#-------------------------------------------------------------------------------
# elftools: dwarf/callframe.py
#
# DWARF call frame information
#
# Eli Bendersky (eliben@gmail.com)
# This code is in the public domain
#-------------------------------------------------------------------------------
from ..common.utils import (struct_parse, dwarf_assert, preserve_stream_pos)
from .structs import DWARFStructs
from .constants import * 


class CallFrameInstruction(object):
    """ A decoded instruction in the CFI section. opcode is the instruction
        opcode, numeric - as it appears in the section. args is a list of
        arguments (including arguments embedded in the low bits of some
        instructions, when applicable).
    """
    def __init__(self, opcode, args):
        self.opcode = opcode
        self.args = args

    def __repr__(self):
        return '%s (0x%x): %s' % (
            instruction_name(self.opcode), self.opcode, self.args)


class CIE(object):
    """ CIE - Common Information Entry.
        Contains a header and a list of instructions (CallFrameInstruction).
        offset: the offset of this entry from the beginning of the section
    """
    def __init__(self, header, instructions, offset):
        self.header = header
        self.instructions = instructions
        self.offset = offset

    def __getitem__(self, name):
        """ Implement dict-like access to header entries
        """
        return self.header[name]


class FDE(object):
    """ FDE - Frame Description Entry.
        Contains a header, a list of instructions (CallFrameInstruction) and a
        reference to the CIE object associated with this FDE.
        offset: the offset of this entry from the beginning of the section
    """
    def __init__(self, header, instructions, offset, cie):
        self.header = header
        self.instructions = instructions
        self.offset = offset
        self.cie = cie

    def __getitem__(self, name):
        """ Implement dict-like access to header entries
        """
        return self.header[name]


class CallFrameInfo(object):
    """ DWARF CFI (Call Frame Info)
        
        stream, size:
            A stream holding the .debug_frame section, and the size of the
            section in it.

        base_structs:
            The structs to be used as the base for parsing this section.
            Eventually, each entry gets its own structs based on the initial
            length field it starts with. The address_size, however, is taken
            from base_structs. This appears to be a limitation of the DWARFv3
            standard, fixed in v4 (where an address_size field exists for each
            CFI. I had a discussion about this on dwarf-discuss that confirms
            this.
            Currently for base_structs I simply use the elfclass of the
            containing file, but more sophisticated methods are used by
            libdwarf and others, such as guessing which CU contains which FDEs
            (based on their address ranges) and taking the address_size from
            those CUs.
    """
    def __init__(self, stream, size, base_structs):
        self.stream = stream
        self.size = size
        self.base_structs = base_structs
        self.entries = None

        # Map between an offset in the stream and the entry object found at this
        # offset. Useful for assigning CIE to FDEs according to the CIE_pointer
        # header field which contains a stream offset.
        self._entry_cache = {}

    def get_entries(self):
        if self.entries is None:
            self.entries = self._parse_entries()
        return self.entries

    def _parse_entries(self):
        entries = []
        offset = 0
        while offset < self.size:
            entries.append(self._parse_entry_at(offset))
            offset = self.stream.tell()
        return entries

    def _parse_entry_at(self, offset):
        """ Parse an entry from self.stream starting with the given offset.
            Return the entry object. self.stream will point right after the
            entry.
        """
        if offset in self._entry_cache:
            return self._entry_cache[offset]

        entry_length = struct_parse(
            self.base_structs.Dwarf_uint32(''), self.stream, offset)
        dwarf_format = 64 if entry_length == 0xFFFFFFFF else 32

        entry_structs = DWARFStructs(
            little_endian=self.base_structs.little_endian,
            dwarf_format=dwarf_format,
            address_size=self.base_structs.address_size)

        # Read the next field to see whether this is a CIE or FDE
        CIE_id = struct_parse(
            entry_structs.Dwarf_offset(''), self.stream)

        is_CIE = (
            (dwarf_format == 32 and CIE_id == 0xFFFFFFFF) or 
            CIE_id == 0xFFFFFFFFFFFFFFFF)

        if is_CIE:
            header_struct = entry_structs.Dwarf_CIE_header
        else:
            header_struct = entry_structs.Dwarf_FDE_header

        # Parse the header, which goes up to and including the
        # return_address_register field
        header = struct_parse(
            header_struct, self.stream, offset)

        # For convenience, compute the end offset for this entry
        end_offset = (
            offset + header.length +
            entry_structs.initial_length_field_size())

