bfd/elflink.c

   1 /* ELF linking support for BFD.
   2    Copyright 1995, 96, 97, 98, 99, 2000 Free Software Foundation, Inc.
   3
   4 This file is part of BFD, the Binary File Descriptor library.
   5
   6 This program is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or
   9 (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  19
  20 #include "bfd.h"
  21 #include "sysdep.h"
  22 #include "bfdlink.h"
  23 #include "libbfd.h"
  24 #define ARCH_SIZE 0
  25 #include "elf-bfd.h"
  26
  27 boolean
  28 _bfd_elf_create_got_section (abfd, info)
  29      bfd *abfd;
  30      struct bfd_link_info *info;
  31 {
  32   flagword flags;
  33   register asection *s;
  34   struct elf_link_hash_entry *h;
  35   struct elf_backend_data *bed = get_elf_backend_data (abfd);
  36   int ptralign;
  37
  38   /* This function may be called more than once.  */
  39   if (bfd_get_section_by_name (abfd, ".got") != NULL)
  40     return true;
  41
  42   switch (bed->s->arch_size)
  43     {
  44     case 32: ptralign = 2; break;
  45     case 64: ptralign = 3; break;
  46     default: abort();
  47     }
  48
  49   flags = (SEC_ALLOC | SEC_LOAD | SEC_HAS_CONTENTS | SEC_IN_MEMORY
  50            | SEC_LINKER_CREATED);
  51
  52   s = bfd_make_section (abfd, ".got");
  53   if (s == NULL
  54       || !bfd_set_section_flags (abfd, s, flags)
  55       || !bfd_set_section_alignment (abfd, s, ptralign))
  56     return false;
  57
  58   if (bed->want_got_plt)
  59     {
  60       s = bfd_make_section (abfd, ".got.plt");
  61       if (s == NULL
  62           || !bfd_set_section_flags (abfd, s, flags)
  63           || !bfd_set_section_alignment (abfd, s, ptralign))
  64         return false;
  65     }
  66
  67   /* Define the symbol _GLOBAL_OFFSET_TABLE_ at the start of the .got
  68      (or .got.plt) section.  We don't do this in the linker script
  69      because we don't want to define the symbol if we are not creating
  70      a global offset table.  */
  71   h = NULL;
  72   if (!(_bfd_generic_link_add_one_symbol
  73         (info, abfd, "_GLOBAL_OFFSET_TABLE_", BSF_GLOBAL, s,
  74          bed->got_symbol_offset, (const char *) NULL, false,
  75          bed->collect, (struct bfd_link_hash_entry **) &h)))
  76     return false;
  77   h->elf_link_hash_flags |= ELF_LINK_HASH_DEF_REGULAR;
  78   h->type = STT_OBJECT;
  79
  80   if (info->shared
  81       && ! _bfd_elf_link_record_dynamic_symbol (info, h))
  82     return false;
  83
  84   elf_hash_table (info)->hgot = h;
  85
  86   /* The first bit of the global offset table is the header.  */
  87   s->_raw_size += bed->got_header_size + bed->got_symbol_offset;
  88
  89   return true;
  90 }
  91 \f
  92
  93 /* Create dynamic sections when linking against a dynamic object.  */
  94
  95 boolean
  96 _bfd_elf_create_dynamic_sections (abfd, info)
  97      bfd *abfd;
  98      struct bfd_link_info *info;
  99 {
 100   flagword flags, pltflags;
 101   register asection *s;
 102   struct elf_backend_data *bed = get_elf_backend_data (abfd);
 103   int ptralign = 0;
 104
 105   switch (bed->s->arch_size)
 106     {
 107     case 32: ptralign = 2; break;
 108     case 64: ptralign = 3; break;
 109     default: abort();
 110     }
 111
 112   /* We need to create .plt, .rel[a].plt, .got, .got.plt, .dynbss, and
 113      .rel[a].bss sections.  */
 114
 115   flags = (SEC_ALLOC | SEC_LOAD | SEC_HAS_CONTENTS | SEC_IN_MEMORY
 116            | SEC_LINKER_CREATED);
 117
 118   pltflags = flags;
 119   pltflags |= SEC_CODE;
 120   if (bed->plt_not_loaded)
 121     pltflags &= ~ (SEC_LOAD | SEC_HAS_CONTENTS);
