
	  & ELF_F_DIRTY))
    {
      ElfW2(LIBELFBITS,Phdr) *tmp_phdr = NULL;
      ElfW2(LIBELFBITS,Phdr) *out_phdr = elf->state.ELFW(elf,LIBELFBITS).phdr;

      /* Maybe the user wants a gap between the ELF header and the program
	 header.  */
      if (ehdr->e_phoff > ehdr->e_ehsize
	  && unlikely (fill (elf->fildes, ehdr->e_ehsize,
			     ehdr->e_phoff - ehdr->e_ehsize, fillbuf, &filled)
		       != 0))
	return 1;

      if (unlikely (change_bo))
	{
	  /* Today there is only one version of the ELF header.  */
#if EV_NUM != 2
	  xfct_t fctp;
	  fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_PHDR];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_PHDR]
#endif

	  /* Allocate sufficient memory.  */
	  tmp_phdr = (ElfW2(LIBELFBITS,Phdr) *)
	    malloc (sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum);
	  if (tmp_phdr == NULL)
	    {
	      __libelf_seterrno (ELF_E_NOMEM);
	      return 1;
	    }

	  /* Write the converted ELF header in a temporary buffer.  */
	  (*fctp) (tmp_phdr, elf->state.ELFW(elf,LIBELFBITS).phdr,
		   sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum, 1);

	  /* This is the buffer we want to write.  */
	  out_phdr = tmp_phdr;
	}

      /* Write out the ELF header.  */
      size_t phdr_size = sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum;
      if (unlikely ((size_t) pwrite_retry (elf->fildes, out_phdr,
					   phdr_size, ehdr->e_phoff)
		    != phdr_size))
	{
	  __libelf_seterrno (ELF_E_WRITE_ERROR);
	  return 1;
	}

      /* This is a no-op we we have not allocated any memory.  */
      free (tmp_phdr);

      elf->state.ELFW(elf,LIBELFBITS).phdr_flags &= ~ELF_F_DIRTY;

      /* We modified the program header.  Maybe this created a gap so
	 we have to write fill bytes, if necessary.  */
      previous_scn_changed = true;
    }

  /* From now on we have to keep track of the last position to eventually
     fill the gaps with the prescribed fill byte.  */
  off_t last_offset;
  if (elf->state.ELFW(elf,LIBELFBITS).phdr == NULL)
    last_offset = elf_typesize (LIBELFBITS, ELF_T_EHDR, 1);
  else
    last_offset = (ehdr->e_phoff + sizeof (ElfW2(LIBELFBITS,Phdr)) * phnum);

  /* Write all the sections.  Well, only those which are modified.  */
  if (shnum > 0)
    {
      if (unlikely (shnum > SIZE_MAX / (sizeof (Elf_Scn *)
					+ sizeof (ElfW2(LIBELFBITS,Shdr)))))
	return 1;

      off_t shdr_offset = elf->start_offset + ehdr->e_shoff;
#if EV_NUM != 2
      xfct_t shdr_fctp = __elf_xfctstom[__libelf_version - 1][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_SHDR];
#else
# undef shdr_fctp
# define shdr_fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][ELF_T_SHDR]
#endif

      ElfW2(LIBELFBITS,Shdr) *shdr_data;
      if (change_bo || elf->state.ELFW(elf,LIBELFBITS).shdr == NULL
	  || (elf->flags & ELF_F_DIRTY))
	shdr_data = (ElfW2(LIBELFBITS,Shdr) *)
	  alloca (shnum * sizeof (ElfW2(LIBELFBITS,Shdr)));
      else
	shdr_data = elf->state.ELFW(elf,LIBELFBITS).shdr;
      int shdr_flags = elf->flags;

      /* Get all sections into the array and sort them.  */
      Elf_ScnList *list = &elf->state.ELFW(elf,LIBELFBITS).scns;
      Elf_Scn **scns = (Elf_Scn **) alloca (shnum * sizeof (Elf_Scn *));
      sort_sections (scns, list);

      for (size_t cnt = 0; cnt < shnum; ++cnt)
	{
	  Elf_Scn *scn = scns[cnt];
	  if (scn->index == 0)
	    {
	      /* The dummy section header entry.  It should not be
		 possible to mark this "section" as dirty.  */
	      assert ((scn->flags & ELF_F_DIRTY) == 0);
	      goto next;
	    }

