#-------------------------------------------------------------------------------
# elftools: dwarf/structs.py
#
# Encapsulation of Construct structs for parsing DWARF, adjusted for correct
# endianness and word-size.
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
from ..construct import (
    UBInt8, UBInt16, UBInt32, UBInt64, ULInt8, ULInt16, ULInt32, ULInt64,
    Adapter, Struct, ConstructError, If, RepeatUntil, Field, Rename, Enum,
    PrefixedArray, CString,
    )

from .enums import *


class DWARFStructs(object):
    """ Exposes Construct structs suitable for parsing information from DWARF 
        sections. Each compile unit in DWARF info can have its own structs
        object. Keep in mind that these structs have to be given a name (by 
        calling them with a name) before being used for parsing (like other
        Construct structs). Those that should be used without a name are marked
        by (+).
    
        Accessible attributes (mostly as described in chapter 7 of the DWARF
        spec v3):
    
            Dwarf_uint{8,16,32,64):
                Data chunks of the common sizes
            
            Dwarf_offset:
                32-bit or 64-bit word, depending on dwarf_format
            
            Dwarf_target_addr:
                32-bit or 64-bit word, depending on address size
            
            Dwarf_initial_length:
                "Initial length field" encoding
                section 7.4
            
            Dwarf_{u,s}leb128:
                ULEB128 and SLEB128 variable-length encoding
            
            Dwarf_CU_header (+):
                Compilation unit header
        
            Dwarf_abbrev_declaration (+):
                Abbreviation table declaration - doesn't include the initial
                code, only the contents.
            
            Dwarf_dw_form (+):
                A dictionary mapping 'DW_FORM_*' keys into construct Structs
                that parse such forms. These Structs have already been given
                dummy names.
        
        See also the documentation of public methods.
    """
    def __init__(self, little_endian, dwarf_format, address_size):
        """ little_endian:
                True if the file is little endian, False if big
            
            dwarf_format:
                DWARF Format: 32 or 64-bit (see spec section 7.4)
            
            address_size:
                Target machine address size, in bytes (4 or 8). (See spec 
                section 7.5.1)
        """
        assert dwarf_format == 32 or dwarf_format == 64
        assert address_size == 8 or address_size == 4
        self.little_endian = little_endian
        self.dwarf_format = dwarf_format  
        self.address_size = address_size
        self._create_structs()

    def initial_length_field_size(self):
        """ Size of an initial length field.
        """
        return 4 if self.dwarf_format == 32 else 12

    def _create_structs(self):
        if self.little_endian:
            self.Dwarf_uint8 = ULInt8
            self.Dwarf_uint16 = ULInt16
            self.Dwarf_uint32 = ULInt32
            self.Dwarf_uint64 = ULInt64
            self.Dwarf_offset = ULInt32 if self.dwarf_format == 32 else ULInt64
            self.Dwarf_target_addr = (
                ULInt32 if self.address_size == 4 else ULInt64)
        else:
            self.Dwarf_uint8 = UBInt8
            self.Dwarf_uint16 = UBInt16
            self.Dwarf_uint32 = UBInt32
            self.Dwarf_uint64 = UBInt64
            self.Dwarf_offset = UBInt32 if self.dwarf_format == 32 else UBInt64
            self.Dwarf_target_addr = (
                UBInt32 if self.address_size == 4 else UBInt64)

        self._create_initial_length()
        self._create_leb128()
        self._create_cu_header()
        self._create_abbrev_declaration()
        self._create_dw_form()

    def _create_initial_length(self):
        def _InitialLength(name):
            # Adapts a Struct that parses forward a full initial length field.
            # Only if the first word is the continuation value, the second 
            # word is parsed from the stream.
            #
            return _InitialLengthAdapter(
                Struct(name,
                    self.Dwarf_uint32('first'),
                    If(lambda ctx: ctx.first == 0xFFFFFFFF,
                        self.Dwarf_uint64('second'),
                        elsevalue=None)))
        self.Dwarf_initial_length = _InitialLength

    def _create_leb128(self):
        self.Dwarf_uleb128 = _ULEB128
        self.Dwarf_sleb128 = _SLEB128

    def _create_cu_header(self):
        self.Dwarf_CU_header = Struct('Dwarf_CU_header',
            self.Dwarf_initial_length('unit_length'),
            self.Dwarf_uint16('version'),
            self.Dwarf_offset('debug_abbrev_offset'),
            self.Dwarf_uint8('address_size'))
    
