diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 84153b09dbb..21b8aa33156 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2013-12-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
+
+	Fix C++0x memory model for unaligned fields in packed, aligned(4)
+	structures with -fno-strict-volatile-bitfields on STRICT_ALIGNMENT
+	targets like arm-none-eabi.
+	* expr.c (expand_assignment): Handle normal fields like bit regions.
+
 2013-12-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
 	PR target/58115
diff --git a/gcc/expr.c b/gcc/expr.c
index aeff2ca58f4..c0539da250c 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -4824,6 +4824,17 @@ expand_assignment (tree to, tree from, bool nontemporal)
       if (TREE_CODE (to) == COMPONENT_REF
 	  && DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
 	get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos, &offset);
+      /* The C++ memory model naturally applies to byte-aligned fields.
+	 However, if we do not have a DECL_BIT_FIELD_TYPE but BITPOS or
+	 BITSIZE are not byte-aligned, there is no need to limit the range
+	 we can access.  This can occur with packed structures in Ada.  */
+      else if (bitsize > 0
+	       && bitsize % BITS_PER_UNIT == 0
+	       && bitpos % BITS_PER_UNIT == 0)
+	{
+	  bitregion_start = bitpos;
+	  bitregion_end = bitpos + bitsize - 1;
+	}
 
       to_rtx = expand_expr (tem, NULL_RTX, VOIDmode, EXPAND_WRITE);
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9c7be13551c..f92967a671c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2013-12-02  Bernd Edlinger  <bernd.edlinger@hotmail.de>
+
+	* gcc.dg/pr56997-4.c: New testcase.
+
 2013-12-02  Marek Polacek  <polacek@redhat.com>
 
 	* c-c++-common/ubsan/vla-1.c: Split the tests into individual
diff --git a/gcc/testsuite/gcc.dg/pr56997-4.c b/gcc/testsuite/gcc.dg/pr56997-4.c
new file mode 100644
index 00000000000..38f6248d2ed
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr56997-4.c
@@ -0,0 +1,23 @@
+/* Test volatile access to unaligned field.  */
+/* { dg-do compile } */
+/* { dg-options "-fno-strict-volatile-bitfields -fdump-rtl-final" } */
+
+#define test_type unsigned short
+
+typedef struct s{
+ unsigned char Prefix[1];
+ volatile test_type Type;
+}__attribute((__packed__,__aligned__(4))) ss;
+
+extern volatile ss v;
+
+void
+foo (test_type u)
+{
+  v.Type = u;
+}
+
+/* The C++ memory model forbids data store race conditions outside the
+   unaligned data member, therefore only QI or HI access is allowed, no SI.  */
+/* { dg-final { scan-rtl-dump-not "mem/v(/.)*:SI" "final" } } */
+/* { dg-final { cleanup-rtl-dump "final" } } */