On Thu, 11 May 2023, Kees Cook via Gcc wrote: > Okay, understood. If this is a C-only thing, we can ignore the C++ > impact.
We're a lot more careful lately in WG14 about checking for C++ compatibility issues and expecting approval from the liaison group for anything with possible compatibility concerns for syntax in the common subset of C and C++. So, no, we can't ignore the C++ impact for adding empty types; it would need careful consideration in the liaison group. > What depends on the "different objects have different addresses" > principle? And why do unions not break this -- they could point to the > same locations within the object? And don't flexible arrays already need > special handling in this regard? "including a pointer to an object and a subobject at its beginning" and "one is a pointer to one past the end of one array object and the other is a pointer to the start of a different array object that happens to immediately follow the first array object in the address space" are both cases included in the semantics for comparison operators. If you allow zero-size objects you get more special cases there (and quite possibly affect optimizations based on points-to analysis that can determine pointers are based on different objects, if an object is not known at compile time to have nonzero size). -- Joseph S. Myers jos...@codesourcery.com
