[U-Boot] [PATCH v3] Makefile: fix SOURCE_DATE_EPOCH for *BSD host

[Andreas Bießmann]

The SOURCE_DATE_EPOCH mechanism for reproducible builds require some date(1)
with -d switch to print the relevant date and time strings of another point of
time.

In other words it requires some date(1) that behaves like the GNU date(1) [1].
The BSD date(1) [2] on the other hand has the same switch but with a different
meaning.

Respect this and check the date(1) abilities before usage, error on non
working version.  Use the well known pre- and suffixes for the GNU variant of
a tool on *BSD hosts to search for a working date(1) version.

[1] http://man7.org/linux/man-pages/man1/date.1.html [2]
http://www.freebsd.org/cgi/man.cgi?query=date

Signed-off-by: Andreas Bießmann <andreas.devel at googlemail.com>
---
This commit tries to figure out if we have a date variant
available that supports the '-u' and '-d "@0"' switches.
It errors on non-working variants of date.

To respect *BSD host systems search for gdate and date.gnu. Those pre- and
suffixes are widespread used for the GNU variant of a tool also avialable on
*BSD systems.

The result is:

---8<---
abiessmann at punisher % PATH=$ARMv5_PATH:$PATH CROSS_COMPILE=arm-v5te-linux-gnueabi- make O=/tmp/picosam ARCH=arm include/generated/timestamp_autogenerated.h
make[1]: Entering directory '/tmp/picosam'
  CHK     include/generated/timestamp_autogenerated.h
  UPD     include/generated/timestamp_autogenerated.h
make[1]: Leaving directory '/tmp/picosam'
abiessmann at punisher % PATH=$ARMv5_PATH:$PATH CROSS_COMPILE=arm-v5te-linux-gnueabi- make O=/tmp/picosam SOURCE_DATE_EPOCH="$(date +'%s')" ARCH=arm include/generated/timestamp_autogenerated.h
make[1]: Entering directory '/tmp/picosam'
  CHK     include/generated/timestamp_autogenerated.h
/home/abiessmann/src/u-boot/Makefile:1311: recipe for target 'include/generated/timestamp_autogenerated.h' failed
make[1]: *** [include/generated/timestamp_autogenerated.h] Error 42
make[1]: Leaving directory '/tmp/picosam'
Makefile:146: recipe for target 'sub-make' failed
make: *** [sub-make] Error 2
--->8---

It applies on top of http://patchwork.ozlabs.org/patch/506856/ (Makefile: Use correct timezone for U_BOOT_TZ).

Changes in v3:
 * move the check in the timestamp.h generation script
 * remove RFC
 * reword commit message

Changes in v2:
 * check for '-u' and '-d "@0"' switch rather than for the GNU variant

 Makefile | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index e8ea71c..81f12b8 100644
--- a/Makefile
+++ b/Makefile
@@ -1279,12 +1279,24 @@ define filechk_version.h
 	echo \#define LD_VERSION_STRING \"$$($(LD) --version | head -n 1)\"; )
 endef
 
+# The SOURCE_DATE_EPOCH mechanism requires a date that behaves like GNU date.
+# The BSD date on the other hand behaves different and would produce errors
+# with the misused '-d' switch.  Respect that and search a working date with
+# well known pre- and suffixes for the GNU variant of date.
 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 "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
+		DATE=""; \
+		for date in gdate date.gnu date; do \
+			$${date} -u -d "$${SOURCE_DATE}" >/dev/null 2>&1 && DATE="$${date}"; \
+		done; \
+		if test -n "$${DATE}"; then \
+			LC_ALL=C $${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"'; \
+		else \
+			return 42; \
+		fi; \
 	else \
 		LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
 		LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
-- 
2.1.4