Re: New C++ ABI: patches.

[Alexandre Petit-Bianco <apbianco at cygnus dot com>]

Bryce McKinlay writes:

> (gdb) p _ZN4java4lang7Integer4TYPEE
> $1 = (java.lang.Class *) 0x0

In the case of `int.class', foo() is given `& _Jv_intClass' as an
argument. I ran the code with `dotclass.class', the code before
calling toString(), yields to:

    mov    0x8(%ebp),%eax
    sub    $0xc,%esp
    mov    (%eax),%edx

Which gets you with
	
  (gdb) x/x $edx

  0x8174fe0 <_ZTVN4java4lang5ClassE>:		0x08175020
  0x8174fe4 <_ZTVN4java4lang5ClassE+4>:		0x00000002
  0x8174fe8 <_ZTVN4java4lang5ClassE+8>:		0x08054230
  0x8174fec <_ZTVN4java4lang5ClassE+12>:	0x08056170
  0x8174ff0 <_ZTVN4java4lang5ClassE+16>:	0x0805a120
  0x8174ff4 <_ZTVN4java4lang5ClassE+20>:	0x08059fb0

And the right function is selected:

    add    $0x14,%edx

In the case of `int.class', which we can print:
(gdb) p _Jv_intClass

$1 = {<Object> = {<_JvObjectPrefix> = {_vptr.: @8174fe8}, 
    static class$: @8175180, sync_info: @820ce88}, static class$: @8175020, 
  next: null, name: @8210f20, accflags: 1041, superclass: null, constants: {
    size: 0, tags: null, data: null}, methods: null, method_count: 73, 
  vtable_method_count: 0, fields: null, size_in_bytes: 4, field_count: 0, 
  static_field_count: 0, vtable: @ffffffff, interfaces: null, loader: null, 
  interface_count: 0, state: 12, thread: null, depth: -1, ancestors: null, 
  idt: null, arrayclass: @8218ea0}

We can see that the content of the vtbl isn't right:

  (gdb) x/x $edx

  0x8174fe8 <_ZTVN4java4lang5ClassE+8>:		0x08054230
  0x8174fec <_ZTVN4java4lang5ClassE+12>:	0x08056170
  0x8174ff0 <_ZTVN4java4lang5ClassE+16>:	0x0805a120
  0x8174ff4 <_ZTVN4java4lang5ClassE+20>:	0x08059fb0

And the wrong method gets selected. Note that:

  (gdb) x/x $edx-8

  0x8174fe0 <_ZTVN4java4lang5ClassE>:	0x08175020
  0x8174fe4 <_ZTVN4java4lang5ClassE+4>:	0x00000002

gives you the missing entry. For some reasons, the first word of
_Jv_intClass points in the middle of the vtbl instead pointing at its
beginning. I guess there's something going wrong with the copy
constructor: I tried this, but it didn't work:

   Class (const Class& x) : Object () {

     _Jv_VTable *avtable = x.vtable;

  +  _Jv_InitClass (this); 

Does anybody have a suggestion?

./A