[U-Boot] [RFC PATCH] Makefile: Add SOURCE_DATE_TZ

[Chris Packham]

Along with SOURCE_DATE_EPOCH SOURCE_DATE_TZ can be used to recreate a
build with a specific date timestamp. This allows the verification of
source supplied with a pre-compiled binary.

If SOURCE_DATE_EPOCH is supplied SOURCE_DATE_TZ can be used to specify
what will appear in the output of the version command. If SOURCE_DATE_TZ
is not specified UTC will be used.  SOURCE_DATE_TZ on it's own will not
have an affect.

Signed-off-by: Chris Packham <judge.packham at gmail.com>
---
This is a quick proof of concept that allows some control of how the
timezone is displayed.

 Makefile | 7 ++++---
 README   | 9 ++++++---
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index f75c730..5102a9c 100644
--- a/Makefile
+++ b/Makefile
@@ -1232,9 +1232,10 @@ endef
 define filechk_timestamp.h
 	(if test -n "$${SOURCE_DATE_EPOCH}"; then \
 		SOURCE_DATE="@$${SOURCE_DATE_EPOCH}"; \
-		LC_ALL=C date -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
-		LC_ALL=C date -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \
-		LC_ALL=C date -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
+		SOURCE_TZ="$${SOURCE_DATE_TZ:-UTC}"; \
+		TZ="$${SOURCE_TZ}" LC_ALL=C date -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
+		TZ="$${SOURCE_TZ}" LC_ALL=C date -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \
+		TZ="$${SOURCE_TZ}" LC_ALL=C date -d "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
 	else \
 		LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
 		LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
diff --git a/README b/README
index 1bcb63c..d2e3e94 100644
--- a/README
+++ b/README
@@ -5087,11 +5087,14 @@ Reproducible builds
 In order to achieve reproducible builds, timestamps used in the U-Boot build
 process have to be set to a fixed value.
 
-This is done using the SOURCE_DATE_EPOCH environment variable.
-SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
-option for U-Boot or an environment variable in U-Boot.
+This is done using the SOURCE_DATE_EPOCH and SOURCE_DATE_TZ environment
+variables. These are to be set on the build host's shell, not as a
+configuration option for U-Boot or an environment variable in U-Boot.
 
 SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
+SOURCE_DATE_TZ will default to UTC but can be set to another timezone and is
+used to determine how the date is displayed (tzselect(1) can be used to
+determine an appropriate value).
 
 Building the Software:
 ======================
-- 
2.5.0.rc0