Makefile 小知识

解决库文件的循环依赖关系

$(EXEC): $(OBJS)
    $(CC) $(LDFLAGS) -o $@ $(OBJS) -Wl,--start-group $(LDLIBS) -Wl,--end-group
    @cp $@ $@.elf

-Wl,--start-group $(LIBS) -Wl,--end-group

以下是英文解释：

    -( archives -) or --start-group archives --end-group

    The archives should be a list of archive files. They may be either explicit file names, or -l options.

    The specified archives are searched repeatedly until no new undefined references are created. Normally, an archive is searched only once in the order that it is specified on the command line. If a symbol in that archive is needed to resolve an undefined symbol referred to by an object in an archive that appears later on the command line, the linker would not be able to resolve that reference. By grouping the archives, they all be searched repeatedly until all possible references are resolved.

    Using this option has a significant performance cost. It is best to use it only when there are unavoidable circular references between two or more archives.

字符串替换命令sed

将makefile 的一行注释掉，然后再去掉注释
源文件内容：include ../ght_sdk.mk
sed -i '/include ..\/ght_sdk.mk/s/include ../#include ../g' Makefile
#include ../ght_sdk.mk
sed -i '/#include ..\/ght_sdk.mk/s/include ../include ../g' Makefile
include ../ght_sdk.mk


改进版的循环替换：
#如果使用这个脚本编译，证明是用户编译单独的sdk,无需包含上一级Makefile
sed -i '/include ..\/ght_sdk.mk/s/include ../#include ../g' Makefile

make clean
make tests_l710

//当grep 查找成功时，返回0；shell 的ture 是0 ,所以查找成功时进入while循环
while grep  "#include ..\/ght_sdk.mk" Makefile > /dev/null
do 
    sed -i '/#include ..\/ght_sdk.mk/s/#include ../include ../g' Makefile
done