Serious bug in VC++.NET 2003 -- invalid v-table

[Colonel Kernel]

I've found what seems to be a very serious (although obscure) bug in
VC++.NET 2003 when using Loki's class hierarchy-generation facilities.
The compiler seems to generate an invalid v-table for my class, which
causes virtual method calls to dispatch incorrectly, causing run-time
errors and crashes. The problem seems to occur because the compiler
doesn't catch the case where I give a template method the same name as
a virtual method defined elsewhere in the same hierarchy.

I have a repro ready to go. It's about as simple as I can make it, but
familiarity with Loki's GenScatterHierarchy and GenLinearHierarchy is
essential to understanding what's going on. Loki is required for the
repro (http://sourceforge.net/projects/loki-lib). If anyone is
interested in the repro (MSVC++ team, take note!), please e-mail me
at:

c_kernel at hotmail dot com

I couldn't find a KB article about this problem, so I assume I'm the
first to find it (lucky me). Although there seems to be a simple
workaround for this instance of the bug, its symptoms are very, very
serious. I urge everyone to watch out for it, and I urge those
responsible to get a fix out ASAP.

Bruce Johnston
Simba Technologies Inc.
www.simba.com

 

[Colonel Kernel]

An update: I've created a (somewhat) simpler repro that doesn't rely
on Loki. If anyone is interested, please e-mail me.

 

[Bronek Kozicki]

An update: I've created a (somewhat) simpler repro that doesn't rely
on Loki. If anyone is interested, please e-mail me.

could you post simplest repre code here ? I'm just curious (I know MC++D
book).


B.

 

[Carl Daniel [VC++ MVP]]

An update: I've created a (somewhat) simpler repro that doesn't rely
on Loki. If anyone is interested, please e-mail me.

You can post the code here, or email it to me (remove the obviously
removeable parts of my email address). If it repros for me and looks like a
bug (not some obscure undefined behavior) I'll get it into the bug pipeline.

-cd

 

[Colonel Kernel]

I simplified the repro even further. Now it's actually small enough to post.


I've already been in contact with the VC++ team via e-mail since yesterday,
so they have this repro already. But here it is anyway, for those who are
curious:

---------------------------------------------------
#include <iostream>


// All this code is an "unrolling" of Loki's class-hierarchy generation
// techniques. I've removed as much template stuff as possible in order to
// isolate the bug as much as possible. Keep in mind that this a repro, not
a
// motivating example. The pattern of inheritance and template instantiation
// that is in this repro occurs somewhat frequently when generating class
// hierarchies using Loki.


// Uncomment this to reproduce the bug.
//#define SHOWBUG


class Interface
{
public:

// This level of delegation is required in order to reproduce the bug.
// main() can't just call doFoo directly, or the bug won't occur.
void foo( int i )
{
this->doFoo( i ) ;
}

protected:

virtual void doFoo( int i ) = 0 ;

virtual ~Interface() {}
} ;



// This class must take its base class as a template parameter in order for
// the bug to occur.
template <class IFace>
class IntermediateBase : public IFace
{
protected:

// This operation needs to be in this intermediate base class in order
// for the bug to occur. Also, it needs to be a template. I think the
// fact that it is a template method with the same name as a virtual
// method in a class hierarchy that is established via template
paramters
// (see IFace above) is the key circumstance of this bug.
template <class T>
#ifndef SHOWBUG
void doFooImpl( T t )
#else
void doFoo( T t )
#endif
{
std::cout << typeid( t ).name() << ": " << t << std::endl ;
}
} ;



class Implementation : public IntermediateBase<Interface>
{
typedef IntermediateBase<Interface> Base ;

protected:

void doFoo( int i )
{
#ifndef SHOWBUG
this->Base::doFooImpl<int>( i ) ;
#else
this->Base::doFoo<int>( i ) ;
#endif
}
} ;



int main()
{
Implementation impl ;

impl.foo( 1 ) ;

return 0 ;
}

 

[Carl Daniel [VC++ MVP]]

I simplified the repro even further. Now it's actually small enough
to post.

I've already been in contact with the VC++ team via e-mail since
yesterday, so they have this repro already. But here it is anyway,
for those who are curious:

Thanks for sharing, and for taking the time to narrow down a concise repro
case - it really makes a difference in getting bugs like this fixed.

-cd