From: Michael Banck <michael.banck@credativ.de>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: pg_verify_checksums and -fno-strict-aliasing
Date: Thu, 30 Aug 2018 10:35:00 +0200
Message-ID: <1535618100.1286.3.camel@credativ.de> (raw)
Hi,
I noticed that pg_verify_checksums computes bogus checksums if I compile
it with '-O2 -Wall' but without -fno-strict-aliasing. Also I am getting
a compile warning then:
|src/bin/pg_verify_checksums$ make CFLAGS='-g -O2 -Wall'
[...]
|gcc -g -O2 -Wall -I../../../src/include
| -I/home/mba/Projekte/OSS/PostgreSQL/git/postgresql/build/../src/include
| -D_GNU_SOURCE -c -o pg_verify_checksums.o
| /home/mba/Projekte/OSS/PostgreSQL/git/postgresql/build/../src/bin/pg_verify_checksums/pg_verify_checksums.c
| -MMD -MP -MF .deps/pg_verify_checksums.Po
|/home/mba/Projekte/OSS/PostgreSQL/git/postgresql/build/../src/bin/pg_verify_checksums/pg_verify_checksums.c:
| In function ‘scan_file’:
|/home/mba/Projekte/OSS/PostgreSQL/git/postgresql/build/../src/bin/pg_verify_checksums/pg_verify_checksums.c:112:3:
| warning: dereferencing type-punned pointer will break strict-aliasing
| rules [-Wstrict-aliasing]
| if (PageIsNew(buf))
| ^~
[...]
|src/bin/pg_verify_checksums$ ./pg_verify_checksums -D ../../test/regress/tmp_check/data
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/global/1233", block 0: calculated checksum FC8A but expected F857
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/global/1233", block 1: calculated checksum F340 but expected A68D
[...]
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/base/12368/2659", block 5: calculated checksum 954D but expected D2ED
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/base/12368/2659", block 6: calculated checksum 361 but expected E7F7
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/base/12368/2659", block 7: calculated checksum 4C0D but expected 4B10
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/base/12368/2659", block 8: calculated checksum 2B9A but expected 71E3
|pg_verify_checksums: checksum verification failed in file "../../test/regress/tmp_check/data/base/12368/2659", block 9: calculated checksum 19CD but expected 541C
|Checksum scan completed
|Data checksum version: 1
|Files scanned: 932
|Blocks scanned: 2789
|Bad checksums: 2789
If I add -fno-strict-aliasing to $CFLAGS, the problem goes away.
Is this something to worry about, or just pilot error cause I am not
using the same $CFLAGS as for the rest of the build? I originally
noticed this problem with my external fork of pg_verify_checksums.
Michael
--
Michael Banck
Projektleiter / Senior Berater
Tel.: +49 2166 9901-171
Fax: +49 2166 9901-100
Email: michael.banck@credativ.de
credativ GmbH, HRB Mönchengladbach 12080
USt-ID-Nummer: DE204566209
Trompeterallee 108, 41189 Mönchengladbach
Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer
Unser Umgang mit personenbezogenen Daten unterliegt
folgenden Bestimmungen: https://www.credativ.de/datenschutz
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: michael.banck@credativ.de
Subject: Re: pg_verify_checksums and -fno-strict-aliasing
In-Reply-To: <1535618100.1286.3.camel@credativ.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox