xref: /external/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugLine.cpp

//===-- DWARFDebugLine.cpp --------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "DWARFDebugLine.h"

//#define ENABLE_DEBUG_PRINTF   // DO NOT LEAVE THIS DEFINED: DEBUG ONLY!!!
#include <assert.h>

#include "lldb/Core/FileSpecList.h"
#include "lldb/Core/Log.h"
#include "lldb/Core/Timer.h"

#include "SymbolFileDWARF.h"
#include "LogChannelDWARF.h"

using namespace lldb_private;
using namespace std;

//----------------------------------------------------------------------
// Parse
//
// Parse all information in the debug_line_data into an internal
// representation.
//----------------------------------------------------------------------
void
DWARFDebugLine::Parse(const DataExtractor& debug_line_data)
{
    m_lineTableMap.clear();
    dw_offset_t offset = 0;
    LineTable::shared_ptr line_table_sp(new LineTable);
    while (debug_line_data.ValidOffset(offset))
    {
        const uint32_t debug_line_offset = offset;

        if (line_table_sp.get() == NULL)
            break;

        if (ParseStatementTable(debug_line_data, &offset, line_table_sp.get()))
        {
            // Make sure we don't don't loop infinitely
            if (offset <= debug_line_offset)
                break;
            //DEBUG_PRINTF("m_lineTableMap[0x%8.8x] = line_table_sp\n", debug_line_offset);
            m_lineTableMap[debug_line_offset] = line_table_sp;
            line_table_sp.reset(new LineTable);
        }
        else
            ++offset;   // Try next byte in line table
    }
}

void
DWARFDebugLine::ParseIfNeeded(const DataExtractor& debug_line_data)
{
    if (m_lineTableMap.empty())
        Parse(debug_line_data);
}


//----------------------------------------------------------------------
// DWARFDebugLine::GetLineTable
//----------------------------------------------------------------------
DWARFDebugLine::LineTable::shared_ptr
DWARFDebugLine::GetLineTable(const dw_offset_t offset) const
{
    DWARFDebugLine::LineTable::shared_ptr line_table_shared_ptr;
    LineTableConstIter pos = m_lineTableMap.find(offset);
    if (pos != m_lineTableMap.end())
        line_table_shared_ptr = pos->second;
    return line_table_shared_ptr;
}


//----------------------------------------------------------------------
// DumpStateToFile
//----------------------------------------------------------------------
static void
DumpStateToFile (dw_offset_t offset, const DWARFDebugLine::State& state, void* userData)
{
    Log *log = (Log *)userData;
    if (state.row == DWARFDebugLine::State::StartParsingLineTable)
    {
        // If the row is zero we are being called with the prologue only
        state.prologue->Dump (log);
        log->PutCString ("Address            Line   Column File");
        log->PutCString ("------------------ ------ ------ ------");
    }
    else if (state.row == DWARFDebugLine::State::DoneParsingLineTable)
    {
        // Done parsing line table
    }
    else
    {
        log->Printf( "0x%16.16llx %6u %6u %6u%s\n", state.address, state.line, state.column, state.file, state.end_sequence ? " END" : "");
    }
}

//----------------------------------------------------------------------
// DWARFDebugLine::DumpLineTableRows
//----------------------------------------------------------------------
bool
DWARFDebugLine::DumpLineTableRows(Log *log, SymbolFileDWARF* dwarf2Data, dw_offset_t debug_line_offset)
{
    const DataExtractor& debug_line_data = dwarf2Data->get_debug_line_data();

    if (debug_line_offset == DW_INVALID_OFFSET)
    {
        // Dump line table to a single file only
        debug_line_offset = 0;
        while (debug_line_data.ValidOffset(debug_line_offset))
            debug_line_offset = DumpStatementTable (log, debug_line_data, debug_line_offset);
    }
    else
    {
        // Dump line table to a single file only
        DumpStatementTable (log, debug_line_data, debug_line_offset);
    }
    return false;
}

//----------------------------------------------------------------------
// DWARFDebugLine::DumpStatementTable
//----------------------------------------------------------------------
dw_offset_t
DWARFDebugLine::DumpStatementTable(Log *log, const DataExtractor& debug_line_data, const dw_offset_t debug_line_offset)
{
    if (debug_line_data.ValidOffset(debug_line_offset))
    {
        uint32_t offset = debug_line_offset;
        log->Printf(  "----------------------------------------------------------------------\n"
                    "debug_line[0x%8.8x]\n"
                    "----------------------------------------------------------------------\n", debug_line_offset);

        if (ParseStatementTable(debug_line_data, &offset, DumpStateToFile, log))
            return offset;
        else
            return debug_line_offset + 1;   // Skip to next byte in .debug_line section
    }

    return DW_INVALID_OFFSET;
}


//----------------------------------------------------------------------
// DumpOpcodes
//----------------------------------------------------------------------
bool
DWARFDebugLine::DumpOpcodes(Log *log, SymbolFileDWARF* dwarf2Data, dw_offset_t debug_line_offset, uint32_t dump_flags)
{
    const DataExtractor& debug_line_data = dwarf2Data->get_debug_line_data();

    if (debug_line_data.GetByteSize() == 0)
    {
        log->Printf( "< EMPTY >\n");
        return false;
    }

    if (debug_line_offset == DW_INVALID_OFFSET)
    {
        // Dump line table to a single file only
        debug_line_offset = 0;
        while (debug_line_data.ValidOffset(debug_line_offset))
            debug_line_offset = DumpStatementOpcodes (log, debug_line_data, debug_line_offset, dump_flags);
    }
    else
    {
        // Dump line table to a single file only
        DumpStatementOpcodes (log, debug_line_data, debug_line_offset, dump_flags);
    }
    return false;
}

