breakpad/src/common/dwarf/dwarf2reader.h

// Copyright 2010 Google Inc. All Rights Reserved.
//
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//
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// This file contains definitions related to the DWARF2/3 reader and
// it's handler interfaces.
// The DWARF2/3 specification can be found at
// http://dwarf.freestandards.org and should be considered required
// reading if you wish to modify the implementation.
// Only a cursory attempt is made to explain terminology that is
// used here, as it is much better explained in the standard documents
#ifndef COMMON_DWARF_DWARF2READER_H__
#define COMMON_DWARF_DWARF2READER_H__

#include <list>
#include <map>
#include <string>
#include <utility>
#include <vector>

#include "common/dwarf/dwarf2enums.h"
#include "common/dwarf/types.h"

using namespace std;

namespace dwarf2reader {
struct LineStateMachine;
class ByteReader;
class Dwarf2Handler;
class LineInfoHandler;

// This maps from a string naming a section to a pair containing a
// the data for the section, and the size of the section.
typedef map<string, pair<const char*, uint64> > SectionMap;
typedef list<pair<enum DwarfAttribute, enum DwarfForm> > AttributeList;
typedef AttributeList::iterator AttributeIterator;
typedef AttributeList::const_iterator ConstAttributeIterator;

struct LineInfoHeader {
  uint64 total_length;
  uint16 version;
  uint64 prologue_length;
  uint8 min_insn_length; // insn stands for instructin
  bool default_is_stmt; // stmt stands for statement
  int8 line_base;
  uint8 line_range;
  uint8 opcode_base;
  // Use a pointer so that signalsafe_addr2line is able to use this structure
  // without heap allocation problem.
  vector<unsigned char> *std_opcode_lengths;
};

class LineInfo {
 public:

  // Initializes a .debug_line reader. Buffer and buffer length point
  // to the beginning and length of the line information to read.
  // Reader is a ByteReader class that has the endianness set
  // properly.
  LineInfo(const char* buffer_, uint64 buffer_length,
           ByteReader* reader, LineInfoHandler* handler);

  virtual ~LineInfo() {
    if (header_.std_opcode_lengths) {
      delete header_.std_opcode_lengths;
    }
  }

  // Start processing line info, and calling callbacks in the handler.
  // Consumes the line number information for a single compilation unit.
  // Returns the number of bytes processed.
  uint64 Start();

  // Process a single line info opcode at START using the state
  // machine at LSM.  Return true if we should define a line using the
  // current state of the line state machine.  Place the length of the
  // opcode in LEN.
  // If LSM_PASSES_PC is non-NULL, this function also checks if the lsm
  // passes the address of PC. In other words, LSM_PASSES_PC will be
  // set to true, if the following condition is met.
  //
  // lsm's old address < PC <= lsm's new address
  static bool ProcessOneOpcode(ByteReader* reader,
                               LineInfoHandler* handler,
                               const struct LineInfoHeader &header,
                               const char* start,
                               struct LineStateMachine* lsm,
                               size_t* len,
                               uintptr pc,
                               bool *lsm_passes_pc);

 private:
  // Reads the DWARF2/3 header for this line info.
  void ReadHeader();

  // Reads the DWARF2/3 line information
  void ReadLines();

  // The associated handler to call processing functions in
  LineInfoHandler* handler_;

  // The associated ByteReader that handles endianness issues for us
  ByteReader* reader_;

  // A DWARF2/3 line info header.  This is not the same size as
  // in the actual file, as the one in the file may have a 32 bit or
  // 64 bit lengths

  struct LineInfoHeader header_;

  // buffer is the buffer for our line info, starting at exactly where
  // the line info to read is.  after_header is the place right after
  // the end of the line information header.
  const char* buffer_;
  uint64 buffer_length_;
  const char* after_header_;
};

// This class is the main interface between the line info reader and
// the client.  The virtual functions inside this get called for
// interesting events that happen during line info reading.  The
// default implementation does nothing

class LineInfoHandler {
 public:
  LineInfoHandler() { }

  virtual ~LineInfoHandler() { }

  // Called when we define a directory.  NAME is the directory name,
  // DIR_NUM is the directory number
  virtual void DefineDir(const string& name, uint32 dir_num) { }

  // Called when we define a filename. NAME is the filename, FILE_NUM
  // is the file number which is -1 if the file index is the next
  // index after the last numbered index (this happens when files are
  // dynamically defined by the line program), DIR_NUM is the
  // directory index for the directory name of this file, MOD_TIME is
  // the modification time of the file, and LENGTH is the length of
  // the file
  virtual void DefineFile(const string& name, int32 file_num,
                          uint32 dir_num, uint64 mod_time,
                          uint64 length) { }

