> > > On Thu, Sep 7, 2023 at 6:09 PM Eric Blake <ebl...@redhat.com> wrote: > >> On Wed, Sep 06, 2023 at 03:08:33PM -0700, Mike Fulton wrote: >> > Hello, >> > >> > The m4 dev line ( git://git.savannah.gnu.org/m4.git ) >> > has the following code: >> > >> > ``` >> > #if 4 < __GNUC__ + (6 <= __GNUC_MINOR__) >> > # pragma GCC diagnostic push >> > # pragma GCC diagnostic ignored "-Wformat-nonliteral" >> > #endif >> > ``` >> >> That expression appears to be designed to reject gcc 3.5 and older, >> while accepting 3.6 and newer. >> > Right - that's my understanding. > >> >> I also wonder if modern gnulib provides a better way to test things >> than just open-coding it (as Bruno has done a lot of work testing >> features of newer compilers). This may be one case where ignoring the >> diagnostic for older builds is desirable - there comes a point where >> you can't please both old and new compilers simultaneously, but the >> target that should be warning-free is the newer compiler. >> > Great question - this seems to be something added before clang and I > wonder if there is a better way to manage diagnostics that are meant > to be 'sort of common?' between GCC and clang. I've just started > using clang on z/OS so I'm not sure how this mapping is done for > GCC compatibility. > >> >> That is, maybe it's time to just rewrite the check to something as >> simple as #if 8 <= __GNUC__ (that is, only add the pragmas on a much >> newer, albeit arbitrary, point in time)? >> >> Conversely, I see that m4 uses gnulib's lib/c-stack.c, which also has: >> >> /* Pacify GCC 9.3.1, which otherwise would complain about segv_handler. >> */ >> # if 4 < __GNUC__ + (6 <= __GNUC_MINOR__) >> # pragma GCC diagnostic ignored "-Wsuggest-attribute=pure" >> # endif >> >> so it's not like m4 is doing anything radically different from gnulib >> when it comes to pragmas for ignoring certain diagnostics; but thd >> difference may be which diagnostic is being ignored. >> >> > >> > This produces an error on the clang compiler I am using on z/OS, which >> is >> > at 4.2 with the xasprintf code that follows, e.g. >> > >> > ``` >> > str = xasprintf (fstart, width, ARG_INT(argc, argv)); >> > ``` >> > >> > If I change the check to: >> > >> > ``` >> > #if 4 < __GNUC__ + (2 <= __GNUC_MINOR__) >> > # pragma GCC diagnostic push >> > # pragma GCC diagnostic ignored "-Wformat-nonliteral" >> > #endif >> > ``` >> > >> > all is good - it compiles clean. The question is whether the check for >> 6 is >> > too high or if the clang compiler on z/OS has a bug (or something else)? >> >> What does clang claim to be? That is, what do you get for >> print '__GNUC__ __GNUC_MINOR__' | clang -E - | tail -n1 >> > On both z/OS as well as my Mac I see: > 4 2 > >> >> and what is the actual compiler error you got when the build failed on >> the original source? >> > CC format.o > format.c:360:28: error: format string is not a string literal > [-Werror,-Wformat-nonliteral] > str = xasprintf (fstart, width, ARG_INT(argc, argv)); > > ^~~~~~ > >> >> > I haven't been able to determine what level of gcc provides this >> diagnostic. >> > What if we just acknowledged the clang compiler and changed the check to:
#if 4 < __GNUC__ + (6 <= __GNUC_MINOR__) || defined(__clang__) ? > > >> > thanks, mike >> >> -- >> Eric Blake, Principal Software Engineer >> Red Hat, Inc. >> Virtualization: qemu.org | libguestfs.org >> >>
