U-BOOT移植过程详解: 附录

 

申明

  本着学习交流的原则, 将个人移植u-boot的过程做一个记录. 文章参考了csdn blog里面的很多内容, 有的已经记不得出处了, 只好把当时的摘要直接贴出来. 如果冒犯, 还请见谅. 如有侵权, 请与我邮件联系. 谢谢!

autoconf.mk

uboot的顶层Makefile中有如下的一段代码

#
# Auto-generate the autoconf.mk file (which is included by all makefiles)
#
# This target actually generates 2 files; autoconf.mk and autoconf.mk.dep.
# the dep file is only include in this top level makefile to determine when
# to regenerate the autoconf.mk file.
$(obj)include/autoconf.mk.dep: $(obj)include/config.h include/common.h
    @$(XECHO) Generating $@ ; \
    set -e ; \
    : Generate the dependancies ; \
    $(CC) -x c -DDO_DEPS_ONLY -M $(CFLAGS) $(CPPFLAGS) \
        -MQ $(obj)include/autoconf.mk include/common.h > $@

$(obj)include/autoconf.mk: $(obj)include/config.h
    @$(XECHO) Generating $@ ; \
    set -e ; \
    : Extract the config macros ; \
    $(CPP) $(CFLAGS) -DDO_DEPS_ONLY -dM include/common.h | \
        sed -n -f tools/scripts/define2mk.sed > [email protected] && \
    mv [email protected] $@

#
# Auto-generate the autoconf.mk file (which is included by all makefiles)
#
# This target actually generates 2 files; autoconf.mk and autoconf.mk.dep.
# the dep file is only include in this top level makefile to determine when
# to regenerate the autoconf.mk file.
$(obj)include/autoconf.mk.dep: $(obj)include/config.h include/common.h
	@$(XECHO) Generating $@ ; \
	set -e ; \
	: Generate the dependancies ; \
	$(CC) -x c -DDO_DEPS_ONLY -M $(CFLAGS) $(CPPFLAGS) \
		-MQ $(obj)include/autoconf.mk include/common.h > $@

$(obj)include/autoconf.mk: $(obj)include/config.h
	@$(XECHO) Generating $@ ; \
	set -e ; \
	: Extract the config macros ; \
	$(CPP) $(CFLAGS) -DDO_DEPS_ONLY -dM include/common.h | \
		sed -n -f tools/scripts/define2mk.sed > [email protected] && \
	mv [email protected] $@

先看第一个:  $(obj)include/autoconf.mk.dep: $(obj)include/config.h include/common.h , 它表示autoconf.mk.dep依赖于config.h和common.h这两个文件.

• @$(XECHO) Generating $@ ; \ 这句话会在编译阶段输出编译信息 Generating include/autoconf.mk.dep
  
• set -e ; \ 这句话表示, 当下面命令返回值不会0时, 整个脚本立即停止退出
  
• : Generate the dependancies ; \  没有明白是啥意思~~
  
• $(CC) -x c -DDO_DEPS_ONLY -M $(CFLAGS) $(CPPFLAGS) -MQ $(obj)include/autoconf.mk include/common.h > $@
  
  • -DDO_DEPS_ONLY: 设置flag, 具体来说, 我们可以在common.h里面看见#ifdef DO_DEPS_ONLY这样的语句, 这个-D就表示DO_DEPS_ONLY被定义了
  • -M : 表示生成依赖关系. 我还专门做了个实验, 如下
    • gcc -M main.c 输出结果为 main.o: main.c
      
  • -MQ: 表示指定依赖关系中target的名称, 看下面的实验
    • gcc -M -MQ newname.mk main.c 输出结果为 newname.mk: main.c
  • 这句话表示: 生成依赖关系 include/autoconf.mk: include/common.h, 结果最终输出到include/autoconf.mk.dep
• 打开编译后生成的include/autoconf.mk.dep, 可以查阅里面的内容. 至于为什么需要生成这个文件, 我现在还不清楚.

再看第二个:  $(obj)include/autoconf.mk: $(obj)include/config.h, 它表示autoconf.mk依赖于include/config.h这个文件

• @$(XECHO) Generating $@ ; \ 这句话会在编译阶段输出编译信息Generating include/autoconf.mk
  
• set -e; \ 同上
• $(CPP) $(CFLAGS) -DDO_DEPS_ONLY -dM include/common.h | sed -n -f tools/scripts/define2mk.sed > [email protected] && mv [email protected] $@
  
  • -DDO_DEPS_ONLY: 同上
    
  • -dM : 作用是输出include/common.h中定义的所有宏
  • |      : shell中的管道, 表示将前面的结果传递给后面的命令
  • define2mk.sed : 查找和处理以“CONFIG_”开头的宏定义的功能, 将处理的结果输出到include/autoconf.mk.tmp
    
  • mv [email protected] $@ : 重命名为include/autoconf.mk. 
    
