gold/target.h

   1 // target.h -- target support for gold   -*- 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 // 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 "parameters.h"
  38
  39 namespace gold
  40 {
  41
  42 class General_options;
  43 class Object;
  44 template<int size, bool big_endian>
  45 class Sized_relobj;
  46 class Relocatable_relocs;
  47 template<int size, bool big_endian>
  48 class Relocate_info;
  49 class Symbol;
  50 template<int size>
  51 class Sized_symbol;
  52 class Symbol_table;
  53 class Output_section;
  54
  55 // The abstract class for target specific handling.
  56
  57 class Target
  58 {
  59  public:
  60   virtual ~Target()
  61   { }
  62
  63   // Return the bit size that this target implements.  This should
  64   // return 32 or 64.
  65   int
  66   get_size() const
  67   { return this->pti_->size; }
  68
  69   // Return whether this target is big-endian.
  70   bool
  71   is_big_endian() const
  72   { return this->pti_->is_big_endian; }
  73
  74   // Machine code to store in e_machine field of ELF header.
  75   elfcpp::EM
  76   machine_code() const
  77   { return this->pti_->machine_code; }
  78
  79   // Whether this target has a specific make_symbol function.
  80   bool
  81   has_make_symbol() const
  82   { return this->pti_->has_make_symbol; }
  83
  84   // Whether this target has a specific resolve function.
  85   bool
  86   has_resolve() const
  87   { return this->pti_->has_resolve; }
  88
  89   // Whether this target has a specific code fill function.
  90   bool
  91   has_code_fill() const
  92   { return this->pti_->has_code_fill; }
  93
  94   // Return the default name of the dynamic linker.
  95   const char*
  96   dynamic_linker() const
  97   { return this->pti_->dynamic_linker; }
  98
  99   // Return the default address to use for the text segment.
 100   uint64_t
 101   default_text_segment_address() const
 102   { return this->pti_->default_text_segment_address; }
 103
 104   // Return the ABI specified page size.
 105   uint64_t
 106   abi_pagesize() const
 107   {
 108     if (parameters->max_page_size() > 0)
 109       return parameters->max_page_size();
 110     else
 111       return this->pti_->abi_pagesize;
 112   }
 113
 114   // Return the common page size used on actual systems.
 115   uint64_t
 116   common_pagesize() const
 117   {
 118     if (parameters->common_page_size() > 0)
 119       return std::min(parameters->common_page_size(),
 120                       this->abi_pagesize());
 121     else
 122       return std::min(this->pti_->common_pagesize,
 123                       this->abi_pagesize());
 124   }
 125
 126   // If we see some object files with .note.GNU-stack sections, and
 127   // some objects files without them, this returns whether we should
 128   // consider the object files without them to imply that the stack
 129   // should be executable.
 130   bool
 131   is_default_stack_executable() const
 132   { return this->pti_->is_default_stack_executable; }
 133
 134   // This is called to tell the target to complete any sections it is
 135   // handling.  After this all sections must have their final size.
 136   void
 137   finalize_sections(Layout* layout)
 138   { return this->do_finalize_sections(layout); }
 139
 140   // Return the value to use for a global symbol which needs a special
 141   // value in the dynamic symbol table.  This will only be called if
 142   // the backend first calls symbol->set_needs_dynsym_value().
 143   uint64_t
 144   dynsym_value(const Symbol* sym) const
 145   { return this->do_dynsym_value(sym); }
 146
 147   // Return a string to use to fill out a code section.  This is
 148   // basically one or more NOPS which must fill out the specified
 149   // length in bytes.
 150   std::string
 151   code_fill(section_size_type length)
 152   { return this->do_code_fill(length); }
 153
 154   // Return whether SYM is known to be defined by the ABI.  This is
 155   // used to avoid inappropriate warnings about undefined symbols.
 156   bool
 157   is_defined_by_abi(Symbol* sym) const
 158   { return this->do_is_defined_by_abi(sym); }
 159
 160  protected:
 161   // This struct holds the constant information for a child class.  We
 162   // use a struct to avoid the overhead of virtual function calls for
 163   // simple information.
 164   struct Target_info
 165   {
 166     // Address size (32 or 64).
 167     int size;
 168     // Whether the target is big endian.
 169     bool is_big_endian;
 170     // The code to store in the e_machine field of the ELF header.
 171     elfcpp::EM machine_code;
 172     // Whether this target has a specific make_symbol function.
 173     bool has_make_symbol;
 174     // Whether this target has a specific resolve function.
 175     bool has_resolve;
 176     // Whether this target has a specific code fill function.
 177     bool has_code_fill;
 178     // Whether an object file with no .note.GNU-stack sections implies
 179     // that the stack should be executable.
 180     bool is_default_stack_executable;
 181     // The default dynamic linker name.
 182     const char* dynamic_linker;
 183     // The default text segment address.
 184     uint64_t default_text_segment_address;
 185     // The ABI specified page size.
 186     uint64_t abi_pagesize;
 187     // The common page size used by actual implementations.
 188     uint64_t common_pagesize;
 189   };
 190
 191   Target(const Target_info* pti)
 192     : pti_(pti)
 193   { }
 194
 195   // Virtual function which may be implemented by the child class.
 196   virtual void
 197   do_finalize_sections(Layout*)
 198   { }
 199
 200   // Virtual function which may be implemented by the child class.
 201   virtual uint64_t
 202   do_dynsym_value(const Symbol*) const
 203   { gold_unreachable(); }
 204
 205   // Virtual function which must be implemented by the child class if
 206   // needed.
