Hi Dmitry, On Thu, 2025-04-03 at 19:09 +0300, Dmitry V. Levin wrote: > 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> [...] > > 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])?
I am afraid I don't remember. Note that 5 years later we just require C11 + stdatomic: https://sourceware.org/cgit/elfutils/commit/?id=d5fe635875628a9de431c883c0e5037dec0f85f3 The check for stdatomic.h is still the same though. But it doesn't set HAVE_STDATOMIC_H anymore and the fallback lib/atomics.h has been removed. I think that means your issue/worry cannot happen anymore. But maybe we should just use AC_CHECK_HEADERS([stdatomic.h]) and drop the AC_COMPILE_IFELSE trick? Cheers, Mark
