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Generating coverage reports

With Zephyr, you can generate code coverage reports to analyze which parts of the code are covered by a given test or application.

You can do this in two ways:

  • In a real embedded target or QEMU, using Zephyr’s gcov integration

  • Directly in your host computer, by compiling your application targeting the POSIX architecture

Test coverage reports in embedded devices or QEMU


GCC GCOV is a test coverage program used together with the GCC compiler to analyze and create test coverage reports for your programs, helping you create more efficient, faster running code and discovering untested code paths

In Zephyr, gcov collects coverage profiling data in RAM (and not to a file system) while your application is running. Support for gcov collection and reporting is limited by available RAM size and so is currently enabled only for QEMU emulation of embedded targets.


There are 2 parts to enable this feature. The first is to enable the coverage for the device and the second to enable in the test application. As explained earlier the code coverage with gcov is a function of RAM available. Therefore ensure that the device has enough RAM when enabling the coverage for it. For example a small device like frdm_k64f can run a simple test application but the more complex test cases which consume more RAM will crash when coverage is enabled.

To enable the device for coverage, select CONFIG_HAS_COVERAGE_SUPPORT in the Kconfig.board file.

To report the coverage for the particular test application set CONFIG_COVERAGE.

Steps to generate code coverage reports

These steps will produce an HTML coverage report for a single application.

  1. Build the code with CONFIG_COVERAGE=y.

    west build -b mps2/an385 -- -DCONFIG_COVERAGE=y -DCONFIG_COVERAGE_DUMP=y
  2. Capture the emulator output into a log file. You may need to terminate the emulator with Ctrl-A X for this to complete after the coverage dump has been printed:

    ninja -Cbuild run | tee log.log


    ninja -Cbuild run | tee log.log
  3. Generate the gcov .gcda and .gcno files from the log file that was saved:

    $ python3 scripts/ -i log.log
  4. Find the gcov binary placed in the SDK. You will need to pass the path to the gcov binary for the appropriate architecture when you later invoke gcovr:

    $ find $ZEPHYR_SDK_INSTALL_DIR -iregex ".*gcov"
  5. Create an output directory for the reports:

    $ mkdir -p gcov_report
  6. Run gcovr to get the reports:

    $ gcovr -r $ZEPHYR_BASE . --html -o gcov_report/coverage.html --html-details --gcov-executable <gcov_path_in_SDK>

Coverage reports using the POSIX architecture

When compiling for the POSIX architecture, you utilize your host native tooling to build a native executable which contains your application, the Zephyr OS, and some basic HW emulation.

That means you can use the same tools you would while developing any other desktop application.

To build your application with gcc’s gcov, simply set CONFIG_COVERAGE before compiling it. When you run your application, gcov coverage data will be dumped into the respective gcda and gcno files. You may postprocess these with your preferred tools. For example:

west build -b native_sim samples/hello_world -- -DCONFIG_COVERAGE=y
$ ./build/zephyr/zephyr.exe
# Press Ctrl+C to exit
lcov --capture --directory ./ --output-file -q --rc lcov_branch_coverage=1
genhtml --output-directory lcov_html -q --ignore-errors source --branch-coverage --highlight --legend


You need a recent version of lcov (at least 1.14) with support for intermediate text format. Such packages exist in recent Linux distributions.

Alternatively, you can use gcovr (at least version 4.2).

Coverage reports using Twister

Zephyr’s twister script can automatically generate a coverage report from the tests which were executed. You just need to invoke it with the --coverage command line option.

For example, you may invoke:

$ twister --coverage -p qemu_x86 -T tests/kernel


$ twister --coverage -p native_sim -T tests/bluetooth

which will produce twister-out/coverage/index.html report as well as the coverage data collected by gcovr tool in twister-out/coverage.json.

Other reports might be chosen with --coverage-tool and --coverage-formats command line options.

The process differs for unit tests, which are built with the host toolchain and require a different board:

$ twister --coverage -p unit_testing -T tests/unit

which produces a report in the same location as non-unit testing.

Using different toolchains

Twister looks at the environment variable ZEPHYR_TOOLCHAIN_VARIANT to check which gcov tool to use by default. The following are used as the default for the Twister --gcov-tool argument default:


--gcov-tool value




llvm-cov gcov