Index: src/gcc-4.5-2010.09/gcc/toplev.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/toplev.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/toplev.c	(working copy)
@@ -1851,6 +1851,13 @@
     sorry ("Graphite loop optimizations cannot be used");
 #endif
 
+  if (flag_strict_volatile_bitfields > 0 && !abi_version_at_least (2))
+    {
+      warning (0, "-fstrict-volatile-bitfield disabled; "
+	       "it is incompatible with ABI versions < 2");
+      flag_strict_volatile_bitfields = 0;
+    }
+
   /* Unrolling all loops implies that standard loop unrolling must also
      be done.  */
   if (flag_unroll_all_loops)
Index: src/gcc-4.5-2010.09/gcc/testsuite/gcc.target/arm/volatile-bitfields-4.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/testsuite/gcc.target/arm/volatile-bitfields-4.c	(revision 0)
+++ src/gcc-4.5-2010.09/gcc/testsuite/gcc.target/arm/volatile-bitfields-4.c	(revision 0)
@@ -0,0 +1,30 @@
+/* { dg-require-effective-target arm_eabi } */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-final { scan-assembler-times "ldr\[\\t \]+\[^\n\]*,\[\\t \]*\\\[\[^\n\]*\\\]" 2 } } */
+/* { dg-final { scan-assembler-times "str\[\\t \]+\[^\n\]*,\[\\t \]*\\\[\[^\n\]*\\\]" 2 } } */
+/* { dg-final { scan-assembler-not "strb" } } */
+
+struct thing {
+  unsigned a: 8;
+  unsigned b: 8;
+  unsigned c: 8;
+  unsigned d: 8;
+};
+
+struct thing2 {
+  volatile unsigned a: 8;
+  volatile unsigned b: 8;
+  volatile unsigned c: 8;
+  volatile unsigned d: 8;
+};
+
+void test1(volatile struct thing *t)
+{
+  t->a = 5;
+}
+
+void test2(struct thing2 *t)
+{
+  t->a = 5;
+}
Index: src/gcc-4.5-2010.09/gcc/testsuite/c-c++-common/abi-bf.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/testsuite/c-c++-common/abi-bf.c	(revision 0)
+++ src/gcc-4.5-2010.09/gcc/testsuite/c-c++-common/abi-bf.c	(revision 0)
@@ -0,0 +1,3 @@
+/* { dg-warning "incompatible" } */
+/* { dg-do compile } */
+/* { dg-options "-fstrict-volatile-bitfields -fabi-version=1" } */
Index: src/gcc-4.5-2010.09/gcc/expr.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/expr.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/expr.c	(working copy)
@@ -5848,6 +5848,8 @@
 		|| bitpos % GET_MODE_ALIGNMENT (mode))
 	       && SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (target)))
 	      || (bitpos % BITS_PER_UNIT != 0)))
+      || (bitsize >= 0 && mode != BLKmode
+	  && GET_MODE_BITSIZE (mode) > bitsize)
       /* If the RHS and field are a constant size and the size of the
 	 RHS isn't the same size as the bitfield, we must use bitfield
 	 operations.  */
Index: src/gcc-4.5-2010.09/gcc/stor-layout.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/stor-layout.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/stor-layout.c	(working copy)
@@ -595,12 +595,13 @@
 	  /* See if we can use an ordinary integer mode for a bit-field.
 	     Conditions are: a fixed size that is correct for another mode,
 	     occupying a complete byte or bytes on proper boundary,
-	     and not volatile or not -fstrict-volatile-bitfields.  */
+	     and not -fstrict-volatile-bitfields.  If the latter is set,
+	     we unfortunately can't check TREE_THIS_VOLATILE, as a cast
+	     may make a volatile object later.  */
 	  if (TYPE_SIZE (type) != 0
 	      && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
 	      && GET_MODE_CLASS (TYPE_MODE (type)) == MODE_INT
-	      && !(TREE_THIS_VOLATILE (decl)
-		   && flag_strict_volatile_bitfields > 0))
+	      && flag_strict_volatile_bitfields <= 0)
 	    {
 	      enum machine_mode xmode
 		= mode_for_size_tree (DECL_SIZE (decl), MODE_INT, 1);
Index: src/gcc-4.5-2010.09/gcc/config/m32c/m32c.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/config/m32c/m32c.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/config/m32c/m32c.c	(working copy)
@@ -430,7 +430,7 @@
     flag_ivopts = 0;
 
   /* This target defaults to strict volatile bitfields.  */
-  if (flag_strict_volatile_bitfields < 0)
+  if (flag_strict_volatile_bitfields < 0 && abi_version_at_least(2))
     flag_strict_volatile_bitfields = 1;
 }
 
Index: src/gcc-4.5-2010.09/gcc/config/rx/rx.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/config/rx/rx.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/config/rx/rx.c	(working copy)
@@ -2191,7 +2191,7 @@
 rx_option_override (void)
 {
   /* This target defaults to strict volatile bitfields.  */
-  if (flag_strict_volatile_bitfields < 0)
+  if (flag_strict_volatile_bitfields < 0 && abi_version_at_least(2))
     flag_strict_volatile_bitfields = 1;
 }
 
Index: src/gcc-4.5-2010.09/gcc/config/sh/sh.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/config/sh/sh.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/config/sh/sh.c	(working copy)
@@ -974,7 +974,7 @@
     sh_fix_range (sh_fixed_range_str);
 
   /* This target defaults to strict volatile bitfields.  */
-  if (flag_strict_volatile_bitfields < 0)
+  if (flag_strict_volatile_bitfields < 0 && abi_version_at_least(2))
     flag_strict_volatile_bitfields = 1;
 }
 
Index: src/gcc-4.5-2010.09/gcc/config/arm/arm.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/config/arm/arm.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/config/arm/arm.c	(working copy)
@@ -1952,7 +1952,8 @@
     set_param_value ("gcse-unrestricted-cost", 2);
 
   /* ARM EABI defaults to strict volatile bitfields.  */
-  if (TARGET_AAPCS_BASED && flag_strict_volatile_bitfields < 0)
+  if (TARGET_AAPCS_BASED && flag_strict_volatile_bitfields < 0
+      && abi_version_at_least(2))
     flag_strict_volatile_bitfields = 1;
 
   /* Register global variables with the garbage collector.  */
Index: src/gcc-4.5-2010.09/gcc/config/h8300/h8300.c
===================================================================
--- src/gcc-4.5-2010.09/gcc/config/h8300/h8300.c	(revision 307813)
+++ src/gcc-4.5-2010.09/gcc/config/h8300/h8300.c	(working copy)
@@ -405,7 +405,7 @@
     }
 
   /* This target defaults to strict volatile bitfields.  */
-  if (flag_strict_volatile_bitfields < 0)
+  if (flag_strict_volatile_bitfields < 0 && abi_version_at_least(2))
     flag_strict_volatile_bitfields = 1;
 }