On Mon, 2 Jun 2014, Florian Weimer wrote: > On 05/31/2014 08:56 AM, Alan Modra wrote: > > > > It's fine to change ABI when compiling an old-style function > > > definition for which a prototype exists (relative to the > > > non-prototype case). It happens on i386, too. > > > > That might be so, but when compiling the function body you must assume > > the worst case, whatever that might be, at the call site. For K&R > > code, our error was to assume the call was unprototyped (which > > paradoxically is the best case) when compiling the function body. > > Is this really a supported use case? I think I remember tracking down a bug > which was related to a lack of float -> double promotion because the call was > prototyped, and the old-style function definition wasn't. This would have > been on, ugh, SPARC. I think this happened only in certain cases (float > arguments, probably).
ISO C (right back to C90) requires a prototype in scope if a variadic function, or a function whose definition has prototyped argument types changed by the default argument promotions (such as float and short), is called. It probably makes sense by now to enable -Wimplicit-function-declaration by default, though that won't catch cases where the file with the unprototyped call has a non-prototype declaration such as "int foo();". -- Joseph S. Myers jos...@codesourcery.com
