Bug in gcc 2.9x

The JX Application Framework circumvents the bug by using factory methods (Create()). These functions must be called in place of operator new. The code that would trigger the bug is called inside Create() after the constructor returns.

This bug has been fixed in gcc 3.x. The work arounds in the JX Application Framework will be weeded out once gcc 3.x becomes widely used.

The bug appears to mainly affect Linux systems using glibc, because the optimization that causes the problem is supposedly turned off on most other systems, though nobody seems to know exactly which ones. The easiest way to check is to run the test program listed below.

The following code demonstrates a bug in gcc 2.9x when vtable thunks are turned on.

  B
 / \
A   D - E
 \ /
  C

The correct output, produced by gcc 2.7.2, is:

starting test
A::foo  0xbffffb30 1
B::foo  0xbffffb18 1
C::foo  0xbffffb20 1
D::foo  0xbffffb18 1
E::foo  0xbffffb18 1
object constructed
E::foo  0xbffffb18 1
test finished

starting test
A::foo  0xbffffb40 1
B::foo  0xbffffb38 1073783288
C::foo  0xbffffb38 1073783288
D::foo  0xbffffb2c 1073783288
E::foo  0xbffffb28 1
object constructed
E::foo  0xbffffb28 1
test finished

#include <iostream.h>

class A
{
public:

	A() { a=1; bar(); };
	virtual void foo() {
		cout << "A::foo  " << this << ' ' << a << endl; };
	void bar() { foo(); };

private:

	int a;
};

class B : virtual public A
{
public:

	B() { b=1; bar(); };
	virtual void foo() {
		cout << "B::foo  " << this << ' ' << b << endl; };

private:

	int b;
};

class C : virtual public A
{
public:

	C() { c=1; bar(); };
	virtual void foo() {
		cout << "C::foo  " << this << ' ' << c << endl; };

private:

	int c;
};

class D : public B, public C
{
public:

	D() { d=1; bar(); };
	virtual void foo() {
		cout << "D::foo  " << this << ' ' << d << endl; };

private:

	int d;
};

class E : public D
{
public:

	E() { e=1; bar(); };
	virtual void foo() {
		cout << "E::foo  " << this << ' ' << e << endl; };

private:

	int e;
};

int
main()
{
	cout << "starting test" << endl;
	E e;
	cout << "object constructed" << endl;
	e.bar();
	cout << "test finished" << endl;
	return 0;
}