https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91092
--- Comment #15 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- (In reply to Florian Weimer from comment #14) > (In reply to Vincent Lefèvre from comment #13) > > By "implicit function declarations", does this include K&R style > > declarations? > > No, there is nothing implicit about them. OK, but the issue is similar: in both cases, the parameters/arguments are not checked, yielding undefined behavior, so that they fall in the same class. > > I've found out a few days ago that GMP still uses K&R style declarations, > > and that's in a configure script. The issue is that there is a potential > > type mismatch between the caller (long) and the callee (unsigned int), and > > GCC fails to generate "correct" code in such a case. > > GNU CC has supported an extension for many, many years where a K&R function > *definition* with a prior function prototype in scope behaves exactly as a > prototype-style function definition. (On some targets, the two have > substantially different ABIs, beyond how parameters are handled.) Actually I meant K&R function definition (with no previous prototype). > Since the GMP headers use prototypes (they have to, otherwise they would not > be compatible with C++ compilers), GMP necessarily relies on this extension > today. That's in its configure script, unrelated to gmp.h. I can see old PR26732 and PR48091 about K&R function definition, but both are about warnings only.
