From: Matthias Maennich maennich@google.com
[ Upstream commit a979522a1a88556e42a22ce61bccc58e304cb361 ]
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
Signed-off-by: Matthias Maennich maennich@google.com Signed-off-by: Masahiro Yamada masahiroy@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- scripts/mkcompile_h | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h index 87f1fc9801d7..662fe19da990 100755 --- a/scripts/mkcompile_h +++ b/scripts/mkcompile_h @@ -78,15 +78,23 @@ UTS_TRUNCATE="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