  • 最终就会生成include/autoconf.mk
•  include/common.h文件包含了include/config.h文件，而include/config.h文件又包含了config_defaults.h等uboot下的通用头文件, 还会包含<configs/${CONFIG_NAME}.h>, 这个.h是我们自己创建的, 可以在里面添加自己的"CONFIG_"宏定义. 已决定开启哪些功能.
  

至此, 我们知道, 系统中所有的"CONFIG_"开头的宏开关, 都被放到了include/autoconf.mk中. 

depend

在uboot的顶层Makefile中, 我们经常会看到类似的代码片段

$(obj)spl/u-boot-spl.bin:   $(SUBDIR_TOOLS) <span style="color: rgb(255, 0, 0);">depend</span>
        $(MAKE) -C spl all

$(obj)spl/u-boot-spl.bin:	$(SUBDIR_TOOLS) <span style="color:#ff00;">depend</span>
		$(MAKE) -C spl all

这个depend是什么意思呢, Makefile中有如下一段代码

# Explicitly make _depend in subdirs containing multiple targets to prevent
# parallel sub-makes creating .depend files simultaneously.
depend dep: $(TIMESTAMP_FILE) $(VERSION_FILE) \
        $(obj)include/spl-autoconf.mk \
        $(obj)include/tpl-autoconf.mk \
        $(obj)include/autoconf.mk \
        $(obj)include/generated/generic-asm-offsets.h \
        $(obj)include/generated/asm-offsets.h
        for dir in $(SUBDIRS) $(CPUDIR) $(LDSCRIPT_MAKEFILE_DIR) ; do \
            $(MAKE) -C $$dir _depend ; done

# Explicitly make _depend in subdirs containing multiple targets to prevent
# parallel sub-makes creating .depend files simultaneously.
depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) \
		$(obj)include/spl-autoconf.mk \
		$(obj)include/tpl-autoconf.mk \
		$(obj)include/autoconf.mk \
		$(obj)include/generated/generic-asm-offsets.h \
		$(obj)include/generated/asm-offsets.h
		for dir in $(SUBDIRS) $(CPUDIR) $(LDSCRIPT_MAKEFILE_DIR) ; do \
			$(MAKE) -C $$dir _depend ; done

• depend dep : 它表示这个规则有两个目标. 也就是你自己的目标依赖depend或者dep都会跑到这里来继续.
• $(obj)include/spl-autoconf.mk \ : 表示depend依赖spl-autoconf.mk. 这个mk的生成规则也在Makefile中有定义. 细节方面参考上面的autoconf.mk
  
• $(obj)include/tpl-autoconf.mk \ : 同上
  
• $(obj)include/autoconf.mk \     : 同上
  
• $(obj)include/generated/generic-asm-offsets.h \ : 暂不分析
  
• $(obj)include/generated/asm-offsets.h : 暂不分析
  
• for dir in $(SUBDIRS) $(CPUDIR) $(LDSCRIPT_MAKEFILE_DIR) ; do $(MAKE) -C $$dir _depend ; done
  
  • 这句话表示去上面各个目录下执行 make _depend命令.

那我们看看对应子目录下的Makefile, 例如$(CPUDIR) , 会看到如下的代码片段

# defines $(obj).depend target
include $(SRCTREE)/rules.mk

sinclude $(obj).depend

# defines $(obj).depend target
include $(SRCTREE)/rules.mk

sinclude $(obj).depend

并没有看到_depend这个目标, 那make _depend在这个目录下如何执行呢? 来看看它include的rules.mk

_depend:    $(obj).depend

# Split the source files into two camps: those in the current directory, and
# those somewhere else. For the first camp we want to support CPPFLAGS_<fname>
# and for the second we don't / can't.
PWD_SRCS := $(filter $(notdir $(SRCS)),$(SRCS))
OTHER_SRCS := $(filter-out $(notdir $(SRCS)),$(SRCS))

