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