1 files changed, 69 insertions, 12 deletions

diff --git a/gl/m4/stddef_h.m4 b/gl/m4/stddef_h.m4
index 5da8ab1e..a2322ebb 100644
--- a/gl/m4/stddef_h.m4
+++ b/gl/m4/stddef_h.m4
@@ -1,19 +1,61 @@
-dnl A placeholder for POSIX 2008 <stddef.h>, for platforms that have issues.
-# stddef_h.m4 serial 4
-dnl Copyright (C) 2009-2013 Free Software Foundation, Inc.
+# stddef_h.m4 serial 13
+dnl Copyright (C) 2009-2023 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.
 
-AC_DEFUN([gl_STDDEF_H],
+dnl A placeholder for <stddef.h>, for platforms that have issues.
+
+AC_DEFUN_ONCE([gl_STDDEF_H],
 [
   AC_REQUIRE([gl_STDDEF_H_DEFAULTS])
   AC_REQUIRE([gt_TYPE_WCHAR_T])
-  STDDEF_H=
+
+  dnl Persuade OpenBSD <stddef.h> to declare max_align_t.
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  GL_GENERATE_STDDEF_H=false
+
+  dnl Test whether the type max_align_t exists and whether its alignment
+  dnl "is as great as is supported by the implementation in all contexts".
+  AC_CACHE_CHECK([for good max_align_t],
+    [gl_cv_type_max_align_t],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[/* On FreeBSD 12.0/x86, max_align_t defined by <stddef.h> has
+               the correct alignment with the default (wrong) definition of
+               _Alignof, but a wrong alignment as soon as we activate an
+               ISO C compliant _Alignof definition.  */
+            #if ((defined __GNUC__ && 4 <= __GNUC__) || defined __clang__) && !defined __cplusplus
+             #define _Alignof(type) __builtin_offsetof (struct { char __a; type __b; }, __b)
+            #endif
+            #include <stddef.h>
+            unsigned int s = sizeof (max_align_t);
+            #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
+            int check1[2 * (__alignof__ (double) <= __alignof__ (max_align_t)) - 1];
+            int check2[2 * (__alignof__ (long double) <= __alignof__ (max_align_t)) - 1];
+            #endif
+            typedef struct { char a; max_align_t b; } max_helper;
+            typedef struct { char a; long b; } long_helper;
+            typedef struct { char a; double b; } double_helper;
+            typedef struct { char a; long double b; } long_double_helper;
+            int check3[2 * (offsetof (long_helper, b) <= offsetof (max_helper, b)) - 1];
+            int check4[2 * (offsetof (double_helper, b) <= offsetof (max_helper, b)) - 1];
+            int check5[2 * (offsetof (long_double_helper, b) <= offsetof (max_helper, b)) - 1];
+          ]])],
+       [gl_cv_type_max_align_t=yes],
+       [gl_cv_type_max_align_t=no])
+    ])
+  if test $gl_cv_type_max_align_t = no; then
+    HAVE_MAX_ALIGN_T=0
+    GL_GENERATE_STDDEF_H=true
+  fi
+
   if test $gt_cv_c_wchar_t = no; then
     HAVE_WCHAR_T=0
-    STDDEF_H=stddef.h
+    GL_GENERATE_STDDEF_H=true
   fi
+
   AC_CACHE_CHECK([whether NULL can be used in arbitrary expressions],
     [gl_cv_decl_null_works],
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stddef.h>
@@ -23,25 +65,40 @@ AC_DEFUN([gl_STDDEF_H],
       [gl_cv_decl_null_works=no])])
   if test $gl_cv_decl_null_works = no; then
     REPLACE_NULL=1
-    STDDEF_H=stddef.h
+    GL_GENERATE_STDDEF_H=true
   fi
-  AC_SUBST([STDDEF_H])
-  AM_CONDITIONAL([GL_GENERATE_STDDEF_H], [test -n "$STDDEF_H"])
-  if test -n "$STDDEF_H"; then
+
+  if $GL_GENERATE_STDDEF_H; then
     gl_NEXT_HEADERS([stddef.h])
   fi
 ])
 
+# gl_STDDEF_MODULE_INDICATOR([modulename])
+# sets the shell variable that indicates the presence of the given module
+# to a C preprocessor expression that will evaluate to 1.
+# This macro invocation must not occur in macros that are AC_REQUIREd.
 AC_DEFUN([gl_STDDEF_MODULE_INDICATOR],
 [
-  dnl Use AC_REQUIRE here, so that the default settings are expanded once only.
-  AC_REQUIRE([gl_STDDEF_H_DEFAULTS])
+  dnl Ensure to expand the default settings once only.
+  gl_STDDEF_H_REQUIRE_DEFAULTS
   gl_MODULE_INDICATOR_SET_VARIABLE([$1])
 ])
 
+# Initializes the default values for AC_SUBSTed shell variables.
+# This macro must not be AC_REQUIREd.  It must only be invoked, and only
+# outside of macros or in macros that are not AC_REQUIREd.
+AC_DEFUN([gl_STDDEF_H_REQUIRE_DEFAULTS],
+[
+  m4_defun(GL_MODULE_INDICATOR_PREFIX[_STDDEF_H_MODULE_INDICATOR_DEFAULTS], [
+  ])
+  m4_require(GL_MODULE_INDICATOR_PREFIX[_STDDEF_H_MODULE_INDICATOR_DEFAULTS])
+  AC_REQUIRE([gl_STDDEF_H_DEFAULTS])
+])
+
 AC_DEFUN([gl_STDDEF_H_DEFAULTS],
 [
   dnl Assume proper GNU behavior unless another module says otherwise.
   REPLACE_NULL=0;                AC_SUBST([REPLACE_NULL])
+  HAVE_MAX_ALIGN_T=1;            AC_SUBST([HAVE_MAX_ALIGN_T])
   HAVE_WCHAR_T=1;                AC_SUBST([HAVE_WCHAR_T])
 ])