//----------------------------------------------------------------------
// DumpStatementOpcodes
//----------------------------------------------------------------------
dw_offset_t
DWARFDebugLine::DumpStatementOpcodes(Log *log, const DataExtractor& debug_line_data, const dw_offset_t debug_line_offset, uint32_t flags)
{
    uint32_t offset = debug_line_offset;
    if (debug_line_data.ValidOffset(offset))
    {
        Prologue prologue;

        if (ParsePrologue(debug_line_data, &offset, &prologue))
        {
            log->PutCString ("----------------------------------------------------------------------");
            log->Printf     ("debug_line[0x%8.8x]", debug_line_offset);
            log->PutCString ("----------------------------------------------------------------------\n");
            prologue.Dump (log);
        }
        else
        {
            offset = debug_line_offset;
            log->Printf( "0x%8.8x: skipping pad byte %2.2x", offset, debug_line_data.GetU8(&offset));
            return offset;
        }

        Row row(prologue.default_is_stmt);
        const dw_offset_t end_offset = debug_line_offset + prologue.total_length + sizeof(prologue.total_length);

        assert(debug_line_data.ValidOffset(end_offset-1));

        while (offset < end_offset)
        {
            const uint32_t op_offset = offset;
            uint8_t opcode = debug_line_data.GetU8(&offset);
            switch (opcode)
            {
            case 0: // Extended Opcodes always start with a zero opcode followed by
                {   // a uleb128 length so you can skip ones you don't know about

                    dw_offset_t ext_offset = offset;
                    dw_uleb128_t len = debug_line_data.GetULEB128(&offset);
                    dw_offset_t arg_size = len - (offset - ext_offset);
                    uint8_t sub_opcode = debug_line_data.GetU8(&offset);
//                    if (verbose)
//                        log->Printf( "Extended: <%u> %2.2x ", len, sub_opcode);

                    switch (sub_opcode)
                    {
                    case DW_LNE_end_sequence    :
                        log->Printf( "0x%8.8x: DW_LNE_end_sequence", op_offset);
                        row.Dump(log);
                        row.Reset(prologue.default_is_stmt);
                        break;

                    case DW_LNE_set_address     :
                        {
                            row.address = debug_line_data.GetMaxU64(&offset, arg_size);
                            log->Printf( "0x%8.8x: DW_LNE_set_address (0x%llx)", op_offset, row.address);
                        }
                        break;

                    case DW_LNE_define_file:
                        {
                            FileNameEntry fileEntry;
                            fileEntry.name      = debug_line_data.GetCStr(&offset);
                            fileEntry.dir_idx   = debug_line_data.GetULEB128(&offset);
                            fileEntry.mod_time  = debug_line_data.GetULEB128(&offset);
                            fileEntry.length    = debug_line_data.GetULEB128(&offset);
                            log->Printf( "0x%8.8x: DW_LNE_define_file('%s', dir=%i, mod_time=0x%8.8x, length=%i )",
                                    op_offset,
                                    fileEntry.name.c_str(),
                                    fileEntry.dir_idx,
                                    fileEntry.mod_time,
                                    fileEntry.length);
                            prologue.file_names.push_back(fileEntry);
                        }
                        break;

                    default:
                        log->Printf( "0x%8.8x: DW_LNE_??? (%2.2x) - Skipping unknown upcode", op_offset, opcode);
                        // Length doesn't include the zero opcode byte or the length itself, but
                        // it does include the sub_opcode, so we have to adjust for that below
                        offset += arg_size;
                        break;
                    }
                }
                break;

            // Standard Opcodes
            case DW_LNS_copy:
                log->Printf( "0x%8.8x: DW_LNS_copy", op_offset);
                row.Dump (log);
                break;

            case DW_LNS_advance_pc:
                {
                    dw_uleb128_t addr_offset_n = debug_line_data.GetULEB128(&offset);
                    dw_uleb128_t addr_offset = addr_offset_n * prologue.min_inst_length;
                    log->Printf( "0x%8.8x: DW_LNS_advance_pc (0x%llx)", op_offset, addr_offset);
                    row.address += addr_offset;
                }
                break;

            case DW_LNS_advance_line:
                {
                    dw_sleb128_t line_offset = debug_line_data.GetSLEB128(&offset);
                    log->Printf( "0x%8.8x: DW_LNS_advance_line (%i)", op_offset, line_offset);
                    row.line += line_offset;
                }
                break;

            case DW_LNS_set_file:
                row.file = debug_line_data.GetULEB128(&offset);
                log->Printf( "0x%8.8x: DW_LNS_set_file (%u)", op_offset, row.file);
                break;

            case DW_LNS_set_column:
                row.column = debug_line_data.GetULEB128(&offset);
                log->Printf( "0x%8.8x: DW_LNS_set_column (%u)", op_offset, row.column);
                break;

            case DW_LNS_negate_stmt:
                row.is_stmt = !row.is_stmt;
                log->Printf( "0x%8.8x: DW_LNS_negate_stmt", op_offset);
                break;

            case DW_LNS_set_basic_block:
                row.basic_block = true;
                log->Printf( "0x%8.8x: DW_LNS_set_basic_block", op_offset);
                break;

            case DW_LNS_const_add_pc:
                {
                    uint8_t adjust_opcode = 255 - prologue.opcode_base;
                    dw_addr_t addr_offset = (adjust_opcode / prologue.line_range) * prologue.min_inst_length;
                    log->Printf( "0x%8.8x: DW_LNS_const_add_pc (0x%8.8llx)", op_offset, addr_offset);
                    row.address += addr_offset;
                }
                break;

            case DW_LNS_fixed_advance_pc:
                {
                    uint16_t pc_offset = debug_line_data.GetU16(&offset);
                    log->Printf( "0x%8.8x: DW_LNS_fixed_advance_pc (0x%4.4x)", op_offset, pc_offset);
                    row.address += pc_offset;
                }
                break;

            case DW_LNS_set_prologue_end:
                row.prologue_end = true;
                log->Printf( "0x%8.8x: DW_LNS_set_prologue_end", op_offset);
                break;

            case DW_LNS_set_epilogue_begin:
                row.epilogue_begin = true;
                log->Printf( "0x%8.8x: DW_LNS_set_epilogue_begin", op_offset);
                break;

            case DW_LNS_set_isa:
                row.isa = debug_line_data.GetULEB128(&offset);
                log->Printf( "0x%8.8x: DW_LNS_set_isa (%u)", op_offset, row.isa);
                break;

