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   // This is called to tell the target to complete any sections it is
 145   // handling.  After this all sections must have their final size.
 146   void
 147   finalize_sections(Layout* layout)
 148   { return this->do_finalize_sections(layout); }
 149
 150   // Return the value to use for a global symbol which needs a special
 151   // value in the dynamic symbol table.  This will only be called if
 152   // the backend first calls symbol->set_needs_dynsym_value().
 153   uint64_t
 154   dynsym_value(const Symbol* sym) const
 155   { return this->do_dynsym_value(sym); }
 156
 157   // Return a string to use to fill out a code section.  This is
 158   // basically one or more NOPS which must fill out the specified
 159   // length in bytes.
 160   std::string
 161   code_fill(section_size_type length) const
 162   { return this->do_code_fill(length); }
 163
 164   // Return whether SYM is known to be defined by the ABI.  This is
 165   // used to avoid inappropriate warnings about undefined symbols.
 166   bool
 167   is_defined_by_abi(const Symbol* sym) const
 168   { return this->do_is_defined_by_abi(sym); }
 169
 170   // Adjust the output file header before it is written out.  VIEW
 171   // points to the header in external form.  LEN is the length.
 172   void
 173   adjust_elf_header(unsigned char* view, int len) const
 174   { return this->do_adjust_elf_header(view, len); }
 175
 176  protected:
 177   // This struct holds the constant information for a child class.  We
 178   // use a struct to avoid the overhead of virtual function calls for
 179   // simple information.
 180   struct Target_info
 181   {
 182     // Address size (32 or 64).
 183     int size;
 184     // Whether the target is big endian.
 185     bool is_big_endian;
 186     // The code to store in the e_machine field of the ELF header.
 187     elfcpp::EM machine_code;
 188     // Whether this target has a specific make_symbol function.
 189     bool has_make_symbol;
 190     // Whether this target has a specific resolve function.
 191     bool has_resolve;
 192     // Whether this target has a specific code fill function.
 193     bool has_code_fill;
 194     // Whether an object file with no .note.GNU-stack sections implies
 195     // that the stack should be executable.
 196     bool is_default_stack_executable;
 197     // Prefix character to strip when checking for wrapping.
 198     char wrap_char;
 199     // The default dynamic linker name.
 200     const char* dynamic_linker;
 201     // The default text segment address.
 202     uint64_t default_text_segment_address;
 203     // The ABI specified page size.
 204     uint64_t abi_pagesize;
 205     // The common page size used by actual implementations.
 206     uint64_t common_pagesize;
 207   };
 208
 209   Target(const Target_info* pti)
 210     : pti_(pti)
 211   { }
 212
 213   // Virtual function which may be implemented by the child class.
 214   virtual void
 215   do_finalize_sections(Layout*)
 216   { }
 217
 218   // Virtual function which may be implemented by the child class.
 219   virtual uint64_t
 220   do_dynsym_value(const Symbol*) const
 221   { gold_unreachable(); }
 222
 223   // Virtual function which must be implemented by the child class if
 224   // needed.
 225   virtual std::string
 226   do_code_fill(section_size_type) const
 227   { gold_unreachable(); }
 228
 229   // Virtual function which may be implemented by the child class.
 230   virtual bool
 231   do_is_defined_by_abi(const Symbol*) const
 232   { return false; }
 233
 234   // Adjust the output file header before it is written out.  VIEW
 235   // points to the header in external form.  LEN is the length, and
 236   // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.
 237   // By default, we do nothing.
 238   virtual void
 239   do_adjust_elf_header(unsigned char*, int) const
 240   { }
 241
 242  private:
 243   Target(const Target&);
 244   Target& operator=(const Target&);
 245
 246   // The target information.
 247   const Target_info* pti_;
 248 };
 249
 250 // The abstract class for a specific size and endianness of target.
 251 // Each actual target implementation class should derive from an
 252 // instantiation of Sized_target.
 253
 254 template<int size, bool big_endian>
 255 class Sized_target : public Target
 256 {
 257  public:
 258   // Make a new symbol table entry for the target.  This should be
 259   // overridden by a target which needs additional information in the
 260   // symbol table.  This will only be called if has_make_symbol()
 261   // returns true.
 262   virtual Sized_symbol<size>*
 263   make_symbol() const
 264   { gold_unreachable(); }
 265
 266   // Resolve a symbol for the target.  This should be overridden by a
 267   // target which needs to take special action.  TO is the
 268   // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.
 269   // VERSION is the version of SYM.  This will only be called if
 270   // has_resolve() returns true.
 271   virtual void
 272   resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
 273           const char*)
 274   { gold_unreachable(); }
 275
 276   // Process the relocs for a section, and record information of the
 277   // mapping from source to destination sections. This mapping is later
 278   // used to determine unreferenced garbage sections. This procedure is
 279   // only called during garbage collection.
