gold/target.h

   1 // target.h -- target support for gold   -*- C++ -*-
   2
   3 // Copyright 2006, 2007, 2008, 2009 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 // The abstract class Target is the interface for target specific
  24 // support.  It defines abstract methods which each target must
  25 // implement.  Typically there will be one target per processor, but
  26 // in some cases it may be necessary to have subclasses.
  27
  28 // For speed and consistency we want to use inline functions to handle
  29 // relocation processing.  So besides implementations of the abstract
  30 // methods, each target is expected to define a template
  31 // specialization of the relocation functions.
  32
  33 #ifndef GOLD_TARGET_H
  34 #define GOLD_TARGET_H
  35
  36 #include "elfcpp.h"
  37 #include "options.h"
  38 #include "parameters.h"
  39 #include "debug.h"
  40
  41 namespace gold
  42 {
  43
  44 class Object;
  45 class Relobj;
  46 template<int size, bool big_endian>
  47 class Sized_relobj;
  48 class Relocatable_relocs;
  49 template<int size, bool big_endian>
  50 class Relocate_info;
  51 class Reloc_symbol_changes;
  52 class Symbol;
  53 template<int size>
  54 class Sized_symbol;
  55 class Symbol_table;
  56 class Output_section;
  57
  58 // The abstract class for target specific handling.
  59
  60 class Target
  61 {
  62  public:
  63   virtual ~Target()
  64   { }
  65
  66   // Return the bit size that this target implements.  This should
  67   // return 32 or 64.
  68   int
  69   get_size() const
  70   { return this->pti_->size; }
  71
  72   // Return whether this target is big-endian.
  73   bool
  74   is_big_endian() const
  75   { return this->pti_->is_big_endian; }
  76
  77   // Machine code to store in e_machine field of ELF header.
  78   elfcpp::EM
  79   machine_code() const
  80   { return this->pti_->machine_code; }
  81
  82   // Whether this target has a specific make_symbol function.
  83   bool
  84   has_make_symbol() const
  85   { return this->pti_->has_make_symbol; }
  86
  87   // Whether this target has a specific resolve function.
  88   bool
  89   has_resolve() const
  90   { return this->pti_->has_resolve; }
  91
  92   // Whether this target has a specific code fill function.
  93   bool
  94   has_code_fill() const
  95   { return this->pti_->has_code_fill; }
  96
  97   // Return the default name of the dynamic linker.
  98   const char*
  99   dynamic_linker() const
 100   { return this->pti_->dynamic_linker; }
 101
 102   // Return the default address to use for the text segment.
 103   uint64_t
 104   default_text_segment_address() const
 105   { return this->pti_->default_text_segment_address; }
 106
 107   // Return the ABI specified page size.
 108   uint64_t
 109   abi_pagesize() const
 110   {
 111     if (parameters->options().max_page_size() > 0)
 112       return parameters->options().max_page_size();
 113     else
 114       return this->pti_->abi_pagesize;
 115   }
 116
 117   // Return the common page size used on actual systems.
 118   uint64_t
 119   common_pagesize() const
 120   {
 121     if (parameters->options().common_page_size() > 0)
 122       return std::min(parameters->options().common_page_size(),
 123                       this->abi_pagesize());
 124     else
 125       return std::min(this->pti_->common_pagesize,
 126                       this->abi_pagesize());
 127   }
 128
 129   // If we see some object files with .note.GNU-stack sections, and
 130   // some objects files without them, this returns whether we should
 131   // consider the object files without them to imply that the stack
 132   // should be executable.
 133   bool
 134   is_default_stack_executable() const
 135   { return this->pti_->is_default_stack_executable; }
 136
 137   // Return a character which may appear as a prefix for a wrap
 138   // symbol.  If this character appears, we strip it when checking for
 139   // wrapping and add it back when forming the final symbol name.
 140   // This should be '\0' if not special prefix is required, which is
 141   // the normal case.
 142   char
 143   wrap_char() const
 144   { return this->pti_->wrap_char; }
 145
 146   // Return the special section index which indicates a small common
 147   // symbol.  This will return SHN_UNDEF if there are no small common
 148   // symbols.
