gold/target-reloc.h

   1 // target-reloc.h -- target specific relocation support  -*- C++ -*-
   2
   3 // Copyright 2006, 2007, 2008 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #ifndef GOLD_TARGET_RELOC_H
  24 #define GOLD_TARGET_RELOC_H
  25
  26 #include "elfcpp.h"
  27 #include "symtab.h"
  28 #include "reloc.h"
  29 #include "reloc-types.h"
  30
  31 namespace gold
  32 {
  33
  34 // This function implements the generic part of reloc scanning.  The
  35 // template parameter Scan must be a class type which provides two
  36 // functions: local() and global().  Those functions implement the
  37 // machine specific part of scanning.  We do it this way to
  38 // avoidmaking a function call for each relocation, and to avoid
  39 // repeating the generic code for each target.
  40
  41 template<int size, bool big_endian, typename Target_type, int sh_type,
  42          typename Scan>
  43 inline void
  44 scan_relocs(
  45     const General_options& options,
  46     Symbol_table* symtab,
  47     Layout* layout,
  48     Target_type* target,
  49     Sized_relobj<size, big_endian>* object,
  50     unsigned int data_shndx,
  51     const unsigned char* prelocs,
  52     size_t reloc_count,
  53     Output_section* output_section,
  54     bool needs_special_offset_handling,
  55     size_t local_count,
  56     const unsigned char* plocal_syms)
  57 {
  58   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
  59   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
  60   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
  61   Scan scan;
  62
  63   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
  64     {
  65       Reltype reloc(prelocs);
  66
  67       if (needs_special_offset_handling
  68           && !output_section->is_input_address_mapped(object, data_shndx,
  69                                                       reloc.get_r_offset()))
  70         continue;
  71
  72       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
  73       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
  74       unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
  75
  76       if (r_sym < local_count)
  77         {
  78           gold_assert(plocal_syms != NULL);
  79           typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
  80                                                       + r_sym * sym_size);
  81           const unsigned int shndx = lsym.get_st_shndx();
  82           if (shndx < elfcpp::SHN_LORESERVE
  83               && shndx != elfcpp::SHN_UNDEF
  84               && !object->is_section_included(lsym.get_st_shndx()))
  85             {
  86               // RELOC is a relocation against a local symbol in a
  87               // section we are discarding.  We can ignore this
  88               // relocation.  It will eventually become a reloc
  89               // against the value zero.
  90               //
  91               // FIXME: We should issue a warning if this is an
  92               // allocated section; is this the best place to do it?
  93               //
  94               // FIXME: The old GNU linker would in some cases look
  95               // for the linkonce section which caused this section to
  96               // be discarded, and, if the other section was the same
  97               // size, change the reloc to refer to the other section.
  98               // That seems risky and weird to me, and I don't know of
  99               // any case where it is actually required.
 100
 101               continue;
 102             }
 103
 104           scan.local(options, symtab, layout, target, object, data_shndx,
 105                      output_section, reloc, r_type, lsym);
 106         }
 107       else
 108         {
 109           Symbol* gsym = object->global_symbol(r_sym);
 110           gold_assert(gsym != NULL);
 111           if (gsym->is_forwarder())
 112             gsym = symtab->resolve_forwards(gsym);
 113
 114           scan.global(options, symtab, layout, target, object, data_shndx,
 115                       output_section, reloc, r_type, gsym);
 116         }
 117     }
 118 }
 119
 120 // This function implements the generic part of relocation processing.
 121 // The template parameter Relocate must be a class type which provides
 122 // a single function, relocate(), which implements the machine
 123 // specific part of a relocation.
 124
 125 // SIZE is the ELF size: 32 or 64.  BIG_ENDIAN is the endianness of
 126 // the data.  SH_TYPE is the section type: SHT_REL or SHT_RELA.
 127 // RELOCATE implements operator() to do a relocation.
 128
 129 // PRELOCS points to the relocation data.  RELOC_COUNT is the number
 130 // of relocs.  OUTPUT_SECTION is the output section.
 131 // NEEDS_SPECIAL_OFFSET_HANDLING is true if input offsets need to be
 132 // mapped to output offsets.
 133
 134 // VIEW is the section data, VIEW_ADDRESS is its memory address, and
 135 // VIEW_SIZE is the size.  These refer to the input section, unless
 136 // NEEDS_SPECIAL_OFFSET_HANDLING is true, in which case they refer to
 137 // the output section.
