[deliverable/binutils-gdb.git] / bfd / elf-ifunc.c

/* ELF STT_GNU_IFUNC support.
   Copyright 2009-2013
   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 (info->shared)
    {
      /* 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 (!info->shared
      && (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 (info->shared && !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 (!info->shared
      || !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
      || (info->shared
	  && (h->dynindx == -1
	      || h->forced_local))
      || (!info->shared
	  && !h->pointer_equality_needed)
      || (info->executable && info->shared)
      || 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 (info->shared)
	htab->srelgot->size += sizeof_reloc;
    }

  return TRUE;
}
Commit	Line	Data
6de2ae4a	1	/* ELF STT_GNU_IFUNC support.
a9ea330b	2	Copyright 2009-2013
6de2ae4a L	3	Free Software Foundation, Inc.
	4
	5	This file is part of BFD, the Binary File Descriptor library.
	6
	7	This program is free software; you can redistribute it and/or modify
	8	it under the terms of the GNU General Public License as published by
	9	the Free Software Foundation; either version 3 of the License, or
	10	(at your option) any later version.
	11
	12	This program is distributed in the hope that it will be useful,
	13	but WITHOUT ANY WARRANTY; without even the implied warranty of
	14	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	15	GNU General Public License for more details.
	16
	17	You should have received a copy of the GNU General Public License
	18	along with this program; if not, write to the Free Software
	19	Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
	20	MA 02110-1301, USA. */
	21
	22	#include "sysdep.h"
	23	#include "bfd.h"
	24	#include "bfdlink.h"
	25	#include "libbfd.h"
	26	#define ARCH_SIZE 0
	27	#include "elf-bfd.h"
	28	#include "safe-ctype.h"
	29	#include "libiberty.h"
	30	#include "objalloc.h"
	31
	32	/* Create sections needed by STT_GNU_IFUNC symbol. */
	33
	34	bfd_boolean
	35	_bfd_elf_create_ifunc_sections (bfd abfd, struct bfd_link_info info)
	36	{
	37	flagword flags, pltflags;
	38	asection *s;
	39	const struct elf_backend_data *bed = get_elf_backend_data (abfd);
	40	struct elf_link_hash_table *htab = elf_hash_table (info);
	41
	42	if (htab->irelifunc != NULL \|\| htab->iplt != NULL)
	43	return TRUE;
	44
	45	flags = bed->dynamic_sec_flags;
	46	pltflags = flags;
	47	if (bed->plt_not_loaded)
	48	/* We do not clear SEC_ALLOC here because we still want the OS to
	49	allocate space for the section; it's just that there's nothing
	50	to read in from the object file. */
	51	pltflags &= ~ (SEC_CODE \| SEC_LOAD \| SEC_HAS_CONTENTS);
	52	else
	53	pltflags \|= SEC_ALLOC \| SEC_CODE \| SEC_LOAD;
	54	if (bed->plt_readonly)
	55	pltflags \|= SEC_READONLY;
	56
	57	if (info->shared)
	58	{
	59	/* We need to create .rel[a].ifunc for shared objects. */
	60	const char *rel_sec = (bed->rela_plts_and_copies_p
	61	? ".rela.ifunc" : ".rel.ifunc");
	62
	63	s = bfd_make_section_with_flags (abfd, rel_sec,
	64	flags \| SEC_READONLY);
	65	if (s == NULL
	66	\|\| ! bfd_set_section_alignment (abfd, s,
67	bed->s->log_file_align))
68	return FALSE;
69	htab->irelifunc = s;
70	}
71	else
72	{
73	/* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt
