>From 9ad02f1a789a74678d429085199e19b04e8b844a Mon Sep 17 00:00:00 2001
From: Peter O'Gorman <address@hidden>
Date: Mon, 6 Sep 2010 17:20:44 -0500
Subject: [PATCH 3/3] Check if struct packing is required.

* am/pack.m4: Check if naturally aligned structs are the correct size.
* src/cpiohdr.h: define ATTRIB_PACKED to be empty if not using the attribute.
---
 am/pack.m4    |   58 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/cpiohdr.h |    2 +
 2 files changed, 60 insertions(+), 0 deletions(-)

diff --git a/am/pack.m4 b/am/pack.m4
index c03c948..85ee6ea 100644
--- a/am/pack.m4
+++ b/am/pack.m4
@@ -16,6 +16,63 @@
 
 # CPIO_PACKED_STRUCTS is based on code from ClamAV
 AC_DEFUN([CPIO_PACKED_STRUCTS],[
+  AC_MSG_CHECKING([if we need to explicitly pack some cpio structs])
+  AC_CACHE_VAL([cpio_cv_explicit_pack],[
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+struct old_cpio_header
+{
+  unsigned short c_magic;
+  unsigned short c_dev;
+  unsigned short c_ino;
+  unsigned short c_mode;
+  unsigned short c_uid;
+  unsigned short c_gid;
+  unsigned short c_nlink;
+  unsigned short c_rdev;
+  unsigned short c_mtimes[2];
+  unsigned short c_namesize;
+  unsigned short c_filesizes[2];
+};
+struct old_ascii_header
+{
+  char c_magic[6];
+  char c_dev[6];
+  char c_ino[6];
+  char c_mode[6];
+  char c_uid[6];
+  char c_gid[6];
+  char c_nlink[6];
+  char c_rdev[6];
+  char c_mtime[11];
+  char c_namesize[6];
+  char c_filesize[11];
+};
+struct new_ascii_header
+{
+  char c_magic[6];
+  char c_ino[8];
+  char c_mode[8];
+  char c_uid[8];
+  char c_gid[8];
+  char c_nlink[8];
+  char c_mtime[8];
+  char c_filesize[8];
+  char c_dev_maj[8];
+  char c_dev_min[8];
+  char c_rdev_maj[8];
+  char c_rdev_min[8];
+  char c_namesize[8];
+  char c_chksum[8];
+};
+]],[[
+char a[sizeof(struct new_ascii_header)==110?1:-1];
+char b[sizeof(struct old_ascii_header)==76?1:-1];
+char c[sizeof(struct old_cpio_header)==26?1:-1];
+return sizeof(a) + sizeof(b) + sizeof(c) == 3?0:1;
+]])],[cpio_cv_explicit_pack=no],[cpio_cv_explicit_pack=yes])])
+AC_MSG_RESULT($cpio_cv_explicit_pack)
+
+if test "$cpio_cv_explicit_pack" = yes; then
   dnl check for __attribute__((packed))
   AC_MSG_CHECKING([for structure packing via __attribute__((packed))])
   AC_CACHE_VAL(cpio_cv_have_attrib_packed,[
@@ -64,4 +121,5 @@ AC_DEFUN([CPIO_PACKED_STRUCTS],[
   if test "$have_attrib_packed" = yes; then
     AC_DEFINE(HAVE_ATTRIB_PACKED, 1, [attrib packed])
   fi
+fi
 ])
diff --git a/src/cpiohdr.h b/src/cpiohdr.h
index 86ec988..5367fe9 100644
--- a/src/cpiohdr.h
+++ b/src/cpiohdr.h
@@ -24,6 +24,8 @@
 
 # ifdef HAVE_ATTRIB_PACKED
 #  define ATTRIB_PACKED __attribute__((packed))
+# else
+#  define ATTRIB_PACKED
 # endif
 
 # ifdef HAVE_PRAGMA_PACK
-- 
1.7.0.1