Re: Potential us of initialized memory in xlogrecovery.c

On 06/06/2023 10:24, Tristan Partin wrote:
> Hello,
>
> Today, I compiled the master branch of Postgres with the following GCC
> version:
>
> gcc (GCC) 13.1.1 20230511 (Red Hat 13.1.1-2)
>
> I got the following warning:
>
> [701/2058] Compiling C object src/backend/postgres_lib.a.p/access_transam_xlogrecovery.c.o
> In function ‘recoveryStopsAfter’,
> inlined from ‘PerformWalRecovery’ at ../src/backend/access/transam/xlogrecovery.c:1749:8:
> ../src/backend/access/transam/xlogrecovery.c:2756:42: warning: ‘recordXtime’ may be used uninitialized [-Wmaybe-uninitialized]
> 2756 | recoveryStopTime = recordXtime;
> | ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
> ../src/backend/access/transam/xlogrecovery.c: In function ‘PerformWalRecovery’:
> ../src/backend/access/transam/xlogrecovery.c:2647:21: note: ‘recordXtime’ was declared here
> 2647 | TimestampTz recordXtime;
> | ^~~~~~~~~~~
>
> Investigating this issue I see a potential assignment in
> xlogrecovery.c:2715. Best I can tell the warning looks real. Similar
> functions in this file seem to initialize recordXtime to 0. Attached is
> a patch which does just that.

Thank you! My refactoring in commit c945af80cf introduced this. Looking
at getRecordTimestamp(), it will always return true and set recordXtime
for the commit and abort records, and some compilers can deduce that.

Initializing to 0 makes sense, I'll commit that fix later tonight.

--
Heikki Linnakangas
Neon (https://neon.tech)