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DWARF expr: removing old GenericExprVisitor
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@eliben
eliben committed Mar 14, 2020
1 parent 3d97b6e commit 4cf5cb0
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Showing 2 changed files with 1 addition and 168 deletions.
2 changes: 1 addition & 1 deletion elftools/dwarf/descriptions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
from collections import defaultdict

from .constants import *
from .dwarf_expr import GenericExprVisitor, parse_expr
from .dwarf_expr import parse_expr
from .die import DIE
from ..common.utils import preserve_stream_pos, dwarf_assert
from ..common.py3compat import bytes2str
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167 changes: 0 additions & 167 deletions elftools/dwarf/dwarf_expr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -104,173 +104,6 @@ def _generate_dynamic_values(map, prefix, index_start, index_end, value_start):
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('')))


DwarfExprOp = namedtuple('DwarfExprOp', 'op op_name args')


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