[ipxe-devel] [PATCH] reproducible timestamp

[Neil Roza]

Hello ipxe-devel,

While I work on a reproducible build-id, there's no reason this patch for a
reproducible timestamp needs to wait for it. Hence, the attached (and below
inlined) patch diff allows a reproducible `BUILD_TIMESTAMP` when the
following criteria are satisfied:

* `git` command is available
* the ipxe source tree is a git checkout
* the git checkout is "clean" (no diff between working tree and index)

If the aforementioned are satisfied, then the `BUILD_TIMESTAMP` is assigned
the Unix timestamp of the HEAD commit. Otherwise, the `BUILD_TIMESTAMP` is
assigned the Unix timestamp of "now"; i.e., heretofore legacy behavior.

Inline diff follows...

diff --git a/src/Makefile.housekeeping b/src/Makefile.housekeeping
index 1dd14794..126a082a 100644
--- a/src/Makefile.housekeeping
+++ b/src/Makefile.housekeeping
@@ -1168,9 +1168,14 @@ blib : $(BLIB)
 #
 BUILD_ID_CMD := perl -e 'printf "0x%08x", int ( rand ( 0xffffffff ) );'

+# assumes first element in MAKEFILE_LIST is src/Makefile:
+IPXE_DIR := $(abspath $(dir $(abspath $(firstword $(MAKEFILE_LIST))))/..)
+
 # Build timestamp
 #
-BUILD_TIMESTAMP := $(shell date +%s)
+BUILD_TIMESTAMP := $(shell git -C $(IPXE_DIR) diff-files --quiet \
+  && git -C $(IPXE_DIR) show -s --format=%ct HEAD \
+  || date +%s)

 # Build version
 #
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