path: root/bfd/elf-eh-frame.c

/* .eh_frame section optimization.
   Copyright 2001, 2002, 2003, 2004, 2005, 2006, 2007
   Free Software Foundation, Inc.
   Written by Jakub Jelinek <jakub@redhat.com>.

   This file is part of BFD, the Binary File Descriptor library.

   This program 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 2 of the License, or
   (at your option) any later version.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */

#include "sysdep.h"
#include "bfd.h"
#include "libbfd.h"
#include "elf-bfd.h"
#include "elf/dwarf2.h"

#define EH_FRAME_HDR_SIZE 8

struct cie
{
  unsigned int length;
  unsigned int hash;
  unsigned char version;
  char augmentation[20];
  bfd_vma code_align;
  bfd_signed_vma data_align;
  bfd_vma ra_column;
  bfd_vma augmentation_size;
  struct elf_link_hash_entry *personality;
  asection *output_sec;
  struct eh_cie_fde *cie_inf;
  unsigned char per_encoding;
  unsigned char lsda_encoding;
  unsigned char fde_encoding;
  unsigned char initial_insn_length;
  unsigned char make_relative;
  unsigned char make_lsda_relative;
  unsigned char initial_instructions[50];
};



/* If *ITER hasn't reached END yet, read the next byte into *RESULT and
   move onto the next byte.  Return true on success.  */

static inline bfd_boolean
read_byte (bfd_byte **iter, bfd_byte *end, unsigned char *result)
{
  if (*iter >= end)
    return FALSE;
  *result = *((*iter)++);
  return TRUE;
}

/* Move *ITER over LENGTH bytes, or up to END, whichever is closer.
   Return true it was possible to move LENGTH bytes.  */

static inline bfd_boolean
skip_bytes (bfd_byte **iter, bfd_byte *end, bfd_size_type length)
{
  if ((bfd_size_type) (end - *iter) < length)
    {
      *iter = end;
      return FALSE;
    }
  *iter += length;
  return TRUE;
}

/* Move *ITER over an leb128, stopping at END.  Return true if the end
   of the leb128 was found.  */

static bfd_boolean
skip_leb128 (bfd_byte **iter, bfd_byte *end)
{
  unsigned char byte;
  do
    if (!read_byte (iter, end, &byte))
      return FALSE;
  while (byte & 0x80);
  return TRUE;
}

/* Like skip_leb128, but treat the leb128 as an unsigned value and
   store it in *VALUE.  */

static bfd_boolean
read_uleb128 (bfd_byte **iter, bfd_byte *end, bfd_vma *value)
{
  bfd_byte *start, *p;

  start = *iter;
  if (!skip_leb128 (iter, end))
    return FALSE;

  p = *iter;
  *value = *--p;
  while (p > start)
    *value = (*value << 7) | (*--p & 0x7f);

  return TRUE;
}

/* Like read_uleb128, but for signed values.  */

static bfd_boolean
read_sleb128 (bfd_byte **iter, bfd_byte *end, bfd_signed_vma *value)
{
  bfd_byte *start, *p;

  start = *iter;
  if (!skip_leb128 (iter, end))
    return FALSE;

  p = *iter;
  *value = ((*--p & 0x7f) ^ 0x40) - 0x40;
  while (p > start)
    *value = (*value << 7) | (*--p & 0x7f);

  return TRUE;
}

/* Return 0 if either encoding is variable width, or not yet known to bfd.  */

static
int get_DW_EH_PE_width (int encoding, int ptr_size)
{
  /* DW_EH_PE_ values of 0x60 and 0x70 weren't defined at the time .eh_frame
     was added to bfd.  */
  if ((encoding & 0x60) == 0x60)
    return 0;

  switch (encoding & 7)
    {
    case DW_EH_PE_udata2: return 2;
    case DW_EH_PE_udata4: return 4;
    case DW_EH_PE_udata8: return 8;
    case DW_EH_PE_absptr: return ptr_size;
    default:
      break;
    }

  return 0;
}

#define get_DW_EH_PE_signed(encoding) (((encoding) & DW_EH_PE_signed) != 0)

/* Read a width sized value from memory.  */

static bfd_vma
read_value (bfd *abfd, bfd_byte *buf, int width, int is_signed)
{
  bfd_vma value;

  switch (width)
    {
    case 2:
      if (is_signed)
	value = bfd_get_signed_16 (abfd, buf);
      else
	value = bfd_get_16 (abfd, buf);
      break;
    case 4:
      if (is_signed)
	value = bfd_get_signed_32 (abfd, buf);
      else
	value = bfd_get_32 (abfd, buf);
      break;
    case 8:
      if (is_signed)
	value = bfd_get_signed_64 (abfd, buf);
      else
	value = bfd_get_64 (abfd, buf);
      break;
    default:
      BFD_FAIL ();
      return 0;
    }

  return value;
}

/* Store a width sized value to memory.  */

static void
write_value (bfd *abfd, bfd_byte *buf, bfd_vma value, int width)
{
  switch (width)
    {
    case 2: bfd_put_16 (abfd, value, buf); break;
    case 4: bfd_put_32 (abfd, value, buf); break;
    case 8: bfd_put_64 (abfd, value, buf); break;
    default: BFD_FAIL ();
    }
}

/* Return one if C1 and C2 CIEs can be merged.  */

static int
cie_eq (const void *e1, const void *e2)
{
  const struct cie *c1 = e1;
  const struct cie *c2 = e2;

  if (c1->hash == c2->hash
      && c1->length == c2->length
      && c1->version == c2->version
      && strcmp (c1->augmentation, c2->augmentation) == 0
      && strcmp (c1->augmentation, "eh") != 0
      && c1->code_align == c2->code_align
      && c1->data_align == c2->data_align
      && c1->ra_column == c2->ra_column
      && c1->augmentation_size == c2->augmentation_size
      && c1->personality == c2->personality
      && c1->output_sec == c2->output_sec
      && c1->per_encoding == c2->per_encoding
      && c1->lsda_encoding == c2->lsda_encoding
      && c1->fde_encoding == c2->fde_encoding
      && c1->initial_insn_length == c2->initial_insn_length
      && memcmp (c1->initial_instructions,
		 c2->initial_instructions,
		 c1->initial_insn_length) == 0)
    return 1;

  return 0;
}

static hashval_t
cie_hash (const void *e)
{
  const struct cie *c = e;
  return c->hash;
}

static hashval_t
cie_compute_hash (struct cie *c)
{
  hashval_t h = 0;
  h = iterative_hash_object (c->length, h);
  h = iterative_hash_object (c->version, h);
  h = iterative_hash (c->augmentation, strlen (c->augmentation) + 1, h);
  h = iterative_hash_object (c->code_align, h);
  h = iterative_hash_object (c->data_align, h);
  h = iterative_hash_object (c->ra_column, h);
  h = iterative_hash_object (c->augmentation_size, h);
  h = iterative_hash_object (c->personality, h);
  h = iterative_hash_object (c->output_sec, h);
  h = iterative_hash_object (c->per_encoding, h);
  h = iterative_hash_object (c->lsda_encoding, h);
  h = iterative_hash_object (c->fde_encoding, h);
  h = iterative_hash_object (c->initial_insn_length, h);
  h = iterative_hash (c->initial_instructions, c->initial_insn_length, h);
  c->hash = h;
  return h;
}

