segmentation fault when starting offload

Runtimes OpenMP
#1

Hi,
I just built the llvm+clang+openmp on 2 workstations.
One of them works fine but the other one cannot even start a toy code.
Any clue what is going on?

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x00007ffff71cf718 in RTLsTy::LoadRTLs (this=0x7ffff73f82c8 ) at /home/yeluo/opt/llvm-clang/sources/llvm/projects/openmp/libomptarget/src/rtl.cpp:48
#2 0x00007ffff71d7e31 in std::__invoke_impl<void, void (RTLsTy::)(), RTLsTy> (__f=@0x7fffffffda70: (void (RTLsTy::)(RTLsTy * const)) 0x7ffff71cf630 RTLsTy::LoadRTLs(),
__t=@0x7fffffffda68: 0x7ffff73f82c8 ) at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/bits/invoke.h:73
#3 0x00007ffff71d7d92 in std::__invoke<void (RTLsTy::)(), RTLsTy*> (__fn=@0x7fffffffda70: (void (RTLsTy::)(RTLsTy * const)) 0x7ffff71cf630 RTLsTy::LoadRTLs(),
__args=@0x7fffffffda68: 0x7ffff73f82c8 ) at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/bits/invoke.h:95
#4 0x00007ffff71d7d4c in void std::call_once<void (RTLsTy::)(), RTLsTy*>(std::once_flag&, void (RTLsTy::&&)(), RTLsTy&&)::{lambda()#1}::operator()() const (this=0x7fffffffd808)
at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/mutex:672
#5 0x00007ffff71d7d07 in void std::call_once<void (RTLsTy::)(), RTLsTy>(std::once_flag&, void (RTLsTy::&&)(), RTLsTy&&)::{lambda()#2}::operator()() const (this=0x7ffff7dce7b8)
at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/mutex:677
#6 0x00007ffff71d7cd9 in void std::call_once<void (RTLsTy::)(), RTLsTy>(std::once_flag&, void (RTLsTy::&&)(), RTLsTy&&)::{lambda()#2}::__invoke() ()
at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/mutex:677
#7 0x00007ffff6d9e827 in __pthread_once_slow (once_control=0x7ffff73f82c8 , init_routine=0x7ffff7b08760 <__once_proxy>) at pthread_once.c:116
#8 0x00007ffff71d7cab in __gthread_once (__once=0x7ffff73f82c8 , __func=0x7ffff7b08760 <__once_proxy>)
at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/x86_64-linux-gnu/c++/8/bits/gthr-default.h:699
#9 0x00007ffff71d06c4 in std::call_once<void (RTLsTy::)(), RTLsTy> (__once=…, __f=@0x7fffffffda70: (void (RTLsTy::*)(RTLsTy * const)) 0x7ffff71cf630 RTLsTy::LoadRTLs(),
__args=@0x7fffffffda68: 0x7ffff73f82c8 ) at /usr/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/mutex:684
#10 0x00007ffff71cff41 in RTLsTy::RegisterLib (this=0x7ffff73f82c8 , desc=0x4018d0 <.omp_offloading.descriptor>)
at /home/yeluo/opt/llvm-clang/sources/llvm/projects/openmp/libomptarget/src/rtl.cpp:191
#11 0x00007ffff71ce13f in __tgt_register_lib (desc=0x4018d0 <.omp_offloading.descriptor>) at /home/yeluo/opt/llvm-clang/sources/llvm/projects/openmp/libomptarget/src/interface.cpp:74
#12 0x0000000000400d87 in .omp_offloading.descriptor_reg.nvptx64-nvidia-cuda ()
#13 0x000000000040170d in __libc_csu_init ()
#14 0x00007ffff69bfb28 in __libc_start_main (main=0x400ec0 , argc=1, argv=0x7fffffffdbf8, init=0x4016c0 <__libc_csu_init>, fini=, rtld_fini=, stack_end=0x7fffffffdbe8)
at …/csu/libc-start.c:266
#15 0x0000000000400dfa in _start ()

Ye

#2

Null ptr deteference in LoadRTLs suggests maybe the RTL wasn’t found. Are the file systems of these two systems identical?

Jeff

#3

Hi,

can you post your toy code, please?
What is linked into your binary?
rtl.cpp:48 tries to call __kmpc_get_target_offload, which is implemented in libomp.so.

My best guess is that your system fetches a different version of libomp.so, which does not implement this function. So, what is the result of ldd on your binary on both systems?

- Joachim

#4

@Jeff two systems are different.

@Joachim ldd shows that my program was picking up the wrong libomp which was installed via ubuntu package manager.

I just cleaned them up and the code is working fine now.
Thank you Jeff and Joachim

Ye