https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83334
--- Comment #2 from zenith432 at users dot sourceforge.net --- You're misquoting my summary. It does not say sysv ABI varargs function. It says sys ABI function. Check the samples. A __builtin_ms_va_list is constructed (__builtin_ms_va_started) in an ms ABI varargs function, then passed as an argument to a sysv ABI function. sysv ABI functions can already iterate over __builtin_ms_va_lists today with __builtin_va_arg. But using __builtin_ms_va_copy on a __builtin_ms_va_list in a sysv ABI function (that got one passed in as a parameter) emits incorrect code. These features are all non-standard and undocumented, so it is difficult to separate a "bug report" from a "feature request". A __builtin_ms_va_list is a char*, and calling __builtin_ms_va_copy on it is just to assign the pointer to another pointer. It is the same complexity as passing it as an argument. On the other hand, iterating over a __builtin_ms_va_list (with __builtin_va_arg) emits more complicated code, and this can already be done in a sysv ABI function. So it seems like an omission or bug that __builtin_ms_va_copy doesn't work in a sysv ABI function.
