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