Thanks for the patience.
Here the output diverges from the guide:
$ git bisect start Ubuntu-2.6.38-8.40 Ubuntu-2.6.38-7.39 Switched to branch 'mybisect' Bisecting: a merge base must be tested [521cb40b0c44418a4fd36dc633f575813d59a43d] Linux 2.6.38
Thanks for the patience.
Here the output diverges from the guide:
$ git bisect start Ubuntu-2.6.38-8.40 Ubuntu-2.6.38-7.39 8a4fd36dc633f57 5813d59a43d] Linux 2.6.38
Switched to branch 'mybisect'
Bisecting: a merge base must be tested
[521cb40b0c4441