  // Called when the line info reader has a new line, address pair
  // ready for us. ADDRESS is the address of the code, LENGTH is the
  // length of its machine code in bytes, FILE_NUM is the file number
  // containing the code, LINE_NUM is the line number in that file for
  // the code, and COLUMN_NUM is the column number the code starts at,
  // if we know it (0 otherwise).
  virtual void AddLine(uint64 address, uint64 length,
                       uint32 file_num, uint32 line_num, uint32 column_num) { }
};

// The base of DWARF2/3 debug info is a DIE (Debugging Information
// Entry.
// DWARF groups DIE's into a tree and calls the root of this tree a
// "compilation unit".  Most of the time, there is one compilation
// unit in the .debug_info section for each file that had debug info
// generated.
// Each DIE consists of

// 1. a tag specifying a thing that is being described (ie
// DW_TAG_subprogram for functions, DW_TAG_variable for variables, etc
// 2. attributes (such as DW_AT_location for location in memory,
// DW_AT_name for name), and data for each attribute.
// 3. A flag saying whether the DIE has children or not

// In order to gain some amount of compression, the format of
// each DIE (tag name, attributes and data forms for the attributes)
// are stored in a separate table called the "abbreviation table".
// This is done because a large number of DIEs have the exact same tag
// and list of attributes, but different data for those attributes.
// As a result, the .debug_info section is just a stream of data, and
// requires reading of the .debug_abbrev section to say what the data
// means.

// As a warning to the user, it should be noted that the reason for
// using absolute offsets from the beginning of .debug_info is that
// DWARF2/3 supports referencing DIE's from other DIE's by their offset
// from either the current compilation unit start, *or* the beginning
// of the .debug_info section.  This means it is possible to reference
// a DIE in one compilation unit from a DIE in another compilation
// unit.  This style of reference is usually used to eliminate
// duplicated information that occurs across compilation
// units, such as base types, etc.  GCC 3.4+ support this with
// -feliminate-dwarf2-dups.  Other toolchains will sometimes do
// duplicate elimination in the linker.

class CompilationUnit {
 public:

  // Initialize a compilation unit.  This requires a map of sections,
  // the offset of this compilation unit in the .debug_info section, a
  // ByteReader, and a Dwarf2Handler class to call callbacks in.
  CompilationUnit(const SectionMap& sections, uint64 offset,
                  ByteReader* reader, Dwarf2Handler* handler);
  virtual ~CompilationUnit() {
    if (abbrevs_) delete abbrevs_;
  }

  // Begin reading a Dwarf2 compilation unit, and calling the
  // callbacks in the Dwarf2Handler

  // Return the full length of the compilation unit, including
  // headers. This plus the starting offset passed to the constructor
  // is the offset of the end of the compilation unit --- and the
  // start of the next compilation unit, if there is one.
  uint64 Start();

 private:

  // This struct represents a single DWARF2/3 abbreviation
  // The abbreviation tells how to read a DWARF2/3 DIE, and consist of a
  // tag and a list of attributes, as well as the data form of each attribute.
  struct Abbrev {
    uint32 number;
    enum DwarfTag tag;
    bool has_children;
    AttributeList attributes;
  };

  // A DWARF2/3 compilation unit header.  This is not the same size as
  // in the actual file, as the one in the file may have a 32 bit or
  // 64 bit length.
  struct CompilationUnitHeader {
    uint64 length;
    uint16 version;
    uint64 abbrev_offset;
    uint8 address_size;
  } header_;

  // Reads the DWARF2/3 header for this compilation unit.
  void ReadHeader();

  // Reads the DWARF2/3 abbreviations for this compilation unit
  void ReadAbbrevs();

  // Processes a single DIE for this compilation unit and return a new
  // pointer just past the end of it
  const char* ProcessDIE(uint64 dieoffset,
                                  const char* start,
                                  const Abbrev& abbrev);

  // Processes a single attribute and return a new pointer just past the
  // end of it
  const char* ProcessAttribute(uint64 dieoffset,
                                        const char* start,
                                        enum DwarfAttribute attr,
                                        enum DwarfForm form);

  // Processes all DIEs for this compilation unit
  void ProcessDIEs();

  // Skips the die with attributes specified in ABBREV starting at
  // START, and return the new place to position the stream to.
  const char* SkipDIE(const char* start,
                               const Abbrev& abbrev);