/* Return the number of extra bytes that we'll be inserting into
   ENTRY's augmentation string.  */

static INLINE unsigned int
extra_augmentation_string_bytes (struct eh_cie_fde *entry)
{
  unsigned int size = 0;
  if (entry->cie)
    {
      if (entry->add_augmentation_size)
	size++;
      if (entry->add_fde_encoding)
	size++;
    }
  return size;
}

/* Likewise ENTRY's augmentation data.  */

static INLINE unsigned int
extra_augmentation_data_bytes (struct eh_cie_fde *entry)
{
  unsigned int size = 0;
  if (entry->cie)
    {
      if (entry->add_augmentation_size)
	size++;
      if (entry->add_fde_encoding)
	size++;
    }
  else
    {
      if (entry->cie_inf->add_augmentation_size)
	size++;
    }
  return size;
}

/* Return the size that ENTRY will have in the output.  ALIGNMENT is the
   required alignment of ENTRY in bytes.  */

static unsigned int
size_of_output_cie_fde (struct eh_cie_fde *entry, unsigned int alignment)
{
  if (entry->removed)
    return 0;
  if (entry->size == 4)
    return 4;
  return (entry->size
	  + extra_augmentation_string_bytes (entry)
	  + extra_augmentation_data_bytes (entry)
	  + alignment - 1) & -alignment;
}

/* Assume that the bytes between *ITER and END are CFA instructions.
   Try to move *ITER past the first instruction and return true on
   success.  ENCODED_PTR_WIDTH gives the width of pointer entries.  */

static bfd_boolean
skip_cfa_op (bfd_byte **iter, bfd_byte *end, unsigned int encoded_ptr_width)
{
  bfd_byte op;
  bfd_vma length;

  if (!read_byte (iter, end, &op))
    return FALSE;

  switch (op & 0xc0 ? op & 0xc0 : op)
    {
    case DW_CFA_nop:
    case DW_CFA_advance_loc:
    case DW_CFA_restore:
    case DW_CFA_remember_state:
    case DW_CFA_restore_state:
    case DW_CFA_GNU_window_save:
      /* No arguments.  */
      return TRUE;

    case DW_CFA_offset:
    case DW_CFA_restore_extended:
    case DW_CFA_undefined:
    case DW_CFA_same_value:
    case DW_CFA_def_cfa_register:
    case DW_CFA_def_cfa_offset:
    case DW_CFA_def_cfa_offset_sf:
    case DW_CFA_GNU_args_size:
      /* One leb128 argument.  */
      return skip_leb128 (iter, end);

    case DW_CFA_val_offset:
    case DW_CFA_val_offset_sf:
    case DW_CFA_offset_extended:
    case DW_CFA_register:
    case DW_CFA_def_cfa:
    case DW_CFA_offset_extended_sf:
    case DW_CFA_GNU_negative_offset_extended:
    case DW_CFA_def_cfa_sf:
      /* Two leb128 arguments.  */
      return (skip_leb128 (iter, end)
	      && skip_leb128 (iter, end));

    case DW_CFA_def_cfa_expression:
      /* A variable-length argument.  */
      return (read_uleb128 (iter, end, &length)
	      && skip_bytes (iter, end, length));

    case DW_CFA_expression:
    case DW_CFA_val_expression:
      /* A leb128 followed by a variable-length argument.  */
      return (skip_leb128 (iter, end)
	      && read_uleb128 (iter, end, &length)
	      && skip_bytes (iter, end, length));

    case DW_CFA_set_loc:
      return skip_bytes (iter, end, encoded_ptr_width);

    case DW_CFA_advance_loc1:
      return skip_bytes (iter, end, 1);

    case DW_CFA_advance_loc2:
      return skip_bytes (iter, end, 2);

    case DW_CFA_advance_loc4:
      return skip_bytes (iter, end, 4);

    case DW_CFA_MIPS_advance_loc8:
      return skip_bytes (iter, end, 8);

    default:
      return FALSE;
    }
}

/* Try to interpret the bytes between BUF and END as CFA instructions.
   If every byte makes sense, return a pointer to the first DW_CFA_nop
   padding byte, or END if there is no padding.  Return null otherwise.
   ENCODED_PTR_WIDTH is as for skip_cfa_op.  */

static bfd_byte *
skip_non_nops (bfd_byte *buf, bfd_byte *end, unsigned int encoded_ptr_width,
	       unsigned int *set_loc_count)
{
  bfd_byte *last;

  last = buf;
  while (buf < end)
    if (*buf == DW_CFA_nop)
      buf++;
    else
      {
	if (*buf == DW_CFA_set_loc)
	  ++*set_loc_count;
	if (!skip_cfa_op (&buf, end, encoded_ptr_width))
	  return 0;
	last = buf;
      }
  return last;
}

/* This function is called for each input file before the .eh_frame
   section is relocated.  It discards duplicate CIEs and FDEs for discarded
   functions.  The function returns TRUE iff any entries have been
   deleted.  */

bfd_boolean
_bfd_elf_discard_section_eh_frame
   (bfd *abfd, struct bfd_link_info *info, asection *sec,
    bfd_boolean (*reloc_symbol_deleted_p) (bfd_vma, void *),
    struct elf_reloc_cookie *cookie)
{
#define REQUIRE(COND)					\
  do							\
    if (!(COND))					\
      goto free_no_table;				\
  while (0)

  bfd_byte *ehbuf = NULL, *buf;
  bfd_byte *last_fde;
  struct eh_cie_fde *ent, *this_inf;
  unsigned int hdr_length, hdr_id;
  struct extended_cie
    {
      struct cie cie;
      unsigned int offset;
      unsigned int usage_count;
      unsigned int entry;
    } *ecies = NULL, *ecie;
  unsigned int ecie_count = 0, ecie_alloced = 0;
  struct cie *cie;
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;
  struct eh_frame_sec_info *sec_info = NULL;
  unsigned int offset;
  unsigned int ptr_size;
  unsigned int entry_alloced;

  if (sec->size == 0)
    {
      /* This file does not contain .eh_frame information.  */
      return FALSE;
    }

  if (bfd_is_abs_section (sec->output_section))
    {
      /* At least one of the sections is being discarded from the
	 link, so we should just ignore them.  */
      return FALSE;
    }

