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 General_options;
  45 class Object;
  46 class Relobj;
  47 template<int size, bool big_endian>
  48 class Sized_relobj;
  49 class Relocatable_relocs;
  50 template<int size, bool big_endian>
  51 class Relocate_info;
  52 class Reloc_symbol_changes;
  53 class Symbol;
  54 template<int size>
  55 class Sized_symbol;
  56 class Symbol_table;
  57 class Output_section;
  58
  59 // The abstract class for target specific handling.
  60
  61 class Target
  62 {
  63  public:
  64   virtual ~Target()
  65   { }
  66
  67   // Return the bit size that this target implements.  This should
  68   // return 32 or 64.
  69   int
  70   get_size() const
  71   { return this->pti_->size; }
  72
  73   // Return whether this target is big-endian.
  74   bool
  75   is_big_endian() const
  76   { return this->pti_->is_big_endian; }
  77
  78   // Machine code to store in e_machine field of ELF header.
  79   elfcpp::EM
  80   machine_code() const
  81   { return this->pti_->machine_code; }
  82
  83   // Whether this target has a specific make_symbol function.
  84   bool
  85   has_make_symbol() const
  86   { return this->pti_->has_make_symbol; }
  87
  88   // Whether this target has a specific resolve function.
  89   bool
  90   has_resolve() const
  91   { return this->pti_->has_resolve; }
  92
  93   // Whether this target has a specific code fill function.
  94   bool
  95   has_code_fill() const
  96   { return this->pti_->has_code_fill; }
  97
  98   // Return the default name of the dynamic linker.
  99   const char*
 100   dynamic_linker() const
 101   { return this->pti_->dynamic_linker; }
 102
 103   // Return the default address to use for the text segment.
 104   uint64_t
 105   default_text_segment_address() const
 106   { return this->pti_->default_text_segment_address; }
 107
 108   // Return the ABI specified page size.
 109   uint64_t
 110   abi_pagesize() const
 111   {
 112     if (parameters->options().max_page_size() > 0)
 113       return parameters->options().max_page_size();
 114     else
 115       return this->pti_->abi_pagesize;
 116   }
 117
 118   // Return the common page size used on actual systems.
 119   uint64_t
 120   common_pagesize() const
 121   {
 122     if (parameters->options().common_page_size() > 0)
 123       return std::min(parameters->options().common_page_size(),
 124                       this->abi_pagesize());
 125     else
 126       return std::min(this->pti_->common_pagesize,
 127                       this->abi_pagesize());
 128   }
 129
 130   // If we see some object files with .note.GNU-stack sections, and
 131   // some objects files without them, this returns whether we should
 132   // consider the object files without them to imply that the stack
 133   // should be executable.
 134   bool
 135   is_default_stack_executable() const
 136   { return this->pti_->is_default_stack_executable; }
 137
 138   // Return a character which may appear as a prefix for a wrap
 139   // symbol.  If this character appears, we strip it when checking for
 140   // wrapping and add it back when forming the final symbol name.
 141   // This should be '\0' if not special prefix is required, which is
 142   // the normal case.
 143   char
 144   wrap_char() const
 145   { return this->pti_->wrap_char; }
 146
 147   // Return the special section index which indicates a small common
 148   // symbol.  This will return SHN_UNDEF if there are no small common
 149   // symbols.
 150   elfcpp::Elf_Half
 151   small_common_shndx() const
 152   { return this->pti_->small_common_shndx; }
 153
 154   // Return values to add to the section flags for the section holding
 155   // small common symbols.
 156   elfcpp::Elf_Xword
 157   small_common_section_flags() const
 158   {
 159     gold_assert(this->pti_->small_common_shndx != elfcpp::SHN_UNDEF);
 160     return this->pti_->small_common_section_flags;
 161   }
 162
 163   // Return the special section index which indicates a large common
 164   // symbol.  This will return SHN_UNDEF if there are no large common
 165   // symbols.
 166   elfcpp::Elf_Half
 167   large_common_shndx() const
 168   { return this->pti_->large_common_shndx; }
 169
 170   // Return values to add to the section flags for the section holding
 171   // large common symbols.
