c++ - compiler - g++ mac

¿Cuál es la ubicación de VTable Layout y VTable Pointer en C++ Objects en GCC 3.x y 4.x?

Question

Estoy buscando detalles de la estructura, orden y contenido de la VTable, y la ubicación de los punteros vtable dentro de los objetos.

Idealmente, esto cubrirá la herencia única, la herencia múltiple y la herencia virtual.

Las referencias a la documentación externa también serían apreciadas

La documentación del diseño de la clase GCC 4.0x está aquí y los documentos de diseño Itanium, y más ampliamente GNU, ABI están aquí .

Answer 1

Generalmente, una tabla virtual se trata como una matriz de indicadores de función, aunque los compiladores pueden poner punteros de datos (en escenarios MI y VI, o typeinfos), enteros (para reparaciones) o elementos centinela (como punteros NULL) en ella. también. El diseño generalmente es específico del compilador (o específico de ABI donde varios compiladores de C ++ comparten un ABI), pero estable siempre que las clases compiladas tengan interfaces estables (de lo contrario tendrías que recompilar tu código todo el tiempo, y eso es un arrastre) . También hay tablas adicionales que se necesitan para manejar casos de esquina que implican herencia virtual y múltiple, y para asegurarse de que las llamadas virtuales durante la construcción de clase derivada se comporten como el estándar dice que deberían en esas circunstancias (eso es lo que los VTT y tablas de construcción en el el resultado a continuación es para).

En cuanto al caso específico de GCC 4.x: el -fdump-class-hierarchy actúa tal como se describe (y luego algo). Lo probé en Coliru usando el siguiente código de muestra:

struct Base
{
    virtual ~Base() {}
    virtual void f() = 0;
};

struct OtherBase
{
    virtual ~OtherBase() {}
    virtual void g() {}
};

struct Derived: public Base
{
    virtual ~Derived() {}
    virtual void f() {}
};

struct MultiplyDerived: public Base, public OtherBase
{
    virtual ~MultiplyDerived() {}
    virtual void f() {}
    virtual void g() {}
};

struct OtherDerived: public Base
{
    virtual ~OtherDerived() {}
    virtual void f() {}
};

struct DiamondDerived: public Derived, public OtherDerived
{
    virtual ~DiamondDerived() {}
    virtual void f() {}
};

struct VirtuallyDerived: virtual public Base
{
    virtual ~VirtuallyDerived() {}
    virtual void f() {}
};

struct OtherVirtuallyDerived: virtual public Base
{
    virtual ~OtherVirtuallyDerived() {}
    virtual void f() {}
};

struct VirtuallyDiamondDerived: public VirtuallyDerived, public OtherVirtuallyDerived
{
    virtual ~VirtuallyDiamondDerived() {}
    virtual void f() {}
};

struct DoublyVirtuallyDiamondDerived: virtual public VirtuallyDerived, virtual public OtherVirtuallyDerived
{
    virtual ~DoublyVirtuallyDiamondDerived() {}
    virtual void f() {}
};

struct MixedVirtuallyDerived: virtual public Base, public OtherBase
{
    virtual ~MixedVirtuallyDerived() {}
};

struct MixedVirtuallyDiamondDerived: public VirtuallyDerived, public MixedVirtuallyDerived
{
    virtual ~MixedVirtuallyDiamondDerived() {}
    virtual void f() {}
    virtual void g() {}
};

struct VirtuallyMultiplyDerived: virtual public Base, virtual public OtherBase
{
    virtual ~VirtuallyMultiplyDerived() {}
};

struct OtherVirtuallyMultiplyDerived: virtual public Base, virtual public OtherBase
{
    virtual ~OtherVirtuallyMultiplyDerived() {}
};

struct MultiplyVirtuallyDiamondDerived: public VirtuallyMultiplyDerived, public OtherVirtuallyMultiplyDerived
{
    virtual ~MultiplyVirtuallyDiamondDerived() {}
    virtual void f() {}
    virtual void g() {}
};

y recibido de G ++ (guía de nombres truncados: los TI son typeinfos, los TV son vtables, y los Th''s y los Tv son thunks utilizados para realizar llamadas virtuales correctas en presencia de herencia múltiple y / o virtual):

