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Re: [PATCH] Define libc_max_align_t
- From: Florian Weimer <fweimer at redhat dot com>
- To: Andreas Schwab <schwab at linux-m68k dot org>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 02 Apr 2015 10:15:52 +0200
- Subject: Re: [PATCH] Define libc_max_align_t
- Authentication-results: sourceware.org; auth=none
- References: <551C1A60 dot 4080507 at redhat dot com> <87h9szqzi9 dot fsf at igel dot home> <551C6E87 dot 2090607 at redhat dot com> <mvm1tk33rpz dot fsf at hawking dot suse dot de>
On 04/02/2015 09:38 AM, Andreas Schwab wrote:
> Florian Weimer <fweimer@redhat.com> writes:
>
>> On 04/02/2015 12:01 AM, Andreas Schwab wrote:
>>> Florian Weimer <fweimer@redhat.com> writes:
>>>
>>>> +/* This mirrors the C11 max_align_t type provided by GCC, but it is
>>>> + also available in C99 mode. */
>>>> +typedef struct {
>>>> + long long ll __attribute__ ((__aligned__ (__alignof__ (long long))));
>>>> + long double ld __attribute__ ((__aligned__ (__alignof__ (long double))));
>>>> +} libc_max_align_t;
>>>
>>> Why aren't the attributes no-ops?
>>
>> Quoting Joseph:
>>
>> âThe attributes there are because some targets may give types lower
>> alignment inside structures and unions than outside; 32-bit x86 in
>> particular.â
>
> This should probably be added to the comment.
Well, the GCC folks thought it wasn't necessary, but I agree that a
comment cannot hurt.
Is this okay?
--
Florian Weimer / Red Hat Product Security
>From 1d39ccadab8f2c11ac54242c9faaf0396f760c15 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Thu, 2 Apr 2015 10:07:04 +0200
Subject: [PATCH] Define libc_max_align_t for internal use
---
ChangeLog | 4 ++++
include/libc-internal.h | 9 +++++++++
2 files changed, 13 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index c687d13..b0a48ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2015-04-02 Florian Weimer <fweimer@redhat.com>
+
+ * include/libc-internal.h (libc_max_align_t): Define.
+
2015-04-02 Mel Gorman <mgorman@suse.de>
[BZ #17195]
diff --git a/include/libc-internal.h b/include/libc-internal.h
index bca59a4..b37388e 100644
--- a/include/libc-internal.h
+++ b/include/libc-internal.h
@@ -107,4 +107,13 @@ extern void __init_misc (int, char **, char **);
#define DIAG_IGNORE_NEEDS_COMMENT(version, option) \
_Pragma (_DIAG_STR (GCC diagnostic ignored option))
+/* This mirrors the C11 max_align_t type provided by GCC, but it is
+ also available in C99 mode. The aligned attributes are required
+ because some ABIs have reduced alignment requirements for struct
+ and union members. */
+typedef struct {
+ long long ll __attribute__ ((__aligned__ (__alignof__ (long long))));
+ long double ld __attribute__ ((__aligned__ (__alignof__ (long double))));
+} libc_max_align_t;
+
#endif /* _LIBC_INTERNAL */
--
2.1.0