 172   elfcpp::Elf_Xword
 173   large_common_section_flags() const
 174   {
 175     gold_assert(this->pti_->large_common_shndx != elfcpp::SHN_UNDEF);
 176     return this->pti_->large_common_section_flags;
 177   }
 178
 179   // This hook is called when an output section is created.
 180   void
 181   new_output_section(Output_section* os) const
 182   { this->do_new_output_section(os); }
 183
 184   // This is called to tell the target to complete any sections it is
 185   // handling.  After this all sections must have their final size.
 186   void
 187   finalize_sections(Layout* layout)
 188   { return this->do_finalize_sections(layout); }
 189
 190   // Return the value to use for a global symbol which needs a special
 191   // value in the dynamic symbol table.  This will only be called if
 192   // the backend first calls symbol->set_needs_dynsym_value().
 193   uint64_t
 194   dynsym_value(const Symbol* sym) const
 195   { return this->do_dynsym_value(sym); }
 196
 197   // Return a string to use to fill out a code section.  This is
 198   // basically one or more NOPS which must fill out the specified
 199   // length in bytes.
 200   std::string
 201   code_fill(section_size_type length) const
 202   { return this->do_code_fill(length); }
 203
 204   // Return whether SYM is known to be defined by the ABI.  This is
 205   // used to avoid inappropriate warnings about undefined symbols.
 206   bool
 207   is_defined_by_abi(const Symbol* sym) const
 208   { return this->do_is_defined_by_abi(sym); }
 209
 210   // Adjust the output file header before it is written out.  VIEW
 211   // points to the header in external form.  LEN is the length.
 212   void
 213   adjust_elf_header(unsigned char* view, int len) const
 214   { return this->do_adjust_elf_header(view, len); }
 215
 216   // Return whether NAME is a local label name.  This is used to implement the
 217   // --discard-locals options.
 218   bool
 219   is_local_label_name(const char* name) const
 220   { return this->do_is_local_label_name(name); }
 221
 222   // A function starts at OFFSET in section SHNDX in OBJECT.  That
 223   // function was compiled with -fsplit-stack, but it refers to a
 224   // function which was compiled without -fsplit-stack.  VIEW is a
 225   // modifiable view of the section; VIEW_SIZE is the size of the
 226   // view.  The target has to adjust the function so that it allocates
 227   // enough stack.
 228   void
 229   calls_non_split(Relobj* object, unsigned int shndx,
 230                   section_offset_type fnoffset, section_size_type fnsize,
 231                   unsigned char* view, section_size_type view_size,
 232                   std::string* from, std::string* to) const
 233   {
 234     this->do_calls_non_split(object, shndx, fnoffset, fnsize, view, view_size,
 235                              from, to);
 236   }
 237
 238   // Make an ELF object.
 239   template<int size, bool big_endian>
 240   Object*
 241   make_elf_object(const std::string& name, Input_file* input_file,
 242                   off_t offset, const elfcpp::Ehdr<size, big_endian>& ehdr)
 243   { return this->do_make_elf_object(name, input_file, offset, ehdr); }
 244
 245   // Make an output section.
 246   Output_section*
 247   make_output_section(const char* name, elfcpp::Elf_Word type,
 248                       elfcpp::Elf_Xword flags)
 249   { return this->do_make_output_section(name, type, flags); }
 250
 251   // Return true if target wants to perform relaxation.
 252   bool
 253   may_relax() const
 254   {
 255     // Run the dummy relaxation pass twice if relaxation debugging is enabled.
 256     if (is_debugging_enabled(DEBUG_RELAXATION))
 257       return true;
 258
 259      return this->do_may_relax();
 260   }
 261
 262   // Perform a relaxation pass.  Return true if layout may be changed.
 263   bool
 264   relax(int pass, const Input_objects* input_objects, Symbol_table* symtab,
 265         Layout* layout)
 266   {
 267     // Run the dummy relaxation pass twice if relaxation debugging is enabled.
