xen/docs/misc/coverage.markdown

Coverage support for Xen

Coverare support allow you to get coverage information from Xen execution. You can see how many times a line is executed.

Some compilers have specific options that enable the collection of this information. Every basic block in the code will be instrumented by the compiler to compute these statistics. It should not be used in production as it slows down your hypervisor.

Enable coverage

Test coverage support can be turned on compiling Xen with the coverage option set to y.

Something like:

cd xen
make coverage=y

(or change your .config file).

Extract coverage data

The way GCC and other tools deal with coverage information is to use some files created during build phase (.gcno) and some files produced by executing the program (.gcda). The program in this case is Xen but Xen cannot write files so the way you can use coverage from Xen is extract coverage data from Xen and then split these information into files.

To extract data you use a simple utility called xencov. Mainly xencore allows you to do 3 operations:

• xencov read extract data
• xencov reset reset all coverage counters
• xencov read-reset extract data and reset counters at the same time.

Another utility (xencov_split) is used to split extracted data file into files needed by userspace tools.

Split coverage data

Once you extracted data from Xen, it is time to create files which the coverage tools can understand. To do it you need to run xencov_split utility.

The utility just takes an input file and splits the blob into gcc .gcda files in the same directory that you execute the script. As file names are generated relative to the current directory, it could be a good idea to run the script from / on your build machine.

Code for splitting the blob is put in another utility for some reason:

• It is simpler to maintain a high level script than a C program;
• You don't need to execute on the Xen host so you just need to copy the file to your development box (you usually need development files anyway).

Possible use

This section is just an example on how to use these tools!

This example assumes you compiled Xen from ~/xen-unstable and installed into the host. Consider that if you even recompile Xen you are not able to use blob extracted from xencov!

• Ensure the lcov package is installed

• From the Xen host machine extract the coverage blob

    cd /root
    xencov read coverage.dat
  

• Copy the extracted blob to your dev machine

    cd ~
    scp root@myhost:coverage.dat
  

• Extract the coverage information

    (cd / && xencov_split ~/coverage.dat)
  

• Produce coverage html output

    cd ~/xen-unstable
    rm -rf cov.info cov
    geninfo -o cov.info xen
    mkdir cov
    genhtml -o cov cov.info
  

• See output in a browser

    firefox cov/index.html