https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90036
--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> --- (In reply to Dmitry G. Dyachenko from comment #3) The null pointer detection was added in r265648 so that would be the change responsible for the warning. As Jeff noted, the root cause of false positives here isn't the warning itself but a missing optimization. We will be making some design changes to the printf warning pass in GCC 10 that could affect the false positive rate so they might also give us an opportunity to look into the missed dom optimization. (In reply to Segher Boessenkool from comment #4) I agree the underlining could stand to be improved here (tracking is separately would increase the odds of it getting fixed). A conversion specification is what follows the % character (i.e., just the 's' in in something like "%3s", with the 's' being called a conversion specifier). A directive either includes the % character and whatever follows up to the end of the conversion specification, or is a plain character. For simplicity, -Wformat-overflow refers to whole strings of one or more ordinary characters that don't form a conversion specification as directives. The use of plain here null comes -Wnonnull: null argument where non-null required. I don't see that as a problem but I also wouldn't have an issue with changing both to "null pointer" (like -Wformat prints) just as long as it's done consistently.