74	for static executables. */
75	s = bfd_make_section_with_flags (abfd, ".iplt", pltflags);
76	if (s == NULL
77	\|\| ! bfd_set_section_alignment (abfd, s, bed->plt_alignment))
78	return FALSE;
79	htab->iplt = s;
80
81	s = bfd_make_section_with_flags (abfd,
82	(bed->rela_plts_and_copies_p
83	? ".rela.iplt" : ".rel.iplt"),
84	flags \| SEC_READONLY);
85	if (s == NULL
86	\|\| ! bfd_set_section_alignment (abfd, s,
87	bed->s->log_file_align))
88	return FALSE;
89	htab->irelplt = s;
90
91	/* We don't need the .igot section if we have the .igot.plt
92	section. */
93	if (bed->want_got_plt)
94	s = bfd_make_section_with_flags (abfd, ".igot.plt", flags);
95	else
96	s = bfd_make_section_with_flags (abfd, ".igot", flags);
97	if (s == NULL
98	\|\| !bfd_set_section_alignment (abfd, s,
99	bed->s->log_file_align))
100	return FALSE;
101	htab->igotplt = s;
102	}
103
104	return TRUE;
105	}
e03a8ed8	106
e03a8ed8 L	107	/* Allocate space in .plt, .got and associated reloc sections for
	108	dynamic relocs against a STT_GNU_IFUNC symbol definition. */
	109
	110	bfd_boolean
	111	_bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info,
	112	struct elf_link_hash_entry *h,
	113	struct elf_dyn_relocs **head,
	114	unsigned int plt_entry_size,
7b70956d	115	unsigned int plt_header_size,
e03a8ed8 L	116	unsigned int got_entry_size)
	117	{
	118	asection plt, gotplt, *relplt;
	119	struct elf_dyn_relocs *p;
	120	unsigned int sizeof_reloc;
	121	const struct elf_backend_data *bed;
	122	struct elf_link_hash_table *htab;
	123
	124	/* When a shared library references a STT_GNU_IFUNC symbol defined
	125	in executable, the address of the resolved function may be used.
	126	But in non-shared executable, the address of its .plt slot may
	127	be used. Pointer equality may not work correctly. PIE should
	128	be used if pointer equality is required here. */
	129	if (!info->shared
	130	&& (h->dynindx != -1
	131	\|\| info->export_dynamic)
	132	&& h->pointer_equality_needed)
	133	{
68ffbac6	134	info->callbacks->einfo
e03a8ed8 L	135	(_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer "
	136	"equality in `%B' can not be used when making an "
	137	"executable; recompile with -fPIE and relink with -pie\n"),
	138	h->root.root.string,
	139	h->root.u.def.section->owner);
	140	bfd_set_error (bfd_error_bad_value);
	141	return FALSE;
	142	}
	143
004fb780 L	144	htab = elf_hash_table (info);
004fb780 L	145
1622ff3b L	146	/* When building shared library, we need to handle the case where it is
	147	marked with regular reference, but not non-GOT reference since the
	148	non-GOT reference bit may not be set here. */
	149	if (info->shared && !h->non_got_ref && h->ref_regular)
	150	for (p = *head; p != NULL; p = p->next)
	151	if (p->count)
	152	{
	153	h->non_got_ref = 1;
	154	goto keep;
	155	}
	156
bb1cb422 L	157	/* Support garbage collection against STT_GNU_IFUNC symbols. */
	158	if (h->plt.refcount <= 0 && h->got.refcount <= 0)
	159	{
7be86737 L	160	h->got = htab->init_got_offset;
	161	h->plt = htab->init_plt_offset;
	162	*head = NULL;
	163	return TRUE;
bb1cb422 L	164	}
bb1cb422 L	165
e03a8ed8 L	166	/* Return and discard space for dynamic relocations against it if
	167	it is never referenced in a non-shared object. */
	168	if (!h->ref_regular)
	169	{