 268     if (is_debugging_enabled(DEBUG_RELAXATION))
 269       return pass < 2;
 270
 271     return this->do_relax(pass, input_objects, symtab, layout);
 272   }
 273
 274  protected:
 275   // This struct holds the constant information for a child class.  We
 276   // use a struct to avoid the overhead of virtual function calls for
 277   // simple information.
 278   struct Target_info
 279   {
 280     // Address size (32 or 64).
 281     int size;
 282     // Whether the target is big endian.
 283     bool is_big_endian;
 284     // The code to store in the e_machine field of the ELF header.
 285     elfcpp::EM machine_code;
 286     // Whether this target has a specific make_symbol function.
 287     bool has_make_symbol;
 288     // Whether this target has a specific resolve function.
 289     bool has_resolve;
 290     // Whether this target has a specific code fill function.
 291     bool has_code_fill;
 292     // Whether an object file with no .note.GNU-stack sections implies
 293     // that the stack should be executable.
 294     bool is_default_stack_executable;
 295     // Prefix character to strip when checking for wrapping.
 296     char wrap_char;
 297     // The default dynamic linker name.
 298     const char* dynamic_linker;
 299     // The default text segment address.
 300     uint64_t default_text_segment_address;
 301     // The ABI specified page size.
 302     uint64_t abi_pagesize;
 303     // The common page size used by actual implementations.
 304     uint64_t common_pagesize;
 305     // The special section index for small common symbols; SHN_UNDEF
 306     // if none.
 307     elfcpp::Elf_Half small_common_shndx;
 308     // The special section index for large common symbols; SHN_UNDEF
 309     // if none.
 310     elfcpp::Elf_Half large_common_shndx;
 311     // Section flags for small common section.
 312     elfcpp::Elf_Xword small_common_section_flags;
 313     // Section flags for large common section.
 314     elfcpp::Elf_Xword large_common_section_flags;
 315   };
 316
 317   Target(const Target_info* pti)
 318     : pti_(pti)
 319   { }
 320
 321   // Virtual function which may be implemented by the child class.
 322   virtual void
 323   do_new_output_section(Output_section*) const
 324   { }
 325
 326   // Virtual function which may be implemented by the child class.
 327   virtual void
 328   do_finalize_sections(Layout*)
 329   { }
 330
 331   // Virtual function which may be implemented by the child class.
 332   virtual uint64_t
 333   do_dynsym_value(const Symbol*) const
 334   { gold_unreachable(); }
 335
 336   // Virtual function which must be implemented by the child class if
 337   // needed.
 338   virtual std::string
 339   do_code_fill(section_size_type) const
 340   { gold_unreachable(); }
 341
 342   // Virtual function which may be implemented by the child class.
 343   virtual bool
 344   do_is_defined_by_abi(const Symbol*) const
 345   { return false; }
 346
 347   // Adjust the output file header before it is written out.  VIEW
 348   // points to the header in external form.  LEN is the length, and
 349   // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.
 350   // By default, we do nothing.
 351   virtual void
 352   do_adjust_elf_header(unsigned char*, int) const
 353   { }
 354
 355   // Virtual function which may be overriden by the child class.
 356   virtual bool
 357   do_is_local_label_name(const char*) const;
 358
 359   // Virtual function which may be overridden by the child class.
 360   virtual void
 361   do_calls_non_split(Relobj* object, unsigned int, section_offset_type,
 362                      section_size_type, unsigned char*, section_size_type,
 363                      std::string*, std::string*) const;
 364
 365   // make_elf_object hooks.  There are four versions of these for
 366   // different address sizes and endianities.
 367
 368 #ifdef HAVE_TARGET_32_LITTLE
 369   // Virtual functions which may be overriden by the child class.
 370   virtual Object*
 371   do_make_elf_object(const std::string&, Input_file*, off_t,
 372                      const elfcpp::Ehdr<32, false>&);
 373 #endif
 374
 375 #ifdef HAVE_TARGET_32_BIG
 376   // Virtual functions which may be overriden by the child class.
 377   virtual Object*
 378   do_make_elf_object(const std::string&, Input_file*, off_t,
 379                      const elfcpp::Ehdr<32, true>&);
 380 #endif
 381
 382 #ifdef HAVE_TARGET_64_LITTLE
 383   // Virtual functions which may be overriden by the child class.
