I'd like to rebase to a specific commit, not to a HEAD of the other branch:
A --- B --- C master
\
\-- D topic
to
A --- B --- C master
\
\-- D topic
instead of
A --- B --- C master
\
\-- D topic
How can I achieve that?
You can avoid using the --onto parameter by making a temp branch on the commit you like and then use rebase in its simple form:
git branch temp master^
git checkout topic
git rebase temp
git branch -d temp