C++ linker gives me undefined reference to vtable error

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I am writing a kernel, the base is working fine, but when i went to add I/O ports, with this header:

C++

#ifndef __PORT_H
#define __PORT_H

class Port {
    protected: //protected:
    Port(uint16_t _portNum);
    ~Port();
    uint16_t portNum;
};

class Port8Bit: public Port {
    public:
    using Port::Port;
    Port8Bit(uint16_t _portNum);
    ~Port8Bit();

    virtual uint8_t read();
    virtual void write(uint8_t data);

    protected:
    static inline uint8_t read8(uint16_t _port) {
        uint8_t result;
        __asm__ volatile("inb %1, %0" : "=a" (result) : "Nd" (_port));
        return result;
    }

    static inline void write8(uint16_t _port, uint8_t _data) {
        __asm__ volatile("outb %0, %1" : : "a" (_data), "Nd" (_port));
    }
};
#endif

And this .cpp file:

C++

#include "port.h"

Port::Port(uint16_t _portNum) {
    portNum = _portNum;
}
Port::~Port() {}

Port8Bit::Port8Bit(uint16_t _portNum) : Port(_portNum) {}
Port8Bit::~Port8Bit() {}

void Port8Bit::write(uint8_t data) {
    write8(portNum, data);
}

uint8_t Port8Bit::read() {
    return read8(portNum);
}

I get the following error:

ld: lib/io/port.o:(.data.rel.ro._ZTI8Port8Bit[_ZTI8Port8Bit]+0x0): undefined reference to `vtable for __cxxabiv1::__vmi_class_type_info'
ld: lib/io/port.o:(.data.rel.ro._ZTI4Port[_ZTI4Port]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info'
make: *** [Makefile:42: link] Error 1

I am using gcc as a compiler

What I have tried:

I tried removing the

C++

using Port::Port

and got this error:

ld: lib/io/port.o:(.data.rel.ro._ZTI8Port8Bit[_ZTI8Port8Bit]+0x0): undefined reference to `vtable for __cxxabiv1::__vmi_class_type_info'
ld: lib/io/port.o:(.data.rel.ro._ZTI4Port[_ZTI4Port]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info'
make: *** [Makefile:42: link] Error 1

If i (in port.cpp) comment everything out under

C++

Port::~Port() {}

it compiles fine.

But when i then add

C++

Port8Bit::Port8Bit(uint16_t _portNum) : Port(_portNum) {}

it gives me the following error:

ld: lib/io/port.o: in function `Port8Bit::Port8Bit(unsigned short)':
port.cpp:(.text+0x5f): undefined reference to `vtable for Port8Bit'
make: *** [Makefile:42: link] Error 1

If I do like this (port.cpp):

C++

#include "port.h"

Port::Port(uint16_t _portNum) {
    portNum = _portNum;
}
Port::~Port() {}

//Port8Bit::Port8Bit(uint16_t _portNum) : Port(_portNum) {}
//Port8Bit::~Port8Bit() {}

void Port8Bit::write(uint8_t data) {
    write8(portNum, data);
}
/*
uint8_t Port8Bit::read() {
    return read8(portNum);
}
*/

It compiles, but when i add the read function:

C++

#include "port.h"

Port::Port(uint16_t _portNum) {
    portNum = _portNum;
}
Port::~Port() {}

//Port8Bit::Port8Bit(uint16_t _portNum) : Port(_portNum) {}
//Port8Bit::~Port8Bit() {}

void Port8Bit::write(uint8_t data) {
    write8(portNum, data);
}

uint8_t Port8Bit::read() {
    return read8(portNum);
}

It once again fails and gives me this code:

ld: lib/io/port.o:(.data.rel.ro._ZTI8Port8Bit[_ZTI8Port8Bit]+0x0): undefined reference to `vtable for __cxxabiv1::__vmi_class_type_info'
ld: lib/io/port.o:(.data.rel.ro._ZTI4Port[_ZTI4Port]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info'
make: *** [Makefile:42: link] Error 1

I really hope somebody can help me with this, it's incredibly confusing and I have no idea what the compiler is doing at all, why will only it work implementing the write, not the read? Even if i comment out

C++

return read8(portNum);

so it's literally just an empty function it still gives the same error.

Posted 8-Nov-22 11:15am

Member 14769677

Updated 8-Nov-22 17:10pm

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Rick York · Answer 1 · 2022-11-08T17:10:00

I got this code to compile with just a few tweaks. I used Visual Studio 2022. Here are the modules :

C++

#pragma once
#define PORT_H

class Port
{
protected:
    Port( uint16_t portNum );
    ~Port();

    uint16_t m_PortNum;
};


class Port8Bit : public Port
{
public:
    Port8Bit( uint16_t portNum );
    ~Port8Bit();

    virtual uint8_t read();
    virtual void    write( uint8_t data );

protected:
    static inline uint8_t read8( uint16_t port )
    {
        printf( "reading from port %5d\n", port );
        uint8_t result = 0;
        result = uint8_t( rand() & 256 );
//      __asm__ volatile("inb %1, %0" : "=a" (result) : "Nd" (_port));
        return result;
    }

    static inline void write8( uint16_t port, uint8_t data )
    {
//      __asm__ volatile("outb %0, %1" : : "a" (_data), "Nd" (_port));
        printf( "writing %3d to port %5d : %04X\n", data, port, port );
    }
};

//
// Port.cpp
//

#include "Port.h"

Port::Port( uint16_t portNum )
{
    m_PortNum = portNum;
}

Port::~Port()
{
}

Port8Bit::Port8Bit( uint16_t portNum )
    : Port( portNum )
{
}

Port8Bit::~Port8Bit()
{
}

void Port8Bit::write( uint8_t data )
{
    write8( m_PortNum, data );
}

uint8_t Port8Bit::read()
{
    return read8( m_PortNum );
}

// instantiation code

    uint16_t port = 5342;
    Port8Bit ioport( port );
    uint8_t value = ioport.read();
    ioport.write( value );

k5054 · Answer 2 · 2022-11-08T15:38:00

Quote:
I am using gcc as a compiler

I hope that means you're using g++, and not gcc.
You've not shown your main() class, but the given code compiles cleanly to a .o file

Shell

g++ -Wall -Wextra -c -o port.o port.cpp

so the problem must be when trying to produce a final executable. While gcc can compile C++ files, there's a lot of hoops you have to jump through to get vanilla gcc to link c++ object files together. That's true whether you create the object files individually, or do a compile/link in a single command with something like

Shell

gcc port.cpp main.cpp -o main

. When you use g++ for the final linking phase, it knows what the extra steps are to get C++ object files to link together e.g.

Shell

g++ port.cpp main.cpp -o main

If you're using make, be sure that the recipe for the final executable uses g++ and not gcc to construct the final executable.

C++ linker gives me undefined reference to vtable error

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C++ linker gives me undefined reference to vtable error

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