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/* ELF STT_GNU_IFUNC support.

   Copyright (C) 2009-2015 Free Software Foundation, Inc.

   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 3 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 "bfdlink.h"

#include "libbfd.h"

#define ARCH_SIZE 0

#include "elf-bfd.h"

#include "safe-ctype.h"

#include "libiberty.h"

#include "objalloc.h"

/* Create sections needed by STT_GNU_IFUNC symbol.  */

bfd_boolean

_bfd_elf_create_ifunc_sections (bfd *abfd, struct bfd_link_info *info)

{

  flagword flags, pltflags;

  asection *s;

  const struct elf_backend_data *bed = get_elf_backend_data (abfd);

  struct elf_link_hash_table *htab = elf_hash_table (info);

  if (htab->irelifunc != NULL || htab->iplt != NULL)

    return TRUE;

  flags = bed->dynamic_sec_flags;

  pltflags = flags;

  if (bed->plt_not_loaded)

    /* We do not clear SEC_ALLOC here because we still want the OS to

       allocate space for the section; it's just that there's nothing

       to read in from the object file.  */

    pltflags &= ~ (SEC_CODE | SEC_LOAD | SEC_HAS_CONTENTS);

  else

    pltflags |= SEC_ALLOC | SEC_CODE | SEC_LOAD;

  if (bed->plt_readonly)

    pltflags |= SEC_READONLY;

  if (bfd_link_pic (info))

    {

      /* We need to create .rel[a].ifunc for shared objects.  */

      const char *rel_sec = (bed->rela_plts_and_copies_p

			     ? ".rela.ifunc" : ".rel.ifunc");

      s = bfd_make_section_with_flags (abfd, rel_sec,

				       flags | SEC_READONLY);

      if (s == NULL

	  || ! bfd_set_section_alignment (abfd, s,

					  bed->s->log_file_align))

	return FALSE;

      htab->irelifunc = s;

    }

  else

    {

      /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt

	 for static executables.   */

      s = bfd_make_section_with_flags (abfd, ".iplt", pltflags);

      if (s == NULL

	  || ! bfd_set_section_alignment (abfd, s, bed->plt_alignment))

	return FALSE;

      htab->iplt = s;

      s = bfd_make_section_with_flags (abfd,

				       (bed->rela_plts_and_copies_p

					? ".rela.iplt" : ".rel.iplt"),

				       flags | SEC_READONLY);

      if (s == NULL

	  || ! bfd_set_section_alignment (abfd, s,

					  bed->s->log_file_align))

	return FALSE;

      htab->irelplt = s;

      /* We don't need the .igot section if we have the .igot.plt

	 section.  */

      if (bed->want_got_plt)

	s = bfd_make_section_with_flags (abfd, ".igot.plt", flags);

      else

	s = bfd_make_section_with_flags (abfd, ".igot", flags);

      if (s == NULL

	  || !bfd_set_section_alignment (abfd, s,

					 bed->s->log_file_align))

	return FALSE;

      htab->igotplt = s;

    }

  return TRUE;

}

/* Allocate space in .plt, .got and associated reloc sections for

   dynamic relocs against a STT_GNU_IFUNC symbol definition.  */

bfd_boolean

_bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info,

				    struct elf_link_hash_entry *h,

				    struct elf_dyn_relocs **head,

				    unsigned int plt_entry_size,

				    unsigned int plt_header_size,

				    unsigned int got_entry_size)

{

  asection *plt, *gotplt, *relplt;

  struct elf_dyn_relocs *p;

  unsigned int sizeof_reloc;

  const struct elf_backend_data *bed;

  struct elf_link_hash_table *htab;

  /* When a shared library references a STT_GNU_IFUNC symbol defined

     in executable, the address of the resolved function may be used.

