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// target.h -- target support for gold   -*- C++ -*-

// Copyright 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.

// Written by Ian Lance Taylor <iant@google.com>.

// This file is part of gold.

// This program is free software; you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation; either version 3 of the License, or

// (at your option) any later version.

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License

// along with this program; if not, write to the Free Software

// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,

// MA 02110-1301, USA.

// The abstract class Target is the interface for target specific

// support.  It defines abstract methods which each target must

// implement.  Typically there will be one target per processor, but

// in some cases it may be necessary to have subclasses.

// For speed and consistency we want to use inline functions to handle

// relocation processing.  So besides implementations of the abstract

// methods, each target is expected to define a template

// specialization of the relocation functions.

#ifndef GOLD_TARGET_H

#define GOLD_TARGET_H

#include "elfcpp.h"

#include "options.h"

#include "parameters.h"

#include "debug.h"

namespace gold

{

class Object;

class Relobj;

template<int size, bool big_endian>

class Sized_relobj;

template<int size, bool big_endian>

class Sized_relobj_file;

class Relocatable_relocs;

template<int size, bool big_endian>

class Relocate_info;

class Reloc_symbol_changes;

class Symbol;

template<int size>

class Sized_symbol;

class Symbol_table;

class Output_data;

class Output_data_got_base;

class Output_section;

class Input_objects;

class Task;

// The abstract class for target specific handling.

class Target

{

 public:

  virtual ~Target()

  { }

  // Return the bit size that this target implements.  This should

  // return 32 or 64.

  int

  get_size() const

  { return this->pti_->size; }

  // Return whether this target is big-endian.

  bool

  is_big_endian() const

  { return this->pti_->is_big_endian; }

  // Machine code to store in e_machine field of ELF header.

  elfcpp::EM

  machine_code() const

  { return this->pti_->machine_code; }

  // Processor specific flags to store in e_flags field of ELF header.

  elfcpp::Elf_Word

  processor_specific_flags() const

  { return this->processor_specific_flags_; }

  // Whether processor specific flags are set at least once.

  bool

  are_processor_specific_flags_set() const

  { return this->are_processor_specific_flags_set_; }

  // Whether this target has a specific make_symbol function.

  bool

  has_make_symbol() const

  { return this->pti_->has_make_symbol; }

  // Whether this target has a specific resolve function.

  bool

  has_resolve() const

  { return this->pti_->has_resolve; }

  // Whether this target has a specific code fill function.

  bool

  has_code_fill() const

  { return this->pti_->has_code_fill; }

  // Return the default name of the dynamic linker.

  const char*

  dynamic_linker() const

  { return this->pti_->dynamic_linker; }

  // Return the default address to use for the text segment.

  uint64_t

  default_text_segment_address() const

  { return this->pti_->default_text_segment_address; }

  // Return the ABI specified page size.

  uint64_t

  abi_pagesize() const

  {

    if (parameters->options().max_page_size() > 0)

      return parameters->options().max_page_size();

    else

      return this->pti_->abi_pagesize;

  }

  // Return the common page size used on actual systems.

  uint64_t

  common_pagesize() const

  {

    if (parameters->options().common_page_size() > 0)

      return std::min(parameters->options().common_page_size(),

                      this->abi_pagesize());

    else

      return std::min(this->pti_->common_pagesize,

                      this->abi_pagesize());

  }

  // If we see some object files with .note.GNU-stack sections, and

  // some objects files without them, this returns whether we should

  // consider the object files without them to imply that the stack

  // should be executable.

  bool

  is_default_stack_executable() const

  { return this->pti_->is_default_stack_executable; }

  // Return a character which may appear as a prefix for a wrap

  // symbol.  If this character appears, we strip it when checking for

  // wrapping and add it back when forming the final symbol name.

