Why does gcc ignore __attribute__((stdcall))?

Question

When I compile the following C source with gcc version 8.1.1, I get a warning: ‘stdcall’ attribute ignored [-Wattributes].

Why does gcc choose to ignore this attribute and what can I do to make it accept it?

__attribute__((stdcall)) int S(int a) {
    return a * (a+1);
}

int main() {
    return S(6);
}

Pigeontoed

What architecture are you compiling for? – Syphilis

Move to a 32-bit x86 platform. – Suicide

Answer 1

The gcc documentation says:

stdcall

On x86-32 targets, the stdcall attribute causes the compiler to assume that the called function pops off the stack space used to pass arguments, unless it takes a variable number of arguments.

(Emphasis mine.)

So if you're not compiling for a 32-bit machine, stdcall can't be used.

Lysis

Is there a technical reason that stdcall is not possible on non-x86-32 targets? – Unbridled

@RenéNyffenegger x86-64 doesn't pass arguments on the stack (or rather, it prefers using registers before using the stack), so there's little point in defining and using different incompatible conventions for adjusting the stack. – Lysis

Thanks for clearing that up to me. I was completely unaware of the shift between 32 and 64 bit x86 regarding calling conventions. – Unbridled

Is it possible to turn this warning off? – Halfslip