  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;

  if (hdr_info->cies == NULL && !info->relocatable)
    hdr_info->cies = htab_try_create (1, cie_hash, cie_eq, free);

  /* Read the frame unwind information from abfd.  */

  REQUIRE (bfd_malloc_and_get_section (abfd, sec, &ehbuf));

  if (sec->size >= 4
      && bfd_get_32 (abfd, ehbuf) == 0
      && cookie->rel == cookie->relend)
    {
      /* Empty .eh_frame section.  */
      free (ehbuf);
      return FALSE;
    }

  /* If .eh_frame section size doesn't fit into int, we cannot handle
     it (it would need to use 64-bit .eh_frame format anyway).  */
  REQUIRE (sec->size == (unsigned int) sec->size);

  ptr_size = (get_elf_backend_data (abfd)
	      ->elf_backend_eh_frame_address_size (abfd, sec));
  REQUIRE (ptr_size != 0);

  buf = ehbuf;
  sec_info = bfd_zmalloc (sizeof (struct eh_frame_sec_info)
			  + 99 * sizeof (struct eh_cie_fde));
  REQUIRE (sec_info);

  entry_alloced = 100;

#define ENSURE_NO_RELOCS(buf)				\
  REQUIRE (!(cookie->rel < cookie->relend		\
	     && (cookie->rel->r_offset			\
		 < (bfd_size_type) ((buf) - ehbuf))	\
	     && cookie->rel->r_info != 0))

#define SKIP_RELOCS(buf)				\
  while (cookie->rel < cookie->relend			\
	 && (cookie->rel->r_offset			\
	     < (bfd_size_type) ((buf) - ehbuf)))	\
    cookie->rel++

#define GET_RELOC(buf)					\
  ((cookie->rel < cookie->relend			\
    && (cookie->rel->r_offset				\
	== (bfd_size_type) ((buf) - ehbuf)))		\
   ? cookie->rel : NULL)

  for (;;)
    {
      char *aug;
      bfd_byte *start, *end, *insns, *insns_end;
      bfd_size_type length;
      unsigned int set_loc_count;

      if (sec_info->count == entry_alloced)
	{
	  sec_info = bfd_realloc (sec_info,
				  sizeof (struct eh_frame_sec_info)
				  + ((entry_alloced + 99)
				     * sizeof (struct eh_cie_fde)));
	  REQUIRE (sec_info);

	  memset (&sec_info->entry[entry_alloced], 0,
		  100 * sizeof (struct eh_cie_fde));
	  entry_alloced += 100;
	}

      this_inf = sec_info->entry + sec_info->count;
      last_fde = buf;

      if ((bfd_size_type) (buf - ehbuf) == sec->size)
	break;

      /* Read the length of the entry.  */
      REQUIRE (skip_bytes (&buf, ehbuf + sec->size, 4));
      hdr_length = bfd_get_32 (abfd, buf - 4);

      /* 64-bit .eh_frame is not supported.  */
      REQUIRE (hdr_length != 0xffffffff);

      /* The CIE/FDE must be fully contained in this input section.  */
      REQUIRE ((bfd_size_type) (buf - ehbuf) + hdr_length <= sec->size);
      end = buf + hdr_length;

      this_inf->offset = last_fde - ehbuf;
      this_inf->size = 4 + hdr_length;

      if (hdr_length == 0)
	{
	  /* A zero-length CIE should only be found at the end of
	     the section.  */
	  REQUIRE ((bfd_size_type) (buf - ehbuf) == sec->size);
	  ENSURE_NO_RELOCS (buf);
	  sec_info->count++;
	  break;
	}

      REQUIRE (skip_bytes (&buf, end, 4));
      hdr_id = bfd_get_32 (abfd, buf - 4);

      if (hdr_id == 0)
	{
	  unsigned int initial_insn_length;

	  /* CIE  */
	  this_inf->cie = 1;

	  if (ecie_count == ecie_alloced)
	    {
	      ecies = bfd_realloc (ecies,
				   (ecie_alloced + 20) * sizeof (*ecies));
	      REQUIRE (ecies);
	      memset (&ecies[ecie_alloced], 0, 20 * sizeof (*ecies));
	      ecie_alloced += 20;
	    }

	  cie = &ecies[ecie_count].cie;
	  ecies[ecie_count].offset = this_inf->offset;
	  ecies[ecie_count++].entry = sec_info->count;
	  cie->length = hdr_length;
	  start = buf;
	  REQUIRE (read_byte (&buf, end, &cie->version));

	  /* Cannot handle unknown versions.  */
	  REQUIRE (cie->version == 1 || cie->version == 3);
	  REQUIRE (strlen ((char *) buf) < sizeof (cie->augmentation));

	  strcpy (cie->augmentation, (char *) buf);
	  buf = (bfd_byte *) strchr ((char *) buf, '\0') + 1;
	  ENSURE_NO_RELOCS (buf);
	  if (buf[0] == 'e' && buf[1] == 'h')
	    {
	      /* GCC < 3.0 .eh_frame CIE */
	      /* We cannot merge "eh" CIEs because __EXCEPTION_TABLE__
		 is private to each CIE, so we don't need it for anything.
		 Just skip it.  */
	      REQUIRE (skip_bytes (&buf, end, ptr_size));
	      SKIP_RELOCS (buf);
	    }
	  REQUIRE (read_uleb128 (&buf, end, &cie->code_align));
	  REQUIRE (read_sleb128 (&buf, end, &cie->data_align));
	  if (cie->version == 1)
	    {
	      REQUIRE (buf < end);
	      cie->ra_column = *buf++;
	    }
	  else
	    REQUIRE (read_uleb128 (&buf, end, &cie->ra_column));
	  ENSURE_NO_RELOCS (buf);
	  cie->lsda_encoding = DW_EH_PE_omit;
	  cie->fde_encoding = DW_EH_PE_omit;
	  cie->per_encoding = DW_EH_PE_omit;
	  aug = cie->augmentation;
	  if (aug[0] != 'e' || aug[1] != 'h')
	    {
	      if (*aug == 'z')
		{
		  aug++;
		  REQUIRE (read_uleb128 (&buf, end, &cie->augmentation_size));
	  	  ENSURE_NO_RELOCS (buf);
		}

	      while (*aug != '\0')
		switch (*aug++)
		  {
		  case 'L':
		    REQUIRE (read_byte (&buf, end, &cie->lsda_encoding));
		    ENSURE_NO_RELOCS (buf);
		    REQUIRE (get_DW_EH_PE_width (cie->lsda_encoding, ptr_size));
		    break;
		  case 'R':
		    REQUIRE (read_byte (&buf, end, &cie->fde_encoding));
		    ENSURE_NO_RELOCS (buf);
		    REQUIRE (get_DW_EH_PE_width (cie->fde_encoding, ptr_size));
		    break;
		  case 'S':
		    break;
		  case 'P':
		    {
		      int per_width;