  // Skips the attribute starting at START, with FORM, and return the
  // new place to position the stream to.
  const char* SkipAttribute(const char* start,
                                     enum DwarfForm form);

  // Offset from section start is the offset of this compilation unit
  // from the beginning of the .debug_info section.
  uint64 offset_from_section_start_;

  // buffer is the buffer for our CU, starting at .debug_info + offset
  // passed in from constructor.
  // after_header points to right after the compilation unit header.
  const char* buffer_;
  uint64 buffer_length_;
  const char* after_header_;

  // The associated ByteReader that handles endianness issues for us
  ByteReader* reader_;

  // The map of sections in our file to buffers containing their data
  const SectionMap& sections_;

  // The associated handler to call processing functions in
  Dwarf2Handler* handler_;

  // Set of DWARF2/3 abbreviations for this compilation unit.  Indexed
  // by abbreviation number, which means that abbrevs_[0] is not
  // valid.
  vector<Abbrev>* abbrevs_;

  // String section buffer and length, if we have a string section.
  // This is here to avoid doing a section lookup for strings in
  // ProcessAttribute, which is in the hot path for DWARF2 reading.
  const char* string_buffer_;
  uint64 string_buffer_length_;
};

// This class is the main interface between the reader and the
// client.  The virtual functions inside this get called for
// interesting events that happen during DWARF2 reading.
// The default implementation skips everything.

class Dwarf2Handler {
 public:
  Dwarf2Handler() { }

  virtual ~Dwarf2Handler() { }

  // Start to process a compilation unit at OFFSET from the beginning of the
  // .debug_info section. Return false if you would like to skip this
  // compilation unit.
  virtual bool StartCompilationUnit(uint64 offset, uint8 address_size,
                                    uint8 offset_size, uint64 cu_length,
                                    uint8 dwarf_version) { return false; }

  // Start to process a DIE at OFFSET from the beginning of the .debug_info
  // section. Return false if you would like to skip this DIE.
  virtual bool StartDIE(uint64 offset, enum DwarfTag tag,
                        const AttributeList& attrs) { return false; }

  // Called when we have an attribute with unsigned data to give to our
  // handler. The attribute is for the DIE at OFFSET from the beginning of the
  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
  // DATA.
  virtual void ProcessAttributeUnsigned(uint64 offset,
                                        enum DwarfAttribute attr,
                                        enum DwarfForm form,
                                        uint64 data) { }

  // Called when we have an attribute with signed data to give to our handler.
  // The attribute is for the DIE at OFFSET from the beginning of the
  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
  // DATA.
  virtual void ProcessAttributeSigned(uint64 offset,
                                      enum DwarfAttribute attr,
                                      enum DwarfForm form,
                                      int64 data) { }

  // Called when we have an attribute whose value is a reference to
  // another DIE. The attribute belongs to the DIE at OFFSET from the
  // beginning of the .debug_info section. Its name is ATTR, its form
  // is FORM, and the offset of the DIE being referred to from the
  // beginning of the .debug_info section is DATA.
  virtual void ProcessAttributeReference(uint64 offset,
                                         enum DwarfAttribute attr,
                                         enum DwarfForm form,
                                         uint64 data) { }

  // Called when we have an attribute with a buffer of data to give to our
  // handler. The attribute is for the DIE at OFFSET from the beginning of the
  // .debug_info section. Its name is ATTR, its form is FORM, DATA points to
  // the buffer's contents, and its length in bytes is LENGTH. The buffer is
  // owned by the caller, not the callee, and may not persist for very long.
  // If you want the data to be available later, it needs to be copied.
  virtual void ProcessAttributeBuffer(uint64 offset,
                                      enum DwarfAttribute attr,
                                      enum DwarfForm form,
                                      const char* data,
                                      uint64 len) { }

  // Called when we have an attribute with string data to give to our handler.
  // The attribute is for the DIE at OFFSET from the beginning of the
  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
  // DATA.
  virtual void ProcessAttributeString(uint64 offset,
                                      enum DwarfAttribute attr,
                                      enum DwarfForm form,
                                      const string& data) { }

  // Called when finished processing the DIE at OFFSET.
  // Because DWARF2/3 specifies a tree of DIEs, you may get starts
  // before ends of the previous DIE, as we process children before
  // ending the parent.
  virtual void EndDIE(uint64 offset) { }

};


}  // namespace dwarf2reader

#endif  // UTIL_DEBUGINFO_DWARF2READER_H__