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"""
Expression reducer:
Apply reduction rules to an Expression ast
"""
import logging
from miasm2.expression.expression import ExprInt, ExprId, ExprOp, ExprSlice,\
ExprCompose, ExprMem, ExprCond
log_reduce = logging.getLogger("expr_reduce")
console_handler = logging.StreamHandler()
console_handler.setFormatter(logging.Formatter("%(levelname)-5s: %(message)s"))
log_reduce.addHandler(console_handler)
log_reduce.setLevel(logging.WARNING)
class ExprNode(object):
"""Clone of Expression object with additionnal information"""
def __init__(self, expr):
self.expr = expr
# Generic field to store custom node information
self.info = None
self.arg, self.args = None, None
self.cond, self.src1, self.src2 = None, None, None
def __repr__(self):
expr = self.expr
if self.info is not None:
out = repr(self.info)
elif isinstance(expr, (ExprInt, ExprId)):
out = str(None)
elif isinstance(expr, ExprMem):
out = "@%d[%r]" % (self.expr.size, self.arg)
elif isinstance(expr, ExprSlice):
out = "%r[%d:%d]" % (self.arg, expr.start, expr.stop)
elif isinstance(expr, ExprOp):
if len(self.args) == 1:
out = "%s(%s)" % (expr.op, self.args[0])
else:
out = expr.op.join([repr(arg) for arg in self.args])
elif isinstance(expr, ExprCompose):
out = "{%s}" % ', '.join([repr(arg) for arg in self.args])
elif isinstance(expr, ExprCond):
out = "%r?%r:%r" % (self.cond, self.src1, self.src2)
else:
raise TypeError("Unknown node Type %r", type(expr))
return out
class ExprReducer(object):
"""Apply reduction rules to an expr
reduction_rules: list of ordered reduction rules
List of function representing reduction rules
Function API:
reduction_xxx(self, node, lvl=0)
with:
* node: the ExprNode to qualify
* lvl: [optional] the recursion level
Returns:
* None if the reduction rule is not applied
* the resulting information to store in the ExprNode.info
allow_none_result: allow missing reduction rules
"""
reduction_rules = []
allow_none_result = False
def expr2node(self, expr):
"""Build ExprNode mirror of @expr
@expr: Expression to analyze
"""
if isinstance(expr, (ExprId, ExprInt)):
node = ExprNode(expr)
elif isinstance(expr, (ExprMem, ExprSlice)):
son = self.expr2node(expr.arg)
node = ExprNode(expr)
node.arg = son
elif isinstance(expr, ExprOp):
sons = [self.expr2node(arg) for arg in expr.args]
node = ExprNode(expr)
node.args = sons
elif isinstance(expr, ExprCompose):
sons = [self.expr2node(arg) for arg in expr.args]
node = ExprNode(expr)
node.args = sons
elif isinstance(expr, ExprCond):
node = ExprNode(expr)
node.cond = self.expr2node(expr.cond)
node.src1 = self.expr2node(expr.src1)
node.src2 = self.expr2node(expr.src2)
else:
raise TypeError("Unknown Expr Type %r", type(expr))
return node
def reduce(self, expr):
"""Returns an ExprNode tree mirroring @expr tree. The ExprNode is
computed by applying reduction rules to the expression @expr
@expr: an Expression
"""
node = self.expr2node(expr)
return self.categorize(node, 0)
def categorize(self, node, lvl=0):
"""Recursively apply rules to @node
@node: ExprNode to analyze
@lvl: actual recusion level
"""
expr = node.expr
log_reduce.debug("\t" * lvl + "Reduce...: %s", node.expr)
if isinstance(expr, (ExprId, ExprInt)):
pass
elif isinstance(expr, ExprMem):
arg = self.categorize(node.arg, lvl + 1)
node = ExprNode(ExprMem(arg.expr, expr.size))
node.arg = arg
elif isinstance(expr, ExprSlice):
arg = self.categorize(node.arg, lvl + 1)
node = ExprNode(ExprSlice(arg.expr, expr.start, expr.stop))
node.arg = arg
elif isinstance(expr, ExprOp):
new_args = []
for arg in node.args:
new_a = self.categorize(arg, lvl + 1)
assert new_a.expr.size == arg.expr.size
new_args.append(new_a)
node = ExprNode(ExprOp(expr.op, *[x.expr for x in new_args]))
node.args = new_args
expr = node.expr
elif isinstance(expr, ExprCompose):
new_args = []
new_expr_args = []
for arg in node.args:
arg = self.categorize(arg, lvl + 1)
new_args.append(arg)
new_expr_args.append(arg.expr)
new_expr = ExprCompose(*new_expr_args)
node = ExprNode(new_expr)
node.args = new_args
elif isinstance(expr, ExprCond):
cond = self.categorize(node.cond, lvl + 1)
src1 = self.categorize(node.src1, lvl + 1)
src2 = self.categorize(node.src2, lvl + 1)
node = ExprNode(ExprCond(cond.expr, src1.expr, src2.expr))
node.cond, node.src1, node.src2 = cond, src1, src2
else:
raise TypeError("Unknown Expr Type %r", type(expr))
node.info = self.apply_rules(node, lvl)
log_reduce.debug("\t" * lvl + "Reduce result: %s %r",
node.expr, node.info)
return node
def apply_rules(self, node, lvl=0):
"""Find and apply reduction rules to @node
@node: ExprNode to analyse
@lvl: actuel recusion level
"""
for rule in self.reduction_rules:
ret = rule(self, node, lvl)
if ret is not None:
log_reduce.debug("\t" * lvl + "Rule found: %r", rule)
return ret
if not self.allow_none_result:
raise RuntimeError('Missing reduction rule for %r' % node.expr)
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