		      REQUIRE (read_byte (&buf, end, &cie->per_encoding));
		      per_width = get_DW_EH_PE_width (cie->per_encoding,
						      ptr_size);
		      REQUIRE (per_width);
		      if ((cie->per_encoding & 0xf0) == DW_EH_PE_aligned)
			{
			  length = -(buf - ehbuf) & (per_width - 1);
			  REQUIRE (skip_bytes (&buf, end, length));
			}
		      ENSURE_NO_RELOCS (buf);
		      /* Ensure we have a reloc here, against
			 a global symbol.  */
		      if (GET_RELOC (buf) != NULL)
			{
			  unsigned long r_symndx;

#ifdef BFD64
			  if (ptr_size == 8)
			    r_symndx = ELF64_R_SYM (cookie->rel->r_info);
			  else
#endif
			    r_symndx = ELF32_R_SYM (cookie->rel->r_info);
			  if (r_symndx >= cookie->locsymcount)
			    {
			      struct elf_link_hash_entry *h;

			      r_symndx -= cookie->extsymoff;
			      h = cookie->sym_hashes[r_symndx];

			      while (h->root.type == bfd_link_hash_indirect
				     || h->root.type == bfd_link_hash_warning)
				h = (struct elf_link_hash_entry *)
				    h->root.u.i.link;

			      cie->personality = h;
			    }
			  /* Cope with MIPS-style composite relocations.  */
			  do
			    cookie->rel++;
			  while (GET_RELOC (buf) != NULL);
			}
		      REQUIRE (skip_bytes (&buf, end, per_width));
		      REQUIRE (cie->personality);
		    }
		    break;
		  default:
		    /* Unrecognized augmentation. Better bail out.  */
		    goto free_no_table;
		  }
	    }

	  /* For shared libraries, try to get rid of as many RELATIVE relocs
	     as possible.  */
	  if (info->shared
	      && (get_elf_backend_data (abfd)
		  ->elf_backend_can_make_relative_eh_frame
		  (abfd, info, sec)))
	    {
	      if ((cie->fde_encoding & 0xf0) == DW_EH_PE_absptr)
		cie->make_relative = 1;
	      /* If the CIE doesn't already have an 'R' entry, it's fairly
		 easy to add one, provided that there's no aligned data
		 after the augmentation string.  */
	      else if (cie->fde_encoding == DW_EH_PE_omit
		       && (cie->per_encoding & 0xf0) != DW_EH_PE_aligned)
		{
		  if (*cie->augmentation == 0)
		    this_inf->add_augmentation_size = 1;
		  this_inf->add_fde_encoding = 1;
		  cie->make_relative = 1;
		}
	    }

	  if (info->shared
	      && (get_elf_backend_data (abfd)
		  ->elf_backend_can_make_lsda_relative_eh_frame
		  (abfd, info, sec))
	      && (cie->lsda_encoding & 0xf0) == DW_EH_PE_absptr)
	    cie->make_lsda_relative = 1;

	  /* If FDE encoding was not specified, it defaults to
	     DW_EH_absptr.  */
	  if (cie->fde_encoding == DW_EH_PE_omit)
	    cie->fde_encoding = DW_EH_PE_absptr;

	  initial_insn_length = end - buf;
	  if (initial_insn_length <= sizeof (cie->initial_instructions))
	    {
	      cie->initial_insn_length = initial_insn_length;
	      memcpy (cie->initial_instructions, buf, initial_insn_length);
	    }
	  insns = buf;
	  buf += initial_insn_length;
	  ENSURE_NO_RELOCS (buf);
	}
      else
	{
	  /* Find the corresponding CIE.  */
	  unsigned int cie_offset = this_inf->offset + 4 - hdr_id;
	  for (ecie = ecies; ecie < ecies + ecie_count; ++ecie)
	    if (cie_offset == ecie->offset)
	      break;

	  /* Ensure this FDE references one of the CIEs in this input
	     section.  */
	  REQUIRE (ecie != ecies + ecie_count);
	  cie = &ecie->cie;

	  ENSURE_NO_RELOCS (buf);
	  REQUIRE (GET_RELOC (buf));

	  if ((*reloc_symbol_deleted_p) (buf - ehbuf, cookie))
	    /* This is a FDE against a discarded section.  It should
	       be deleted.  */
	    this_inf->removed = 1;
	  else
	    {
	      if (info->shared
		  && (((cie->fde_encoding & 0xf0) == DW_EH_PE_absptr
		       && cie->make_relative == 0)
		      || (cie->fde_encoding & 0xf0) == DW_EH_PE_aligned))
		{
		  /* If a shared library uses absolute pointers
		     which we cannot turn into PC relative,
		     don't create the binary search table,
		     since it is affected by runtime relocations.  */
		  hdr_info->table = FALSE;
		  (*info->callbacks->einfo)
		    (_("%P: fde encoding in %B(%A) prevents .eh_frame_hdr"
		       " table being created.\n"), abfd, sec);
		}
	      ecie->usage_count++;
	      hdr_info->fde_count++;
	      this_inf->cie_inf = (void *) (ecie - ecies);
	    }

	  /* Skip the initial location and address range.  */
	  start = buf;
	  length = get_DW_EH_PE_width (cie->fde_encoding, ptr_size);
	  REQUIRE (skip_bytes (&buf, end, 2 * length));

	  /* Skip the augmentation size, if present.  */
	  if (cie->augmentation[0] == 'z')
	    REQUIRE (read_uleb128 (&buf, end, &length));
	  else
	    length = 0;

	  /* Of the supported augmentation characters above, only 'L'
	     adds augmentation data to the FDE.  This code would need to
	     be adjusted if any future augmentations do the same thing.  */
	  if (cie->lsda_encoding != DW_EH_PE_omit)
	    {
	      this_inf->lsda_offset = buf - start;
	      /* If there's no 'z' augmentation, we don't know where the
		 CFA insns begin.  Assume no padding.  */
	      if (cie->augmentation[0] != 'z')
		length = end - buf;
	    }

