gold/target-reloc.h

   1 // target-reloc.h -- target specific relocation support  -*- C++ -*-
   2
   3 // Copyright 2006, 2007 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->output_is_shared())
 221         gold_undefined_symbol(sym, relinfo, i, offset);
 222
 223       if (sym != NULL && sym->has_warning())
 224         relinfo->symtab->issue_warning(sym, relinfo, i, offset);
 225     }
 226 }
 227
 228 // This class may be used as a typical class for the
 229 // Scan_relocatable_reloc parameter to scan_relocatable_relocs.  The
 230 // template parameter Classify_reloc must be a class type which
 231 // provides a function get_size_for_reloc which returns the number of
 232 // bytes to which a reloc applies.  This class is intended to capture
 233 // the most typical target behaviour, while still permitting targets
 234 // to define their own independent class for Scan_relocatable_reloc.
 235
 236 template<int sh_type, typename Classify_reloc>
 237 class Default_scan_relocatable_relocs
 238 {
 239  public:
 240   // Return the strategy to use for a local symbol which is not a
 241   // section symbol, given the relocation type.
 242   inline Relocatable_relocs::Reloc_strategy
 243   local_non_section_strategy(unsigned int, Relobj*)
 244   { return Relocatable_relocs::RELOC_COPY; }
 245
 246   // Return the strategy to use for a local symbol which is a section
 247   // symbol, given the relocation type.
 248   inline Relocatable_relocs::Reloc_strategy
 249   local_section_strategy(unsigned int r_type, Relobj* object)
 250   {
 251     if (sh_type == elfcpp::SHT_RELA)
 252       return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA;
 253     else
 254       {
 255         Classify_reloc classify;
 256         switch (classify.get_size_for_reloc(r_type, object))
 257           {
 258           case 0:
 259             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0;
 260           case 1:
 261             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1;
 262           case 2:
 263             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2;
 264           case 4:
 265             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4;
 266           case 8:
 267             return Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8;
 268           default:
 269             gold_unreachable();
 270           }
 271       }
 272   }
 273
 274   // Return the strategy to use for a global symbol, given the
 275   // relocation type, the object, and the symbol index.
 276   inline Relocatable_relocs::Reloc_strategy
 277   global_strategy(unsigned int, Relobj*, unsigned int)
 278   { return Relocatable_relocs::RELOC_COPY; }
 279 };
 280
 281 // Scan relocs during a relocatable link.  This is a default
 282 // definition which should work for most targets.
 283 // Scan_relocatable_reloc must name a class type which provides three
 284 // functions which return a Relocatable_relocs::Reloc_strategy code:
 285 // global_strategy, local_non_section_strategy, and
 286 // local_section_strategy.  Most targets should be able to use
 287 // Default_scan_relocatable_relocs as this class.
 288
 289 template<int size, bool big_endian, int sh_type,
 290          typename Scan_relocatable_reloc>
 291 void
 292 scan_relocatable_relocs(
 293     const General_options&,
 294     Symbol_table*,
 295     Layout*,
 296     Sized_relobj<size, big_endian>* object,
 297     unsigned int data_shndx,
 298     const unsigned char* prelocs,
 299     size_t reloc_count,
 300     Output_section* output_section,
 301     bool needs_special_offset_handling,
 302     size_t local_symbol_count,
 303     const unsigned char* plocal_syms,
 304     Relocatable_relocs* rr)
 305 {
 306   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 307   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 308   const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
 309   Scan_relocatable_reloc scan;
 310
 311   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 312     {
 313       Reltype reloc(prelocs);
 314
 315       Relocatable_relocs::Reloc_strategy strategy;
 316
 317       if (needs_special_offset_handling
 318           && !output_section->is_input_address_mapped(object, data_shndx,
 319                                                       reloc.get_r_offset()))
 320         strategy = Relocatable_relocs::RELOC_DISCARD;
 321       else
 322         {
 323           typename elfcpp::Elf_types<size>::Elf_WXword r_info =
 324             reloc.get_r_info();
 325           const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 326           const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
 327
 328           if (r_sym >= local_symbol_count)
 329             strategy = scan.global_strategy(r_type, object, r_sym);
 330           else
 331             {
 332               gold_assert(plocal_syms != NULL);
 333               typename elfcpp::Sym<size, big_endian> lsym(plocal_syms
 334                                                           + r_sym * sym_size);
 335               const unsigned int shndx = lsym.get_st_shndx();
 336               if (shndx < elfcpp::SHN_LORESERVE
 337                   && shndx != elfcpp::SHN_UNDEF
 338                   && !object->is_section_included(lsym.get_st_shndx()))
 339                 {
 340                   // RELOC is a relocation against a local symbol
 341                   // defined in a section we are discarding.  Discard
 342                   // the reloc.  FIXME: Should we issue a warning?
