1 files changed, 140 insertions, 66 deletions

diff --git a/gl/m4/stdalign.m4 b/gl/m4/stdalign.m4
index dc297175..885feafd 100644
--- a/gl/m4/stdalign.m4
+++ b/gl/m4/stdalign.m4
@@ -1,20 +1,25 @@
-# Check for alignas and alignof that conform to C23.
-
-dnl Copyright 2011-2023 Free Software Foundation, Inc.
+# stdalign.m4
+# 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,
 dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+# Check for alignas and alignof that conform to C23.
+
+dnl Written by Paul Eggert and Bruno Haible.
 
 # Prepare for substituting <stdalign.h> if it is not supported.
 
-AC_DEFUN([gl_STDALIGN_H],
+AC_DEFUN([gl_ALIGNASOF],
 [
   AC_CACHE_CHECK([for alignas and alignof],
     [gl_cv_header_working_stdalign_h],
-    [gl_save_CFLAGS=$CFLAGS
+    [gl_saved_CFLAGS=$CFLAGS
      for gl_working in "yes, keywords" "yes, <stdalign.h> macros"; do
       AS_CASE([$gl_working],
-        [*stdalign.h*], [CFLAGS="$gl_save_CFLAGS -DINCLUDE_STDALIGN_H"])
+        [*stdalign.h*], [CFLAGS="$gl_saved_CFLAGS -DINCLUDE_STDALIGN_H"])
       AC_COMPILE_IFELSE(
        [AC_LANG_PROGRAM(
           [[#include <stdint.h>
@@ -54,85 +59,154 @@ AC_DEFUN([gl_STDALIGN_H],
        [gl_cv_header_working_stdalign_h=$gl_working],
        [gl_cv_header_working_stdalign_h=no])
 
-      CFLAGS=$gl_save_CFLAGS
+      CFLAGS=$gl_saved_CFLAGS
       test "$gl_cv_header_working_stdalign_h" != no && break
      done])
 
-  GL_GENERATE_STDALIGN_H=false
   AS_CASE([$gl_cv_header_working_stdalign_h],
-    [no],
-      [GL_GENERATE_STDALIGN_H=true],
     [yes*keyword*],
       [AC_DEFINE([HAVE_C_ALIGNASOF], [1],
          [Define to 1 if the alignas and alignof keywords work.])])
 
