path: root/gold/object.h

// object.h -- support for an object file for linking in gold  -*- C++ -*-

// Copyright 2006, 2007 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.

#ifndef GOLD_OBJECT_H
#define GOLD_OBJECT_H

#include <string>
#include <vector>

#include "elfcpp.h"
#include "elfcpp_file.h"
#include "fileread.h"
#include "target.h"

namespace gold
{

class General_options;
class Layout;
class Output_section;
class Output_file;
class Dynobj;

template<typename Stringpool_char>
class Stringpool_template;

// Data to pass from read_symbols() to add_symbols().

struct Read_symbols_data
{
  // Section headers.
  File_view* section_headers;
  // Section names.
  File_view* section_names;
  // Size of section name data in bytes.
  off_t section_names_size;
  // Symbol data.
  File_view* symbols;
  // Size of symbol data in bytes.
  off_t symbols_size;
  // Symbol names.
  File_view* symbol_names;
  // Size of symbol name data in bytes.
  off_t symbol_names_size;

  // Version information.  This is only used on dynamic objects.
  // Version symbol data (from SHT_GNU_versym section).
  File_view* versym;
  off_t versym_size;
  // Version definition data (from SHT_GNU_verdef section).
  File_view* verdef;
  off_t verdef_size;
  unsigned int verdef_info;
  // Needed version data  (from SHT_GNU_verneed section).
  File_view* verneed;
  off_t verneed_size;
  unsigned int verneed_info;
};

// Data about a single relocation section.  This is read in
// read_relocs and processed in scan_relocs.

struct Section_relocs
{
  // Index of reloc section.
  unsigned int reloc_shndx;
  // Index of section that relocs apply to.
  unsigned int data_shndx;
  // Contents of reloc section.
  File_view* contents;
  // Reloc section type.
  unsigned int sh_type;
  // Number of reloc entries.
  size_t reloc_count;
};

// Relocations in an object file.  This is read in read_relocs and
// processed in scan_relocs.

struct Read_relocs_data
{
  typedef std::vector<Section_relocs> Relocs_list;
  // The relocations.
  Relocs_list relocs;
  // The local symbols.
  File_view* local_symbols;
};

// Object is an abstract base class which represents either a 32-bit
// or a 64-bit input object.  This can be a regular object file
// (ET_REL) or a shared object (ET_DYN).

class Object
{
 public:
  // NAME is the name of the object as we would report it to the user
  // (e.g., libfoo.a(bar.o) if this is in an archive.  INPUT_FILE is
  // used to read the file.  OFFSET is the offset within the input
  // file--0 for a .o or .so file, something else for a .a file.
  Object(const std::string& name, Input_file* input_file, bool is_dynamic,
	 off_t offset = 0)
    : name_(name), input_file_(input_file), offset_(offset), shnum_(-1U),
      is_dynamic_(is_dynamic), target_(NULL)
  { }

  virtual ~Object()
  { }

  // Return the name of the object as we would report it to the tuser.
  const std::string&
  name() const
  { return this->name_; }

  // Return whether this is a dynamic object.
  bool
  is_dynamic() const
  { return this->is_dynamic_; }

  // Return the target structure associated with this object.
  Target*
  target() const
  { return this->target_; }

  // Lock the underlying file.
  void
  lock()
  { this->input_file_->file().lock(); }

  // Unlock the underlying file.
  void
  unlock()
  { this->input_file_->file().unlock(); }

  // Return whether the underlying file is locked.
  bool
  is_locked() const
  { return this->input_file_->file().is_locked(); }

  // Return the sized target structure associated with this object.
  // This is like the target method but it returns a pointer of
  // appropriate checked type.
  template<int size, bool big_endian>
  Sized_target<size, big_endian>*
  sized_target(ACCEPT_SIZE_ENDIAN_ONLY);

  // Get the number of sections.
  unsigned int
  shnum() const
  { return this->shnum_; }

