From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <aekorotkov@gmail.com>
cc: Heikki Linnakangas <hlinnaka@iki.fi>,
        Alexander Korotkov <akorotkov@postgresql.org>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Detecting pointer misalignment (was Re: pgsql: Implementation of
 subscripting for jsonb)
In-reply-to: <475514.1612745257@sss.pgh.pa.us>
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Sun, 07 Feb 2021 19:47:37 -0500"
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Date: Sun, 07 Feb 2021 20:20:00 -0500
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I wrote:
> * Both clang and gcc seem to be happy with the same spelling of the
> function attribute, which is fortunate.  However, I seriously doubt
> that bare "#ifdef __GNUC__" is going to be good enough.  At the very
> least there's going to need to be a compiler version test in there,
> and we might end up needing to get the configure script involved.

After digging in gcc's release history, it seems they invented
"-fsanitize=alignment" in GCC 5, so we can make this work for gcc
by writing

#if __GNUC__ >= 5

(the likely() macro already uses a similar approach).  Can't say
if that's close enough for clang too.

			regards, tom lane