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

/* ELF STT_GNU_IFUNC support.
   Copyright 2009
   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;
}

/* For a STT_GNU_IFUNC symbol, create a dynamic reloc section, SRELOC,
   for the input section, SEC, and append this reloc to HEAD.  */

asection *
_bfd_elf_create_ifunc_dyn_reloc (bfd *abfd, struct bfd_link_info *info,
				 asection *sec, asection *sreloc,
				 struct elf_dyn_relocs **head)
{
  struct elf_dyn_relocs *p;
  struct elf_link_hash_table *htab = elf_hash_table (info);

  if (sreloc == NULL)
    {
      const struct elf_backend_data *bed = get_elf_backend_data (abfd);

      if (htab->dynobj == NULL)
	htab->dynobj = abfd;

      sreloc = _bfd_elf_make_dynamic_reloc_section (sec, htab->dynobj,
						    bed->s->log_file_align,
						    abfd,
						    bed->rela_plts_and_copies_p); 
      if (sreloc == NULL)
	return NULL;
    }
		      
  p = *head;
  if (p == NULL || p->sec != sec)
    {
      bfd_size_type amt = sizeof *p;

      p = ((struct elf_dyn_relocs *) bfd_alloc (htab->dynobj, amt));
      if (p == NULL)
	return NULL;
      p->next = *head;
      *head = p;
      p->sec = sec;
      p->count = 0;
      p->pc_count = 0;
    }
  p->count += 1;

  return sreloc;
}

/* 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 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);

  /* 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;
    }

  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_entry_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.  */
  for (p = *head; p != NULL; p = p->next)
    htab->irelifunc->size += p->count * sizeof_reloc;

