These binary packages represent builds of the mainline or stable Linux kernel tree at the commit below:
v3.12.40 (129ea38d9c66e0df4556168b1c57a9119c157d9a)
To obtain the source from which they are built fetch the commit below:
git://git.launchpad.net/~ubuntu-kernel-test/ubuntu/+source/linux/+git/mainline-crack v3.12.40
and apply the following patches on top in the order below:
0001-base-packaging.patch
0002-debian-changelog.patch
0003-configs-based-on-Ubuntu-3.12.0-2.7.patch
This is summarised in the SOURCES file included with these binaries.
For further information see: http://wiki.ubuntu.com/Kernel/MainlineBuilds