关于makefile的rules.mk 解读

在linux kernel与Uboot中，rules.mk 被包含到没有子目录的makefile文件中，用于产生文件依赖关系文件.depend文件，下面我们看一下uboot的rules.mk文件：

# # (C) Copyright 2006 # Wolfgang Denk, DENX Software Engineering, wd@denx.de. # # See file CREDITS for list of people who contributed to this # project. # # 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; either version 2 of # the License, or (at your option) any later version. # # 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. # # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place, Suite 330, Boston, # MA 02111-1307 USA # ######################################################################### _depend: $(obj).depend $(obj).depend: $(src)Makefile $(TOPDIR)/config.mk $(SRCS) $(HOSTSRCS) @rm -f $@ @touch $@ @for f in $(SRCS); do / g=`basename $$f | sed -e 's//(.*/)/./w//1.o/'`; / $(CC) -M $(CPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; / done @for f in $(HOSTSRCS); do / g=`basename $$f | sed -e 's//(.*/)/./w//1.o/'`; / $(HOSTCC) -M $(HOSTCPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; / done $(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

$(obj).depend: $(src)Makefile $(TOPDIR)/config.mk $(SRCS) $(HOSTSRCS)    //描述.depend 的依赖关系
  @rm -f $@                                                                                                     //强制删掉所有的目标文件，即*.depend文件
  @touch $@                                                                                                   //强制更新目标文件属性，以便使文件过期  
  @for f in $(SRCS); do /                                                                                  //for循环读取子目录下的文件
   g=`basename $$f | sed -e 's//(.*/)/./w//1.o/'`; /                                       

   //这一段比较难懂，我们把它分开来看，“basename $$f” 代表去变量$f的文件名，去掉路径等信息。“$f”为SRCS目录下的具体文  

//件。“|”为管道描述，“sed -e 's//(.*/)/./w//1.o/'`”为一个sed命令的文本处理部分，”-e“ 命令行，"s/.../.."为替换命令，

//“/(.*/)/./w”代表匹配任意除换行符开始的任意长度的字符接着是”.“字符最后是一个匹配字母或数字或下划线或汉字，"//1.O/" /1为前

//面的.*/匹配字符串 ,".O"加上.o。简单的说，此句实现的功能为将一个源文件替换为一个.o的OBJ文件，e.g..将一个.c的问题变成.o文件.

//对于这一部分如果仍然不是很清楚，可以看一下正则表达式文档。。。

   $(CC) -M $(CPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; /

//产生依靠文件
  done
  @for f in $(HOSTSRCS); do /
   g=`basename $$f | sed -e 's//(.*/)/./w//1.o/'`; /
   $(HOSTCC) -M $(HOSTCPPFLAGS) -MQ $(obj)$$g $$f >> $@ ; /
  done

 

//下面为.c编译规则

$(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