--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2011-10-31  Paul Eggert  <eggert@cs.ucla.edu>
+
+	stdalign: port better to MSVC and to Sun C 5.11
+	I think these problems were reported by Bruno Haible, in email
+	that I've unfortunately misplaced.
+	* doc/posix-headers/stdalign.texi (stdalign.h): Document more
+	shortcomings of MSVC and of Sun C 5.11.
+	* lib/stdalign.in.h (_Alignas): Omit bogus extra parenthesis
+	around __declspec arg.
+	* modules/stdalign-tests (Files): Add tests/macros.h.
+	* tests/test-stdalign.c: Do not include <stdlib.h>; no longer needed.
+	Include macros.h, for ASSERT.
+	(DECLARE_ALIGNED): Remove.
+	(TEST_ALIGNMENT): Define to 16 if alignment is supported (more likely
+	to catch bug), and to 1 if not (simplifies the rest of the code).
+	(CHECK_STATIC): Always declare the alignment test vars; that's simpler.
+	(CHECK_AUTO): Remove.
+	(CHECK_ALIGNED): Check only the alignment of the static vars,
+	since auto var alignment isn't supported by Sun C 5.11.
+	(CHECK_TYPES): Remove.  All uses replaced by inline code, so that
+	ASSERT failures are easier to diagnose.
+
 2011-10-31  Bruno Haible  <bruno@clisp.org>
 
 	doc about some IRIX 5.3 problems.

--- a/doc/posix-headers/stdalign.texi
+++ b/doc/posix-headers/stdalign.texi
@@ -24,6 +24,20 @@
 Supported compilers include GCC, IBM C, Sun C 5.11 and later,
 and MSVC 7.0 and later.
 @item
+Some compilers do not support alignment via
+@code{alignas}/@code{_Alignas} of @code{auto} variables (i.e.,
+variables on the stack).  They diagnose and ignore the alignment: Sun
+C 5.11.
+@item
+Some compilers require the operand of @code{_Alignas}/@code{alignas}
+to be a single integer constant, not an expression: MSVC 7.0 through
+at least 10.0.
+@item
+The Sun C 5.11 compiler sometimes mishandles the alignment of multiple
+external variables that are declared close together with
+@code{_Alignas}/@code{alignas}.  This compiler bug causes the Gnulib
+module @code{stdalign-tests} to fail.
+@item
 @code{<stdalign.h>} must be #included before @samp{_Alignas} and
 @samp{_Alignof} can be used.
 @item

--- a/lib/stdalign.in.h
+++ b/lib/stdalign.in.h
@@ -62,7 +62,11 @@
 
    A should be a power of two that is at least the type's alignment
    and at most the implementation's alignment limit.  This limit is
-   2**28 on typical GNUish hosts, and 2**13 on MSVC.
+   2**28 on typical GNUish hosts, and 2**13 on MSVC.  To be portable
+   to MSVC through at least version 10.0, A should be an integer
+   constant, as MSVC does not support expressions such as 1 << 3.
+   To be portable to Sun C 5.11, do not align auto variables to
+   anything stricter than their default alignment.
 
    The following draft C1X requirements are not supported here:
 
@@ -75,7 +79,7 @@
 #if __GNUC__ || __IBMC__ || __IBMCPP__ || 0x5110 <= __SUNPRO_C
 # define _Alignas(a) __attribute__ ((__aligned__ (a)))
 #elif 1300 <= _MSC_VER
-# define _Alignas(a) __declspec ((align (a)))
+# define _Alignas(a) __declspec (align (a))
 #endif
 #ifdef _Alignas
 # define alignas _Alignas

--- a/modules/stdalign-tests
+++ b/modules/stdalign-tests
@@ -1,5 +1,6 @@
 Files:
 tests/test-stdalign.c
+tests/macros.h
 
 Depends-on:
 verify

--- a/tests/test-stdalign.c
+++ b/tests/test-stdalign.c
@@ -22,10 +22,11 @@
 
 #include <stddef.h>
 #include <stdint.h>
-#include <stdlib.h>
 
 #include "verify.h"
 