 280   virtual void
 281   gc_process_relocs(const General_options& options,
 282               Symbol_table* symtab,
 283               Layout* layout,
 284               Sized_relobj<size, big_endian>* object,
 285               unsigned int data_shndx,
 286               unsigned int sh_type,
 287               const unsigned char* prelocs,
 288               size_t reloc_count,
 289               Output_section* output_section,
 290               bool needs_special_offset_handling,
 291               size_t local_symbol_count,
 292               const unsigned char* plocal_symbols) = 0;
 293
 294   // Scan the relocs for a section, and record any information
 295   // required for the symbol.  OPTIONS is the command line options.
 296   // SYMTAB is the symbol table.  OBJECT is the object in which the
 297   // section appears.  DATA_SHNDX is the section index that these
 298   // relocs apply to.  SH_TYPE is the type of the relocation section,
 299   // SHT_REL or SHT_RELA.  PRELOCS points to the relocation data.
 300   // RELOC_COUNT is the number of relocs.  LOCAL_SYMBOL_COUNT is the
 301   // number of local symbols.  OUTPUT_SECTION is the output section.
 302   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
 303   // sections are not mapped as usual.  PLOCAL_SYMBOLS points to the
 304   // local symbol data from OBJECT.  GLOBAL_SYMBOLS is the array of
 305   // pointers to the global symbol table from OBJECT.
 306   virtual void
 307   scan_relocs(const General_options& options,
 308               Symbol_table* symtab,
 309               Layout* layout,
 310               Sized_relobj<size, big_endian>* object,
 311               unsigned int data_shndx,
 312               unsigned int sh_type,
 313               const unsigned char* prelocs,
 314               size_t reloc_count,
 315               Output_section* output_section,
 316               bool needs_special_offset_handling,
 317               size_t local_symbol_count,
 318               const unsigned char* plocal_symbols) = 0;
 319
 320   // Relocate section data.  SH_TYPE is the type of the relocation
 321   // section, SHT_REL or SHT_RELA.  PRELOCS points to the relocation
 322   // information.  RELOC_COUNT is the number of relocs.
 323   // OUTPUT_SECTION is the output section.
 324   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
 325   // to correspond to the output section.  VIEW is a view into the
 326   // output file holding the section contents, VIEW_ADDRESS is the
 327   // virtual address of the view, and VIEW_SIZE is the size of the
 328   // view.  If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
 329   // parameters refer to the complete output section data, not just
 330   // the input section data.
 331   virtual void
 332   relocate_section(const Relocate_info<size, big_endian>*,
 333                    unsigned int sh_type,
 334                    const unsigned char* prelocs,
 335                    size_t reloc_count,
 336                    Output_section* output_section,
 337                    bool needs_special_offset_handling,
 338                    unsigned char* view,
 339                    typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 340                    section_size_type view_size) = 0;
 341
 342   // Scan the relocs during a relocatable link.  The parameters are
 343   // like scan_relocs, with an additional Relocatable_relocs
 344   // parameter, used to record the disposition of the relocs.
 345   virtual void
 346   scan_relocatable_relocs(const General_options& options,
 347                           Symbol_table* symtab,
 348                           Layout* layout,
 349                           Sized_relobj<size, big_endian>* object,
 350                           unsigned int data_shndx,
 351                           unsigned int sh_type,
 352                           const unsigned char* prelocs,
 353                           size_t reloc_count,
 354                           Output_section* output_section,
 355                           bool needs_special_offset_handling,
 356                           size_t local_symbol_count,
 357                           const unsigned char* plocal_symbols,
 358                           Relocatable_relocs*) = 0;
 359
 360   // Relocate a section during a relocatable link.  The parameters are
 361   // like relocate_section, with additional parameters for the view of
 362   // the output reloc section.
 363   virtual void
 364   relocate_for_relocatable(const Relocate_info<size, big_endian>*,
 365                            unsigned int sh_type,
 366                            const unsigned char* prelocs,
 367                            size_t reloc_count,
 368                            Output_section* output_section,
 369                            off_t offset_in_output_section,
 370                            const Relocatable_relocs*,
 371                            unsigned char* view,
 372                            typename elfcpp::Elf_types<size>::Elf_Addr
 373                              view_address,
 374                            section_size_type view_size,
 375                            unsigned char* reloc_view,
 376                            section_size_type reloc_view_size) = 0;
 377
 378  protected:
 379   Sized_target(const Target::Target_info* pti)
 380     : Target(pti)
 381   {
 382     gold_assert(pti->size == size);
 383     gold_assert(pti->is_big_endian ? big_endian : !big_endian);
 384   }
 385 };
 386
 387 } // End namespace gold.
 388
 389 #endif // !defined(GOLD_TARGET_H)