On NetBSD 8.0/x86 I'm seeing this compilation failure:
In file included from ../../gltests/test-stddef.c:24:0:
../../gltests/../gllib/verify.h:207:21: error: static assertion failed: "verify
(__alignof__ (double) <= __alignof__ (max_align_t))"
# define _GL_VERIFY _Static_assert
^
../../gltests/../gllib/verify.h:252:20: note: in expansion of macro '_GL_VERIFY'
# define verify(R) _GL_VERIFY (R, "verify (" #R ")")
^
../../gltests/test-stddef.c:63:1: note: in expansion of macro 'verify'
verify (__alignof__ (double) <= __alignof__ (max_align_t));
^
Makefile:8514: recipe for target 'test-stddef.o' failed
The reason is that NetBSD 8.0 defines max_align_t, but they do so
without using the GCC built-in __alignof__. Hence, the "alignment
for optimization" that GCC knows about is not large enough. I refer
to Paul's explanations in
<https://sourceware.org/ml/libc-alpha/2015-04/msg00026.html>
<https://lists.gnu.org/archive/html/bug-gnulib/2015-04/msg00006.html>
This patch fixes it.
2018-09-06 Bruno Haible <br...@clisp.org>
stddef: Override max_align_t on NetBSD 8.0/x86.
* m4/stddef_h.m4 (gl_STDDEF_H): When testing for max_align_t, test also
the value of __alignof__ (max_align_t).
* doc/posix-headers/stddef.texi: Mention the issue.
diff --git a/doc/posix-headers/stddef.texi b/doc/posix-headers/stddef.texi
index f5b6696..a27b597 100644
--- a/doc/posix-headers/stddef.texi
+++ b/doc/posix-headers/stddef.texi
@@ -12,6 +12,10 @@ Some platforms fail to provide @code{max_align_t}, which was
added in C11:
Solaris 11.0 and others.
@item
+@code{max_align_t} does not have the expected alignment on some platforms:
+NetBSD 8.0/x86.
+
+@item
Some old platforms fail to provide @code{wchar_t}.
@item
diff --git a/m4/stddef_h.m4 b/m4/stddef_h.m4
index ba3d201..07b040a 100644
--- a/m4/stddef_h.m4
+++ b/m4/stddef_h.m4
@@ -1,5 +1,5 @@
dnl A placeholder for <stddef.h>, for platforms that have issues.
-# stddef_h.m4 serial 5
+# stddef_h.m4 serial 6
dnl Copyright (C) 2009-2018 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -10,13 +10,33 @@ AC_DEFUN([gl_STDDEF_H],
AC_REQUIRE([gl_STDDEF_H_DEFAULTS])
AC_REQUIRE([gt_TYPE_WCHAR_T])
STDDEF_H=
- AC_CHECK_TYPE([max_align_t], [], [HAVE_MAX_ALIGN_T=0; STDDEF_H=stddef.h],
- [[#include <stddef.h>
- ]])
+
+ 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(
+ [[#include <stddef.h>
+ unsigned int s = sizeof (max_align_t);
+ #if defined __GNUC__ || 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
+ ]])],
+ [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
+ STDDEF_H=stddef.h
+ fi
+
if test $gt_cv_c_wchar_t = no; then
HAVE_WCHAR_T=0
STDDEF_H=stddef.h
fi
+
AC_CACHE_CHECK([whether NULL can be used in arbitrary expressions],
[gl_cv_decl_null_works],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stddef.h>
@@ -28,6 +48,7 @@ AC_DEFUN([gl_STDDEF_H],
REPLACE_NULL=1
STDDEF_H=stddef.h
fi
+
AC_SUBST([STDDEF_H])
AM_CONDITIONAL([GL_GENERATE_STDDEF_H], [test -n "$STDDEF_H"])
if test -n "$STDDEF_H"; then