 122   if (bed->plt_readonly)
 123     pltflags |= SEC_READONLY;
 124
 125   s = bfd_make_section (abfd, ".plt");
 126   if (s == NULL
 127       || ! bfd_set_section_flags (abfd, s, pltflags)
 128       || ! bfd_set_section_alignment (abfd, s, bed->plt_alignment))
 129     return false;
 130
 131   if (bed->want_plt_sym)
 132     {
 133       /* Define the symbol _PROCEDURE_LINKAGE_TABLE_ at the start of the
 134          .plt section.  */
 135       struct elf_link_hash_entry *h = NULL;
 136       if (! (_bfd_generic_link_add_one_symbol
 137              (info, abfd, "_PROCEDURE_LINKAGE_TABLE_", BSF_GLOBAL, s,
 138               (bfd_vma) 0, (const char *) NULL, false,
 139               get_elf_backend_data (abfd)->collect,
 140               (struct bfd_link_hash_entry **) &h)))
 141         return false;
 142       h->elf_link_hash_flags |= ELF_LINK_HASH_DEF_REGULAR;
 143       h->type = STT_OBJECT;
 144
 145       if (info->shared
 146           && ! _bfd_elf_link_record_dynamic_symbol (info, h))
 147         return false;
 148     }
 149
 150   s = bfd_make_section (abfd,
 151                         bed->default_use_rela_p ? ".rela.plt" : ".rel.plt");
 152   if (s == NULL
 153       || ! bfd_set_section_flags (abfd, s, flags | SEC_READONLY)
 154       || ! bfd_set_section_alignment (abfd, s, ptralign))
 155     return false;
 156
 157   if (! _bfd_elf_create_got_section (abfd, info))
 158     return false;
 159
 160   if (bed->want_dynbss)
 161     {
 162       /* The .dynbss section is a place to put symbols which are defined
 163          by dynamic objects, are referenced by regular objects, and are
 164          not functions.  We must allocate space for them in the process
 165          image and use a R_*_COPY reloc to tell the dynamic linker to
 166          initialize them at run time.  The linker script puts the .dynbss
 167          section into the .bss section of the final image.  */
 168       s = bfd_make_section (abfd, ".dynbss");
 169       if (s == NULL
 170           || ! bfd_set_section_flags (abfd, s, SEC_ALLOC))
 171         return false;
 172
 173       /* The .rel[a].bss section holds copy relocs.  This section is not
 174      normally needed.  We need to create it here, though, so that the
 175      linker will map it to an output section.  We can't just create it
 176      only if we need it, because we will not know whether we need it
 177      until we have seen all the input files, and the first time the
 178      main linker code calls BFD after examining all the input files
 179      (size_dynamic_sections) the input sections have already been
 180      mapped to the output sections.  If the section turns out not to
 181      be needed, we can discard it later.  We will never need this
 182      section when generating a shared object, since they do not use
 183      copy relocs.  */
 184       if (! info->shared)
 185         {
 186           s = bfd_make_section (abfd,
 187                                 (bed->default_use_rela_p
 188                                  ? ".rela.bss" : ".rel.bss"));
 189           if (s == NULL
 190               || ! bfd_set_section_flags (abfd, s, flags | SEC_READONLY)
 191               || ! bfd_set_section_alignment (abfd, s, ptralign))
 192             return false;
 193         }
 194     }
 195
 196   return true;
 197 }
 198 \f
 199
 200 /* Record a new dynamic symbol.  We record the dynamic symbols as we
 201    read the input files, since we need to have a list of all of them
 202    before we can determine the final sizes of the output sections.
