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

Alexey Bataev via cfe-dev cfe-dev at lists.llvm.org
Tue Dec 22 18:21:03 PST 2020 

Just add  -L/usr/lib/llvm-10/lib to your compilation command.

Best regards,
Alexey Bataev

22 дек. 2020 г., в 21:00, Керим Хемраев via cfe-dev <cfe-dev at lists.llvm.org> написал(а):


$ 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</compose?To=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</compose?To=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</compose?To=cfe%2ddev at lists.llvm.org>
>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>
>>> С уважением,
>>> Керим Хемраев
>>> kerim.khemraev at mail.ru</compose?To=kerim.khemraev at mail.ru>
>>>
>
>
> С уважением,
> Керим Хемраев
> kerim.khemraev at mail.ru</compose?To=kerim.khemraev at mail.ru>
>


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

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