Re: pg_verify_checksums and -fno-strict-aliasing

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_verify_checksums and -fno-strict-aliasing
Date: 2018-08-31 14:55:06
Message-ID: 28226.1535727306@sss.pgh.pa.us
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Michael Paquier <michael(at)paquier(dot)xyz> writes:
> On Thu, Aug 30, 2018 at 07:37:37PM -0400, Tom Lane wrote:
>> Anyway, I'll work on a patch for that, unless you were on it already?

> I have begun working on that and am less than halfway through it as I
> needed a fresh problem, however I am not sure I would be able to finish
> it today, perhaps tomorrow... If you have time and want to press on as
> 11 would release soon, of course feel free to wrap up more quickly than
> I can.

Some of these places might be performance-critical enough that adding
a palloc/pfree cycle would not be nice. What I was considering doing
was inventing something like

typedef union PGAlignedBuffer
{
char data[BLCKSZ];
double force_align;
} PGAlignedBuffer;

and replacing plain char[] variables with that as appropriate.
We might need one for XLOG_BLCKSZ too.

Since this'd be used in frontend as well as backend, it'd likely
have to end up in c.h, which is slightly annoying but not really
a big deal as long as we pick a nonconflicting type name.

regards, tom lane

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