Hi Mark, On Fri, Apr 04, 2025 at 01:38:01PM +0200, Mark Wielaard wrote: > 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.
Sorry, I must have been looking at some old commit and missed that lib/atomics.h has been removed. > But maybe we should just use AC_CHECK_HEADERS([stdatomic.h]) and drop > the AC_COMPILE_IFELSE trick? Sure. And if we want to keep AC_MSG_ERROR, then AC_CHECK_HEADERS([stdatomic.h], [], [AC_MSG_ERROR([stdatomic.h required])]) should be fine. -- ldv
