elftools/dwarf/dwarf_expr.py

   1 #-------------------------------------------------------------------------------
   2 # elftools: dwarf/dwarf_expr.py
   3 #
   4 # Decoding DWARF expressions
   5 #
   6 # Eli Bendersky (eliben@gmail.com)
   7 # This code is in the public domain
   8 #-------------------------------------------------------------------------------
   9 from collections import namedtuple
  10 from io import BytesIO
  11
  12 from ..common.utils import struct_parse, bytelist2string, read_blob
  13 from ..common.exceptions import DWARFError
  14
  15
  16 # DWARF expression opcodes. name -> opcode mapping
  17 DW_OP_name2opcode = dict(
  18     DW_OP_addr=0x03,
  19     DW_OP_deref=0x06,
  20     DW_OP_const1u=0x08,
  21     DW_OP_const1s=0x09,
  22     DW_OP_const2u=0x0a,
  23     DW_OP_const2s=0x0b,
  24     DW_OP_const4u=0x0c,
  25     DW_OP_const4s=0x0d,
  26     DW_OP_const8u=0x0e,
  27     DW_OP_const8s=0x0f,
  28     DW_OP_constu=0x10,
  29     DW_OP_consts=0x11,
  30     DW_OP_dup=0x12,
  31     DW_OP_drop=0x13,
  32     DW_OP_over=0x14,
  33     DW_OP_pick=0x15,
  34     DW_OP_swap=0x16,
  35     DW_OP_rot=0x17,
  36     DW_OP_xderef=0x18,
  37     DW_OP_abs=0x19,
  38     DW_OP_and=0x1a,
  39     DW_OP_div=0x1b,
  40     DW_OP_minus=0x1c,
  41     DW_OP_mod=0x1d,
  42     DW_OP_mul=0x1e,
  43     DW_OP_neg=0x1f,
  44     DW_OP_not=0x20,
  45     DW_OP_or=0x21,
  46     DW_OP_plus=0x22,
  47     DW_OP_plus_uconst=0x23,
  48     DW_OP_shl=0x24,
  49     DW_OP_shr=0x25,
  50     DW_OP_shra=0x26,
  51     DW_OP_xor=0x27,
  52     DW_OP_bra=0x28,
  53     DW_OP_eq=0x29,
  54     DW_OP_ge=0x2a,
  55     DW_OP_gt=0x2b,
  56     DW_OP_le=0x2c,
  57     DW_OP_lt=0x2d,
  58     DW_OP_ne=0x2e,
  59     DW_OP_skip=0x2f,
  60     DW_OP_regx=0x90,
  61     DW_OP_fbreg=0x91,
  62     DW_OP_bregx=0x92,
  63     DW_OP_piece=0x93,
  64     DW_OP_deref_size=0x94,
  65     DW_OP_xderef_size=0x95,
  66     DW_OP_nop=0x96,
  67     DW_OP_push_object_address=0x97,
  68     DW_OP_call2=0x98,
  69     DW_OP_call4=0x99,
  70     DW_OP_call_ref=0x9a,
  71     DW_OP_form_tls_address=0x9b,
  72     DW_OP_call_frame_cfa=0x9c,
  73     DW_OP_bit_piece=0x9d,
  74     DW_OP_implicit_value=0x9e,
  75     DW_OP_stack_value=0x9f,
  76     DW_OP_implicit_pointer=0xa0,
  77     DW_OP_addrx=0xa1,
  78     DW_OP_constx=0xa2,
  79     DW_OP_entry_value=0xa3,
  80     DW_OP_const_type=0xa4,
  81     DW_OP_regval_type=0xa5,
  82     DW_OP_deref_type=0xa6,
  83     DW_OP_xderef_type=0xa7,
  84     DW_OP_convert=0xa8,
  85     DW_OP_reinterpret=0xa9,
  86     DW_OP_lo_user=0xe0,
  87     DW_OP_GNU_push_tls_address=0xe0,
  88     DW_OP_WASM_location=0xed,
  89     DW_OP_GNU_implicit_pointer=0xf2,
  90     DW_OP_GNU_entry_value=0xf3,
  91     DW_OP_GNU_const_type=0xf4,
  92     DW_OP_GNU_regval_type=0xf5,
  93     DW_OP_GNU_deref_type=0xf6,
  94     DW_OP_GNU_convert=0xf7,
  95     DW_OP_GNU_parameter_ref=0xfa,
  96     DW_OP_hi_user=0xff,
  97 )
  98
  99 def _generate_dynamic_values(map, prefix, index_start, index_end, value_start):
 100     """ Generate values in a map (dict) dynamically. Each key starts with
 101         a (string) prefix, followed by an index in the inclusive range
 102         [index_start, index_end]. The values start at value_start.
 103     """
 104     for index in range(index_start, index_end + 1):
 105         name = '%s%s' % (prefix, index)
 106         value = value_start + index - index_start
 107         map[name] = value
 108
 109 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_lit', 0, 31, 0x30)
 110 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_reg', 0, 31, 0x50)
 111 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_breg', 0, 31, 0x70)
 112
 113 # opcode -> name mapping
 114 DW_OP_opcode2name = dict((v, k) for k, v in DW_OP_name2opcode.items())
 115
 116
 117 # Each parsed DWARF expression is returned as this type with its numeric opcode,
 118 # op name (as a string) and a list of arguments.
