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binexport2: prune operands more precisely

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This commit is contained in:
Willi Ballenthin
2024-12-05 14:28:32 +00:00
committed by Willi Ballenthin
parent 1f374e4986
commit 95fc747e6f
1 changed files with 20 additions and 41 deletions
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61
capa/features/extractors/binexport2/helpers.py
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@@ -50,6 +50,25 @@ def is_vertex_type(vertex: BinExport2.CallGraph.Vertex, type_: BinExport2.CallGr
return vertex.HasField("type") and vertex.type == type_
# internal to `build_expression_tree`
# this is unstable: it is subject to change, so don't rely on it!
def _prune_expression_tree_references_to_tree_index(
expression_tree: list[list[int]],
tree_index: int,
):
# `i` is the index of the tree node that we'll search for `tree_index`
# if we remove `tree_index` from it, and it is now empty,
# then we'll need to prune references to `i`.
for i, tree_node in enumerate(expression_tree):
if tree_index in tree_node:
tree_node.remove(tree_index)
if len(tree_node) == 0:
# if the parent node is now empty,
# remove references to that parent node.
_prune_expression_tree_references_to_tree_index(expression_tree, i)
# internal to `build_expression_tree`
# this is unstable: it is subject to change, so don't rely on it!
def _prune_expression_tree_empty_shifts(
@@ -70,9 +89,7 @@ def _prune_expression_tree_empty_shifts(
#
# Which seems to be as if the shift wasn't there (shift of #0)
# so we want to remove references to this node from any parent nodes.
for tree_node in expression_tree:
if tree_index in tree_node:
tree_node.remove(tree_index)
_prune_expression_tree_references_to_tree_index(expression_tree, tree_index)
return
@@ -80,42 +97,6 @@ def _prune_expression_tree_empty_shifts(
_prune_expression_tree_empty_shifts(be2, operand, expression_tree, child_tree_index)
# internal to `build_expression_tree`
# this is unstable: it is subject to change, so don't rely on it!
def _prune_expression_tree_empty_commas(
be2: BinExport2,
operand: BinExport2.Operand,
expression_tree: list[list[int]],
tree_index: int,
):
expression_index = operand.expression_index[tree_index]
expression = be2.expression[expression_index]
children_tree_indexes: list[int] = expression_tree[tree_index]
if expression.type == BinExport2.Expression.OPERATOR:
if len(children_tree_indexes) == 1 and expression.symbol == ",":
# Due to the above pruning of empty LSL or LSR expressions,
# the parents might need to be fixed up.
#
# Specifically, if the pruned node was part of a comma list with two children,
# now there's only a single child, which renders as an extra comma,
# so we replace references to the comma node with the immediate child.
#
# A more correct way of doing this might be to walk up the parents and do fixups,
# but I'm not quite sure how to do this yet. Just do two passes right now.
child = children_tree_indexes[0]
for tree_node in expression_tree:
tree_node.index
if tree_index in tree_node:
tree_node[tree_node.index(tree_index)] = child
return
for child_tree_index in children_tree_indexes:
_prune_expression_tree_empty_commas(be2, operand, expression_tree, child_tree_index)
# internal to `build_expression_tree`
# this is unstable: it is subject to change, so don't rely on it!
def _prune_expression_tree(
@@ -124,7 +105,6 @@ def _prune_expression_tree(
expression_tree: list[list[int]],
):
_prune_expression_tree_empty_shifts(be2, operand, expression_tree, 0)
_prune_expression_tree_empty_commas(be2, operand, expression_tree, 0)
# this is unstable: it is subject to change, so don't rely on it!
@@ -173,7 +153,6 @@ def _build_expression_tree(
tree.append(children)
_prune_expression_tree(be2, operand, tree)
_prune_expression_tree(be2, operand, tree)
return tree