[RFC, RFT] imagebuilder: introduce Device Tree Blob rebuild option

Wed May 28 08:02:30 PDT 2025

From: Tomasz Maciej Nowak <tmn505 at gmail.com>

Various advanced users have added or modified hardware for OpenWrt
supported boards. Naturally those mods can't be accepted in the
repository, so users of those modifications need to do full buildroot
build. This means almost every addition of package needs another rebuild
and flashing of new firmware complicating already running setup.
Fortunately ImageBuilder has almost all necessary resources to rebuild
Device Tree Blob (DTB), which almost all targets rely on to describe the
hardware. Using ImageBuilder to build modified firmware cuts necessary
time to few minutes. Another benefit is ability to use official package
repository, esspecialy for kmods, which otherwise would conflict with
kernel package hash. Thus I'm introducing this patch applicable directly
on 24.10.x ImageBuilder for ease of testing and comments. This patch is
"would be" result of apllying paches from this tree [1], except
_get_bindings target which downloads SDK to copy matching dt-bindings.
Some devices need kernel+dtb wrapped in some kind of loader, so
REBUILD_DTB option downloads matching toolchain, which alows to recompile
the loader. The REBUILD_DTB option is limited to release artifacts, since
SNAPSHOT(s) artifacts are ephemeral, so using outdated ImageBuilder from
snapshots directory won't cause unnecessary strain on OpenWrt human
resources.

Please test by modifying ImageBuilder dts in (depending on target)

target/linux/(target)/dts
or
build_dir/target-*/linux-(target)/linux-(version)/arch/*/boot/dts

and don't shy commenting on the issues.

I've used these changes for a long time on ath79 or ramips, and because
questions about modifying firmware, which has still full benefit of
official repo packages, pop up frequently, I've decided to share this
and prepare patches for inclusion in official repo after initial test
and comment round.

1. https://github.com/tmn505/openwrt/tree/rebuild-dtb

Signed-off-by: Tomasz Maciej Nowak <tmn505 at gmail.com>
---
 Makefile         | 77 ++++++++++++++++++++++++++++++++++++++++++++++--
 include/image.mk | 11 ++-----
 2 files changed, 77 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index e9e08fb2765b..8ccbb66423b6 100644
--- a/Makefile
+++ b/Makefile
@@ -54,6 +54,15 @@ image:
 	make image DISABLED_SERVICES="<svc1> [<svc2> [<svc3> ..]]" # Which services in /etc/init.d/ should be disabled
 	make image ADD_LOCAL_KEY=1 # store locally generated signing key in built images
 	make image ROOTFS_PARTSIZE="<size>" # override the default rootfs partition size in MegaBytes
+endef
+$(eval $(call shexport,Helptext))
+
+define HelptextRelease
+	make image REBUILD_DTB=1 # force rebuild of Device Tree Blob
+endef
+$(eval $(call shexport,HelptextRelease))
+
+define HelptextContinued
 
 manifest:
 	List "all" packages which get installed into the image.
@@ -77,10 +86,14 @@ package_depends:
 	make package_depends PACKAGE="<pkg>"
 
 endef
-$(eval $(call shexport,Helptext))
+$(eval $(call shexport,HelptextContinued))
 
 help: FORCE
 	echo "$$$(call shvar,Helptext)"
+  ifneq ($(VERSION_NUMBER),SNAPSHOT)
+	echo "$$$(call shvar,HelptextRelease)"
+  endif
+	echo "$$$(call shvar,HelptextContinued)"
 
 
 # override variables from rules.mk
@@ -266,10 +279,12 @@ build_image: FORCE
 	@echo Building images...
 	rm -rf $(BUILD_DIR)/json_info_files/
 	if [ -d "target/linux/feeds/$(BOARD)" ]; then \
-		$(NO_TRACE_MAKE) -C target/linux/feeds/$(BOARD)/image install TARGET_BUILD=1 IB=1 EXTRA_IMAGE_NAME="$(EXTRA_IMAGE_NAME)" \
+		$(NO_TRACE_MAKE) -C target/linux/feeds/$(BOARD)/image install TARGET_BUILD=1 EXTRA_IMAGE_NAME="$(EXTRA_IMAGE_NAME)" \
+			$(if $(REBUILD_DTB),IB=REBUILD_DTB,IB=1) \
 			$(if $(USER_PROFILE),PROFILE="$(USER_PROFILE)"); \
 	else \
-		$(NO_TRACE_MAKE) -C target/linux/$(BOARD)/image install TARGET_BUILD=1 IB=1 EXTRA_IMAGE_NAME="$(EXTRA_IMAGE_NAME)" \
+		$(NO_TRACE_MAKE) -C target/linux/$(BOARD)/image install TARGET_BUILD=1 EXTRA_IMAGE_NAME="$(EXTRA_IMAGE_NAME)" \
+			$(if $(REBUILD_DTB),IB=REBUILD_DTB,IB=1) \
 			$(if $(USER_PROFILE),PROFILE="$(USER_PROFILE)"); \
 	fi
 
