ubuntu build kernel from git with a source change, how to ignore 'unrepresentable changes to source' error

Question

I have modified a source file in the i915 source code. I have just edited the file and made a change to one line.

I have not made a patch file because I couldn't work out how to do that. When I build with

make -j `getconf _NPROCESSORS_ONLN` deb-pkg LOCALVERSION=-custom

or with

make -j `getconf _NPROCESSORS_ONLN` deb-pkg LOCALVERSION=-custom -i

I get

 update-version-dkms
dpkg-source: info: use the '3.0 (quilt)' format to have separate and documented changes to upstream files, see dpkg-source(1)
dpkg-source: error: unrepresentable changes to source
dpkg-buildpackage: error: dpkg-source -i.git -b ubuntu-bionic subprocess returned exit status 1
scripts/package/Makefile:71: recipe for target 'deb-pkg' failed
make[1]: [deb-pkg] Error 1 (ignored)

Then I committed that change tp a new branch and checked out a standard tag (a standard upstream version). Previously it built. Now it doesn't, same error.

the answer here hints at some bad files (example vim swap files) but I can't work out what the problems may be: "dpkg-source: unrepresentable changes to source" when trying to debuild a modified package does not help me.

Answer 1

Ah, my local changes were a red-herring. somehow a python script got added in part of the source tree, some kind of debugging assistant.

To fix: 1 Following instructions here to remove all non-tracked files from the working tree

https://koukia.ca/how-to-remove-local-untracked-files-from-the-current-git-branch- 571c6ce9b6b1

I did

To remove ignored and non-ignored files, run git clean -f -x or git clean -fx

2. Return to the instructions here: https://wiki.ubuntu.com/KernelTeam/GitKernelBuild

at step 4, copy the config in.

Then it builds.

these are my complete notes. Some of these steps are unnecessary but they don't hurt. Obviously, ignore the cherry-pick.

fakeroot debian/rules clean
cp /boot/config-`uname -r` .config
yes '' | make oldconfig
make clean
#remove the non git files
git clean -f
rm vmlinux-gdb.py
#make sure there is no linux*.tar too
rm ../linux*.gz

#cherry pick RC6 hack
git cherry-pick 0c6b6fa52c6ad54332eed64acb6aebc59f75e0b2

#
make -j `getconf _NPROCESSORS_ONLN` deb-pkg LOCALVERSION=-custom
cd ..