  /* For STT_GNU_IFUNC symbol, .got.plt has the real function addres
     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 ((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 L	1	/* ELF STT_GNU_IFUNC support.
	2	Copyright 2009
	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 L	106
	107	/* For a STT_GNU_IFUNC symbol, create a dynamic reloc section, SRELOC,
	108	for the input section, SEC, and append this reloc to HEAD. */
	109
	110	asection *
	111	_bfd_elf_create_ifunc_dyn_reloc (bfd abfd, struct bfd_link_info info,
	112	asection sec, asection sreloc,
	113	struct elf_dyn_relocs **head)
	114	{
	115	struct elf_dyn_relocs *p;
	116	struct elf_link_hash_table *htab = elf_hash_table (info);
	117
	118	if (sreloc == NULL)
	119	{
	120	const struct elf_backend_data *bed = get_elf_backend_data (abfd);
	121
	122	if (htab->dynobj == NULL)
	123	htab->dynobj = abfd;
	124
	125	sreloc = _bfd_elf_make_dynamic_reloc_section (sec, htab->dynobj,
	126	bed->s->log_file_align,
	127	abfd,
	128	bed->rela_plts_and_copies_p);
	129	if (sreloc == NULL)
	130	return NULL;
	131	}
	132
	133	p = *head;
	134	if (p == NULL \|\| p->sec != sec)
	135	{
	136	bfd_size_type amt = sizeof *p;
	137
	138	p = ((struct elf_dyn_relocs *) bfd_alloc (htab->dynobj, amt));
	139	if (p == NULL)
	140	return NULL;
	141	p->next = *head;
	142	*head = p;
	143	p->sec = sec;
	144	p->count = 0;
	145	p->pc_count = 0;
	146	}
	147	p->count += 1;
	148
	149	return sreloc;
	150	}
	151
	152	/* Allocate space in .plt, .got and associated reloc sections for
	153	dynamic relocs against a STT_GNU_IFUNC symbol definition. */
	154
	155	bfd_boolean
	156	_bfd_elf_allocate_ifunc_dyn_relocs (struct bfd_link_info *info,
	157	struct elf_link_hash_entry *h,
	158	struct elf_dyn_relocs **head,
	159	unsigned int plt_entry_size,
	160	unsigned int got_entry_size)
	161	{
	162	asection plt, gotplt, *relplt;
	163	struct elf_dyn_relocs *p;
	164	unsigned int sizeof_reloc;
	165	const struct elf_backend_data *bed;
	166	struct elf_link_hash_table *htab;
	167
	168	/* When a shared library references a STT_GNU_IFUNC symbol defined
	169	in executable, the address of the resolved function may be used.
170	But in non-shared executable, the address of its .plt slot may
171	be used. Pointer equality may not work correctly. PIE should
172	be used if pointer equality is required here. */
173	if (!info->shared
174	&& (h->dynindx != -1
175	\|\| info->export_dynamic)
176	&& h->pointer_equality_needed)
177	{
178	info->callbacks->einfo
179	(_("%F%P: dynamic STT_GNU_IFUNC symbol `%s' with pointer "
180	"equality in `%B' can not be used when making an "
181	"executable; recompile with -fPIE and relink with -pie\n"),
182	h->root.root.string,
183	h->root.u.def.section->owner);
184	bfd_set_error (bfd_error_bad_value);
185	return FALSE;
186	}
187
004fb780 L	188	htab = elf_hash_table (info);
004fb780 L	189
e03a8ed8 L	190	/* Return and discard space for dynamic relocations against it if
	191	it is never referenced in a non-shared object. */
	192	if (!h->ref_regular)
	193	{
	194	if (h->plt.refcount > 0
	195	\|\| h->got.refcount > 0)
	196	abort ();
004fb780 L	197	h->got = htab->init_got_offset;
004fb780 L	198	h->plt = htab->init_plt_offset;
e03a8ed8 L	199	*head = NULL;
	200	return TRUE;
	201	}
	202
	203	bed = get_elf_backend_data (info->output_bfd);
	204	if (bed->rela_plts_and_copies_p)
	205	sizeof_reloc = bed->s->sizeof_rela;
	206	else
	207	sizeof_reloc = bed->s->sizeof_rel;
	208
e03a8ed8 L	209	/* When building a static executable, use .iplt, .igot.plt and
	210	.rel[a].iplt sections for STT_GNU_IFUNC symbols. */
	211	if (htab->splt != NULL)
	212	{
	213	plt = htab->splt;
	214	gotplt = htab->sgotplt;
	215	relplt = htab->srelplt;
	216
	217	/* If this is the first .plt entry, make room for the special
	218	first entry. */
	219	if (plt->size == 0)
	220	plt->size += plt_entry_size;
	221	}
	222	else
	223	{
	224	plt = htab->iplt;
	225	gotplt = htab->igotplt;
	226	relplt = htab->irelplt;
	227	}
	228
	229	/* Don't update value of STT_GNU_IFUNC symbol to PLT. We need
	230	the original value for R__IRELATIVE. /
	231	h->plt.offset = plt->size;
	232
	233	/* Make room for this entry in the .plt/.iplt section. */
	234	plt->size += plt_entry_size;
	235
	236	/* We also need to make an entry in the .got.plt/.got.iplt section,
	237	which will be placed in the .got section by the linker script. */
	238	gotplt->size += got_entry_size;
	239
	240	/* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
	241	section. */
	242	relplt->size += sizeof_reloc;
	243	relplt->reloc_count++;
	244
	245	/* We need dynamic relocation for STT_GNU_IFUNC symbol only when
	246	there is a non-GOT reference in a shared object. */
	247	if (!info->shared
	248	\|\| !h->non_got_ref)
	249	*head = NULL;
	250
	251	/* Finally, allocate space. */
	252	for (p = *head; p != NULL; p = p->next)
	253	htab->irelifunc->size += p->count * sizeof_reloc;
	254
	255	/* For STT_GNU_IFUNC symbol, .got.plt has the real function addres
	256	and .got has the PLT entry adddress. We will load the GOT entry
	257	with the PLT entry in finish_dynamic_symbol if it is used. For
	258	branch, it uses .got.plt. For symbol value,
	259	1. Use .got.plt in a shared object if it is forced local or not
	260	dynamic.
	261	2. Use .got.plt in a non-shared object if pointer equality isn't
	262	needed.
	263	3. Use .got.plt in PIE.
	264	4. Use .got.plt if .got isn't used.
	265	5. Otherwise use .got so that it can be shared among different
	266	objects at run-time.
	267	We only need to relocate .got entry in shared object. */
	268	if ((info->shared
	269	&& (h->dynindx == -1
	270	\|\| h->forced_local))
	271	\|\| (!info->shared
	272	&& !h->pointer_equality_needed)
273	\|\| (info->executable && info->shared)
274	\|\| htab->sgot == NULL)
275	{
276	/* Use .got.plt. */
277	h->got.offset = (bfd_vma) -1;
278	}
279	else
280	{
281	h->got.offset = htab->sgot->size;
282	htab->sgot->size += got_entry_size;
283	if (info->shared)
284	htab->srelgot->size += sizeof_reloc;
285	}
286
287	return TRUE;
288	}