From 7c36869fdff2cdff1373b895c9424cb89dc08e67 Mon Sep 17 00:00:00 2001
From: Mukund Sivaraman <muks@isc.org>
Date: Mon, 22 Jan 2018 13:35:29 +0530
Subject: [PATCH] Fix configure issue detecting stdatomic.h support (#46959)

(cherry picked from commit 63d0c6a3fc890ff02bd8f0f6215e5b495eb076b8)
(cherry picked from commit 7e1ed157621bf554d5f2dff29a3c249037d214f3)
(cherry picked from commit fd82c70695888c134287b8018296028c252d100e)
---
 CHANGES      |  4 ++++
 config.h.in  |  3 ---
 configure    | 40 +++++++++++++++++++++++++++-------------
 configure.in | 19 ++++++++++++++-----
 4 files changed, 45 insertions(+), 21 deletions(-)

diff --git a/CHANGES b/CHANGES
index cc6fe7e53b..2a3955c155 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+4871.	[bug]		Fix configure glitch in detecting stdatomic.h
+			support on systems with multiple compilers.
+			[RT #46959]
+
 4870.	[test]		Update included ATF library to atf-0.21 preserving
 			the ATF tool. [RT #46967]
 
diff --git a/config.h.in b/config.h.in
index 3ff8f1639a..49eaffb3dd 100644
--- a/config.h.in
+++ b/config.h.in
@@ -453,9 +453,6 @@ int sigwait(const unsigned int *set, int *sig);
 /* Define to 1 if you have the `setresuid' function. */
 #undef HAVE_SETRESUID
 
-/* Define to 1 if you have the <stdatomic.h> header file. */
-#undef HAVE_STDATOMIC_H
-
 /* Define to 1 if you have the <stdint.h> header file. */
 #undef HAVE_STDINT_H
 
diff --git a/configure b/configure
index 4eba85a05a..5fbd916b1b 100755
--- a/configure
+++ b/configure
@@ -20093,22 +20093,36 @@ done
 # Machine architecture dependent features
 #
 have_stdatomic=no
-for ac_header in stdatomic.h
-do :
-  ac_fn_c_check_header_mongrel "$LINENO" "stdatomic.h" "ac_cv_header_stdatomic_h" "$ac_includes_default"
-if test "x$ac_cv_header_stdatomic_h" = xyes; then :
-  cat >>confdefs.h <<_ACEOF
-#define HAVE_STDATOMIC_H 1
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for usable stdatomic.h" >&5
+$as_echo_n "checking for usable stdatomic.h... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#include <stdio.h>
+#include <stdatomic.h>
+
+int
+main ()
+{
+
+atomic_int_fast32_t val = 0; atomic_fetch_add_explicit(&val, 1, memory_order_relaxed);
+
+  ;
+  return 0;
+}
 _ACEOF
- have_stdatomic=yes
-		  ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"
+if ac_fn_c_try_compile "$LINENO"; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+	 have_stdatomic=yes
+	 ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"
 else
-  have_stdatomic=no
-		  ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+	 have_stdatomic=no
+	 ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"
 fi
-
-done
-
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
 # Check whether --enable-atomic was given.
 if test "${enable_atomic+set}" = set; then :
diff --git a/configure.in b/configure.in
index 924585ed5d..cefbeba2de 100644
--- a/configure.in
+++ b/configure.in
@@ -4037,11 +4037,20 @@ AC_CHECK_FUNCS(nanosleep usleep explicit_bzero)
 # Machine architecture dependent features
 #
 have_stdatomic=no
-AC_CHECK_HEADERS(stdatomic.h,
-		 [have_stdatomic=yes
-		  ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"],
-		 [have_stdatomic=no
-		  ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"])
+AC_MSG_CHECKING(for usable stdatomic.h)
+AC_TRY_COMPILE([
+#include <stdio.h>
+#include <stdatomic.h>
+],
+[
+atomic_int_fast32_t val = 0; atomic_fetch_add_explicit(&val, 1, memory_order_relaxed);
+],
+        [AC_MSG_RESULT(yes)
+	 have_stdatomic=yes
+	 ISC_PLATFORM_HAVESTDATOMIC="#define ISC_PLATFORM_HAVESTDATOMIC 1"],
+	[AC_MSG_RESULT(no)
+	 have_stdatomic=no
+	 ISC_PLATFORM_HAVESTDATOMIC="#undef ISC_PLATFORM_HAVESTDATOMIC"])
 
 AC_ARG_ENABLE(atomic,
 	      AS_HELP_STRING([--enable-atomic],