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From: Paul Eggert <eggert@cs.ucla.edu>
To: Khem Raj <raj.khem@gmail.com>
Cc: bug-gnulib@gnu.org
Subject: Re: [PATCH v2] Define alignof_slot using _Alignof when using C11 or newer
Date: Sat, 14 Jan 2023 17:51:59 -0800	[thread overview]
Message-ID: <c3943fc1-58af-0bf0-7005-77aaeea8c865@cs.ucla.edu> (raw)
In-Reply-To: <20230115012007.2175339-1-raj.khem@gmail.com>

[-- Attachment #1: Type: text/plain, Size: 751 bytes --]

On 2023-01-14 17:20, Khem Raj wrote:
> +/* 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.  */
> +#elif (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
> +       || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
> +           && !defined __clang__) \
> +       || (defined __clang__ && __clang_major__ < 8))

We already have two copies of that stuff elsewhere (in lib/stdalign.in.h 
and m4/stdalign.m4), for reasons that currently escape me. Let's not 
balloon the number of copies to three.

I installed the attached smaller patch which should do the trick for C.

Is there a similar problem with C++.

[-- Attachment #2: 0001-alignof-port-to-strict-C23.patch --]
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From 2d404c7dd974cc65f894526f4a1b76bc1dcd8d82 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 14 Jan 2023 17:48:18 -0800
Subject: [PATCH] alignof: port to strict C23

Problem reported by Khem Raj in:
https://lists.gnu.org/r/bug-gnulib/2023-01/msg00111.html
* lib/alignof.h (alignof_slot) [!__cplusplus]: Use C23-style alignof.
* modules/alignof (Depends-on): Add stdalign.
---
 ChangeLog       | 6 ++++++
 lib/alignof.h   | 4 ++--
 modules/alignof | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 0900c54c1d..fa684131db 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2023-01-14  Paul Eggert  <eggert@cs.ucla.edu>
 
+	alignof: port to strict C23
+	Problem reported by Khem Raj in:
+	https://lists.gnu.org/r/bug-gnulib/2023-01/msg00111.html
+	* lib/alignof.h (alignof_slot) [!__cplusplus]: Use C23-style alignof.
+	* modules/alignof (Depends-on): Add stdalign.
+
 	test-framework-sh: work around AIX 7.2 diff bugs
 	* tests/init.sh (compare_dev_null_): Run diff in the C locale.
 	AIX 7.2 diff messes up in UTF-8 locales; for example,
diff --git a/lib/alignof.h b/lib/alignof.h
index 505ad97aa4..2ded1c7884 100644
--- a/lib/alignof.h
+++ b/lib/alignof.h
@@ -22,14 +22,14 @@
 /* alignof_slot (TYPE)
    Determine the alignment of a structure slot (field) of a given type,
    at compile time.  Note that the result depends on the ABI.
-   This is the same as alignof (TYPE) and _Alignof (TYPE).
+   This is the same as alignof (TYPE).
    Note: The result cannot be used as a value for an 'enum' constant,
    due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc.  */
 #if defined __cplusplus
   template <class type> struct alignof_helper { char __slot1; type __slot2; };
 # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2)
 #else
-# define alignof_slot(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
+# define alignof_slot(type) alignof (type)
 #endif
 
 /* alignof_type (TYPE)
diff --git a/modules/alignof b/modules/alignof
index 4345eaca12..c78ab4a3c5 100644
--- a/modules/alignof
+++ b/modules/alignof
@@ -5,6 +5,7 @@ Files:
 lib/alignof.h
 
 Depends-on:
+stdalign
 
 configure.ac:
 
-- 
2.37.2


  reply	other threads:[~2023-01-15  1:52 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-15  1:20 [PATCH v2] Define alignof_slot using _Alignof when using C11 or newer Khem Raj
2023-01-15  1:51 ` Paul Eggert [this message]
2023-01-15 19:52   ` Paul Eggert
2023-01-15 19:56     ` Paul Eggert
2023-01-15 23:05     ` Khem Raj
2023-01-16 17:01     ` Bruno Haible

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