Nathan,

The gcc syntax definitely makes everything but the first string in the asm
optional.
For instance
   asm("nop")
Rather than
  asm("nop" :::)

However xlc appears to be a little bit more restricted by not accepting a
subset of the grammar.

-Paul [Sent from my phone]

On Wednesday, May 4, 2016, Nathan Hjelm <hje...@lanl.gov> wrote:

>
> Go ahead, I don't have access to xlc so I couldn't verify myself. I
> don't fully understand why the last : can be omitted when there are no
> clobbers.
>
> -Nathan
>
> On Wed, May 04, 2016 at 01:34:48PM -0500, Josh Hursey wrote:
> >    Did someone pick this up to merge into master & v2.x?
> >    I can confirm that Paul's patch fixes the issue for XL compilers. I
> didn't
> >    see a PR for it, but can file one if no one has yet.
> >    On Mon, May 2, 2016 at 6:55 PM, Paul Hargrove <phhargr...@lbl.gov
> <javascript:;>> wrote:
> >
> >      It appears that xlc's support for gcc-style inline asm does not
> allow an
> >      empty clobbers list.
> >      The failure I see is
> >      libtool: compile:  xlc -DHAVE_CONFIG_H -I.
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/asm
> >      -I../../opal/include -I../../ompi/include -I../../oshmem/include
> >      -I../../opal/mca/hwloc/hwloc1112/hwloc/include/private/autogen
> >      -I../../opal/mca/hwloc/hwloc1112/hwloc/include/hwloc/autogen
> >      -I../../ompi/mpiext/cuda/c
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2
> >      -I../..
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/orte/include
> >      -I../../orte/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/ompi/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/oshmem/include
> >      -D_REENTRANT
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/mca/hwloc/hwloc1112/hwloc/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/BLD/opal/mca/hwloc/hwloc1112/hwloc/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/mca/event/libevent2022/libevent
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/mca/event/libevent2022/libevent/include
> >
> -I/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/BLD/opal/mca/event/libevent2022/libevent/include
> >      -q64 -g -c
> >
> /home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/asm/asm.c
> >      -Wp,-qmakedep=gcc,-MF.deps/asm.TPlo  -qpic -DPIC -o .libs/asm.o
> >
> "/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/include/opal/sys/powerpc/atomic.h",
> >      line 150.27: 1506-276 (S) Syntax error: possible missing string
> literal?
> >
> "/home/hargrove/SCRATCH/OMPI/openmpi-2.0.0rc2-linux-ppc64-xlc-12.1/openmpi-2.0.0rc2/opal/include/opal/sys/powerpc/atomic.h",
> >      line 239.27: 1506-276 (S) Syntax error: possible missing string
> literal?
> >      make[2]: *** [asm.lo] Error 1
> >      The code corresponding to the first error message is
> >
> >           143  static inline int32_t opal_atomic_ll_32 (volatile int32_t
> >        *addr)
> >           144  {
> >           145     int32_t ret;
> >           146
> >           147     __asm__ __volatile__ ("lwarx   %0, 0, %1  \n\t"
> >           148                           : "=&r" (ret)
> >           149                           : "r" (addr)
> >           150                           :);
> >           151     return ret;
> >           152  }
> >
> >      And the second error is the identical line as it appears in
> >      opal_atomic_ll_64().
> >      The following patch to remove the "trailing" colons was sufficient
> to
> >      fix this problem.
> >      --- openmpi-2.0.0rc2/opal/include/opal/sys/powerpc/atomic.h~
> >       2016-05-02 23:37:13.597782000 +0000
> >      +++ openmpi-2.0.0rc2/opal/include/opal/sys/powerpc/atomic.h
> >      2016-05-02 23:36:11.615404378 +0000
> >      @@ -147,7 +147,7 @@
> >          __asm__ __volatile__ ("lwarx   %0, 0, %1  \n\t"
> >                                : "=&r" (ret)
> >                                : "r" (addr)
> >      -                         :);
> >      +                          );
> >          return ret;
> >       }
> >      @@ -236,7 +236,7 @@
> >          __asm__ __volatile__ ("ldarx   %0, 0, %1  \n\t"
> >                                : "=&r" (ret)
> >                                : "r" (addr)
> >      -                         :);
> >      +                          );
> >          return ret;
> >       }
> >      -Paul
> >      --
> >      Paul H. Hargrove                          phhargr...@lbl.gov
> <javascript:;>
> >      Computer Languages & Systems Software (CLaSS) Group
> >      Computer Science Department               Tel: +1-510-495-2352
> >      Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900
> >      _______________________________________________
> >      devel mailing list
> >      de...@open-mpi.org <javascript:;>
> >      Subscription: https://www.open-mpi.org/mailman/listinfo.cgi/devel
> >      Link to this post:
> >      http://www.open-mpi.org/community/lists/devel/2016/05/18886.php
>
> > _______________________________________________
> > devel mailing list
> > de...@open-mpi.org <javascript:;>
> > Subscription: https://www.open-mpi.org/mailman/listinfo.cgi/devel
> > Link to this post:
> http://www.open-mpi.org/community/lists/devel/2016/05/18906.php
>
>

-- 
Paul H. Hargrove                          phhargr...@lbl.gov
Computer Languages & Systems Software (CLaSS) Group
Computer Science Department               Tel: +1-510-495-2352
Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900

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