@@ -331,9 +346,65 @@ else
 endif
 endif
 
+ifneq ($(VERSION_NUMBER),SNAPSHOT)
+HOST_OS:=$(shell uname)
+HOST_ARCH:=$(shell uname -m)
+TARGET_URL:=$(VERSION_REPO)/targets/$(BOARD)/$(SUBTARGET)
+TOOLCHAIN_NAME:=$(VERSION_DIST_SANITIZED)-toolchain-$(if $(CONFIG_VERSION_FILENAMES),$(VERSION_NUMBER)-)$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))_gcc-$(GCCV)$(DIR_SUFFIX).$(HOST_OS)-$(HOST_ARCH)
+TOOLCHAIN_HASH:=$(shell wget -q -O- $(TARGET_URL)/sha256sums | awk '/$(TOOLCHAIN_NAME)/ {printf $$1}')
+
+_get_toolchain: FORCE
+  ifeq ($(TOOLCHAIN_HASH),)
+	@echo "Cant't obtain checksum for toolchain archive from $(TARGET_URL)/sha256sums"
+	@exit 1
+  else
+	mkdir -p $(DL_DIR)
+	DOWNLOAD_CHECK_CERTIFICATE=1 $(SCRIPT_DIR)/download.pl \
+		$(DL_DIR) \
+		$(TOOLCHAIN_NAME).tar.zst \
+		$(TOOLCHAIN_HASH) \
+		$(TARGET_URL)
+	$(TAR) -x --strip-components=1 \
+		-f $(DL_DIR)/$(TOOLCHAIN_NAME).tar.zst \
+		-C $(TOPDIR)/staging_dir \
+		$(TOOLCHAIN_NAME)/$(TOOLCHAIN_DIR_NAME)
+  endif
+
+SDK_NAME:=$(VERSION_DIST_SANITIZED)-sdk-$(if $(CONFIG_VERSION_FILENAMES),$(VERSION_NUMBER)-)$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))_gcc-$(GCCV)$(DIR_SUFFIX).$(HOST_OS)-$(HOST_ARCH)
+SDK_HASH:=$(shell wget -q -O- $(TARGET_URL)/sha256sums | awk '/$(SDK_NAME)/ {printf $$1}')
+
+_get_bindings: FORCE
+  ifeq ($(SDK_HASH),)
+	@echo "Cant't obtain checksum for sdk archive from $(TARGET_URL)/sha256sums"
+	@exit 1
+  else
+	mkdir -p \
+		$(DL_DIR) \
+		$(LINUX_DIR)/include \
+		$(TMP_DIR)
+	DOWNLOAD_CHECK_CERTIFICATE=1 $(SCRIPT_DIR)/download.pl \
+		$(DL_DIR) \
+		$(SDK_NAME).tar.zst \
+		$(SDK_HASH) \
+		$(TARGET_URL)
+	$(TAR) -x \
+		-f $(DL_DIR)/$(SDK_NAME).tar.zst \
+		-C $(TMP_DIR)
+	$(CP) -L \
+		$(TMP_DIR)/$(SDK_NAME)/build_dir/$(TARGET_DIR_NAME)/linux-$(BOARD)_$(SUBTARGET)/linux-$(LINUX_VERSION)/include/dt-bindings \
+		$(LINUX_DIR)/include
+  endif
+endif
+
 image:
 	$(MAKE) -s _check_profile
 	$(MAKE) -s _check_keys
+  ifneq ($(VERSION_NUMBER),SNAPSHOT)
+    ifeq ($(REBUILD_DTB),1)
+	$(MAKE) -s _get_toolchain
+	$(MAKE) -s _get_bindings
+    endif
+  endif
 	(unset PROFILE FILES PACKAGES MAKEFLAGS; \
 	$(MAKE) -s _call_image \
 		$(if $(PROFILE),USER_PROFILE="$(PROFILE_FILTER)") \
diff --git a/include/image.mk b/include/image.mk
index 9a4dff2167a1..f27f18513eb5 100644
--- a/include/image.mk
+++ b/include/image.mk
@@ -210,7 +210,7 @@ endef
 # $(3) extra CPP flags
 # $(4) extra DTC flags
 define Image/BuildDTB/sub
-	$(TARGET_CROSS)cpp -nostdinc -x assembler-with-cpp \
+	$(if IB,,$(TARGET_CROSS))cpp -nostdinc -x assembler-with-cpp \
 		$(DTS_CPPFLAGS) \
 		-I$(DTS_DIR) \
 		-I$(DTS_DIR)/include \
@@ -662,7 +662,6 @@ define Device/Build/compile
 
 endef
 
-ifndef IB
 define Device/Build/dtb
   ifndef BUILD_DTS_$(1)
   BUILD_DTS_$(1) := 1
@@ -684,7 +683,6 @@ define Device/Build/dtbo
   endif
 
 endef
-endif
 
 define Device/Build/kernel
   $$(eval $$(foreach dts,$$(DEVICE_DTS), \
@@ -705,10 +703,7 @@ define Device/Build/kernel
   $(call Device/Export,$$(KDIR_KERNEL_IMAGE),$(1))
   $(BIN_DIR)/$$(KERNEL_IMAGE): $$(KDIR_KERNEL_IMAGE)
 	cp $$^ $$@
-  ifndef IB
-    ifdef CONFIG_IB
-      install: $$(KDIR_KERNEL_IMAGE)
-    endif
+  ifneq ($(IB),1)
     $$(KDIR_KERNEL_IMAGE): $(KDIR)/$$(KERNEL_NAME) $(CURDIR)/Makefile $$(KERNEL_DEPENDS) image_prepare
 	@rm -f $$@
 	$$(call concat_cmd,$$(KERNEL))
@@ -932,7 +927,7 @@ define BuildImage
   clean:
   image_prepare:
 
-  ifeq ($(IB),)
+  ifneq ($(IB),1)
     .PHONY: download prepare compile compile-dtb clean image_prepare kernel_prepare install install-images
     compile:
 		$(call Build/Compile)
-- 
2.49.0