  // This should be '\0' if not special prefix is required, which is

  // the normal case.

  char

  wrap_char() const

  { return this->pti_->wrap_char; }

  // Return the special section index which indicates a small common

  // symbol.  This will return SHN_UNDEF if there are no small common

  // symbols.

  elfcpp::Elf_Half

  small_common_shndx() const

  { return this->pti_->small_common_shndx; }

  // Return values to add to the section flags for the section holding

  // small common symbols.

  elfcpp::Elf_Xword

  small_common_section_flags() const

  {

    gold_assert(this->pti_->small_common_shndx != elfcpp::SHN_UNDEF);

    return this->pti_->small_common_section_flags;

  }

  // Return the special section index which indicates a large common

  // symbol.  This will return SHN_UNDEF if there are no large common

  // symbols.

  elfcpp::Elf_Half

  large_common_shndx() const

  { return this->pti_->large_common_shndx; }

  // Return values to add to the section flags for the section holding

  // large common symbols.

  elfcpp::Elf_Xword

  large_common_section_flags() const

  {

    gold_assert(this->pti_->large_common_shndx != elfcpp::SHN_UNDEF);

    return this->pti_->large_common_section_flags;

  }

  // This hook is called when an output section is created.

  void

  new_output_section(Output_section* os) const

  { this->do_new_output_section(os); }

  // This is called to tell the target to complete any sections it is

  // handling.  After this all sections must have their final size.

  void

  finalize_sections(Layout* layout, const Input_objects* input_objects,

                    Symbol_table* symtab)

  { return this->do_finalize_sections(layout, input_objects, symtab); }

  // Return the value to use for a global symbol which needs a special

  // value in the dynamic symbol table.  This will only be called if

  // the backend first calls symbol->set_needs_dynsym_value().

  uint64_t

  dynsym_value(const Symbol* sym) const

  { return this->do_dynsym_value(sym); }

  // Return a string to use to fill out a code section.  This is

  // basically one or more NOPS which must fill out the specified

  // length in bytes.

  std::string

  code_fill(section_size_type length) const

  { return this->do_code_fill(length); }

  // Return whether SYM is known to be defined by the ABI.  This is

  // used to avoid inappropriate warnings about undefined symbols.

  bool

  is_defined_by_abi(const Symbol* sym) const

  { return this->do_is_defined_by_abi(sym); }

  // Adjust the output file header before it is written out.  VIEW

  // points to the header in external form.  LEN is the length.

  void

  adjust_elf_header(unsigned char* view, int len) const

  { return this->do_adjust_elf_header(view, len); }

  // Return whether NAME is a local label name.  This is used to implement the

  // --discard-locals options.

  bool

  is_local_label_name(const char* name) const

  { return this->do_is_local_label_name(name); }

  // Get the symbol index to use for a target specific reloc.

  unsigned int

  reloc_symbol_index(void* arg, unsigned int type) const

  { return this->do_reloc_symbol_index(arg, type); }

  // Get the addend to use for a target specific reloc.

  uint64_t

  reloc_addend(void* arg, unsigned int type, uint64_t addend) const

  { return this->do_reloc_addend(arg, type, addend); }

  // Return the PLT address to use for a global symbol.  This is used

  // for STT_GNU_IFUNC symbols.  The symbol's plt_offset is relative

  // to this PLT address.

  uint64_t

  plt_address_for_global(const Symbol* sym) const

  { return this->do_plt_address_for_global(sym); }

  // Return the PLT address to use for a local symbol.  This is used

  // for STT_GNU_IFUNC symbols.  The symbol's plt_offset is relative

  // to this PLT address.

  uint64_t

  plt_address_for_local(const Relobj* object, unsigned int symndx) const

  { return this->do_plt_address_for_local(object, symndx); }

  // Return whether this target can use relocation types to determine

  // if a function's address is taken.

  bool

  can_check_for_function_pointers() const

  { return this->do_can_check_for_function_pointers(); }

  // Return whether a relocation to a merged section can be processed

  // to retrieve the contents.

  bool

  can_icf_inline_merge_sections () const

  { return this->pti_->can_icf_inline_merge_sections; }

  // Whether a section called SECTION_NAME may have function pointers to

  // sections not eligible for safe ICF folding.

