egcs bug?

[Joyce Janczyn]

I'm not positive this is an egcs bug since this is pretty wicked code.
It does work correctly on other compilers though.

The problem seem to be with calling a member function via a pointer
when the function is a virtual and the class its in has multiple
inheritence. 

	(object.*fooFunc)();

If you look at the address of object prior to the call and then
at the value of this in Tobject::foo() you will see the adress of
object has been decremented by 4 in foo().  This results in bogus
data when you call valid() which should return 0x12345678.

It appears egcs is inserting a __thunk_4__ in the call to bump the
pointer to allow for a virtual pointer.   It appears this isn't the
right thing to do when the method is being called via a function pointer.


This is on Intel Linux 2.0.34 with the egcs.1.1.1.

Compile with:

	c++ -g -o bug  bug.cpp

If the error occurs you will see:

	!!!!!!!!!!!!! invalid object .....

#include <stream.h>

class Tbase
{
public:
	virtual ~Tbase();

	// If this method is virtual then the object passed
	// through the member function pointer is invalid
	// Its ben thunked when it shouldn't be.
	//
	virtual void	foo () const;
};

class Tbase2
{
public:
	virtual		~Tbase2();
};

class Tobject : public Tbase2, public Tbase {
public:
			Tobject() { fValid = 0x12345678; };
	virtual		~Tobject();

	virtual void	foo () const;

	int		valid() const { return fValid; };

private:
	int		fValid;
};

class Tfoo
{
public:
    typedef void (Tobject::*TfooFunc)() const;
};


main()
{
	Tfoo::TfooFunc fooFunc;
	fooFunc = (Tfoo::TfooFunc)&Tobject::foo;

	Tobject object;
	(object.*fooFunc)();
}


void
Tobject::foo () const
{
	if(valid() != 0x12345678) {
		cerr << "!!!!!!!!!!!!! invalid object " << valid() << "\n";
	}else{
		cerr << "OK\n";
	}
}

void
Tbase::foo () const
{ }

Tbase::~Tbase()
{ }

Tobject::~Tobject()
{ }

Tbase2::~Tbase2()
{ }


-- 
Joyce Janczyn
Cygnus Solutions
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