 343                   strategy = Relocatable_relocs::RELOC_DISCARD;
 344                 }
 345               else if (lsym.get_st_type() != elfcpp::STT_SECTION)
 346                 strategy = scan.local_non_section_strategy(r_type, object);
 347               else
 348                 {
 349                   strategy = scan.local_section_strategy(r_type, object);
 350                   if (strategy != Relocatable_relocs::RELOC_DISCARD)
 351                     {
 352                       section_offset_type dummy;
 353                       Output_section* os = object->output_section(shndx,
 354                                                                   &dummy);
 355                       os->set_needs_symtab_index();
 356                     }
 357                 }
 358             }
 359         }
 360
 361       rr->set_next_reloc_strategy(strategy);
 362     }
 363 }
 364
 365 // Relocate relocs during a relocatable link.  This is a default
 366 // definition which should work for most targets.
 367
 368 template<int size, bool big_endian, int sh_type>
 369 void
 370 relocate_for_relocatable(
 371     const Relocate_info<size, big_endian>* relinfo,
 372     const unsigned char* prelocs,
 373     size_t reloc_count,
 374     Output_section* output_section,
 375     off_t offset_in_output_section,
 376     const Relocatable_relocs* rr,
 377     unsigned char* view,
 378     typename elfcpp::Elf_types<size>::Elf_Addr,
 379     section_size_type,
 380     unsigned char* reloc_view,
 381     section_size_type reloc_view_size)
 382 {
 383   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc Reltype;
 384   typedef typename Reloc_types<sh_type, size, big_endian>::Reloc_write
 385     Reltype_write;
 386   const int reloc_size = Reloc_types<sh_type, size, big_endian>::reloc_size;
 387
 388   Sized_relobj<size, big_endian>* const object = relinfo->object;
 389   const unsigned int local_count = object->local_symbol_count();
 390
 391   unsigned char* pwrite = reloc_view;
 392
 393   for (size_t i = 0; i < reloc_count; ++i, prelocs += reloc_size)
 394     {
 395       Relocatable_relocs::Reloc_strategy strategy = rr->strategy(i);
 396       if (strategy == Relocatable_relocs::RELOC_DISCARD)
 397         continue;
 398
 399       Reltype reloc(prelocs);
 400       Reltype_write reloc_write(pwrite);
 401
 402       typename elfcpp::Elf_types<size>::Elf_WXword r_info = reloc.get_r_info();
 403       const unsigned int r_sym = elfcpp::elf_r_sym<size>(r_info);
 404       const unsigned int r_type = elfcpp::elf_r_type<size>(r_info);
 405
 406       // Get the new symbol index.
 407
 408       unsigned int new_symndx;
 409       if (r_sym < local_count)
 410         {
 411           switch (strategy)
 412             {
 413             case Relocatable_relocs::RELOC_COPY:
 414               new_symndx = object->symtab_index(r_sym);
 415               gold_assert(new_symndx != -1U);
 416               break;
 417
 418             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
 419             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
 420             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
 421             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
 422             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
 423             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
 424               {
 425                 // We are adjusting a section symbol.  We need to find
 426                 // the symbol table index of the section symbol for
 427                 // the output section corresponding to input section
 428                 // in which this symbol is defined.
