[U-Boot] [PATCH] Reproducible U-Boot build support, using SOURCE_DATE_EPOCH

[Paul Kocialkowski]

In order to achieve reproducible builds in U-Boot, timestamps that are defined
at build-time have to be somewhat eliminated. The SOURCE_DATE_EPOCH environment
variable allows setting a fixed value for those timestamps.

Simply by setting SOURCE_DATE_EPOCH to a fixed value, a number of targets can be
built reproducibly. This is the case for e.g. sunxi devices.

However, some other devices might need some more tweaks, especially regarding
the image generation tools.

Signed-off-by: Paul Kocialkowski <contact at paulk.fr>
---
 Makefile              |  7 ++++---
 tools/default_image.c | 21 ++++++++++++++++++++-
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 37cc4c3..71aeac7 100644
--- a/Makefile
+++ b/Makefile
@@ -1231,9 +1231,10 @@ define filechk_version.h
 endef
 
 define filechk_timestamp.h
-	(LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
-	LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
-	LC_ALL=C date +'#define U_BOOT_TZ "%z"')
+	(SOURCE_DATE="$${SOURCE_DATE_EPOCH:+@$$SOURCE_DATE_EPOCH}"; \
+	LC_ALL=C date -u -d "$${SOURCE_DATE:-now}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
+	LC_ALL=C date -u -d "$${SOURCE_DATE:-now}" +'#define U_BOOT_TIME "%T"'; \
+	LC_ALL=C date -u -d "$${SOURCE_DATE:-now}" +'#define U_BOOT_TZ "%z"' )
 endef
 
 $(version_h): include/config/uboot.release FORCE
diff --git a/tools/default_image.c b/tools/default_image.c
index cf5c0d4..18940af 100644
--- a/tools/default_image.c
+++ b/tools/default_image.c
@@ -88,6 +88,9 @@ static void image_set_header(void *ptr, struct stat *sbuf, int ifd,
 				struct image_tool_params *params)
 {
 	uint32_t checksum;
+	char *source_date_epoch;
+	struct tm *time_universal;
+	time_t time;
 
 	image_header_t * hdr = (image_header_t *)ptr;
 
@@ -96,9 +99,25 @@ 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");
+	if (source_date_epoch != NULL) {
+		time = (time_t) strtol(source_date_epoch, NULL, 10);
+
+		time_universal = gmtime(&time);
+		if (time_universal == NULL) {
+			fprintf(stderr, "%s: SOURCE_DATE_EPOCH is not valid\n",
+				__func__);
+			time = 0;
+		} else {
+			time = mktime(time_universal);
+		}
+	} else {
+		time = sbuf->st_mtime;
+	}
+
 	/* Build new header */
 	image_set_magic(hdr, IH_MAGIC);
-	image_set_time(hdr, sbuf->st_mtime);
+	image_set_time(hdr, time);
 	image_set_size(hdr, sbuf->st_size - sizeof(image_header_t));
 	image_set_load(hdr, params->addr);
 	image_set_ep(hdr, params->ep);
-- 
1.9.1