	  /* Skip over the augmentation data.  */
	  REQUIRE (skip_bytes (&buf, end, length));
	  insns = buf;

	  buf = last_fde + 4 + hdr_length;
	  SKIP_RELOCS (buf);
	}

      /* Try to interpret the CFA instructions and find the first
	 padding nop.  Shrink this_inf's size so that it doesn't
	 include the padding.  */
      length = get_DW_EH_PE_width (cie->fde_encoding, ptr_size);
      set_loc_count = 0;
      insns_end = skip_non_nops (insns, end, length, &set_loc_count);
      /* If we don't understand the CFA instructions, we can't know
	 what needs to be adjusted there.  */
      if (insns_end == NULL
	  /* For the time being we don't support DW_CFA_set_loc in
	     CIE instructions.  */
	  || (set_loc_count && this_inf->cie))
	goto free_no_table;
      this_inf->size -= end - insns_end;
      if (insns_end != end && this_inf->cie)
	{
	  cie->initial_insn_length -= end - insns_end;
	  cie->length -= end - insns_end;
	}
      if (set_loc_count
	  && ((cie->fde_encoding & 0xf0) == DW_EH_PE_pcrel
	      || cie->make_relative))
	{
	  unsigned int cnt;
	  bfd_byte *p;

	  this_inf->set_loc = bfd_malloc ((set_loc_count + 1)
					  * sizeof (unsigned int));
	  REQUIRE (this_inf->set_loc);
	  this_inf->set_loc[0] = set_loc_count;
	  p = insns;
	  cnt = 0;
	  while (p < end)
	    {
	      if (*p == DW_CFA_set_loc)
		this_inf->set_loc[++cnt] = p + 1 - start;
	      REQUIRE (skip_cfa_op (&p, end, length));
	    }
	}

      this_inf->fde_encoding = cie->fde_encoding;
      this_inf->lsda_encoding = cie->lsda_encoding;
      sec_info->count++;
    }

  elf_section_data (sec)->sec_info = sec_info;
  sec->sec_info_type = ELF_INFO_TYPE_EH_FRAME;

  /* Look at all CIEs in this section and determine which can be
     removed as unused, which can be merged with previous duplicate
     CIEs and which need to be kept.  */
  for (ecie = ecies; ecie < ecies + ecie_count; ++ecie)
    {
      if (ecie->usage_count == 0)
	{
	  sec_info->entry[ecie->entry].removed = 1;
	  continue;
	}
      ecie->cie.output_sec = sec->output_section;
      ecie->cie.cie_inf = sec_info->entry + ecie->entry;
      cie_compute_hash (&ecie->cie);
      if (hdr_info->cies != NULL)
	{
	  void **loc = htab_find_slot_with_hash (hdr_info->cies, &ecie->cie,
						 ecie->cie.hash, INSERT);
	  if (loc != NULL)
	    {
	      if (*loc != HTAB_EMPTY_ENTRY)
		{
		  sec_info->entry[ecie->entry].removed = 1;
		  ecie->cie.cie_inf = ((struct cie *) *loc)->cie_inf;
		  continue;
		}

	      *loc = malloc (sizeof (struct cie));
	      if (*loc == NULL)
		*loc = HTAB_DELETED_ENTRY;
	      else
		memcpy (*loc, &ecie->cie, sizeof (struct cie));
	    }
	}
      ecie->cie.cie_inf->make_relative = ecie->cie.make_relative;
      ecie->cie.cie_inf->make_lsda_relative = ecie->cie.make_lsda_relative;
      ecie->cie.cie_inf->per_encoding_relative
	= (ecie->cie.per_encoding & 0x70) == DW_EH_PE_pcrel;
    }

  /* Ok, now we can assign new offsets.  */
  offset = 0;
  for (ent = sec_info->entry; ent < sec_info->entry + sec_info->count; ++ent)
    if (!ent->removed)
      {
	if (!ent->cie)
	  {
	    ecie = ecies + (unsigned long) ent->cie_inf;
	    ent->cie_inf = ecie->cie.cie_inf;
	  }
	ent->new_offset = offset;
	offset += size_of_output_cie_fde (ent, ptr_size);
      }

  /* Resize the sec as needed.  */
  sec->rawsize = sec->size;
  sec->size = offset;

  free (ehbuf);
  if (ecies)
    free (ecies);
  return offset != sec->rawsize;

free_no_table:
  (*info->callbacks->einfo)
    (_("%P: error in %B(%A); no .eh_frame_hdr table will be created.\n"),
     abfd, sec);
  if (ehbuf)
    free (ehbuf);
  if (sec_info)
    free (sec_info);
  if (ecies)
    free (ecies);
  hdr_info->table = FALSE;
  return FALSE;

#undef REQUIRE
}

/* This function is called for .eh_frame_hdr section after
   _bfd_elf_discard_section_eh_frame has been called on all .eh_frame
   input sections.  It finalizes the size of .eh_frame_hdr section.  */

bfd_boolean
_bfd_elf_discard_section_eh_frame_hdr (bfd *abfd, struct bfd_link_info *info)
{
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;
  asection *sec;

  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;

  if (hdr_info->cies != NULL)
    {
      htab_delete (hdr_info->cies);
      hdr_info->cies = NULL;
    }

  sec = hdr_info->hdr_sec;
  if (sec == NULL)
    return FALSE;

  sec->size = EH_FRAME_HDR_SIZE;
  if (hdr_info->table)
    sec->size += 4 + hdr_info->fde_count * 8;

  elf_tdata (abfd)->eh_frame_hdr = sec;
  return TRUE;
}

/* This function is called from size_dynamic_sections.
   It needs to decide whether .eh_frame_hdr should be output or not,
   because when the dynamic symbol table has been sized it is too late
   to strip sections.  */

bfd_boolean
_bfd_elf_maybe_strip_eh_frame_hdr (struct bfd_link_info *info)
{
  asection *o;
  bfd *abfd;
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;

  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;
  if (hdr_info->hdr_sec == NULL)
    return TRUE;

  if (bfd_is_abs_section (hdr_info->hdr_sec->output_section))
    {
      hdr_info->hdr_sec = NULL;
      return TRUE;
    }

  abfd = NULL;
  if (info->eh_frame_hdr)
    for (abfd = info->input_bfds; abfd != NULL; abfd = abfd->link_next)
      {
	/* Count only sections which have at least a single CIE or FDE.
	   There cannot be any CIE or FDE <= 8 bytes.  */
	o = bfd_get_section_by_name (abfd, ".eh_frame");
	if (o && o->size > 8 && !bfd_is_abs_section (o->output_section))
	  break;
      }

  if (abfd == NULL)
    {
      hdr_info->hdr_sec->flags |= SEC_EXCLUDE;
      hdr_info->hdr_sec = NULL;
      return TRUE;
    }

  hdr_info->table = TRUE;
  return TRUE;
}

/* Adjust an address in the .eh_frame section.  Given OFFSET within
   SEC, this returns the new offset in the adjusted .eh_frame section,
   or -1 if the address refers to a CIE/FDE which has been removed
   or to offset with dynamic relocation which is no longer needed.  */

bfd_vma
_bfd_elf_eh_frame_section_offset (bfd *output_bfd ATTRIBUTE_UNUSED,
				  struct bfd_link_info *info,
				  asection *sec,
				  bfd_vma offset)
{
  struct eh_frame_sec_info *sec_info;
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;
  unsigned int lo, hi, mid;

  if (sec->sec_info_type != ELF_INFO_TYPE_EH_FRAME)
    return offset;
  sec_info = elf_section_data (sec)->sec_info;

  if (offset >= sec->rawsize)
    return offset - sec->rawsize + sec->size;

