4.0 regression: g++ class layout on PPC32 has changed

[Andrew Haley]

I've had a gcj bug report saying that some CNI code has ceased to work
on PPC 32, but I'm not sure that this is a gcj bug at all.  The bug is
that gcj and g++ no longer have comptabile class layout -- members are
at different offsets.


If you run the appended code with g++ version 3.4.1, you get

 $ g++ -m32 thing.cc -save-temps && ./a.out
56

With 4.0, you get

 $ PATH=/local/aph/install/bin/:$PATH g++ -m32 thing.cc -save-temps 
-fabi-version=0 && ./a.out
52


So, apparently class layout has changed, but there doesn't seem to be
anything I can do with -fabi-version= to match the layout of the 3.4.1
compiler.

Does anyone understand what is going on here?

Thanks,
Andrew.


#include <stdio.h>

namespace java
{
  namespace lang
  {
    class Object;
  }
}

namespace x
{
  class Parent;
  class Child$Nested;
  class Child;
}


class java::lang::Object
{
protected:
  virtual void finalize (void) { }
public:

  Object (void) { }
};

class x::Parent : public ::java::lang::Object
{
public:
  Parent () { }
public:
  long long __attribute__((aligned(__alignof__( ::java::lang::Object )))) l;
  long long m;
  long long o;
  long long p;
  long long q;
public:
  void *scratch;
};

class x::Child$Nested : public ::x::Parent
{
public:
  virtual void f ();
  Child$Nested (::x::Child *);
private:
  ::x::Child * __attribute__((aligned(__alignof__( ::x::Parent )))) this$0;
public:
  bool b;

  friend class x_Child$Nested;
};


void
x::Child$Nested::f ()
{
  printf ("%d\n", ((char*)&(this$0) - (char*)this));
}

::x::Child$Nested::Child$Nested(x::Child* p)
{
  this$0 = p;
}

int main (int argc, char **argv)
{
  ::x::Child$Nested inst ((::x::Child *)NULL);
  inst.f ();

  return 0;
}