From 4ab26a52ef687a42a318d52440e27d0f5a8d6769 Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@openwrt.org>
Date: Wed, 6 Jan 2016 18:38:49 +0000
Subject: [PATCH] build: skip rebuild of kernel images if the source did not
 change

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 48145
---
 include/image.mk           | 14 ++++++--------
 include/kernel-defaults.mk | 16 +++++++++-------
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/image.mk b/include/image.mk
index 053bb08ed2..4eee4adfaf 100644
--- a/include/image.mk
+++ b/include/image.mk
@@ -357,7 +357,7 @@ endef
 
 define Build/kernel-bin
 	rm -f $@
-	cp $^ $@
+	cp $< $@
 endef
 
 define Build/patch-cmdline
@@ -444,6 +444,7 @@ define Device/Init
   KERNEL_INITRAMFS_NAME = $$(KERNEL_NAME)-initramfs
   KERNEL_INSTALL :=
   KERNEL_NAME := vmlinux
+  KERNEL_DEPENDS :=
   KERNEL_SIZE :=
 
   FILESYSTEMS := $(TARGET_FILESYSTEMS)
@@ -468,11 +469,11 @@ define Device/Build/initramfs
   $(call Device/Export,$(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE),$(1))
   $$(_TARGET): $(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE)
 
-  $(KDIR)/$$(KERNEL_INITRAMFS_NAME): image_prepare
+  $(KDIR)/$$(KERNEL_INITRAMFS_NAME):: image_prepare
   $(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE)
 	cp $$^ $$@
 
-  $(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/$$(KERNEL_INITRAMFS_NAME)
+  $(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/$$(KERNEL_INITRAMFS_NAME) $(CURDIR)/Makefile $$(KERNEL_DEPENDS)
 	@rm -f $$@
 	$$(call concat_cmd,$$(KERNEL_INITRAMFS))
 endef
@@ -495,7 +496,7 @@ endef
 
 define Device/Build/kernel
   _KERNEL_IMAGES += $(KDIR)/$$(KERNEL_NAME)
-  $(KDIR)/$$(KERNEL_NAME): image_prepare
+  $(KDIR)/$$(KERNEL_NAME):: image_prepare
   $$(_TARGET): $$(if $$(KERNEL_INSTALL),$(BIN_DIR)/$$(KERNEL_IMAGE))
   $(call Device/Export,$(KDIR)/$$(KERNEL_IMAGE),$(1))
   $(BIN_DIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_IMAGE)
@@ -504,7 +505,7 @@ define Device/Build/kernel
     ifdef CONFIG_IB
       install: $(KDIR)/$$(KERNEL_IMAGE)
     endif
-    $(KDIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_NAME)
+    $(KDIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_NAME) $(CURDIR)/Makefile $$(KERNEL_DEPENDS)
 	@rm -f $$@
 	$$(call concat_cmd,$$(KERNEL))
 	$$(if $$(KERNEL_SIZE),$$(call Device/Build/check_size,$$(KERNEL_SIZE)))
@@ -581,9 +582,6 @@ define BuildImage
   $(foreach device,$(TARGET_DEVICES),$(call Device,$(device)))
   $(foreach fs,$(TARGET_FILESYSTEMS) $(fs-subtypes-y),$(call BuildImage/mkfs,$(fs)))
 
-  $$(sort $$(_KERNEL_IMAGES)):
-	@touch $$@
-
   install: kernel_prepare
 	$(foreach fs,$(TARGET_FILESYSTEMS),
 		$(call Image/Build,$(fs))
diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index f3b5e421d1..052b2b3a7b 100644
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -138,13 +138,15 @@ IMAGES_DIR:=../../x86/boot
 endif
 
 define Kernel/CopyImage
-	$(KERNEL_CROSS)objcopy -O binary $(OBJCOPY_STRIP) -S $(LINUX_DIR)/vmlinux $(LINUX_KERNEL)$(1)
-	$(KERNEL_CROSS)objcopy $(OBJCOPY_STRIP) -S $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).elf
-	$(CP) $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux.debug
-	$(foreach k, \
-		$(if $(KERNEL_IMAGES),$(KERNEL_IMAGES),$(filter-out dtbs,$(KERNELNAME))), \
-		$(CP) $(LINUX_DIR)/arch/$(LINUX_KARCH)/boot/$(IMAGES_DIR)/$(k) $(KERNEL_BUILD_DIR)/$(k)$(1); \
-	)
+	cmp -s $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).debug || { \
+		$(KERNEL_CROSS)objcopy -O binary $(OBJCOPY_STRIP) -S $(LINUX_DIR)/vmlinux $(LINUX_KERNEL)$(1); \
+		$(KERNEL_CROSS)objcopy $(OBJCOPY_STRIP) -S $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).elf; \
+		$(CP) $(LINUX_DIR)/vmlinux $(KERNEL_BUILD_DIR)/vmlinux$(1).debug; \
+		$(foreach k, \
+			$(if $(KERNEL_IMAGES),$(KERNEL_IMAGES),$(filter-out dtbs,$(KERNELNAME))), \
+			$(CP) $(LINUX_DIR)/arch/$(LINUX_KARCH)/boot/$(IMAGES_DIR)/$(k) $(KERNEL_BUILD_DIR)/$(k)$(1); \
+		) \
+	}
 endef
 
 define Kernel/CompileImage/Default