Respect SOURCE_DATE_EPOCH when building FIT images.

Embedding timestamps in FIT images results in unreproducible builds
for targets that generate a fit image, such as dra7xx_evm.

This patch uses the SOURCE_DATE_EPOCH environment variable, when set,
to use specified value for the date.

Thanks to HW42 for debugging the issue and providing the patch:

  https://lists.alioth.debian.org/pipermail/reproducible-builds/Week-of-Mon-20160606/005722.html

For more information about reproducible builds and the
SOURCE_DATE_EPOCH specification:

  https://reproducible-builds.org/specs/source-date-epoch/
  https://reproducible-builds.org/

Signed-off-by: Vagrant Cascadian <vagrant@debian.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

tools/default_image.c

@@ -88,7 +88,6 @@ static void image_set_header(void *ptr, struct stat *sbuf, int ifd,
 				struct image_tool_params *params)
 {
 	uint32_t checksum;
-	char *source_date_epoch;
 	time_t time;
 
 	image_header_t * hdr = (image_header_t *)ptr;
@@ -98,18 +97,7 @@ static void image_set_header(void *ptr, struct stat *sbuf, int ifd,
 				sizeof(image_header_t)),
 			sbuf->st_size - sizeof(image_header_t));
 
-	source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+	time = imagetool_get_source_date(params, sbuf->st_mtime);
-	if (source_date_epoch != NULL) {
-		time = (time_t) strtol(source_date_epoch, NULL, 10);
-
-		if (gmtime(&time) == NULL) {
-			fprintf(stderr, "%s: SOURCE_DATE_EPOCH is not valid\n",
-				__func__);
-			time = 0;
-		}
-	} else {
-		time = sbuf->st_mtime;
-	}
 
 	/* Build new header */
 	image_set_magic(hdr, IH_MAGIC);

tools/fit_image.c

@@ -51,8 +51,10 @@ static int fit_add_file_data(struct image_tool_params *params, size_t size_inc,
 	}
 
 	/* for first image creation, add a timestamp at offset 0 i.e., root  */
-	if (params->datafile)
+	if (params->datafile) {
-		ret = fit_set_timestamp(ptr, 0, sbuf.st_mtime);
+		time_t time = imagetool_get_source_date(params, sbuf.st_mtime);
+		ret = fit_set_timestamp(ptr, 0, time);
+	}
 
 	if (!ret) {
 		ret = fit_add_verification_data(params->keydir, dest_blob, ptr,

tools/imagetool.c

@@ -115,3 +115,23 @@ int imagetool_get_filesize(struct image_tool_params *params, const char *fname)
 
 	return sbuf.st_size;
 }
+
+time_t imagetool_get_source_date(
+	 struct image_tool_params *params,
+	 time_t fallback)
+{
+	char *source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+
+	if (source_date_epoch == NULL)
+		return fallback;
+
+	time_t time = (time_t) strtol(source_date_epoch, NULL, 10);
+
+	if (gmtime(&time) == NULL) {
+		fprintf(stderr, "%s: SOURCE_DATE_EPOCH is not valid\n",
+			params->cmdname);
+		time = 0;
+	}
+
+	return time;
+}

tools/imagetool.h

@@ -206,6 +206,22 @@ int imagetool_save_subimage(
  */
 int imagetool_get_filesize(struct image_tool_params *params, const char *fname);
 
+/**
+ * imagetool_get_source_date() - Get timestamp for build output.
+ *
+ * Gets a timestamp for embedding it in a build output. If set
+ * SOURCE_DATE_EPOCH is used. Else the given fallback value is returned. Prints
+ * an error message if SOURCE_DATE_EPOCH contains an invalid value and returns
+ * 0.
+ *
+ * @params:	mkimage parameters
+ * @fallback:	timestamp to use if SOURCE_DATE_EPOCH isn't set
+ * @return timestamp based on SOURCE_DATE_EPOCH
+ */
+time_t imagetool_get_source_date(
+	struct image_tool_params *params,
+	time_t fallback);
+
 /*
  * There is a c file associated with supported image type low level code
  * for ex. default_image.c, fit_image.c