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

[Johannes Doerfert via cfe-dev]

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
>