  virtual bool

  section_may_have_icf_unsafe_pointers(const char* section_name) const

  { return this->do_section_may_have_icf_unsafe_pointers(section_name); }

  // Return the base to use for the PC value in an FDE when it is

  // encoded using DW_EH_PE_datarel.  This does not appear to be

  // documented anywhere, but it is target specific.  Any use of

  // DW_EH_PE_datarel in gcc requires defining a special macro

  // (ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX) to output the value.

  uint64_t

  ehframe_datarel_base() const

  { return this->do_ehframe_datarel_base(); }

  // Return true if a reference to SYM from a reloc of type R_TYPE

  // means that the current function may call an object compiled

  // without -fsplit-stack.  SYM is known to be defined in an object

  // compiled without -fsplit-stack.

  bool

  is_call_to_non_split(const Symbol* sym, unsigned int r_type) const

  { return this->do_is_call_to_non_split(sym, r_type); }

  // A function starts at OFFSET in section SHNDX in OBJECT.  That

  // function was compiled with -fsplit-stack, but it refers to a

  // function which was compiled without -fsplit-stack.  VIEW is a

  // modifiable view of the section; VIEW_SIZE is the size of the

  // view.  The target has to adjust the function so that it allocates

  // enough stack.

  void

  calls_non_split(Relobj* object, unsigned int shndx,

                  section_offset_type fnoffset, section_size_type fnsize,

                  unsigned char* view, section_size_type view_size,

                  std::string* from, std::string* to) const

  {

    this->do_calls_non_split(object, shndx, fnoffset, fnsize, view, view_size,

                             from, to);

  }

  // Make an ELF object.

  template<int size, bool big_endian>

  Object*

  make_elf_object(const std::string& name, Input_file* input_file,

                  off_t offset, const elfcpp::Ehdr<size, big_endian>& ehdr)

  { return this->do_make_elf_object(name, input_file, offset, ehdr); }

  // Make an output section.

  Output_section*

  make_output_section(const char* name, elfcpp::Elf_Word type,

                      elfcpp::Elf_Xword flags)

  { return this->do_make_output_section(name, type, flags); }

  // Return true if target wants to perform relaxation.

  bool

  may_relax() const

  {

    // Run the dummy relaxation pass twice if relaxation debugging is enabled.

    if (is_debugging_enabled(DEBUG_RELAXATION))

      return true;

     return this->do_may_relax();

  }

  // Perform a relaxation pass.  Return true if layout may be changed.

  bool

  relax(int pass, const Input_objects* input_objects, Symbol_table* symtab,

        Layout* layout, const Task* task)

  {

    // Run the dummy relaxation pass twice if relaxation debugging is enabled.

    if (is_debugging_enabled(DEBUG_RELAXATION))

      return pass < 2;

    return this->do_relax(pass, input_objects, symtab, layout, task);

  }

  // Return the target-specific name of attributes section.  This is

  // NULL if a target does not use attributes section or if it uses

  // the default section name ".gnu.attributes".

  const char*

  attributes_section() const

  { return this->pti_->attributes_section; }

  // Return the vendor name of vendor attributes.

  const char*

  attributes_vendor() const

  { return this->pti_->attributes_vendor; }

  // Whether a section called NAME is an attribute section.

  bool

  is_attributes_section(const char* name) const

  {

    return ((this->pti_->attributes_section != NULL

             && strcmp(name, this->pti_->attributes_section) == 0)

            || strcmp(name, ".gnu.attributes") == 0);

  }

  // Return a bit mask of argument types for attribute with TAG.

  int

  attribute_arg_type(int tag) const

  { return this->do_attribute_arg_type(tag); }

  // Return the attribute tag of the position NUM in the list of fixed

  // attributes.  Normally there is no reordering and

  // attributes_order(NUM) == NUM.

