On Sat, 11 Apr 2015, Michal Marek wrote: > Dne 11.4.2015 v 15:20 Nicholas Mc Guire napsal(a): > > On Sat, 11 Apr 2015, Jonathan Corbet wrote: > > > >> On Sun, 5 Apr 2015 08:44:28 +0200 > >> Nicholas Mc Guire <hof...@osadl.org> wrote: > >> > >>> KBUILD_BUILD_VERSION is currently not documented but it is > >>> needed when rebuilding a kernel that should result in the identical > >>> binary. This is a brief documentation of KBUILD_BUILD_VERSION. > >> > >> Can we add something like the above to the document itself so that > >> readers have an idea of why they might want to tweak this? > >> > >> Either way, I can take it in the docs tree if that's best..Michal? > >> > > I thought of that but it would be inconsistent as all other descriptions > > here are only the function not the use. > > Most of the entries in this file predate efforts at deterministic > builds, so I'd prefer usefulness over consistency here :-). > > > > I did not find a file where > > the problem of identical rebuild would really fit. > > ... unless, of course, you want to start a new file covering this topic. > Because it's not just the few override variables, but also some options > have to be turned off (I remember CONFIG_GCOV_KERNEL) and the paths must > be the same, or relative paths must be used. > The identical path really only should be needed for GCOV as it compiles path info into the binary - are you aware of any other cnfig option that would need the same path ?
It could be in a short document but it could also just be placed right under the descriptions of the relevant variables - something like: Use of KBUILD_BUILD_{TIMESTAMP,VERSION,USER,HOST} -------------------------------------------------- When the kernel is built, Kbuild stores the build timestamp, version, user and hostname in include/generated/compile.h. By default this information is extracted from the build-environment on every build. To override this behavior and rebuild an identical binary kernel, given a running kernel, the original compile time information needs to be passed to Kbuild. Prerequisites: * Original kernel config available (e.g extract it from /proc/config.gz) * Identical source tree * Identical toolchain * Same source path if building with CONFIG_GCOV_KERNEL * Module signature (CONFIG_MODULE_SIG) must be disabled The build process for rebuilding the identical binary kernel can extract the remaining necessary information from dmesg and set the Kbuild and make env: from the boot log or dmesg in the running system: [ 0.000000] Linux version 4.0.0-rc6-sil2 (hofrat@debian) (gcc version 4.7.2 (Debian 4.7.2-5) ) #0 SMP Mon Apr 6 01:49:56 EDT 2015 ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^ KBUILD_BUILD_VERSION---' | KBUILD_BUILD_TIMESTAMP---------------' $ export KBUILD_BUILD_VERSION=0 $ export KBUILD_BUILD_TIMESTAMP="Mon Apr 6 01:49:56 EDT 2015" $ export KBUILD_BUILD_USER=hofrat $ export KBUILD_BUILD_HOST=debian $ git reset --hard v4.0-rc6 $ zcat /proc/config.gz > .config $ make oldconfig $ make -j 8 EXTRAVERSION=-rc6-sil2 probably not quite sufficient yet - but atleast for defconfigs and a few other trials it worked for me. If that makes sense to cleanup I'll try to figure out what other config options could cause problems and submit it as a patch to kbuild.txt thx! hofrat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/