build: try to find some kind of atomic ops

Either one of:
- ISO C11
- gcc __atomic_*
- gcc/clang __sync_*

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 66 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index b8cebd8d23..4875a6849d 100755
--- a/configure.ac
+++ b/configure.ac
@@ -541,6 +541,72 @@ AC_CHECK_HEADERS([stropts.h sys/ksym.h \
 	linux/version.h asm/types.h \
 	sys/cdefs.h])
 
+ac_stdatomic_ok=false
+AC_DEFINE(FRR_AUTOCONF_ATOMIC, 1, [did autoconf checks for atomic funcs])
+AC_CHECK_HEADER([stdatomic.h],[
+
+  AC_MSG_CHECKING([whether _Atomic qualifier works])
+  AC_LINK_IFELSE([AC_LANG_SOURCE([[
+#include <stdatomic.h>
+int main(int argc, char **argv) {
+  _Atomic int i = 0;
+  return i;
+}
+]])], [
+    AC_DEFINE(HAVE_STDATOMIC_H, 1, [found stdatomic.h])
+    AC_MSG_RESULT([yes])
+    ac_stdatomic_ok=true
+  ], [
+    AC_MSG_RESULT([no])
+  ])
+])
+
+AS_IF([$ac_stdatomic_ok], [true], [
+  AC_MSG_CHECKING([for __atomic_* builtins])
+  AC_LINK_IFELSE([AC_LANG_SOURCE([[
+int main(int argc, char **argv) {
+  volatile int i = 1;
+  __atomic_store_n (&i, 0, __ATOMIC_RELEASE);
+  return __atomic_load_n (&i, __ATOMIC_ACQUIRE);
+}
+]])], [
+    AC_DEFINE(HAVE___ATOMIC, 1, [found __atomic builtins])
+    AC_MSG_RESULT([yes])
+  ], [
+    AC_MSG_RESULT([no])
+
+    dnl FreeBSD 9 has a broken stdatomic.h where _Atomic doesn't work
+    AC_MSG_CHECKING([for __sync_* builtins])
+    AC_LINK_IFELSE([AC_LANG_SOURCE([[
+int main(int argc, char **argv) {
+  volatile int i = 1;
+  __sync_fetch_and_sub (&i, 1);
+  return __sync_val_compare_and_swap (&i, 0, 1);
+}
+]])], [
+      AC_DEFINE(HAVE___SYNC, 1, [found __sync builtins])
+      AC_MSG_RESULT([yes])
+
+      AC_MSG_CHECKING([for __sync_swap builtin])
+      AC_LINK_IFELSE([AC_LANG_SOURCE([[
+int main(int argc, char **argv) {
+  volatile int i = 1;
+  return __sync_swap (&i, 2);
+}
+]])], [
+        AC_DEFINE(HAVE___SYNC_SWAP, 1, [found __sync_swap builtin])
+        AC_MSG_RESULT([yes])
+      ], [
+        AC_MSG_RESULT([no])
+      ])
+
+    ], [
+      AC_MSG_RESULT([no])
+      AC_MSG_FAILURE([stdatomic.h unavailable and $CC has neither __atomic nor __sync builtins])
+    ])
+  ])
+])
+
 dnl Utility macro to avoid retyping includes all the time
 m4_define([FRR_INCLUDES],
 [#ifdef SUNOS_5