            // Special Opcodes
            default:
                if (opcode < prologue.opcode_base)
                {
                    // We have an opcode that this parser doesn't know about, skip
                    // the number of ULEB128 numbers that is says to skip in the
                    // prologue's standard_opcode_lengths array
                    uint8_t n = prologue.standard_opcode_lengths[opcode-1];
                    log->Printf( "0x%8.8x: Special : Unknown skipping %u ULEB128 values.", op_offset, n);
                    while (n > 0)
                    {
                        debug_line_data.GetULEB128(&offset);
                        --n;
                    }
                }
                else
                {
                    uint8_t adjust_opcode = opcode - prologue.opcode_base;
                    dw_addr_t addr_offset = (adjust_opcode / prologue.line_range) * prologue.min_inst_length;
                    int32_t line_offset = prologue.line_base + (adjust_opcode % prologue.line_range);
                    log->Printf("0x%8.8x: address += 0x%llx,  line += %i\n", op_offset, (uint64_t)addr_offset, line_offset);
                    row.address += addr_offset;
                    row.line += line_offset;
                    row.Dump (log);
                }
                break;
            }
        }
        return end_offset;
    }
    return DW_INVALID_OFFSET;
}




//----------------------------------------------------------------------
// Parse
//
// Parse the entire line table contents calling callback each time a
// new prologue is parsed and every time a new row is to be added to
// the line table.
//----------------------------------------------------------------------
void
DWARFDebugLine::Parse(const DataExtractor& debug_line_data, DWARFDebugLine::State::Callback callback, void* userData)
{
    uint32_t offset = 0;
    if (debug_line_data.ValidOffset(offset))
    {
        if (!ParseStatementTable(debug_line_data, &offset, callback, userData))
            ++offset;   // Skip to next byte in .debug_line section
    }
}


//----------------------------------------------------------------------
// DWARFDebugLine::ParsePrologue
//----------------------------------------------------------------------
bool
DWARFDebugLine::ParsePrologue(const DataExtractor& debug_line_data, dw_offset_t* offset_ptr, Prologue* prologue)
{
//  const uint32_t prologue_offset = *offset_ptr;

    //DEBUG_PRINTF("0x%8.8x: ParsePrologue()\n", *offset_ptr);

    prologue->Clear();
    uint32_t i;
    const char * s;
    prologue->total_length      = debug_line_data.GetU32(offset_ptr);
    prologue->version           = debug_line_data.GetU16(offset_ptr);
    if (prologue->version != 2)
      return false;

    prologue->prologue_length   = debug_line_data.GetU32(offset_ptr);
    const dw_offset_t end_prologue_offset = prologue->prologue_length + *offset_ptr;
    prologue->min_inst_length   = debug_line_data.GetU8(offset_ptr);
    prologue->default_is_stmt   = debug_line_data.GetU8(offset_ptr);
    prologue->line_base         = debug_line_data.GetU8(offset_ptr);
    prologue->line_range        = debug_line_data.GetU8(offset_ptr);
    prologue->opcode_base       = debug_line_data.GetU8(offset_ptr);

    prologue->standard_opcode_lengths.reserve(prologue->opcode_base-1);

    for (i=1; i<prologue->opcode_base; ++i)
    {
        uint8_t op_len = debug_line_data.GetU8(offset_ptr);
        prologue->standard_opcode_lengths.push_back(op_len);
    }

    while (*offset_ptr < end_prologue_offset)
    {
        s = debug_line_data.GetCStr(offset_ptr);
        if (s && s[0])
            prologue->include_directories.push_back(s);
        else
            break;
    }

    while (*offset_ptr < end_prologue_offset)
    {
        const char* name = debug_line_data.GetCStr( offset_ptr );
        if (name && name[0])
        {
            FileNameEntry fileEntry;
            fileEntry.name      = name;
            fileEntry.dir_idx   = debug_line_data.GetULEB128( offset_ptr );
            fileEntry.mod_time  = debug_line_data.GetULEB128( offset_ptr );
            fileEntry.length    = debug_line_data.GetULEB128( offset_ptr );
            prologue->file_names.push_back(fileEntry);
        }
        else
            break;
    }

    assert(*offset_ptr == end_prologue_offset);
    return end_prologue_offset;
}

bool
DWARFDebugLine::ParseSupportFiles(const DataExtractor& debug_line_data, const char *cu_comp_dir, dw_offset_t stmt_list, FileSpecList &support_files)
{
    uint32_t offset = stmt_list + 4;    // Skip the total length
    const char * s;
    uint32_t version = debug_line_data.GetU16(&offset);
    if (version != 2)
      return false;

    const dw_offset_t end_prologue_offset = debug_line_data.GetU32(&offset) + offset;
    // Skip instruction length, default is stmt, line base, line range and
    // opcode base, and all opcode lengths
    offset += 4;
    const uint8_t opcode_base = debug_line_data.GetU8(&offset);
    offset += opcode_base - 1;
    std::vector<std::string> include_directories;
    include_directories.push_back("");  // Directory at index zero doesn't exist
    while (offset < end_prologue_offset)
    {
        s = debug_line_data.GetCStr(&offset);
        if (s && s[0])
            include_directories.push_back(s);
        else
            break;
    }
    std::string fullpath;
    while (offset < end_prologue_offset)
    {
        const char* path = debug_line_data.GetCStr( &offset );
        if (path && path[0])
        {
            uint32_t dir_idx    = debug_line_data.GetULEB128( &offset );
            debug_line_data.Skip_LEB128(&offset); // Skip mod_time
            debug_line_data.Skip_LEB128(&offset); // Skip length

            if (path[0] == '/')
            {
                // The path starts with a directory delimiter, so we are done.
                fullpath = path;
            }
            else
            {
                if (dir_idx > 0 && dir_idx < include_directories.size())
                {
                    if (cu_comp_dir && include_directories[dir_idx][0] != '/')
                    {
                        fullpath = cu_comp_dir;

                        if (*fullpath.rbegin() != '/')
                            fullpath += '/';
                        fullpath += include_directories[dir_idx];

