Use repeatable timestamps
This moves all of the date references under build/ to using a single
datetime that can be set manually using BUILD_DATETIME.
It also adds an option, OVERRIDE_C_DATE_TIME, that if set to true, will
redefine __DATE__ and __TIME__ for all C/C++ files so that it matches
BUILD_DATETIME.
Bug: 23117013
Change-Id: I7c17a32b794a5adf40b9cd69136fb0ff9f6084ec
diff --git a/core/config.mk b/core/config.mk
index 876161b..be2340c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -161,6 +161,23 @@
# are specific to the user's build configuration.
include $(BUILD_SYSTEM)/envsetup.mk
+# ---------------------------------------------------------------
+# Allow the C/C++ macros __DATE__ and __TIME__ to be set to the
+# build date and time, so that a build may be repeated.
+# Write the date and time to a file so that the command line
+# doesn't change every time, which would cause ninja to rebuild
+# the files.
+$(shell mkdir -p $(OUT_DIR) && \
+ $(DATE) "+%b %_d %Y" > $(OUT_DIR)/build_c_date.txt && \
+ $(DATE) +%T > $(OUT_DIR)/build_c_time.txt)
+BUILD_DATETIME_C_DATE := $$(cat $(OUT_DIR)/build_c_date.txt)
+BUILD_DATETIME_C_TIME := $$(cat $(OUT_DIR)/build_c_time.txt)
+
+ifeq ($(OVERRIDE_C_DATE_TIME),true)
+COMMON_GLOBAL_CFLAGS += -Wno-builtin-macro-redefined -D__DATE__="\"$(BUILD_DATETIME_C_DATE)\"" -D__TIME__=\"$(BUILD_DATETIME_C_TIME)\"
+COMMON_GLOBAL_CPPFLAGS += -Wno-builtin-macro-redefined -D__DATE__="\"$(BUILD_DATETIME_C_DATE)\"" -D__TIME__=\"$(BUILD_DATETIME_C_TIME)\"
+endif
+
# The build system exposes several variables for where to find the kernel
# headers:
# TARGET_DEVICE_KERNEL_HEADERS is automatically created for the current