The may_alias attribute was part of a forward-looking attribute checking, at a
time where few compiler supported them. This explains why they are not widely
used in the library itself. Moreover, as they do not affect the compilation
itself (as your test highlights this is not the issue with the icc 2011.6.233
compiler), there is no urge to remove the may_alias support.
I just got that particular version of the compiler installed on one of our
machines. I'll give it a try over the weekend.
george.
On Oct 7, 2011, at 20:21 , Larry Baker wrote:
> The test for the __may_alias_ attribute uses the following short code snippet:
>
>> int * p_value __attribute__ ((__may_alias__));
>> int
>> main ()
>> {
>>
>> ;
>> return 0;
>> }
>
> Indeed, for Intel 2011 compilers prior to 2011.6.233, this results in a
> warning:
>
>> root@hydra openmpi-1.4.3]# module load compilers/intel/2011.5.220
>> [root@hydra openmpi-1.4.3]# icc -c may_alias_test.c
>> may_alias_test.c(123): warning #1292: attribute "__may_alias__" ignored
>> int * p_value __attribute__ ((__may_alias__));
>> ^
>>
>> [root@hydra openmpi-1.4.3]# module unload compilers/intel/2011.5.220
>
>> [root@hydra openmpi-1.4.3]# module load compilers/intel/2011.6.233
>> [root@hydra openmpi-1.4.3]# icc -c may_alias_test.c
>
>
> I modified ./configure to force
>
>> ompi_cv___attribute__may_alias=0
>
>
> Then I compiled and tested the library. Unfortunately, the results were
> exactly the same:
>
>> make check-TESTS
>> make[3]: Entering directory
>> `/state/partition1/root/src/openmpi-1.4.3/test/datatype'
>> /bin/sh: line 4: 26326 Segmentation fault ${dir}$tst
>> FAIL: checksum
>> /bin/sh: line 4: 26359 Segmentation fault ${dir}$tst
>> FAIL: position
>> ========================================================
>> 2 of 2 tests failed
>> Please report to http://www.open-mpi.org/community/help/
>> ========================================================
>
>
> I could not find any use of the may_alias attribute, other than in a #define
> in opal/include/opal_config_bottom.h. Is OMPI_HAVE_ATTRIBUTE_MAY_ALIAS just
> cruft that can be removed?
>
> Larry Baker
> US Geological Survey
> 650-329-5608
> ba...@usgs.gov
>
> On 7 Oct 2011, at 11:08 AM, Larry Baker wrote:
>
>> I ran into a problem this past week trying to upgrade our OpenMPI 1.4.3 for
>> the latest Intel 2011 compiler, 2011.6.233.
>>
>> make check fails with Segmentation Fault errors:
>>
>>> [root@hydra openmpi-1.4.3]# tail -20 ../openmpi-1.4.3-check-intel.6.233.log
>>> /bin/sh ../../libtool --tag=CC --mode=link icc -DNDEBUG -g -O3
>>> -finline-functions -fno-strict-aliasing -restrict -pthread
>>> -fvisibility=hidden -shared-intel -export-dynamic -shared-intel -o
>>> ddt_pack ddt_pack.o ../../ompi/libmpi.la -lnsl -lutil
>>> libtool: link: icc -DNDEBUG -g -O3 -finline-functions -fno-strict-aliasing
>>> -restrict -pthread -fvisibility=hidden -shared-intel -shared-intel -o
>>> .libs/ddt_pack ddt_pack.o -Wl,--export-dynamic ../../ompi/.libs/libmpi.so
>>> /usr/local/src/openmpi-1.4.3/orte/.libs/libopen-rte.so
>>> /usr/local/src/openmpi-1.4.3/opal/.libs/libopen-pal.so -ldl -lnsl -lutil
>>> -pthread -Wl,-rpath -Wl,/usr/local/lib
>>> make[3]: Leaving directory
>>> `/state/partition1/root/src/openmpi-1.4.3/test/datatype'
>>> make check-TESTS
>>> make[3]: Entering directory
>>> `/state/partition1/root/src/openmpi-1.4.3/test/datatype'
>>> /bin/sh: line 4: 6322 Segmentation fault ${dir}$tst
>>> FAIL: checksum
>>> /bin/sh: line 4: 6355 Segmentation fault ${dir}$tst
>>> FAIL: position
>>> ========================================================
>>> 2 of 2 tests failed
>>> Please report to http://www.open-mpi.org/community/help/
>>> ========================================================
>>> make[3]: *** [check-TESTS] Error 1
>>> make[3]: Leaving directory
>>> `/state/partition1/root/src/openmpi-1.4.3/test/datatype'
>>> make[2]: *** [check-am] Error 2
>>> make[2]: Leaving directory
>>> `/state/partition1/root/src/openmpi-1.4.3/test/datatype'
>>> make[1]: *** [check-recursive] Error 1
>>> make[1]: Leaving directory `/state/partition1/root/src/openmpi-1.4.3/test'
>>> make: *** [check-recursive] Error 1
>>
>>
>> Before trying to track down the problem, I thought I'd describe what I see
>> here in case someone recognizes what might be happening.