 149   elfcpp::Elf_Half
 150   small_common_shndx() const
 151   { return this->pti_->small_common_shndx; }
 152
 153   // Return values to add to the section flags for the section holding
 154   // small common symbols.
 155   elfcpp::Elf_Xword
 156   small_common_section_flags() const
 157   {
 158     gold_assert(this->pti_->small_common_shndx != elfcpp::SHN_UNDEF);
 159     return this->pti_->small_common_section_flags;
 160   }
 161
 162   // Return the special section index which indicates a large common
 163   // symbol.  This will return SHN_UNDEF if there are no large common
 164   // symbols.
 165   elfcpp::Elf_Half
 166   large_common_shndx() const
 167   { return this->pti_->large_common_shndx; }
 168
 169   // Return values to add to the section flags for the section holding
 170   // large common symbols.
 171   elfcpp::Elf_Xword
 172   large_common_section_flags() const
 173   {
 174     gold_assert(this->pti_->large_common_shndx != elfcpp::SHN_UNDEF);
 175     return this->pti_->large_common_section_flags;
 176   }
 177
 178   // This hook is called when an output section is created.
 179   void
 180   new_output_section(Output_section* os) const
 181   { this->do_new_output_section(os); }
 182
 183   // This is called to tell the target to complete any sections it is
 184   // handling.  After this all sections must have their final size.
 185   void
 186   finalize_sections(Layout* layout)
 187   { return this->do_finalize_sections(layout); }
 188
 189   // Return the value to use for a global symbol which needs a special
 190   // value in the dynamic symbol table.  This will only be called if
 191   // the backend first calls symbol->set_needs_dynsym_value().
 192   uint64_t
 193   dynsym_value(const Symbol* sym) const
 194   { return this->do_dynsym_value(sym); }
 195
 196   // Return a string to use to fill out a code section.  This is
 197   // basically one or more NOPS which must fill out the specified
 198   // length in bytes.
 199   std::string
 200   code_fill(section_size_type length) const
 201   { return this->do_code_fill(length); }
 202
 203   // Return whether SYM is known to be defined by the ABI.  This is
 204   // used to avoid inappropriate warnings about undefined symbols.
 205   bool
 206   is_defined_by_abi(const Symbol* sym) const
 207   { return this->do_is_defined_by_abi(sym); }
 208
 209   // Adjust the output file header before it is written out.  VIEW
 210   // points to the header in external form.  LEN is the length.
 211   void
 212   adjust_elf_header(unsigned char* view, int len) const
 213   { return this->do_adjust_elf_header(view, len); }
 214
 215   // Return whether NAME is a local label name.  This is used to implement the
 216   // --discard-locals options.
 217   bool
 218   is_local_label_name(const char* name) const
 219   { return this->do_is_local_label_name(name); }
 220
 221   // A function starts at OFFSET in section SHNDX in OBJECT.  That
 222   // function was compiled with -fsplit-stack, but it refers to a
 223   // function which was compiled without -fsplit-stack.  VIEW is a
 224   // modifiable view of the section; VIEW_SIZE is the size of the
 225   // view.  The target has to adjust the function so that it allocates
 226   // enough stack.
 227   void
 228   calls_non_split(Relobj* object, unsigned int shndx,
 229                   section_offset_type fnoffset, section_size_type fnsize,
 230                   unsigned char* view, section_size_type view_size,
 231                   std::string* from, std::string* to) const
 232   {
 233     this->do_calls_non_split(object, shndx, fnoffset, fnsize, view, view_size,
 234                              from, to);
 235   }
 236
 237   // Make an ELF object.
 238   template<int size, bool big_endian>
 239   Object*
 240   make_elf_object(const std::string& name, Input_file* input_file,
 241                   off_t offset, const elfcpp::Ehdr<size, big_endian>& ehdr)
 242   { return this->do_make_elf_object(name, input_file, offset, ehdr); }
 243
 244   // Make an output section.
 245   Output_section*
 246   make_output_section(const char* name, elfcpp::Elf_Word type,
 247                       elfcpp::Elf_Xword flags)
 248   { return this->do_make_output_section(name, type, flags); }
 249
 250   // Return true if target wants to perform relaxation.
 251   bool
 252   may_relax() const
 253   {
 254     // Run the dummy relaxation pass twice if relaxation debugging is enabled.
