[coreboot-gerrit] Change in coreboot[master]: Makefile.inc: Update `build.h` when needed

[Alex Thiessen (Code Review)]

Alex Thiessen has uploaded this change for review. ( https://review.coreboot.org/25685


Change subject: Makefile.inc: Update `build.h` when needed
......................................................................

Makefile.inc: Update `build.h` when needed

Update `build.h` when its content is out of date. This condition depends
on a few parameters, e.g. TIMELESS_BUILD variable or `git` status, so
it's not easy to track the dependencies by means of the usual `make`
prerequisite mechanism. Re-creating `build.h` needlessly every time
would cause a cascade of target updates, which is undesirable.

Create a new temporary `build.h` and check if its content has changed
compared to the existing one. If so, rename the file to `build.h`, else
don't touch `build.h` at all.

Change-Id: Iabd1a1ef78b38dab124944fbc837838daee6155e
Signed-off-by: Alex Thiessen <alex.thiessen.de+coreboot at gmail.com>
---
M Makefile.inc
A util/genbuild_h/genbuild_h_update.sh
2 files changed, 50 insertions(+), 4 deletions(-)



  git pull ssh://review.coreboot.org:29418/coreboot refs/changes/85/25685/1

diff --git a/Makefile.inc b/Makefile.inc
index b11f6e2..264faa1 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -456,11 +456,10 @@
 
 #######################################################################
 # generate build support files
-$(obj)/build.h: .xcompile
+$(obj)/build.h: $(shell util/genbuild_h/genbuild_h_update.sh $(obj)/build.h) \
+		       .xcompile
 	@printf "    GEN        build.h\n"
-	rm -f $(obj)/build.h
-	util/genbuild_h/genbuild_h.sh > $(obj)/build.ht
-	mv $(obj)/build.ht $(obj)/build.h
+	mv $< $@
 
 build-dirs:
 	mkdir -p $(objcbfs) $(objgenerated)
diff --git a/util/genbuild_h/genbuild_h_update.sh b/util/genbuild_h/genbuild_h_update.sh
new file mode 100644
index 0000000..33aa7ac
--- /dev/null
+++ b/util/genbuild_h/genbuild_h_update.sh
@@ -0,0 +1,47 @@
+#!/bin/sh
+
+##
+## This file is part of the coreboot project.
+##
+## Copyright (C) 2018 Alex Thiessen <alex.thiessen.de+coreboot at gmail.com>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; version 3 or later of the License.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## SPDX-License-Identifier: GPL-3.0-or-later
+## <https://spdx.org/licenses/GPL-3.0-or-later.html>
+##
+
+# Purpose of this script is to check if `build.h` is out of date by running
+# `genbuild_h.sh` and comparing its outcome with the existing `build.h`. In case
+# there was a change, file name of the new `build.h` is output so that it can be
+# used as a `make` target prerequisite. Case of missing `build.h` is handled
+# implicitly.
+#
+# Usage: genbuild_h_update.sh FILE
+#        where `FILE` is the name of `build.h`
+#        e.g. `genbuild_h_update.sh build/build.h`
+
+set -e # errexit
+set -u # nounset
+
+BUILD_H=${1}
+
+TMP_BUILD_H=$(mktemp -t "$(basename "${BUILD_H}").XXXXXXXX")
+util/genbuild_h/genbuild_h.sh > "${TMP_BUILD_H}"
+
+if cmp --quiet "${BUILD_H}" "${TMP_BUILD_H}"
+then
+	# same
+	rm "${TMP_BUILD_H}"
+	exit 0
+fi
+
+# different
+echo "${TMP_BUILD_H}"

-- 
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Gerrit-Project: coreboot
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: Iabd1a1ef78b38dab124944fbc837838daee6155e
Gerrit-Change-Number: 25685
Gerrit-PatchSet: 1
Gerrit-Owner: Alex Thiessen <alex.thiessen.de+coreboot at gmail.com>
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