Add #ifdef/#ifndef parsing (#135)

Author: Schamper

dissect/cstruct/parser.py

@@ -49,12 +49,18 @@ def __init__(self, cs: cstruct, compiled: bool = True, align: bool = False):
         self.compiled = compiled
         self.align = align
         self.TOK = self._tokencollection()
+        self._conditionals = []
+        self._conditionals_depth = 0
 
     @staticmethod
     def _tokencollection() -> TokenCollection:
         TOK = TokenCollection()
         TOK.add(r"#\[(?P<values>[^\]]+)\](?=\s*)", "CONFIG_FLAG")
-        TOK.add(r"#define\s+(?P<name>[^\s]+)\s+(?P<value>[^\r\n]+)\s*", "DEFINE")
+        TOK.add(r"#define\s+(?P<name>[^\s]+)(?P<value>[^\r\n]*)", "DEFINE")
+        TOK.add(r"#ifdef\s+(?P<name>[^\s]+)\s*", "IFDEF")
+        TOK.add(r"#ifndef\s+(?P<name>[^\s]+)\s*", "IFNDEF")
+        TOK.add(r"#else\s*", "ELSE")
+        TOK.add(r"#endif\s*", "ENDIF")
         TOK.add(r"typedef(?=\s)", "TYPEDEF")
         TOK.add(r"(?:struct|union)(?=\s|{)", "STRUCT")
         TOK.add(
@@ -80,12 +86,61 @@ def _identifier(self, tokens: TokenConsumer) -> str:
             idents.append(tokens.consume())
         return " ".join([i.value for i in idents])
 
+    def _conditional(self, tokens: TokenConsumer) -> None:
+        token = tokens.consume()
+        pattern = self.TOK.patterns[token.token]
+        match = pattern.match(token.value).groupdict()
+
+        value = match["name"]
+
+        if token.token == self.TOK.IFDEF:
+            self._conditionals.append(value in self.cstruct.consts)
+        elif token.token == self.TOK.IFNDEF:
+            self._conditionals.append(value not in self.cstruct.consts)
+
+    def _check_conditional(self, tokens: TokenConsumer) -> bool:
+        """Check and handle conditionals. Return a boolean indicating if we need to continue to the next token."""
+        if self._conditionals and self._conditionals_depth == len(self._conditionals):
+            # If we have a conditional and the depth matches, handle it accordingly
+            if tokens.next == self.TOK.ELSE:
+                # Flip the last conditional
+                tokens.consume()
+                self._conditionals[-1] = not self._conditionals[-1]
+                return True
+
+            if tokens.next == self.TOK.ENDIF:
+                # Pop the last conditional
+                tokens.consume()
+                self._conditionals.pop()
+                self._conditionals_depth -= 1
+                return True
+
+        if tokens.next in (self.TOK.IFDEF, self.TOK.IFNDEF):
+            # If we encounter a new conditional, increase the depth
+            self._conditionals_depth += 1
+
+        if tokens.next == self.TOK.ENDIF:
+            # Similarly, decrease the depth if needed
+            self._conditionals_depth -= 1
+
+        if self._conditionals and not self._conditionals[-1]:
+            # If the last conditional evaluated to False, skip the next token
+            tokens.consume()
+            return True
+
+        if tokens.next in (self.TOK.IFDEF, self.TOK.IFNDEF):
+            # If the next token is a conditional, process it
+            self._conditional(tokens)
+            return True
+
+        return False
+
     def _constant(self, tokens: TokenConsumer) -> None:
         const = tokens.consume()
         pattern = self.TOK.patterns[self.TOK.DEFINE]
         match = pattern.match(const.value).groupdict()
 
-        value = match["value"]
+        value = match["value"].strip()
         try:
             value = ast.literal_eval(value)
         except (ValueError, SyntaxError):
@@ -208,6 +263,9 @@ def _struct(self, tokens: TokenConsumer, register: bool = False) -> type[Structu
                 tokens.consume()
                 break
 
+            if self._check_conditional(tokens):
+                continue
+
             field = self._parse_field(tokens)
             fields.append(field)
 
@@ -266,7 +324,7 @@ def _parse_field(self, tokens: TokenConsumer) -> Field:
                 return Field(None, type_, None)
 
         if tokens.next != self.TOK.NAME:
-            raise ParserError(f"line {self._lineno(tokens.next)}: expected name")
+            raise ParserError(f"line {self._lineno(tokens.next)}: expected name, got {tokens.next!r}")
         nametok = tokens.consume()
 
         type_, name, bits = self._parse_field_type(type_, nametok.value)
@@ -378,6 +436,9 @@ def parse(self, data: str) -> None:
             if token is None:
                 break
 