Vtable for Base Base::_ZTV4Base: 5u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI4Base) 16 0u 24 0u 32 (int (*)(...))__cxa_pure_virtual Class Base size=8 align=8 base size=8 base align=8 Base (0x0x7fd42c0355a0) 0 nearly-empty vptr=((& Base::_ZTV4Base) + 16u) Vtable for OtherBase OtherBase::_ZTV9OtherBase: 5u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI9OtherBase) 16 (int (*)(...))OtherBase::~OtherBase 24 (int (*)(...))OtherBase::~OtherBase 32 (int (*)(...))OtherBase::g Class OtherBase size=8 align=8 base size=8 base align=8 OtherBase (0x0x7fd42c035600) 0 nearly-empty vptr=((& OtherBase::_ZTV9OtherBase) + 16u) Vtable for Derived Derived::_ZTV7Derived: 5u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI7Derived) 16 (int (*)(...))Derived::~Derived 24 (int (*)(...))Derived::~Derived 32 (int (*)(...))Derived::f Class Derived size=8 align=8 base size=8 base align=8 Derived (0x0x7fd42c02d138) 0 nearly-empty vptr=((& Derived::_ZTV7Derived) + 16u) Base (0x0x7fd42c035660) 0 nearly-empty primary-for Derived (0x0x7fd42c02d138) Vtable for MultiplyDerived MultiplyDerived::_ZTV15MultiplyDerived: 11u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI15MultiplyDerived) 16 (int (*)(...))MultiplyDerived::~MultiplyDerived 24 (int (*)(...))MultiplyDerived::~MultiplyDerived 32 (int (*)(...))MultiplyDerived::f 40 (int (*)(...))MultiplyDerived::g 48 (int (*)(...))-8 56 (int (*)(...))(& _ZTI15MultiplyDerived) 64 (int (*)(...))MultiplyDerived::_ZThn8_N15MultiplyDerivedD1Ev 72 (int (*)(...))MultiplyDerived::_ZThn8_N15MultiplyDerivedD0Ev 80 (int (*)(...))MultiplyDerived::_ZThn8_N15MultiplyDerived1gEv Class MultiplyDerived size=16 align=8 base size=16 base align=8 MultiplyDerived (0x0x7fd42c04aaf0) 0 vptr=((& MultiplyDerived::_ZTV15MultiplyDerived) + 16u) Base (0x0x7fd42c0356c0) 0 nearly-empty primary-for MultiplyDerived (0x0x7fd42c04aaf0) OtherBase (0x0x7fd42c035720) 8 nearly-empty vptr=((& MultiplyDerived::_ZTV15MultiplyDerived) + 64u) Vtable for OtherDerived OtherDerived::_ZTV12OtherDerived: 5u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI12OtherDerived) 16 (int (*)(...))OtherDerived::~OtherDerived 24 (int (*)(...))OtherDerived::~OtherDerived 32 (int (*)(...))OtherDerived::f Class OtherDerived size=8 align=8 base size=8 base align=8 OtherDerived (0x0x7fd42c02d1a0) 0 nearly-empty vptr=((& OtherDerived::_ZTV12OtherDerived) + 16u) Base (0x0x7fd42c035780) 0 nearly-empty primary-for OtherDerived (0x0x7fd42c02d1a0) Vtable for DiamondDerived DiamondDerived::_ZTV14DiamondDerived: 10u entries 0 (int (*)(...))0 8 (int (*)(...))(& _ZTI14DiamondDerived) 16 (int (*)(...))DiamondDerived::~DiamondDerived 24 (int (*)(...))DiamondDerived::~DiamondDerived 32 (int (*)(...))DiamondDerived::f 40 (int (*)(...))-8 48 (int (*)(...))(& _ZTI14DiamondDerived) 56 (int (*)(...))DiamondDerived::_ZThn8_N14DiamondDerivedD1Ev 64 (int (*)(...))DiamondDerived::_ZThn8_N14DiamondDerivedD0Ev 72 (int (*)(...))DiamondDerived::_ZThn8_N14DiamondDerived1fEv Class DiamondDerived size=16 align=8 base size=16 base align=8 DiamondDerived (0x0x7fd42c0625b0) 0 vptr=((& DiamondDerived::_ZTV14DiamondDerived) + 16u) Derived (0x0x7fd42c02d208) 0 nearly-empty primary-for DiamondDerived (0x0x7fd42c0625b0) Base (0x0x7fd42c0357e0) 0 nearly-empty primary-for