Question

I’m still fighting with GCC – compiling the following inline assembly code (with -fasm-blocks, which enables Intel style assembly syntax) nets me a strange error Cannot take the address of ‘this’, which is an rvalue expression…

MyClass::MyFunction()
{
    _asm
    {
        //...
        mov ebx, this // error: Cannot take the address of 'this', which is an rvalue expression
        //...
        mov eax, this // error: Cannot take the address of 'this', which is an rvalue expression
        //...
    };
}

Why can I store pointers to different objects in registers, but can’t use pointer to MyClass instance?

Answer 1

That’s because the compiler might decide on its own to store this in a register (generally ECX) instead of a memory cell, for optimization purposes, or because the calling convention explicitly specifies it should do that.

In that case, you cannot take its address, because registers are not addressable memory.