                    }
                    else
                        fullpath = include_directories[dir_idx];
                }
                else if (cu_comp_dir && cu_comp_dir[0])
                {
                    fullpath = cu_comp_dir;
                }

                if (!fullpath.empty())
                {
                   if (*fullpath.rbegin() != '/')
                        fullpath += '/';
                }
                fullpath += path;
            }

            // We don't need to realpath files in the debug_line tables.
            FileSpec file_spec(fullpath.c_str(), false);
            support_files.Append(file_spec);
        }
    }

    assert(offset == end_prologue_offset);
    return end_prologue_offset;
}

//----------------------------------------------------------------------
// ParseStatementTable
//
// Parse a single line table (prologue and all rows) and call the
// callback function once for the prologue (row in state will be zero)
// and each time a row is to be added to the line table.
//----------------------------------------------------------------------
bool
DWARFDebugLine::ParseStatementTable
(
    const DataExtractor& debug_line_data,
    dw_offset_t* offset_ptr,
    DWARFDebugLine::State::Callback callback,
    void* userData
)
{
    Log *log = LogChannelDWARF::GetLogIfAll(DWARF_LOG_DEBUG_LINE);
    Prologue::shared_ptr prologue(new Prologue());


    const dw_offset_t debug_line_offset = *offset_ptr;

    Timer scoped_timer (__PRETTY_FUNCTION__,
                        "DWARFDebugLine::ParseStatementTable (.debug_line[0x%8.8x])",
                        debug_line_offset);

    if (!ParsePrologue(debug_line_data, offset_ptr, prologue.get()))
    {
        if (log)
            log->Error ("failed to parse DWARF line table prologue");
        // Restore our offset and return false to indicate failure!
        *offset_ptr = debug_line_offset;
        return false;
    }

    if (log)
        prologue->Dump (log);

    const dw_offset_t end_offset = debug_line_offset + prologue->total_length + sizeof(prologue->total_length);

    assert(debug_line_data.ValidOffset(end_offset-1));

    State state(prologue, log, callback, userData);

    while (*offset_ptr < end_offset)
    {
        //DEBUG_PRINTF("0x%8.8x: ", *offset_ptr);
        uint8_t opcode = debug_line_data.GetU8(offset_ptr);

        if (opcode == 0)
        {
            // Extended Opcodes always start with a zero opcode followed by
            // a uleb128 length so you can skip ones you don't know about
            dw_offset_t ext_offset = *offset_ptr;
            dw_uleb128_t len = debug_line_data.GetULEB128(offset_ptr);
            dw_offset_t arg_size = len - (*offset_ptr - ext_offset);

            //DEBUG_PRINTF("Extended: <%2u> ", len);
            uint8_t sub_opcode = debug_line_data.GetU8(offset_ptr);
            switch (sub_opcode)
            {
            case DW_LNE_end_sequence:
                // Set the end_sequence register of the state machine to true and
                // append a row to the matrix using the current values of the
                // state-machine registers. Then reset the registers to the initial
                // values specified above. Every statement program sequence must end
                // with a DW_LNE_end_sequence instruction which creates a row whose
                // address is that of the byte after the last target machine instruction
                // of the sequence.
                state.end_sequence = true;
                state.AppendRowToMatrix(*offset_ptr);
                state.Reset();
                break;

            case DW_LNE_set_address:
                // Takes a single relocatable address as an operand. The size of the
                // operand is the size appropriate to hold an address on the target
                // machine. Set the address register to the value given by the
                // relocatable address. All of the other statement program opcodes
                // that affect the address register add a delta to it. This instruction
                // stores a relocatable value into it instead.
                state.address = debug_line_data.GetAddress(offset_ptr);
                break;

            case DW_LNE_define_file:
                // Takes 4 arguments. The first is a null terminated string containing
                // a source file name. The second is an unsigned LEB128 number representing
                // the directory index of the directory in which the file was found. The
                // third is an unsigned LEB128 number representing the time of last
                // modification of the file. The fourth is an unsigned LEB128 number
                // representing the length in bytes of the file. The time and length
                // fields may contain LEB128(0) if the information is not available.
                //
                // The directory index represents an entry in the include_directories
                // section of the statement program prologue. The index is LEB128(0)
                // if the file was found in the current directory of the compilation,
                // LEB128(1) if it was found in the first directory in the
                // include_directories section, and so on. The directory index is
                // ignored for file names that represent full path names.
                //
                // The files are numbered, starting at 1, in the order in which they
                // appear; the names in the prologue come before names defined by
                // the DW_LNE_define_file instruction. These numbers are used in the
                // the file register of the state machine.
                {
                    FileNameEntry fileEntry;
                    fileEntry.name      = debug_line_data.GetCStr(offset_ptr);
                    fileEntry.dir_idx   = debug_line_data.GetULEB128(offset_ptr);
                    fileEntry.mod_time  = debug_line_data.GetULEB128(offset_ptr);
                    fileEntry.length    = debug_line_data.GetULEB128(offset_ptr);
                    state.prologue->file_names.push_back(fileEntry);
                }
                break;

            default:
                // Length doesn't include the zero opcode byte or the length itself, but
                // it does include the sub_opcode, so we have to adjust for that below
                (*offset_ptr) += arg_size;
                break;
            }
        }
        else if (opcode < prologue->opcode_base)
        {
            switch (opcode)
            {
            // Standard Opcodes
            case DW_LNS_copy:
                // Takes no arguments. Append a row to the matrix using the
                // current values of the state-machine registers. Then set
                // the basic_block register to false.
                state.AppendRowToMatrix(*offset_ptr);
                break;

            case DW_LNS_advance_pc:
                // Takes a single unsigned LEB128 operand, multiplies it by the
                // min_inst_length field of the prologue, and adds the
                // result to the address register of the state machine.
                state.address += debug_line_data.GetULEB128(offset_ptr) * prologue->min_inst_length;
                break;

            case DW_LNS_advance_line:
                // Takes a single signed LEB128 operand and adds that value to
                // the line register of the state machine.
                state.line += debug_line_data.GetSLEB128(offset_ptr);
                break;

