https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114780
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:2afdecccbaf5c5b1c7a235509b37092540906c02 commit r14-10046-g2afdecccbaf5c5b1c7a235509b37092540906c02 Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Apr 20 00:12:36 2024 +0200 c-family: Allow arguments with NULLPTR_TYPE as sentinels [PR114780] While in C++ the ellipsis argument conversions include "An argument that has type cv std::nullptr_t is converted to type void*" in C23 a nullptr_t argument is not promoted in any way, but va_arg description says: "the type of the next argument is nullptr_t and type is a pointer type that has the same representation and alignment requirements as a pointer to a character type." So, while in C++ check_function_sentinel will never see NULLPTR_TYPE, for C23 it can see that and currently we incorrectly warn about those. The only question is whether we should warn on any argument with nullptr_t type or just about nullptr (nullptr_t argument with integer_zerop value). Through undefined behavior guess one could pass non-NULL pointer that way, say by union { void *p; nullptr_t q; } u; u.p = &whatever; and pass u.q to ..., but valid code should always pass something that will read as (char *) 0 when read using va_arg (ap, char *), so I think it is better not to warn rather than warn in those cases. Note, clang seems to pass (void *)0 rather than expression of nullptr_t type to ellipsis in C23 mode as if it did the C++ ellipsis argument conversions, in that case guess not warning about that would be even safer, but what GCC does I think follows the spec more closely, even when in a valid program one shouldn't be able to observe the difference. 2024-04-20 Jakub Jelinek <ja...@redhat.com> PR c/114780 * c-common.cc (check_function_sentinel): Allow as sentinel any argument of NULLPTR_TYPE. * gcc.dg/format/sentinel-2.c: New test.
