| Message ID | 20210612141838.1073085-1-maennich@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set | expand |
On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <maennich@google.com> wrote: > > To avoid unnecessary recompilations, mkcompile_h does not regenerate > compile.h if just the timestamp changed. > Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the > build was requested, in which case we should not ignore it. > > If a user follows the documentation for reproducible builds [1] and > defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean > build will have the correct timestamp. A subsequent cherry-pick (or > amend) changes the commit timestamp and if an incremental build is done > with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken > into consideration. But it should for reproducibility. > > Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore > UTS_VERSION when making a decision about whether the regenerated version > of compile.h should be moved into place. > > [1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html > > Cc: Masahiro Yamada <masahiroy@kernel.org> > Cc: linux-kbuild@vger.kernel.org > Signed-off-by: Matthias Maennich <maennich@google.com> > --- Applied to linux-kbuild. Thanks. > scripts/mkcompile_h | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h > index 4ae735039daf..a72b154de7b0 100755 > --- a/scripts/mkcompile_h > +++ b/scripts/mkcompile_h > @@ -70,15 +70,23 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)" > # Only replace the real compile.h if the new one is different, > # in order to preserve the timestamp and avoid unnecessary > # recompilations. > -# We don't consider the file changed if only the date/time changed. > +# We don't consider the file changed if only the date/time changed, > +# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for > +# reproducible builds with that value referring to a commit timestamp). > # A kernel config change will increase the generation number, thus > # causing compile.h to be updated (including date/time) due to the > # changed comment in the > # first line. > > +if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then > + IGNORE_PATTERN="UTS_VERSION" > +else > + IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED" > +fi > + > if [ -r $TARGET ] && \ > - grep -v 'UTS_VERSION' $TARGET > .tmpver.1 && \ > - grep -v 'UTS_VERSION' .tmpcompile > .tmpver.2 && \ > + grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \ > + grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \ > cmp -s .tmpver.1 .tmpver.2; then > rm -f .tmpcompile > else > -- > 2.32.0.272.g935e593368-goog >
On Thu, Jun 17, 2021 at 10:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <maennich@google.com> wrote: > > > > To avoid unnecessary recompilations, mkcompile_h does not regenerate > > compile.h if just the timestamp changed. > > Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the > > build was requested, in which case we should not ignore it. > > > > If a user follows the documentation for reproducible builds [1] and > > defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean > > build will have the correct timestamp. A subsequent cherry-pick (or > > amend) changes the commit timestamp and if an incremental build is done > > with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken > > into consideration. But it should for reproducibility. > > > > Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore > > UTS_VERSION when making a decision about whether the regenerated version > > of compile.h should be moved into place. > > > > [1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html > > > > Cc: Masahiro Yamada <masahiroy@kernel.org> > > Cc: linux-kbuild@vger.kernel.org > > Signed-off-by: Matthias Maennich <maennich@google.com> > > --- > > > Applied to linux-kbuild. Thanks. > This may not be a big deal, but when KBUILD_BUILD_TIMESTAMP is unset, the timestamp is not updated. It still has a user-specified string.
On Thu, Jun 17, 2021 at 10:43:19AM +0900, Masahiro Yamada wrote: >On Thu, Jun 17, 2021 at 10:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote: >> >> On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <maennich@google.com> wrote: >> > >> > To avoid unnecessary recompilations, mkcompile_h does not regenerate >> > compile.h if just the timestamp changed. >> > Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the >> > build was requested, in which case we should not ignore it. >> > >> > If a user follows the documentation for reproducible builds [1] and >> > defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean >> > build will have the correct timestamp. A subsequent cherry-pick (or >> > amend) changes the commit timestamp and if an incremental build is done >> > with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken >> > into consideration. But it should for reproducibility. >> > >> > Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore >> > UTS_VERSION when making a decision about whether the regenerated version >> > of compile.h should be moved into place. >> > >> > [1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html >> > >> > Cc: Masahiro Yamada <masahiroy@kernel.org> >> > Cc: linux-kbuild@vger.kernel.org >> > Signed-off-by: Matthias Maennich <maennich@google.com> >> > --- >> >> >> Applied to linux-kbuild. Thanks. Thanks! >> > >This may not be a big deal, but when KBUILD_BUILD_TIMESTAMP is unset, >the timestamp is not updated. It still has a user-specified string. I think treating this like any other 'random' prior timestamp is ok. So, I agree: not a big deal. Cheers, Matthias > > > > >-- >Best Regards >Masahiro Yamada
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h index 4ae735039daf..a72b154de7b0 100755 --- a/scripts/mkcompile_h +++ b/scripts/mkcompile_h @@ -70,15 +70,23 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)" # Only replace the real compile.h if the new one is different, # in order to preserve the timestamp and avoid unnecessary # recompilations. -# We don't consider the file changed if only the date/time changed. +# We don't consider the file changed if only the date/time changed, +# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for +# reproducible builds with that value referring to a commit timestamp). # A kernel config change will increase the generation number, thus # causing compile.h to be updated (including date/time) due to the # changed comment in the # first line. +if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then + IGNORE_PATTERN="UTS_VERSION" +else + IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED" +fi + if [ -r $TARGET ] && \ - grep -v 'UTS_VERSION' $TARGET > .tmpver.1 && \ - grep -v 'UTS_VERSION' .tmpcompile > .tmpver.2 && \ + grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \ + grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \ cmp -s .tmpver.1 .tmpver.2; then rm -f .tmpcompile else
To avoid unnecessary recompilations, mkcompile_h does not regenerate compile.h if just the timestamp changed. Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the build was requested, in which case we should not ignore it. If a user follows the documentation for reproducible builds [1] and defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean build will have the correct timestamp. A subsequent cherry-pick (or amend) changes the commit timestamp and if an incremental build is done with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken into consideration. But it should for reproducibility. Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore UTS_VERSION when making a decision about whether the regenerated version of compile.h should be moved into place. [1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: linux-kbuild@vger.kernel.org Signed-off-by: Matthias Maennich <maennich@google.com> --- scripts/mkcompile_h | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)