VM_Memory.memcopy(newFP, myFP, myDepth.toInt());
VM_Memory.memcopy(newFP, myFP, myDepth.toWord().toExtent());
  private static Offset copyStack (byte[] newStack) {    VM_Thread myThread = getCurrentThread();    byte[]     myStack  = myThread.stack;    Address myTop   = VM_Magic.objectAsAddress(myStack).add(myStack.length);    Address newTop  = VM_Magic.objectAsAddress(newStack).add(newStack.length);    Address myFP    = VM_Magic.getFramePointer();    Offset myDepth  = myTop.diff(myFP);    Address newFP   = newTop.sub(myDepth);    // before copying, make sure new stack isn't too small    //    if (VM.VerifyAssertions)      VM._assert(newFP.GE(VM_Magic.objectAsAddress(newStack).add(STACK_SIZE_GUARD)));        VM_Memory.memcopy(newFP, myFP, myDepth.toInt());        return newFP.diff(myFP);  }