 138
 139 template<int size, bool big_endian, typename Target_type, int sh_type,
 140          typename Relocate>
 141 inline void
 142 relocate_section(
 143     const Relocate_info<size, big_endian>* relinfo,
 144     Target_type* target,
 145     const unsigned char* prelocs,
 146     size_t reloc_count,
 147     Output_section* output_section,
 148     bool needs_special_offset_handling,
 149     unsigned char* view,
 150     typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 151     section_size_type view_size)
 152 {
 153   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 154   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 155   Relocate relocate;
 156
 157   Sized_relobj<size, big_endian>* object = relinfo->object;
 158   unsigned int local_count = object->local_symbol_count();
 159
 160   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 161     {
 162       Reltype reloc(prelocs);
 163
 164       section_offset_type offset =
 165         convert_to_section_size_type(reloc.get_r_offset());
 166
 167       if (needs_special_offset_handling)
 168         {
 169           offset = output_section->output_offset(relinfo->object,
 170                                                  relinfo->data_shndx,
 171                                                  offset);
 172           if (offset == -1)
 173             continue;
 174         }
 175
 176       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 177       unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 178       unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
 179
 180       const Sized_symbol<size>* sym;
 181
 182       Symbol_value<size> symval;
 183       const Symbol_value<size> *psymval;
 184       if (r_sym < local_count)
 185         {
 186           sym = NULL;
 187           psymval = object->local_symbol(r_sym);
 188         }
 189       else
 190         {
 191           const Symbol* gsym = object->global_symbol(r_sym);
 192           gold_assert(gsym != NULL);
 193           if (gsym->is_forwarder())
 194             gsym = relinfo->symtab->resolve_forwards(gsym);
 195
 196           sym = static_cast<const Sized_symbol<size>*>(gsym);
 197           if (sym->has_symtab_index())
 198             symval.set_output_symtab_index(sym->symtab_index());
 199           else
 200             symval.set_no_output_symtab_entry();
 201           symval.set_output_value(sym->value());
 202           psymval = &symval;
 203         }
 204
 205       if (!relocate.relocate(relinfo, target, i, reloc, r_type, sym, psymval,
 206                              view + offset, view_address + offset, view_size))
 207         continue;
 208
 209       if (offset < 0 || static_cast<section_size_type>(offset) >= view_size)
 210         {
 211           gold_error_at_location(relinfo, i, offset,
 212                                  _("reloc has bad offset %zu"),
 213                                  static_cast<size_t>(offset));
 214           continue;
 215         }
 216
 217       if (sym != NULL
 218           && sym->is_undefined()
 219           && sym->binding() != elfcpp::STB_WEAK
 220           && (!parameters->options().shared()       // -shared
 221               || parameters->options().defs()))     // -z defs
 222         gold_undefined_symbol(sym, relinfo, i, offset);
 223
 224       if (sym != NULL && sym->has_warning())
 225         relinfo->symtab->issue_warning(sym, relinfo, i, offset);
 226     }
 227 }
 228
 229 // This class may be used as a typical class for the
 230 // Scan_relocatable_reloc parameter to scan_relocatable_relocs.  The
 231 // template parameter Classify_reloc must be a class type which
 232 // provides a function get_size_for_reloc which returns the number of
 233 // bytes to which a reloc applies.  This class is intended to capture
 234 // the most typical target behaviour, while still permitting targets
 235 // to define their own independent class for Scan_relocatable_reloc.
 236
 237 template<int sh_type, typename Classify_reloc>
 238 class Default_scan_relocatable_relocs
 239 {
 240  public:
 241   // Return the strategy to use for a local symbol which is not a
 242   // section symbol, given the relocation type.
 243   inline Relocatable_relocs::Reloc_strategy
 244   local_non_section_strategy(unsigned int, Relobj*)
 245   { return Relocatable_relocs::RELOC_COPY; }
 246
 247   // Return the strategy to use for a local symbol which is a section
 248   // symbol, given the relocation type.
 249   inline Relocatable_relocs::Reloc_strategy
 250   local_section_strategy(unsigned int r_type, Relobj* object)
 251   {
 252     if (sh_type == elfcpp::SHT_RELA)
 253       return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA;
 254     else
 255       {
 256         Classify_reloc classify;
 257         switch (classify.get_size_for_reloc(r_type, object))
 258           {
 259           case 0:
 260             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0;
 261           case 1:
 262             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1;
 263           case 2:
 264             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2;
 265           case 4:
 266             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4;
 267           case 8:
 268             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8;
 269           default:
 270             gold_unreachable();
 271           }
 272       }
 273   }
 274
 275   // Return the strategy to use for a global symbol, given the
 276   // relocation type, the object, and the symbol index.
