Kernel Coverage Testing

This example will explain how gcov can be used to get coverage traces of specific drivers.

Building the kernel

The kernel must be built with certain configurations and enabled and certain Makefiles updated so the specific driver is selected for coverage monitoring. For complete doc look at the kernel.org doc .

In short, configure the kernel with:

CONFIG_DEBUG_FS=y
CONFIG_GCOV_KERNEL=y

select the gcc’s gcov format, default is autodetect based on gcc version:

CONFIG_GCOV_FORMAT_AUTODETECT=y

To select specific drivers or folders update the necessary Makefiles as:

• For a single file (e.g. main.o):

  GCOV_PROFILE_main.o := y
  

• For all files in one directory:

  GCOV_PROFILE := y
  

To exclude files from being profiled even when CONFIG_GCOV_PROFILE_ALL is specified, use:

GCOV_PROFILE_main.o := n

and:

GCOV_PROFILE := n

Only files which are linked to the main kernel image or are compiled as kernel modules are supported by this mechanism.

Collecting logs and generating HTML reports

Once the remote kernel is booted and tests have been run. To collect the gcov traces and to generate the HTML report use the CLI API:

nebula coverage.kernel --ip <ip of DUT> --linux_build_dir <Build directory of kernel>

This will create a directory called html with the generated html report.

Note

For the reports to be generated correctly the necessary compiler must be on path which was used to build the kernel and lcov must be installed.