* Joseph Myers: > On Fri, 21 Oct 2022, Florian Weimer via Gcc wrote: > >> Is this really possible? For function pointers, it's an ABI change. >> int (*) () and int (*) (void) have different calling conventions on some >> ABIs (e.g., powerpc64le-linux-gnu). The ABI difference goes away once >> the callees are rebuilt, and I think such rebuilt callees are compatible >> with either calling convention. > > The semantics of int (*) (void) are a refinement of those of pre-C2x > int (*) (): any non-variadic function whose argument types are unchanged > by the default argument promotions can be called through an int (*) () > pointer, but only functions with no arguments can be called through an > int (*) (void) pointer.
Pre-C2x powerpc64le-linux-gnu, a call through int (*) () with no arguments still sets up a parameter save area, while a call through int (*) (void) does not. With C2x, neither will set up a parameter save area. Hopefully, the current rs6000 backend already uses the parameter save area just for, well, saving parameters, and not for general-purpose spilling. In this case, there won't be any ABI problems from the C2x change for powerpc64le. (Sorry that I keep bringing this up, it's confusing to me, and I once spent quite some time tracking down a stack corruption because glibc's open implementation assumed a parameter save area that the caller did not provide.) Thanks, Florian