 277   inline Relocatable_relocs::Reloc_strategy
 278   global_strategy(unsigned int, Relobj*, unsigned int)
 279   { return Relocatable_relocs::RELOC_COPY; }
 280 };
 281
 282 // Scan relocs during a relocatable link.  This is a default
 283 // definition which should work for most targets.
 284 // Scan_relocatable_reloc must name a class type which provides three
 285 // functions which return a Relocatable_relocs::Reloc_strategy code:
 286 // global_strategy, local_non_section_strategy, and
 287 // local_section_strategy.  Most targets should be able to use
 288 // Default_scan_relocatable_relocs as this class.
 289
 290 template<int size, bool big_endian, int sh_type,
 291          typename Scan_relocatable_reloc>
 292 void
 293 scan_relocatable_relocs(
 294     const General_options&,
 295     Symbol_table*,
 296     Layout*,
 297     Sized_relobj<size, big_endian>* object,
 298     unsigned int data_shndx,
 299     const unsigned char* prelocs,
 300     size_t reloc_count,
 301     Output_section* output_section,
 302     bool needs_special_offset_handling,
 303     size_t local_symbol_count,
 304     const unsigned char* plocal_syms,
 305     Relocatable_relocs* rr)
 306 {
 307   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 308   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 309   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 310   Scan_relocatable_reloc scan;
 311
 312   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 313     {
 314       Reltype reloc(prelocs);
 315
 316       Relocatable_relocs::Reloc_strategy strategy;
 317
 318       if (needs_special_offset_handling
 319           && !output_section->is_input_address_mapped(object, data_shndx,
 320                                                       reloc.get_r_offset()))
 321         strategy = Relocatable_relocs::RELOC_DISCARD;
 322       else
 323         {
 324           typename elfcpp::Elf_types<size>::Elf_WXword r_info =
 325             reloc.get_r_info();
 326           const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 327           const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
 328
 329           if (r_sym >= local_symbol_count)
 330             strategy = scan.global_strategy(r_type, object, r_sym);
 331           else
 332             {
 333               gold_assert(plocal_syms != NULL);
 334               typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 335                                                           + r_sym * sym_size);
 336               const unsigned int shndx = lsym.get_st_shndx();
 337               if (shndx < elfcpp::SHN_LORESERVE
 338                   && shndx != elfcpp::SHN_UNDEF
 339                   && !object->is_section_included(lsym.get_st_shndx()))
 340                 {
 341                   // RELOC is a relocation against a local symbol
 342                   // defined in a section we are discarding.  Discard
 343                   // the reloc.  FIXME: Should we issue a warning?
 344                   strategy = Relocatable_relocs::RELOC_DISCARD;
 345                 }
 346               else if (lsym.get_st_type() != elfcpp::STT_SECTION)
 347                 strategy = scan.local_non_section_strategy(r_type, object);
 348               else
 349                 {
 350                   strategy = scan.local_section_strategy(r_type, object);
 351                   if (strategy != Relocatable_relocs::RELOC_DISCARD)
 352                     {
 353                       section_offset_type dummy;
 354                       Output_section* os = object->output_section(shndx,
 355                                                                   &dummy);
 356                       os->set_needs_symtab_index();
 357                     }
 358                 }
 359             }
 360         }
 361
 362       rr->set_next_reloc_strategy(strategy);
 363     }
 364 }
 365
 366 // Relocate relocs during a relocatable link.  This is a default
 367 // definition which should work for most targets.
 368
 369 template<int size, bool big_endian, int sh_type>
 370 void
 371 relocate_for_relocatable(
 372     const Relocate_info<size, big_endian>* relinfo,
 373     const unsigned char* prelocs,
 374     size_t reloc_count,
 375     Output_section* output_section,
 376     off_t offset_in_output_section,
 377     const Relocatable_relocs* rr,
 378     unsigned char* view,
 379     typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 380     section_size_type,
 381     unsigned char* reloc_view,
 382     section_size_type reloc_view_size)
 383 {
 384   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 385   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc_write
 386     Reltype_write;
 387   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 388
 389   Sized_relobj<size, big_endian>* const object = relinfo->object;
 390   const unsigned int local_count = object->local_symbol_count();
 391
 392   unsigned char* pwrite = reloc_view;
 393
 394   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 395     {
 396       Relocatable_relocs::Reloc_strategy strategy = rr->strategy(i);
 397       if (strategy == Relocatable_relocs::RELOC_DISCARD)
 398         continue;
 399
 400       Reltype reloc(prelocs);
 401       Reltype_write reloc_write(pwrite);
 402
 403       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 404       const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 405       const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
 406
 407       // Get the new symbol index.
