[U-Boot] [RFC PATCH] Makefile: search for GNU date

[Andreas Bießmann]

The SOURCE_DATE_EPOCH mechanism for reproducible builds requires the GNU
variant of date. Respect this and search it, error on missing GNU date.

Signed-off-by: Andreas Bießmann <andreas.devel at googlemail.com>
---
This commit tries to figure out if we have a GNU date variant
available. It errors on missing GNU date when it is required (for
SOURCE_DATE_EPOCH set). The result is:

---8<---
abiessmann at punisher % PATH=$ARMv5_PATH:$PATH CROSS_COMPILE=arm-v5te-linux-gnueabi- make SOURCE_DATE_EPOCH="`date -R`" O=/tmp/picosam ARCH=arm include/generated/timestamp_autogenerated.h
make[1]: Entering directory '/tmp/picosam'
/home/abiessmann/src/u-boot/Makefile:1303: *** "No GNU date found".  Stop.
make[1]: Leaving directory '/tmp/picosam'
Makefile:146: recipe for target 'sub-make' failed
make: *** [sub-make] Error 2
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'
--->8---

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

 Makefile | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index b9b2375..95eae64 100644
--- a/Makefile
+++ b/Makefile
@@ -346,6 +346,9 @@ PERL		= perl
 PYTHON		= python
 DTC		= dtc
 CHECK		= sparse
+GNUDATE	       := $(foreach date,gdate date.gnu date, \
+		    $(shell _date=`which $(date)`; \
+		      $${_date} --version 2> /dev/null | $(AWK) "/GNU coreutils/ { print \"$${_date}\"; }"))
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
 		  -Wbitwise -Wno-return-void -D__CHECK_ENDIAN__ $(CF)
@@ -1281,9 +1284,9 @@ 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 "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
+		LC_ALL=C $(GNUDATE) -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
+		LC_ALL=C $(GNUDATE) -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \
+		LC_ALL=C $(GNUDATE) -u -d "$${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"'; \
@@ -1295,6 +1298,11 @@ $(version_h): include/config/uboot.release FORCE
 	$(call filechk,version.h)
 
 $(timestamp_h): $(srctree)/Makefile FORCE
+ifneq ($(strip $(SOURCE_DATE_EPOCH)),)
+ifeq ($(strip $(GNUDATE)),)
+	$(error "No GNU date found")
+endif
+endif
 	$(call filechk,timestamp.h)
 
 # ---------------------------------------------------------------------------
-- 
2.1.4