From 4161ee66783b665e2a6222373cc13305dd3f8019 Mon Sep 17 00:00:00 2001
From: Martin Willi <martin@revosec.ch>
Date: Wed, 15 Jan 2014 17:01:24 +0100
Subject: [PATCH] configure: Check if __attribute__((packed)) works as expected

This is really hard to detect if not, and is not unlikely. If -mms-bitfields
is given, the attribute does not work. Even worse, that switch is by default
on with GCC/MinGW 4.7+ for Windows targets.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52991
---
 configure.ac | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/configure.ac b/configure.ac
index ca5c63668..4e714237c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -755,6 +755,17 @@ AC_COMPILE_IFELSE(
 AC_SUBST(OPENSSL_LIB, [-l$openssl_lib])
 AM_CONDITIONAL(USE_WINDOWS, [test "x$windows" = xtrue])
 
+AC_MSG_CHECKING([for working __attribute__((packed))])
+AC_COMPILE_IFELSE(
+	[AC_LANG_PROGRAM([], [[
+		struct test { char a; short b; } __attribute__((packed));
+		char x[sizeof(struct test) == sizeof(char) + sizeof(short) ? 1 : -1];
+		return 0;
+	]])],
+	[AC_MSG_RESULT([yes])],
+	[AC_MSG_RESULT([no]); AC_MSG_ERROR([__attribute__((packed)) does not work])]
+)
+
 if test x$printf_hooks = xvstr; then
 	AC_CHECK_LIB([vstr],[main],[LIBS="$LIBS"],[AC_MSG_ERROR([Vstr string library not found])],[])
 	AC_DEFINE([USE_VSTR], [], [use Vstr string library for printf hooks])