  // Return a view of the contents of a section.  Set *PLEN to the
  // size.  CACHE is a hint as in File_read::get_view.
  const unsigned char*
  section_contents(unsigned int shndx, off_t* plen, bool cache);

  // Return the name of a section given a section index.  This is only
  // used for error messages.
  std::string
  section_name(unsigned int shndx)
  { return this->do_section_name(shndx); }

  // Return the section flags given a section index.
  uint64_t
  section_flags(unsigned int shndx)
  { return this->do_section_flags(shndx); }

  // Read the symbol information.
  void
  read_symbols(Read_symbols_data* sd)
  { return this->do_read_symbols(sd); }

  // Pass sections which should be included in the link to the Layout
  // object, and record where the sections go in the output file.
  void
  layout(Symbol_table* symtab, Layout* layout, Read_symbols_data* sd)
  { this->do_layout(symtab, layout, sd); }

  // Add symbol information to the global symbol table.
  void
  add_symbols(Symbol_table* symtab, Read_symbols_data* sd)
  { this->do_add_symbols(symtab, sd); }

  // Functions and types for the elfcpp::Elf_file interface.  This
  // permit us to use Object as the File template parameter for
  // elfcpp::Elf_file.

  // The View class is returned by view.  It must support a single
  // method, data().  This is trivial, because get_view does what we
  // need.
  class View
  {
   public:
    View(const unsigned char* p)
      : p_(p)
    { }

    const unsigned char*
    data() const
    { return this->p_; }

   private:
    const unsigned char* p_;
  };

  // Return a View.
  View
  view(off_t file_offset, off_t data_size)
  { return View(this->get_view(file_offset, data_size, true)); }

  // Report an error.
  void
  error(const char* format, ...) ATTRIBUTE_PRINTF_2;

  // A location in the file.
  struct Location
  {
    off_t file_offset;
    off_t data_size;

    Location(off_t fo, off_t ds)
      : file_offset(fo), data_size(ds)
    { }
  };

  // Get a View given a Location.
  View view(Location loc)
  { return View(this->get_view(loc.file_offset, loc.data_size, true)); }

 protected:
  // Read the symbols--implemented by child class.
  virtual void
  do_read_symbols(Read_symbols_data*) = 0;

  // Lay out sections--implemented by child class.
  virtual void
  do_layout(Symbol_table*, Layout*, Read_symbols_data*) = 0;

  // Add symbol information to the global symbol table--implemented by
  // child class.
  virtual void
  do_add_symbols(Symbol_table*, Read_symbols_data*) = 0;

  // Return the location of the contents of a section.  Implemented by
  // child class.
  virtual Location
  do_section_contents(unsigned int shndx) = 0;

  // Get the name of a section--implemented by child class.
  virtual std::string
  do_section_name(unsigned int shndx) = 0;

  // Get section flags--implemented by child class.
  virtual uint64_t
  do_section_flags(unsigned int shndx) = 0;

  // Get the file.
  Input_file*
  input_file() const
  { return this->input_file_; }

  // Get the offset into the file.
  off_t
  offset() const
  { return this->offset_; }

  // Get a view into the underlying file.
  const unsigned char*
  get_view(off_t start, off_t size, bool cache)
  {
    return this->input_file_->file().get_view(start + this->offset_, size,
					      cache);
  }

  // Get a lasting view into the underlying file.
  File_view*
  get_lasting_view(off_t start, off_t size, bool cache)
  {
    return this->input_file_->file().get_lasting_view(start + this->offset_,
						      size, cache);
  }

  // Read data from the underlying file.
  void
  read(off_t start, off_t size, void* p)
  { this->input_file_->file().read(start + this->offset_, size, p); }

  // Set the target.
  void
  set_target(int machine, int size, bool big_endian, int osabi,
	     int abiversion);

  // Set the number of sections.
  void
  set_shnum(int shnum)
  { this->shnum_ = shnum; }

  // Functions used by both Sized_relobj and Sized_dynobj.

  // Read the section data into a Read_symbols_data object.
  template<int size, bool big_endian>
  void
  read_section_data(elfcpp::Elf_file<size, big_endian, Object>*,
		    Read_symbols_data*);

  // If NAME is the name of a special .gnu.warning section, arrange
  // for the warning to be issued.  SHNDX is the section index.
  // Return whether it is a warning section.
  bool
  handle_gnu_warning_section(const char* name, unsigned int shndx,
			     Symbol_table*);

 private:
  // This class may not be copied.
  Object(const Object&);
  Object& operator=(const Object&);

  // Name of object as printed to user.
  std::string name_;
  // For reading the file.
  Input_file* input_file_;
  // Offset within the file--0 for an object file, non-0 for an
  // archive.
  off_t offset_;
  // Number of input sections.
  unsigned int shnum_;
  // Whether this is a dynamic object.
  bool is_dynamic_;
  // Target functions--may be NULL if the target is not known.
  Target* target_;
};

// Implement sized_target inline for efficiency.  This approach breaks
// static type checking, but is made safe using asserts.

template<int size, bool big_endian>
inline Sized_target<size, big_endian>*
Object::sized_target(ACCEPT_SIZE_ENDIAN_ONLY)
{
  gold_assert(this->target_->get_size() == size);
  gold_assert(this->target_->is_big_endian() ? big_endian : !big_endian);
  return static_cast<Sized_target<size, big_endian>*>(this->target_);
}

// A regular object (ET_REL).  This is an abstract base class itself.
// The implementation is the template class Sized_relobj.

class Relobj : public Object
{
 public:
  Relobj(const std::string& name, Input_file* input_file, off_t offset = 0)
    : Object(name, input_file, false, offset)
  { }

  // Read the relocs.
  void
  read_relocs(Read_relocs_data* rd)
  { return this->do_read_relocs(rd); }

  // Scan the relocs and adjust the symbol table.
  void
  scan_relocs(const General_options& options, Symbol_table* symtab,
	      Layout* layout, Read_relocs_data* rd)
  { return this->do_scan_relocs(options, symtab, layout, rd); }

  // Initial local symbol processing: set the offset where local
  // symbol information will be stored; add local symbol names to
  // *POOL; return the new local symbol index.
  unsigned int
  finalize_local_symbols(unsigned int index, off_t off,
			 Stringpool_template<char>* pool)
  { return this->do_finalize_local_symbols(index, off, pool); }

  // Relocate the input sections and write out the local symbols.
  void
  relocate(const General_options& options, const Symbol_table* symtab,
	   const Layout* layout, Output_file* of)
  { return this->do_relocate(options, symtab, layout, of); }

  // Return whether an input section is being included in the link.
  bool
  is_section_included(unsigned int shndx) const
  {
    gold_assert(shndx < this->map_to_output_.size());
    return this->map_to_output_[shndx].output_section != NULL;
  }

  // Given a section index, return the corresponding Output_section
  // (which will be NULL if the section is not included in the link)
  // and set *POFF to the offset within that section.
  inline Output_section*
  output_section(unsigned int shndx, off_t* poff) const;

  // Set the offset of an input section within its output section.
  void
  set_section_offset(unsigned int shndx, off_t off)
  {
    gold_assert(shndx < this->map_to_output_.size());
    this->map_to_output_[shndx].offset = off;
  }

 protected:
  // What we need to know to map an input section to an output
  // section.  We keep an array of these, one for each input section,
  // indexed by the input section number.
  struct Map_to_output
  {
    // The output section.  This is NULL if the input section is to be
    // discarded.
    Output_section* output_section;
    // The offset within the output section.  This is -1 if the
    // section requires special handling.
    off_t offset;
  };

  // Read the relocs--implemented by child class.
  virtual void
  do_read_relocs(Read_relocs_data*) = 0;

  // Scan the relocs--implemented by child class.
  virtual void
  do_scan_relocs(const General_options&, Symbol_table*, Layout*,
		 Read_relocs_data*) = 0;

