gold/script.h

// script.h -- handle linker scripts for gold   -*- C++ -*-

// Copyright 2006, 2007, 2008 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.

// We implement a subset of the original GNU ld linker script language
// for compatibility.  The goal is not to implement the entire
// language.  It is merely to implement enough to handle common uses.
// In particular we need to handle /usr/lib/libc.so on a typical
// GNU/Linux system, and we want to handle linker scripts used by the
// Linux kernel build.

#ifndef GOLD_SCRIPT_H
#define GOLD_SCRIPT_H

#include <cstdio>
#include <string>
#include <vector>

#include "script-sections.h"

namespace gold
{

class General_options;
class Command_line;
class Symbol_table;
class Layout;
class Mapfile;
class Input_argument;
class Input_objects;
class Input_group;
class Input_file;
class Output_segment;
class Task_token;
class Workqueue;
struct Version_dependency_list;
struct Version_expression_list;
struct Version_tree;

// This class represents an expression in a linker script.

class Expression
{
 protected:
  // These should only be created by child classes.
  Expression()
  { }

 public:
  virtual ~Expression()
  { }

  // Return the value of the expression which is not permitted to
  // refer to the dot symbol.  CHECK_ASSERTIONS is true if we should
  // check whether assertions are true.
  uint64_t
  eval(const Symbol_table*, const Layout*, bool check_assertions);

  // Return the value of an expression which is permitted to refer to
  // the dot symbol.  DOT_VALUE is the absolute value of the dot
  // symbol.  DOT_SECTION is the section in which dot is defined; it
  // should be NULL if the dot symbol has an absolute value (e.g., is
  // defined in a SECTIONS clause outside of any output section
  // definition).  This sets *RESULT_SECTION to indicate where the
  // value is defined.  If the value is absolute *RESULT_SECTION will
  // be NULL.  Note that the returned value is still an absolute
  // value; to get a section relative value the caller must subtract
  // the section address.
  uint64_t
  eval_with_dot(const Symbol_table*, const Layout*, bool check_assertions,
		uint64_t dot_value, Output_section* dot_section,
		Output_section** result_section);

  // Return the value of an expression which may or may not be
  // permitted to refer to the dot symbol, depending on
  // is_dot_available.
  uint64_t
  eval_maybe_dot(const Symbol_table*, const Layout*, bool check_assertions,
		 bool is_dot_available, uint64_t dot_value,
		 Output_section* dot_section,
		 Output_section** result_section);

  // Print the expression to the FILE.  This is for debugging.
  virtual void
  print(FILE*) const = 0;

 protected:
  struct Expression_eval_info;

 public:
  // Compute the value of the expression (implemented by child class).
  // This is public rather than protected because it is called
  // directly by children of Expression on other Expression objects.
  virtual uint64_t
  value(const Expression_eval_info*) = 0;

 private:
  // May not be copied.
  Expression(const Expression&);
  Expression& operator=(const Expression&);
};


// Version_script_info stores information parsed from the version
// script, either provided by --version-script or as part of a linker
// script.  A single Version_script_info object per target is owned by
// Script_options.

class Version_script_info
{
 public:
  ~Version_script_info();

  // Clear everything.
  void
  clear();

  // Return whether any version were defined in the version script.
  bool
  empty() const
  { return this->version_trees_.empty(); }

  // Return the version associated with the given symbol name.
  // Strings are allocated out of the stringpool given in the
  // constructor.  Strings are allocated out of the stringpool given
  // in the constructor.
  const std::string&
  get_symbol_version(const char* symbol) const
  { return get_symbol_version_helper(symbol, true); }

  // Return whether this symbol matches the local: section of a
  // version script (it doesn't matter which).
  bool
  symbol_is_local(const char* symbol) const
  {
    return (get_symbol_version(symbol).empty()
            && !get_symbol_version_helper(symbol, false).empty());
  }

  // Return the names of versions defined in the version script.
  // Strings are allocated out of the stringpool given in the
  // constructor.
  std::vector<std::string>
  get_versions() const;

  // Return the list of dependencies for this version.
  std::vector<std::string>
  get_dependencies(const char* version) const;

  // The following functions should only be used by the bison helper
  // functions.  They allocate new structs whose memory belongs to
  // Version_script_info.  The bison functions copy the information
  // from the version script into these structs.
  struct Version_dependency_list*
  allocate_dependency_list();

  struct Version_expression_list*
  allocate_expression_list();

  struct Version_tree*
  allocate_version_tree();

  // Print contents to the FILE.  This is for debugging.
  void
  print(FILE*) const;

 private:
  void
  print_expression_list(FILE* f, const Version_expression_list*) const;

  const std::string& get_symbol_version_helper(const char* symbol,
                                               bool check_global) const;

  std::vector<struct Version_dependency_list*> dependency_lists_;
  std::vector<struct Version_expression_list*> expression_lists_;
  std::vector<struct Version_tree*> version_trees_;
};

// This class manages assignments to symbols.  These can appear in
// three different locations in scripts: outside of a SECTIONS clause,
// within a SECTIONS clause, and within an output section definition
// within a SECTIONS clause.  This can also appear on the command line
// via the --defsym command line option.

class Symbol_assignment
{
 public:
  Symbol_assignment(const char* name, size_t namelen, Expression* val,
		    bool provide, bool hidden)
    : name_(name, namelen), val_(val), provide_(provide), hidden_(hidden),
      sym_(NULL)
  { }

  // Add the symbol to the symbol table.
  void
  add_to_table(Symbol_table*);

  // Finalize the symbol value.
  void
  finalize(Symbol_table*, const Layout*);