  int

  attributes_order(int num) const

  { return this->do_attributes_order(num); }

  // When a target is selected as the default target, we call this method,

  // which may be used for expensive, target-specific initialization.

  void

  select_as_default_target()

  { this->do_select_as_default_target(); }

  // Return the value to store in the EI_OSABI field in the ELF

  // header.

  elfcpp::ELFOSABI

  osabi() const

  { return this->osabi_; }

  // Set the value to store in the EI_OSABI field in the ELF header.

  void

  set_osabi(elfcpp::ELFOSABI osabi)

  { this->osabi_ = osabi; }

 protected:

  // This struct holds the constant information for a child class.  We

  // use a struct to avoid the overhead of virtual function calls for

  // simple information.

  struct Target_info

  {

    // Address size (32 or 64).

    int size;

    // Whether the target is big endian.

    bool is_big_endian;

    // The code to store in the e_machine field of the ELF header.

    elfcpp::EM machine_code;

    // Whether this target has a specific make_symbol function.

    bool has_make_symbol;

    // Whether this target has a specific resolve function.

    bool has_resolve;

    // Whether this target has a specific code fill function.

    bool has_code_fill;

    // Whether an object file with no .note.GNU-stack sections implies

    // that the stack should be executable.

    bool is_default_stack_executable;

    // Whether a relocation to a merged section can be processed to

    // retrieve the contents.

    bool can_icf_inline_merge_sections;

    // Prefix character to strip when checking for wrapping.

    char wrap_char;

    // The default dynamic linker name.

    const char* dynamic_linker;

    // The default text segment address.

    uint64_t default_text_segment_address;

    // The ABI specified page size.

    uint64_t abi_pagesize;

    // The common page size used by actual implementations.

    uint64_t common_pagesize;

    // The special section index for small common symbols; SHN_UNDEF

    // if none.

    elfcpp::Elf_Half small_common_shndx;

    // The special section index for large common symbols; SHN_UNDEF

    // if none.

    elfcpp::Elf_Half large_common_shndx;

    // Section flags for small common section.

    elfcpp::Elf_Xword small_common_section_flags;

    // Section flags for large common section.

    elfcpp::Elf_Xword large_common_section_flags;

    // Name of attributes section if it is not ".gnu.attributes".

    const char* attributes_section;

    // Vendor name of vendor attributes.

    const char* attributes_vendor;

  };

  Target(const Target_info* pti)

    : pti_(pti), processor_specific_flags_(0),

      are_processor_specific_flags_set_(false), osabi_(elfcpp::ELFOSABI_NONE)

  { }

  // Virtual function which may be implemented by the child class.

  virtual void

  do_new_output_section(Output_section*) const

  { }

  // Virtual function which may be implemented by the child class.

  virtual void

  do_finalize_sections(Layout*, const Input_objects*, Symbol_table*)

  { }

  // Virtual function which may be implemented by the child class.

  virtual uint64_t

  do_dynsym_value(const Symbol*) const

  { gold_unreachable(); }

  // Virtual function which must be implemented by the child class if

  // needed.

  virtual std::string

  do_code_fill(section_size_type) const

  { gold_unreachable(); }

  // Virtual function which may be implemented by the child class.

  virtual bool

  do_is_defined_by_abi(const Symbol*) const

  { return false; }

  // Adjust the output file header before it is written out.  VIEW

  // points to the header in external form.  LEN is the length, and

  // will be one of the values of elfcpp::Elf_sizes<size>::ehdr_size.

