From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Alexander Korotkov <akorotkov@postgresql.org>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Detecting pointer misalignment (was Re: pgsql: Implementation of subscripting for jsonb)
Date: Sun, 07 Feb 2021 19:47:37 -0500
Message-ID: <475514.1612745257@sss.pgh.pa.us> (raw)
In-Reply-To: <CAPpHfdu8Jh0tySa50Zhkyg6gMvi2pQFdHAMiF+UkZNqsDLwTQw@mail.gmail.com>
References: <E1l6Jjn-0000kp-75@gemulon.postgresql.org>
<37bb56a0-391d-759d-771b-9c1d8c15a84b@iki.fi>
<3293925.1612163110@sss.pgh.pa.us>
<CAPpHfdsne3=T=fMNU45PtxdhSL_J2PjLTeS8rwKnJzUR4YNd4w@mail.gmail.com>
<CAPpHfdu8Jh0tySa50Zhkyg6gMvi2pQFdHAMiF+UkZNqsDLwTQw@mail.gmail.com>
[ redirecting to -hackers ]
Alexander Korotkov <aekorotkov@gmail.com> writes:
>> BTW, I managed to reproduce the issue by compiling with CFLAGS="-O0
>> -fsanitize=alignment -fsanitize-trap=alignment" and the patch
>> attached.
>> I can propose the following to catch such issues earlier. We could
>> finish (wrap attribute with macro and apply it to other places with
>> misalignment access if any) and apply the attached patch and make
>> commitfest.cputube.org check patches with CFLAGS="-O0
>> -fsanitize=alignment -fsanitize-trap=alignment". What do you think?
> The revised patch is attached. The attribute is wrapped into
> pg_attribute_no_sanitize_alignment() macro. I've checked it works for
> me with gcc-10 and clang-11.
I found some time to experiment with this today. It is really nice
to be able to detect these problems without using obsolete hardware.
However, I have a few issues:
* Why do you recommend -O0? Seems to me we want to test the code
as we'd normally use it, ie typically -O2.
* -fsanitize-trap=alignment seems to be a clang-ism; gcc won't take it.
However, after some experimenting I found that "-fno-sanitize-recover=all"
(or "-fno-sanitize-recover=alignment" if you prefer) produces roughly
equivalent results on gcc.
* Both clang and gcc seem to be happy with the same spelling of the
function attribute, which is fortunate. However, I seriously doubt
that bare "#ifdef __GNUC__" is going to be good enough. At the very
least there's going to need to be a compiler version test in there,
and we might end up needing to get the configure script involved.
* I think the right place to run such a check is in some buildfarm
animals. The cfbot only sees portions of what goes into our tree.
regards, tom lane
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-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, aekorotkov@gmail.com, hlinnaka@iki.fi, akorotkov@postgresql.org, pgsql-hackers@lists.postgresql.org
Subject: Re: Detecting pointer misalignment (was Re: pgsql: Implementation of subscripting for jsonb)
In-Reply-To: <475514.1612745257@sss.pgh.pa.us>
* 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