From 405a79ca7ff12ec81e4963c51be4729ebd6cc922 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 28 May 2010 11:09:31 +0200
Subject: [PATCH] Add `scm_t_aligned_cell' internal type.

* libguile/_scm.h (struct scm_aligned_cell)[__GNUC__]: New type.
  (union scm_aligned_cell)[!__GNUC__]: New type.
  (scm_t_aligned_cell): New type.

* libguile/vm.c (vm_dispatch_hook): Use it.
---
 libguile/_scm.h | 30 ++++++++++++++++++++++++++++++
 libguile/vm.c   |  6 +-----
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/libguile/_scm.h b/libguile/_scm.h
index 3bb78b466..f18b3a875 100644
--- a/libguile/_scm.h
+++ b/libguile/_scm.h
@@ -63,6 +63,7 @@
 
 #include <errno.h>
 #include <verify.h>
+#include <alignof.h>
 #include "libguile/__scm.h"
 
 /* Include headers for those files central to the implementation.  The
@@ -192,6 +193,35 @@
 #define SCM_OBJCODE_COOKIE                              \
   "GOOF-" SCM_OBJCODE_MACHINE_VERSION_STRING "---"
 
+
+/* Cells have to be 8-byte aligned.  Use `scm_t_aligned_cell' when not
+   allocating on the heap to have this guarantee.  This is similar to the
+   `SCM_ALIGNED' macro but provides an option likely to work with compilers
+   other than GCC.  */
+
+#ifdef __GNUC__
+
+struct scm_aligned_cell
+{
+  scm_t_cell cell __attribute__ ((__aligned__ (8)));
+};
+
+typedef struct scm_aligned_cell scm_t_aligned_cell;
+
+#else /* !__GNUC__ */
+
+union scm_aligned_cell
+{
+  double alignment;
+  scm_t_cell cell;
+};
+
+typedef union scm_aligned_cell scm_t_aligned_cell;
+
+#endif /* !__GNUC__ */
+
+/* Make sure we get the right alignment.  */
+verify (alignof (scm_t_aligned_cell) >= 8);
 
 #endif  /* SCM__SCM_H */
 
diff --git a/libguile/vm.c b/libguile/vm.c
index e036b63e1..972abf847 100644
--- a/libguile/vm.c
+++ b/libguile/vm.c
@@ -190,11 +190,7 @@ vm_dispatch_hook (SCM vm, int hook_num)
   struct scm_vm *vp;
   SCM hook;
   struct scm_frame c_frame;
-  union
-  {
-    double alignment;
-    scm_t_cell cell;
-  } frame;
+  scm_t_aligned_cell frame;
   SCM args[1];
 
   vp = SCM_VM_DATA (vm);
-- 
2.20.1