Derived (0x0x7fd42c02d208) OtherDerived (0x0x7fd42c02d270) 8 nearly-empty vptr=((& DiamondDerived::_ZTV14DiamondDerived) + 56u) Base (0x0x7fd42c035840) 8 nearly-empty primary-for OtherDerived (0x0x7fd42c02d270) Vtable for VirtuallyDerived VirtuallyDerived::_ZTV16VirtuallyDerived: 8u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI16VirtuallyDerived) 40 (int (*)(...))VirtuallyDerived::~VirtuallyDerived 48 (int (*)(...))VirtuallyDerived::~VirtuallyDerived 56 (int (*)(...))VirtuallyDerived::f VTT for VirtuallyDerived VirtuallyDerived::_ZTT16VirtuallyDerived: 2u entries 0 ((& VirtuallyDerived::_ZTV16VirtuallyDerived) + 40u) 8 ((& VirtuallyDerived::_ZTV16VirtuallyDerived) + 40u) Class VirtuallyDerived size=8 align=8 base size=8 base align=8 VirtuallyDerived (0x0x7fd42c02d2d8) 0 nearly-empty vptridx=0u vptr=((& VirtuallyDerived::_ZTV16VirtuallyDerived) + 40u) Base (0x0x7fd42c0358a0) 0 nearly-empty virtual primary-for VirtuallyDerived (0x0x7fd42c02d2d8) vptridx=8u vbaseoffset=-40 Vtable for OtherVirtuallyDerived OtherVirtuallyDerived::_ZTV21OtherVirtuallyDerived: 8u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI21OtherVirtuallyDerived) 40 (int (*)(...))OtherVirtuallyDerived::~OtherVirtuallyDerived 48 (int (*)(...))OtherVirtuallyDerived::~OtherVirtuallyDerived 56 (int (*)(...))OtherVirtuallyDerived::f VTT for OtherVirtuallyDerived OtherVirtuallyDerived::_ZTT21OtherVirtuallyDerived: 2u entries 0 ((& OtherVirtuallyDerived::_ZTV21OtherVirtuallyDerived) + 40u) 8 ((& OtherVirtuallyDerived::_ZTV21OtherVirtuallyDerived) + 40u) Class OtherVirtuallyDerived size=8 align=8 base size=8 base align=8 OtherVirtuallyDerived (0x0x7fd42c02d340) 0 nearly-empty vptridx=0u vptr=((& OtherVirtuallyDerived::_ZTV21OtherVirtuallyDerived) + 40u) Base (0x0x7fd42c035900) 0 nearly-empty virtual primary-for OtherVirtuallyDerived (0x0x7fd42c02d340) vptridx=8u vbaseoffset=-40 Vtable for VirtuallyDiamondDerived VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived: 16u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI23VirtuallyDiamondDerived) 40 (int (*)(...))VirtuallyDiamondDerived::~VirtuallyDiamondDerived 48 (int (*)(...))VirtuallyDiamondDerived::~VirtuallyDiamondDerived 56 (int (*)(...))VirtuallyDiamondDerived::f 64 18446744073709551608u 72 18446744073709551608u 80 18446744073709551608u 88 (int (*)(...))-8 96 (int (*)(...))(& _ZTI23VirtuallyDiamondDerived) 104 (int (*)(...))VirtuallyDiamondDerived::_ZThn8_N23VirtuallyDiamondDerivedD1Ev 112 (int (*)(...))VirtuallyDiamondDerived::_ZThn8_N23VirtuallyDiamondDerivedD0Ev 120 (int (*)(...))VirtuallyDiamondDerived::_ZThn8_N23VirtuallyDiamondDerived1fEv Construction vtable for VirtuallyDerived (0x0x7fd42c02d3a8 instance) in VirtuallyDiamondDerived VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived0_16VirtuallyDerived: 8u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI16VirtuallyDerived) 40 0u 48 0u 56 (int (*)(...))VirtuallyDerived::f Construction vtable for OtherVirtuallyDerived (0x0x7fd42c02d410 instance) in VirtuallyDiamondDerived VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived8_21OtherVirtuallyDerived: 15u entries 0 18446744073709551608u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI21OtherVirtuallyDerived) 40 0u 48 0u 56 (int (*)(...))OtherVirtuallyDerived::f 64 8u 72 8u 80 (int (*)(...))8 88 (int (*)(...))