uboot编译学习----直接执行make all，提示编译失败

参考博客：/article/6967249.html‘

若没有执行过“make <board_name>_config”命令就直接执行“make
all”命令则会出现如下的才错误信息，然后停止编译：

[cpp]
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System not configured - see README

System not configured - see README

U-Boot是如何知道用户没有执行过“make <board_name>_config”命令的呢？阅读U-Boot源代码就可以发现了，Makefile中有如下代码：

[cpp]
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ifeq ($(obj)include/config.mk,$(wildcard $(obj)include/config.mk)) # config.mk存在 all: sinclude $(obj)include/autoconf.mk.dep sinclude $(obj)include/autoconf.mk … … else # config.mk不存在 … … @echo "System not configured - see README" >&2 @ exit 1 … … endif # config.mk

ifeq ($(obj)include/config.mk,$(wildcard $(obj)include/config.mk)) # config.mk存在
all:
sinclude $(obj)include/autoconf.mk.dep
sinclude $(obj)include/autoconf.mk
… …
else        # config.mk不存在
… …
@echo "System not configured - see README" >&2
@ exit 1
… …
endif      # config.mk

若include/config.mk 文件存在，则$(wildcard $(obj)include/config.mk) 命令执行的结果是“$(obj)include/config.mk”展开的字符串，否则结果为空。

由于include/config.mk是“make <board_name>_config”命令执行过程生成的，

若从没有执行过“make <board_name>_config”命令则include/config.mk必然不存在。

因此Make就执行else分支的代码，在输出“System not configured - see README”的信息后就返回了。