https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106924
Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever confirmed|0 |1 Last reconfirmed| |2022-09-14 --- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- Reduced to remove unnecessary virtual functions that are never used, and fix the printf formats, and make it fail at runtime: extern "C" int printf(const char*, ...); extern "C" void abort(); struct BaseA { virtual ~BaseA(){} }; struct BaseB { virtual ~BaseB(){} }; struct DerivedAB; struct FabForB { virtual BaseA* getPtr()=0; virtual ~FabForB(){} }; struct DerivedAB : BaseB, BaseA { struct ABFabNested : FabForB { virtual DerivedAB* getPtr(); }; }; void print(const DerivedAB* dp, const BaseA* ap, bool nested = false) { } DerivedAB d; DerivedAB* DerivedAB::ABFabNested::getPtr() { DerivedAB* p = &d; printf("TEST fab nested: addr %p base %p\n", p, (BaseA*)p); return p; } struct ABFab : FabForB { virtual DerivedAB* getPtr() { DerivedAB* p = &d; printf("TEST fab: addr %p base %p\n", p, (BaseA*)p); return p; } }; int main() { ABFab fab; DerivedAB::ABFabNested fabNested; BaseA* a1 = fab.getPtr(); BaseA* a2 = static_cast<FabForB&>(fab).getPtr(); printf("TEST addr %p %p\n", a1, a2); a1 = fabNested.getPtr(); a2 = static_cast<FabForB&>(fabNested).getPtr(); printf("TEST nested addr %p %p\n", a1, a2); if (a1 != a2) abort(); } G++ prints: TEST fab: addr 0x404060 base 0x404068 TEST fab: addr 0x404060 base 0x404068 TEST addr 0x404068 0x404068 TEST fab nested: addr 0x404060 base 0x404068 TEST fab nested: addr 0x404060 base 0x404068 TEST nested addr 0x404068 0x404060 Aborted (core dumped) When we call fabNested.getPtr() to get a DerivedAB* and then convert to BaseA* at the call site, the pointer is correctly adjusted to the BaseA base subobject. When we call static_cast<FabForB&>(fabNested).getPtr() to get a BaseA* the covariant return is not adjusted, and the address of the DerivedAB complete object is returned, not its BaseA base subobejct..