(& _ZTI21OtherVirtuallyDerived) 96 0u 104 0u 112 (int (*)(...))OtherVirtuallyDerived::_ZTv0_n32_N21OtherVirtuallyDerived1fEv VTT for VirtuallyDiamondDerived VirtuallyDiamondDerived::_ZTT23VirtuallyDiamondDerived: 7u entries 0 ((& VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived) + 40u) 8 ((& VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 16 ((& VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 24 ((& VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived8_21OtherVirtuallyDerived) + 40u) 32 ((& VirtuallyDiamondDerived::_ZTC23VirtuallyDiamondDerived8_21OtherVirtuallyDerived) + 96u) 40 ((& VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived) + 40u) 48 ((& VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived) + 104u) Class VirtuallyDiamondDerived size=16 align=8 base size=16 base align=8 VirtuallyDiamondDerived (0x0x7fd42c07e460) 0 vptridx=0u vptr=((& VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived) + 40u) VirtuallyDerived (0x0x7fd42c02d3a8) 0 nearly-empty primary-for VirtuallyDiamondDerived (0x0x7fd42c07e460) subvttidx=8u Base (0x0x7fd42c035960) 0 nearly-empty virtual primary-for VirtuallyDerived (0x0x7fd42c02d3a8) vptridx=40u vbaseoffset=-40 OtherVirtuallyDerived (0x0x7fd42c02d410) 8 nearly-empty lost-primary subvttidx=24u vptridx=48u vptr=((& VirtuallyDiamondDerived::_ZTV23VirtuallyDiamondDerived) + 104u) Base (0x0x7fd42c035960) alternative-path Vtable for DoublyVirtuallyDiamondDerived DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived: 18u entries 0 8u 8 0u 16 0u 24 0u 32 0u 40 (int (*)(...))0 48 (int (*)(...))(& _ZTI29DoublyVirtuallyDiamondDerived) 56 (int (*)(...))DoublyVirtuallyDiamondDerived::~DoublyVirtuallyDiamondDerived 64 (int (*)(...))DoublyVirtuallyDiamondDerived::~DoublyVirtuallyDiamondDerived 72 (int (*)(...))DoublyVirtuallyDiamondDerived::f 80 18446744073709551608u 88 18446744073709551608u 96 18446744073709551608u 104 (int (*)(...))-8 112 (int (*)(...))(& _ZTI29DoublyVirtuallyDiamondDerived) 120 (int (*)(...))DoublyVirtuallyDiamondDerived::_ZTv0_n24_N29DoublyVirtuallyDiamondDerivedD1Ev 128 (int (*)(...))DoublyVirtuallyDiamondDerived::_ZTv0_n24_N29DoublyVirtuallyDiamondDerivedD0Ev 136 (int (*)(...))DoublyVirtuallyDiamondDerived::_ZTv0_n32_N29DoublyVirtuallyDiamondDerived1fEv Construction vtable for VirtuallyDerived in DoublyVirtuallyDiamondDerived DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived0_16VirtuallyDerived: 8u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI16VirtuallyDerived) 40 0u 48 0u 56 (int (*)(...))VirtuallyDerived::f Construction vtable for OtherVirtuallyDerived in DoublyVirtuallyDiamondDerived DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived8_21OtherVirtuallyDerived: 15u entries 0 18446744073709551608u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI21OtherVirtuallyDerived) 40 0u 48 0u 56 (int (*)(...))OtherVirtuallyDerived::f 64 8u 72 8u 80 (int (*)(...))8 88 (int (*)(...))