答:分析以下makefile即可獲取整個過程

以nxp layerscape系統的編譯過程為例

1.分析target/linux/layerscape/image/Makefile的最後一句,這是一個好的開端

$(eval $(call BuildImage))

2.巨集BuildImage定義在哪裡呢?定義在include/image.mk中,簡化後如下

define BuildImage
    ...
    $(foreach device,$(TARGET_DEVICES),$(call Device,$(device))

    install-images: kernel_prepare $(foreach
 
 fs,$(filter-out $(if $(UBIFS_OPTS),,ubifs),$(TARGET_FILESYSTEMS) $(fs-subtypes-y)),$(KDIR)/root.$(fs))
        $(foreach fs,$(TARGET_FILESYSTEMS),
                $(call Image/Build,$(fs))
        )
     ...
endef

3.在巨集定義BuildImage中會由上到下根據依賴依次執行,我們首先關注

$(foreach device,$(TARGET_DEVICES),$(call Device,$(device))

4.巨集Device又定義在哪裡呢?同樣定義在include/image.mk檔案中,定義簡化後如下

define Device
  ...
  $(call Device/$(if $(DUMP),Dump,Build),$(1))

endef

5.此時會執行巨集Device/Dump或巨集Device/Build,那麼以執行巨集Device/Build為例,巨集Device/Build簡化後如下

define Device/Build
  ...

  $$(eval $$(foreach compile,$$(COMPILE), \
    $$(call Device
 
/Build/compile,$$(compile),$(1))))

  $$(eval $$(foreach image,$$(IMAGES), \
    $$(foreach fs,$$(filter $(TARGET_FILESYSTEMS),$$(FILESYSTEMS)), \
      $$(call Device/Build/image,$$(fs),$$(image),$(1)))))
endef

6.接著執行巨集Device/Build/compile和Device/Build/image,這兩個巨集都定義在include/image.mk中,在Device/Build/image會做根檔案系統製作方面的工作