  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;
  if (hdr_info->offsets_adjusted)
    offset += sec->output_offset;

  lo = 0;
  hi = sec_info->count;
  mid = 0;
  while (lo < hi)
    {
      mid = (lo + hi) / 2;
      if (offset < sec_info->entry[mid].offset)
	hi = mid;
      else if (offset
	       >= sec_info->entry[mid].offset + sec_info->entry[mid].size)
	lo = mid + 1;
      else
	break;
    }

  BFD_ASSERT (lo < hi);

  /* FDE or CIE was removed.  */
  if (sec_info->entry[mid].removed)
    return (bfd_vma) -1;

  /* If converting to DW_EH_PE_pcrel, there will be no need for run-time
     relocation against FDE's initial_location field.  */
  if (!sec_info->entry[mid].cie
      && sec_info->entry[mid].cie_inf->make_relative
      && offset == sec_info->entry[mid].offset + 8)
    return (bfd_vma) -2;

  /* If converting LSDA pointers to DW_EH_PE_pcrel, there will be no need
     for run-time relocation against LSDA field.  */
  if (!sec_info->entry[mid].cie
      && sec_info->entry[mid].cie_inf->make_lsda_relative
      && (offset == (sec_info->entry[mid].offset + 8
		     + sec_info->entry[mid].lsda_offset))
      && (sec_info->entry[mid].cie_inf->need_lsda_relative
	  || !hdr_info->offsets_adjusted))
    {
      sec_info->entry[mid].cie_inf->need_lsda_relative = 1;
      return (bfd_vma) -2;
    }

  /* If converting to DW_EH_PE_pcrel, there will be no need for run-time
     relocation against DW_CFA_set_loc's arguments.  */
  if (sec_info->entry[mid].set_loc
      && (sec_info->entry[mid].cie
	  ? sec_info->entry[mid].make_relative
	  : sec_info->entry[mid].cie_inf->make_relative)
      && (offset >= sec_info->entry[mid].offset + 8
		    + sec_info->entry[mid].set_loc[1]))
    {
      unsigned int cnt;

      for (cnt = 1; cnt <= sec_info->entry[mid].set_loc[0]; cnt++)
	if (offset == sec_info->entry[mid].offset + 8
		      + sec_info->entry[mid].set_loc[cnt])
	  return (bfd_vma) -2;
    }

  if (hdr_info->offsets_adjusted)
    offset -= sec->output_offset;
  /* Any new augmentation bytes go before the first relocation.  */
  return (offset + sec_info->entry[mid].new_offset
	  - sec_info->entry[mid].offset
	  + extra_augmentation_string_bytes (sec_info->entry + mid)
	  + extra_augmentation_data_bytes (sec_info->entry + mid));
}

/* Write out .eh_frame section.  This is called with the relocated
   contents.  */

bfd_boolean
_bfd_elf_write_section_eh_frame (bfd *abfd,
				 struct bfd_link_info *info,
				 asection *sec,
				 bfd_byte *contents)
{
  struct eh_frame_sec_info *sec_info;
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;
  unsigned int ptr_size;
  struct eh_cie_fde *ent;

  if (sec->sec_info_type != ELF_INFO_TYPE_EH_FRAME)
    return bfd_set_section_contents (abfd, sec->output_section, contents,
				     sec->output_offset, sec->size);

  ptr_size = (get_elf_backend_data (abfd)
	      ->elf_backend_eh_frame_address_size (abfd, sec));
  BFD_ASSERT (ptr_size != 0);

  sec_info = elf_section_data (sec)->sec_info;
  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;

  /* First convert all offsets to output section offsets, so that a
     CIE offset is valid if the CIE is used by a FDE from some other
     section.  This can happen when duplicate CIEs are deleted in
     _bfd_elf_discard_section_eh_frame.  We do all sections here because
     this function might not be called on sections in the same order as
     _bfd_elf_discard_section_eh_frame.  */
  if (!hdr_info->offsets_adjusted)
    {
      bfd *ibfd;
      asection *eh;
      struct eh_frame_sec_info *eh_inf;

      for (ibfd = info->input_bfds; ibfd != NULL; ibfd = ibfd->link_next)
	{
	  if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour
	      || (ibfd->flags & DYNAMIC) != 0)
	    continue;

	  eh = bfd_get_section_by_name (ibfd, ".eh_frame");
	  if (eh == NULL || eh->sec_info_type != ELF_INFO_TYPE_EH_FRAME)
	    continue;

	  eh_inf = elf_section_data (eh)->sec_info;
	  for (ent = eh_inf->entry; ent < eh_inf->entry + eh_inf->count; ++ent)
	    {
	      ent->offset += eh->output_offset;
	      ent->new_offset += eh->output_offset;
	    }
	}
      hdr_info->offsets_adjusted = TRUE;
    }

  if (hdr_info->table && hdr_info->array == NULL)
    hdr_info->array
      = bfd_malloc (hdr_info->fde_count * sizeof(*hdr_info->array));
  if (hdr_info->array == NULL)
    hdr_info = NULL;

  /* The new offsets can be bigger or smaller than the original offsets.
     We therefore need to make two passes over the section: one backward
     pass to move entries up and one forward pass to move entries down.
     The two passes won't interfere with each other because entries are
     not reordered  */
  for (ent = sec_info->entry + sec_info->count; ent-- != sec_info->entry;)
    if (!ent->removed && ent->new_offset > ent->offset)
      memmove (contents + ent->new_offset - sec->output_offset,
	       contents + ent->offset - sec->output_offset, ent->size);

  for (ent = sec_info->entry; ent < sec_info->entry + sec_info->count; ++ent)
    if (!ent->removed && ent->new_offset < ent->offset)
      memmove (contents + ent->new_offset - sec->output_offset,
	       contents + ent->offset - sec->output_offset, ent->size);

  for (ent = sec_info->entry; ent < sec_info->entry + sec_info->count; ++ent)
    {
      unsigned char *buf, *end;
      unsigned int new_size;

      if (ent->removed)
	continue;

      if (ent->size == 4)
	{
	  /* Any terminating FDE must be at the end of the section.  */
	  BFD_ASSERT (ent == sec_info->entry + sec_info->count - 1);
	  continue;
	}

      buf = contents + ent->new_offset - sec->output_offset;
      end = buf + ent->size;
      new_size = size_of_output_cie_fde (ent, ptr_size);