(& _ZTI21OtherVirtuallyDerived) 96 0u 104 0u 112 (int (*)(...))OtherVirtuallyDerived::_ZTv0_n32_N21OtherVirtuallyDerived1fEv VTT for DoublyVirtuallyDiamondDerived DoublyVirtuallyDiamondDerived::_ZTT29DoublyVirtuallyDiamondDerived: 8u entries 0 ((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 56u) 8 ((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 56u) 16 ((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 56u) 24 ((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 120u) 32 ((& DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 40 ((& DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 48 ((& DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived8_21OtherVirtuallyDerived) + 40u) 56 ((& DoublyVirtuallyDiamondDerived::_ZTC29DoublyVirtuallyDiamondDerived8_21OtherVirtuallyDerived) + 96u) Class DoublyVirtuallyDiamondDerived size=16 align=8 base size=8 base align=8 DoublyVirtuallyDiamondDerived (0x0x7fd42c07ea10) 0 nearly-empty vptridx=0u vptr=((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 56u) VirtuallyDerived (0x0x7fd42c02d478) 0 nearly-empty virtual primary-for DoublyVirtuallyDiamondDerived (0x0x7fd42c07ea10) subvttidx=32u vptridx=8u vbaseoffset=-48 Base (0x0x7fd42c035a80) 0 nearly-empty virtual primary-for VirtuallyDerived (0x0x7fd42c02d478) vptridx=16u vbaseoffset=-40 OtherVirtuallyDerived (0x0x7fd42c02d4e0) 8 nearly-empty virtual lost-primary subvttidx=48u vptridx=24u vbaseoffset=-56 vptr=((& DoublyVirtuallyDiamondDerived::_ZTV29DoublyVirtuallyDiamondDerived) + 120u) Base (0x0x7fd42c035a80) alternative-path Vtable for MixedVirtuallyDerived MixedVirtuallyDerived::_ZTV21MixedVirtuallyDerived: 13u entries 0 8u 8 (int (*)(...))0 16 (int (*)(...))(& _ZTI21MixedVirtuallyDerived) 24 0u 32 0u 40 (int (*)(...))OtherBase::g 48 0u 56 18446744073709551608u 64 (int (*)(...))-8 72 (int (*)(...))(& _ZTI21MixedVirtuallyDerived) 80 0u 88 0u 96 (int (*)(...))__cxa_pure_virtual VTT for MixedVirtuallyDerived MixedVirtuallyDerived::_ZTT21MixedVirtuallyDerived: 2u entries 0 ((& MixedVirtuallyDerived::_ZTV21MixedVirtuallyDerived) + 24u) 8 ((& MixedVirtuallyDerived::_ZTV21MixedVirtuallyDerived) + 80u) Class MixedVirtuallyDerived size=16 align=8 base size=8 base align=8 MixedVirtuallyDerived (0x0x7fd42c07eee0) 0 nearly-empty vptridx=0u vptr=((& MixedVirtuallyDerived::_ZTV21MixedVirtuallyDerived) + 24u) Base (0x0x7fd42c035c60) 8 nearly-empty virtual vptridx=8u vbaseoffset=-24 vptr=((& MixedVirtuallyDerived::_ZTV21MixedVirtuallyDerived) + 80u) OtherBase (0x0x7fd42c035cc0) 0 nearly-empty primary-for MixedVirtuallyDerived (0x0x7fd42c07eee0) Vtable for MixedVirtuallyDiamondDerived MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived: 15u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI28MixedVirtuallyDiamondDerived) 40 (int (*)(...))MixedVirtuallyDiamondDerived::~MixedVirtuallyDiamondDerived 48 (int (*)(...))MixedVirtuallyDiamondDerived::~MixedVirtuallyDiamondDerived 56 (int (*)(...))MixedVirtuallyDiamondDerived::f 64 (int (*)(...))MixedVirtuallyDiamondDerived::g 72 18446744073709551608u 80 (int (*)(...))-8 88 (int (*)(...))(& _ZTI28MixedVirtuallyDiamondDerived) 96 (int (*)(...))MixedVirtuallyDiamondDerived::_ZThn8_N28MixedVirtuallyDiamondDerivedD1Ev 104 (int (*)(...))MixedVirtuallyDiamondDerived::_ZThn8_N28MixedVirtuallyDiamondDerivedD0Ev 112 (int (*)(...))MixedVirtuallyDiamondDerived::_ZThn8_N28MixedVirtuallyDiamondDerived1gEv Construction vtable for VirtuallyDerived (0x0x7fd42c02d750 instance) in MixedVirtuallyDiamondDerived MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived0_16VirtuallyDerived: 8u entries 0 0u 8 0u 16 0u 24 (int (*)(...))0 32 (int (*)(...))