 255     if (is_debugging_enabled(DEBUG_RELAXATION))
 256       return true;
 257
 258      return this->do_may_relax();
 259   }
 260
 261   // Perform a relaxation pass.  Return true if layout may be changed.
 262   bool
 263   relax(int pass, const Input_objects* input_objects, Symbol_table* symtab,
 264         Layout* layout)
 265   {
 266     // Run the dummy relaxation pass twice if relaxation debugging is enabled.
 267     if (is_debugging_enabled(DEBUG_RELAXATION))
 268       return pass < 2;
 269
 270     return this->do_relax(pass, input_objects, symtab, layout);
 271   }
 272
 273  protected:
 274   // This struct holds the constant information for a child class.  We
 275   // use a struct to avoid the overhead of virtual function calls for
 276   // simple information.
 277   struct Target_info
 278   {
 279     // Address size (32 or 64).
 280     int size;
 281     // Whether the target is big endian.
 282     bool is_big_endian;
 283     // The code to store in the e_machine field of the ELF header.
 284     elfcpp::EM machine_code;
 285     // Whether this target has a specific make_symbol function.
 286     bool has_make_symbol;
 287     // Whether this target has a specific resolve function.
 288     bool has_resolve;
 289     // Whether this target has a specific code fill function.
 290     bool has_code_fill;
 291     // Whether an object file with no .note.GNU-stack sections implies
 292     // that the stack should be executable.
 293     bool is_default_stack_executable;
 294     // Prefix character to strip when checking for wrapping.
 295     char wrap_char;
 296     // The default dynamic linker name.
 297     const char* dynamic_linker;
 298     // The default text segment address.
 299     uint64_t default_text_segment_address;
 300     // The ABI specified page size.
 301     uint64_t abi_pagesize;
 302     // The common page size used by actual implementations.
 303     uint64_t common_pagesize;
 304     // The special section index for small common symbols; SHN_UNDEF
 305     // if none.
 306     elfcpp::Elf_Half small_common_shndx;
 307     // The special section index for large common symbols; SHN_UNDEF
 308     // if none.
 309     elfcpp::Elf_Half large_common_shndx;
 310     // Section flags for small common section.
 311     elfcpp::Elf_Xword small_common_section_flags;
 312     // Section flags for large common section.
 313     elfcpp::Elf_Xword large_common_section_flags;
 314   };
 315
 316   Target(const Target_info* pti)
 317     : pti_(pti)
 318   { }
 319
 320   // Virtual function which may be implemented by the child class.
 321   virtual void
 322   do_new_output_section(Output_section*) const
 323   { }
 324
 325   // Virtual function which may be implemented by the child class.
 326   virtual void
 327   do_finalize_sections(Layout*)
 328   { }
 329
 330   // Virtual function which may be implemented by the child class.
 331   virtual uint64_t
 332   do_dynsym_value(const Symbol*) const
 333   { gold_unreachable(); }
 334
 335   // Virtual function which must be implemented by the child class if
 336   // needed.
 337   virtual std::string
 338   do_code_fill(section_size_type) const
 339   { gold_unreachable(); }
 340
 341   // Virtual function which may be implemented by the child class.
 342   virtual bool
 343   do_is_defined_by_abi(const Symbol*) const
 344   { return false; }
 345
 346   // Adjust the output file header before it is written out.  VIEW
 347   // points to the header in external form.  LEN is the length, and
 348   // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.
 349   // By default, we do nothing.
 350   virtual void
 351   do_adjust_elf_header(unsigned char*, int) const
 352   { }
 353
 354   // Virtual function which may be overriden by the child class.
 355   virtual bool
 356   do_is_local_label_name(const char*) const;
 357
 358   // Virtual function which may be overridden by the child class.
 359   virtual void
 360   do_calls_non_split(Relobj* object, unsigned int, section_offset_type,
 361                      section_size_type, unsigned char*, section_size_type,
 362                      std::string*, std::string*) const;
 363
 364   // make_elf_object hooks.  There are four versions of these for
 365   // different address sizes and endianities.
 366
 367 #ifdef HAVE_TARGET_32_LITTLE
 368   // Virtual functions which may be overriden by the child class.
