MethodHandle.vmentry offset problem on 64-bit

[Christian Thalinger]

Hi John!

I'm currently porting the interpreter to x86_64 and there is a problem
that took me almost two days to find: it's the MethodHandle.vmentry
field-type change.

For whatever reason on 64-bit it calculates the offset to 24, which
actually should be 16, and that results to this:

sun.dyn.DirectMethodHandle
 - klass: 'sun/dyn/DirectMethodHandle'
 - ---- fields (total size 6 words):
 - private 'vmentry' 'J' @24  4329412000 (20d95a0 1)
 - protected 'vmtarget' 'Ljava/lang/Object;' @24  ### BAD OOP
0x1020d95a0 ### (20d95a0 1)
 - private 'type' 'Ljava/dyn/MethodType;' @32  a 'java/dyn/MethodType' =
(II)I (5040e38 1)
 - private final 'vmindex' 'I' @40  -2 (fffffffe)

Nice, isn't it? :-)

So, there is a problem somewhere in
ClassFileParser::java_dyn_MethodHandle_fix_pre and the attached patch
fix it.  But I'm very sure this is not correct as the field should
really be a double field and not a word field.  What is the "correct"
fix for this problem?

-- Christian


diff --git a/src/share/vm/classfile/classFileParser.cpp
b/src/share/vm/classfile/classFileParser.cpp
--- a/src/share/vm/classfile/classFileParser.cpp
+++ b/src/share/vm/classfile/classFileParser.cpp
@@ -2514,23 +2514,23 @@
       fac_ptr->nonstatic_byte_count -= 1;
       (*fields_ptr)->ushort_at_put(i +
instanceKlass::signature_index_offset,
                                    word_sig_index);
-      if (wordSize == jintSize) {
+//       if (wordSize == jintSize) {
         fac_ptr->nonstatic_word_count += 1;
-      } else {
-        fac_ptr->nonstatic_double_count += 1;
-      }
-
-      FieldAllocationType atype = (FieldAllocationType)
(*fields_ptr)->ushort_at(i+4);
+//       } else {
+//         fac_ptr->nonstatic_double_count += 1;
+//       }
+
+      FieldAllocationType atype = (FieldAllocationType)
(*fields_ptr)->ushort_at(i + instanceKlass::low_offset);
       assert(atype == NONSTATIC_BYTE, "");
       FieldAllocationType new_atype = NONSTATIC_WORD;
-      if (wordSize > jintSize) {
-        if (Universe::field_type_should_be_aligned(T_LONG)) {
-          atype = NONSTATIC_ALIGNED_DOUBLE;
-        } else {
-          atype = NONSTATIC_DOUBLE;
-        }
-      }
-      (*fields_ptr)->ushort_at_put(i+4, new_atype);
+//       if (wordSize > jintSize) {
+//         if (Universe::field_type_should_be_aligned(T_LONG)) {
+//           atype = NONSTATIC_ALIGNED_DOUBLE;
+//         } else {
+//           atype = NONSTATIC_DOUBLE;
+//         }
+//       }
+      (*fields_ptr)->ushort_at_put(i + instanceKlass::low_offset,
new_atype);

       found_vmentry = true;
       break;