 207   virtual std::string
 208   do_code_fill(section_size_type)
 209   { gold_unreachable(); }
 210
 211   // Virtual function which may be implemented by the child class.
 212   virtual bool
 213   do_is_defined_by_abi(Symbol*) const
 214   { return false; }
 215
 216  private:
 217   Target(const Target&);
 218   Target& operator=(const Target&);
 219
 220   // The target information.
 221   const Target_info* pti_;
 222 };
 223
 224 // The abstract class for a specific size and endianness of target.
 225 // Each actual target implementation class should derive from an
 226 // instantiation of Sized_target.
 227
 228 template<int size, bool big_endian>
 229 class Sized_target : public Target
 230 {
 231  public:
 232   // Make a new symbol table entry for the target.  This should be
 233   // overridden by a target which needs additional information in the
 234   // symbol table.  This will only be called if has_make_symbol()
 235   // returns true.
 236   virtual Sized_symbol<size>*
 237   make_symbol() const
 238   { gold_unreachable(); }
 239
 240   // Resolve a symbol for the target.  This should be overridden by a
 241   // target which needs to take special action.  TO is the
 242   // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.
 243   // VERSION is the version of SYM.  This will only be called if
 244   // has_resolve() returns true.
 245   virtual void
 246   resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,
 247           const char*)
 248   { gold_unreachable(); }
 249
 250   // Scan the relocs for a section, and record any information
 251   // required for the symbol.  OPTIONS is the command line options.
 252   // SYMTAB is the symbol table.  OBJECT is the object in which the
 253   // section appears.  DATA_SHNDX is the section index that these
 254   // relocs apply to.  SH_TYPE is the type of the relocation section,
 255   // SHT_REL or SHT_RELA.  PRELOCS points to the relocation data.
 256   // RELOC_COUNT is the number of relocs.  LOCAL_SYMBOL_COUNT is the
 257   // number of local symbols.  OUTPUT_SECTION is the output section.
 258   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output
 259   // sections are not mapped as usual.  PLOCAL_SYMBOLS points to the
 260   // local symbol data from OBJECT.  GLOBAL_SYMBOLS is the array of
 261   // pointers to the global symbol table from OBJECT.
 262   virtual void
 263   scan_relocs(const General_options& options,
 264               Symbol_table* symtab,
 265               Layout* layout,
 266               Sized_relobj<size, big_endian>* object,
 267               unsigned int data_shndx,
 268               unsigned int sh_type,
 269               const unsigned char* prelocs,
 270               size_t reloc_count,
 271               Output_section* output_section,
 272               bool needs_special_offset_handling,
 273               size_t local_symbol_count,
 274               const unsigned char* plocal_symbols) = 0;
 275
 276   // Relocate section data.  SH_TYPE is the type of the relocation
 277   // section, SHT_REL or SHT_RELA.  PRELOCS points to the relocation
 278   // information.  RELOC_COUNT is the number of relocs.
 279   // OUTPUT_SECTION is the output section.
 280   // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets must be mapped
 281   // to correspond to the output section.  VIEW is a view into the
 282   // output file holding the section contents, VIEW_ADDRESS is the
 283   // virtual address of the view, and VIEW_SIZE is the size of the
 284   // view.  If NEEDS_SPECIAL_OFFSET_HANDLING is true, the VIEW_xx
 285   // parameters refer to the complete output section data, not just
 286   // the input section data.
 287   virtual void
 288   relocate_section(const Relocate_info<size, big_endian>*,
 289                    unsigned int sh_type,
 290                    const unsigned char* prelocs,
 291                    size_t reloc_count,
 292                    Output_section* output_section,
 293                    bool needs_special_offset_handling,
 294                    unsigned char* view,
 295                    typename elfcpp::Elf_types<size>::Elf_Addr view_address,
 296                    section_size_type view_size) = 0;
 297
 298   // Scan the relocs during a relocatable link.  The parameters are
 299   // like scan_relocs, with an additional Relocatable_relocs
 300   // parameter, used to record the disposition of the relocs.
 301   virtual void
 302   scan_relocatable_relocs(const General_options& options,
 303                           Symbol_table* symtab,
 304                           Layout* layout,
 305                           Sized_relobj<size, big_endian>* object,
 306                           unsigned int data_shndx,
 307                           unsigned int sh_type,
 308                           const unsigned char* prelocs,
 309                           size_t reloc_count,
 310                           Output_section* output_section,
 311                           bool needs_special_offset_handling,
 312                           size_t local_symbol_count,
 313                           const unsigned char* plocal_symbols,
 314                           Relocatable_relocs*) = 0;
 315
 316   // Relocate a section during a relocatable link.  The parameters are
 317   // like relocate_section, with additional parameters for the view of
 318   // the output reloc section.
 319   virtual void
 320   relocate_for_relocatable(const Relocate_info<size, big_endian>*,
 321                            unsigned int sh_type,
 322                            const unsigned char* prelocs,
 323                            size_t reloc_count,
 324                            Output_section* output_section,
 325                            off_t offset_in_output_section,
 326                            const Relocatable_relocs*,
 327                            unsigned char* view,
 328                            typename elfcpp::Elf_types<size>::Elf_Addr
 329                              view_address,
 330                            section_size_type view_size,
 331                            unsigned char* reloc_view,
 332                            section_size_type reloc_view_size) = 0;
 333
 334  protected:
 335   Sized_target(const Target::Target_info* pti)
 336     : Target(pti)
 337   {
 338     gold_assert(pti->size == size);
 339     gold_assert(pti->is_big_endian ? big_endian : !big_endian);
 340   }
 341 };
 342
 343 } // End namespace gold.
 344
 345 #endif // !defined(GOLD_TARGET_H)