Commit Message
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:
>>
>> “The attributes there are because some targets may give types lower
>> alignment inside structures and unions than outside; 32-bit x86 in
>> particular.”
>
> 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?
Comments
On 04/02/2015 01:15 AM, Florian Weimer wrote:
> Is this okay?
That looks good to me; thanks.
Also, Andreas, thanks for bringing this point up, as it exposed a bug in
the Gnulib implementation of max_align_t for pre-C11 GCC on x86. I'll
follow up with a patch to bug-gnulib@gnu.org.
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(+)
@@ -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]
@@ -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