 369   virtual Object*
 370   do_make_elf_object(const std::string&, Input_file*, off_t,
 371                      const elfcpp::Ehdr<32, false>&);
 372 #endif
 373
 374 #ifdef HAVE_TARGET_32_BIG
 375   // Virtual functions which may be overriden by the child class.
 376   virtual Object*
 377   do_make_elf_object(const std::string&, Input_file*, off_t,
 378                      const elfcpp::Ehdr<32, true>&);
 379 #endif
 380
 381 #ifdef HAVE_TARGET_64_LITTLE
 382   // Virtual functions which may be overriden by the child class.
 383   virtual Object*
 384   do_make_elf_object(const std::string&, Input_file*, off_t,
 385                      const elfcpp::Ehdr<64, false>& ehdr);
 386 #endif
 387
 388 #ifdef HAVE_TARGET_64_BIG
 389   // Virtual functions which may be overriden by the child class.
 390   virtual Object*
 391   do_make_elf_object(const std::string& name, Input_file* input_file,
 392                      off_t offset, const elfcpp::Ehdr<64, true>& ehdr);
 393 #endif
 394
 395   // Virtual functions which may be overriden by the child class.
 396   virtual Output_section*
 397   do_make_output_section(const char* name, elfcpp::Elf_Word type,
 398                          elfcpp::Elf_Xword flags);
 399
 400   // Virtual function which may be overriden by the child class.
 401   virtual bool
 402   do_may_relax() const
 403   { return parameters->options().relax(); }
 404
 405   // Virtual function which may be overriden by the child class.
 406   virtual bool
 407   do_relax(int, const Input_objects*, Symbol_table*, Layout*)
 408   { return false; }
 409
 410   // A function for targets to call.  Return whether BYTES/LEN matches
 411   // VIEW/VIEW_SIZE at OFFSET.
 412   bool
 413   match_view(const unsigned char* view, section_size_type view_size,
 414              section_offset_type offset, const char* bytes, size_t len) const;
 415
 416   // Set the contents of a VIEW/VIEW_SIZE to nops starting at OFFSET
 417   // for LEN bytes.
 418   void
 419   set_view_to_nop(unsigned char* view, section_size_type view_size,
 420                   section_offset_type offset, size_t len) const;
 421
 422  private:
 423   // The implementations of the four do_make_elf_object virtual functions are
 424   // almost identical except for their sizes and endianity.  We use a template.
 425   // for their implementations.
 426   template<int size, bool big_endian>
 427   inline Object*
 428   do_make_elf_object_implementation(const std::string&, Input_file*, off_t,
 429                                     const elfcpp::Ehdr<size, big_endian>&);
 430
 431   Target(const Target&);
 432   Target& operator=(const Target&);
 433
 434   // The target information.
 435   const Target_info* pti_;
 436 };
 437
 438 // The abstract class for a specific size and endianness of target.
 439 // Each actual target implementation class should derive from an
 440 // instantiation of Sized_target.
 441
 442 template<int size, bool big_endian>
 443 class Sized_target : public Target
 444 {
 445  public:
 446   // Make a new symbol table entry for the target.  This should be
 447   // overridden by a target which needs additional information in the
 448   // symbol table.  This will only be called if has_make_symbol()
 449   // returns true.
 450   virtual Sized_symbol<size>*
 451   make_symbol() const
 452   { gold_unreachable(); }
 453
 454   // Resolve a symbol for the target.  This should be overridden by a
 455   // target which needs to take special action.  TO is the
 456   // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.
 457   // VERSION is the version of SYM.  This will only be called if
 458   // has_resolve() returns true.
 459   virtual void
 460   resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
 461           const char*)
 462   { gold_unreachable(); }
 463
 464   // Process the relocs for a section, and record information of the
 465   // mapping from source to destination sections. This mapping is later
 466   // used to determine unreferenced garbage sections. This procedure is
 467   // only called during garbage collection.