            case DW_LNS_set_file:
                // Takes a single unsigned LEB128 operand and stores it in the file
                // register of the state machine.
                state.file = debug_line_data.GetULEB128(offset_ptr);
                break;

            case DW_LNS_set_column:
                // Takes a single unsigned LEB128 operand and stores it in the
                // column register of the state machine.
                state.column = debug_line_data.GetULEB128(offset_ptr);
                break;

            case DW_LNS_negate_stmt:
                // Takes no arguments. Set the is_stmt register of the state
                // machine to the logical negation of its current value.
                state.is_stmt = !state.is_stmt;
                break;

            case DW_LNS_set_basic_block:
                // Takes no arguments. Set the basic_block register of the
                // state machine to true
                state.basic_block = true;
                break;

            case DW_LNS_const_add_pc:
                // Takes no arguments. Add to the address register of the state
                // machine the address increment value corresponding to special
                // opcode 255. The motivation for DW_LNS_const_add_pc is this:
                // when the statement program needs to advance the address by a
                // small amount, it can use a single special opcode, which occupies
                // a single byte. When it needs to advance the address by up to
                // twice the range of the last special opcode, it can use
                // DW_LNS_const_add_pc followed by a special opcode, for a total
                // of two bytes. Only if it needs to advance the address by more
                // than twice that range will it need to use both DW_LNS_advance_pc
                // and a special opcode, requiring three or more bytes.
                {
                    uint8_t adjust_opcode = 255 - prologue->opcode_base;
                    dw_addr_t addr_offset = (adjust_opcode / prologue->line_range) * prologue->min_inst_length;
                    state.address += addr_offset;
                }
                break;

            case DW_LNS_fixed_advance_pc:
                // Takes a single uhalf operand. Add to the address register of
                // the state machine the value of the (unencoded) operand. This
                // is the only extended opcode that takes an argument that is not
                // a variable length number. The motivation for DW_LNS_fixed_advance_pc
                // is this: existing assemblers cannot emit DW_LNS_advance_pc or
                // special opcodes because they cannot encode LEB128 numbers or
                // judge when the computation of a special opcode overflows and
                // requires the use of DW_LNS_advance_pc. Such assemblers, however,
                // can use DW_LNS_fixed_advance_pc instead, sacrificing compression.
                state.address += debug_line_data.GetU16(offset_ptr);
                break;

            case DW_LNS_set_prologue_end:
                // Takes no arguments. Set the prologue_end register of the
                // state machine to true
                state.prologue_end = true;
                break;

            case DW_LNS_set_epilogue_begin:
                // Takes no arguments. Set the basic_block register of the
                // state machine to true
                state.epilogue_begin = true;
                break;

            case DW_LNS_set_isa:
                // Takes a single unsigned LEB128 operand and stores it in the
                // column register of the state machine.
                state.isa = debug_line_data.GetULEB128(offset_ptr);
                break;

            default:
                // Handle any unknown standard opcodes here. We know the lengths
                // of such opcodes because they are specified in the prologue
                // as a multiple of LEB128 operands for each opcode.
                {
                    uint8_t i;
                    assert (opcode - 1 < prologue->standard_opcode_lengths.size());
                    const uint8_t opcode_length = prologue->standard_opcode_lengths[opcode - 1];
                    for (i=0; i<opcode_length; ++i)
                        debug_line_data.Skip_LEB128(offset_ptr);
                }
                break;
            }
        }
        else
        {
            // Special Opcodes

            // A special opcode value is chosen based on the amount that needs
            // to be added to the line and address registers. The maximum line
            // increment for a special opcode is the value of the line_base
            // field in the header, plus the value of the line_range field,
            // minus 1 (line base + line range - 1). If the desired line
            // increment is greater than the maximum line increment, a standard
            // opcode must be used instead of a special opcode. The “address
            // advance” is calculated by dividing the desired address increment
            // by the minimum_instruction_length field from the header. The
            // special opcode is then calculated using the following formula:
            //
            //  opcode = (desired line increment - line_base) + (line_range * address advance) + opcode_base
            //
            // If the resulting opcode is greater than 255, a standard opcode
            // must be used instead.
            //
            // To decode a special opcode, subtract the opcode_base from the
            // opcode itself to give the adjusted opcode. The amount to
            // increment the address register is the result of the adjusted
            // opcode divided by the line_range multiplied by the
            // minimum_instruction_length field from the header. That is:
            //
            //  address increment = (adjusted opcode / line_range) * minimim_instruction_length
            //
            // The amount to increment the line register is the line_base plus
            // the result of the adjusted opcode modulo the line_range. That is:
            //
            // line increment = line_base + (adjusted opcode % line_range)

            uint8_t adjust_opcode = opcode - prologue->opcode_base;
            dw_addr_t addr_offset = (adjust_opcode / prologue->line_range) * prologue->min_inst_length;
            int32_t line_offset = prologue->line_base + (adjust_opcode % prologue->line_range);
            state.line += line_offset;
            state.address += addr_offset;
            state.AppendRowToMatrix(*offset_ptr);
        }
    }

    state.Finalize( *offset_ptr );

    return end_offset;
}


//----------------------------------------------------------------------
// ParseStatementTableCallback
//----------------------------------------------------------------------
static void
ParseStatementTableCallback(dw_offset_t offset, const DWARFDebugLine::State& state, void* userData)
{
    DWARFDebugLine::LineTable* line_table = (DWARFDebugLine::LineTable*)userData;
    if (state.row == DWARFDebugLine::State::StartParsingLineTable)
    {
        // Just started parsing the line table, so lets keep a reference to
        // the prologue using the supplied shared pointer
        line_table->prologue = state.prologue;
    }
    else if (state.row == DWARFDebugLine::State::DoneParsingLineTable)
    {
        // Done parsing line table, nothing to do for the cleanup
    }
    else
    {
        // We have a new row, lets append it
        line_table->AppendRow(state);
    }
}

