On Fri, Oct 21, 2022 at 5:00 PM Nicolas Schier <n.schier@xxxxxx> wrote: > > On Thu, Oct 20, 2022 at 06:48:20PM -0700, Dan Li wrote: > > > > > > On 10/20/22 07:05, Bagas Sanjaya wrote: > > > On Thu, Oct 20, 2022 at 03:38:23AM -0700, Dan Li wrote: > > > > diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst > > > > index 071f0151a7a4..13397f38c358 100644 > > > > --- a/Documentation/kbuild/reproducible-builds.rst > > > > +++ b/Documentation/kbuild/reproducible-builds.rst > > > > @@ -119,6 +119,16 @@ To avoid this, you can make the vDSO different for different > > > > kernel versions by including an arbitrary string of "salt" in it. > > > > This is specified by the Kconfig symbol ``CONFIG_BUILD_SALT``. > > > > +Git > > > > +----------------------- > > > > + > > > > +Uncommitted changes or different commit ids in git can also lead > > > > +to different compilation results. For example, after executing > > > > +``git reset HEAD^``, even if the code is the same, the > > > > +``include/config/kernel.release`` generated during compilation > > > > +will be different, which will eventually lead to binary differences. > > > > +See ``scripts/setlocalversion`` for details. > > > > + > > > > > > Briefly read the script, I don't see what the correlation between git > > > reset with LOCALVERSION thing is. Also, does the exact state of git > > > repository required for reproducible builds? > > > > > > > Hi Bagas, > > > > The Makefile has the following code: > > filechk_kernel.release = \ > > echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))" > > > > The output of setlocalversion affects kernel.release, while the output > > of setlocalversion is related to the state of git when the git repository > > exists (see function scm_version). > > > > So changes in git state will result in changes to kernel.release, and > > this information will be included in the final output vmlinux/modules > > and in turn affect reproducible builds. > > > > For example: > > $ git log > > commit 4cd155a93eec...... > > $ make ... > > $ cat include/config/kernel.release > > 6.0.0-rc4-00025-g4cd155a93eec > > > > $ git reset HEAD^ > > $ git log > > commit 7b4d266b0c41...... > > $ make ... > > $ cat include/config/kernel.release > > 6.0.0-rc4-00024-g7b4d266b0c41-dirty > > > > > > AFAICT, in the presence of a git repository, we can compile a reproducible > > build kernel in any git state, but we need to ensure that the git state is > > always the same between compilations (or the same from the perspective of > > the scm_version function). > > yes, that definitely true. Absence or presence of git tags can change > the output of setlocalversion even more drastically. > > I think it is sensible to add a stanza about git in > Documentation/kbuild/reproducible-builds.rst. Make sense. Applied to linux-kbuild. Thanks. -- Best Regards Masahiro Yamada
