HOW TO COLLECT KERNEL CODE COVERAGE FROM A TEST RUN

1. Build and use a kernel with GCOV profile enabled

Build and install with scripts

Build and install a GCOV kernel on a Cuttlefish or physical device with one of the following commands:

$ kernel/tests/tools/launch_cvd.sh --gcov

$ kernel/tests/tools/flash_device.sh --gcov

To view available options, run the scripts with --help.

Build on your own

Build a kernel with --gcov option. This will also trigger the build to save the required *.gcno files needed to viewing the collected count data.

For example, build a Cuttlefish kernel with GCOV:

$ tools/bazel run --gcov //common-modules/virtual-device:virtual_device_x86_64_dist

2. Run tests with kernel coverage collection enabled

run_test_only.sh

Collect test coverage data with run_test_only.sh --gcov and the required options. For example,

$ kernel/tests/tools/run_test_only.sh --gcov \
    --serial 0.0.0.0:6520 --test='selftests kselftest_net_socket'

To view available options, run the script with --help.

tradefed.sh

Adding the appropriate coverage flags to the tradefed call will trigger it to take care of mounting debugfs, reseting the gcov counts prior to test run, and collecting gcov data files from debugfs after test completion. These coverage arguments are:

--coverage --coverage-toolchain GCOV_KERNEL --auto-collect GCOV_KERNEL_COVERAGE

The following is a full example call running just the kselftest_net_socket test in the selftests test suite that exists under the out/tests/testcases directory. The artifact output has been redirected to tf-logs for easier reference needed in the next step.

$ prebuilts/tradefed/filegroups/tradefed/tradefed.sh run commandAndExit \
    template/local_min --template:map test=suite/test_mapping_suite     \
    --include-filter 'selftests kselftest_net_socket'                   \
    --tests-dir=out/tests/testcases                                     \
    --primary-abi-only --log-file-path tf-logs                          \
    --coverage --coverage-toolchain GCOV_KERNEL                         \
    --auto-collect GCOV_KERNEL_COVERAGE

3. Create an lcov tracefile out of the gcov tar artifact from test run

The previously mentioned run_test_only.sh or tradefed.sh run will produce a tar file artifact in the log folder with a name like <test>_kernel_coverage_*.tar.gz. This tar file is an archive of all the gcov data files collected into debugfs from the profiled device. In order to make it easier to work with this data, it needs to be converted to a single lcov tracefile.

The script create-tracefile.py facilitates this generation by handling the required unpacking, file path corrections and ultimate lcov call. run_test_only.sh calls create-tracefile.py automatically if it can locate the kernel source. Otherwise, it shows the arguments for you to run create-tracefile.py in the kernel source tree.

If you use tradefed.sh, you need to issue the create-tracefile.py command. The following is an example where we generate a tracefile named cov.info only including results from net/socket.c. (If no source files are specified as included, then all source file data is used.)

$ kernel/tests/tools/create-tracefile.py -t tf-logs --include net/socket.c

4. Visualizing results

With the created tracefile, there are a number of different ways to view coverage data from it. Check out man lcov for more options.

Summary

$ lcov --summary --rc lcov_branch_coverage=1 cov.info
Reading tracefile cov.info_fix
Summary coverage rate:
  lines......: 6.0% (81646 of 1370811 lines)
  functions..: 9.6% (10285 of 107304 functions)
  branches...: 3.7% (28639 of 765538 branches)

List

$ lcov --list --rc lcov_branch_coverage=1 cov.info
Reading tracefile cov.info_fix
                                               |Lines      |Functions|Branches
Filename                                       |Rate    Num|Rate  Num|Rate   Num
================================================================================
[/usr/local/google/home/joefradley/dev/common-android-mainline-2/common/]
arch/x86/crypto/aesni-intel_glue.c             |23.9%   623|22.2%  36|15.0%  240
arch/x86/crypto/blake2s-glue.c                 |50.0%    28|50.0%   2|16.7%   30
arch/x86/crypto/chacha_glue.c                  | 0.0%   157| 0.0%  10| 0.0%   80
<truncated>
virt/lib/irqbypass.c                           | 0.0%   137| 0.0%   6| 0.0%   88
================================================================================
                                         Total:| 6.0% 1369k| 9.6%  0M| 3.7% 764k

HTML

The lcov tool genhtml is used to generate html. To create html with the default settings:

$ genhtml --branch-coverage -o html cov.info

The page can be viewed at html/index.html.

Options of interest:

• --frame: Creates a left hand macro view in a source file view.
• --missed: Helpful if you want to sort by what source is missing the most as opposed to the default coverage percentages.