+#include "macros.h"
+
 typedef long double longdouble;
 typedef struct { char a[1]; } struct1;
 typedef struct { char a[2]; } struct2;
@@ -42,15 +43,11 @@
 # ifndef alignas
 #  error "alignas is not a macro"
 # endif
-# define DECLARE_ALIGNED(type, name) \
-    type alignas (1 << 3) name##_alignas; \
-    type _Alignas (1 << 3) name##_Alignas;
-# define CHECK_ALIGNED(name) \
-    (((uintptr_t) &name##_alignas % (1 << 3) ? abort () : (void) 0), \
-     ((uintptr_t) &name##_Alignas % (1 << 3) ? abort () : (void) 0))
+# define TEST_ALIGNMENT 16
 #else
-# define DECLARE_ALIGNED(type, name)
-# define CHECK_ALIGNED(name) ((void) 0)
+# define _Alignas(alignment)
+# define alignas(alignment)
+# define TEST_ALIGNMENT 1
 #endif
 
 #define CHECK_STATIC(type) \
@@ -58,40 +55,54 @@
   verify (alignof (type) == offsetof (type##_helper, slot2)); \
   verify (_Alignof (type) == alignof (type)); \
   const int type##_alignment = alignof (type); \
-  DECLARE_ALIGNED(type, static_##type)
+  type alignas (TEST_ALIGNMENT) static_##type##_alignas; \
+  type _Alignas (TEST_ALIGNMENT) static_##type##_Alignas
 
-#define CHECK_AUTO(type) \
-  { \
-    DECLARE_ALIGNED(type, auto_##type) \
-    CHECK_ALIGNED(static_##type); \
-    CHECK_ALIGNED(auto_##type); \
-  }
-
-#ifdef INT64_MAX
-# define if_INT64_MAX(x) x
-#else
-# define if_INT64_MAX(x)
-#endif
+#define CHECK_ALIGNED(var) ASSERT ((uintptr_t) &(var) % TEST_ALIGNMENT == 0)
 
-#define CHECK_TYPES(check) \
-  check (char) \
-  check (short) \
-  check (int) \
-  check (long) \
-  if_INT64_MAX (check (int64_t)) \
-  check (float) \
-  check (double) \
-  check (longdouble) \
-  check (struct1) \
-  check (struct2) \
-  check (struct3) \
-  check (struct4)
-
-CHECK_TYPES (CHECK_STATIC)
+CHECK_STATIC (char);
+CHECK_STATIC (short);
+CHECK_STATIC (int);
+CHECK_STATIC (long);
+#ifdef INT64_MAX
+CHECK_STATIC (int64_t);
+#endif
+CHECK_STATIC (float);
+CHECK_STATIC (double);
+CHECK_STATIC (longdouble);
+CHECK_STATIC (struct1);
+CHECK_STATIC (struct2);
+CHECK_STATIC (struct3);
+CHECK_STATIC (struct4);
 
 int
 main ()
 {
-  CHECK_TYPES (CHECK_AUTO)
+  CHECK_ALIGNED (static_char_alignas);
+  CHECK_ALIGNED (static_char_Alignas);
+  CHECK_ALIGNED (static_short_alignas);
+  CHECK_ALIGNED (static_short_Alignas);
+  CHECK_ALIGNED (static_int_alignas);
+  CHECK_ALIGNED (static_int_Alignas);
+  CHECK_ALIGNED (static_long_alignas);
+  CHECK_ALIGNED (static_long_Alignas);
+#ifdef INT64_MAX
+  CHECK_ALIGNED (static_int64_t_alignas);
+  CHECK_ALIGNED (static_int64_t_Alignas);
+#endif
+  CHECK_ALIGNED (static_float_alignas);
+  CHECK_ALIGNED (static_float_Alignas);
+  CHECK_ALIGNED (static_double_alignas);
+  CHECK_ALIGNED (static_double_Alignas);
+  CHECK_ALIGNED (static_longdouble_alignas);
+  CHECK_ALIGNED (static_longdouble_Alignas);
+  CHECK_ALIGNED (static_struct1_alignas);
+  CHECK_ALIGNED (static_struct1_Alignas);
+  CHECK_ALIGNED (static_struct2_alignas);
+  CHECK_ALIGNED (static_struct2_Alignas);
+  CHECK_ALIGNED (static_struct3_alignas);
+  CHECK_ALIGNED (static_struct3_Alignas);
+  CHECK_ALIGNED (static_struct4_alignas);
+  CHECK_ALIGNED (static_struct4_Alignas);
   return 0;
 }