From: Tom Lane <tgl@sss.pgh.pa.us>
To: exclusion@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17920: Incorrect memory access in array_position(s) is
 detected (or not)
In-reply-to: <17920-f7c228c627b6d02e@postgresql.org>
References: <17920-f7c228c627b6d02e@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Thu, 04 May 2023 13:00:00 -0000"
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Date: Thu, 04 May 2023 11:53:48 -0400
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PG Bug reporting form <noreply@postgresql.org> writes:
> When the following script:
> SELECT array_positions('{}'::int[], 1); SELECT array_positions('{}'::int=
[],
> 1)
> is executed under Valgrind, an incorrect memory access is detected:
> =3D=3D00:00:00:04.955 1823064=3D=3D Invalid read of size 4

> =3D=3D00:00:00:04.955 1823064=3D=3D    at 0x5EDBD0: array_positions
> (array_userfuncs.c:806)

Fixed, thanks for the report!

> I was surprised by the fact, that Valgrind doesn't complain for the sing=
le
> query execution:
> SELECT array_positions('{}'::int[], 1)
> IIUC, this is explained by the lack of red zones around palloc'ed memory
> areas.
> sed "s/VALGRIND_CREATE_MEMPOOL(\(.*\), 0, false);/VALGRIND_CREATE_MEMPOO=
L(\1, 16, false);/" -i
> src/backend/utils/mmgr/mcxt.c
> on master (after 414d66220) helps Valgrind to detect the invalid read on
> the single query execution too:

I didn't try valgrind'ing this on HEAD, but I think this situation
might have been improved by 414d66220.

			regards, tom lane