From 9a34ab0fb90494ed36d47a4259d1f3f8490af1ce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Gr=C3=B6ber?= <dxld@darkboxed.org>
Date: Sat, 23 Sep 2023 22:38:18 +0200
Subject: [PATCH] Introduce GIT_EPOCH for getting SOURCE_DATE_EPOCH date in
 tarball

---
 .gitepoch            |  1 +
 Makefile             | 11 +----------
 docs/Makefile        |  5 +++++
 docs/images/Makefile |  4 ++--
 git.mk               | 16 ++++++++++++++++
 5 files changed, 25 insertions(+), 12 deletions(-)
 create mode 100644 .gitepoch
 create mode 100644 git.mk

diff --git a/.gitepoch b/.gitepoch
new file mode 100644
index 00000000000..2707647aacc
--- /dev/null
+++ b/.gitepoch
@@ -0,0 +1 @@
+$Format:%ct$
diff --git a/Makefile b/Makefile
index fa95b7b7035..08cf1d98dc6 100644
--- a/Makefile
+++ b/Makefile
@@ -143,16 +143,7 @@ endif
 
 YOSYS_VER := 0.33+0
 
-# Note: We arrange for .gitcommit to contain the (short) commit hash in
-# tarballs generated with git-archive(1) using .gitattributes. The git repo
-# will have this file in its unexpanded form tough, in which case we fall
-# back to calling git directly.
-TARBALL_GIT_REV := $(shell cat $(YOSYS_SRC)/.gitcommit)
-ifeq ($(TARBALL_GIT_REV),$$Format:%h$$)
-GIT_REV := $(shell GIT_DIR=$(YOSYS_SRC)/.git git rev-parse --short=9 HEAD || echo UNKNOWN)
-else
-GIT_REV := $(TARBALL_GIT_REV)
-endif
+include git.mk #< sets $(GIT_REV)
 
 OBJS = kernel/version_$(GIT_REV).o
 
diff --git a/docs/Makefile b/docs/Makefile
index 2319e1665c3..f18b45dc1f5 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -14,6 +14,11 @@ ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) sou
 # the i18n builder cannot share the environment and doctrees with the others
 I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) source
 
+# Reproducibility
+include ../git.mk #< sets $(GIT_EPOCH)
+export FORCE_SOURCE_DATE ?= 1
+export SOURCE_DATE_EPOCH ?= $(GIT_EPOCH)
+
 .PHONY: help
 help:
 	@echo "Please use \`make <target>' where <target> is one of"
diff --git a/docs/images/Makefile b/docs/images/Makefile
index 5b3c0350c81..497472cf792 100644
--- a/docs/images/Makefile
+++ b/docs/images/Makefile
@@ -21,9 +21,9 @@ dots: $(DOT_PDF)
 tex: $(TEX_PDF)
 svg: $(SVG_OUTPUT)
 
+include ../../git.mk #< sets $(GIT_EPOCH)
 export FORCE_SOURCE_DATE ?= 1
-export SOURCE_DATE_EPOCH ?= 1640991600
-#^ 2022-01-01 00:00:00
+export SOURCE_DATE_EPOCH ?= $(GIT_EPOCH)
 
 011/%.pdf: $(DOT_LOC)/%.dot
 	dot -Tpdf -o $@ $<
diff --git a/git.mk b/git.mk
new file mode 100644
index 00000000000..512d1161d1d
--- /dev/null
+++ b/git.mk
@@ -0,0 +1,16 @@
+GIT_METADATA_DIR := $(dir $(lastword $(MAKEFILE_LIST)))
+
+# Note: We arrange for .gitcommit to contain the (short) commit hash in
+# tarballs generated with git-archive(1) using .gitattributes. The git repo
+# will have this file in its unexpanded form tough, in which case we fall
+# back to calling git directly.
+
+TARBALL_GIT_REV := $(shell cat $(GIT_METADATA_DIR)/.gitcommit)
+ifeq ($(TARBALL_GIT_REV),$$Format:%h$$)
+GIT_REV := $(shell GIT_DIR=$(GIT_METADATA_DIR)/.git git rev-parse --short=9 HEAD || echo UNKNOWN)
+GIT_EPOCH = $(shell GIT_DIR=$(GIT_METADATA_DIR)/.git git show --format=%ct -q || echo 1640991600)
+#^ 1640991600 == 2022-01-01 00:00:00
+else
+GIT_REV := $(TARBALL_GIT_REV)
+GIT_EPOCH = $(shell cat $(GIT_METADATA_DIR)/.gitepoch)
+endif