diff --git a/core/Makefile b/core/Makefile
index f7f6e48..cc54836 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -114,7 +114,7 @@
   ifneq ($(filter eng.%,$(BUILD_NUMBER)),)
     # Trim down BUILD_FINGERPRINT: the default BUILD_NUMBER makes it easily exceed
     # the Android system property length limit (PROPERTY_VALUE_MAX=92).
-    BF_BUILD_NUMBER := $(USER)$(shell date +%m%d%H%M)
+    BF_BUILD_NUMBER := $(USER)$(shell date -d "$(BUILD_DATETIME)" +%m%d%H%M)
   else
     BF_BUILD_NUMBER := $(BUILD_NUMBER)
   endif
@@ -197,6 +197,7 @@
 			PRIVATE_BUILD_DESC="$(PRIVATE_BUILD_DESC)" \
 			BUILD_ID="$(BUILD_ID)" \
 			BUILD_DISPLAY_ID="$(BUILD_DISPLAY_ID)" \
+			BUILD_DATETIME="$(BUILD_DATETIME_FROM_FILE)" \
 			BUILD_NUMBER="$(BUILD_NUMBER_FROM_FILE)" \
 			BOARD_BUILD_SYSTEM_ROOT_IMAGE="$(BOARD_BUILD_SYSTEM_ROOT_IMAGE)" \
 			PLATFORM_VERSION="$(PLATFORM_VERSION)" \
@@ -246,8 +247,8 @@
 	@echo Target vendor buildinfo: $@
 	@mkdir -p $(dir $@)
 	$(hide) echo > $@
-	$(hide) echo ro.vendor.build.date=`date`>>$@
-	$(hide) echo ro.vendor.build.date.utc=`date +%s`>>$@
+	$(hide) echo ro.vendor.build.date=`date -d "$(BUILD_DATETIME_FROM_FILE)"`>>$@
+	$(hide) echo ro.vendor.build.date.utc=`date -d "$(BUILD_DATETIME_FROM_FILE)" +%s`>>$@
 	$(hide) echo ro.vendor.build.fingerprint="$(BUILD_FINGERPRINT_FROM_FILE)">>$@
 endif
 
@@ -262,8 +263,8 @@
 	@echo Target bootimage buildinfo: $@
 	@mkdir -p $(dir $@)
 	$(hide) echo > $@
-	$(hide) echo ro.bootimage.build.date=`date`>>$@
-	$(hide) echo ro.bootimage.build.date.utc=`date +%s`>>$@
+	$(hide) echo ro.bootimage.build.date=`date -d "$(BUILD_DATETIME_FROM_FILE)"`>>$@
+	$(hide) echo ro.bootimage.build.date.utc=`date -d "$(BUILD_DATETIME_FROM_FILE)" +%s`>>$@
 	$(hide) echo ro.bootimage.build.fingerprint="$(BUILD_FINGERPRINT_FROM_FILE)">>$@
 
 # -----------------------------------------------------------------
diff --git a/core/config.mk b/core/config.mk
index fec018b..3b31f80 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 $(OUT_DIR) && \
+    date -d "$(BUILD_DATETIME)" "+%b %_d %Y" > $(OUT_DIR)/build_c_date.txt && \
+    date -d "$(BUILD_DATETIME)" +%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
diff --git a/core/droiddoc.mk b/core/droiddoc.mk
index 417d4fd..37eade6 100644
--- a/core/droiddoc.mk
+++ b/core/droiddoc.mk
@@ -132,7 +132,7 @@
 
 $(full_target): PRIVATE_DOCLETPATH := $(HOST_OUT_JAVA_LIBRARIES)/jsilver$(COMMON_JAVA_PACKAGE_SUFFIX):$(HOST_OUT_JAVA_LIBRARIES)/doclava$(COMMON_JAVA_PACKAGE_SUFFIX)
 $(full_target): PRIVATE_CURRENT_BUILD := -hdf page.build $(BUILD_ID)-$(BUILD_NUMBER_FROM_FILE)
-$(full_target): PRIVATE_CURRENT_TIME :=  -hdf page.now "$$(date "+%d %b %Y %k:%M")"
+$(full_target): PRIVATE_CURRENT_TIME :=  -hdf page.now "$$(date -d "$(BUILD_DATETIME_FROM_FILE)" "+%d %b %Y %k:%M")"
 $(full_target): PRIVATE_CUSTOM_TEMPLATE_DIR := $(LOCAL_DROIDDOC_CUSTOM_TEMPLATE_DIR)
 $(full_target): PRIVATE_IN_CUSTOM_ASSET_DIR := $(LOCAL_DROIDDOC_CUSTOM_TEMPLATE_DIR)/$(LOCAL_DROIDDOC_CUSTOM_ASSET_DIR)
 $(full_target): PRIVATE_OUT_ASSET_DIR := $(out_dir)/$(LOCAL_DROIDDOC_ASSET_DIR)
diff --git a/core/main.mk b/core/main.mk
index b290ce1..87bcd13 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -102,8 +102,11 @@
 # Write the build number to a file so it can be read back in
 # without changing the command line every time.  Avoids rebuilds
 # when using ninja.
-$(shell mkdir -p $(OUT_DIR) && echo -n $(BUILD_NUMBER) > $(OUT_DIR)/build_number.txt)
+$(shell mkdir -p $(OUT_DIR) && \
+    echo -n $(BUILD_NUMBER) > $(OUT_DIR)/build_number.txt && \
+    echo -n "$(BUILD_DATETIME)" > $(OUT_DIR)/build_date.txt)
 BUILD_NUMBER_FROM_FILE := $$(cat $(OUT_DIR)/build_number.txt)
+BUILD_DATETIME_FROM_FILE := $$(cat $(OUT_DIR)/build_date.txt)
 
 # CTS-specific config.
 -include cts/build/config.mk
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index f3b2297..9b2ecf2 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -24,6 +24,7 @@
 #     DEFAULT_APP_TARGET_SDK
 #     BUILD_ID
 #     BUILD_NUMBER
+#     BUILD_DATETIME
 #
 
 # Look for an optional file containing overrides of the defaults,
@@ -89,6 +90,12 @@
   BUILD_ID := UNKNOWN
 endif
 
+ifeq "" "$(BUILD_DATETIME)"
+  # Used to reproduce builds by setting the same time. Must be in a
+  # format understood by `date`
+  BUILD_DATETIME := $(shell date)
+endif
+
 ifeq "" "$(BUILD_NUMBER)"
   # BUILD_NUMBER should be set to the source control value that
   # represents the current state of the source code.  E.g., a
@@ -99,5 +106,5 @@
   # If no BUILD_NUMBER is set, create a useful "I am an engineering build
   # from this date/time" value.  Make it start with a non-digit so that
   # anyone trying to parse it as an integer will probably get "0".
-  BUILD_NUMBER := eng.$(USER).$(shell date +%Y%m%d.%H%M%S)
+  BUILD_NUMBER := eng.$(USER).$(shell date -d "$(BUILD_DATETIME)" +%Y%m%d.%H%M%S)
 endif