[cfe-dev] Can't compile simple OpenMP code with clang 5.0.0

Tue Dec 22 18:07:09 PST 2020

Yes, it is

The command:

$ clang++ -fopenmp foo.cxx -I/home/../usr/lib/llvm-10/include/openmp/ -L/home/../usr/lib/llvm-10/lib

gives the error:
/usr/bin/ld: cannot find /lib64/libpthread.so.0
/usr/bin/ld: cannot find /usr/lib64/libpthread_nonshared.a
clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)

>Среда, 23 декабря 2020, 5:02 +03:00 от Johannes Doerfert <johannesdoerfert at gmail.com>:
> 
>Ok, closer. is there a symlink from libomp.so to libomp.so.5 in
>/home/../usr/lib/llvm-10/lib ?
>If not, create one. Then try:
>
>clang++ -fopenmp foo.cxx -I/home/../usr/lib/llvm-10/include/openmp/ -L/home/../usr/lib/llvm-10/lib
>
>
>
>On 12/22/20 8:00 PM, Керим Хемраев wrote:
>> $ clang++ -fopenmp foo.cxx
>>
>> gives:
>> foo.cxx:2:10: fatal error: 'omp.h' file not found
>> #include "omp.h"
>>          ^~~~~~~
>> 1 error generated.
>>
>>
>> Then I try:
>>
>> $ clang++ -fopenmp foo.cxx -I/home/../usr/lib/llvm-10/include/openmp/
>>
>> this produces the error:
>> /usr/bin/ld: cannot find -lomp
>> clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
>>
>> The dir:  -I/home/../usr/lib/llvm-10/include/openmp/ contains omp.h
>>
>>> Среда, 23 декабря 2020, 4:56 +03:00 от Johannes Doerfert < johannesdoerfert at gmail.com >:
>>>
>>> -fopenmp will add the -lomp, which will look for libomp.so in your
>>> library path.
>>>
>>> Again, libomp.so versioning is not related to clang versioning.
>>>
>>> What is the output of
>>>
>>> clang++ -fopenmp foo.cxx
>>>
>>>
>>>
>>> On 12/22/20 7:33 PM, Керим Хемраев wrote:
>>>> It seems I know where is my fault (it
>>>>
>>>>
>>>> using clang 5.0 with libomp.so.5 is probably not going to work.
>>>>
>>>> is was very obvious) but I can’t understand how can I link external library to clang.
>>>>
>>>> In the folder  /home/../usr/lib/llvm-10/lib I have a file called  libomp.so.5 (as I understood it is a library of version 5)   and I strongly believe that I need to link this library when parsing commands to clang++:
>>>>
>>>> $ clang++ -fopenmp foo.cxx -I/home/../usr/lib/llvm-10/include/openmp/ -L/home/../usr/lib/llvm-10/lib libomp.so.5
>>>>
>>>> gives me error:
>>>> clang-5.0: error: no such file or directory: 'libomp.so.5'
>>>>
>>>> How to link  libomp.so.5 ? Can’t find it in google yet
>>>>
>>>>
>>>>> Среда, 23 декабря 2020, 2:33 +03:00 от Johannes Doerfert <  johannesdoerfert at gmail.com >:
>>>>>
>>>>> I think libomp is still on version 5.0, (I know, I know).
>>>>> It is not coupled to LLVM wrt. version numbers.
>>>>>
>>>>> Last time I checked, LLVM build for debian (and Ububuntu)
>>>>> came bundled with the OpenMP runtimes (for the host). That
>>>>> means you should not need libomp-5-dev but just clang-10.
>>>>> libomp-5-dev is useful if you *don't* want clang but still
>>>>> target libomp, which is the LLVM OpenMP host runtime, from
>>>>> gcc, thus use it as a replacement of libgomp.
>>>>>
>>>>> All that said, doesn't `clang-10 -fopenmp ...` "just work"?
>>>>>
>>>>> ~ Johannes
>>>>>
>>>>>
>>>>> On 12/22/20 5:28 PM, Керим Хемраев wrote:
>>>>>> Hi Johannes,
>>>>>>
>>>>>> Thank you for response
>>>>>>
>>>>>> It seems that I don’t have   libthread. Moreover it is highly likely that omp.h and libomp.so that I used to provide as parameters to clang are not shipped with clang 5 :)
>>>>>>
>>>>>> I think I should now forget about xeus-cling for a while and simply build the code with latest (or any) version of clang with OpenMP.
>>>>>>
>>>>>> I’ve tried to do the following:
>>>>>> $ sudo apt-get install clang-10
>>>>>> $ sudo apt-get install libomp-5-dev
>>>>>>
>>>>>> Now I want to find where are these packages were installed:
