gcno directory layout differs from *.gcda files location, e.g.
gcno:
hotspot/server
jdk/java.base/libjava
jdk/java.management/libmanagement

gcda:
hotspot/linux_amd64_compiler2/fastdebug
support/native/java.base/libjava
support/native/java.management/libmanagement

It is unhandy because we need gcda and gcno files in the same directory to generate coverage report.