gcc/ChangeLog:

2015-02-09  Max Ostapenko  <m.ostapenko@partner.samsung.com>

	PR sanitizer/64820
        * cfgexpand.c (align_base): New function.
        (alloc_stack_frame_space): Call it.
        (expand_stack_vars): Align prev_frame to be sure
        data->asan_vec elements aligned properly.

gcc/testsuite/ChangeLog:

2015-02-09  Max Ostapenko  <m.ostapenko@partner.samsung.com>

	PR sanitizer/64820
        * c-c++-common/asan/pr64820.c: New test.

diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 7dfe1f6..7845a17 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -282,6 +282,15 @@ align_local_variable (tree decl)
   return align / BITS_PER_UNIT;
 }
 
+/* Align given offset BASE with ALIGN.  Truncate up if ALIGN_UP is true,
+   down otherwise.  Return truncated BASE value.  */
+
+static inline unsigned HOST_WIDE_INT
+align_base (HOST_WIDE_INT base, unsigned HOST_WIDE_INT align, bool align_up)
+{
+  return align_up ? (base + align - 1) & -align : base & -align;
+}
+
 /* Allocate SIZE bytes at byte alignment ALIGN from the stack frame.
    Return the frame offset.  */
 
@@ -293,17 +302,15 @@ alloc_stack_frame_space (HOST_WIDE_INT size, unsigned HOST_WIDE_INT align)
   new_frame_offset = frame_offset;
   if (FRAME_GROWS_DOWNWARD)
     {
-      new_frame_offset -= size + frame_phase;
-      new_frame_offset &= -align;
-      new_frame_offset += frame_phase;
+      new_frame_offset
+	= align_base (frame_offset - frame_phase - size,
+		      align, false) + frame_phase;
       offset = new_frame_offset;
     }
   else
     {
-      new_frame_offset -= frame_phase;
-      new_frame_offset += align - 1;
-      new_frame_offset &= -align;
-      new_frame_offset += frame_phase;
+      new_frame_offset
+	= align_base (frame_offset - frame_phase, align, true) + frame_phase;
       offset = new_frame_offset;
       new_frame_offset += size;
     }
@@ -1031,13 +1038,16 @@ expand_stack_vars (bool (*pred) (size_t), struct stack_vars_data *data)
 	  base = virtual_stack_vars_rtx;
 	  if ((flag_sanitize & SANITIZE_ADDRESS) && ASAN_STACK && pred)
 	    {
-	      HOST_WIDE_INT prev_offset = frame_offset;
+	      HOST_WIDE_INT prev_offset
+		= align_base (frame_offset,
+			      MAX (alignb, ASAN_RED_ZONE_SIZE),
+			      FRAME_GROWS_DOWNWARD);
 	      tree repr_decl = NULL_TREE;
-
 	      offset
 		= alloc_stack_frame_space (stack_vars[i].size
 					   + ASAN_RED_ZONE_SIZE,
 					   MAX (alignb, ASAN_RED_ZONE_SIZE));
+
 	      data->asan_vec.safe_push (prev_offset);
 	      data->asan_vec.safe_push (offset + stack_vars[i].size);
 	      /* Find best representative of the partition.
diff --git a/gcc/testsuite/c-c++-common/asan/pr64820.c b/gcc/testsuite/c-c++-common/asan/pr64820.c
new file mode 100644
index 0000000..885a662
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/pr64820.c
@@ -0,0 +1,31 @@
+/* { dg-do run } */
+/* { dg-require-effective-target fstack_protector } */
+/* { dg-options "-fstack-protector-strong" } */
+/* { dg-set-target-env-var ASAN_OPTIONS "detect_stack_use_after_return=1" } */
+/* { dg-shouldfail "asan" } */
+
+__attribute__((noinline))
+char *Ident(char *x) {
+  return x;
+}
+
+__attribute__((noinline))
+char *Func1() {
+  char local[1 << 12];
+  return Ident(local);
+}
+
+__attribute__((noinline))
+void Func2(char *x) {
+  *x = 1;
+}
+int main(int argc, char **argv) {
+  Func2(Func1());
+  return 0;
+}
+
+/* { dg-output "AddressSanitizer: stack-use-after-return on address 0x\[0-9a-f\]+\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "WRITE of size 1 at .* thread T0.*" } */
+/* { dg-output "    #0.*(Func2)?.*pr64820.(c:21)?.*" } */
+/* { dg-output "is located in stack of thread T0 at offset.*" } */