On Mon, Feb 25, 2019 at 05:54:44PM -0800, Bob Deen via fortran wrote: > On 2/19/19 2:44 PM, Thomas Koenig wrote: > > Bob, > > > >> Some of us still use varargs interfaces (in my case, Fortran calling C > >> stdarg subroutines). > > > > The problem for us is that that sometimes using varargs made standard- > > conforming Fortran code like, in file a.f > > > > subroutine foo(a) > > print *,a > > end > > > > and in file main.f > > > > programme main > > call foo(1.0) > > end > > > > depend ABI details: The call to foo used to be called using > > the varargs convention, and the subroutine foo was compiled > > as a non-varargs function. > > > > This "worked" until PR 87689 showed that this breaks > > standard-conforming Fortran code on a primary gcc platform. > > > > I don't know if that makes a difference for the platform you work > > on. For the System V AMD64 ABI, I suspect it actually might not > > matter (at least from glancing at the corresponding Wikipedia > > article), but I am _not_ an expert in this field, so please take this > > with a chunk of rock salt of appropriate size. > > > > So, we cannot really keep this as a feature (note that varargs > > are also not C interoperable). > > Okay. But I hope you don't let the perfect be the enemy of the good. > That particular platform is not a concern for us, so if you break it > there I'm not happy, but it's not the end of the world either. But > please don't break it other places just because it doesn't work on that > one platform. I know it's not good design practice to have that kind of > platform-dependent behavior, but sometimes practicalities force less > than ideal choices. >
Instead of fixing a bug in the compiler and conforming to the Fortran standard, we should just let this one go as an "enhancement". How many more of these "enhancements" should be allowed? If an "enhancement" works on one architecture but not on another, we'll need to start adding pre-processing directives into otherwise machine-independent code. It becomes a maintainence nightmare. We have these maintainence issues in libgfortran, where we do have to take the architecture into consider. Keeping things working for everyone can be (ahem) fun. If you need a vararg-like interface, it seems you should consider encapulating the specific routines in a module and build a generic interface with optional arguments. -- Steve
