This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] Define libc_max_align_t
- From: pinskia at gmail dot com
- To: Rich Felker <dalias at libc dot org>
- Cc: Andreas Schwab <schwab at linux-m68k dot org>, Florian Weimer <fweimer at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 2 Apr 2015 09:36:56 +0800
- 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> <20150402004025 dot GQ6817 at brightrain dot aerifal dot cx>
> On Apr 2, 2015, at 8:40 AM, Rich Felker <dalias@libc.org> wrote:
>
>> On Thu, Apr 02, 2015 at 12:01:34AM +0200, 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?
>
> Because gcc is insane.
No. Just some abi's are insane.
>
> On gcc, __alignof__ returns the "preferred alignment for optimization"
> that gcc would use allocating such objects individually, not the "ABI
> alignment" that would be used in structs, etc.
Except some abis talk about different alignment for where the field is located.
>
> Rich