 384   virtual Object*
 385   do_make_elf_object(const std::string&, Input_file*, off_t,
 386                      const elfcpp::Ehdr<64, false>& ehdr);
 387 #endif
 388
 389 #ifdef HAVE_TARGET_64_BIG
 390   // Virtual functions which may be overriden by the child class.
 391   virtual Object*
 392   do_make_elf_object(const std::string& name, Input_file* input_file,
 393                      off_t offset, const elfcpp::Ehdr<64, true>& ehdr);
 394 #endif
 395
 396   // Virtual functions which may be overriden by the child class.
 397   virtual Output_section*
 398   do_make_output_section(const char* name, elfcpp::Elf_Word type,
 399                          elfcpp::Elf_Xword flags);
 400
 401   // Virtual function which may be overriden by the child class.
 402   virtual bool
 403   do_may_relax() const
 404   { return parameters->options().relax(); }
 405
 406   // Virtual function which may be overriden by the child class.
 407   virtual bool
 408   do_relax(int, const Input_objects*, Symbol_table*, Layout*)
 409   { return false; }
 410
 411   // A function for targets to call.  Return whether BYTES/LEN matches
 412   // VIEW/VIEW_SIZE at OFFSET.
 413   bool
 414   match_view(const unsigned char* view, section_size_type view_size,
 415              section_offset_type offset, const char* bytes, size_t len) const;
 416
 417   // Set the contents of a VIEW/VIEW_SIZE to nops starting at OFFSET
 418   // for LEN bytes.
 419   void
 420   set_view_to_nop(unsigned char* view, section_size_type view_size,
 421                   section_offset_type offset, size_t len) const;
 422
 423  private:
 424   // The implementations of the four do_make_elf_object virtual functions are
 425   // almost identical except for their sizes and endianity.  We use a template.
 426   // for their implementations.
 427   template<int size, bool big_endian>
 428   inline Object*
 429   do_make_elf_object_implementation(const std::string&, Input_file*, off_t,
 430                                     const elfcpp::Ehdr<size, big_endian>&);
 431
 432   Target(const Target&);
 433   Target& operator=(const Target&);
 434
 435   // The target information.
 436   const Target_info* pti_;
 437 };
 438
 439 // The abstract class for a specific size and endianness of target.
 440 // Each actual target implementation class should derive from an
 441 // instantiation of Sized_target.
 442
 443 template<int size, bool big_endian>
 444 class Sized_target : public Target
 445 {
 446  public:
 447   // Make a new symbol table entry for the target.  This should be
 448   // overridden by a target which needs additional information in the
 449   // symbol table.  This will only be called if has_make_symbol()
 450   // returns true.
 451   virtual Sized_symbol<size>*
 452   make_symbol() const
 453   { gold_unreachable(); }
 454
 455   // Resolve a symbol for the target.  This should be overridden by a
 456   // target which needs to take special action.  TO is the
 457   // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.
 458   // VERSION is the version of SYM.  This will only be called if
 459   // has_resolve() returns true.
 460   virtual void
 461   resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
 462           const char*)
 463   { gold_unreachable(); }
 464
 465   // Process the relocs for a section, and record information of the
 466   // mapping from source to destination sections. This mapping is later
 467   // used to determine unreferenced garbage sections. This procedure is
 468   // only called during garbage collection.
 469   virtual void
 470   gc_process_relocs(const General_options& options,
 471               Symbol_table* symtab,
 472               Layout* layout,
 473               Sized_relobj<size, big_endian>* object,
 474               unsigned int data_shndx,
 475               unsigned int sh_type,
 476               const unsigned char* prelocs,
 477               size_t reloc_count,
 478               Output_section* output_section,
 479               bool needs_special_offset_handling,
 480               size_t local_symbol_count,
 481               const unsigned char* plocal_symbols) = 0;
 482
 483   // Scan the relocs for a section, and record any information
 484   // required for the symbol.  OPTIONS is the command line options.