     But in non-shared executable, the address of its .plt slot may

     be used.  Pointer equality may not work correctly.  PIE should

     be used if pointer equality is required here.  */

  if (!bfd_link_pic (info)

      && (h->dynindx != -1

	  || info->export_dynamic)

      && h->pointer_equality_needed)

    {

      info->callbacks->einfo

	(_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer "

	   "equality in `%B' can not be used when making an "

	   "executable; recompile with -fPIE and relink with -pie\n"),

	 h->root.root.string,

	 h->root.u.def.section->owner);

      bfd_set_error (bfd_error_bad_value);

      return FALSE;

    }

  htab = elf_hash_table (info);

  /* When building shared library, we need to handle the case where it is

     marked with regular reference, but not non-GOT reference since the

     non-GOT reference bit may not be set here.  */

  if (bfd_link_pic (info) && !h->non_got_ref && h->ref_regular)

    for (p = *head; p != NULL; p = p->next)

      if (p->count)

	{

	  h->non_got_ref = 1;

	  goto keep;

	}

  /* Support garbage collection against STT_GNU_IFUNC symbols.  */

  if (h->plt.refcount <= 0 && h->got.refcount <= 0)

    {

      h->got = htab->init_got_offset;

      h->plt = htab->init_plt_offset;

      *head = NULL;

      return TRUE;

    }

  /* Return and discard space for dynamic relocations against it if

     it is never referenced in a non-shared object.  */

  if (!h->ref_regular)

    {

      if (h->plt.refcount > 0

	  || h->got.refcount > 0)

	abort ();

      h->got = htab->init_got_offset;

      h->plt = htab->init_plt_offset;

      *head = NULL;

      return TRUE;

    }

keep:

  bed = get_elf_backend_data (info->output_bfd);

  if (bed->rela_plts_and_copies_p)

    sizeof_reloc = bed->s->sizeof_rela;

  else

    sizeof_reloc = bed->s->sizeof_rel;

  /* When building a static executable, use .iplt, .igot.plt and

     .rel[a].iplt sections for STT_GNU_IFUNC symbols.  */

  if (htab->splt != NULL)

    {

      plt = htab->splt;

      gotplt = htab->sgotplt;

      relplt = htab->srelplt;

      /* If this is the first .plt entry, make room for the special

	 first entry.  */

      if (plt->size == 0)

	plt->size += plt_header_size;

    }

  else

    {

      plt = htab->iplt;

      gotplt = htab->igotplt;

      relplt = htab->irelplt;

    }

  /* Don't update value of STT_GNU_IFUNC symbol to PLT.  We need

     the original value for R_*_IRELATIVE.  */

  h->plt.offset = plt->size;

  /* Make room for this entry in the .plt/.iplt section.  */

  plt->size += plt_entry_size;

  /* We also need to make an entry in the .got.plt/.got.iplt section,

     which will be placed in the .got section by the linker script.  */

  gotplt->size += got_entry_size;

  /* We also need to make an entry in the .rel[a].plt/.rel[a].iplt

     section.  */

  relplt->size += sizeof_reloc;

  relplt->reloc_count++;

  /* We need dynamic relocation for STT_GNU_IFUNC symbol only when

     there is a non-GOT reference in a shared object.  */

  if (!bfd_link_pic (info)

      || !h->non_got_ref)

    *head = NULL;

  /* Finally, allocate space.  */

  p = *head;

  if (p != NULL)

    {

      bfd_size_type count = 0;

      do

	{

	  count += p->count;

	  p = p->next;

	}

      while (p != NULL);

      htab->irelifunc->size += count * sizeof_reloc;

    }

  /* For STT_GNU_IFUNC symbol, .got.plt has the real function address

     and .got has the PLT entry adddress.  We will load the GOT entry

     with the PLT entry in finish_dynamic_symbol if it is used.  For

     branch, it uses .got.plt.  For symbol value,

     1. Use .got.plt in a shared object if it is forced local or not

     dynamic.

     2. Use .got.plt in a non-shared object if pointer equality isn't

     needed.

     3. Use .got.plt in PIE.

     4. Use .got.plt if .got isn't used.

     5. Otherwise use .got so that it can be shared among different

     objects at run-time.

     We only need to relocate .got entry in shared object.  */

  if (h->got.refcount <= 0

      || (bfd_link_pic (info)

	  && (h->dynindx == -1

	      || h->forced_local))

      || (!bfd_link_pic (info)

	  && !h->pointer_equality_needed)

      || bfd_link_pie (info)

      || htab->sgot == NULL)

    {

      /* Use .got.plt.  */

      h->got.offset = (bfd_vma) -1;

    }

  else

    {

      h->got.offset = htab->sgot->size;

      htab->sgot->size += got_entry_size;

      if (bfd_link_pic (info))

	htab->srelgot->size += sizeof_reloc;

    }

  return TRUE;

