Crash when using dynamic_cast<>

[Jean-Jacques]

The C++ runtime from the Windows SDK seems to have a problem with multiple inheritance.

Here is a minimal reproduction :

struct Base1 {

    int N1{};

    virtual ~Base1() = default;

};

struct Base2 {

    int N2{};

    virtual ~Base2() = default;

};

struct Derived : public Base1, public Base2 {

    int D{};

    virtual ~Derived() = default;

};

void test()

{

    Base1* foo1 = new Derived;

    Base1* bar1 = dynamic_cast<Base1*>(foo1);

    Base2* baz1 = dynamic_cast<Base2*>(foo1);

    Base2* foo2 = new Derived;

    Base2* baz2 = dynamic_cast<Base2*>(foo2);

    Base1* bar2 = dynamic_cast<Base1*>(foo2); // => only this one crashes, only on windows with the sgx runtime

}

The call-stack at the crash is :

enclave.signed.dll!abort() Line 1054 (c:\SGXWindows\src_Release\windows-trunk\sdk\trts\win\trts_pic.asm:1054)
enclave.signed.dll!__assert(const char * file, int line, const char * func, const char * failedexpr) Line 50 (c:\SGXWindows\src_Release\windows-trunk\sdk\tlibc\gen\assert.c:50)
enclave.signed.dll!get_cross_cast_result(const _rtti_base_descriptor * ptarget_type_bcd, const _rtti_base_descriptor * psrc_type_bcd) Line 71 (c:\SGXWindows\src_Release\windows-trunk\sdk\cpprt\win\rtti\rtti.cpp:71)
enclave.signed.dll!get_multiple_inheritance_bcd(const void * pcomplete_object, const _rtti_complete_object_locator * pcomplete_object_locator, const _rtti_type_descriptor * psrc_type_id, __int64 inptr_delta, const _rtti_type_descriptor * ptarget_type_id) Line 201 (c:\SGXWindows\src_Release\windows-trunk\sdk\cpprt\win\rtti\rtti.cpp:201)
enclave.signed.dll!__RTDynamicCast(void * inptr, long vf_delta, void * src_type, void * target_type, int is_reference) Line 390 (c:\SGXWindows\src_Release\windows-trunk\sdk\cpprt\win\rtti\rtti.cpp:390)

Note that this works on Linux, and when the inheritance is virtual.

By the way, is there a reason why the SDK is open-source on Linux and not on Windows ? My guess is that with the actual sources mentioned in the call-stack, a fix and a pull-request might have been possible.

[Sahira_Intel]

Hi,

I am looking into this and will get back to you shortly.

Sincerely,

Sahira

[Sahira_Intel]

Hi Jean-Jacques,

Thanks for your patience, I've escalated this issue to engineering to look at. I will let you know when I have more information.

Sincerely,

Sahira

[Sahira_Intel · Accepted solution]

Hi Jean-Jacques,

This was a bug that has been fixed and will be part of the next release. 

Sincerely,

Sahira