Fwd: Re: make check-world regress failed

Hi,

Thanks Andres, i686 check-world passed with your
atomic-uint64-alignment.patch.

Vladimir Kokovic
Belgrade Serbia, 9.Jan 2015

------- Forwarded message -------
From: "Andres Freund" <andres(at)2ndquadrant(dot)com>
To: "Heikki Linnakangas" <hlinnakangas(at)vmware(dot)com>
Cc: "Vladimir Koković" <vladimir(dot)kokovic(at)gmail(dot)com>,
"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] make check-world regress failed
Date: Thu, 08 Jan 2015 21:46:35 +0100

On 2014-12-04 16:38:45 +0200, Heikki Linnakangas wrote:
> On 11/23/2014 08:37 PM, Vladimir Koković wrote:
> >PostgreSQL check-world regress failed with current GIT HEAD on my
> Kubuntu
> >14.10.
> >
> >uname -a
> >Linux vlD-kuci 3.16.0-24-generic #32-Ubuntu SMP Tue Oct 28 13:13:18 UTC
> >2014 i686 athlon i686 GNU/Linux
> >
> >gdb -d /home/src/postgresql-devel/postgresql-git/postgresql/src -c core
> >...
> >Loaded symbols for
> >/home/src/postgresql-devel/dev-build/src/test/regress/regress.so
> >(gdb) bt
> >#0 0xb76ecc7c in __kernel_vsyscall ()
> >#1 0xb7075577 in __GI_raise (sig=sig(at)entry=6) at
> >../nptl/sysdeps/unix/sysv/linux/raise.c:56
> >#2 0xb7076cf3 in __GI_abort () at abort.c:89
> >#3 0x084c326a in ?? ()
> >#4 0x0a56c3b8 in ?? ()
> >#5 0xb76d232f in pg_atomic_init_u64 (ptr=0xbfa16fd4, val=0) at
> >/home/src/postgresql-devel/postgresql-git/postgresql/src/include/port/atomics.h:445
> >#6 0xb76d50e4 in test_atomic_uint64 () at
> >/home/src/postgresql-devel/postgresql-git/postgresql/src/test/regress/regress.c:1022
> >#7 0xb76d5756 in test_atomic_ops (fcinfo=0xa57c76c) at
> >/home/src/postgresql-devel/postgresql-git/postgresql/src/test/regress/regress.c:1114
> >#8 0x0825bfee in ?? ()
> >...
>
> Andres, have you had a chance to look at this?

Nope, missed it somehow.

> On 32-bit x86, arch-x86.h leaves PG_HAVE_ATOMIC_U64_SUPPORT undefined.
> But
> generic-gcc.h, which is included later, then defines it.

That's fine. The only reason arch-x86.h implements anything itself is
that that allows older compilers than relying on intrinsics. But
implementing 64bit atomics is too annoying by hand and isn't currently
required.

> pg_atomic_init_u64 does AssertPointerAlignment(ptr, 8) on the variable,
> but
> there is no guarantee that it is 8-bytes aligned on x86.

Hrmpf. Annoying. Gcc for a while claimed that was guaranteed, but, if I
understood the tickets correctly, gave up on that.

Unfortunately we have to rely (IIRC) on that for (quite old) x86s and
some other architectures. It doesn't seem to be a problem on any native
64bit platform, because 64bit variables are 8byte aligned natively
there.

I think it can relatively easily be fixed by something like the
attached. Don't have a pure 32bit environment to test though - the
problem isn't reproducable in a 32bit chroot...

Vladimir, if you apply that patch, do things work for you?

Greetings,

Andres Freund

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