On Thu, Aug 29, 2019 at 03:16:12PM +0200, Mark Wielaard wrote: > From: Jonathon Anderson <jm...@rice.edu> > > Uses the stdatomic.h provided by FreeBSD when GCC doesn't (ie. GCC < 4.9) > > Signed-off-by: Jonathon Anderson <jm...@rice.edu> > Signed-off-by: Srđan Milaković <sm...@rice.edu> > --- > configure.ac | 12 ++ > lib/ChangeLog | 6 + > lib/Makefile.am | 3 +- > lib/atomics.h | 37 ++++ > lib/stdatomic-fbsd.h | 442 +++++++++++++++++++++++++++++++++++++++++++ > 5 files changed, 499 insertions(+), 1 deletion(-) > create mode 100644 lib/atomics.h > create mode 100644 lib/stdatomic-fbsd.h > > diff --git a/configure.ac b/configure.ac > index c443fa3b..b8aba460 100644 > --- a/configure.ac > +++ b/configure.ac > @@ -226,6 +226,18 @@ LDFLAGS="$save_LDFLAGS"]) > AS_IF([test "x$ac_cv_tls" != xyes], > AC_MSG_ERROR([__thread support required])) > > +dnl Before 4.9 gcc doesn't ship stdatomic.h, but the nessesary atomics are > +dnl available by (at least) 4.7. So if the system doesn't have a stdatomic.h > we > +dnl fall back on one copied from FreeBSD that handles the difference. > +AC_CACHE_CHECK([whether gcc provides stdatomic.h], ac_cv_has_stdatomic, > + [AC_COMPILE_IFELSE([AC_LANG_SOURCE([[#include <stdatomic.h>]])], > + ac_cv_has_stdatomic=yes, ac_cv_has_stdatomic=no)]) > +AM_CONDITIONAL(HAVE_STDATOMIC_H, test "x$ac_cv_has_stdatomic" = xyes) > +AS_IF([test "x$ac_cv_has_stdatomic" = xyes], [AC_DEFINE(HAVE_STDATOMIC_H)]) > + > +AH_TEMPLATE([HAVE_STDATOMIC_H], [Define to 1 if `stdatomic.h` is provided by > the > + system, 0 otherwise.]) > + > dnl This test must come as early as possible after the compiler configuration > dnl tests, because the choice of the file model can (in principle) affect > dnl whether functions and headers are available, whether they work, etc.
Sorry, do you remember why stdatomic.h availability check had to be so complicated instead of straightforward AC_CHECK_HEADERS([stdatomic.h])? The reason why I'm interested is that I accidentally noticed that the check doesn't work as expected because ... > [...] > diff --git a/lib/atomics.h b/lib/atomics.h > new file mode 100644 > index 00000000..ffd12f87 > --- /dev/null > +++ b/lib/atomics.h > @@ -0,0 +1,37 @@ > +/* Conditional wrapper header for C11-style atomics. > + Copyright (C) 2019-2019 Red Hat, Inc. > + This file is part of elfutils. > + > + This file is free software; you can redistribute it and/or modify > + it under the terms of either > + > + * the GNU Lesser General Public License as published by the Free > + Software Foundation; either version 3 of the License, or (at > + your option) any later version > + > + or > + > + * the GNU General Public License as published by the Free > + Software Foundation; either version 2 of the License, or (at > + your option) any later version > + > + or both in parallel, as here. > + > + elfutils is distributed in the hope that it will be useful, but > + WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + General Public License for more details. > + > + You should have received copies of the GNU General Public License and > + the GNU Lesser General Public License along with this program. If > + not, see <http://www.gnu.org/licenses/>. */ > + > +#include "config.h" > + > +#if HAVE_STDATOMIC_H ... here it's assumed that HAVE_STDATOMIC_H is always defined (to either 1 or 0) which is not the case: AS_IF([test "x$ac_cv_has_stdatomic" = xyes], [AC_DEFINE(HAVE_STDATOMIC_H)]) means that HAVE_STDATOMIC_H is defined only if $ac_cv_has_stdatomic == "yes". -- ldv