//----------------------------------------------------------------------
// ParseStatementTable
//
// Parse a line table at offset and populate the LineTable class with
// the prologue and all rows.
//----------------------------------------------------------------------
bool
DWARFDebugLine::ParseStatementTable(const DataExtractor& debug_line_data, uint32_t* offset_ptr, LineTable* line_table)
{
    return ParseStatementTable(debug_line_data, offset_ptr, ParseStatementTableCallback, line_table);
}


inline bool
DWARFDebugLine::Prologue::IsValid() const
{
    return SymbolFileDWARF::SupportedVersion(version);
}

//----------------------------------------------------------------------
// DWARFDebugLine::Prologue::Dump
//----------------------------------------------------------------------
void
DWARFDebugLine::Prologue::Dump(Log *log)
{
    uint32_t i;

    log->Printf( "Line table prologue:");
    log->Printf( "   total_length: 0x%8.8x", total_length);
    log->Printf( "        version: %u", version);
    log->Printf( "prologue_length: 0x%8.8x", prologue_length);
    log->Printf( "min_inst_length: %u", min_inst_length);
    log->Printf( "default_is_stmt: %u", default_is_stmt);
    log->Printf( "      line_base: %i", line_base);
    log->Printf( "     line_range: %u", line_range);
    log->Printf( "    opcode_base: %u", opcode_base);

    for (i=0; i<standard_opcode_lengths.size(); ++i)
    {
        log->Printf( "standard_opcode_lengths[%s] = %u", DW_LNS_value_to_name(i+1), standard_opcode_lengths[i]);
    }

    if (!include_directories.empty())
    {
        for (i=0; i<include_directories.size(); ++i)
        {
            log->Printf( "include_directories[%3u] = '%s'", i+1, include_directories[i].c_str());
        }
    }

    if (!file_names.empty())
    {
        log->PutCString ("                Dir  Mod Time   File Len   File Name");
        log->PutCString ("                ---- ---------- ---------- ---------------------------");
        for (i=0; i<file_names.size(); ++i)
        {
            const FileNameEntry& fileEntry = file_names[i];
            log->Printf ("file_names[%3u] %4u 0x%8.8x 0x%8.8x %s",
                i+1,
                fileEntry.dir_idx,
                fileEntry.mod_time,
                fileEntry.length,
                fileEntry.name.c_str());
        }
    }
}


//----------------------------------------------------------------------
// DWARFDebugLine::ParsePrologue::Append
//
// Append the contents of the prologue to the binary stream buffer
//----------------------------------------------------------------------
//void
//DWARFDebugLine::Prologue::Append(BinaryStreamBuf& buff) const
//{
//  uint32_t i;
//
//  buff.Append32(total_length);
//  buff.Append16(version);
//  buff.Append32(prologue_length);
//  buff.Append8(min_inst_length);
//  buff.Append8(default_is_stmt);
//  buff.Append8(line_base);
//  buff.Append8(line_range);
//  buff.Append8(opcode_base);
//
//  for (i=0; i<standard_opcode_lengths.size(); ++i)
//      buff.Append8(standard_opcode_lengths[i]);
//
//  for (i=0; i<include_directories.size(); ++i)
//      buff.AppendCStr(include_directories[i].c_str());
//  buff.Append8(0);    // Terminate the include directory section with empty string
//
//  for (i=0; i<file_names.size(); ++i)
//  {
//      buff.AppendCStr(file_names[i].name.c_str());
//      buff.Append32_as_ULEB128(file_names[i].dir_idx);
//      buff.Append32_as_ULEB128(file_names[i].mod_time);
//      buff.Append32_as_ULEB128(file_names[i].length);
//  }
//  buff.Append8(0);    // Terminate the file names section with empty string
//}


bool DWARFDebugLine::Prologue::GetFile(uint32_t file_idx, std::string& path, std::string& directory) const
{
    uint32_t idx = file_idx - 1;    // File indexes are 1 based...
    if (idx < file_names.size())
    {
        path = file_names[idx].name;
        uint32_t dir_idx = file_names[idx].dir_idx - 1;
        if (dir_idx < include_directories.size())
            directory = include_directories[dir_idx];
        else
            directory.clear();
        return true;
    }
    return false;
}

//----------------------------------------------------------------------
// DWARFDebugLine::LineTable::Dump
//----------------------------------------------------------------------
void
DWARFDebugLine::LineTable::Dump(Log *log) const
{
    if (prologue.get())
        prologue->Dump (log);

    if (!rows.empty())
    {
        log->PutCString ("Address            Line   Column File   ISA Flags");
        log->PutCString ("------------------ ------ ------ ------ --- -------------");
        Row::const_iterator pos = rows.begin();
        Row::const_iterator end = rows.end();
        while (pos != end)
        {
            (*pos).Dump (log);
            ++pos;
        }
    }
}


void
DWARFDebugLine::LineTable::AppendRow(const DWARFDebugLine::Row& state)
{
    rows.push_back(state);
}



//----------------------------------------------------------------------
// Compare function for the binary search in DWARFDebugLine::LineTable::LookupAddress()
//----------------------------------------------------------------------
static bool FindMatchingAddress (const DWARFDebugLine::Row& row1, const DWARFDebugLine::Row& row2)
{
    return row1.address < row2.address;
}


//----------------------------------------------------------------------
// DWARFDebugLine::LineTable::LookupAddress
//----------------------------------------------------------------------
uint32_t
DWARFDebugLine::LineTable::LookupAddress(dw_addr_t address, dw_addr_t cu_high_pc) const
{
    uint32_t index = UINT32_MAX;
    if (!rows.empty())
    {
        // Use the lower_bound algorithm to perform a binary search since we know
        // that our line table data is ordered by address.
        DWARFDebugLine::Row row;
        row.address = address;
        Row::const_iterator begin_pos = rows.begin();
        Row::const_iterator end_pos = rows.end();
        Row::const_iterator pos = lower_bound(begin_pos, end_pos, row, FindMatchingAddress);
        if (pos == end_pos)
        {
            if (address < cu_high_pc)
                return rows.size()-1;
        }
        else
        {
            // Rely on fact that we are using a std::vector and we can do
            // pointer arithmetic to find the row index (which will be one less
            // that what we found since it will find the first position after
            // the current address) since std::vector iterators are just
            // pointers to the container type.
            index = pos - begin_pos;
            if (pos->address > address)
            {
                if (index > 0)
                    --index;
                else
                    index = UINT32_MAX;
            }
        }
    }
    return index;   // Failed to find address
}


