Can I use Thread Sanitizer for OpenMP programs?

Question

Consider the following example:

#include <iostream> 

int main () {
    int i = 0;
    #pragma omp parallel
    {
        #pragma omp critical
        {
            ++i;
        }
    }
    std::cout << i;
}

Compiling with g++ -fopenmp -fsanitize=thread and running yields

WARNING: ThreadSanitizer: data race (pid=9576)
Read of size 4 at 0x7ffdc170f600 by thread T1:
#0 main._omp_fn.0 (a.out+0x000000400d20)
#1 gomp_thread_start /build/gcc/src/gcc-5.2.0/libgomp/team.c:118 (libgomp.so.1+0x00000000f42d)

Previous write of size 4 at 0x7ffdc170f600 by thread T2:
#0 main._omp_fn.0 (a.out+0x000000400d35)
#1 gomp_thread_start /build/gcc/src/gcc-5.2.0/libgomp/team.c:118 (libgomp.so.1+0x00000000f42d)

Location is stack of main thread.

Thread T1 (tid=9578, running) created by main thread at:
#0 pthread_create /build/gcc/src/gcc-5.2.0/libsanitizer/tsan/tsan_interceptors.cc:895 (libtsan.so.0+0x000000027a37)
#1 gomp_team_start /build/gcc/src/gcc-5.2.0/libgomp/team.c:796 (libgomp.so.1+0x00000000f98f)
#2 __libc_start_main (libc.so.6+0x00000002060f)

Thread T2 (tid=9579, running) created by main thread at:
#0 pthread_create /build/gcc/src/gcc-5.2.0/libsanitizer/tsan/tsan_interceptors.cc:895 (libtsan.so.0+0x000000027a37)
#1 gomp_team_start /build/gcc/src/gcc-5.2.0/libgomp/team.c:796 (libgomp.so.1+0x00000000f98f)
#2 __libc_start_main (libc.so.6+0x00000002060f)

SUMMARY: ThreadSanitizer: data race ??:0 main._omp_fn.0

As far as I can see, this is a false positive. Is there a way to avoid this?

(Something working with clang and libomp would be fine too.)

You would need to build the OpenMP runtime library with TSAN as well if you want to analyze the code; otherwise add a suppression? — Kerrek SB
– Kerrek SB, Commented Oct 8, 2015 at 0:59
@KerrekSB I was afraid that this is the only answer. Building modern stuff on my Ubuntu 12.04 work machine and getting it to work is not very fun. — Baum mit Augen
– Baum mit Augen ♦, Commented Oct 8, 2015 at 1:06
@KerrekSB Can you elaborate on the suppression stuff? Do I need to do that for every false hit? In our production code, there are many, and if I have to check all of them "by hand", the sanitizer kind of loses its sense. — Baum mit Augen
– Baum mit Augen ♦, Commented Oct 8, 2015 at 1:15
I think you should be able to suppress by code location. I've never done that (the last suppression set I wrote was for Valgrind), but check out the wiki: github.com/google/sanitizers/wiki/ThreadSanitizerSuppressions — Kerrek SB
– Kerrek SB, Commented Oct 8, 2015 at 8:52

jhasse · Accepted Answer · 2019-03-13 16:57:40Z

18

Yes, at least with Clang this is relatively easy. You'll need to build libomp (which Clang uses instead of libgomp) with ThreadSanitizer support. This doesn't take that long:

git clone https://github.com/llvm/llvm-project
cd llvm-project
mkdir build
cd build
cmake -DLIBOMP_TSAN_SUPPORT=1 ../openmp
sudo cmake --build . --target install

(sudo and --target install is optional if you adjust the path to libomp.so below)

Now running your example works without any errors if you use this libomp.so instead of the system one:

clang++ -fsanitize=thread -fopenmp main.cpp
env LD_PRELOAD=/usr/local/lib/libomp.so ./a.out

answered Mar 13, 2019 at 16:57

jhasse

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3 Comments

Cris Luengo Over a year ago

Apparently this only works on Linux with a 64-bit Intel CPU. The CMake script checks if("${CMAKE_SYSTEM_NAME}" MATCHES "Linux" AND ${INTEL64}).

jhasse Over a year ago

INTEL64 will be set for AMD CPUs (or other x86_64 CPUs). See the root CMakeLists.txt of llvm-project

Cris Luengo Over a year ago

Sure. But for me the important bit there was to boot Linux, this unfortunately doesn't work on macOS. I thought it was relevant information to add to the answer. Once I was on Linux, this worked brilliantly! Many thanks!

Simone Atzeni · Accepted Answer · 2016-02-25 06:14:49Z

6

even with the suppression you will still get false positives on the OpenMP runtime because there are some synchronization mechanism within the runtime that Tsan is not able to understand.

We worked on the OpenMP runtime to make Tsan understand this synchronization points and remove all the false positives.

Take a look to this project:

https://github.com/PRUNER/archer

Let me know if you need more help.

Best,

Simone

answered Feb 25, 2016 at 6:14

Simone Atzeni

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1 Comment

Baum mit Augen Over a year ago

Thanks, I'll check it out when I get the chance. Might be a bit though, I'm working on something else now and a colleague does the sanitizer stuff.

Yuri Kashpurovich · Accepted Answer · 2025-11-09 22:26:56Z

0

Just in case someone would search for the answer as me.

As @jhasse said it is really easy with Clang. All you need to do is just to build clang with openmp runtime support, so working set of build commands would be like

git clone https://github.com/llvm/llvm-project
cd llvm-project
mkdir build
cd build
cmake -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_RUNTIMES="openmp;compiler-rt" -DLLVM_TARGETS_TO_BUILD="host" -DLLVM_USE_SANITIZER="" -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr/local/llvm -G "Unix Makefiles" ../llvm

in build directory inside llvm-project one. Then you can also make installation. Or you really can dive into separate OpenMP build.

See also here (there is in-build tool called Archer that was mentioned by @
Simone Atzeni).

edited Nov 9 at 22:26

answered Nov 9 at 22:23

Yuri Kashpurovich

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