(& _ZTI16VirtuallyDerived) 40 0u 48 0u 56 (int (*)(...))VirtuallyDerived::f Construction vtable for MixedVirtuallyDerived (0x0x7fd42c0b5380 instance) in MixedVirtuallyDiamondDerived MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived8_21MixedVirtuallyDerived: 13u entries 0 18446744073709551608u 8 (int (*)(...))0 16 (int (*)(...))(& _ZTI21MixedVirtuallyDerived) 24 0u 32 0u 40 (int (*)(...))OtherBase::g 48 0u 56 8u 64 (int (*)(...))8 72 (int (*)(...))(& _ZTI21MixedVirtuallyDerived) 80 0u 88 0u 96 (int (*)(...))__cxa_pure_virtual VTT for MixedVirtuallyDiamondDerived MixedVirtuallyDiamondDerived::_ZTT28MixedVirtuallyDiamondDerived: 7u entries 0 ((& MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived) + 40u) 8 ((& MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 16 ((& MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived0_16VirtuallyDerived) + 40u) 24 ((& MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived8_21MixedVirtuallyDerived) + 24u) 32 ((& MixedVirtuallyDiamondDerived::_ZTC28MixedVirtuallyDiamondDerived8_21MixedVirtuallyDerived) + 80u) 40 ((& MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived) + 40u) 48 ((& MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived) + 96u) Class MixedVirtuallyDiamondDerived size=16 align=8 base size=16 base align=8 MixedVirtuallyDiamondDerived (0x0x7fd42c0b5310) 0 vptridx=0u vptr=((& MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived) + 40u) VirtuallyDerived (0x0x7fd42c02d750) 0 nearly-empty primary-for MixedVirtuallyDiamondDerived (0x0x7fd42c0b5310) subvttidx=8u Base (0x0x7fd42c035d20) 0 nearly-empty virtual primary-for VirtuallyDerived (0x0x7fd42c02d750) vptridx=40u vbaseoffset=-40 MixedVirtuallyDerived (0x0x7fd42c0b5380) 8 nearly-empty subvttidx=24u vptridx=48u vptr=((& MixedVirtuallyDiamondDerived::_ZTV28MixedVirtuallyDiamondDerived) + 96u) Base (0x0x7fd42c035d20) alternative-path OtherBase (0x0x7fd42c035d80) 8 nearly-empty primary-for MixedVirtuallyDerived (0x0x7fd42c0b5380) Vtable for VirtuallyMultiplyDerived VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived: 16u entries 0 8u 8 0u 16 0u 24 0u 32 (int (*)(...))0 40 (int (*)(...))(& _ZTI24VirtuallyMultiplyDerived) 48 0u 56 0u 64 (int (*)(...))__cxa_pure_virtual 72 0u 80 18446744073709551608u 88 (int (*)(...))-8 96 (int (*)(...))(& _ZTI24VirtuallyMultiplyDerived) 104 0u 112 0u 120 (int (*)(...))OtherBase::g VTT for VirtuallyMultiplyDerived VirtuallyMultiplyDerived::_ZTT24VirtuallyMultiplyDerived: 3u entries 0 ((& VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived) + 48u) 8 ((& VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived) + 48u) 16 ((& VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived) + 104u) Class VirtuallyMultiplyDerived size=16 align=8 base size=8 base align=8 VirtuallyMultiplyDerived (0x0x7fd42c0b59a0) 0 nearly-empty vptridx=0u vptr=((& VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived) + 48u) Base (0x0x7fd42c035e40) 0 nearly-empty virtual primary-for VirtuallyMultiplyDerived (0x0x7fd42c0b59a0) vptridx=8u vbaseoffset=-40 OtherBase (0x0x7fd42c035ea0) 8 nearly-empty virtual vptridx=16u vbaseoffset=-48 vptr=((& VirtuallyMultiplyDerived::_ZTV24VirtuallyMultiplyDerived) + 104u) Vtable for OtherVirtuallyMultiplyDerived OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived: 16u entries 0 8u 8 0u 16 0u 24 0u 32 (int (*)(...))0 40 (int (*)(...))