gcov -r generates no gcov file - c++

Question

I want to generate a coverage report for my github repo, it's a big C++ project built with CMake.
I add --coverage(equals to -fprofile-arcs -ftest-coverage) option to g++ build and link arguments in my CMakeLists.txt, and I use gcov to generate code coverage data and upload the data to codecov.io.
These automated builds and tests are done in my Jenkins CI. The related code of Jenkins's execute shell is here:
cmake -DCODE_COVERAGE=ON -Dasan=OFF -DNEBULA_ASAN_PRELOAD= ..
make -j8
ctest -j8
#generate code coverage report and upload it to codecov.io
TEST_FILES=$(find . -name '*.cpp.o')
#gcov -abcr $TEST_FILES
for test_file in $TEST_FILES; do gcov -abcr $test_file; done
curl -s https://codecov.io/bash | bash -s - -t c85ebdca-ec7c-4301-a6ed-7967cf175db5
When Jenkins excutes make -j8 and ctest -j8, and gcov -abcr $test_file I do get the related .gcno files, .gcda files, and gcov files. But when Jenkins excutes curl -s https://codecov.io/bash | bash -s - -t c85ebdca-ec7c-4301-a6ed-7967cf175db5 to upload the data files to codecov, the output seems strange. I see a lot of similar errors like:
ExecutionPlan.gcno:'_ZNK6nebula4cpp29ValueType8get_typeEv' has arcs to entry block
ExecutionPlan.gcno:'_ZNK6nebula4cpp29ValueType8get_typeEv' has arcs from exit block
And the -r option of gcov seems doesn't work because I also get a lot of coverage report of system header files.
And at the last the Jenkins tells me the build fails, so I can't see the coverage report in codecov.
Ps:
The source cpp files is not in the same directory with the .cpp.o(CMake's default C++ object type is .cpp.o not .o) files. And I do the above excute shell's code in the build directory, the .gcno, .gcda, and .gcov files are generated in the same directory.
Bucause the CMake's default object type is .cpp.o, the gcno and gcda files type generated is .cpp.gcno and .cpp.gcdas. So I use gcov filename.cpp.o insead of gcov filename.cpp which will tell me couldn't open filename.gcno errors.
I do some experiments to find the reason of errors. I find when I give gcov one input file like gcov 1.cpp.o, I will get no has arcs from exit block errors, but when I give gcov more than one input files like gcov 1.cpp.o 2.cpp.o , I get the errors of has arcs from exit block. I think a probably reason is about combing multiple gcov files.