  // By default, we set the EI_OSABI field if requested (in

  // Sized_target).

  virtual void

  do_adjust_elf_header(unsigned char*, int) const = 0;

  // Virtual function which may be overridden by the child class.

  virtual bool

  do_is_local_label_name(const char*) const;

  // Virtual function that must be overridden by a target which uses

  // target specific relocations.

  virtual unsigned int

  do_reloc_symbol_index(void*, unsigned int) const

  { gold_unreachable(); }

  // Virtual function that must be overridden by a target which uses

  // target specific relocations.

  virtual uint64_t

  do_reloc_addend(void*, unsigned int, uint64_t) const

  { gold_unreachable(); }

  // Virtual functions that must be overridden by a target that uses

  // STT_GNU_IFUNC symbols.

  virtual uint64_t

  do_plt_address_for_global(const Symbol*) const

  { gold_unreachable(); }

  virtual uint64_t

  do_plt_address_for_local(const Relobj*, unsigned int) const

  { gold_unreachable(); }

  // Virtual function which may be overriden by the child class.

  virtual bool

  do_can_check_for_function_pointers() const

  { return false; }

  // Virtual function which may be overridden by the child class.  We

  // recognize some default sections for which we don't care whether

  // they have function pointers.

  virtual bool

  do_section_may_have_icf_unsafe_pointers(const char* section_name) const

  {

    // We recognize sections for normal vtables, construction vtables and

    // EH frames.

    return (!is_prefix_of(".rodata._ZTV", section_name)

            && !is_prefix_of(".data.rel.ro._ZTV", section_name)

            && !is_prefix_of(".rodata._ZTC", section_name)

            && !is_prefix_of(".data.rel.ro._ZTC", section_name)

            && !is_prefix_of(".eh_frame", section_name));

  }

  virtual uint64_t

  do_ehframe_datarel_base() const

  { gold_unreachable(); }

  // Virtual function which may be overridden by the child class.  The

  // default implementation is that any function not defined by the

  // ABI is a call to a non-split function.

  virtual bool

  do_is_call_to_non_split(const Symbol* sym, unsigned int) const;

  // Virtual function which may be overridden by the child class.

  virtual void

  do_calls_non_split(Relobj* object, unsigned int, section_offset_type,

                     section_size_type, unsigned char*, section_size_type,

                     std::string*, std::string*) const;

  // make_elf_object hooks.  There are four versions of these for

  // different address sizes and endianness.

  // Set processor specific flags.

  void

  set_processor_specific_flags(elfcpp::Elf_Word flags)

  {

    this->processor_specific_flags_ = flags;

    this->are_processor_specific_flags_set_ = true;

  }

#ifdef HAVE_TARGET_32_LITTLE

  // Virtual functions which may be overridden by the child class.

  virtual Object*

  do_make_elf_object(const std::string&, Input_file*, off_t,

                     const elfcpp::Ehdr<32, false>&);

#endif

#ifdef HAVE_TARGET_32_BIG

  // Virtual functions which may be overridden by the child class.

  virtual Object*

  do_make_elf_object(const std::string&, Input_file*, off_t,

                     const elfcpp::Ehdr<32, true>&);

#endif

#ifdef HAVE_TARGET_64_LITTLE

  // Virtual functions which may be overridden by the child class.

  virtual Object*

  do_make_elf_object(const std::string&, Input_file*, off_t,

                     const elfcpp::Ehdr<64, false>& ehdr);

#endif

#ifdef HAVE_TARGET_64_BIG

  // Virtual functions which may be overridden by the child class.

  virtual Object*

  do_make_elf_object(const std::string& name, Input_file* input_file,

                     off_t offset, const elfcpp::Ehdr<64, true>& ehdr);

#endif

  // Virtual functions which may be overridden by the child class.

  virtual Output_section*

  do_make_output_section(const char* name, elfcpp::Elf_Word type,

                         elfcpp::Elf_Xword flags);

  // Virtual function which may be overridden by the child class.

  virtual bool

  do_may_relax() const

  { return parameters->options().relax(); }

  // Virtual function which may be overridden by the child class.

  virtual bool

  do_relax(int, const Input_objects*, Symbol_table*, Layout*, const Task*)

  { return false; }

  // A function for targets to call.  Return whether BYTES/LEN matches

  // VIEW/VIEW_SIZE at OFFSET.

  bool

  match_view(const unsigned char* view, section_size_type view_size,

             section_offset_type offset, const char* bytes, size_t len) const;