# This is a list of dependency files to generate
DEPS := $(basename $(patsubst %,$(obj).depend.%,$(PWD_SRCS)))

# Join all the dependencies into a single file, in three parts
#   1 .Concatenate all the generated depend files together
#   2. Add in the deps from OTHER_SRCS which we couldn't process
#   3. Add in the HOSTSRCS
$(obj).depend:  $(src)Makefile $(TOPDIR)/config.mk $(DEPS) $(OTHER_SRCS) \
        $(HOSTSRCS)
    cat /dev/null $(DEPS) >$@
    @for f in $(OTHER_SRCS); do \
        g=`basename $$f | sed -e 's/\(.*\)\.[[:alnum:]_]/\1.o/'`; \
        $(CC) -M $(CPPFLAGS) -MQ $(obj) 
      
       g   
      f >> $@ ; \
    done
    @for f in $(HOSTSRCS); do \
        g=`basename $$f | sed -e 's/\(.*\)\.[[:alnum:]_]/\1.o/'`; \
        $(HOSTCC) -M $(HOSTCPPFLAGS) -MQ $(obj) 
      
       g   
      f >> $@ ; \
    done

MAKE_DEPEND = $(CC) -M $(CPPFLAGS) $(EXTRA_CPPFLAGS_DEP) \
        -MQ $(addsuffix .o,$(obj)$(basename $<)) $< >$@


$(obj).depend.%:    %.c
    $(MAKE_DEPEND)

$(obj).depend.%:    %.S
    $(MAKE_DEPEND)

$(HOSTOBJS): $(obj)%.o: %.c
    $(HOSTCC) $(HOSTCFLAGS) $(HOSTCFLAGS_$(@F)) $(HOSTCFLAGS_$(BCURDIR)) -o $@ $< -c
$(NOPEDOBJS): $(obj)%.o: %.c
    $(HOSTCC) $(HOSTCFLAGS_NOPED) $(HOSTCFLAGS_$(@F)) $(HOSTCFLAGS_$(BCURDIR)) -o $@ $< -c

#########################################################################

_depend:	$(obj).depend

# Split the source files into two camps: those in the current directory, and
# those somewhere else. For the first camp we want to support CPPFLAGS_<fname>
# and for the second we don't / can't.
PWD_SRCS := $(filter $(notdir $(SRCS)),$(SRCS))
OTHER_SRCS := $(filter-out $(notdir $(SRCS)),$(SRCS))

# This is a list of dependency files to generate
DEPS := $(basename $(patsubst %,$(obj).depend.%,$(PWD_SRCS)))

# Join all the dependencies into a single file, in three parts
#	1 .Concatenate all the generated depend files together
#	2. Add in the deps from OTHER_SRCS which we couldn't process
#	3. Add in the HOSTSRCS
$(obj).depend:	$(src)Makefile $(TOPDIR)/config.mk $(DEPS) $(OTHER_SRCS) \
		$(HOSTSRCS)
	cat /dev/null $(DEPS) >$@
	@for f in $(OTHER_SRCS); do \
		g=`basename $$f | sed -e 's/\(.*\)\.[[:alnum:]_]/\1.o/'`; \
		$(CC) -M $(CPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; \
	done
	@for f in $(HOSTSRCS); do \
		g=`basename $$f | sed -e 's/\(.*\)\.[[:alnum:]_]/\1.o/'`; \
		$(HOSTCC) -M $(HOSTCPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; \
	done

MAKE_DEPEND = $(CC) -M $(CPPFLAGS) $(EXTRA_CPPFLAGS_DEP) \
		-MQ $(addsuffix .o,$(obj)$(basename $<)) $< >$@


$(obj).depend.%:	%.c
	$(MAKE_DEPEND)

$(obj).depend.%:	%.S
	$(MAKE_DEPEND)

$(HOSTOBJS): $(obj)%.o: %.c
	$(HOSTCC) $(HOSTCFLAGS) $(HOSTCFLAGS_$(@F)) $(HOSTCFLAGS_$(BCURDIR)) -o $@ $< -c
$(NOPEDOBJS): $(obj)%.o: %.c
	$(HOSTCC) $(HOSTCFLAGS_NOPED) $(HOSTCFLAGS_$(@F)) $(HOSTCFLAGS_$(BCURDIR)) -o $@ $< -c

#########################################################################

这里有_depend目标, make _depend的时候, 执行的其实就是这里的_depend. 这个里面的细节不分析了, 大体来说有几点

• $(obj).depend: obj一般为空, 所以这里会在当前目录下生成一个.depend文件
  
• .depend里面的内容就是类似于 : main.o : main.c main.h . 
  • 想深究的话可以参考这里 : http://blog.csdn.net/panfengsoftware/article/details/7877864

最后在Makefile里面引用了当前目录下的这个.depend