 468   virtual void
 469   gc_process_relocs(Symbol_table* symtab,
 470                     Layout* layout,
 471                     Sized_relobj<size, big_endian>* object,
 472                     unsigned int data_shndx,
 473                     unsigned int sh_type,
 474                     const unsigned char* prelocs,
 475                     size_t reloc_count,
 476                     Output_section* output_section,
 477                     bool needs_special_offset_handling,
 478                     size_t local_symbol_count,
 479                     const unsigned char* plocal_symbols) = 0;
 480
 481   // Scan the relocs for a section, and record any information
 482   // required for the symbol.  SYMTAB is the symbol table.  OBJECT is
 483   // the object in which the section appears.  DATA_SHNDX is the
 484   // section index that these relocs apply to.  SH_TYPE is the type of
 485   // the relocation section, SHT_REL or SHT_RELA.  PRELOCS points to
 486   // the relocation data.  RELOC_COUNT is the number of relocs.
 487   // LOCAL_SYMBOL_COUNT is the number of local symbols.
 488   // OUTPUT_SECTION is the output section.
 489   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
 490   // sections are not mapped as usual.  PLOCAL_SYMBOLS points to the
 491   // local symbol data from OBJECT.  GLOBAL_SYMBOLS is the array of
 492   // pointers to the global symbol table from OBJECT.
 493   virtual void
 494   scan_relocs(Symbol_table* symtab,
 495               Layout* layout,
 496               Sized_relobj<size, big_endian>* object,
 497               unsigned int data_shndx,
 498               unsigned int sh_type,
 499               const unsigned char* prelocs,
 500               size_t reloc_count,
 501               Output_section* output_section,
 502               bool needs_special_offset_handling,
 503               size_t local_symbol_count,
 504               const unsigned char* plocal_symbols) = 0;
 505
 506   // Relocate section data.  SH_TYPE is the type of the relocation
 507   // section, SHT_REL or SHT_RELA.  PRELOCS points to the relocation
 508   // information.  RELOC_COUNT is the number of relocs.
 509   // OUTPUT_SECTION is the output section.
 510   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
 511   // to correspond to the output section.  VIEW is a view into the
 512   // output file holding the section contents, VIEW_ADDRESS is the
 513   // virtual address of the view, and VIEW_SIZE is the size of the
 514   // view.  If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
 515   // parameters refer to the complete output section data, not just
 516   // the input section data.
 517   virtual void
 518   relocate_section(const Relocate_info<size, big_endian>*,
 519                    unsigned int sh_type,
 520                    const unsigned char* prelocs,
 521                    size_t reloc_count,
 522                    Output_section* output_section,
 523                    bool needs_special_offset_handling,
 524                    unsigned char* view,
 525                    typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 526                    section_size_type view_size,
 527                    const Reloc_symbol_changes*) = 0;
 528
 529   // Scan the relocs during a relocatable link.  The parameters are
 530   // like scan_relocs, with an additional Relocatable_relocs
 531   // parameter, used to record the disposition of the relocs.
 532   virtual void
 533   scan_relocatable_relocs(Symbol_table* symtab,
 534                           Layout* layout,
 535                           Sized_relobj<size, big_endian>* object,
 536                           unsigned int data_shndx,
 537                           unsigned int sh_type,
 538                           const unsigned char* prelocs,
 539                           size_t reloc_count,
 540                           Output_section* output_section,
 541                           bool needs_special_offset_handling,
 542                           size_t local_symbol_count,
 543                           const unsigned char* plocal_symbols,
 544                           Relocatable_relocs*) = 0;
 545
 546   // Relocate a section during a relocatable link.  The parameters are
 547   // like relocate_section, with additional parameters for the view of
 548   // the output reloc section.
 549   virtual void
 550   relocate_for_relocatable(const Relocate_info<size, big_endian>*,
 551                            unsigned int sh_type,
 552                            const unsigned char* prelocs,
 553                            size_t reloc_count,
 554                            Output_section* output_section,
 555                            off_t offset_in_output_section,
 556                            const Relocatable_relocs*,
 557                            unsigned char* view,
 558                            typename elfcpp::Elf_types<size>::Elf_Addr
 559                              view_address,
 560                            section_size_type view_size,
 561                            unsigned char* reloc_view,
 562                            section_size_type reloc_view_size) = 0;
 563
 564  protected:
 565   Sized_target(const Target::Target_info* pti)
 566     : Target(pti)
 567   {
 568     gold_assert(pti->size == size);
 569     gold_assert(pti->is_big_endian ? big_endian : !big_endian);
 570   }
 571 };
 572
 573 } // End namespace gold.
 574
 575 #endif // !defined(GOLD_TARGET_H)