A couple of weeks ago, I created a repository of example code for C and C++ courses. The examples include a source file that uses the Threading Building Blocks (oneTBB) library. Since the examples are rather small, I included no Makefile. Instead, I wrote a Bash script using clang++ and a Ninja build file using g++. Strangely, the clang++ build worked, but the g++ version complained about symbols in the linking phase. The linking errors look horrible. Here is the top of the long list of errors (added here for search engines to find the error):
/usr/bin/ld: /tmp/cc4i6mNS.o: in function `tbb::detail::d1::wait_context::add_reference(long)':
parallel_algorithms.cpp:(.text._ZN3tbb6detail2d112wait_context13add_referenceEl[_ZN3tbb6detail2d112wait_context13add_referenceEl]+0x6c): undefined reference to `tbb::detail::r1::notify_waiters(unsigned long)'
/usr/bin/ld: /tmp/cc4i6mNS.o: in function `tbb::detail::d1::execution_slot(tbb::detail::d1::execution_data const&)':
parallel_algorithms.cpp:(.text._ZN3tbb6detail2d114execution_slotERKNS1_14execution_dataE[_ZN3tbb6detail2d114execution_slotERKNS1_14execution_dataE]+0x14): undefined reference to `tbb::detail::r1::execution_slot(tbb::detail::d1::execution_data const*)'
/usr/bin/ld: /tmp/cc4i6mNS.o: in function `tbb::detail::d1::spawn(tbb::detail::d1::task&, tbb::detail::d1::task_group_context&)':
parallel_algorithms.cpp:(.text._ZN3tbb6detail2d15spawnERNS1_4taskERNS1_18task_group_contextE[_ZN3tbb6detail2d15spawnERNS1_4taskERNS1_18task_group_contextE]+0x30): undefined reference to `tbb::detail::r1::spawn(tbb::detail::d1::task&, tbb::detail::d1::task_group_context&)'
/usr/bin/ld: /tmp/cc4i6mNS.o: in function `tbb::detail::d1::execute_and_wait(tbb::detail::d1::task&, tbb::detail::d1::task_group_context&, tbb::detail::d1::wait_context&, tbb::detail::d1::task_group_context&)':
parallel_algorithms.cpp:(.text._ZN3tbb6detail2d116execute_and_waitERNS1_4taskERNS1_18task_group_contextERNS1_12wait_contextES5_[_ZN3tbb6detail2d116execute_and_waitERNS1_4taskERNS1_18task_group_contextERNS1_12wait_contextES5_]+0x2c): undefined reference to `tbb::detail::r1::execute_and_wait(tbb::detail::d1::task&, tbb::detail::d1::task_group_context&, tbb::detail::d1::wait_context&, tbb::detail::d1::task_group_context&)'…
There was no obvious difference between the compiler calls.
g++ -Wall -Werror -Wpedantic -std=c++20 -ltbb -g -O0 -o parallel_algorithms parallel_algorithms.cpp
clang++ -Wall -Werror -Wpedantic -std=c++20 -ltbb -march=native -o parallel_algorithms parallel_algorithms.cpp
After browsing through a lot of search results that don’t explain the problem, I tried to put the -ltbb at the end of the command. If you do this, then everything works fine with g++:
g++ -Wall -Werror -Wpedantic -std=c++20 -g -O0 -o parallel_algorithms parallel_algorithms.cpp -ltbb
🥳 oneTBB doesn’t require much, but its link option has to be at the end of the compiler command. Apparently clang++ does something different when resolving symbols. Good to know.