 119 DWARFExprOp = namedtuple('DWARFExprOp', 'op op_name args offset')
 120
 121
 122 class DWARFExprParser(object):
 123     """DWARF expression parser.
 124
 125     When initialized, requires structs to cache a dispatch table. After that,
 126     parse_expr can be called repeatedly - it's stateless.
 127     """
 128
 129     def __init__(self, structs):
 130         self._dispatch_table = _init_dispatch_table(structs)
 131
 132     def parse_expr(self, expr):
 133         """ Parses expr (a list of integers) into a list of DWARFExprOp.
 134
 135         The list can potentially be nested.
 136         """
 137         stream = BytesIO(bytelist2string(expr))
 138         parsed = []
 139
 140         while True:
 141             # Get the next opcode from the stream. If nothing is left in the
 142             # stream, we're done.
 143             offset = stream.tell()
 144             byte = stream.read(1)
 145             if len(byte) == 0:
 146                 break
 147
 148             # Decode the opcode and its name.
 149             op = ord(byte)
 150             op_name = DW_OP_opcode2name.get(op, 'OP:0x%x' % op)
 151
 152             # Use dispatch table to parse args.
 153             arg_parser = self._dispatch_table[op]
 154             args = arg_parser(stream)
 155
 156             parsed.append(DWARFExprOp(op=op, op_name=op_name, args=args, offset=offset))
 157
 158         return parsed
 159
 160
 161 def _init_dispatch_table(structs):
 162     """Creates a dispatch table for parsing args of an op.
 163
 164     Returns a dict mapping opcode to a function. The function accepts a stream
 165     and return a list of parsed arguments for the opcode from the stream;
 166     the stream is advanced by the function as needed.
 167     """
 168     table = {}
 169     def add(opcode_name, func):
 170         table[DW_OP_name2opcode[opcode_name]] = func
 171
 172     def parse_noargs():
 173         return lambda stream: []
 174
 175     def parse_op_addr():
 176         return lambda stream: [struct_parse(structs.Dwarf_target_addr(''),
 177                                             stream)]
 178
 179     def parse_arg_struct(arg_struct):
 180         return lambda stream: [struct_parse(arg_struct, stream)]
 181
 182     def parse_arg_struct2(arg1_struct, arg2_struct):
 183         return lambda stream: [struct_parse(arg1_struct, stream),
 184                                struct_parse(arg2_struct, stream)]
 185
 186     # ULEB128, then an expression of that length
 187     def parse_nestedexpr():
 188         def parse(stream):
 189             size = struct_parse(structs.Dwarf_uleb128(''), stream)
 190             nested_expr_blob = read_blob(stream, size)
 191             return [DWARFExprParser(structs).parse_expr(nested_expr_blob)]
 192         return parse
 193
 194     # ULEB128, then a blob of that size
 195     def parse_blob():
 196         return lambda stream: [read_blob(stream, struct_parse(structs.Dwarf_uleb128(''), stream))]
 197
 198     # ULEB128 with datatype DIE offset, then byte, then a blob of that size
 199     def parse_typedblob():
 200         return lambda stream: [struct_parse(structs.Dwarf_uleb128(''), stream), read_blob(stream, struct_parse(structs.Dwarf_uint8(''), stream))]
 201
 202     # https://yurydelendik.github.io/webassembly-dwarf/
 203     # Byte, then variant: 0, 1, 2 => uleb128, 3 => uint32
 204     def parse_wasmloc():
 205         def parse(stream):
 206             op = struct_parse(structs.Dwarf_uint8(''), stream)
 207             if 0 <= op <= 2:
 208                 return [op, struct_parse(structs.Dwarf_uleb128(''), stream)]
 209             elif op == 3:
 210                 return [op, struct_parse(structs.Dwarf_uint32(''), stream)]
 211             else:
 212                 raise DWARFError("Unknown operation code in DW_OP_WASM_location: %d" % (op,))
 213         return parse
 214
 215     add('DW_OP_addr', parse_op_addr())
 216     add('DW_OP_addrx', parse_arg_struct(structs.Dwarf_uleb128('')))
 217     add('DW_OP_const1u', parse_arg_struct(structs.Dwarf_uint8('')))
 218     add('DW_OP_const1s', parse_arg_struct(structs.Dwarf_int8('')))
 219     add('DW_OP_const2u', parse_arg_struct(structs.Dwarf_uint16('')))