 429                 gold_assert(r_sym < local_count);
 430                 unsigned int shndx = object->local_symbol_input_shndx(r_sym);
 431                 section_offset_type dummy;
 432                 Output_section* os = object->output_section(shndx, &dummy);
 433                 gold_assert(os != NULL);
 434                 gold_assert(os->needs_symtab_index());
 435                 new_symndx = os->symtab_index();
 436               }
 437               break;
 438
 439             default:
 440               gold_unreachable();
 441             }
 442         }
 443       else
 444         {
 445           const Symbol* gsym = object->global_symbol(r_sym);
 446           gold_assert(gsym != NULL);
 447           if (gsym->is_forwarder())
 448             gsym = relinfo->symtab->resolve_forwards(gsym);
 449
 450           gold_assert(gsym->has_symtab_index());
 451           new_symndx = gsym->symtab_index();
 452         }
 453
 454       // Get the new offset--the location in the output section where
 455       // this relocation should be applied.
 456
 457       off_t offset = reloc.get_r_offset();
 458       off_t new_offset;
 459       if (offset_in_output_section != -1)
 460         new_offset = offset + offset_in_output_section;
 461       else
 462         {
 463           new_offset = output_section->output_offset(object,
 464                                                      relinfo->data_shndx,
 465                                                      offset);
 466           gold_assert(new_offset != -1);
 467         }
 468
 469       reloc_write.put_r_offset(new_offset);
 470       reloc_write.put_r_info(elfcpp::elf_r_info<size>(new_symndx, r_type));
 471
 472       // Handle the reloc addend based on the strategy.
 473
 474       if (strategy == Relocatable_relocs::RELOC_COPY)
 475         {
 476           if (sh_type == elfcpp::SHT_RELA)
 477             Reloc_types<sh_type, size, big_endian>::
 478               copy_reloc_addend(&reloc_write,
 479                                 &reloc);
 480         }
 481       else
 482         {
 483           // The relocation uses a section symbol in the input file.
 484           // We are adjusting it to use a section symbol in the output
 485           // file.  The input section symbol refers to some address in
 486           // the input section.  We need the relocation in the output
 487           // file to refer to that same address.  This adjustment to
 488           // the addend is the same calculation we use for a simple
 489           // absolute relocation for the input section symbol.
 490
 491           const Symbol_value<size>* psymval = object->local_symbol(r_sym);
 492
 493           unsigned char* padd = view + offset;
 494           switch (strategy)
 495             {
 496             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_RELA:
 497               {
 498                 typename elfcpp::Elf_types<size>::Elf_Swxword addend;
 499                 addend = Reloc_types<sh_type, size, big_endian>::
 500                            get_reloc_addend(&reloc);
 501                 addend = psymval->value(object, addend);
 502                 Reloc_types<sh_type, size, big_endian>::
 503                   set_reloc_addend(&reloc_write, addend);
 504               }
 505               break;
 506
 507             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_0:
 508               break;
 509
 510             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_1:
 511               Relocate_functions<size, big_endian>::rel8(padd, object,
 512                                                          psymval);
 513               break;
 514
 515             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_2:
 516               Relocate_functions<size, big_endian>::rel16(padd, object,
 517                                                           psymval);
 518               break;
 519
 520             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_4:
 521               Relocate_functions<size, big_endian>::rel32(padd, object,
 522                                                           psymval);
 523               break;
 524
 525             case Relocatable_relocs::RELOC_ADJUST_FOR_SECTION_8:
 526               Relocate_functions<size, big_endian>::rel64(padd, object,
 527                                                           psymval);
 528               break;
 529
 530             default:
 531               gold_unreachable();
 532             }
 533         }
 534
 535       pwrite += reloc_size;
 536     }
 537
 538   gold_assert(static_cast<section_size_type>(pwrite - reloc_view)
 539               == reloc_view_size);
 540 }
 541
 542 } // End namespace gold.
 543
 544 #endif // !defined(GOLD_TARGET_RELOC_H)