 203    Note that we may actually call this function even though we are not
 204    going to output any dynamic symbols; in some cases we know that a
 205    symbol should be in the dynamic symbol table, but only if there is
 206    one.  */
 207
 208 boolean
 209 _bfd_elf_link_record_dynamic_symbol (info, h)
 210      struct bfd_link_info *info;
 211      struct elf_link_hash_entry *h;
 212 {
 213   if (h->dynindx == -1)
 214     {
 215       struct bfd_strtab_hash *dynstr;
 216       char *p, *alc;
 217       const char *name;
 218       boolean copy;
 219       bfd_size_type indx;
 220
 221       /* XXX: The ABI draft says the linker must turn hidden and
 222          internal symbols into STB_LOCAL symbols when producing the
 223          DSO. However, if ld.so honors st_other in the dynamic table,
 224          this would not be necessary.  */
 225       switch (ELF_ST_VISIBILITY (h->other))
 226         {
 227         case STV_INTERNAL:
 228         case STV_HIDDEN:
 229           /* This symbol must be defined in the shared object or
 230              executable.  */
 231           if (h->root.type == bfd_link_hash_undefined)
 232             {
 233               bfd * abfd = h->root.u.undef.abfd;
 234               const char * name = h->root.root.string;
 235
 236               (*info->callbacks->undefined_symbol)
 237                 (info, name, abfd, bfd_und_section_ptr, 0, true);
 238             }
 239
 240           h->elf_link_hash_flags |= ELF_LINK_FORCED_LOCAL;
 241           return true;
 242
 243         default:
 244           break;
 245         }
 246
 247       h->dynindx = elf_hash_table (info)->dynsymcount;
 248       ++elf_hash_table (info)->dynsymcount;
 249
 250       dynstr = elf_hash_table (info)->dynstr;
 251       if (dynstr == NULL)
 252         {
 253           /* Create a strtab to hold the dynamic symbol names.  */
 254           elf_hash_table (info)->dynstr = dynstr = _bfd_elf_stringtab_init ();
 255           if (dynstr == NULL)
 256             return false;
 257         }
 258
 259       /* We don't put any version information in the dynamic string
 260          table.  */
 261       name = h->root.root.string;
 262       p = strchr (name, ELF_VER_CHR);
 263       if (p == NULL)
 264         {
 265           alc = NULL;
 266           copy = false;
 267         }
 268       else
 269         {
 270           alc = bfd_malloc (p - name + 1);
 271           if (alc == NULL)
 272             return false;
 273           strncpy (alc, name, p - name);
 274           alc[p - name] = '\0';
 275           name = alc;
 276           copy = true;
 277         }
 278
 279       indx = _bfd_stringtab_add (dynstr, name, true, copy);
 280
 281       if (alc != NULL)
 282         free (alc);
 283
 284       if (indx == (bfd_size_type) -1)
 285         return false;
 286       h->dynstr_index = indx;
 287     }
 288
 289   return true;
 290 }
 291
 292 /* Return the dynindex of a local dynamic symbol.  */
 293
 294 long
 295 _bfd_elf_link_lookup_local_dynindx (info, input_bfd, input_indx)
 296      struct bfd_link_info *info;
 297      bfd *input_bfd;
 298      long input_indx;
 299 {
 300   struct elf_link_local_dynamic_entry *e;
 301
 302   for (e = elf_hash_table (info)->dynlocal; e ; e = e->next)
 303     if (e->input_bfd == input_bfd && e->input_indx == input_indx)
 304       return e->dynindx;
 305   return -1;
 306 }
 307
 308 /* This function is used to renumber the dynamic symbols, if some of
 309    them are removed because they are marked as local.  This is called
 310    via elf_link_hash_traverse.  */
 311
 312 static boolean elf_link_renumber_hash_table_dynsyms
 313   PARAMS ((struct elf_link_hash_entry *, PTR));
 314
 315 static boolean
 316 elf_link_renumber_hash_table_dynsyms (h, data)
 317      struct elf_link_hash_entry *h;
 318      PTR data;
 319 {
 320   size_t *count = (size_t *) data;
 321
 322   if (h->dynindx != -1)
 323     h->dynindx = ++(*count);
 324
 325   return true;
 326 }
 327
 328 /* Assign dynsym indicies.  In a shared library we generate a section
 329    symbol for each output section, which come first.  Next come all of