(& _ZTI29OtherVirtuallyMultiplyDerived) 48 0u 56 0u 64 (int (*)(...))__cxa_pure_virtual 72 0u 80 18446744073709551608u 88 (int (*)(...))-8 96 (int (*)(...))(& _ZTI29OtherVirtuallyMultiplyDerived) 104 0u 112 0u 120 (int (*)(...))OtherBase::g VTT for OtherVirtuallyMultiplyDerived OtherVirtuallyMultiplyDerived::_ZTT29OtherVirtuallyMultiplyDerived: 3u entries 0 ((& OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived) + 48u) 8 ((& OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived) + 48u) 16 ((& OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived) + 104u) Class OtherVirtuallyMultiplyDerived size=16 align=8 base size=8 base align=8 OtherVirtuallyMultiplyDerived (0x0x7fd42c0b5d90) 0 nearly-empty vptridx=0u vptr=((& OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived) + 48u) Base (0x0x7fd42c035f00) 0 nearly-empty virtual primary-for OtherVirtuallyMultiplyDerived (0x0x7fd42c0b5d90) vptridx=8u vbaseoffset=-40 OtherBase (0x0x7fd42c035f60) 8 nearly-empty virtual vptridx=16u vbaseoffset=-48 vptr=((& OtherVirtuallyMultiplyDerived::_ZTV29OtherVirtuallyMultiplyDerived) + 104u) Vtable for MultiplyVirtuallyDiamondDerived MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived: 26u entries 0 16u 8 0u 16 0u 24 0u 32 (int (*)(...))0 40 (int (*)(...))(& _ZTI31MultiplyVirtuallyDiamondDerived) 48 (int (*)(...))MultiplyVirtuallyDiamondDerived::~MultiplyVirtuallyDiamondDerived 56 (int (*)(...))MultiplyVirtuallyDiamondDerived::~MultiplyVirtuallyDiamondDerived 64 (int (*)(...))MultiplyVirtuallyDiamondDerived::f 72 (int (*)(...))MultiplyVirtuallyDiamondDerived::g 80 8u 88 18446744073709551608u 96 18446744073709551608u 104 18446744073709551608u 112 (int (*)(...))-8 120 (int (*)(...))(& _ZTI31MultiplyVirtuallyDiamondDerived) 128 (int (*)(...))MultiplyVirtuallyDiamondDerived::_ZThn8_N31MultiplyVirtuallyDiamondDerivedD1Ev 136 (int (*)(...))MultiplyVirtuallyDiamondDerived::_ZThn8_N31MultiplyVirtuallyDiamondDerivedD0Ev 144 0u 152 18446744073709551600u 160 18446744073709551600u 168 (int (*)(...))-16 176 (int (*)(...))(& _ZTI31MultiplyVirtuallyDiamondDerived) 184 (int (*)(...))MultiplyVirtuallyDiamondDerived::_ZTv0_n24_N31MultiplyVirtuallyDiamondDerivedD1Ev 192 (int (*)(...))MultiplyVirtuallyDiamondDerived::_ZTv0_n24_N31MultiplyVirtuallyDiamondDerivedD0Ev 200 (int (*)(...))MultiplyVirtuallyDiamondDerived::_ZTv0_n32_N31MultiplyVirtuallyDiamondDerived1gEv Construction vtable for VirtuallyMultiplyDerived (0x0x7fd42bcdf230 instance) in MultiplyVirtuallyDiamondDerived MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived0_24VirtuallyMultiplyDerived: 16u entries 0 16u 8 0u 16 0u 24 0u 32 (int (*)(...))0 40 (int (*)(...))(& _ZTI24VirtuallyMultiplyDerived) 48 0u 56 0u 64 (int (*)(...))__cxa_pure_virtual 72 0u 80 18446744073709551600u 88 (int (*)(...))-16 96 (int (*)(...))(& _ZTI24VirtuallyMultiplyDerived) 104 0u 112 0u 120 (int (*)(...))OtherBase::g Construction vtable for OtherVirtuallyMultiplyDerived (0x0x7fd42bcdf2a0 instance) in MultiplyVirtuallyDiamondDerived MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived8_29OtherVirtuallyMultiplyDerived: 23u entries 0 8u 8 18446744073709551608u 16 18446744073709551608u 24 0u 32 (int (*)(...))0 40 (int (*)(...))