Re: BUG #15121: Multiple UBSAN errors

On 19 March 2018 at 15:26, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> On 03/19/2018 09:59 AM, Martin Liška wrote:
>> On 19 March 2018 at 01:34, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>>
>> ...
>>>
>>> Again, the line numbers don't really match the code I have, but I guess
>>> it's the same issue as for pg_comp_crc32c_sse42. This is apparently
>>> related to array serialization, and I guess we have a compact structure
>>> (intentionally, to make it smaller), and we accept the unaligned access.
>>
>> Note that building postgresql with -03, I see some array tests failing.
>>
>
> I'm unable to reproduce that. I do get a bunch of compile-time warnings
> about possibly uninitialized variables (which seem bogus after a quick
> inspection), but no failures.

Note that the errrors I reported come from running an instrumented postgres
with "-fsanitize=undefined -g" option.

>
> Which gcc version are you using? Mine is 6.4.1. Do the failures happen
> every time or rarely?

Every time with current GCC trunk:

./xgcc -v
Using built-in specs.
COLLECT_GCC=./xgcc
Target: x86_64-pc-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran
--disable-bootstrap --prefix=/home/marxin/bin/gcc : (reconfigured)
../configure --enable-languages=c,c++,fortran --disable-bootstrap
--prefix=/home/marxin/bin/gcc
Thread model: posix
gcc version 8.0.1 20180319 (experimental) (GCC)

But using latest release GCC 7.3.0 should provide similar _runtime_ errors.

Martin

>
> regards
>
> --
> Tomas Vondra http://www.2ndQuadrant.com
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services