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 ..common.py3compat import BytesIO, iteritems
  10 from ..common.utils import struct_parse, bytelist2string
  11
  12
  13 # DWARF expression opcodes. name -> opcode mapping
  14 DW_OP_name2opcode = dict(
  15     DW_OP_addr=0x03,
  16     DW_OP_deref=0x06,
  17     DW_OP_const1u=0x08,
  18     DW_OP_const1s=0x09,
  19     DW_OP_const2u=0x0a,
  20     DW_OP_const2s=0x0b,
  21     DW_OP_const4u=0x0c,
  22     DW_OP_const4s=0x0d,
  23     DW_OP_const8u=0x0e,
  24     DW_OP_const8s=0x0f,
  25     DW_OP_constu=0x10,
  26     DW_OP_consts=0x11,
  27     DW_OP_dup=0x12,
  28     DW_OP_drop=0x13,
  29     DW_OP_over=0x14,
  30     DW_OP_pick=0x15,
  31     DW_OP_swap=0x16,
  32     DW_OP_rot=0x17,
  33     DW_OP_xderef=0x18,
  34     DW_OP_abs=0x19,
  35     DW_OP_and=0x1a,
  36     DW_OP_div=0x1b,
  37     DW_OP_minus=0x1c,
  38     DW_OP_mod=0x1d,
  39     DW_OP_mul=0x1e,
  40     DW_OP_neg=0x1f,
  41     DW_OP_not=0x20,
  42     DW_OP_or=0x21,
  43     DW_OP_plus=0x22,
  44     DW_OP_plus_uconst=0x23,
  45     DW_OP_shl=0x24,
  46     DW_OP_shr=0x25,
  47     DW_OP_shra=0x26,
  48     DW_OP_xor=0x27,
  49     DW_OP_bra=0x28,
  50     DW_OP_eq=0x29,
  51     DW_OP_ge=0x2a,
  52     DW_OP_gt=0x2b,
  53     DW_OP_le=0x2c,
  54     DW_OP_lt=0x2d,
  55     DW_OP_ne=0x2e,
  56     DW_OP_skip=0x2f,
  57     DW_OP_regx=0x90,
  58     DW_OP_fbreg=0x91,
  59     DW_OP_bregx=0x92,
  60     DW_OP_piece=0x93,
  61     DW_OP_deref_size=0x94,
  62     DW_OP_xderef_size=0x95,
  63     DW_OP_nop=0x96,
  64     DW_OP_push_object_address=0x97,
  65     DW_OP_call2=0x98,
  66     DW_OP_call4=0x99,
  67     DW_OP_call_ref=0x9a,
  68     DW_OP_form_tls_address=0x9b,
  69     DW_OP_call_frame_cfa=0x9c,
  70     DW_OP_bit_piece=0x9d,
  71 )
  72
  73 def _generate_dynamic_values(map, prefix, index_start, index_end, value_start):
  74     """ Generate values in a map (dict) dynamically. Each key starts with
  75         a (string) prefix, followed by an index in the inclusive range
  76         [index_start, index_end]. The values start at value_start.
  77     """
  78     for index in range(index_start, index_end + 1):
  79         name = '%s%s' % (prefix, index)
  80         value = value_start + index - index_start
  81         map[name] = value
  82
  83 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_lit', 0, 31, 0x30)
  84 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_reg', 0, 31, 0x50)
  85 _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_breg', 0, 31, 0x70)
  86
  87 # opcode -> name mapping
  88 DW_OP_opcode2name = dict((v, k) for k, v in iteritems(DW_OP_name2opcode))
  89
  90
  91 class GenericExprVisitor(object):
  92     """ A DWARF expression is a sequence of instructions encoded in a block
  93         of bytes. This class decodes the sequence into discrete instructions
  94         with their arguments and allows generic "visiting" to process them.
