C++ with vtable and regparm=N seems to cause mismatch between callsite and subroutine

[erique]

When a class method is called via vtable, and -mregparm is used, the callsite passes this in a0, while the subroutine assumes this being passed on the stack.

CEX: http://franke.ms/cex/z/xTj5Yr

Subroutine TheClass::Reset() is called like

void* r = static_cast<TheClass*>(c)->Reset(); // 'this' passed via a0

which translates to

        move.l (a2),a0
        move.l (a0),a1
        move.l d0,a0
        jsr (a1)

While TheClass::Reset() itself will try to use this from the stack:

__ZN8TheClass5ResetEv:
        move.l (4,sp),d0
        move.l d0,a0
        clr.b (4,a0)
        rts

( This example works fine in x86 GCC : https://godbolt.org/z/Exncnjqh4 )

[bebbo]

confirmed: http://franke.ms/cex/z/5v88oo

[erique]

confirmed working - thanks!