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 <[email protected]>
Cc: [email protected]
Signed-off-by: Matthias Maennich <[email protected]>
---
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 $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \
cmp -s .tmpver.1 .tmpver.2; then
rm -f .tmpcompile
else
--
2.32.0.272.g935e593368-goog
On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <[email protected]> wrote:
>
> To avoid unnecessary recompilations, mkcompile_h does not regenerate
> compile.h if just the timestamp changed.
> Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the
> build was requested, in which case we should not ignore it.
>
> If a user follows the documentation for reproducible builds [1] and
> defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean
> build will have the correct timestamp. A subsequent cherry-pick (or
> amend) changes the commit timestamp and if an incremental build is done
> with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken
> into consideration. But it should for reproducibility.
>
> Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore
> UTS_VERSION when making a decision about whether the regenerated version
> of compile.h should be moved into place.
>
> [1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html
>
> Cc: Masahiro Yamada <[email protected]>
> Cc: [email protected]
> Signed-off-by: Matthias Maennich <[email protected]>
> ---
Applied to linux-kbuild. Thanks.
> scripts/mkcompile_h | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
> index 4ae735039daf..a72b154de7b0 100755
> --- a/scripts/mkcompile_h
> +++ b/scripts/mkcompile_h
> @@ -70,15 +70,23 @@ UTS_VERSION="$(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
>
--
Best Regards
Masahiro Yamada
On Thu, Jun 17, 2021 at 10:05 AM Masahiro Yamada <[email protected]> wrote:
>
> On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <[email protected]> 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 <[email protected]>
> > Cc: [email protected]
> > Signed-off-by: Matthias Maennich <[email protected]>
> > ---
>
>
> 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.
--
Best Regards
Masahiro Yamada
On Thu, Jun 17, 2021 at 10:43:19AM +0900, Masahiro Yamada wrote:
>On Thu, Jun 17, 2021 at 10:05 AM Masahiro Yamada <[email protected]> wrote:
>>
>> On Sat, Jun 12, 2021 at 11:18 PM Matthias Maennich <[email protected]> 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 <[email protected]>
>> > Cc: [email protected]
>> > Signed-off-by: Matthias Maennich <[email protected]>
>> > ---
>>
>>
>> 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