  // Finalize the symbol value when it can refer to the dot symbol.
  void
  finalize_with_dot(Symbol_table*, const Layout*, uint64_t dot_value,
		    Output_section* dot_section);

  // Set the symbol value, but only if the value is absolute.  This is
  // used while processing a SECTIONS clause.  We assume that dot is
  // an absolute value here.  We do not check assertions.
  void
  set_if_absolute(Symbol_table*, const Layout*, bool is_dot_available,
		  uint64_t dot_value);

  // Print the assignment to the FILE.  This is for debugging.
  void
  print(FILE*) const;

 private:
  // Shared by finalize and finalize_with_dot.
  void
  finalize_maybe_dot(Symbol_table*, const Layout*, bool is_dot_available,
		     uint64_t dot_value, Output_section* dot_section);

  // Sized version of finalize.
  template<int size>
  void
  sized_finalize(Symbol_table*, const Layout*, bool is_dot_available,
		 uint64_t dot_value, Output_section*);

  // Symbol name.
  std::string name_;
  // Expression to assign to symbol.
  Expression* val_;
  // Whether the assignment should be provided (only set if there is
  // an undefined reference to the symbol.
  bool provide_;
  // Whether the assignment should be hidden.
  bool hidden_;
  // The entry in the symbol table.
  Symbol* sym_;
};

// This class manages assertions in linker scripts.  These can appear
// in all the places where a Symbol_assignment can appear.

class Script_assertion
{
 public:
  Script_assertion(Expression* check, const char* message,
		   size_t messagelen)
    : check_(check), message_(message, messagelen)
  { }

  // Check the assertion.
  void
  check(const Symbol_table*, const Layout*);

  // Print the assertion to the FILE.  This is for debugging.
  void
  print(FILE*) const;

 private:
  // The expression to check.
  Expression* check_;
  // The message to issue if the expression fails.
  std::string message_;
};

// We can read a linker script in two different contexts: when
// initially parsing the command line, and when we find an input file
// which is actually a linker script.  Also some of the data which can
// be set by a linker script can also be set via command line options
// like -e and --defsym.  This means that we have a type of data which
// can be set both during command line option parsing and while
// reading input files.  We store that data in an instance of this
// object.  We will keep pointers to that instance in both the
// Command_line and Layout objects.

class Script_options
{
 public:
  Script_options();

  // Add a symbol to be defined.
  void
  add_symbol_assignment(const char* name, size_t length, Expression* value,
			bool provide, bool hidden);

  // Add an assertion.
  void
  add_assertion(Expression* check, const char* message, size_t messagelen);

  // Define a symbol from the command line.
  bool
  define_symbol(const char* definition);

  // Create sections required by any linker scripts.
  void
  create_script_sections(Layout*);

  // Add all symbol definitions to the symbol table.
  void
  add_symbols_to_table(Symbol_table*);

  // Finalize the symbol values.  Also check assertions.
  void
  finalize_symbols(Symbol_table*, const Layout*);

  // Version information parsed from a version script.  Everything
  // else has a pointer to this object.
  Version_script_info*
  version_script_info()
  { return &this->version_script_info_; }

  const Version_script_info*
  version_script_info() const
  { return &this->version_script_info_; }

  // A SECTIONS clause parsed from a linker script.  Everything else
  // has a pointer to this object.
  Script_sections*
  script_sections()
  { return &this->script_sections_; }

  const Script_sections*
  script_sections() const
  { return &this->script_sections_; }

  // Whether we saw a SECTIONS clause.
  bool
  saw_sections_clause() const
  { return this->script_sections_.saw_sections_clause(); }

  // Whether we saw a PHDRS clause.
  bool
  saw_phdrs_clause() const
  { return this->script_sections_.saw_phdrs_clause(); }

  // Set section addresses using a SECTIONS clause.  Return the
  // segment which should hold the file header and segment headers;
  // this may return NULL, in which case the headers are not in a
  // loadable segment.
  Output_segment*
  set_section_addresses(Symbol_table*, Layout*);

  // Print the script to the FILE.  This is for debugging.
  void
  print(FILE*) const;

 private:
  // We keep a list of symbol assignments which occur outside of a
  // SECTIONS clause.
  typedef std::vector<Symbol_assignment*> Symbol_assignments;

  // We keep a list of all assertions whcih occur outside of a
  // SECTIONS clause.
  typedef std::vector<Script_assertion*> Assertions;

  // The entry address.  This will be empty if not set.
  std::string entry_;
  // Symbols to set.
  Symbol_assignments symbol_assignments_;
  // Assertions to check.
  Assertions assertions_;
  // Version information parsed from a version script.
  Version_script_info version_script_info_;
  // Information from any SECTIONS clauses.
  Script_sections script_sections_;
};

// FILE was found as an argument on the command line, but was not
// recognized as an ELF file.  Try to read it as a script.  Return
// true if the file was handled.  This has to handle /usr/lib/libc.so
// on a GNU/Linux system.  *USED_NEXT_BLOCKER is set to indicate
// whether the function took over NEXT_BLOCKER.

bool
read_input_script(Workqueue*, const General_options&, Symbol_table*, Layout*,
		  Dirsearch*, Input_objects*, Mapfile*, Input_group*,
		  const Input_argument*, Input_file*,
		  Task_token* next_blocker, bool* used_next_blocker);

// FILE was found as an argument to --script (-T).
// Read it as a script, and execute its contents immediately.

bool
read_commandline_script(const char* filename, Command_line*);

// FILE was found as an argument to --version-script.  Read it as a
// version script, and store its contents in
// cmdline->script_options()->version_script_info().

bool
read_version_script(const char* filename, Command_line* cmdline);


} // End namespace gold.

#endif // !defined(GOLD_SCRIPT_H)