    def _create_abbrev_declaration(self):
        self.Dwarf_abbrev_declaration = Struct('Dwarf_abbrev_entry',
            Enum(self.Dwarf_uleb128('tag'), **ENUM_DW_TAG),
            Enum(self.Dwarf_uint8('children_flag'), **ENUM_DW_CHILDREN),
            RepeatUntil(
                lambda obj, ctx: 
                    obj.name == 'DW_AT_null' and obj.form == 'DW_FORM_null',
                Struct('attr_spec',
                    Enum(self.Dwarf_uleb128('name'), **ENUM_DW_AT),
                    Enum(self.Dwarf_uleb128('form'), **ENUM_DW_FORM))))

    def _create_dw_form(self):
        self.Dwarf_dw_form = dict(
            DW_FORM_addr=self.Dwarf_target_addr(''),
            
            DW_FORM_block1=self._make_block_struct(self.Dwarf_uint8),
            DW_FORM_block2=self._make_block_struct(self.Dwarf_uint16),
            DW_FORM_block4=self._make_block_struct(self.Dwarf_uint32),
            DW_FORM_block=self._make_block_struct(self.Dwarf_uleb128),
            
            # All DW_FORM_data<n> forms are assumed to be unsigned
            DW_FORM_data1=self.Dwarf_uint8(''),
            DW_FORM_data2=self.Dwarf_uint16(''),
            DW_FORM_data4=self.Dwarf_uint32(''),
            DW_FORM_data8=self.Dwarf_uint64(''),
            DW_FORM_sdata=self.Dwarf_sleb128(''),
            DW_FORM_udata=self.Dwarf_uleb128(''),
            
            DW_FORM_string=CString(''),
            DW_FORM_strp=self.Dwarf_offset(''),
            DW_FORM_flag=self.Dwarf_uint8(''),
            
            DW_FORM_ref1=self.Dwarf_uint8(''),
            DW_FORM_ref2=self.Dwarf_uint16(''),
            DW_FORM_ref4=self.Dwarf_uint32(''),
            DW_FORM_ref8=self.Dwarf_uint64(''),
            DW_FORM_ref_udata=self.Dwarf_uleb128(''),
            DW_FORM_ref_addr=self.Dwarf_offset(''),
            
            DW_FORM_indirect=self.Dwarf_uleb128(''),
        )

    def _make_block_struct(self, length_field):
        """ Create a struct for DW_FORM_block<size> 
        """
        return PrefixedArray(
                    subcon=self.Dwarf_uint8('elem'),
                    length_field=length_field(''))


class _InitialLengthAdapter(Adapter):
    """ A standard Construct adapter that expects a sub-construct
        as a struct with one or two values (first, second).
    """
    def _decode(self, obj, context):
        if obj.first < 0xFFFFFF00:
            return obj.first
        else:
            if obj.first == 0xFFFFFFFF:
                return obj.second
            else:
                raise ConstructError("Failed decoding initial length for %X" % (
                    obj.first))


def _LEB128_reader():
    """ Read LEB128 variable-length data from the stream. The data is terminated
        by a byte with 0 in its highest bit.
    """
    return RepeatUntil(
                lambda obj, ctx: ord(obj) < 0x80,
                Field(None, 1))


class _ULEB128Adapter(Adapter):
    """ An adapter for ULEB128, given a sequence of bytes in a sub-construct.
    """
    def _decode(self, obj, context):
        value = 0
        for b in reversed(obj):
            value = (value << 7) + (ord(b) & 0x7F)
        return value


class _SLEB128Adapter(Adapter):
    """ An adapter for SLEB128, given a sequence of bytes in a sub-construct.
    """
    def _decode(self, obj, context):
        value = 0
        for b in reversed(obj):
            value = (value << 7) + (ord(b) & 0x7F)
        if ord(obj[-1]) & 0x40:
            # negative -> sign extend
            #
            value |= - (1 << (7 * len(obj)))
        return value


def _ULEB128(name):
    """ A construct creator for ULEB128 encoding.
    """
    return Rename(name, _ULEB128Adapter(_LEB128_reader()))


def _SLEB128(name):
    """ A construct creator for SLEB128 encoding.
    """
    return Rename(name, _SLEB128Adapter(_LEB128_reader()))