Running kunit_tool on unclean trees

[Marcelo Schmitt]

Hi, a friend and I were chasing bug 205219 [1] listed in Bugzilla.
We step into something a little bit different when trying to reproduce
the buggy behavior. In our try, compilation failed with a message form
make asking us to clean the source tree. We couldn't run kunit_tool
after compiling the kernel for x86, as described by Ted in the
discussion pointed out by the bug report.

Steps to reproduce:

0) Run kunit_tool
$ ./tools/testing/kunit/kunit.py run
Works fine with a clean tree.

1) Compile the kernel for some architecture (we did it for x86_64).

2) Run kunit_tool again
$ ./tools/testing/kunit/kunit.py run
Fails with a message form make asking us to clean the source tree.

Removing the clean source tree check from the top-level Makefile gives
us a similar error to what was described in the bug report. We see that
after running `git clean -fdx` kunit_tool runs nicely again. However,
this is not a real solution since some kernel binaries are erased by git.

We also had a look into the commit messages of Masahiro Yamada but
couldn't quite grasp why the check for the tree to be clean was added.
We could invest more time in this issue but actually don't know how to
proceed. We'd be glad to receive any comment about it. We could also try
something else if it's a too hard issue for beginners.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=205219


Best Regards,

Marcelo