Adjust code generation for the function pointer type. (#327)

* Create draft PR for #322

* Add special case for function pointer type variable declarations

* Fix missing comma in function pointer variables declaration

* Add test cases

* Improve readability of format_variables_declaration(Type,list[str])

---------

Co-authored-by: rihi <[email protected]>
Co-authored-by: rihi <[email protected]>

decompiler/backend/cexpressiongenerator.py

@@ -1,10 +1,9 @@
 import logging
 from ctypes import c_byte, c_int, c_long, c_short, c_ubyte, c_uint, c_ulong, c_ushort
 from itertools import chain, repeat
-from typing import Union
 
 from decompiler.structures import pseudo as expressions
-from decompiler.structures.pseudo import Float, Integer, OperationType, StringSymbol
+from decompiler.structures.pseudo import Float, FunctionTypeDef, Integer, OperationType, Pointer, StringSymbol, Type
 from decompiler.structures.pseudo import instructions as instructions
 from decompiler.structures.pseudo import operations as operations
 from decompiler.structures.visitors.interfaces import DataflowObjectVisitorInterface
@@ -361,3 +360,14 @@ def _format_string_literal(constant: expressions.Constant) -> str:
             escaped = string_representation.replace('"', '\\"')
             return f'"{escaped}"'
         return f"{constant}"
+
+    @staticmethod
+    def format_variables_declaration(var_type: Type, var_names: list[str]) -> str:
+        """ Return a string representation of variable declarations."""
+        match var_type:
+            case Pointer(type=FunctionTypeDef() as fun_type):
+                parameter_names = ", ".join(str(parameter) for parameter in fun_type.parameters)
+                declarations_without_return_type = [f"(* {var_name})({parameter_names})" for var_name in var_names]
+                return f"{fun_type.return_type} {', '.join(declarations_without_return_type)}"
+            case _:
+                return f"{var_type} {', '.join(var_names)}"

decompiler/backend/codegenerator.py

@@ -2,6 +2,7 @@
 from string import Template
 from typing import Iterable, List
 
+from decompiler.backend.cexpressiongenerator import CExpressionGenerator
 from decompiler.backend.codevisitor import CodeVisitor
 from decompiler.backend.variabledeclarations import GlobalDeclarationGenerator, LocalDeclarationGenerator
 from decompiler.task import DecompilerTask
@@ -37,7 +38,10 @@ def generate_function(self, task: DecompilerTask) -> str:
         return self.TEMPLATE.substitute(
             return_type=task.function_return_type,
             name=task.name,
-            parameters=", ".join(map(lambda param: f"{param.type} {param.name}", task.function_parameters)),
+            parameters=", ".join(map(
+                lambda param: CExpressionGenerator.format_variables_declaration(param.type, [param.name]),
+                task.function_parameters
+            )),
             local_declarations=LocalDeclarationGenerator.from_task(task) if not task.failed else "",
             function_body=CodeVisitor(task).visit(task.syntax_tree.root) if not task.failed else task.failure_message,
         )

decompiler/backend/variabledeclarations.py

@@ -2,6 +2,7 @@
 from collections import defaultdict
 from typing import Iterable, Iterator, List, Set
 
+from decompiler.backend.cexpressiongenerator import CExpressionGenerator
 from decompiler.structures.ast.ast_nodes import ForLoopNode, LoopNode
 from decompiler.structures.ast.syntaxtree import AbstractSyntaxTree
 from decompiler.structures.pseudo import (
@@ -61,19 +62,19 @@ def visit_unary_operation(self, unary: UnaryOperation):
                 else:
                     self.visit(unary.operand.left)
 