 485   // SYMTAB is the symbol table.  OBJECT is the object in which the
 486   // section appears.  DATA_SHNDX is the section index that these
 487   // relocs apply to.  SH_TYPE is the type of the relocation section,
 488   // SHT_REL or SHT_RELA.  PRELOCS points to the relocation data.
 489   // RELOC_COUNT is the number of relocs.  LOCAL_SYMBOL_COUNT is the
 490   // number of local symbols.  OUTPUT_SECTION is the output section.
 491   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
 492   // sections are not mapped as usual.  PLOCAL_SYMBOLS points to the
 493   // local symbol data from OBJECT.  GLOBAL_SYMBOLS is the array of
 494   // pointers to the global symbol table from OBJECT.
 495   virtual void
 496   scan_relocs(const General_options& options,
 497               Symbol_table* symtab,
 498               Layout* layout,
 499               Sized_relobj<size, big_endian>* object,
 500               unsigned int data_shndx,
 501               unsigned int sh_type,
 502               const unsigned char* prelocs,
 503               size_t reloc_count,
 504               Output_section* output_section,
 505               bool needs_special_offset_handling,
 506               size_t local_symbol_count,
 507               const unsigned char* plocal_symbols) = 0;
 508
 509   // Relocate section data.  SH_TYPE is the type of the relocation
 510   // section, SHT_REL or SHT_RELA.  PRELOCS points to the relocation
 511   // information.  RELOC_COUNT is the number of relocs.
 512   // OUTPUT_SECTION is the output section.
 513   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
 514   // to correspond to the output section.  VIEW is a view into the
 515   // output file holding the section contents, VIEW_ADDRESS is the
 516   // virtual address of the view, and VIEW_SIZE is the size of the
 517   // view.  If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
 518   // parameters refer to the complete output section data, not just
 519   // the input section data.
 520   virtual void
 521   relocate_section(const Relocate_info<size, big_endian>*,
 522                    unsigned int sh_type,
 523                    const unsigned char* prelocs,
 524                    size_t reloc_count,
 525                    Output_section* output_section,
 526                    bool needs_special_offset_handling,
 527                    unsigned char* view,
 528                    typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 529                    section_size_type view_size,
 530                    const Reloc_symbol_changes*) = 0;
 531
 532   // Scan the relocs during a relocatable link.  The parameters are
 533   // like scan_relocs, with an additional Relocatable_relocs
 534   // parameter, used to record the disposition of the relocs.
 535   virtual void
 536   scan_relocatable_relocs(const General_options& options,
 537                           Symbol_table* symtab,
 538                           Layout* layout,
 539                           Sized_relobj<size, big_endian>* object,
 540                           unsigned int data_shndx,
 541                           unsigned int sh_type,
 542                           const unsigned char* prelocs,
 543                           size_t reloc_count,
 544                           Output_section* output_section,
 545                           bool needs_special_offset_handling,
 546                           size_t local_symbol_count,
 547                           const unsigned char* plocal_symbols,
 548                           Relocatable_relocs*) = 0;
 549
 550   // Relocate a section during a relocatable link.  The parameters are
 551   // like relocate_section, with additional parameters for the view of
 552   // the output reloc section.
 553   virtual void
 554   relocate_for_relocatable(const Relocate_info<size, big_endian>*,
 555                            unsigned int sh_type,
 556                            const unsigned char* prelocs,
 557                            size_t reloc_count,
 558                            Output_section* output_section,
 559                            off_t offset_in_output_section,
 560                            const Relocatable_relocs*,
 561                            unsigned char* view,
 562                            typename elfcpp::Elf_types<size>::Elf_Addr
 563                              view_address,
 564                            section_size_type view_size,
 565                            unsigned char* reloc_view,
 566                            section_size_type reloc_view_size) = 0;
 567
 568  protected:
 569   Sized_target(const Target::Target_info* pti)
 570     : Target(pti)
 571   {
 572     gold_assert(pti->size == size);
 573     gold_assert(pti->is_big_endian ? big_endian : !big_endian);
 574   }
 575 };
 576
 577 } // End namespace gold.
 578
 579 #endif // !defined(GOLD_TARGET_H)