  // Finalize local symbols--implemented by child class.
  virtual unsigned int
  do_finalize_local_symbols(unsigned int, off_t,
			    Stringpool_template<char>*) = 0;

  // Relocate the input sections and write out the local
  // symbols--implemented by child class.
  virtual void
  do_relocate(const General_options& options, const Symbol_table* symtab,
	      const Layout*, Output_file* of) = 0;

  // Return the vector mapping input sections to output sections.
  std::vector<Map_to_output>&
  map_to_output()
  { return this->map_to_output_; }

  const std::vector<Map_to_output>&
  map_to_output() const
  { return this->map_to_output_; }

 private:
  // Mapping from input sections to output section.
  std::vector<Map_to_output> map_to_output_;
};

// Implement Object::output_section inline for efficiency.
inline Output_section*
Relobj::output_section(unsigned int shndx, off_t* poff) const
{
  gold_assert(shndx < this->map_to_output_.size());
  const Map_to_output& mo(this->map_to_output_[shndx]);
  *poff = mo.offset;
  return mo.output_section;
}

// This POD class is holds the value of a symbol.  This is used for
// local symbols, and for all symbols during relocation processing.
// In order to process relocs we need to be able to handle SHF_MERGE
// sections correctly.

template<int size>
class Symbol_value
{
 public:
  typedef typename elfcpp::Elf_types<size>::Elf_Addr Value;

  Symbol_value()
    : output_symtab_index_(0), input_shndx_(0), is_section_symbol_(false),
      needs_output_address_(false), value_(0)
  { }

  // Get the value of this symbol.  OBJECT is the object in which this
  // symbol is defined, and ADDEND is an addend to add to the value.
  template<bool big_endian>
  Value
  value(const Sized_relobj<size, big_endian>* object, Value addend) const
  {
    if (!this->needs_output_address_)
      return this->value_ + addend;
    return object->local_value(this->input_shndx_, this->value_,
			       this->is_section_symbol_, addend);
  }

  // Set the value of this symbol in the output symbol table.
  void
  set_output_value(Value value)
  {
    this->value_ = value;
    this->needs_output_address_ = false;
  }

  // If this symbol is mapped to an output section which requires
  // special handling to determine the output value, we store the
  // value of the symbol in the input file.  This is used for
  // SHF_MERGE sections.
  void
  set_input_value(Value value)
  {
    this->value_ = value;
    this->needs_output_address_ = true;
  }

  // Return whether this symbol should go into the output symbol
  // table.
  bool
  needs_output_symtab_entry() const
  {
    gold_assert(this->output_symtab_index_ != 0);
    return this->output_symtab_index_ != -1U;
  }

  // Return the index in the output symbol table.
  unsigned int
  output_symtab_index() const
  {
    gold_assert(this->output_symtab_index_ != 0);
    return this->output_symtab_index_;
  }

  // Set the index in the output symbol table.
  void
  set_output_symtab_index(unsigned int i)
  {
    gold_assert(this->output_symtab_index_ == 0);
    this->output_symtab_index_ = i;
  }

  // Record that this symbol should not go into the output symbol
  // table.
  void
  set_no_output_symtab_entry()
  {
    gold_assert(this->output_symtab_index_ == 0);
    this->output_symtab_index_ = -1U;
  }

  // Set the index of the input section in the input file.
  void
  set_input_shndx(unsigned int i)
  { this->input_shndx_ = i; }

  // Record that this is a section symbol.
  void
  set_is_section_symbol()
  { this->is_section_symbol_ = true; }

 private:
  // The index of this local symbol in the output symbol table.  This
  // will be -1 if the symbol should not go into the symbol table.
  unsigned int output_symtab_index_;
  // The section index in the input file in which this symbol is
  // defined.
  unsigned int input_shndx_ : 30;
  // Whether this is a STT_SECTION symbol.
  bool is_section_symbol_ : 1;
  // Whether getting the value of this symbol requires calling an
  // Output_section method.  For example, this will be true of a
  // symbol in a SHF_MERGE section.
  bool needs_output_address_ : 1;
  // The value of the symbol.  If !needs_output_address_, this is the
  // value in the output file.  If needs_output_address_, this is the
  // value in the input file.
  Value value_;
};

