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Re: [std-proposals] std::any::base

From: Frederick Virchanza Gotham <cauldwell.thomas_at_[hidden]>
Date: Wed, 17 Apr 2024 10:37:04 +0100
On Wed, Apr 17, 2024 at 12:07 AM Thiago wrote:
> > If you use Visual Studio 2022 to build your program as x86_32, then
> > they are just normal 32-Bit pointers. However if you build your
> > program as x86_64, then they are 32-Bit offsets which you add to the
> > return address from "GetModuleHandleA(nullptr)".
> I see. So can they point to structures found in dllimport'ed libraries? Well,
> they can't, so how the hell can dynamic_cast cast across DLLs?

    struct RTTICompleteObjectLocator {
        unsigned long signature;
        unsigned long offset;
        unsigned long cdOffset;
        int pTypeDescriptor;
        int pClassDescriptor;
        int pSelf;

The last member of the struct, "pSelf", is the 32-Bit offset from the
module's base address to the current "RTTICompleteObjectLocator"
object. So in order to get the module's base address, you do:

    void *module = (char*)&locator - locator.pSelf;

Presumably that's what Microsoft uses to throw exceptions from DLL's
to EXE's on x86_64 computers.

I'm very close to having __RTDynamicCast reverse-engineered to find
the ThrowInfo. All the structs are nicely described here:

Received on 2024-04-17 09:37:17