>>>>>> $ find  /usr -iname clang-10
>>>>>> /usr/lib/llvm-10/bin/clang-10
>>>>>> /usr/lib/cmake/clang-10
>>>>>> /usr/share/doc/clang-10
>>>>>> /usr/share/bash-completion/completions/clang-10
>>>>>> /usr/share/lintian/overrides/clang-10
>>>>>> /usr/bin/clang-10
>>>>>>
>>>>>> $ find  /usr -iname libomp-10-dev
>>>>>> /usr/share/doc/libomp-10-dev
>>>>>>
>>>>>> So I’m afraid that  libomp-10-dev  contains only some docs and there is no library   libomp-10-dev.so (or something)
>>>>>>
>>>>>> Could you please guide me how to properly install clang with OpenMP that I could build my test script?
>>>>>>
>>>>>> I’m on Ubuntu  20.04, x64
>>>>>> $ cat /etc/lsb-release
>>>>>> DISTRIB_ID=Ubuntu
>>>>>> DISTRIB_RELEASE=20.04
>>>>>> DISTRIB_CODENAME=focal
>>>>>> DISTRIB_DESCRIPTION="Ubuntu 20.04.1 LTS"
>>>>>>
>>>>>>> Среда, 23 декабря 2020, 0:48 +03:00 от Johannes Doerfert <  johannesdoerfert at gmail.com >:
>>>>>>>
>>>>>>> Hi Kerim,
>>>>>>>
>>>>>>> I tried to help below. Looking at xeus-cling I did not immediately see
>>>>>>> why clang 5 is
>>>>>>> required. If this doesn't work as described below, I might spend time
>>>>>>> trying to get it
>>>>>>> to run with clang 11 ;)
>>>>>>>
>>>>>>> On 12/22/20 1:57 PM, Керим Хемраев via cfe-dev wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> I’m struggling with compiling simple OpenMP program with clang 5.0.0.
>>>>>>>> Here is the code (foo.cxx):
>>>>>>>>
>>>>>>>> #include   "omp.h"
>>>>>>>> #include   <stdio.h>
>>>>>>>> int   main ( void ) {
>>>>>>>>    #pragma   omp   parallel
>>>>>>>>    printf ( "thread %d \n " ,  omp_get_thread_num ());
>>>>>>>> }
>>>>>>>>
>>>>>>>> As I use clang as part of xeus-cling my clang installation is inside conda packages:
>>>>>>>> $ which clang
>>>>>>>> /home/tasik/miniconda3/envs/cling/bin/clang
>>>>>>>>
>>>>>>>> As this clang package does’t have omp.h I provide additional directories to find omp.h and libomp.so
>>>>>>>> To compile the code I use the command:
>>>>>>>> $ clang -fopenmp -I/home/../usr/lib/llvm-10/include/openmp/ -L/home/../usr/lib/llvm-10/lib foo.cxx
>>>>>>>>
>>>>>>>> And I get errors:
>>>>>>>> /usr/bin/ld: cannot find /lib64/libpthread.so.0
>>>>>>>> /usr/bin/ld: cannot find /usr/lib64/libpthread_nonshared.a
>>>>>>>> clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
>>>>>>> The error basically means clang looks for the libthread libraries and
>>>>>>> cannot find them.
>>>>>>> Check on you system where they are and provide the path via -L to clang.
>>>>>>> That might allow
>>>>>>> you to proceed. That said, I don't think you are able to mix clang 5 and
>>>>>>> llvm 10 as you
>>>>>>> do now. The headers and libraries clang might pick up need to be
>>>>>>> consistent (with the clang
>>>>>>> version). At least, you need to make sure `omp.h` and `libomp.so` are
>>>>>>> the ones shipped with
>>>>>>> clang 5.
>>>>>>>
>>>>>>> ~ Johannes
>>>>>>>
>>>>>>>
>>>>>>>> I really need some help to undertand how to work with clang 5.0.0 OpenMP
>>>>>>>> And I think that it is difficult to update clang’s version as xeus-cling requires mentioned 5.0.0 version...
>>>>>>>>
>>>>>>>>
>>>>>>>> With respect,
>>>>>>>> kerim
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> cfe-dev mailing list
>>>>>>>>  cfe-dev at lists.llvm.org
>>>>>>>>  https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>> С уважением,
>>>>>> Керим Хемраев
>>>>>>  kerim.khemraev at mail.ru
>>>>>>
>>>>
>>>> С уважением,
>>>> Керим Хемраев
>>>>  kerim.khemraev at mail.ru
>>>>
>>
>>
>> С уважением,
>> Керим Хемраев
>>  kerim.khemraev at mail.ru
>> 

С уважением,
Керим Хемраев
kerim.khemraev at mail.ru

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