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[/] [open8_urisc/] [trunk/] [gnu/] [binutils/] [bfd/] [elf-ifunc.c] - Blame information for rev 146

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1 14 khays
/* 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
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   GNU General Public License for more details.
16
 
17
   You should have received a copy of the GNU General Public License
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   along with this program; if not, write to the Free Software
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   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
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   MA 02110-1301, USA.  */
21
 
22
#include "sysdep.h"
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#include "bfd.h"
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#include "bfdlink.h"
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#include "libbfd.h"
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#define ARCH_SIZE 0
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#include "elf-bfd.h"
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#include "safe-ctype.h"
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#include "libiberty.h"
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#include "objalloc.h"
31
 
32
/* Create sections needed by STT_GNU_IFUNC symbol.  */
33
 
34
bfd_boolean
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_bfd_elf_create_ifunc_sections (bfd *abfd, struct bfd_link_info *info)
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{
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  flagword flags, pltflags;
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  asection *s;
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  const struct elf_backend_data *bed = get_elf_backend_data (abfd);
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  struct elf_link_hash_table *htab = elf_hash_table (info);
41
 
42
  if (htab->irelifunc != NULL || htab->iplt != NULL)
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    return TRUE;
44
 
45
  flags = bed->dynamic_sec_flags;
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  pltflags = flags;
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  if (bed->plt_not_loaded)
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    /* We do not clear SEC_ALLOC here because we still want the OS to
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       allocate space for the section; it's just that there's nothing
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       to read in from the object file.  */
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    pltflags &= ~ (SEC_CODE | SEC_LOAD | SEC_HAS_CONTENTS);
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  else
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    pltflags |= SEC_ALLOC | SEC_CODE | SEC_LOAD;
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  if (bed->plt_readonly)
55
    pltflags |= SEC_READONLY;
56
 
57
  if (info->shared)
58
    {
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      /* We need to create .rel[a].ifunc for shared objects.  */
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      const char *rel_sec = (bed->rela_plts_and_copies_p
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                             ? ".rela.ifunc" : ".rel.ifunc");
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63
      s = bfd_make_section_with_flags (abfd, rel_sec,
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                                       flags | SEC_READONLY);
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      if (s == NULL
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          || ! bfd_set_section_alignment (abfd, s,
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                                          bed->s->log_file_align))
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        return FALSE;
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      htab->irelifunc = s;
70
    }
71
  else
72
    {
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      /* We need to create .iplt, .rel[a].iplt, .igot and .igot.plt
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         for static executables.   */
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      s = bfd_make_section_with_flags (abfd, ".iplt", pltflags);
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      if (s == NULL
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          || ! bfd_set_section_alignment (abfd, s, bed->plt_alignment))
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        return FALSE;
79
      htab->iplt = s;
80
 
81
      s = bfd_make_section_with_flags (abfd,
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                                       (bed->rela_plts_and_copies_p
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                                        ? ".rela.iplt" : ".rel.iplt"),
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                                       flags | SEC_READONLY);
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      if (s == NULL
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          || ! bfd_set_section_alignment (abfd, s,
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                                          bed->s->log_file_align))
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        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)
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        s = bfd_make_section_with_flags (abfd, ".igot.plt", flags);
95
      else
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        s = bfd_make_section_with_flags (abfd, ".igot", flags);
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      if (s == NULL
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          || !bfd_set_section_alignment (abfd, s,
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                                         bed->s->log_file_align))
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        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,
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   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,
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                                 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
 
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
 
226
keep:
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
}

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