* doc/gnulib.texi (alignof):
Improve doc to match implementationa better.
* m4/stdalign.m4 (alignas): Do not define to _Alignas
if __xlC__ claims to conform to C11, because _Alignas fails with
weird diagnostics "Unexpected text %1$s encountered."
* tests/test-alignasof.c (TEST_ALIGNMENT, alignas):
Follow doc advice.
---
ChangeLog | 11 +++++++++++
doc/gnulib.texi | 23 ++++++++++++++++++++---
m4/stdalign.m4 | 5 +++--
tests/test-alignasof.c | 5 ++---
4 files changed, 36 insertions(+), 8 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 283f98849d..a2495cc31a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2025-01-18 Paul Eggert <egg...@cs.ucla.edu>
+
+ alignasof: port to IBM XL C 16.1
+ * doc/gnulib.texi (alignof):
+ Improve doc to match implementationa better.
+ * m4/stdalign.m4 (alignas): Do not define to _Alignas
+ if __xlC__ claims to conform to C11, because _Alignas fails with
+ weird diagnostics "Unexpected text %1$s encountered."
+ * tests/test-alignasof.c (TEST_ALIGNMENT, alignas):
+ Follow doc advice.
+
2025-01-18 Collin Funk <collin.fu...@gmail.com>
renameatu: Work around a GNU/Hurd bug.
diff --git a/doc/gnulib.texi b/doc/gnulib.texi
index 81f8399d59..5eed50d4e0 100644
--- a/doc/gnulib.texi
+++ b/doc/gnulib.texi
@@ -970,9 +970,6 @@ to be more like standard C@.
Portability problems fixed by Gnulib:
@itemize
-@item
-Pre-C11 platforms lack @code{alignas} and @code{alignof}.
-
@item
On pre-C23 platforms, @code{<stdalign.h>} must be included before
using @code{alignas} or @code{alignof}.
@@ -981,6 +978,26 @@ using @code{alignas} or @code{alignof}.
Portability problems not fixed by Gnulib:
@itemize
+@item
+The set of alignments supported by @code{alignas} is implementation
+dependent, and implementations need not support alignments greater
+than @code{alignof (max_align_t)}.
+
+@item
+Some older platforms do not support @code{alignas}.
+To test this, use the @code{alignasof} module
+along with the @code{#if} conditional
+@code{(defined alignas || defined __alignas_is_defined
+|| 202311 <= __STDC_VERSION__ || 201103 <= __cplusplus)}.
+Platforms where @code{alignas} does not work include:
+IBM XL C for AIX V16.1.
+
+@item
+On some platforms, the argument of @code{alignas} must be an integer
+constant like @samp{8}, instead of an integer constant expression
+like @samp{4 + 4} that evaluates to 8:
+GCC 4.9.
+
@item
On pre-C23 platforms, @code{alignas} and @code{alignof} are macros.
@end itemize
diff --git a/m4/stdalign.m4 b/m4/stdalign.m4
index bd4ec12e89..885feafdd8 100644
--- a/m4/stdalign.m4
+++ b/m4/stdalign.m4
@@ -1,5 +1,5 @@
# stdalign.m4
-# serial 2
+# serial 3
dnl Copyright 2011-2025 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -181,7 +181,8 @@ AC_DEFUN([gl_ALIGNASOF],
# if ((defined _Alignas \
&& !(defined __cplusplus \
&& (201103 <= __cplusplus || defined _MSC_VER))) \
- || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
+ || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__ \
+ && !defined __xlC__))
# define alignas _Alignas
# endif
# endif
diff --git a/tests/test-alignasof.c b/tests/test-alignasof.c
index 638b4be281..b0c74f848f 100644
--- a/tests/test-alignasof.c
+++ b/tests/test-alignasof.c
@@ -29,13 +29,12 @@ typedef struct { char a[2]; } struct2;
typedef struct { char a[3]; } struct3;
typedef struct { char a[4]; } struct4;
-#if (202311 <= __STDC_VERSION__ || __alignas_is_defined \
- || 201103 <= __cplusplus)
+#if (defined alignas || __alignas_is_defined \
+ || 202311 <= __STDC_VERSION__ || 201103 <= __cplusplus)
/* mingw can go up only to 8. 8 is all that GNU Emacs needs, so let's
limit the test to 8 for now. */
# define TEST_ALIGNMENT 8
#else
-# undef alignas
# define alignas(alignment)
# define TEST_ALIGNMENT 1
#endif
--
2.45.2