//----------------------------------------------------------------------
// DWARFDebugLine::Row::Row
//----------------------------------------------------------------------
DWARFDebugLine::Row::Row(bool default_is_stmt) :
    address(0),
    line(1),
    column(0),
    file(1),
    is_stmt(default_is_stmt),
    basic_block(false),
    end_sequence(false),
    prologue_end(false),
    epilogue_begin(false),
    isa(0)
{
}

//----------------------------------------------------------------------
// Called after a row is appended to the matrix
//----------------------------------------------------------------------
void
DWARFDebugLine::Row::PostAppend()
{
    basic_block = false;
    prologue_end = false;
    epilogue_begin = false;
}


//----------------------------------------------------------------------
// DWARFDebugLine::Row::Reset
//----------------------------------------------------------------------
void
DWARFDebugLine::Row::Reset(bool default_is_stmt)
{
    address = 0;
    line = 1;
    column = 0;
    file = 1;
    is_stmt = default_is_stmt;
    basic_block = false;
    end_sequence = false;
    prologue_end = false;
    epilogue_begin = false;
    isa = 0;
}
//----------------------------------------------------------------------
// DWARFDebugLine::Row::Dump
//----------------------------------------------------------------------
void
DWARFDebugLine::Row::Dump(Log *log) const
{
    log->Printf( "0x%16.16llx %6u %6u %6u %3u %s%s%s%s%s",
                address,
                line,
                column,
                file,
                isa,
                is_stmt ? " is_stmt" : "",
                basic_block ? " basic_block" : "",
                prologue_end ? " prologue_end" : "",
                epilogue_begin ? " epilogue_begin" : "",
                end_sequence ? " end_sequence" : "");
}

//----------------------------------------------------------------------
// Compare function LineTable structures
//----------------------------------------------------------------------
static bool AddressLessThan (const DWARFDebugLine::Row& a, const DWARFDebugLine::Row& b)
{
    return a.address < b.address;
}



// Insert a row at the correct address if the addresses can be out of
// order which can only happen when we are linking a line table that
// may have had it's contents rearranged.
void
DWARFDebugLine::Row::Insert(Row::collection& state_coll, const Row& state)
{
    // If we don't have anything yet, or if the address of the last state in our
    // line table is less than the current one, just append the current state
    if (state_coll.empty() || AddressLessThan(state_coll.back(), state))
    {
        state_coll.push_back(state);
    }
    else
    {
        // Do a binary search for the correct entry
        pair<Row::iterator, Row::iterator> range(equal_range(state_coll.begin(), state_coll.end(), state, AddressLessThan));

        // If the addresses are equal, we can safely replace the previous entry
        // with the current one if the one it is replacing is an end_sequence entry.
        // We currently always place an extra end sequence when ever we exit a valid
        // address range for a function in case the functions get rearranged by
        // optmimizations or by order specifications. These extra end sequences will
        // disappear by getting replaced with valid consecutive entries within a
        // compile unit if there are no gaps.
        if (range.first == range.second)
        {
            state_coll.insert(range.first, state);
        }
        else
        {
            if ((distance(range.first, range.second) == 1) && range.first->end_sequence == true)
            {
                *range.first = state;
            }
            else
            {
                state_coll.insert(range.second, state);
            }
        }
    }
}

void
DWARFDebugLine::Row::Dump(Log *log, const Row::collection& state_coll)
{
    std::for_each (state_coll.begin(), state_coll.end(), bind2nd(std::mem_fun_ref(&Row::Dump),log));
}


//----------------------------------------------------------------------
// DWARFDebugLine::State::State
//----------------------------------------------------------------------
DWARFDebugLine::State::State(Prologue::shared_ptr& p, Log *l, DWARFDebugLine::State::Callback cb, void* userData) :
    Row (p->default_is_stmt),
    prologue (p),
    log (l),
    callback (cb),
    callbackUserData (userData),
    row (StartParsingLineTable)
{
    // Call the callback with the initial row state of zero for the prologue
    if (callback)
        callback(0, *this, callbackUserData);
}

//----------------------------------------------------------------------
// DWARFDebugLine::State::Reset
//----------------------------------------------------------------------
void
DWARFDebugLine::State::Reset()
{
    Row::Reset(prologue->default_is_stmt);
}

//----------------------------------------------------------------------
// DWARFDebugLine::State::AppendRowToMatrix
//----------------------------------------------------------------------
void
DWARFDebugLine::State::AppendRowToMatrix(dw_offset_t offset)
{
    // Each time we are to add an entry into the line table matrix
    // call the callback funtion so that someone can do something with
    // the current state of the state machine (like build a line table
    // or dump the line table!)
    if (log)
    {
        if (row == 0)
        {
            log->PutCString ("Address            Line   Column File   ISA Flags");
            log->PutCString ("------------------ ------ ------ ------ --- -------------");
        }
        Dump (log);
    }

    ++row;  // Increase the row number before we call our callback for a real row
    if (callback)
        callback(offset, *this, callbackUserData);
    PostAppend();
}

//----------------------------------------------------------------------
// DWARFDebugLine::State::Finalize
//----------------------------------------------------------------------
void
DWARFDebugLine::State::Finalize(dw_offset_t offset)
{
    // Call the callback with a special row state when we are done parsing a
    // line table
    row = DoneParsingLineTable;
    if (callback)
        callback(offset, *this, callbackUserData);
}

