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