I've been following [RFC] Enabling -Wstrict-prototypes by default in C <https://discourse.llvm.org/t/rfc-enabling-wstrict-prototypes-by-default-in-c/60521/25>
and I've just realized that treating extern int foo(); as a prototype declaration (with the same ABI as extern "C" int foo(); in C++) introduces a minor ABI break if the caller is compiled in C2X mode, but the definition is not. Without the prototype (C18 mode and earlier), the caller needs to create a parameter save area per the powerpc64le ABI. With the prototype (C2X mode), I would expect the compiler to omit the parameter save area. Unfortunately, this creates an ABI quirk if the C2X status doesn't match between caller and function implementation. I believe GCC uses the parameter save area for general-purpose spilling, so it's still used in a prototype-less function definition without any parameters. That's why this is a minor ABI break. It's probably not much to worry about, but I'd like to point it out nevertheless. Thanks, Florian
