RE: [PATCH] sbuild: Fix low hit ratio for ccache on linux kernel rebuild

["Moessbauer, Felix" <felix.moessbauer@siemens.com>]

> -----Original Message-----
> From: isar-users@googlegroups.com <isar-users@googlegroups.com> On
> Behalf Of Uladzimir Bely
> Sent: Friday, July 15, 2022 1:27 PM
> To: isar-users@googlegroups.com
> Subject: [PATCH] sbuild: Fix low hit ratio for ccache on linux kernel rebuild
> 
> For some targets defconfig for linux recipe includes option
> CONFIG_DEBUG_INFO that embeds absolute path to the source files into
> compiled binaries.
> 
> While sbuild uses unique directory to place sources for each build by default, it
> happens that ccache hits ration is to small on rebuild.
> 
> This patch makes sbuild use the same build directory for sequential builds. While
> several packages can be built in parallel (e.g. same package for different
> architectures), WORKDIR is used to generate hash part for the build directory of
> sbuild.
> 
> Signed-off-by: Uladzimir Bely <ubely@ilbers.de>
> ---
>  meta/classes/dpkg.bbclass | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/meta/classes/dpkg.bbclass b/meta/classes/dpkg.bbclass index
> b726ea9d..016e46c4 100644
> --- a/meta/classes/dpkg.bbclass
> +++ b/meta/classes/dpkg.bbclass
> @@ -82,6 +82,8 @@ dpkg_runbuild() {
>      sh -c "cd ${WORKDIR}; dpkg-source -q -b ${PPS}"
>      DSC_FILE=$(find ${WORKDIR} -name "${DEB_SOURCE_NAME}*.dsc" -print)
> 
> +    build_path_hash=$(echo "${WORKDIR}" | md5sum | cut -b1-6)
> +
>      sbuild -A -n -c ${SBUILD_CHROOT} --extra-repository="${ISAR_APT_REPO}" \
>          --host=${PACKAGE_ARCH} --build=${SBUILD_HOST_ARCH} ${profiles} \
>          --no-run-lintian --no-run-piuparts --no-run-autopkgtest --resolve-
> alternatives \ @@ -91,6 +93,7 @@ dpkg_runbuild() {
>          --finished-build-commands="cp -n --no-preserve=owner ${deb_dir}/*.deb -t
> ${ext_deb_dir}/ || :" \
>          --finished-build-commands="cp /var/log/dpkg.log
> ${ext_root}/dpkg_partial.log" \
>          --debbuildopts="--source-option=-I" \
> +        --build-path="/build/${PN}-${build_path_hash}" \

This is just a workaround that hides the problem.
Debian takes a lot of care to improve the reproducibility of their packages.
IIRC then reproducibility issues will be treated as bugs from bookworm on.
Could we please do the same and fix the corresponding recipes (like the kernel recipe)?

Please also have a look at the reproducibility section of dpkg-buildflags.
The only reason the kernel is affected from this is, that the kbuild only uses KCFLAGS, not CFLAGS.
At least the flags about reproducibility should be added to all kernel builds done via ISAR.

In short: I'm strictly against this workaround.
Having things that are not reproducible should hurt and not become accepted.

Felix

>          --build-dir=${WORKDIR} --dist="isar" ${DSC_FILE}
> 
>      sbuild_dpkg_log_export "${WORKDIR}/rootfs/dpkg_partial.log"
> --
> 2.20.1
> 
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