Makefile judge custom variables

We know makefile The judgment variable in is ifeq, This ifeq It can judge the variables passed in from the command line , And you can judge makefile Customized variables in .

ifeq ($(platform), )
files:=$(foreach directory, $(dirs), $(wildcard $(directory)/*.config))
OBJ:=$(notdir $(files))
else
$(info no such platform of $(platform)) # You need to write in the top box 
##### If it's not empty , The description defines the compilation platform , Get from the specified platform 
files:= $(foreach directory, $(dirs), $(wildcard $(directory)/$(platform)*.config))
ifeq ("$(files)", " ") # If the above match fails, a space will be returned , Not empty 
$(error no such files of $(files)) # You need to write in the top box 
else
OBJ:= $(notdir $(files))
endif
endif

As above ifeq ($(platform), ) Is a judgment platform Is it empty , This can be passed in from the command line parameter , Such as make platform=hisiv200. and ifeq ("$(files)", " ") Is the judgment variable files Whether it is a space , This judgment is because foreach and wildcard When used together , When the result cannot be matched , It returns a space . Use alone wildcard And if it doesn't match, it will return null , You can use ifeq ($(files), ) Judge .