Reproducible U-Boot build support, using SOURCE_DATE_EPOCH
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@paulk.fr>
diff --git a/README b/README
index 4e0ff9f..1bcb63c 100644
--- a/README
+++ b/README
@@ -5081,6 +5081,18 @@
- CONFIG_SYS_MEM_TOP_HIDE_MIN
Define minimum DDR size to be hided from top of the DDR memory
+Reproducible builds
+-------------------
+
+In order to achieve reproducible builds, timestamps used in the U-Boot build
+process have to be set to a fixed value.
+
+This is done using the SOURCE_DATE_EPOCH environment variable.
+SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
+option for U-Boot or an environment variable in U-Boot.
+
+SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
+
Building the Software:
======================