#------------------------------------------------------------------------------- # elftools: dwarf/dwarf_expr.py # # Decoding DWARF expressions # # Eli Bendersky (eliben@gmail.com) # This code is in the public domain #------------------------------------------------------------------------------- from ..common.py3compat import BytesIO, iteritems from ..common.utils import struct_parse, bytelist2string # DWARF expression opcodes. name -> opcode mapping DW_OP_name2opcode = dict( DW_OP_addr=0x03, DW_OP_deref=0x06, DW_OP_const1u=0x08, DW_OP_const1s=0x09, DW_OP_const2u=0x0a, DW_OP_const2s=0x0b, DW_OP_const4u=0x0c, DW_OP_const4s=0x0d, DW_OP_const8u=0x0e, DW_OP_const8s=0x0f, DW_OP_constu=0x10, DW_OP_consts=0x11, DW_OP_dup=0x12, DW_OP_drop=0x13, DW_OP_over=0x14, DW_OP_pick=0x15, DW_OP_swap=0x16, DW_OP_rot=0x17, DW_OP_xderef=0x18, DW_OP_abs=0x19, DW_OP_and=0x1a, DW_OP_div=0x1b, DW_OP_minus=0x1c, DW_OP_mod=0x1d, DW_OP_mul=0x1e, DW_OP_neg=0x1f, DW_OP_not=0x20, DW_OP_or=0x21, DW_OP_plus=0x22, DW_OP_plus_uconst=0x23, DW_OP_shl=0x24, DW_OP_shr=0x25, DW_OP_shra=0x26, DW_OP_xor=0x27, DW_OP_bra=0x28, DW_OP_eq=0x29, DW_OP_ge=0x2a, DW_OP_gt=0x2b, DW_OP_le=0x2c, DW_OP_lt=0x2d, DW_OP_ne=0x2e, DW_OP_skip=0x2f, DW_OP_regx=0x90, DW_OP_fbreg=0x91, DW_OP_bregx=0x92, DW_OP_piece=0x93, DW_OP_deref_size=0x94, DW_OP_xderef_size=0x95, DW_OP_nop=0x96, DW_OP_push_object_address=0x97, DW_OP_call2=0x98, DW_OP_call4=0x99, DW_OP_call_ref=0x9a, DW_OP_form_tls_address=0x9b, DW_OP_call_frame_cfa=0x9c, DW_OP_bit_piece=0x9d, ) def _generate_dynamic_values(map, prefix, index_start, index_end, value_start): """ Generate values in a map (dict) dynamically. Each key starts with a (string) prefix, followed by an index in the inclusive range [index_start, index_end]. The values start at value_start. """ for index in range(index_start, index_end + 1): name = '%s%s' % (prefix, index) value = value_start + index - index_start map[name] = value _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_lit', 0, 31, 0x30) _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_reg', 0, 31, 0x50) _generate_dynamic_values(DW_OP_name2opcode, 'DW_OP_breg', 0, 31, 0x70) # opcode -> name mapping DW_OP_opcode2name = dict((v, k) for k, v in iteritems(DW_OP_name2opcode)) class GenericExprVisitor(object): """ A DWARF expression is a sequence of instructions encoded in a block of bytes. This class decodes the sequence into discrete instructions with their arguments and allows generic "visiting" to process them. Usage: subclass this class, and override the needed methods. The easiest way would be to just override _after_visit, which gets passed each decoded instruction (with its arguments) in order. Clients of the visitor then just execute process_expr. The subclass can keep its own internal information updated in _after_visit and provide methods to extract it. For a good example of this usage, see the ExprDumper class in the descriptions module. A more complex usage could be to override visiting methods for specific instructions, by placing them into the dispatch table. """ def __init__(self, structs): self.structs = structs self._init_dispatch_table() self.stream = None self._cur_opcode = None self._cur_opcode_name = None self._cur_args = [] def process_expr(self, expr): """ Process (visit) a DWARF expression. expr should be a list of (integer) byte values. """ self.stream = BytesIO(bytelist2string(expr)) while True: # Get the next opcode from the stream. If nothing is left in the # stream, we're done. byte = self.stream.read(1) if len(byte) == 0: break # Decode the opcode and its name self._cur_opcode = ord(byte) self._cur_opcode_name = DW_OP_opcode2name.get( self._cur_opcode, 'OP:0x%x' % self._cur_opcode) # Will be filled in by visitors self._cur_args = [] # Dispatch to a visitor function visitor = self._dispatch_table.get( self._cur_opcode, self._default_visitor) visitor(self._cur_opcode, self._cur_opcode_name) # Finally call the post-visit function