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
34bfd_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}
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
110asection *
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
155bfd_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
188  htab = elf_hash_table (info);
189
190  /* Support garbage collection against STT_GNU_IFUNC symbols.  */
191  if (h->plt.refcount <= 0 && h->got.refcount <= 0)
192    {
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.  */
197      if (info->shared
198	  && !h->non_got_ref
199	  && h->ref_regular)
200	for (p = *head; p != NULL; p = p->next)
201	  if (p->count)
202	    {
203	      h->non_got_ref = 1;
204	      goto keep;
205	    }
206
207      h->got = htab->init_got_offset;
208      h->plt = htab->init_plt_offset;
209      *head = NULL;
210      return TRUE;
211    }
212
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 ();
220      h->got = htab->init_got_offset;
221      h->plt = htab->init_plt_offset;
222      *head = NULL;
223      return TRUE;
224    }
225
226keep:
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
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.  */
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    }
288
289  /* For STT_GNU_IFUNC symbol, .got.plt has the real function address
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.  */
302  if ((info->shared
303       && (h->dynindx == -1
304	   || h->forced_local))
305      || (!info->shared
306	  && !h->pointer_equality_needed)
307      || (info->executable && info->shared)
308      || htab->sgot == NULL)
309    {
310      /* Use .got.plt.  */
311      h->got.offset = (bfd_vma) -1;
312    }
313  else
314    {
315      h->got.offset = htab->sgot->size;
316      htab->sgot->size += got_entry_size;
317      if (info->shared)
318	htab->srelgot->size += sizeof_reloc;
319    }
320
321  return TRUE;
322}
323