[Gc] libatomic-ops-7.4.0 not compatible with ppc64le architecture

Lennart Sorensen lsorense at csclub.uwaterloo.ca
Fri Dec 20 06:44:38 PST 2013

On Fri, Dec 20, 2013 at 10:48:14AM +0530, Deepak C Shetty wrote:
> On 12/19/2013 03:27 AM, Lennart Sorensen wrote:
> >On Wed, Dec 18, 2013 at 04:30:54PM +0530, Madhu Pavan wrote:
> >>Hi Ivan Maidanski,
> >>
> >>We are in the process of adding support for new arch (ppc64le) and
> >>as part of that we wanted to send patches for config.guess and
> >>configure as appropriate.
> >>
> >>libatomic-ops-7.4.0 could not be built on ppc64le because it had an
> >>outdated configure/config.guess/libtool.m4. Since your pkg uses
> >>libtool and the latest tarball of your pkg didn't build on ppc64le
> >>due to outdated libtool present on your system. We wanted to request
> >>you to upgrade your libtool to the alpha release of libtool which
> >>has all the bits and pieces needed for ppc64le support.
> >>
> >>In that context, I wanted to confirm the below
> >>
> >>1) Should we send patches to 'gc at linux.hpl.hp.com' mailing list or
> >>there is some other mailing list ?
> >>
> >>2) New libtool alpha release which supports ppc64le arch is
> >>available, you may  pick up the alpha release from either of the
> >>below :
> >>
> >>ftp://alpha.gnu.org/gnu/libtool/libtool- (1.6MB)
> >>
> >>ftp://alpha.gnu.org/gnu/libtool/libtool- (920KB)
> >>
> >>It would be great if you can install this new libtool which supports
> >>ppc64le, and spin the pkg and let us know the new tar availability.
> >>We can test it on ppc64le architecture for you. Please let me know
> >>if you are planning to release or spin newer version.
> >>
> >>Currently I used
> >>
> >>https://www.hpl.hp.com/research/linux/atomic_ops/download.php4
> >>
> >>Which does not have ppc64le support.
> >>
> >>Your response is highly appreciated.
> >Well in my experience libatomic-ops doesn't work at all on powerpc,
> >at least if run on a power7.  The testsuite fails.  It seems to somehow
> >get by on power6 and older.  Many things have had bugs exposed by power7
> >since it seems the power7 really relies on the memory model rules of
> >the power architecture in ways previous designs did not.  Use of memory
> >barriers have to be done correctly to work on the power7, otherwise
> >different CPUs will often see different values in memory due to caching.
> Hi Lennart,
>     Thanks for letting us know. We were not aware of it.
> Would you know if someone from community/IBM is looking/working on
> this and/or there is any effort to get this working on Power7
> systems ?

I am not aware of anyone working on it.  I looked at it, but it is beyond
my skill set at this time.  I think given the complexity of doing atomic
ops safely on a multi cpu system, it might need the help of someone at
IBM that really knows the architecture.

I just know about it because we have a power6 and a power7 IBM system
we run Debian on as a build system, and pixman failed the testsuite on
the power7, but passed on the power6.

I have been tempted to "fix" the problem by just putting locks in place
and not caring that it completely defeats the purpose of the library.
At least it would work.

Len Sorensen

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