	170	if (h->plt.refcount > 0
	171	\|\| h->got.refcount > 0)
	172	abort ();
004fb780 L	173	h->got = htab->init_got_offset;
004fb780 L	174	h->plt = htab->init_plt_offset;
e03a8ed8 L	175	*head = NULL;
	176	return TRUE;
	177	}
	178
7be86737	179	keep:
e03a8ed8 L	180	bed = get_elf_backend_data (info->output_bfd);
	181	if (bed->rela_plts_and_copies_p)
	182	sizeof_reloc = bed->s->sizeof_rela;
	183	else
	184	sizeof_reloc = bed->s->sizeof_rel;
	185
e03a8ed8 L	186	/* When building a static executable, use .iplt, .igot.plt and
	187	.rel[a].iplt sections for STT_GNU_IFUNC symbols. */
	188	if (htab->splt != NULL)
	189	{
	190	plt = htab->splt;
	191	gotplt = htab->sgotplt;
	192	relplt = htab->srelplt;
	193
	194	/* If this is the first .plt entry, make room for the special
	195	first entry. */
	196	if (plt->size == 0)
7b70956d	197	plt->size += plt_header_size;
e03a8ed8 L	198	}
	199	else
	200	{
	201	plt = htab->iplt;
	202	gotplt = htab->igotplt;
	203	relplt = htab->irelplt;
	204	}
	205
	206	/* Don't update value of STT_GNU_IFUNC symbol to PLT. We need
68ffbac6	207	the original value for R__IRELATIVE. /
e03a8ed8 L	208	h->plt.offset = plt->size;
	209
	210	/* Make room for this entry in the .plt/.iplt section. */
	211	plt->size += plt_entry_size;
	212
	213	/* We also need to make an entry in the .got.plt/.got.iplt section,
	214	which will be placed in the .got section by the linker script. */
	215	gotplt->size += got_entry_size;
	216
	217	/* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
	218	section. */
	219	relplt->size += sizeof_reloc;
	220	relplt->reloc_count++;
	221
	222	/* We need dynamic relocation for STT_GNU_IFUNC symbol only when
	223	there is a non-GOT reference in a shared object. */
	224	if (!info->shared
	225	\|\| !h->non_got_ref)
	226	*head = NULL;
	227
	228	/* Finally, allocate space. */
7be86737 L	229	p = *head;
	230	if (p != NULL)
	231	{
	232	bfd_size_type count = 0;
	233	do
	234	{
	235	count += p->count;
	236	p = p->next;
	237	}
	238	while (p != NULL);
	239	htab->irelifunc->size += count * sizeof_reloc;
	240	}
e03a8ed8	241
7be86737	242	/* For STT_GNU_IFUNC symbol, .got.plt has the real function address
e03a8ed8 L	243	and .got has the PLT entry adddress. We will load the GOT entry
	244	with the PLT entry in finish_dynamic_symbol if it is used. For
	245	branch, it uses .got.plt. For symbol value,
	246	1. Use .got.plt in a shared object if it is forced local or not
	247	dynamic.
	248	2. Use .got.plt in a non-shared object if pointer equality isn't
	249	needed.
	250	3. Use .got.plt in PIE.
	251	4. Use .got.plt if .got isn't used.
	252	5. Otherwise use .got so that it can be shared among different
	253	objects at run-time.
	254	We only need to relocate .got entry in shared object. */
7b5b197e L	255	if (h->got.refcount <= 0
	256	\|\| (info->shared
	257	&& (h->dynindx == -1
	258	\|\| h->forced_local))
e03a8ed8 L	259	\|\| (!info->shared
	260	&& !h->pointer_equality_needed)
	261	\|\| (info->executable && info->shared)
	262	\|\| htab->sgot == NULL)
	263	{
	264	/* Use .got.plt. */
	265	h->got.offset = (bfd_vma) -1;
	266	}
	267	else
	268	{
	269	h->got.offset = htab->sgot->size;
	270	htab->sgot->size += got_entry_size;
	271	if (info->shared)
	272	htab->srelgot->size += sizeof_reloc;
	273	}
	274
	275	return TRUE;
	276	}