self._after_visit( self._cur_opcode, self._cur_opcode_name, self._cur_args) def _after_visit(self, opcode, opcode_name, args): pass def _default_visitor(self, opcode, opcode_name): pass def _visit_OP_with_no_args(self, opcode, opcode_name): self._cur_args = [] def _visit_OP_addr(self, opcode, opcode_name): self._cur_args = [ struct_parse(self.structs.Dwarf_target_addr(''), self.stream)] def _make_visitor_arg_struct(self, struct_arg): """ Create a visitor method for an opcode that that accepts a single argument, specified by a struct. """ def visitor(opcode, opcode_name): self._cur_args = [struct_parse(struct_arg, self.stream)] return visitor def _make_visitor_arg_struct2(self, struct_arg1, struct_arg2): """ Create a visitor method for an opcode that that accepts two arguments, specified by structs. """ def visitor(opcode, opcode_name): self._cur_args = [ struct_parse(struct_arg1, self.stream), struct_parse(struct_arg2, self.stream)] return visitor def _init_dispatch_table(self): self._dispatch_table = {} def add(opcode_name, func): self._dispatch_table[DW_OP_name2opcode[opcode_name]] = func add('DW_OP_addr', self._visit_OP_addr) add('DW_OP_const1u', self._make_visitor_arg_struct(self.structs.Dwarf_uint8(''))) add('DW_OP_const1s', self._make_visitor_arg_struct(self.structs.Dwarf_int8(''))) add('DW_OP_const2u', self._make_visitor_arg_struct(self.structs.Dwarf_uint16(''))) add('DW_OP_const2s', self._make_visitor_arg_struct(self.structs.Dwarf_int16(''))) add('DW_OP_const4u', self._make_visitor_arg_struct(self.structs.Dwarf_uint32(''))) add('DW_OP_const4s', self._make_visitor_arg_struct(self.structs.Dwarf_int32(''))) add('DW_OP_const8u', self._make_visitor_arg_struct2( self.structs.Dwarf_uint32(''), self.structs.Dwarf_uint32(''))) add('DW_OP_const8s', self._make_visitor_arg_struct2( self.structs.Dwarf_int32(''), self.structs.Dwarf_int32(''))) add('DW_OP_constu', self._make_visitor_arg_struct(self.structs.Dwarf_uleb128(''))) add('DW_OP_consts', self._make_visitor_arg_struct(self.structs.Dwarf_sleb128(''))) add('DW_OP_pick', self._make_visitor_arg_struct(self.structs.Dwarf_uint8(''))) add('DW_OP_plus_uconst', self._make_visitor_arg_struct(self.structs.Dwarf_uleb128(''))) add('DW_OP_bra', self._make_visitor_arg_struct(self.structs.Dwarf_int16(''))) add('DW_OP_skip', self._make_visitor_arg_struct(self.structs.Dwarf_int16(''))) for opname in [ 'DW_OP_deref', 'DW_OP_dup', 'DW_OP_drop', 'DW_OP_over', 'DW_OP_swap', 'DW_OP_swap', 'DW_OP_rot', 'DW_OP_xderef', 'DW_OP_abs', 'DW_OP_and', 'DW_OP_div', 'DW_OP_minus', 'DW_OP_mod', 'DW_OP_mul', 'DW_OP_neg', 'DW_OP_not', 'DW_OP_plus', 'DW_OP_shl', 'DW_OP_shr', 'DW_OP_shra', 'DW_OP_xor', 'DW_OP_eq', 'DW_OP_ge', 'DW_OP_gt', 'DW_OP_le', 'DW_OP_lt', 'DW_OP_ne', 'DW_OP_nop', 'DW_OP_push_object_address', 'DW_OP_form_tls_address', 'DW_OP_call_frame_cfa']: add(opname, self._visit_OP_with_no_args) for n in range(0, 32): add('DW_OP_lit%s' % n, self._visit_OP_with_no_args) add('DW_OP_reg%s' % n, self._visit_OP_with_no_args) add('DW_OP_breg%s' % n, self._make_visitor_arg_struct(self.structs.Dwarf_sleb128(''))) add('DW_OP_fbreg', self._make_visitor_arg_struct(self.structs.Dwarf_sleb128(''))) add('DW_OP_regx', self._make_visitor_arg_struct(self.structs.Dwarf_uleb128(''))) add('DW_OP_bregx', self._make_visitor_arg_struct2( self.structs.Dwarf_uleb128(''), self.structs.Dwarf_sleb128(''))) add('DW_OP_piece', self._make_visitor_arg_struct(self.structs.Dwarf_uleb128(''))) add('DW_OP_bit_piece', self._make_visitor_arg_struct2( self.structs.Dwarf_uleb128(''), self.structs.Dwarf_uleb128(''))) add('DW_OP_deref_size', self._make_visitor_arg_struct(self.structs.Dwarf_int8(''))) add('DW_OP_xderef_size', self._make_visitor_arg_struct(self.structs.Dwarf_int8(''))) add('DW_OP_call2', self._make_visitor_arg_struct(self.structs.Dwarf_uint16(''))) add('DW_OP_call4', self._make_visitor_arg_struct(self.structs.Dwarf_uint32(''))) add('DW_OP_call_ref', self._make_visitor_arg_struct(self.structs.Dwarf_offset('')))