// A regular object file.  This is size and endian specific.

template<int size, bool big_endian>
class Sized_relobj : public Relobj
{
 public:
  typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
  typedef std::vector<Symbol_value<size> > Local_values;

  Sized_relobj(const std::string& name, Input_file* input_file, off_t offset,
	       const typename elfcpp::Ehdr<size, big_endian>&);

  ~Sized_relobj();

  // Set up the object file based on the ELF header.
  void
  setup(const typename elfcpp::Ehdr<size, big_endian>&);

  // Return the index of local symbol SYM in the ordinary symbol
  // table.  A value of -1U means that the symbol is not being output.
  unsigned int
  symtab_index(unsigned int sym) const
  {
    gold_assert(sym < this->local_values_.size());
    return this->local_values_[sym].output_symtab_index();
  }

  // Read the symbols.
  void
  do_read_symbols(Read_symbols_data*);

  // Lay out the input sections.
  void
  do_layout(Symbol_table*, Layout*, Read_symbols_data*);

  // Add the symbols to the symbol table.
  void
  do_add_symbols(Symbol_table*, Read_symbols_data*);

  // Read the relocs.
  void
  do_read_relocs(Read_relocs_data*);

  // Scan the relocs and adjust the symbol table.
  void
  do_scan_relocs(const General_options&, Symbol_table*, Layout*,
		 Read_relocs_data*);

  // Finalize the local symbols.
  unsigned int
  do_finalize_local_symbols(unsigned int, off_t,
			    Stringpool_template<char>*);

  // Relocate the input sections and write out the local symbols.
  void
  do_relocate(const General_options& options, const Symbol_table* symtab,
	      const Layout*, Output_file* of);

  // Get the name of a section.
  std::string
  do_section_name(unsigned int shndx)
  { return this->elf_file_.section_name(shndx); }

  // Return the location of the contents of a section.
  Object::Location
  do_section_contents(unsigned int shndx)
  { return this->elf_file_.section_contents(shndx); }

  // Return section flags.
  uint64_t
  do_section_flags(unsigned int shndx)
  { return this->elf_file_.section_flags(shndx); }

  // Return the appropriate Sized_target structure.
  Sized_target<size, big_endian>*
  sized_target()
  {
    return this->Object::sized_target
      SELECT_SIZE_ENDIAN_NAME(size, big_endian) (
          SELECT_SIZE_ENDIAN_ONLY(size, big_endian));
  }

  // Return the value of a local symbol define in input section SHNDX,
  // with value VALUE, adding addend ADDEND.  IS_SECTION_SYMBOL
  // indicates whether the symbol is a section symbol.  This handles
  // SHF_MERGE sections.
  Address
  local_value(unsigned int shndx, Address value, bool is_section_symbol,
	      Address addend) const;

 private:
  // For convenience.
  typedef Sized_relobj<size, big_endian> This;
  static const int ehdr_size = elfcpp::Elf_sizes<size>::ehdr_size;
  static const int shdr_size = elfcpp::Elf_sizes<size>::shdr_size;
  static const int sym_size = elfcpp::Elf_sizes<size>::sym_size;
  typedef elfcpp::Shdr<size, big_endian> Shdr;

  // Find the SHT_SYMTAB section, given the section headers.
  void
  find_symtab(const unsigned char* pshdrs);

  // Whether to include a section group in the link.
  bool
  include_section_group(Layout*, unsigned int,
			const elfcpp::Shdr<size, big_endian>&,
			std::vector<bool>*);

  // Whether to include a linkonce section in the link.
  bool
  include_linkonce_section(Layout*, const char*,
			   const elfcpp::Shdr<size, big_endian>&);

  // Views and sizes when relocating.
  struct View_size
  {
    unsigned char* view;
    typename elfcpp::Elf_types<size>::Elf_Addr address;
    off_t offset;
    off_t view_size;
  };

  typedef std::vector<View_size> Views;