(& _ZTI29OtherVirtuallyMultiplyDerived) 48 0u 56 0u 64 (int (*)(...))__cxa_pure_virtual 72 0u 80 8u 88 (int (*)(...))8 96 (int (*)(...))(& _ZTI29OtherVirtuallyMultiplyDerived) 104 0u 112 0u 120 (int (*)(...))__cxa_pure_virtual 128 0u 136 18446744073709551608u 144 (int (*)(...))-8 152 (int (*)(...))(& _ZTI29OtherVirtuallyMultiplyDerived) 160 0u 168 0u 176 (int (*)(...))OtherBase::g VTT for MultiplyVirtuallyDiamondDerived MultiplyVirtuallyDiamondDerived::_ZTT31MultiplyVirtuallyDiamondDerived: 10u entries 0 ((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 48u) 8 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived0_24VirtuallyMultiplyDerived) + 48u) 16 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived0_24VirtuallyMultiplyDerived) + 48u) 24 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived0_24VirtuallyMultiplyDerived) + 104u) 32 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived8_29OtherVirtuallyMultiplyDerived) + 48u) 40 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived8_29OtherVirtuallyMultiplyDerived) + 104u) 48 ((& MultiplyVirtuallyDiamondDerived::_ZTC31MultiplyVirtuallyDiamondDerived8_29OtherVirtuallyMultiplyDerived) + 160u) 56 ((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 48u) 64 ((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 184u) 72 ((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 128u) Class MultiplyVirtuallyDiamondDerived size=24 align=8 base size=16 base align=8 MultiplyVirtuallyDiamondDerived (0x0x7fd42bcdf1c0) 0 vptridx=0u vptr=((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 48u) VirtuallyMultiplyDerived (0x0x7fd42bcdf230) 0 nearly-empty primary-for MultiplyVirtuallyDiamondDerived (0x0x7fd42bcdf1c0) subvttidx=8u Base (0x0x7fd42bce2000) 0 nearly-empty virtual primary-for VirtuallyMultiplyDerived (0x0x7fd42bcdf230) vptridx=56u vbaseoffset=-40 OtherBase (0x0x7fd42bce2060) 16 nearly-empty virtual vptridx=64u vbaseoffset=-48 vptr=((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 184u) OtherVirtuallyMultiplyDerived (0x0x7fd42bcdf2a0) 8 nearly-empty lost-primary subvttidx=32u vptridx=72u vptr=((& MultiplyVirtuallyDiamondDerived::_ZTV31MultiplyVirtuallyDiamondDerived) + 128u) Base (0x0x7fd42bce2000) alternative-path OtherBase (0x0x7fd42bce2060) alternative-path

Answer 2

La mayoría de las implementaciones del compilador que he visto simplemente "incrustan" el objeto base en el objeto derivado. Se vuelve irrelevante dónde se guarda el vtable porque el desplazamiento relativo en el objeto simplemente se agregará en el momento de la compilación a medida que se evalúan las referencias.

La herencia múltiple y virtual es más complicada y puede requerir un desplazamiento diferente según lo que se está accediendo.

Recomiendo leer este artículo sobre Code Project: The Imposibly Fast C ++ Delegates

Brillantemente da una imagen amplia de cómo los diferentes compiladores manejan varios aspectos de la herencia. Lectura fantástica si le interesa el funcionamiento de bajo nivel de diferentes compiladores.

Editar: he vinculado el artículo incorrecto allí. Corregido