binutils-gdb/bfd/elf-eh-frame.c

/* .eh_frame section optimization.
   Copyright 2001, 2002, 2003, 2004, 2005, 2006 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 "bfd.h"
#include "sysdep.h"
#include "libbfd.h"
#include "elf-bfd.h"
#include "elf/dwarf2.h"

#define EH_FRAME_HDR_SIZE 8

/* 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 zero if C1 and C2 CIEs can be merged.  */

static
int cie_compare (struct cie *c1, struct cie *c2)
{
  if (c1->hdr.length == c2->hdr.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->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 0;

  return 1;
}

/* 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 & 0x80 ? op & 0xc0 : op)
    {
    case DW_CFA_nop:
    case DW_CFA_advance_loc:
    case DW_CFA_restore:
      /* 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_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:
      /* 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)
{
  bfd_byte *last;

  last = buf;
  while (buf < end)
    if (*buf == DW_CFA_nop)
      buf++;
    else
      {
	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_cie, *last_fde;
  struct eh_cie_fde *ent, *last_cie_inf, *this_inf;
  struct cie_header hdr;
  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 cie_usage_count, offset;
  unsigned int ptr_size;

  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;

  /* 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;
  last_cie = NULL;
  last_cie_inf = NULL;
  memset (&cie, 0, sizeof (cie));
  cie_usage_count = 0;
  sec_info = bfd_zmalloc (sizeof (struct eh_frame_sec_info)
			  + 99 * sizeof (struct eh_cie_fde));
  REQUIRE (sec_info);

  sec_info->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;
      bfd_size_type length;

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

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

	  /* Now fix any pointers into the array.  */
	  if (last_cie_inf >= old_entry
	      && last_cie_inf < old_entry + sec_info->count)
	    last_cie_inf = sec_info->entry + (last_cie_inf - old_entry);
	}

      this_inf = sec_info->entry + sec_info->count;
      last_fde = buf;
      /* If we are at the end of the section, we still need to decide
	 on whether to output or discard last encountered CIE (if any).  */
      if ((bfd_size_type) (buf - ehbuf) == sec->size)
	{
	  hdr.length = 0;
	  hdr.id = (unsigned int) -1;
	  end = buf;
	}
      else
	{
	  /* 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++;
	      /* Now just finish last encountered CIE processing and break
		 the loop.  */
	      hdr.id = (unsigned int) -1;
	    }
	  else
	    {
	      REQUIRE (skip_bytes (&buf, end, 4));
	      hdr.id = bfd_get_32 (abfd, buf - 4);
	      REQUIRE (hdr.id != (unsigned int) -1);
	    }
	}

      if (hdr.id == 0 || hdr.id == (unsigned int) -1)
	{
	  unsigned int initial_insn_length;

	  /* CIE  */
	  if (last_cie != NULL)
	    {
	      /* Now check if this CIE is identical to the last CIE,
		 in which case we can remove it provided we adjust
		 all FDEs.  Also, it can be removed if we have removed
		 all FDEs using it.  */
	      if ((!info->relocatable
		   && hdr_info->last_cie_sec
		   && (sec->output_section
		       == hdr_info->last_cie_sec->output_section)
		   && cie_compare (&cie, &hdr_info->last_cie) == 0)
		  || cie_usage_count == 0)
		last_cie_inf->removed = 1;
	      else
		{
		  hdr_info->last_cie = cie;
		  hdr_info->last_cie_sec = sec;
		  last_cie_inf->make_relative = cie.make_relative;
		  last_cie_inf->make_lsda_relative = cie.make_lsda_relative;
		  last_cie_inf->per_encoding_relative
		    = (cie.per_encoding & 0x70) == DW_EH_PE_pcrel;
		}
	    }

	  if (hdr.id == (unsigned int) -1)
	    break;

	  last_cie_inf = this_inf;
	  this_inf->cie = 1;

	  cie_usage_count = 0;
	  memset (&cie, 0, sizeof (cie));
	  cie.hdr = hdr;
	  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));
		    }
		    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 <= 50)
	    {
	      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);
	  last_cie = last_fde;
	}
      else
	{
	  /* Ensure this FDE uses the last CIE encountered.  */
	  REQUIRE (last_cie);
	  REQUIRE (hdr.id == (unsigned int) (buf - 4 - last_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;
		}
	      cie_usage_count++;
	      hdr_info->fde_count++;
	    }
	  /* 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
	 including the padding.  */
      length = get_DW_EH_PE_width (cie.fde_encoding, ptr_size);
      insns = skip_non_nops (insns, end, length);
      if (insns != 0)
	this_inf->size -= end - insns;

      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;

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

  /* Resize the sec as needed.  */
  sec->rawsize = sec->size;
  sec->size = offset;
  if (sec->size == 0)
    sec->flags |= SEC_EXCLUDE;

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

free_no_table:
  if (ehbuf)
    free (ehbuf);
  if (sec_info)
    free (sec_info);
  hdr_info->table = FALSE;
  hdr_info->last_cie.hdr.length = 0;
  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;
  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 (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;

	  /* 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);
	    }

	  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;
	    }
	}
    }

  /* 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;
}