  // Write section data to the output file.  Record the views and
  // sizes in VIEWS for use when relocating.
  void
  write_sections(const unsigned char* pshdrs, Output_file*, Views*);

  // Relocate the sections in the output file.
  void
  relocate_sections(const General_options& options, const Symbol_table*,
		    const Layout*, const unsigned char* pshdrs, Views*);

  // Write out the local symbols.
  void
  write_local_symbols(Output_file*,
		      const Stringpool_template<char>*);

  // General access to the ELF file.
  elfcpp::Elf_file<size, big_endian, Object> elf_file_;
  // Index of SHT_SYMTAB section.
  unsigned int symtab_shndx_;
  // The number of local symbols.
  unsigned int local_symbol_count_;
  // The number of local symbols which go into the output file.
  unsigned int output_local_symbol_count_;
  // The entries in the symbol table for the external symbols.
  Symbol** symbols_;
  // File offset for local symbols.
  off_t local_symbol_offset_;
  // Values of local symbols.
  Local_values local_values_;
};

// A class to manage the list of all objects.

class Input_objects
{
 public:
  Input_objects()
    : relobj_list_(), dynobj_list_(), target_(NULL), sonames_()
  { }

  // The type of the list of input relocateable objects.
  typedef std::vector<Relobj*> Relobj_list;
  typedef Relobj_list::const_iterator Relobj_iterator;

  // The type of the list of input dynamic objects.
  typedef std::vector<Dynobj*> Dynobj_list;
  typedef Dynobj_list::const_iterator Dynobj_iterator;

  // Add an object to the list.  Return true if all is well, or false
  // if this object should be ignored.
  bool
  add_object(Object*);

  // Get the target we should use for the output file.
  Target*
  target() const
  { return this->target_; }

  // Iterate over all regular objects.

  Relobj_iterator
  relobj_begin() const
  { return this->relobj_list_.begin(); }

  Relobj_iterator
  relobj_end() const
  { return this->relobj_list_.end(); }

  // Iterate over all dynamic objects.

  Dynobj_iterator
  dynobj_begin() const
  { return this->dynobj_list_.begin(); }

  Dynobj_iterator
  dynobj_end() const
  { return this->dynobj_list_.end(); }

  // Return whether we have seen any dynamic objects.
  bool
  any_dynamic() const
  { return !this->dynobj_list_.empty(); }

 private:
  Input_objects(const Input_objects&);
  Input_objects& operator=(const Input_objects&);

  // The list of ordinary objects included in the link.
  Relobj_list relobj_list_;
  // The list of dynamic objects included in the link.
  Dynobj_list dynobj_list_;
  // The target.
  Target* target_;
  // SONAMEs that we have seen.
  Unordered_set<std::string> sonames_;
};

// Some of the information we pass to the relocation routines.  We
// group this together to avoid passing a dozen different arguments.

template<int size, bool big_endian>
struct Relocate_info
{
  // Command line options.
  const General_options* options;
  // Symbol table.
  const Symbol_table* symtab;
  // Layout.
  const Layout* layout;
  // Object being relocated.
  Sized_relobj<size, big_endian>* object;
  // Number of local symbols.
  unsigned int local_symbol_count;
  // Values of local symbols.
  const typename Sized_relobj<size, big_endian>::Local_values* local_values;
  // Global symbols.
  const Symbol* const * symbols;
  // Section index of relocation section.
  unsigned int reloc_shndx;
  // Section index of section being relocated.
  unsigned int data_shndx;

  // Return a string showing the location of a relocation.  This is
  // only used for error messages.
  std::string
  location(size_t relnum, off_t reloffset) const;
};

// Return an Object appropriate for the input file.  P is BYTES long,
// and holds the ELF header.

extern Object*
make_elf_object(const std::string& name, Input_file*,
		off_t offset, const unsigned char* p,
		off_t bytes);

} // end namespace gold

#endif // !defined(GOLD_OBJECT_H)