        # At this point self.stream is at the start of the instruction list
        # for this entry
        instructions = self._parse_instructions(
            entry_structs, self.stream.tell(), end_offset)

        if is_CIE:
            self._entry_cache[offset] = CIE(
                header=header, instructions=instructions, offset=offset)
        else: # FDE
            with preserve_stream_pos(self.stream):
                cie = self._parse_entry_at(header['CIE_pointer'])
            self._entry_cache[offset] = FDE(
                header=header, instructions=instructions, offset=offset,
                cie=cie)
        return self._entry_cache[offset]

    def _parse_instructions(self, structs, offset, end_offset):
        """ Parse a list of CFI instructions from self.stream, starting with
            the offset and until (not including) end_offset.
            Return a list of CallFrameInstruction objects.
        """
        instructions = []
        while offset < end_offset:
            opcode = struct_parse(structs.Dwarf_uint8(''), self.stream, offset)
            args = []

            primary = opcode & _PRIMARY_MASK
            primary_arg = opcode & _PRIMARY_ARG_MASK
            if primary == DW_CFA_advance_loc:
                args = [primary_arg]
            elif primary == DW_CFA_offset:
                args = [
                    primary_arg,
                    struct_parse(structs.Dwarf_uleb128(''), self.stream)]
            elif primary == DW_CFA_restore:
                args = [primary_arg]
            # primary == 0 and real opcode is extended
            elif opcode in (DW_CFA_nop, DW_CFA_remember_state,
                            DW_CFA_restore_state):
                args = []
            elif opcode == DW_CFA_set_loc:
                args = [
                    struct_parse(structs.Dwarf_target_addr(''), self.stream)]
            elif opcode == DW_CFA_advance_loc1:
                args = [struct_parse(structs.Dwarf_uint8(''), self.stream)]
            elif opcode == DW_CFA_advance_loc2:
                args = [struct_parse(structs.Dwarf_uint16(''), self.stream)]
            elif opcode == DW_CFA_advance_loc4:
                args = [struct_parse(structs.Dwarf_uint32(''), self.stream)]
            elif opcode in (DW_CFA_offset_extended, DW_CFA_register,
                            DW_CFA_def_cfa, DW_CFA_val_offset):
                args = [
                    struct_parse(structs.Dwarf_uleb128(''), self.stream),
                    struct_parse(structs.Dwarf_uleb128(''), self.stream)]
            elif opcode in (DW_CFA_restore_extended, DW_CFA_undefined,
                            DW_CFA_same_value, DW_CFA_def_cfa_register,
                            DW_CFA_def_cfa_offset):
                args = [struct_parse(structs.Dwarf_uleb128(''), self.stream)]
            elif opcode == DW_CFA_def_cfa_offset_sf:
                args = [struct_parse(structs.Dwarf_sleb128(''), self.stream)]
            elif opcode == DW_CFA_def_cfa_expression:
                args = [struct_parse(
                    structs.Dwarf_dw_form['DW_FORM_block'], self.stream)]
            elif opcode in (DW_CFA_expression, DW_CFA_val_expression):
                arsg = [
                    struct_parse(structs.Dwarf_uleb128(''), self.stream),
                    struct_parse(
                        structs.Dwarf_dw_form['DW_FORM_block'], self.stream)]
            elif opcode in (DW_CFA_offset_extended_sf,
                            DW_CFA_def_cfa_sf, DW_CFA_val_offset_sf):
                args = [
                    struct_parse(structs.Dwarf_uleb128(''), self.stream),
                    struct_parse(structs.Dwarf_sleb128(''), self.stream)]
            else:
                dwarf_assert(False, 'Unknown CFI opcode: 0x%x' % opcode)

            instructions.append(CallFrameInstruction(opcode=opcode, args=args))
            offset = self.stream.tell()
        return instructions


def instruction_name(opcode):
    """ Given an opcode, return the instruction name.
    """
    primary = opcode & _PRIMARY_MASK
    if primary == 0:
        return _OPCODE_NAME_MAP[opcode]
    else:
        return _OPCODE_NAME_MAP[primary]


#---------------- PRIVATE ----------------#

_PRIMARY_MASK = 0b11000000
_PRIMARY_ARG_MASK = 0b00111111

# This dictionary is filled by automatically scanning the constants module
# for DW_CFA_* instructions, and mapping their values to names. Since all
# names were imported from constants with `import *`, we look in globals()
_OPCODE_NAME_MAP = {}
for name in list(globals().iterkeys()):
    if name.startswith('DW_CFA'):
        _OPCODE_NAME_MAP[globals()[name]] = name