      /* Update the size.  It may be shrinked.  */
      bfd_put_32 (abfd, new_size - 4, buf);

      /* Filling the extra bytes with DW_CFA_nops.  */
      if (new_size != ent->size)
	memset (end, 0, new_size - ent->size);

      if (ent->cie)
	{
	  /* CIE */
	  if (ent->make_relative
	      || ent->need_lsda_relative
	      || ent->per_encoding_relative)
	    {
	      char *aug;
	      unsigned int action, extra_string, extra_data;
	      unsigned int per_width, per_encoding;

	      /* Need to find 'R' or 'L' augmentation's argument and modify
		 DW_EH_PE_* value.  */
	      action = ((ent->make_relative ? 1 : 0)
			| (ent->need_lsda_relative ? 2 : 0)
			| (ent->per_encoding_relative ? 4 : 0));
	      extra_string = extra_augmentation_string_bytes (ent);
	      extra_data = extra_augmentation_data_bytes (ent);

	      /* Skip length, id and version.  */
	      buf += 9;
	      aug = (char *) buf;
	      buf += strlen (aug) + 1;
	      skip_leb128 (&buf, end);
	      skip_leb128 (&buf, end);
	      skip_leb128 (&buf, end);
	      if (*aug == 'z')
		{
		  /* The uleb128 will always be a single byte for the kind
		     of augmentation strings that we're prepared to handle.  */
		  *buf++ += extra_data;
		  aug++;
		}

	      /* Make room for the new augmentation string and data bytes.  */
	      memmove (buf + extra_string + extra_data, buf, end - buf);
	      memmove (aug + extra_string, aug, buf - (bfd_byte *) aug);
	      buf += extra_string;
	      end += extra_string + extra_data;

	      if (ent->add_augmentation_size)
		{
		  *aug++ = 'z';
		  *buf++ = extra_data - 1;
		}
	      if (ent->add_fde_encoding)
		{
		  BFD_ASSERT (action & 1);
		  *aug++ = 'R';
		  *buf++ = DW_EH_PE_pcrel;
		  action &= ~1;
		}

	      while (action)
		switch (*aug++)
		  {
		  case 'L':
		    if (action & 2)
		      {
			BFD_ASSERT (*buf == ent->lsda_encoding);
			*buf |= DW_EH_PE_pcrel;
			action &= ~2;
		      }
		    buf++;
		    break;
		  case 'P':
		    per_encoding = *buf++;
		    per_width = get_DW_EH_PE_width (per_encoding, ptr_size);
		    BFD_ASSERT (per_width != 0);
		    BFD_ASSERT (((per_encoding & 0x70) == DW_EH_PE_pcrel)
				== ent->per_encoding_relative);
		    if ((per_encoding & 0xf0) == DW_EH_PE_aligned)
		      buf = (contents
			     + ((buf - contents + per_width - 1)
				& ~((bfd_size_type) per_width - 1)));
		    if (action & 4)
		      {
			bfd_vma val;

			val = read_value (abfd, buf, per_width,
					  get_DW_EH_PE_signed (per_encoding));
			val += ent->offset - ent->new_offset;
			val -= extra_string + extra_data;
			write_value (abfd, buf, val, per_width);
			action &= ~4;
		      }
		    buf += per_width;
		    break;
		  case 'R':
		    if (action & 1)
		      {
			BFD_ASSERT (*buf == ent->fde_encoding);
			*buf |= DW_EH_PE_pcrel;
			action &= ~1;
		      }
		    buf++;
		    break;
		  case 'S':
		    break;
		  default:
		    BFD_FAIL ();
		  }
	    }
	}
      else
	{
	  /* FDE */
	  bfd_vma value, address;
	  unsigned int width;
	  bfd_byte *start;

	  /* Skip length.  */
	  buf += 4;
	  value = ent->new_offset + 4 - ent->cie_inf->new_offset;
	  bfd_put_32 (abfd, value, buf);
	  buf += 4;
	  width = get_DW_EH_PE_width (ent->fde_encoding, ptr_size);
	  value = read_value (abfd, buf, width,
			      get_DW_EH_PE_signed (ent->fde_encoding));
	  address = value;
	  if (value)
	    {
	      switch (ent->fde_encoding & 0xf0)
		{
		case DW_EH_PE_indirect:
		case DW_EH_PE_textrel:
		  BFD_ASSERT (hdr_info == NULL);
		  break;
		case DW_EH_PE_datarel:
		  {
		    asection *got = bfd_get_section_by_name (abfd, ".got");

		    BFD_ASSERT (got != NULL);
		    address += got->vma;
		  }
		  break;
		case DW_EH_PE_pcrel:
		  value += ent->offset - ent->new_offset;
		  address += sec->output_section->vma + ent->offset + 8;
		  break;
		}
	      if (ent->cie_inf->make_relative)
		value -= sec->output_section->vma + ent->new_offset + 8;
	      write_value (abfd, buf, value, width);
	    }

	  start = buf;

	  if (hdr_info)
	    {
	      hdr_info->array[hdr_info->array_count].initial_loc = address;
	      hdr_info->array[hdr_info->array_count++].fde
		= sec->output_section->vma + ent->new_offset;
	    }

	  if ((ent->lsda_encoding & 0xf0) == DW_EH_PE_pcrel
	      || ent->cie_inf->need_lsda_relative)
	    {
	      buf += ent->lsda_offset;
	      width = get_DW_EH_PE_width (ent->lsda_encoding, ptr_size);
	      value = read_value (abfd, buf, width,
				  get_DW_EH_PE_signed (ent->lsda_encoding));
	      if (value)
		{
		  if ((ent->lsda_encoding & 0xf0) == DW_EH_PE_pcrel)
		    value += ent->offset - ent->new_offset;
		  else if (ent->cie_inf->need_lsda_relative)
		    value -= (sec->output_section->vma + ent->new_offset + 8
			      + ent->lsda_offset);
		  write_value (abfd, buf, value, width);
		}
	    }
	  else if (ent->cie_inf->add_augmentation_size)
	    {
	      /* Skip the PC and length and insert a zero byte for the
		 augmentation size.  */
	      buf += width * 2;
	      memmove (buf + 1, buf, end - buf);
	      *buf = 0;
	    }

	  if (ent->set_loc)
	    {
	      /* Adjust DW_CFA_set_loc.  */
	      unsigned int cnt, width;
	      bfd_vma new_offset;

	      width = get_DW_EH_PE_width (ent->fde_encoding, ptr_size);
	      new_offset = ent->new_offset + 8
			   + extra_augmentation_string_bytes (ent)
			   + extra_augmentation_data_bytes (ent);

	      for (cnt = 1; cnt <= ent->set_loc[0]; cnt++)
		{
		  bfd_vma value;
		  buf = start + ent->set_loc[cnt];

		  value = read_value (abfd, buf, width,
				      get_DW_EH_PE_signed (ent->fde_encoding));
		  if (!value)
		    continue;

		  if ((ent->fde_encoding & 0xf0) == DW_EH_PE_pcrel)
		    value += ent->offset + 8 - new_offset;
		  if (ent->cie_inf->make_relative)
		    value -= sec->output_section->vma + new_offset
			     + ent->set_loc[cnt];
		  write_value (abfd, buf, value, width);
		}
	    }
	}
    }