//void
//DWARFDebugLine::AppendLineTableData
//(
//  const DWARFDebugLine::Prologue* prologue,
//  const DWARFDebugLine::Row::collection& state_coll,
//  const uint32_t addr_size,
//  BinaryStreamBuf &debug_line_data
//)
//{
//  if (state_coll.empty())
//  {
//      // We have no entries, just make an empty line table
//      debug_line_data.Append8(0);
//      debug_line_data.Append8(1);
//      debug_line_data.Append8(DW_LNE_end_sequence);
//  }
//  else
//  {
//      DWARFDebugLine::Row::const_iterator pos;
//      Row::const_iterator end = state_coll.end();
//      bool default_is_stmt = prologue->default_is_stmt;
//      const DWARFDebugLine::Row reset_state(default_is_stmt);
//      const DWARFDebugLine::Row* prev_state = &reset_state;
//      const int32_t max_line_increment_for_special_opcode = prologue->MaxLineIncrementForSpecialOpcode();
//      for (pos = state_coll.begin(); pos != end; ++pos)
//      {
//          const DWARFDebugLine::Row& curr_state = *pos;
//          int32_t line_increment  = 0;
//          dw_addr_t addr_offset   = curr_state.address - prev_state->address;
//          dw_addr_t addr_advance  = (addr_offset) / prologue->min_inst_length;
//          line_increment = (int32_t)(curr_state.line - prev_state->line);
//
//          // If our previous state was the reset state, then let's emit the
//          // address to keep GDB's DWARF parser happy. If we don't start each
//          // sequence with a DW_LNE_set_address opcode, the line table won't
//          // get slid properly in GDB.
//
//          if (prev_state == &reset_state)
//          {
//              debug_line_data.Append8(0); // Extended opcode
//              debug_line_data.Append32_as_ULEB128(addr_size + 1); // Length of opcode bytes
//              debug_line_data.Append8(DW_LNE_set_address);
//              debug_line_data.AppendMax64(curr_state.address, addr_size);
//              addr_advance = 0;
//          }
//
//          if (prev_state->file != curr_state.file)
//          {
//              debug_line_data.Append8(DW_LNS_set_file);
//              debug_line_data.Append32_as_ULEB128(curr_state.file);
//          }
//
//          if (prev_state->column != curr_state.column)
//          {
//              debug_line_data.Append8(DW_LNS_set_column);
//              debug_line_data.Append32_as_ULEB128(curr_state.column);
//          }
//
//          // Don't do anything fancy if we are at the end of a sequence
//          // as we don't want to push any extra rows since the DW_LNE_end_sequence
//          // will push a row itself!
//          if (curr_state.end_sequence)
//          {
//              if (line_increment != 0)
//              {
//                  debug_line_data.Append8(DW_LNS_advance_line);
//                  debug_line_data.Append32_as_SLEB128(line_increment);
//              }
//
//              if (addr_advance > 0)
//              {
//                  debug_line_data.Append8(DW_LNS_advance_pc);
//                  debug_line_data.Append32_as_ULEB128(addr_advance);
//              }
//
//              // Now push the end sequence on!
//              debug_line_data.Append8(0);
//              debug_line_data.Append8(1);
//              debug_line_data.Append8(DW_LNE_end_sequence);
//
//              prev_state = &reset_state;
//          }
//          else
//          {
//              if (line_increment || addr_advance)
//              {
//                  if (line_increment > max_line_increment_for_special_opcode)
//                  {
//                      debug_line_data.Append8(DW_LNS_advance_line);
//                      debug_line_data.Append32_as_SLEB128(line_increment);
//                      line_increment = 0;
//                  }
//
//                  uint32_t special_opcode = (line_increment >= prologue->line_base) ? ((line_increment - prologue->line_base) + (prologue->line_range * addr_advance) + prologue->opcode_base) : 256;
//                  if (special_opcode > 255)
//                  {
//                      // Both the address and line won't fit in one special opcode
//                      // check to see if just the line advance will?
//                      uint32_t special_opcode_line = ((line_increment >= prologue->line_base) && (line_increment != 0)) ?
//                              ((line_increment - prologue->line_base) + prologue->opcode_base) : 256;
//
//
//                      if (special_opcode_line > 255)
//                      {
//                          // Nope, the line advance won't fit by itself, check the address increment by itself
//                          uint32_t special_opcode_addr = addr_advance ?
//                              ((0 - prologue->line_base) + (prologue->line_range * addr_advance) + prologue->opcode_base) : 256;
//
//                          if (special_opcode_addr > 255)
//                          {
//                              // Neither the address nor the line will fit in a
//                              // special opcode, we must manually enter both then
//                              // do a DW_LNS_copy to push a row (special opcode
//                              // automatically imply a new row is pushed)
//                              if (line_increment != 0)
//                              {
//                                  debug_line_data.Append8(DW_LNS_advance_line);
//                                  debug_line_data.Append32_as_SLEB128(line_increment);
//                              }
//
//                              if (addr_advance > 0)
//                              {
//                                  debug_line_data.Append8(DW_LNS_advance_pc);
//                                  debug_line_data.Append32_as_ULEB128(addr_advance);
//                              }
//
//                              // Now push a row onto the line table manually
//                              debug_line_data.Append8(DW_LNS_copy);
//
//                          }
//                          else
//                          {
//                              // The address increment alone will fit into a special opcode
//                              // so modify our line change, then issue a special opcode
//                              // for the address increment and it will push a row into the
//                              // line table
//                              if (line_increment != 0)
//                              {
//                                  debug_line_data.Append8(DW_LNS_advance_line);
//                                  debug_line_data.Append32_as_SLEB128(line_increment);
//                              }
//
//                              // Advance of line and address will fit into a single byte special opcode
//                              // and this will also push a row onto the line table
//                              debug_line_data.Append8(special_opcode_addr);
//                          }
//                      }
//                      else
//                      {
//                          // The line change alone will fit into a special opcode
//                          // so modify our address increment first, then issue a
//                          // special opcode for the line change and it will push
//                          // a row into the line table
//                          if (addr_advance > 0)
//                          {
//                              debug_line_data.Append8(DW_LNS_advance_pc);
//                              debug_line_data.Append32_as_ULEB128(addr_advance);
//                          }
//
//                          // Advance of line and address will fit into a single byte special opcode
//                          // and this will also push a row onto the line table
//                          debug_line_data.Append8(special_opcode_line);
//                      }
//                  }
//                  else
//                  {
//                      // Advance of line and address will fit into a single byte special opcode
//                      // and this will also push a row onto the line table
//                      debug_line_data.Append8(special_opcode);
//                  }
//              }
//              prev_state = &curr_state;
//          }
//      }
//  }
//}