As part of the reproducible builds project, the SOURCE_DATE_EPOCH environment variable has been specified as a project- and distribution-independent means to specify a timestamp at build time: https://reproducible-builds.org/specs/source-date-epoch/ Add support for this by converting it to KBUILD_BUILD_TIMESTAMP if they aren't both set. Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- Documentation/kbuild/kbuild.txt | 15 +++++++++------ Makefile | 10 ++++++++++ 2 files changed, 19 insertions(+), 6 deletions(-) diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt index 0ff6a46..9f95228 100644 --- a/Documentation/kbuild/kbuild.txt +++ b/Documentation/kbuild/kbuild.txt @@ -211,12 +211,15 @@ KBUILD_ENABLE_EXTRA_GCC_CHECKS If enabled over the make command line with "W=1", it turns on additional gcc -W... options for more extensive build-time checking. -KBUILD_BUILD_TIMESTAMP --------------------------------------------------- -Setting this to a date string overrides the timestamp used in the -UTS_VERSION definition (uname -v in the running kernel). The value has to -be a string that can be passed to date -d. The default value -is the output of the date command at one point during build. +KBUILD_BUILD_TIMESTAMP, SOURCE_DATE_EPOCH +-------------------------------------------------- +Setting KBUILD_BUILD_TIMESTAMP to a date string overrides the +timestamp used in the UTS_VERSION definition (uname -v in the running +kernel). The value has to be a string that can be passed to date -d. +The default value is the output of the date command at one point +during build. Alternately, the timestamp may be specified in +SOURCE_DATE_EPOCH as the number of whole non-leap seconds since the +epoch. KBUILD_BUILD_USER, KBUILD_BUILD_HOST -------------------------------------------------- diff --git a/Makefile b/Makefile index 1d341eb..bfb0243 100644 --- a/Makefile +++ b/Makefile @@ -417,6 +417,16 @@ export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL export KBUILD_ARFLAGS +ifndef KBUILD_BUILD_TIMESTAMP + # If SOURCE_DATE_EPOCH is set in the environment (only), then + # generate a timestamp string based on that, independent of the + # current time zone and locale. + ifeq ("$(origin SOURCE_DATE_EPOCH)", "environment") + KBUILD_BUILD_TIMESTAMP := $(shell LC_TIME=C date -u -d@$(SOURCE_DATE_EPOCH)) + export KBUILD_BUILD_TIMESTAMP + endif +endif + # When compiling out-of-tree modules, put MODVERDIR in the module # tree rather than in the kernel tree. The kernel tree might # even be read-only. -- Ben Hutchings When in doubt, use brute force. - Ken Thompson
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