 220     add('DW_OP_const2s', parse_arg_struct(structs.Dwarf_int16('')))
 221     add('DW_OP_const4u', parse_arg_struct(structs.Dwarf_uint32('')))
 222     add('DW_OP_const4s', parse_arg_struct(structs.Dwarf_int32('')))
 223     add('DW_OP_const8u', parse_arg_struct(structs.Dwarf_uint64('')))
 224     add('DW_OP_const8s', parse_arg_struct(structs.Dwarf_int64('')))
 225     add('DW_OP_constu', parse_arg_struct(structs.Dwarf_uleb128('')))
 226     add('DW_OP_consts', parse_arg_struct(structs.Dwarf_sleb128('')))
 227     add('DW_OP_pick', parse_arg_struct(structs.Dwarf_uint8('')))
 228     add('DW_OP_plus_uconst', parse_arg_struct(structs.Dwarf_uleb128('')))
 229     add('DW_OP_bra', parse_arg_struct(structs.Dwarf_int16('')))
 230     add('DW_OP_skip', parse_arg_struct(structs.Dwarf_int16('')))
 231
 232     for opname in [ 'DW_OP_deref', 'DW_OP_dup', 'DW_OP_drop', 'DW_OP_over',
 233                     'DW_OP_swap', 'DW_OP_swap', 'DW_OP_rot', 'DW_OP_xderef',
 234                     'DW_OP_abs', 'DW_OP_and', 'DW_OP_div', 'DW_OP_minus',
 235                     'DW_OP_mod', 'DW_OP_mul', 'DW_OP_neg', 'DW_OP_not',
 236                     'DW_OP_or', 'DW_OP_plus', 'DW_OP_shl', 'DW_OP_shr',
 237                     'DW_OP_shra', 'DW_OP_xor', 'DW_OP_eq', 'DW_OP_ge',
 238                     'DW_OP_gt', 'DW_OP_le', 'DW_OP_lt', 'DW_OP_ne', 'DW_OP_nop',
 239                     'DW_OP_push_object_address', 'DW_OP_form_tls_address',
 240                     'DW_OP_call_frame_cfa', 'DW_OP_stack_value',
 241                     'DW_OP_GNU_push_tls_address']:
 242         add(opname, parse_noargs())
 243
 244     for n in range(0, 32):
 245         add('DW_OP_lit%s' % n, parse_noargs())
 246         add('DW_OP_reg%s' % n, parse_noargs())
 247         add('DW_OP_breg%s' % n, parse_arg_struct(structs.Dwarf_sleb128('')))
 248
 249     add('DW_OP_fbreg', parse_arg_struct(structs.Dwarf_sleb128('')))
 250     add('DW_OP_regx', parse_arg_struct(structs.Dwarf_uleb128('')))
 251     add('DW_OP_bregx', parse_arg_struct2(structs.Dwarf_uleb128(''),
 252                                          structs.Dwarf_sleb128('')))
 253     add('DW_OP_piece', parse_arg_struct(structs.Dwarf_uleb128('')))
 254     add('DW_OP_bit_piece', parse_arg_struct2(structs.Dwarf_uleb128(''),
 255                                              structs.Dwarf_uleb128('')))
 256     add('DW_OP_deref_size', parse_arg_struct(structs.Dwarf_int8('')))
 257     add('DW_OP_xderef_size', parse_arg_struct(structs.Dwarf_int8('')))
 258     add('DW_OP_call2', parse_arg_struct(structs.Dwarf_uint16('')))
 259     add('DW_OP_call4', parse_arg_struct(structs.Dwarf_uint32('')))
 260     add('DW_OP_call_ref', parse_arg_struct(structs.Dwarf_offset('')))
 261     add('DW_OP_implicit_value', parse_blob())
 262     add('DW_OP_entry_value', parse_nestedexpr())
 263     add('DW_OP_const_type', parse_typedblob())
 264     add('DW_OP_regval_type', parse_arg_struct2(structs.Dwarf_uleb128(''),
 265                                                    structs.Dwarf_uleb128('')))
 266     add('DW_OP_deref_type', parse_arg_struct2(structs.Dwarf_uint8(''),
 267                                               structs.Dwarf_uleb128('')))
 268     add('DW_OP_implicit_pointer', parse_arg_struct2(structs.Dwarf_offset(''),
 269                                                         structs.Dwarf_sleb128('')))
 270     add('DW_OP_convert', parse_arg_struct(structs.Dwarf_uleb128('')))
 271     add('DW_OP_GNU_entry_value', parse_nestedexpr())
 272     add('DW_OP_GNU_const_type', parse_typedblob())
 273     add('DW_OP_GNU_regval_type', parse_arg_struct2(structs.Dwarf_uleb128(''),
 274                                                    structs.Dwarf_uleb128('')))
 275     add('DW_OP_GNU_deref_type', parse_arg_struct2(structs.Dwarf_uint8(''),
 276                                                    structs.Dwarf_uleb128('')))
 277     add('DW_OP_GNU_implicit_pointer', parse_arg_struct2(structs.Dwarf_offset(''),
 278                                                         structs.Dwarf_sleb128('')))
 279     add('DW_OP_GNU_parameter_ref', parse_arg_struct(structs.Dwarf_offset('')))
 280     add('DW_OP_GNU_convert', parse_arg_struct(structs.Dwarf_uleb128('')))
 281     add('DW_OP_WASM_location', parse_wasmloc())
 282
 283     return table