	  ElfW2(LIBELFBITS,Shdr) *shdr = scn->shdr.ELFW(e,LIBELFBITS);
	  if (shdr->sh_type == SHT_NOBITS)
	    goto next;

	  off_t scn_start = elf->start_offset + shdr->sh_offset;
	  Elf_Data_List *dl = &scn->data_list;
	  bool scn_changed = false;

	  if (scn->data_list_rear != NULL)
	    do
	      {
		/* If there is a gap, fill it.  */
		if (scn_start + dl->data.d.d_off > last_offset
		    && ((previous_scn_changed && dl->data.d.d_off == 0)
			|| ((scn->flags | dl->flags | elf->flags)
			    & ELF_F_DIRTY) != 0))
		  {
		    if (unlikely (fill (elf->fildes, last_offset,
					(scn_start + dl->data.d.d_off)
					- last_offset, fillbuf,
					&filled) != 0))
		      return 1;
		  }

		if ((scn->flags | dl->flags | elf->flags) & ELF_F_DIRTY)
		  {
		    char tmpbuf[MAX_TMPBUF];
		    void *buf = dl->data.d.d_buf;

		    /* Let it go backward if the sections use a bogus
		       layout with overlaps.  We'll overwrite the stupid
		       user's section data with the latest one, rather than
		       crashing.  */

		    last_offset = scn_start + dl->data.d.d_off;

		    if (unlikely (change_bo))
		      {
#if EV_NUM != 2
			xfct_t fctp;
			fctp = __elf_xfctstom[__libelf_version - 1][dl->data.d.d_version - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][dl->data.d.d_type];
#else
# undef fctp
# define fctp __elf_xfctstom[0][EV_CURRENT - 1][ELFW(ELFCLASS, LIBELFBITS) - 1][dl->data.d.d_type]
#endif

			buf = tmpbuf;
			if (dl->data.d.d_size > MAX_TMPBUF)
			  {
			    buf = malloc (dl->data.d.d_size);
			    if (buf == NULL)
			      {
				__libelf_seterrno (ELF_E_NOMEM);
				return 1;
			      }
			  }

			/* Do the real work.  */
			(*fctp) (buf, dl->data.d.d_buf, dl->data.d.d_size, 1);
		      }

		    ssize_t n = pwrite_retry (elf->fildes, buf,
					      dl->data.d.d_size,
					      last_offset);
		    if (unlikely ((size_t) n != dl->data.d.d_size))
		      {
			if (buf != dl->data.d.d_buf && buf != tmpbuf)
			  free (buf);

			__libelf_seterrno (ELF_E_WRITE_ERROR);
			return 1;
		      }

		    if (buf != dl->data.d.d_buf && buf != tmpbuf)
		      free (buf);

		    scn_changed = true;
		  }

		last_offset += dl->data.d.d_size;

		dl->flags &= ~ELF_F_DIRTY;

		dl = dl->next;
	      }
	    while (dl != NULL);
	  else
	    {
	      /* If the previous section (or the ELF/program
		 header) changed we might have to fill the gap.  */
	      if (scn_start > last_offset && previous_scn_changed)
		{
		  if (unlikely (fill (elf->fildes, last_offset,
				      scn_start - last_offset, fillbuf,
				      &filled) != 0))
		    return 1;
		}

	      last_offset = scn_start + shdr->sh_size;
	    }

	  previous_scn_changed = scn_changed;
	next:
	  /* Collect the section header table information.  */
	  if (unlikely (change_bo))
	    (*shdr_fctp) (&shdr_data[scn->index],
			  scn->shdr.ELFW(e,LIBELFBITS),
			  sizeof (ElfW2(LIBELFBITS,Shdr)), 1);
	  else if (elf->state.ELFW(elf,LIBELFBITS).shdr == NULL
		   || (elf->flags & ELF_F_DIRTY))
	    memcpy (&shdr_data[scn->index], scn->shdr.ELFW(e,LIBELFBITS),
		    sizeof (ElfW2(LIBELFBITS,Shdr)));

	  shdr_flags |= scn->shdr_flags;
	  scn->shdr_flags &= ~ELF_F_DIRTY;
	}

      /* Fill the gap between last section and section header table if
	 necessary.  */
      if ((elf->flags & ELF_F_DIRTY) && last_offset < shdr_offset
	  && unlikely (fill (elf->fildes, last_offset,
			     shdr_offset - last_offset,
			     fillbuf, &filled) != 0))
	return 1;

      /* Write out the section header table.  */
      if (shdr_flags & ELF_F_DIRTY
	  && unlikely ((size_t) pwrite_retry (elf->fildes, shdr_data,
					      sizeof (ElfW2(LIBELFBITS,Shdr))
					      * shnum, shdr_offset)
		       != sizeof (ElfW2(LIBELFBITS,Shdr)) * shnum))
	{
	  __libelf_seterrno (ELF_E_WRITE_ERROR);
	  return 1;
	}
    }

  /* That was the last part.  Clear the overall flag.  */
  elf->flags &= ~ELF_F_DIRTY;

  return 0;
}