Horton

Re: Clang UndefinedBehaviorSanitize (Postgres14) Detected undefined-behavior

Peter Geoghegan <pg@bowt.ie>

View thread View on postgr.es
From: Peter Geoghegan <pg@bowt.ie>
To: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Ranier Vilela <ranier.vf@gmail.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>, Noah Misch <noah@leadboat.com>
Date: 2020-08-31T19:38:51Z
Lists: pgsql-hackers 
On Mon, Aug 31, 2020 at 11:42 AM Andres Freund <andres@anarazel.de> wrote:
> Unsigned integer overflow is well defined in the standard. So I don't understand what this is purporting to warn about.

Presumably it's simply warning that the value -4294901760 (i.e. the
result of 3 - 4294901763) cannot be faithfully represented as an
unsigned int. This is true, of course. It's just not relevant.

I'm pretty sure that UBSan does not actually state that this is
undefined behavior. At least Ranier's sample output didn't seem to
indicate it.

-- 
Peter Geoghegan

Commits

  1. Avoid memcpy() with a NULL source pointer and count == 0

  2. Avoid calling memcpy() with a NULL source pointer and count == 0.