feature extractor: null: add get_base_address()

closes #88

capa/features/extractors/__init__.py

@@ -180,6 +180,7 @@ class NullFeatureExtractor(FeatureExtractor):
     example::
 
         extractor = NullFeatureExtractor({
+            'base address: 0x401000,
             'file features': [
                 (0x402345, capa.features.Characteristic('embedded pe')),
             ],
@@ -214,6 +215,9 @@ class NullFeatureExtractor(FeatureExtractor):
         super(NullFeatureExtractor, self).__init__()
         self.features = features
 
+    def get_base_address(self):
+        return self.features["base address"]
+
     def extract_file_features(self):
         for p in self.features.get("file features", []):
             va, feature = p

tests/test_freeze.py

@@ -10,6 +10,7 @@ from fixtures import *
 
 EXTRACTOR = capa.features.extractors.NullFeatureExtractor(
     {
+        "base address": 0x401000,
         "file features": [(0x402345, capa.features.Characteristic("embedded pe")),],
         "functions": {
             0x401000: {