Re: Detecting pointer misalignment (was Re: pgsql: Implementation of subscripting for jsonb)

On Fri, Feb 12, 2021 at 8:19 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I've updated buildfarm member longfin to use "-fsanitize=alignment
> -fsanitize-trap=alignment", and it just got through a run successfully
> with that.  It'd be good perhaps if some other buildfarm owners
> followed suit (mumble JIT coverage mumble).
>
> Looking around at other recent reports, it looks like we'll need to tweak
> the compiler version cutoffs a bit.  I see for instance that spurfowl,
> with gcc (Ubuntu 5.4.0-6ubuntu1~16.04.11) 5.4.0 20160609, is whining:
>
> pg_crc32c_sse42.c:24:1: warning: \342\200\230no_sanitize\342\200\231 attribute directive ignored [-Wattributes]
>
> So maybe it'd better be __GNUC__ >= 6 not __GNUC__ >= 5.  I think
> we can wait a little bit for more reports before messing with that,
> though.

I've rechecked this in the documentation. no_sanitize attribute seems
to appear since gcc 8.0.  Much later than alignment sanitizer itself.
https://gcc.gnu.org/gcc-8/changes.html
"A new attribute no_sanitize can be applied to functions to instruct
the compiler not to do sanitization of the options provided as
arguments to the attribute. Acceptable values for no_sanitize match
those acceptable by the -fsanitize command-line option."

Yes, let's wait for more feedback from buildfarm and fix the version
requirement.

> Once this does settle, should we consider back-patching so that it's
> possible to run alignment checks in the back branches too?

+1

------
Regards,
Alexander Korotkov