>>
>> We have been using OpenMPI 1.4.3 compiled with the Intel 2011.3.174
>> compiler. I've updated the Intel 2011 compilers as they have come out with
>> new versions: 2011.4.191, 2011.5.220, and now 2011.6.233. However, I've not
>> recompiled OpenMPI 1.4.3 until now.
>>
>> Since the original compilation of OpenMPI 1.4.3 with the Intel 2011.3.174
>> compilers, I have installed libnuma and libnuma-devel RPMs on our cluster
>> front end. I noticed that changed the OpenMPI 1.4.3 ./configure output. To
>> test that this was not the cause of the problem, I recompiled OpenMPI 1.4.3
>> using both the CentOS/Rocks GNU compilers and the Intel 2011.3.174
>> compilers. They both passed all the make check tests.
>>
>> To find out when this problem first occurs, I systematically configured,
>> compiled, and checked OpenMPI 1.4.3 with all four versions of the Intel 2011
>> compilers we have. We use the modules package to load the compiler
>> environment:
>>
>>> [root@hydra openmpi-1.4.3]# env | grep /opt/intel
>>> LD_LIBRARY_PATH=/opt/intel/composer_xe_2011_sp1.6.233/compiler/lib/intel64:/opt/intel/composer_xe_2011_sp1.6.233/mkl/lib/intel64
>>> PATH=/opt/intel/composer_xe_2011_sp1.6.233/bin/intel64:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/java/latest/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/opt/eclipse:/opt/ganglia/bin:/opt/ganglia/sbin:/opt/maui/bin:/opt/torque/bin:/opt/torque/sbin:/opt/rocks/bin:/opt/rocks/sbin:/root/bin
>>
>>
>> Here's the steps I use to make and test OpenMPI 1.4.3 (I use a patched
>> version to accommodate the six compilers we have; I've submitted those
>> patches here in the past):
>>
>>> # cd /usr/local/src
>>> # tar -xjf openmpi-1.4.3-patched.tar.bz2
>>> # cd openmpi-1.4.3
>>> # module load compilers/intel/2011.6.233
>>> # ./configure >../openmpi-1.4.3-configure-intel.6.233.log 2>&1 --with-tm
>>> --with-openib --without-valgrind --without-udapl
>>> --enable-contrib-no-build=vt --with-wrapper-ldflags="-shared-intel"
>>> CC="icc" CFLAGS="-g -O3" CXX="icpc" CXXFLAGS="-g -O3" FC="ifort"
>>> FCFLAGS="-g -O3" F77="ifort" FFLAGS="-g -O3" LDFLAGS="-shared-intel"
>>> # make >../openmpi-1.4.3-make-intel.6.233.log 2>&1
>>> # make check >../openmpi-1.4.3-check-intel.6.233.log 2>&1
>>
>> (When I generate the OpenMPI 1.4.3 library we actually use, I also add a
>> --prefix. But, that complicates diff's of the stdout files for these steps,
>> so it is not used here. Thus, I do NOT proceed to make install any of these
>> libraries.)
>>
>> The three earlier versions of the Intel 2011 compilers all pass the make
>> check tests. When I compare the ./configure stdout files, they are all
>> identical. However, the ./configure stdout file for the Intel 2011.6.233
>> compilers has one difference:
>>
>>> [root@hydra openmpi-1.4.3]# diff
>>> ../openmpi-1.4.3-configure-intel.{5.220,6.233}.log
>>> 178c178
>>> < checking for __attribute__(may_alias)... no
>>> ---
>>> > checking for __attribute__(may_alias)... yes
>>
>> That is obviously where I will start looking for the source of the problem.
>>
>> Maybe someone reading this list knows what the purpose of that test is,
>> whether the Intel 2011 compilers are expected to have this feature enabled,
>> and whether the code this enables can cause this problem if the Intel
>> 2011.6.233 compilers do not fully support whatever this test is intended to
>> discern.
>>
>> Larry Baker
>> US Geological Survey
>> 650-329-5608
>> ba...@usgs.gov
>>
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>
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