On 2023-12-21 03:46, Dimitry Andric wrote:

The problem is that c99 effectively runs "cc -std=iso9899:1999 -pedantic". _Generic is a C11 extension so it will then warn about that.

Thanks for doing the testing. I ran into that bug with _Generic on FreeBSD 14 and installed the following workaround, which fixed things for me: https://mm.icann.org/pipermail/tz/2023-December/033364.html so if you do a "git pull" I hope this problem is fixed on FreeBSD 15-CURRENT as well. I view this as merely a bug in how clang does things. When you run 'make' in POSIX mode (by putting a ".POSIX:" line at the start of the Makefile), 'make' defaults CC to c99 (as current POSIX requires). In tzcode, even before the abovementioned patch, all uses of _Generic were protected by "#if __has_extension(c_generic_selections)" but clang complain about the uses anyway. The patch works around this clang bug by ignoring '#if __has_extension(c_generic_selections)' when it succeeds. If clang is going to diagnose any use of an extension X, then __has_extension(X) should be false. Perhaps the clang folks could implement this suggestion.

The easiest workaround is to not use c99, but "cc -std=c11", optionally with "-pedantic", that will work just fine even with ce293ccb574a77956c758a81287dbc8ef4f4eedf reverted.

You can do that by editing the "#CC = ..." line in the tzcode Makefile, or by running "make CC='cc -std=c11'". We can't make these changes in tzcode's distributed Makefile, though, as that wouldn't be portable.

In addition, -pedantic is known to complain about GNU extensions such as __builtin_offsetof. There is not much you can do about that, since we make extensive use of such extensions in the FreeBSD system headers.

Yes, your email contained the following messages indicating this problem:

zic.c:2395:11: warning: defining a type within '__builtin_offsetof' is a Clang extension [-Wgnu-offsetof-extensions] 2395 | alignof(zic_t))); | ^~~~~~~~~~~~~~ zic.c:74:33: note: expanded from macro 'alignof' 74 | # define alignof(type) offsetof(struct { char a; type b; }, b) | ^~~~~~ /usr/include/stddef.h:71:42: note: expanded from macro 'offsetof' 71 | #define offsetof(type, field) __offsetof(type, field) | ^~~~ /usr/include/sys/cdefs.h:424:53: note: expanded from macro '__offsetof' 424 | #define __offsetof(type, field) __builtin_offsetof(type, field) | ^~~~

I don't see this message in FreeBSD 14, so this is a regression in FreeBSD 15. And it appears to be another bug in FreeBSD and/or clang. First, any code using __builtin_offsetof is using a GNU extension, so why warn about __builtin_offsetof with a particular argument that happens to be a new type? And second, "__builtin_offsetof(struct { char a; type b; }, b)" doesn't define any type that can be used anywhere else, so why warn about the type? And third, there's nothing in C99 that prohibits the use of "offsetof(struct { char a; type b; }, b)" and it works on every C99 platform, so why warn about it? I reproduced the problem on Fedora 39 with "make CC='clang -std=iso9899:1999 -pedantic'", and attempted to pacify clang with the attached patch, but that merely changed the diagnostics to be something like this: zic.c:2408:11: warning: '_Alignof' is a C11 extension [-Wc11-extensions] 2408 | alignof(zic_t))); | ^ /usr/bin/../lib/clang/17/include/stdalign.h:19:17: note: expanded from macro 'alignof' 19 | #define alignof _Alignof | ^ 1 warning generated. Since this bug is only a warning, perhaps we should give up trying to work around it. I hope the clang folks fix the bug eventually.