  /* We don't align the section to its section alignment since the
     runtime library only expects all CIE/FDE records aligned at
     the pointer size. _bfd_elf_discard_section_eh_frame should 
     have padded CIE/FDE records to multiple of pointer size with
     size_of_output_cie_fde.  */
  if ((sec->size % ptr_size) != 0)
    abort ();

  return bfd_set_section_contents (abfd, sec->output_section,
				   contents, (file_ptr) sec->output_offset,
				   sec->size);
}

/* Helper function used to sort .eh_frame_hdr search table by increasing
   VMA of FDE initial location.  */

static int
vma_compare (const void *a, const void *b)
{
  const struct eh_frame_array_ent *p = a;
  const struct eh_frame_array_ent *q = b;
  if (p->initial_loc > q->initial_loc)
    return 1;
  if (p->initial_loc < q->initial_loc)
    return -1;
  return 0;
}

/* Write out .eh_frame_hdr section.  This must be called after
   _bfd_elf_write_section_eh_frame has been called on all input
   .eh_frame sections.
   .eh_frame_hdr format:
   ubyte version		(currently 1)
   ubyte eh_frame_ptr_enc  	(DW_EH_PE_* encoding of pointer to start of
				 .eh_frame section)
   ubyte fde_count_enc		(DW_EH_PE_* encoding of total FDE count
				 number (or DW_EH_PE_omit if there is no
				 binary search table computed))
   ubyte table_enc		(DW_EH_PE_* encoding of binary search table,
				 or DW_EH_PE_omit if not present.
				 DW_EH_PE_datarel is using address of
				 .eh_frame_hdr section start as base)
   [encoded] eh_frame_ptr	(pointer to start of .eh_frame section)
   optionally followed by:
   [encoded] fde_count		(total number of FDEs in .eh_frame section)
   fde_count x [encoded] initial_loc, fde
				(array of encoded pairs containing
				 FDE initial_location field and FDE address,
				 sorted by increasing initial_loc).  */

bfd_boolean
_bfd_elf_write_section_eh_frame_hdr (bfd *abfd, struct bfd_link_info *info)
{
  struct elf_link_hash_table *htab;
  struct eh_frame_hdr_info *hdr_info;
  asection *sec;
  bfd_byte *contents;
  asection *eh_frame_sec;
  bfd_size_type size;
  bfd_boolean retval;
  bfd_vma encoded_eh_frame;

  htab = elf_hash_table (info);
  hdr_info = &htab->eh_info;
  sec = hdr_info->hdr_sec;
  if (sec == NULL)
    return TRUE;

  size = EH_FRAME_HDR_SIZE;
  if (hdr_info->array && hdr_info->array_count == hdr_info->fde_count)
    size += 4 + hdr_info->fde_count * 8;
  contents = bfd_malloc (size);
  if (contents == NULL)
    return FALSE;

  eh_frame_sec = bfd_get_section_by_name (abfd, ".eh_frame");
  if (eh_frame_sec == NULL)
    {
      free (contents);
      return FALSE;
    }

  memset (contents, 0, EH_FRAME_HDR_SIZE);
  contents[0] = 1;				/* Version.  */
  contents[1] = get_elf_backend_data (abfd)->elf_backend_encode_eh_address
    (abfd, info, eh_frame_sec, 0, sec, 4,
     &encoded_eh_frame);			/* .eh_frame offset.  */

  if (hdr_info->array && hdr_info->array_count == hdr_info->fde_count)
    {
      contents[2] = DW_EH_PE_udata4;		/* FDE count encoding.  */
      contents[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4; /* Search table enc.  */
    }
  else
    {
      contents[2] = DW_EH_PE_omit;
      contents[3] = DW_EH_PE_omit;
    }
  bfd_put_32 (abfd, encoded_eh_frame, contents + 4);

  if (contents[2] != DW_EH_PE_omit)
    {
      unsigned int i;

      bfd_put_32 (abfd, hdr_info->fde_count, contents + EH_FRAME_HDR_SIZE);
      qsort (hdr_info->array, hdr_info->fde_count, sizeof (*hdr_info->array),
	     vma_compare);
      for (i = 0; i < hdr_info->fde_count; i++)
	{
	  bfd_put_32 (abfd,
		      hdr_info->array[i].initial_loc
		      - sec->output_section->vma,
		      contents + EH_FRAME_HDR_SIZE + i * 8 + 4);
	  bfd_put_32 (abfd,
		      hdr_info->array[i].fde - sec->output_section->vma,
		      contents + EH_FRAME_HDR_SIZE + i * 8 + 8);
	}
    }

  retval = bfd_set_section_contents (abfd, sec->output_section,
				     contents, (file_ptr) sec->output_offset,
				     sec->size);
  free (contents);
  return retval;
}

/* Return the width of FDE addresses.  This is the default implementation.  */

unsigned int
_bfd_elf_eh_frame_address_size (bfd *abfd, asection *sec ATTRIBUTE_UNUSED)
{
  return elf_elfheader (abfd)->e_ident[EI_CLASS] == ELFCLASS64 ? 8 : 4;
}

/* Decide whether we can use a PC-relative encoding within the given
   EH frame section.  This is the default implementation.  */

bfd_boolean
_bfd_elf_can_make_relative (bfd *input_bfd ATTRIBUTE_UNUSED,
			    struct bfd_link_info *info ATTRIBUTE_UNUSED,
			    asection *eh_frame_section ATTRIBUTE_UNUSED)
{
  return TRUE;
}

/* Select an encoding for the given address.  Preference is given to
   PC-relative addressing modes.  */

bfd_byte
_bfd_elf_encode_eh_address (bfd *abfd ATTRIBUTE_UNUSED,
			    struct bfd_link_info *info ATTRIBUTE_UNUSED,
			    asection *osec, bfd_vma offset,
			    asection *loc_sec, bfd_vma loc_offset,
			    bfd_vma *encoded)
{
  *encoded = osec->vma + offset -
    (loc_sec->output_section->vma + loc_sec->output_offset + loc_offset);
  return DW_EH_PE_pcrel | DW_EH_PE_sdata4;
}