From: Paul Koning <paulkoning@comcast.net>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: "Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>,
"Markus Fröschle" <markus@mubf.de>,
gcc@gcc.gnu.org
Subject: Re: asking for __attribute__((aligned()) clarification
Date: Mon, 19 Aug 2019 14:12:00 -0000 [thread overview]
Message-ID: <C437F8A7-19F6-439F-A01F-C1207A8A3588@comcast.net> (raw)
In-Reply-To: <alpine.LNX.2.20.13.1908191706100.32047@monopod.intra.ispras.ru>
> On Aug 19, 2019, at 10:08 AM, Alexander Monakov <amonakov@ispras.ru> wrote:
>
> On Mon, 19 Aug 2019, Richard Earnshaw (lists) wrote:
>
>> Correct, but note that you can only pack structs and unions, not basic types.
>> there is no way of under-aligning a basic type except by wrapping it in a
>> struct.
>
> I don't think that's true. In GCC-9 the doc for 'aligned' attribute has been
> significantly revised, and now ends with
>
> When used as part of a typedef, the aligned attribute can both increase and
> decrease alignment, and specifying the packed attribute generates a warning.
>
> (but I'm sure defacto behavior of accepting and honoring reduced alignment on
> a typedef'ed scalar type goes way earlier than gcc-9)
Interesting. It certainly wasn't that way a decade ago. And for the old code pattern to generate a warning seems like a bad incompatible change. Honoring reducing alignments is one thing, complaining about packed is not good.
paul
next prev parent reply other threads:[~2019-08-19 14:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 12:46 "Markus Fröschle"
2019-08-19 13:57 ` Paul Koning
2019-08-19 14:01 ` Richard Earnshaw (lists)
2019-08-19 14:08 ` Alexander Monakov
2019-08-19 14:12 ` Paul Koning [this message]
2019-08-20 5:46 ` Aw: " "Markus Fröschle"
2019-08-21 14:29 ` Alexander Monakov
2019-08-21 14:32 ` Paul Koning
2019-08-21 14:58 ` Alexander Monakov
2019-08-21 16:50 ` Paul Koning
2019-08-21 17:35 ` Jonathan Wakely
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