Fix bug in gdb-debughelpers

Author: dominikmascherbauer

substratevm/debug/gdbpy/gdb-debughelpers.py

@@ -141,7 +141,7 @@ def get_uncompressed_type(cls, t: gdb.Type) -> gdb.Type:
         # compressed types only exist for java type which are either struct or union
         if t.code != gdb.TYPE_CODE_STRUCT and t.code != gdb.TYPE_CODE_UNION:
             return t
-        result = cls.get_base_class(t) if cls.is_compressed(t) else t
+        result = cls.get_base_class(t) if (cls.is_compressed(t) and t != cls.hub_type) else t
         trace(f'<SVMUtil> - get_uncompressed_type({t}) = {result}')
         return result
 
@@ -177,7 +177,7 @@ def get_compressed_oop(cls, obj: gdb.Value) -> int:
         # recreate compressed oop from the object address
         # this reverses the uncompress expression from
         # com.oracle.objectfile.elf.dwarf.DwarfInfoSectionImpl#writeIndirectOopConversionExpression
-        is_hub = cls.get_rtt(obj) == cls.hub_type
+        is_hub = cls.get_basic_type(obj.type) == cls.hub_type
         compression_shift = cls.compression_shift
         num_reserved_bits = int.bit_count(cls.reserved_bits_mask)
         num_alignment_bits = int.bit_count(cls.object_alignment - 1)
@@ -205,6 +205,11 @@ def get_unqualified_type_name(cls, qualified_type_name: str) -> str:
 
     @classmethod
     def is_compressed(cls, t: gdb.Type) -> bool:
+        # for the hub type we always want handle it as compressed as there is no clear distinction in debug info for
+        # the hub field, and it may always have an expression in the type's data_location attribute
+        if cls.get_basic_type(t) == cls.hub_type:
+            return True
+
         type_name = cls.get_basic_type(t).name
         if type_name is None:
             # fallback to the GDB type printer for t
@@ -363,6 +368,9 @@ def get_classloader_namespace(cls, obj: gdb.Value) -> str:
     def get_rtt(cls, obj: gdb.Value) -> gdb.Type:
         static_type = cls.get_basic_type(obj.type)
 
+        if static_type == cls.hub_type:
+            return cls.hub_type
+
         # check for interfaces and cast them to Object to make the hub accessible
         if cls.get_uncompressed_type(cls.get_basic_type(obj.type)).code == gdb.TYPE_CODE_UNION:
             obj = cls.cast_to(obj, cls.object_type)

substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/debug/helper/test_svm_util.py

@@ -96,10 +96,9 @@ def test_compressed_hub_oop(self):
         z_hub = gdb.parse_and_eval('strList.hub')
         self.assertNotEqual(int(z_hub), 0)
         self.assertTrue(SVMUtil.is_compressed(z_hub.type))
-        # get the uncompressed value for the hub
+        # the hub field type does not have an 'uncompressed' type
+        # we can just check if an absolute address is converted correctly to a compressed oop
         hub = z_hub.dereference()
-        hub = hub.cast(SVMUtil.get_uncompressed_type(hub.type))
-        self.assertFalse(SVMUtil.is_compressed(hub.type))
         self.assertEqual(SVMUtil.get_compressed_oop(hub), int(z_hub))
 
         hub_str = str(hub)