  // Set the contents of a VIEW/VIEW_SIZE to nops starting at OFFSET

  // for LEN bytes.

  void

  set_view_to_nop(unsigned char* view, section_size_type view_size,

                  section_offset_type offset, size_t len) const;

  // This must be overridden by the child class if it has target-specific

  // attributes subsection in the attribute section. 

  virtual int

  do_attribute_arg_type(int) const

  { gold_unreachable(); }

  // This may be overridden by the child class.

  virtual int

  do_attributes_order(int num) const

  { return num; }

  // This may be overridden by the child class.

  virtual void

  do_select_as_default_target()

  { }

 private:

  // The implementations of the four do_make_elf_object virtual functions are

  // almost identical except for their sizes and endianness.  We use a template.

  // for their implementations.

  template<int size, bool big_endian>

  inline Object*

  do_make_elf_object_implementation(const std::string&, Input_file*, off_t,

                                    const elfcpp::Ehdr<size, big_endian>&);

  Target(const Target&);

  Target& operator=(const Target&);

  // The target information.

  const Target_info* pti_;

  // Processor-specific flags.

  elfcpp::Elf_Word processor_specific_flags_;

  // Whether the processor-specific flags are set at least once.

  bool are_processor_specific_flags_set_;

  // If not ELFOSABI_NONE, the value to put in the EI_OSABI field of

  // the ELF header.  This is handled at this level because it is

  // OS-specific rather than processor-specific.

  elfcpp::ELFOSABI osabi_;

};

// The abstract class for a specific size and endianness of target.

// Each actual target implementation class should derive from an

// instantiation of Sized_target.

template<int size, bool big_endian>

class Sized_target : public Target

{

 public:

  // Make a new symbol table entry for the target.  This should be

  // overridden by a target which needs additional information in the

  // symbol table.  This will only be called if has_make_symbol()

  // returns true.

  virtual Sized_symbol<size>*

  make_symbol() const

  { gold_unreachable(); }

  // Resolve a symbol for the target.  This should be overridden by a

  // target which needs to take special action.  TO is the

  // pre-existing symbol.  SYM is the new symbol, seen in OBJECT.

  // VERSION is the version of SYM.  This will only be called if

  // has_resolve() returns true.

  virtual void

  resolve(Symbol*, const elfcpp::Sym<size, big_endian>&, Object*,

          const char*)

  { gold_unreachable(); }

  // Process the relocs for a section, and record information of the

  // mapping from source to destination sections. This mapping is later

  // used to determine unreferenced garbage sections. This procedure is

  // only called during garbage collection.

  virtual void

  gc_process_relocs(Symbol_table* symtab,

                    Layout* layout,

                    Sized_relobj_file<size, big_endian>* object,

                    unsigned int data_shndx,

                    unsigned int sh_type,

                    const unsigned char* prelocs,

                    size_t reloc_count,

                    Output_section* output_section,

                    bool needs_special_offset_handling,

                    size_t local_symbol_count,

                    const unsigned char* plocal_symbols) = 0;

  // Scan the relocs for a section, and record any information

  // required for the symbol.  SYMTAB is the symbol table.  OBJECT is

  // the object in which the section appears.  DATA_SHNDX is the

  // section index that these relocs apply to.  SH_TYPE is the type of

  // the relocation section, SHT_REL or SHT_RELA.  PRELOCS points to

  // the relocation data.  RELOC_COUNT is the number of relocs.

  // LOCAL_SYMBOL_COUNT is the number of local symbols.

  // OUTPUT_SECTION is the output section.

  // NEEDS_SPECIAL_OFFSET_HANDLING is true if offsets to the output

  // sections are not mapped as usual.  PLOCAL_SYMBOLS points to the

  // local symbol data from OBJECT.  GLOBAL_SYMBOLS is the array of

  // pointers to the global symbol table from OBJECT.

  virtual void

  scan_relocs(Symbol_table* symtab,

              Layout* layout,