+            if self._check_conditional(tokens):
+                continue
+
             if token == self.TOK.CONFIG_FLAG:
                 self._config_flag(tokens)
             elif token == self.TOK.DEFINE:
@@ -395,6 +456,9 @@ def parse(self, data: str) -> None:
             else:
                 raise ParserError(f"line {self._lineno(token)}: unexpected token {token!r}")
 
+        if self._conditionals:
+            raise ParserError(f"line {self._lineno(tokens.previous)}: unclosed conditional statement")
+
 
 class CStyleParser(Parser):
     """Definition parser for C-like structure syntax.

tests/test_parser.py

@@ -1,18 +1,15 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
 from unittest.mock import Mock
 
 import pytest
 
+from dissect.cstruct import cstruct
 from dissect.cstruct.exceptions import ParserError
 from dissect.cstruct.parser import TokenParser
 from dissect.cstruct.types import BaseArray, Pointer, Structure
 from tests.utils import verify_compiled
 
-if TYPE_CHECKING:
-    from dissect.cstruct import cstruct
-
 
 def test_nested_structs(cs: cstruct, compiled: bool) -> None:
     cdef = """
@@ -164,3 +161,123 @@ def test_typedef_pointer(cs: cstruct) -> None:
     assert cs.IMAGE_DATA_DIRECTORY is cs._IMAGE_DATA_DIRECTORY
     assert issubclass(cs.PIMAGE_DATA_DIRECTORY, Pointer)
     assert cs.PIMAGE_DATA_DIRECTORY.type == cs._IMAGE_DATA_DIRECTORY
+
+
+def test_conditional_ifdef(cs: cstruct) -> None:
+    cdef = """
+    #define MY_CONST 42
+
+    #ifdef MY_CONST
+    struct test {
+        uint32 a;
+    };
+    #endif
+    """
+    cs.load(cdef)
+
+    assert "test" in cs.typedefs
+
+
+def test_conditional_ifndef(cs: cstruct) -> None:
+    cdef = """
+    #ifndef MYVAR
+        #define MYVAR  (1)
+    #endif
+    """
+    cs.load(cdef)
+
+    assert "MYVAR" in cs.consts
+    assert cs.consts["MYVAR"] == 1
+
+
+def test_conditional_ifndef_guard(cs: cstruct) -> None:
+    cdef = """
+    /* Define Guard */
+    #ifndef __MYGUARD
+    #define __MYGUARD
+
+    typedef struct myStruct
+    {
+        char   charVal[16];
+    }
+    #endif // __MYGUARD
+    """
+    cs.load(cdef)
+
+    assert "__MYGUARD" in cs.consts
+    assert "myStruct" in cs.typedefs
+
+
+def test_conditional_nested() -> None:
+    cdef = """
+    #ifndef MYSWITCH1
+        #define MYVAR1 (1)
+    #else
+        #ifdef MYSWITCH2
+            #define MYVAR1 (2)
+        #else
+            #define MYVAR1 (3)
+        #endif
+    #endif
+    """
+    cs = cstruct().load(cdef)
+
+    assert "MYVAR1" in cs.consts
+    assert cs.consts["MYVAR1"] == 1
+
+    cs = cstruct().load("#define MYSWITCH1")
+
+    assert "MYSWITCH1" in cs.consts
+
+    cs.load(cdef)
+
+    assert "MYVAR1" in cs.consts
+    assert cs.consts["MYVAR1"] == 3
+
+
+def test_conditional_in_struct(cs: cstruct) -> None:
+    cdef = """
+    struct t_bitfield {
+        union {
+            struct {
+                uint32_t bit0:1;
+                uint32_t bit1:1;
+                #ifdef MYSWT
+                uint32_t bit2:1;
+                #endif
+            } fval;
+            uint32_t bits;
+        };
+    };
+    """
+    cs.load(cdef)
+
+    assert "t_bitfield" in cs.typedefs
+    assert "fval" in cs.t_bitfield.fields
+    assert "bit0" in cs.t_bitfield.fields["fval"].type.fields
+    assert "bit1" in cs.t_bitfield.fields["fval"].type.fields
+    assert "bit2" not in cs.t_bitfield.fields["fval"].type.fields
+
+
+def test_conditional_parsing_error(cs: cstruct) -> None:
+    cdef = """
+    #ifndef __HELP
+    #define __HELP
+    #endif
+    struct test {
+        uint32 a;
+    };
+    #endif
+    """
+    with pytest.raises(ParserError, match="line 8: unexpected token .+ENDIF"):
+        cs.load(cdef)
+
+    cdef = """
+    #ifndef __HELP
+    #define __HELP
+    struct test {
+        uint32 a;
+    };
+    """
+    with pytest.raises(ParserError, match="line 6: unclosed conditional statement"):
+        cs.load(cdef)