From dd1d33cf7c97da68f541ba497524a998bc228058 Mon Sep 17 00:00:00 2001
From: Vincent Bernat <bernat@luffy.cx>
Date: Sat, 23 Nov 2013 10:03:42 +0100
Subject: [PATCH] marshal: use __alignof__ operator if available

---
 configure.ac  |  1 +
 m4/alignof.m4 | 14 ++++++++++++++
 src/marshal.c |  6 +++++-
 3 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 m4/alignof.m4

diff --git a/configure.ac b/configure.ac
index 1e409e14..9e1ac0ef 100644
--- a/configure.ac
+++ b/configure.ac
@@ -93,6 +93,7 @@ AC_CACHE_SAVE
 
 # Checks for typedefs, structures, and compiler characteristics.
 lldp_CHECK___PROGNAME
+lldp_CHECK_ALIGNOF
 
 # Checks for library functions.
 AC_CONFIG_LIBOBJ_DIR([src/compat])
diff --git a/m4/alignof.m4 b/m4/alignof.m4
new file mode 100644
index 00000000..f45caae7
--- /dev/null
+++ b/m4/alignof.m4
@@ -0,0 +1,14 @@
+#
+# lldp_CHECK_ALIGNOF
+#
+AC_DEFUN([lldp_CHECK_ALIGNOF],[
+  AC_CACHE_CHECK([whether compiler understands __alignof__], lldp_cv_check_alignof, [
+    AC_TRY_COMPILE([],
+	[ return __alignof__(long); ],
+	[ lldp_cv_check_alignof="yes" ],
+	[ lldp_cv_check_alignof="no" ])
+  ])
+  if test x"$lldp_cv_check_alignof" = x"yes"; then
+     AC_DEFINE([HAVE_ALIGNOF], [1], [Define if __alignof__ operator is available])
+  fi
+])
diff --git a/src/marshal.c b/src/marshal.c
index 45c46cbc..8a57d305 100644
--- a/src/marshal.c
+++ b/src/marshal.c
@@ -31,7 +31,11 @@
 #include "lldpd-structs.h"
 
 /* Stolen from CCAN */
-#define ALIGNOF(t) ((sizeof(t) > 1)?((char *)(&((struct { char c; t _h; } *)0)->_h) - (char *)0):1)
+#if HAVE_ALIGNOF
+# define ALIGNOF(t) (__alignof__(t))
+#else
+# define ALIGNOF(t) ((sizeof(t) > 1)?((char *)(&((struct { char c; t _h; } *)0)->_h) - (char *)0):1)
+#endif
 
 /* A serialized object */
 struct marshal_serialized {
-- 
2.39.5