On June 2, 2014 11:30:20 PM CEST, "Joseph S. Myers" <jos...@codesourcery.com> wrote: >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();".
There is an old patch of mine warning for this case... Google for -Wunprototyped-calls Richard.