 330    the back-end allocated local dynamic syms, followed by the rest of
 331    the global symbols.  */
 332
 333 unsigned long
 334 _bfd_elf_link_renumber_dynsyms (output_bfd, info)
 335      bfd *output_bfd;
 336      struct bfd_link_info *info;
 337 {
 338   unsigned long dynsymcount = 0;
 339
 340   if (info->shared)
 341     {
 342       asection *p;
 343       for (p = output_bfd->sections; p ; p = p->next)
 344         elf_section_data (p)->dynindx = ++dynsymcount;
 345     }
 346
 347   if (elf_hash_table (info)->dynlocal)
 348     {
 349       struct elf_link_local_dynamic_entry *p;
 350       for (p = elf_hash_table (info)->dynlocal; p ; p = p->next)
 351         p->dynindx = ++dynsymcount;
 352     }
 353
 354   elf_link_hash_traverse (elf_hash_table (info),
 355                           elf_link_renumber_hash_table_dynsyms,
 356                           &dynsymcount);
 357
 358   /* There is an unused NULL entry at the head of the table which
 359      we must account for in our count.  Unless there weren't any
 360      symbols, which means we'll have no table at all.  */
 361   if (dynsymcount != 0)
 362     ++dynsymcount;
 363
 364   return elf_hash_table (info)->dynsymcount = dynsymcount;
 365 }
 366 \f
 367 /* Create a special linker section, or return a pointer to a linker
 368    section already created */
 369
 370 elf_linker_section_t *
 371 _bfd_elf_create_linker_section (abfd, info, which, defaults)
 372      bfd *abfd;
 373      struct bfd_link_info *info;
 374      enum elf_linker_section_enum which;
 375      elf_linker_section_t *defaults;
 376 {
 377   bfd *dynobj = elf_hash_table (info)->dynobj;
 378   elf_linker_section_t *lsect;
 379
 380   /* Record the first bfd section that needs the special section */
 381   if (!dynobj)
 382     dynobj = elf_hash_table (info)->dynobj = abfd;
 383
 384   /* If this is the first time, create the section */
 385   lsect = elf_linker_section (dynobj, which);
 386   if (!lsect)
 387     {
 388       asection *s;
 389
 390       lsect = (elf_linker_section_t *)
 391         bfd_alloc (dynobj, sizeof (elf_linker_section_t));
 392
 393       *lsect = *defaults;
 394       elf_linker_section (dynobj, which) = lsect;
 395       lsect->which = which;
 396       lsect->hole_written_p = false;
 397
 398       /* See if the sections already exist */
 399       lsect->section = s = bfd_get_section_by_name (dynobj, lsect->name);
 400       if (!s || (s->flags & defaults->flags) != defaults->flags)
 401         {
 402           lsect->section = s = bfd_make_section_anyway (dynobj, lsect->name);
 403
 404           if (s == NULL)
 405             return (elf_linker_section_t *)0;
 406
 407           bfd_set_section_flags (dynobj, s, defaults->flags);
 408           bfd_set_section_alignment (dynobj, s, lsect->alignment);
 409         }
 410       else if (bfd_get_section_alignment (dynobj, s) < lsect->alignment)
 411         bfd_set_section_alignment (dynobj, s, lsect->alignment);
 412
 413       s->_raw_size = align_power (s->_raw_size, lsect->alignment);
 414
 415       /* Is there a hole we have to provide?  If so check whether the segment is
 416          too big already */
 417       if (lsect->hole_size)
 418         {
 419           lsect->hole_offset = s->_raw_size;
 420           s->_raw_size += lsect->hole_size;
 421           if (lsect->hole_offset > lsect->max_hole_offset)
 422             {
 423               (*_bfd_error_handler) (_("%s: Section %s is already to large to put hole of %ld bytes in"),
 424                                      bfd_get_filename (abfd),
 425                                      lsect->name,
 426                                      (long)lsect->hole_size);
 427
 428               bfd_set_error (bfd_error_bad_value);
 429               return (elf_linker_section_t *)0;
 430             }
 431         }
 432
 433 #ifdef DEBUG
 434       fprintf (stderr, "Creating section %s, current size = %ld\n",
 435                lsect->name, (long)s->_raw_size);
 436 #endif
 437
 438       if (lsect->sym_name)
 439         {
 440           struct elf_link_hash_entry *h = NULL;
 441 #ifdef DEBUG
 442           fprintf (stderr, "Adding %s to section %s\n",
