Make sure packed structs follow the gcc memory layout

gcc defaults to using struct layouts that follow the native conventions,
even if __attribute__((packed)) is given. In order to get the layout we
expect, we need to tell gcc to always use the gcc struct layout, at
least for packed structs. To do this, we can use the gcc_struct
attribute.

This is important, not only for porting to windows, but also potentially
for other platforms, as the bugs resulting from struct layout
differences are rather subtle and hard to find.

Signed-off-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index c0034ba4..cb87833c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-08-18  Ulf Hermann  <ulf.hermann@qt.io>
+
+	* configure.ac: Check if the compiler supports
+	__attribute__((gcc_struct)).
+
 2017-09-19  Mark Wielaard  <mark@klomp.org>
 
 	* README: Add basic build instructions.