  95
  96         Usage: subclass this class, and override the needed methods. The
  97         easiest way would be to just override _after_visit, which gets passed
  98         each decoded instruction (with its arguments) in order. Clients of
  99         the visitor then just execute process_expr. The subclass can keep
 100         its own internal information updated in _after_visit and provide
 101         methods to extract it. For a good example of this usage, see the
 102         ExprDumper class in the descriptions module.
 103
 104         A more complex usage could be to override visiting methods for
 105         specific instructions, by placing them into the dispatch table.
 106     """
 107     def __init__(self, structs):
 108         self.structs = structs
 109         self._init_dispatch_table()
 110         self.stream = None
 111         self._cur_opcode = None
 112         self._cur_opcode_name = None
 113         self._cur_args = []
 114
 115     def process_expr(self, expr):
 116         """ Process (visit) a DWARF expression. expr should be a list of
 117             (integer) byte values.
 118         """
 119         self.stream = BytesIO(bytelist2string(expr))
 120
 121         while True:
 122             # Get the next opcode from the stream. If nothing is left in the
 123             # stream, we're done.
 124             byte = self.stream.read(1)
 125             if len(byte) == 0:
 126                 break
 127
 128             # Decode the opcode and its name
 129             self._cur_opcode = ord(byte)
 130             self._cur_opcode_name = DW_OP_opcode2name.get(
 131                 self._cur_opcode, 'OP:0x%x' % self._cur_opcode)
 132             # Will be filled in by visitors
 133             self._cur_args = []
 134
 135             # Dispatch to a visitor function
 136             visitor = self._dispatch_table.get(
 137                     self._cur_opcode,
 138                     self._default_visitor)
 139             visitor(self._cur_opcode, self._cur_opcode_name)
 140
 141             # Finally call the post-visit function
 142             self._after_visit(
 143                     self._cur_opcode, self._cur_opcode_name, self._cur_args)
 144
 145     def _after_visit(self, opcode, opcode_name, args):
 146         pass
 147
 148     def _default_visitor(self, opcode, opcode_name):
 149         pass
 150
 151     def _visit_OP_with_no_args(self, opcode, opcode_name):
 152         self._cur_args = []
 153
 154     def _visit_OP_addr(self, opcode, opcode_name):
 155         self._cur_args = [
 156                 struct_parse(self.structs.Dwarf_target_addr(''), self.stream)]
 157
 158     def _make_visitor_arg_struct(self, struct_arg):
 159         """ Create a visitor method for an opcode that that accepts a single
 160             argument, specified by a struct.
 161         """
 162         def visitor(opcode, opcode_name):
 163             self._cur_args = [struct_parse(struct_arg, self.stream)]
 164         return visitor
 165
 166     def _make_visitor_arg_struct2(self, struct_arg1, struct_arg2):
 167         """ Create a visitor method for an opcode that that accepts two
 168             arguments, specified by structs.
 169         """
 170         def visitor(opcode, opcode_name):
 171             self._cur_args = [
 172                 struct_parse(struct_arg1, self.stream),
 173                 struct_parse(struct_arg2, self.stream)]
 174         return visitor
 175
 176     def _init_dispatch_table(self):
 177         self._dispatch_table = {}
 178         def add(opcode_name, func):
 179             self._dispatch_table[DW_OP_name2opcode[opcode_name]] = func
 180
 181         add('DW_OP_addr', self._visit_OP_addr)
 182         add('DW_OP_const1u',
 183             self._make_visitor_arg_struct(self.structs.Dwarf_uint8('')))
 184         add('DW_OP_const1s',
