From a private discussion about preventing CFLAGS getting -std=gnu99 twice, that leads to a bug report for gnulib and maybe autoconf too...
Begin forwarded message: > From: "Gary V. Vaughan" <g...@gnu.org> > Subject: Re: Getting AC_PROG_CC_C99 > Date: 28 September 2011 12:38:33 GMT+07:00 > To: Reuben Thomas <r...@sc3d.org> > > Hi Reuben, > > On 27 Sep 2011, at 20:16, Reuben Thomas wrote: > >> According to the Zile commit logs: >> >> configury: remove duplicate AC_GNU_SOURCE et al >> >> AC_GNU_SOURCE and AC_PROG_CC_C99 are automatically required by gl_INIT, >> no need to specify them again in configure.ac (which results in running >> `gcc -std=gnu99 -std=gnu99'. >> >> I hasten to add there's nothing going wrong in Zile AFAICS. >> >> However, in another project (occurs, as mentioned yesterday), I don't >> automatically get AC_PROG_CC_C99, even though I'm using gnulib, and >> definitely have the extensions module in there. I've looked at the >> configure files (sadly hard to examine as there are no comments >> telling you which bit was expanded from which configure.ac line), and >> can't see anything obvious. I've stared at the configure.ac files, >> natch, and ditto. >> >> Any hints? I have also looked at the list of gnulib modules for each >> project and can't see anything there. > > Actually, AC_PROG_CC_C99 is automatically called in autoconf's own macros > by AC_PROG_CC_STDC (see /usr/share/autoconf/autoconf/c.m4), and it is *that* > macro that gnulib is hooking automatically. By grepping through the Zile > m4 directory after bootstrapping I quickly came across this in gnulib-comp.m4: > > # Code from module stdarg: > dnl Some compilers (e.g., AIX 5.3 cc) need to be in c99 mode > dnl for the builtin va_copy to work. With Autoconf 2.60 or later, > dnl AC_PROG_CC_STDC arranges for this. With older Autoconf AC_PROG_CC_STDC > dnl shouldn't hurt, though installers are on their own to set c99 mode. > AC_REQUIRE([AC_PROG_CC_STDC]) > > The stdarg module is listed explicitly in Zile's bootstrap.conf module list, > so that is how Zile gets an expansion of AC_PROG_CC_STDC (and the c99 mode > setting option tests) for free. > > Now, the interesting thing is that if I grep through the gnulib/modules > directory for AC_PROG_CC_STDC calls, *only* stdarg has it. That strikes me > as kind of odd. Shouldn't all the C99 related modules be calling at least > AC_PROG_CC_C99 if not the whole AC_PROG_CC_STDC set? > > And that points to another problem, because AC_PROG_CC_STDC is not safe > to call multiple times, since it adds another --std=gnu99 to CFLAGS every > time it is invoked (at least the version in my Apple suppied Autoconf-2.61), > so gnulib should probably also have some multiple expansion protection code > for at least us poor Mac based devs using Homebrew (untested!!): > > dnl make sure we only expand AC_PROG_CC_STDC once > AC_DEFUN_ONCE([gl_PROG_CC_C99], [ > AC_PROVIDE_IFELSE([AC_PROG_CC_C99], > [], > [AC_PROG_CC_C99])m4_define([AC_PROG_CC_C99])]) > > And then add gl_PROG_CC_C99 to all the C99 modules. > >> It's not a big problem, as I can just reinstate AC_PROG_CC_C99 in >> occurs's configure.ac, but it suggests I'm not understanding >> something. > > Might as well try to fix it right in gnulib though, and maybe in autoconf > too if the latest release hasn't made it multi-call safe yet. > > Cheers, > -- > Gary V. Vaughan (gary AT gnu DOT org)