 408
 409       unsigned int new_symndx;
 410       if (r_sym < local_count)
 411         {
 412           switch (strategy)
 413             {
 414             case Relocatable_relocs::RELOC_COPY:
 415               new_symndx = object->symtab_index(r_sym);
 416               gold_assert(new_symndx != -1U);
 417               break;
 418
 419             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
 420             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
 421             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
 422             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
 423             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
 424             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
 425               {
 426                 // We are adjusting a section symbol.  We need to find
 427                 // the symbol table index of the section symbol for
 428                 // the output section corresponding to input section
 429                 // in which this symbol is defined.
 430                 gold_assert(r_sym < local_count);
 431                 unsigned int shndx = object->local_symbol_input_shndx(r_sym);
 432                 section_offset_type dummy;
 433                 Output_section* os = object->output_section(shndx, &dummy);
 434                 gold_assert(os != NULL);
 435                 gold_assert(os->needs_symtab_index());
 436                 new_symndx = os->symtab_index();
 437               }
 438               break;
 439
 440             default:
 441               gold_unreachable();
 442             }
 443         }
 444       else
 445         {
 446           const Symbol* gsym = object->global_symbol(r_sym);
 447           gold_assert(gsym != NULL);
 448           if (gsym->is_forwarder())
 449             gsym = relinfo->symtab->resolve_forwards(gsym);
 450
 451           gold_assert(gsym->has_symtab_index());
 452           new_symndx = gsym->symtab_index();
 453         }
 454
 455       // Get the new offset--the location in the output section where
 456       // this relocation should be applied.
 457
 458       off_t offset = reloc.get_r_offset();
 459       off_t new_offset;
 460       if (offset_in_output_section != -1)
 461         new_offset = offset + offset_in_output_section;
 462       else
 463         {
 464           new_offset = output_section->output_offset(object,
 465                                                      relinfo->data_shndx,
 466                                                      offset);
 467           gold_assert(new_offset != -1);
 468         }
 469
 470       // In an object file, r_offset is an offset within the section.
 471       // In an executable or dynamic object, generated by
 472       // --emit-relocs, r_offset is an absolute address.
 473       if (!parameters->options().relocatable())
 474         new_offset += view_address;
 475
 476       reloc_write.put_r_offset(new_offset);
 477       reloc_write.put_r_info(elfcpp::elf_r_info<size>(new_symndx, r_type));
 478
 479       // Handle the reloc addend based on the strategy.
 480
 481       if (strategy == Relocatable_relocs::RELOC_COPY)
 482         {
 483           if (sh_type == elfcpp::SHT_RELA)
 484             Reloc_types<sh_type, size, big_endian>::
 485               copy_reloc_addend(&reloc_write,
 486                                 &reloc);
 487         }
 488       else
 489         {
 490           // The relocation uses a section symbol in the input file.
 491           // We are adjusting it to use a section symbol in the output
 492           // file.  The input section symbol refers to some address in
 493           // the input section.  We need the relocation in the output
 494           // file to refer to that same address.  This adjustment to
 495           // the addend is the same calculation we use for a simple
 496           // absolute relocation for the input section symbol.
 497
 498           const Symbol_value<size>* psymval = object->local_symbol(r_sym);
 499
 500           unsigned char* padd = view + offset;
 501           switch (strategy)
 502             {
 503             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
 504               {
 505                 typename elfcpp::Elf_types<size>::Elf_Swxword addend;
 506                 addend = Reloc_types<sh_type, size, big_endian>::
 507                            get_reloc_addend(&reloc);
 508                 addend = psymval->value(object, addend);
 509                 Reloc_types<sh_type, size, big_endian>::
 510                   set_reloc_addend(&reloc_write, addend);
 511               }
 512               break;
 513
 514             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
 515               break;
 516
 517             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
 518               Relocate_functions<size, big_endian>::rel8(padd, object,
 519                                                          psymval);
 520               break;
 521
 522             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
 523               Relocate_functions<size, big_endian>::rel16(padd, object,
 524                                                           psymval);
 525               break;
 526
 527             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
 528               Relocate_functions<size, big_endian>::rel32(padd, object,
 529                                                           psymval);
 530               break;
 531
 532             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
 533               Relocate_functions<size, big_endian>::rel64(padd, object,
 534                                                           psymval);
 535               break;
 536
 537             default:
 538               gold_unreachable();
 539             }
 540         }
 541
 542       pwrite += reloc_size;
 543     }
 544
 545   gold_assert(static_cast<section_size_type>(pwrite - reloc_view)
 546               == reloc_view_size);
 547 }
 548
 549 } // End namespace gold.
 550
 551 #endif // !defined(GOLD_TARGET_RELOC_H)