}

/* Similar to _bfd_elf_get_synthetic_symtab, optimized for unsorted PLT

   entries.  PLT is the PLT section.  PLT_SYM_VAL is a function pointer

   which returns an array of PLT entry symbol values.  */

long

_bfd_elf_ifunc_get_synthetic_symtab

  (bfd *abfd, long symcount ATTRIBUTE_UNUSED,

   asymbol **syms ATTRIBUTE_UNUSED, long dynsymcount, asymbol **dynsyms,

   asymbol **ret, asection *plt,

   bfd_vma *(*get_plt_sym_val) (bfd *, asymbol **, asection *, asection *))

{

  const struct elf_backend_data *bed = get_elf_backend_data (abfd);

  asection *relplt;

  asymbol *s;

  const char *relplt_name;

  bfd_boolean (*slurp_relocs) (bfd *, asection *, asymbol **, bfd_boolean);

  arelent *p;

  long count, i, n;

  size_t size;

  Elf_Internal_Shdr *hdr;

  char *names;

  bfd_vma *plt_sym_val;

  *ret = NULL;

  if (plt == NULL)

    return 0;

  if ((abfd->flags & (DYNAMIC | EXEC_P)) == 0)

    return 0;

  if (dynsymcount <= 0)

    return 0;

  relplt_name = bed->relplt_name;

  if (relplt_name == NULL)

    relplt_name = bed->rela_plts_and_copies_p ? ".rela.plt" : ".rel.plt";

  relplt = bfd_get_section_by_name (abfd, relplt_name);

  if (relplt == NULL)

    return 0;

  hdr = &elf_section_data (relplt)->this_hdr;

  if (hdr->sh_link != elf_dynsymtab (abfd)

      || (hdr->sh_type != SHT_REL && hdr->sh_type != SHT_RELA))

    return 0;

  slurp_relocs = get_elf_backend_data (abfd)->s->slurp_reloc_table;

  if (! (*slurp_relocs) (abfd, relplt, dynsyms, TRUE))

    return -1;

  count = relplt->size / hdr->sh_entsize;

  size = count * sizeof (asymbol);

  p = relplt->relocation;

  for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel)

    {

      size += strlen ((*p->sym_ptr_ptr)->name) + sizeof ("@plt");

      if (p->addend != 0)

	{

#ifdef BFD64

	  size += sizeof ("+0x") - 1 + 8 + 8 * (bed->s->elfclass == ELFCLASS64);

#else

	  size += sizeof ("+0x") - 1 + 8;

#endif

	}

    }

  plt_sym_val = get_plt_sym_val (abfd, dynsyms, plt, relplt);

  if (plt_sym_val == NULL)

    return -1;

  s = *ret = (asymbol *) bfd_malloc (size);

  if (s == NULL)

    {

      free (plt_sym_val);

      return -1;

    }

  names = (char *) (s + count);

  p = relplt->relocation;

  n = 0;

  for (i = 0; i < count; i++, p += bed->s->int_rels_per_ext_rel)

    {

      size_t len;

      bfd_vma addr;

      addr = plt_sym_val[i];

      if (addr == (bfd_vma) -1)

	continue;

      *s = **p->sym_ptr_ptr;

      /* Undefined syms won't have BSF_LOCAL or BSF_GLOBAL set.  Since

	 we are defining a symbol, ensure one of them is set.  */

      if ((s->flags & BSF_LOCAL) == 0)

	s->flags |= BSF_GLOBAL;

      s->flags |= BSF_SYNTHETIC;

      s->section = plt;

      s->value = addr - plt->vma;

      s->name = names;

      s->udata.p = NULL;

      len = strlen ((*p->sym_ptr_ptr)->name);

      memcpy (names, (*p->sym_ptr_ptr)->name, len);

      names += len;

      if (p->addend != 0)

	{

	  char buf[30], *a;

	  memcpy (names, "+0x", sizeof ("+0x") - 1);

	  names += sizeof ("+0x") - 1;

	  bfd_sprintf_vma (abfd, buf, p->addend);

	  for (a = buf; *a == '0'; ++a)

	    ;

	  len = strlen (a);

	  memcpy (names, a, len);

	  names += len;

	}

      memcpy (names, "@plt", sizeof ("@plt"));

      names += sizeof ("@plt");

      ++s, ++n;

    }

  free (plt_sym_val);

  return n;

}