gcc is executed with the option --coverage.
lcov creates HTML pages containing the source code annotated with
coverage information.

make GCOV=1
make test
make gcov
Look at gcov/html/index.html

v2: declare the weak __gcov_flush
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>