https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78155
--- Comment #8 from Eric Gallager <egallager at gcc dot gnu.org> --- (In reply to Martin Sebor from comment #4) > I don't really see what existing warning this might fall under, except > perhaps -Wchar-subscripts because isalpha and friend use the argument as an > index into an array of 257 characters, but that seems like a stretch. > > I think maybe adding a more general warning option, say something like > -Wargument-range, and using it to diagnose all such problems, might be the > way to go. To generalize the solution I would even consider adding a new > function attribute, let's call it range, to specify the range of valid > values of a function argument. Then isalpha (or any other such function) > could be declared like so: > > __attribute__ ((range (/* position = */1, -1, UCHAR_MAX))) > int isalpha (int); > > GCC would then check every call to the function to see if its argument is in > the expected range and, if not, issue a warning. The attribute could even > be applied multiple times to specify disjoint ranges. Position zero could > denote the return value so that toupper could be declared like so > > __attribute__ ((range (/* returns = */ 0, -1, UCHAR_MAX), > range (/* position = */ 1, -1, UCHAR_MAX))) > int toupper (int); There's been an attempt to add an attribute like this recently on the mailing lists: https://gcc.gnu.org/pipermail/gcc/2022-June/238819.html
