本文主要介绍一下，buildroot(buildroot-2018.02.1)的make menuconfig。众所周知，在我们执行menuconfig时，会生成一个图形化界面，然后进行相关的配置。同样，kernel 也有同样的配置方式，buildroot应该是借鉴kernel的。
那么，这个界面到底是怎样生成的呢？接下来，我来详细的介绍。
1. 顶层Makefile解析
1 menuconfig: $(BUILD_DIR)/buildroot-config/mconf prepare-kconfig 2 $(COMMON_CONFIG_ENV) $< $(CONFIG_CONFIG_IN)
首先看依赖项，有两个，mconf和prepare-kconfig，ok,一个一个解决。
1 HOSTCFLAGS = $(CFLAGS_FOR_BUILD) 2 $(info ${HOSTCFLAGS}) 3 $(info $(origin CFLAGS_FOR_BUILD)) 4 export HOSTCFLAGS 5 6 #mkdir -p /home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config/lxdialog 7 #PKG_CONFIG_PATH="" make CC="/usr/bin/gcc" HOSTCC="/usr/bin/gcc" 8 obj=/home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config -C support/kconfig -f Makefile.br mconf 9 .PHONY: prepare-kconfig 10 prepare-kconfig: outputmakefile $(BUILD_DIR)/.br2-external.in 11 $(Q) echo "1111111111111" 12 $(BUILD_DIR)/buildroot-config/%onf:--->$(BUILD_DIR)/buildroot-config/mconf 13 mkdir -p $(@D)/lxdialog 14 $(info $(HOST_PKG_CONFIG_PATH)) 15 $(info $(origin HOST_PKG_CONFIG_PATH)) 16 $(info $(MAKE)) 17 $(info $(origin MAKE)) 18 $(info $(HOSTCC_NOCCACHE)) 19 $(info $(origin HOSTCC_NOCCACHE)) 20 PKG_CONFIG_PATH="$(HOST_PKG_CONFIG_PATH)" $(MAKE) CC="$(HOSTCC_NOCCACHE)" HOSTCC="$(HOSTCC_NOCCACHE)" 21 obj=$(@D) -C $(CONFIG) -f Makefile.br $(@F) 22 23 DEFCONFIG = $(call qstrip,$(BR2_DEFCONFIG)) 24 25 # We don't want to fully expand BR2_DEFCONFIG here, so Kconfig will 26 # recognize that if it's still at its default $(CONFIG_DIR)/defconfig 27 # BR2_DEFCONFIG='' KCONFIG_AUTOCONFIG=/home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config/auto.conf KCONFIG_AUTOHEADER=/home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config/autoconf.h KCONFIG_TRISTATE=/home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config/tristate.config BR2_CONFIG=/home/frank/test/buildroot/buildroot-2018.02.1/.config HOST_GCC_VERSION="4 8" BUILD_DIR=/home/frank/test/buildroot/buildroot-2018.02.1/output/build SKIP_LEGACY= /home/frank/test/buildroot/buildroot-2018.02.1/output/build/buildroot-config/mconf Config.in 31 32 COMMON_CONFIG_ENV = 33 BR2_DEFCONFIG='$(call qstrip,$(value BR2_DEFCONFIG))' 34 KCONFIG_AUTOCONFIG=$(BUILD_DIR)/buildroot-config/auto.conf 35 KCONFIG_AUTOHEADER=$(BUILD_DIR)/buildroot-config/autoconf.h 36 KCONFIG_TRISTATE=$(BUILD_DIR)/buildroot-config/tristate.config 37 BR2_CONFIG=$(BR2_CONFIG) 38 HOST_GCC_VERSION="$(HOSTCC_VERSION)" 39 BUILD_DIR=$(BUILD_DIR) 40 SKIP_LEGACY=
prepare-kconfig又依赖 outputmakefile 和 $(BUILD_DIR)/.br2-external.in
1 # outputmakefile generates a Makefile in the output directory, if using a 2 # separate output directory. This allows convenient use of make in the 3 # output directory. 4 .PHONY: outputmakefile 5 outputmakefile: 6 echo $(origin NEED_WRAPPER) 7 echo $(origin Q) 8 echo $(origin TOPDIR) 9 echo $(origin O) 10 echo ${NEED_WRAPPER} 11 ifeq ($(NEED_WRAPPER),y) 12 $(info "xxxxxxx") 13 $(Q)$(TOPDIR)/support/scripts/mkmakefile $(TOPDIR) $(O) 14 endif 15 16 # Even though the target is a real file, we mark it as PHONY as we 17 # want it to be re-generated each time make is invoked, in case the 18 # value of BR2_EXTERNAL is changed. 19 # support/scripts/br2-external -k -o "/home/frank/test/buildroot/buildroot-2018.02.1/output/build/.br2-external.in" 20 .PHONY: $(BUILD_DIR)/.br2-external.in 21 $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR) 22 $(Q)support/scripts/br2-external -k -o "$(@)" $(BR2_EXTERNAL)
outputmakefile主要是 看 NEED_WRAPPER的值，由于执行make menuconfig时，NEED_WRAPPER的条件并不满足，所以当前outputmakefile这个目标并没有执行什么实际的动作。
$(BUILD_DIR)/.br2-external.in的作用是 生成.br2-external.in文件，在上面的#19行 已经指出了具体的执行命令。当前并没有太大作用，所以不做过多说明了。
接着我们再看$(BUILD_DIR)/buildroot-config/%onf，主要就是
PKG_CONFIG_PATH="$(HOST_PKG_CONFIG_PATH)" $(MAKE) CC="$(HOSTCC_NOCCACHE)" HOSTCC="$(HOSTCC_NOCCACHE)"
obj=$(@D) -C $(CONFIG) -f Makefile.br $(@F)
这行命令生成了mconf可执行程序。非常重要的节点。
接下来再执行$(COMMON_CONFIG_ENV) $< $(CONFIG_CONFIG_IN)，即 mconf Config.ini，那么最开始给出的图形界面就弹出来了。
备注：上述的Makefile中我自己加了一些调试代码，如$(info ), echo