-  AC_CHECK_HEADERS_ONCE([stdalign.h])
-
   dnl The "zz" puts this toward config.h's end, to avoid potential
   dnl collisions with other definitions.
   AH_VERBATIM([zzalignas],
-[#if !defined HAVE_C_ALIGNASOF && __cplusplus < 201103 && !defined alignof
-# if HAVE_STDALIGN_H
+[#if !defined HAVE_C_ALIGNASOF \
+    && !(defined __cplusplus && 201103 <= __cplusplus) \
+    && !defined alignof
+# if defined HAVE_STDALIGN_H
 #  include <stdalign.h>
-# else
-   /* Substitute.  Keep consistent with gnulib/lib/stdalign.in.h.  */
-#  ifndef _GL_STDALIGN_H
-#   define _GL_STDALIGN_H
-#   undef _Alignas
-#   undef _Alignof
-#   if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
-        || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
-            && !defined __clang__) \
-        || (defined __clang__ && __clang_major__ < 8))
-#    ifdef __cplusplus
-#     if (201103 <= __cplusplus || defined _MSC_VER)
-#      define _Alignof(type) alignof (type)
-#     else
-       template <class __t> struct __alignof_helper { char __a; __t __b; };
-#      define _Alignof(type) offsetof (__alignof_helper<type>, __b)
-#      define _GL_STDALIGN_NEEDS_STDDEF 1
-#     endif
+# endif
+
+/* ISO C23 alignas and alignof for platforms that lack it.
+
+   References:
+   ISO C23 (latest free draft
+   <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf>)
+   sections 6.5.3.4, 6.7.5, 7.15.
+   C++11 (latest free draft
+   <https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf>)
+   section 18.10. */
+
+/* alignof (TYPE), also known as _Alignof (TYPE), yields the alignment
+   requirement of a structure member (i.e., slot or field) that is of
+   type TYPE, as an integer constant expression.
+
+   This differs from GCC's and clang's __alignof__ operator, which can
+   yield a better-performing alignment for an object of that type.  For
+   example, on x86 with GCC and on Linux/x86 with clang,
+   __alignof__ (double) and __alignof__ (long long) are 8, whereas
+   alignof (double) and alignof (long long) are 4 unless the option
+   '-malign-double' is used.
+
+   The result cannot be used as a value for an 'enum' constant, if you
+   want to be portable to HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
+
+/* GCC releases before GCC 4.9 had a bug in _Alignof.  See GCC bug 52023
+   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
+   clang versions < 8.0.0 have the same bug.
+   IBM XL C V16.1.0 cc (non-clang) has the same bug.  */
+#  if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
+       || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
+           && !defined __clang__) \
+       || (defined __clang__ && __clang_major__ < 8) \
+       || defined __xlC__)
+#   undef/**/_Alignof
+#   ifdef __cplusplus
+#    if (201103 <= __cplusplus || defined _MSC_VER)
+#     define _Alignof(type) alignof (type)
 #    else
+      template <class __t> struct __alignof_helper { char __a; __t __b; };
 #     if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
-#      define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
+#      define _Alignof(type) __builtin_offsetof (__alignof_helper<type>, __b)
 #     else
-#      define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
-#      define _GL_STDALIGN_NEEDS_STDDEF 1
+#      define _Alignof(type) offsetof (__alignof_helper<type>, __b)
 #     endif
+#     define _GL_STDALIGN_NEEDS_STDDEF 1
 #    endif
-#   endif
-#   if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
-#    define alignof _Alignof
-#   endif
-#   define __alignof_is_defined 1
-#   if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
-#    if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
-#     define _Alignas(a) alignas (a)
-#    elif (!defined __attribute__ \
-           && ((defined __APPLE__ && defined __MACH__ \
-                ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
-                : __GNUC__ && !defined __ibmxl__) \
-               || (4 <= __clang_major__) \
-               || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
-               || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
-#     define _Alignas(a) __attribute__ ((__aligned__ (a)))
-#    elif 1300 <= _MSC_VER
-#     define _Alignas(a) __declspec (align (a))
+#   else
+#    if (defined __GNUC__ && 4 <= __GNUC__) || defined __clang__
+#     define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
+#    else
+#     define _Alignof(type) offsetof (struct { char __a; type __b; }, __b)
+#     define _GL_STDALIGN_NEEDS_STDDEF 1
 #    endif
 #   endif
-#   if ((defined _Alignas \
-         && !(defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))) \
-        || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
-#    define alignas _Alignas
-#   endif
-#   if (defined alignas \
-        || (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)))
-#    define __alignas_is_defined 1
-#   endif
-#   if _GL_STDALIGN_NEEDS_STDDEF
-#    include <stddef.h>
-#   endif
-#  endif /* _GL_STDALIGN_H */
+#  endif
+#  if ! (defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER))
+#   undef/**/alignof
+#   define alignof _Alignof
+#  endif
+
+/* alignas (A), also known as _Alignas (A), aligns a variable or type
+   to the alignment A, where A is an integer constant expression.  For
+   example:
+
+      int alignas (8) foo;
+      struct s { int a; int alignas (8) bar; };
+
+   aligns the address of FOO and the offset of BAR to be multiples of 8.
+
+   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.  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 C23 requirements are not supported here:
+
+     - If A is zero, alignas has no effect.
+     - alignas can be used multiple times; the strictest one wins.
+     - alignas (TYPE) is equivalent to alignas (alignof (TYPE)).
+
+   */
+# if !defined __STDC_VERSION__ || __STDC_VERSION__ < 201112
+#  if defined __cplusplus && (201103 <= __cplusplus || defined _MSC_VER)
+#   define _Alignas(a) alignas (a)
+#  elif (!defined __attribute__ \
+         && ((defined __APPLE__ && defined __MACH__ \
+              ? 4 < __GNUC__ + (1 <= __GNUC_MINOR__) \
+              : __GNUC__ && !defined __ibmxl__) \
+             || (4 <= __clang_major__) \
+             || (__ia64 && (61200 <= __HP_cc || 61200 <= __HP_aCC)) \
+             || __ICC || 0x590 <= __SUNPRO_C || 0x0600 <= __xlC__))
+#   define _Alignas(a) __attribute__ ((__aligned__ (a)))
+#  elif 1300 <= _MSC_VER
+#   define _Alignas(a) __declspec (align (a))
+#  endif
+# endif
+# if !defined HAVE_STDALIGN_H
+#  if ((defined _Alignas \
+        && !(defined __cplusplus \
+             && (201103 <= __cplusplus || defined _MSC_VER))) \
+       || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__ \
+           && !defined __xlC__))
+#   define alignas _Alignas
+#  endif
+# endif
+
+# if defined _GL_STDALIGN_NEEDS_STDDEF
+#  include <stddef.h>
 # endif
 #endif])
 ])
+
+AC_DEFUN([gl_STDALIGN_H],
+[
+  AC_REQUIRE([gl_ALIGNASOF])
+  if test "$gl_cv_header_working_stdalign_h" = no; then
+    GL_GENERATE_STDALIGN_H=true
+  else
+    GL_GENERATE_STDALIGN_H=false
+  fi
+
+  gl_CHECK_NEXT_HEADERS([stdalign.h])
+  if test $ac_cv_header_stdalign_h = yes; then
+    HAVE_STDALIGN_H=1
+  else
+    HAVE_STDALIGN_H=0
+  fi
+  AC_SUBST([HAVE_STDALIGN_H])
+])