[thirdparty/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);

  /* Support garbage collection against STT_GNU_IFUNC symbols.  */
  if (h->plt.refcount <= 0 && h->got.refcount <= 0)
    {
      /* When building shared library, we need to handle the case
         where it is marked with regular reference, but not non-GOT
	 reference.  It may happen if we didn't see STT_GNU_IFUNC
	 symbol at the time when checking relocations.  */
      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;
	    }

      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_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.  */
  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 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
bb1cb422 L	190	/* Support garbage collection against STT_GNU_IFUNC symbols. */
	191	if (h->plt.refcount <= 0 && h->got.refcount <= 0)
	192	{
3db2e7dd L	193	/* When building shared library, we need to handle the case
	194	where it is marked with regular reference, but not non-GOT
	195	reference. It may happen if we didn't see STT_GNU_IFUNC
	196	symbol at the time when checking relocations. */
3db2e7dd L	197	if (info->shared
	198	&& !h->non_got_ref
	199	&& h->ref_regular)
7be86737 L	200	for (p = *head; p != NULL; p = p->next)
	201	if (p->count)
	202	{
	203	h->non_got_ref = 1;
	204	goto keep;
	205	}
3db2e7dd	206
7be86737 L	207	h->got = htab->init_got_offset;
	208	h->plt = htab->init_plt_offset;
	209	*head = NULL;
	210	return TRUE;
bb1cb422 L	211	}
bb1cb422 L	212
e03a8ed8 L	213	/* Return and discard space for dynamic relocations against it if
	214	it is never referenced in a non-shared object. */
	215	if (!h->ref_regular)
	216	{
	217	if (h->plt.refcount > 0
	218	\|\| h->got.refcount > 0)
	219	abort ();
004fb780 L	220	h->got = htab->init_got_offset;
004fb780 L	221	h->plt = htab->init_plt_offset;
e03a8ed8 L	222	*head = NULL;
	223	return TRUE;
	224	}
	225
7be86737	226	keep:
e03a8ed8 L	227	bed = get_elf_backend_data (info->output_bfd);
	228	if (bed->rela_plts_and_copies_p)
	229	sizeof_reloc = bed->s->sizeof_rela;
	230	else
	231	sizeof_reloc = bed->s->sizeof_rel;
	232
e03a8ed8 L	233	/* When building a static executable, use .iplt, .igot.plt and
	234	.rel[a].iplt sections for STT_GNU_IFUNC symbols. */
	235	if (htab->splt != NULL)
	236	{
	237	plt = htab->splt;
	238	gotplt = htab->sgotplt;
	239	relplt = htab->srelplt;
	240
	241	/* If this is the first .plt entry, make room for the special
	242	first entry. */
	243	if (plt->size == 0)
	244	plt->size += plt_entry_size;
	245	}
	246	else
	247	{
	248	plt = htab->iplt;
	249	gotplt = htab->igotplt;
	250	relplt = htab->irelplt;
	251	}
	252
	253	/* Don't update value of STT_GNU_IFUNC symbol to PLT. We need
	254	the original value for R__IRELATIVE. /
	255	h->plt.offset = plt->size;
	256
	257	/* Make room for this entry in the .plt/.iplt section. */
	258	plt->size += plt_entry_size;
	259
	260	/* We also need to make an entry in the .got.plt/.got.iplt section,
	261	which will be placed in the .got section by the linker script. */
	262	gotplt->size += got_entry_size;
	263
	264	/* We also need to make an entry in the .rel[a].plt/.rel[a].iplt
	265	section. */
	266	relplt->size += sizeof_reloc;
	267	relplt->reloc_count++;
	268
	269	/* We need dynamic relocation for STT_GNU_IFUNC symbol only when
	270	there is a non-GOT reference in a shared object. */
	271	if (!info->shared
	272	\|\| !h->non_got_ref)
	273	*head = NULL;
	274
	275	/* Finally, allocate space. */
7be86737 L	276	p = *head;
	277	if (p != NULL)
	278	{
	279	bfd_size_type count = 0;
	280	do
	281	{
	282	count += p->count;
	283	p = p->next;
	284	}
	285	while (p != NULL);
	286	htab->irelifunc->size += count * sizeof_reloc;
	287	}
e03a8ed8	288
7be86737	289	/* For STT_GNU_IFUNC symbol, .got.plt has the real function address
e03a8ed8 L	290	and .got has the PLT entry adddress. We will load the GOT entry
	291	with the PLT entry in finish_dynamic_symbol if it is used. For
	292	branch, it uses .got.plt. For symbol value,
	293	1. Use .got.plt in a shared object if it is forced local or not
	294	dynamic.
	295	2. Use .got.plt in a non-shared object if pointer equality isn't
	296	needed.
	297	3. Use .got.plt in PIE.
	298	4. Use .got.plt if .got isn't used.
	299	5. Otherwise use .got so that it can be shared among different
	300	objects at run-time.
	301	We only need to relocate .got entry in shared object. */
7b5b197e L	302	if (h->got.refcount <= 0
	303	\|\| (info->shared
	304	&& (h->dynindx == -1
	305	\|\| h->forced_local))
e03a8ed8 L	306	\|\| (!info->shared
	307	&& !h->pointer_equality_needed)
	308	\|\| (info->executable && info->shared)
	309	\|\| htab->sgot == NULL)
	310	{
	311	/* Use .got.plt. */
	312	h->got.offset = (bfd_vma) -1;
	313	}
	314	else
	315	{
	316	h->got.offset = htab->sgot->size;
	317	htab->sgot->size += got_entry_size;
	318	if (info->shared)
	319	htab->srelgot->size += sizeof_reloc;
	320	}
	321
	322	return TRUE;
	323	}