 443                    lsect->sym_name,
 444                    lsect->name);
 445 #endif
 446           h = (struct elf_link_hash_entry *)
 447             bfd_link_hash_lookup (info->hash, lsect->sym_name, false, false, false);
 448
 449           if ((h == NULL || h->root.type == bfd_link_hash_undefined)
 450               && !(_bfd_generic_link_add_one_symbol (info,
 451                                                      abfd,
 452                                                      lsect->sym_name,
 453                                                      BSF_GLOBAL,
 454                                                      s,
 455                                                      ((lsect->hole_size)
 456                                                       ? s->_raw_size - lsect->hole_size + lsect->sym_offset
 457                                                       : lsect->sym_offset),
 458                                                      (const char *) NULL,
 459                                                      false,
 460                                                      get_elf_backend_data (abfd)->collect,
 461                                                      (struct bfd_link_hash_entry **) &h)))
 462             return (elf_linker_section_t *)0;
 463
 464           if ((defaults->which != LINKER_SECTION_SDATA)
 465               && (defaults->which != LINKER_SECTION_SDATA2))
 466             h->elf_link_hash_flags |= ELF_LINK_HASH_DEF_DYNAMIC;
 467
 468           h->type = STT_OBJECT;
 469           lsect->sym_hash = h;
 470
 471           if (info->shared
 472               && ! _bfd_elf_link_record_dynamic_symbol (info, h))
 473             return (elf_linker_section_t *)0;
 474         }
 475     }
 476
 477 #if 0
 478   /* This does not make sense.  The sections which may exist in the
 479      object file have nothing to do with the sections we want to
 480      create.  */
 481
 482   /* Find the related sections if they have been created */
 483   if (lsect->bss_name && !lsect->bss_section)
 484     lsect->bss_section = bfd_get_section_by_name (dynobj, lsect->bss_name);
 485
 486   if (lsect->rel_name && !lsect->rel_section)
 487     lsect->rel_section = bfd_get_section_by_name (dynobj, lsect->rel_name);
 488 #endif
 489
 490   return lsect;
 491 }
 492
 493 \f
 494 /* Find a linker generated pointer with a given addend and type.  */
 495
 496 elf_linker_section_pointers_t *
 497 _bfd_elf_find_pointer_linker_section (linker_pointers, addend, which)
 498      elf_linker_section_pointers_t *linker_pointers;
 499      bfd_signed_vma addend;
 500      elf_linker_section_enum_t which;
 501 {
 502   for ( ; linker_pointers != NULL; linker_pointers = linker_pointers->next)
 503     {
 504       if (which == linker_pointers->which && addend == linker_pointers->addend)
 505         return linker_pointers;
 506     }
 507
 508   return (elf_linker_section_pointers_t *)0;
 509 }
 510
 511 \f
 512 /* Make the .rela section corresponding to the generated linker section.  */
 513
 514 boolean
 515 _bfd_elf_make_linker_section_rela (dynobj, lsect, alignment)
 516      bfd *dynobj;
 517      elf_linker_section_t *lsect;
 518      int alignment;
 519 {
 520   if (lsect->rel_section)
 521     return true;
 522
 523   lsect->rel_section = bfd_get_section_by_name (dynobj, lsect->rel_name);
 524   if (lsect->rel_section == NULL)
 525     {
 526       lsect->rel_section = bfd_make_section (dynobj, lsect->rel_name);
 527       if (lsect->rel_section == NULL
 528           || ! bfd_set_section_flags (dynobj,
 529                                       lsect->rel_section,
 530                                       (SEC_ALLOC
 531                                        | SEC_LOAD
 532                                        | SEC_HAS_CONTENTS
 533                                        | SEC_IN_MEMORY
 534                                        | SEC_LINKER_CREATED
 535                                        | SEC_READONLY))
 536           || ! bfd_set_section_alignment (dynobj, lsect->rel_section, alignment))
 537         return false;
 538     }
 539
 540   return true;
 541 }