 185             self._make_visitor_arg_struct(self.structs.Dwarf_int8('')))
 186         add('DW_OP_const2u',
 187             self._make_visitor_arg_struct(self.structs.Dwarf_uint16('')))
 188         add('DW_OP_const2s',
 189             self._make_visitor_arg_struct(self.structs.Dwarf_int16('')))
 190         add('DW_OP_const4u',
 191             self._make_visitor_arg_struct(self.structs.Dwarf_uint32('')))
 192         add('DW_OP_const4s',
 193             self._make_visitor_arg_struct(self.structs.Dwarf_int32('')))
 194         add('DW_OP_const8u',
 195             self._make_visitor_arg_struct2(
 196                 self.structs.Dwarf_uint32(''),
 197                 self.structs.Dwarf_uint32('')))
 198         add('DW_OP_const8s',
 199             self._make_visitor_arg_struct2(
 200                 self.structs.Dwarf_int32(''),
 201                 self.structs.Dwarf_int32('')))
 202         add('DW_OP_constu',
 203             self._make_visitor_arg_struct(self.structs.Dwarf_uleb128('')))
 204         add('DW_OP_consts',
 205             self._make_visitor_arg_struct(self.structs.Dwarf_sleb128('')))
 206         add('DW_OP_pick',
 207             self._make_visitor_arg_struct(self.structs.Dwarf_uint8('')))
 208         add('DW_OP_plus_uconst',
 209             self._make_visitor_arg_struct(self.structs.Dwarf_uleb128('')))
 210         add('DW_OP_bra',
 211             self._make_visitor_arg_struct(self.structs.Dwarf_int16('')))
 212         add('DW_OP_skip',
 213             self._make_visitor_arg_struct(self.structs.Dwarf_int16('')))
 214
 215         for opname in [ 'DW_OP_deref', 'DW_OP_dup', 'DW_OP_drop', 'DW_OP_over',
 216                         'DW_OP_swap', 'DW_OP_swap', 'DW_OP_rot', 'DW_OP_xderef',
 217                         'DW_OP_abs', 'DW_OP_and', 'DW_OP_div', 'DW_OP_minus',
 218                         'DW_OP_mod', 'DW_OP_mul', 'DW_OP_neg', 'DW_OP_not',
 219                         'DW_OP_plus', 'DW_OP_shl', 'DW_OP_shr', 'DW_OP_shra',
 220                         'DW_OP_xor', 'DW_OP_eq', 'DW_OP_ge', 'DW_OP_gt',
 221                         'DW_OP_le', 'DW_OP_lt', 'DW_OP_ne', 'DW_OP_nop',
 222                         'DW_OP_push_object_address', 'DW_OP_form_tls_address',
 223                         'DW_OP_call_frame_cfa']:
 224             add(opname, self._visit_OP_with_no_args)
 225
 226         for n in range(0, 32):
 227             add('DW_OP_lit%s' % n, self._visit_OP_with_no_args)
 228             add('DW_OP_reg%s' % n, self._visit_OP_with_no_args)
 229             add('DW_OP_breg%s' % n,
 230                 self._make_visitor_arg_struct(self.structs.Dwarf_sleb128('')))
 231
 232         add('DW_OP_fbreg',
 233             self._make_visitor_arg_struct(self.structs.Dwarf_sleb128('')))
 234         add('DW_OP_regx',
 235             self._make_visitor_arg_struct(self.structs.Dwarf_uleb128('')))
 236         add('DW_OP_bregx',
 237             self._make_visitor_arg_struct2(
 238                 self.structs.Dwarf_uleb128(''),
 239                 self.structs.Dwarf_sleb128('')))
 240         add('DW_OP_piece',
 241             self._make_visitor_arg_struct(self.structs.Dwarf_uleb128('')))
 242         add('DW_OP_bit_piece',
 243             self._make_visitor_arg_struct2(
 244                 self.structs.Dwarf_uleb128(''),
 245                 self.structs.Dwarf_uleb128('')))
 246         add('DW_OP_deref_size',
 247             self._make_visitor_arg_struct(self.structs.Dwarf_int8('')))
 248         add('DW_OP_xderef_size',
 249             self._make_visitor_arg_struct(self.structs.Dwarf_int8('')))
 250         add('DW_OP_call2',
 251             self._make_visitor_arg_struct(self.structs.Dwarf_uint16('')))
 252         add('DW_OP_call4',
 253             self._make_visitor_arg_struct(self.structs.Dwarf_uint32('')))
 254         add('DW_OP_call_ref',
 255             self._make_visitor_arg_struct(self.structs.Dwarf_offset('')))
 256
 257