-    def generate(self, param_names: list = []) -> Iterator[str]:
+    def generate(self, param_names: list[str] = []) -> Iterator[str]:
         """Generate a string containing the variable definitions for the visited variables."""
         variable_type_mapping = defaultdict(list)
         for variable in sorted(self._variables, key=lambda x: str(x)):
-            if not isinstance(variable, GlobalVariable):
+            if not isinstance(variable, GlobalVariable) and variable.name not in param_names:
                 variable_type_mapping[variable.type].append(variable)
 
         for variable_type, variables in sorted(variable_type_mapping.items(), key=lambda x: str(x)):
             for chunked_variables in self._chunks(variables, self._vars_per_line):
-                variable_names = ", ".join([var.name for var in chunked_variables])
-                if variable_names in param_names:
-                    continue
-                yield f"{variable_type} {variable_names};"
+                yield CExpressionGenerator.format_variables_declaration(
+                    variable_type,
+                    [var.name for var in chunked_variables]
+                ) + ";"
 
     @staticmethod
     def _chunks(lst: List, n: int) -> Iterator[List]:

tests/backend/test_codegenerator.py

@@ -11,6 +11,7 @@
 from decompiler.structures.ast.ast_nodes import CodeNode, SeqNode, SwitchNode
 from decompiler.structures.ast.syntaxtree import AbstractSyntaxTree
 from decompiler.structures.logic.logic_condition import LogicCondition
+from decompiler.structures.pseudo import FunctionTypeDef
 from decompiler.structures.pseudo.expressions import (
     Constant,
     DataflowObject,
@@ -75,6 +76,8 @@ def logic_cond(name: str, context) -> LogicCondition:
 var_x_u = Variable("x_u", uint32)
 var_y_u = Variable("y_u", uint32)
 var_p = Variable("p", Pointer(int32))
+var_fun_p = Variable("p", Pointer(FunctionTypeDef(0, int32, (int32,))))
+var_fun_p0 = Variable("p0", Pointer(FunctionTypeDef(0, int32, (int32,))))
 
 const_0 = Constant(0, int32)
 const_1 = Constant(1, int32)
@@ -155,6 +158,15 @@ def test_empty_function_two_parameters(self):
             r"^\s*int +test_function\(\s*int +a\s*,\s*int +b\s*\){\s*}\s*$", self._task(ast, params=[var_a.copy(), var_b.copy()])
         )
 
+    def test_empty_function_two_function_parameters(self):
+        root = SeqNode(LogicCondition.initialize_true(LogicCondition.generate_new_context()))
+        ast = AbstractSyntaxTree(root, {})
+        code_node = ast._add_code_node([])
+        ast._add_edge(root, code_node)
+        assert self._regex_matches(
+            r"^\s*int +test_function\(\s*int +\(\*\s*p\)\(int\)\s*,\s*int +\(\*\s*p0\)\(int\)\s*\){\s*}\s*$", self._task(ast, params=[var_fun_p.copy(), var_fun_p0.copy()])
+        )
+
     def test_function_with_instruction(self):
         root = SeqNode(LogicCondition.initialize_true(LogicCondition.generate_new_context()))
         ast = AbstractSyntaxTree(root, {})
@@ -1069,6 +1081,8 @@ def test_operation(self, op, expected):
             (1, [var_x.copy(), var_y.copy(), var_x_f.copy(), var_y_f.copy()], "float x_f;\nfloat y_f;\nint x;\nint y;"),
             (2, [var_x.copy(), var_y.copy(), var_x_f.copy(), var_y_f.copy()], "float x_f, y_f;\nint x, y;"),
             (1, [var_x.copy(), var_y.copy(), var_p.copy()], "int x;\nint y;\nint * p;"),
+            (1, [var_x.copy(), var_y.copy(), var_fun_p.copy()], "int x;\nint y;\nint (* p)(int);"),
+            (2, [var_x.copy(), var_y.copy(), var_fun_p.copy(), var_fun_p0.copy()], "int x, y;\nint (* p)(int), (* p0)(int);"),
         ],
     )
     def test_variable_declaration(self, vars_per_line: int, variables: List[Variable], expected: str):