Re: alignas (C11)

From: Andres Freund <andres(at)anarazel(dot)de>
To: Peter Eisentraut <peter(at)eisentraut(dot)org>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: alignas (C11)
Date: 2025-11-12 15:17:19
Message-ID: lsgnps74ictxtm5karcobenxtt5rvoylvbvx7ja6r5rjcund7v@owxqgv7gisns
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Hi,

On 2025-11-12 16:09:14 +0100, Peter Eisentraut wrote:
> On 12.11.25 15:02, Andres Freund wrote:
> > Hi,
> >
> > On 2025-11-12 12:39:19 +0100, Peter Eisentraut wrote:
> > > - You cannot use alignas on a typedef. So some uses of the attribute
> > > pg_attribute_aligned() like for PgAioUringContext or the whole int128
> > > business cannot be converted directly. The solution for cases like
> > > PgAioUringContext could be to move the alignas into the struct, but I
> > > haven't studied this code closely enough, so I'm leaving it. For int128,
> > > there is no straightforward solution, so I'm also leaving that as is.
> >
> > Maybe I'm confused, but the aligned attribute for PgAioUringContext is on the
> > struct, not the typedef, no?
>
> Yes, you're right. The immediate problem there is that alignas is not
> syntactically valid at all at that position.

Argh, why couldn't C copy the C++ rules for this :(.

Just moving it to completion_lock would be fine though...

Greetings,

Andres Freund

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