builtroot make menuconfig流程

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

 menuconfig: $(BUILD_DIR)/buildroot-config/mconf prepare-kconfig
     $(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。

 HOSTCFLAGS = $(CFLAGS_FOR_BUILD)
 $(info ${HOSTCFLAGS})
 $(info $(origin CFLAGS_FOR_BUILD))
 export HOSTCFLAGS

 #mkdir -p /home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config/lxdialog
 #PKG_CONFIG_PATH="" make CC="/usr/bin/gcc" HOSTCC="/usr/bin/gcc" \
                 obj=/home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config -C support/kconfig -f Makefile.br mconf
 .PHONY: prepare-kconfig
 prepare-kconfig: outputmakefile $(BUILD_DIR)/.br2-external.in
     $(Q) echo ""
 $(BUILD_DIR)/buildroot-config/%onf:--->$(BUILD_DIR)/buildroot-config/mconf
     mkdir -p $(@D)/lxdialog
     $(info $(HOST_PKG_CONFIG_PATH))
     $(info $(origin HOST_PKG_CONFIG_PATH))
     $(info $(MAKE))
     $(info $(origin MAKE))
     $(info $(HOSTCC_NOCCACHE))
     $(info $(origin HOSTCC_NOCCACHE))
     PKG_CONFIG_PATH="$(HOST_PKG_CONFIG_PATH)" $(MAKE) CC="$(HOSTCC_NOCCACHE)" HOSTCC="$(HOSTCC_NOCCACHE)" \
         obj=$(@D) -C $(CONFIG) -f Makefile.br $(@F)

 DEFCONFIG = $(call qstrip,$(BR2_DEFCONFIG))

 # We don't want to fully expand BR2_DEFCONFIG here, so Kconfig will
 # recognize that if it's still at its default $(CONFIG_DIR)/defconfig
 # BR2_DEFCONFIG='' KCONFIG_AUTOCONFIG=/home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config/auto.conf KCONFIG_AUTOHEADER=/home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config/autoconf.h KCONFIG_TRISTATE=/home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config/tristate.config BR2_CONFIG=/home/frank/test/buildroot/buildroot-2018.02./.config HOST_GCC_VERSION="4 8" BUILD_DIR=/home/frank/test/buildroot/buildroot-2018.02./output/build SKIP_LEGACY= /home/frank/test/buildroot/buildroot-2018.02./output/build/buildroot-config/mconf Config.in
  COMMON_CONFIG_ENV = \
     BR2_DEFCONFIG='$(call qstrip,$(value BR2_DEFCONFIG))' \
     KCONFIG_AUTOCONFIG=$(BUILD_DIR)/buildroot-config/auto.conf \
     KCONFIG_AUTOHEADER=$(BUILD_DIR)/buildroot-config/autoconf.h \
     KCONFIG_TRISTATE=$(BUILD_DIR)/buildroot-config/tristate.config \
     BR2_CONFIG=$(BR2_CONFIG) \
     HOST_GCC_VERSION="$(HOSTCC_VERSION)" \
     BUILD_DIR=$(BUILD_DIR) \
     SKIP_LEGACY=

prepare-kconfig又依赖 outputmakefile 和 $(BUILD_DIR)/.br2-external.in

 # outputmakefile generates a Makefile in the output directory, if using a
 # separate output directory. This allows convenient use of make in the
 # output directory.
 .PHONY: outputmakefile
 outputmakefile:
     echo $(origin NEED_WRAPPER)
     echo $(origin Q)
     echo $(origin TOPDIR)
     echo $(origin O)
     echo ${NEED_WRAPPER}
 ifeq ($(NEED_WRAPPER),y)
     $(info "xxxxxxx")
     $(Q)$(TOPDIR)/support/scripts/mkmakefile $(TOPDIR) $(O)
 endif

 # Even though the target is a real file, we mark it as PHONY as we
 # want it to be re-generated each time make is invoked, in case the
 # value of BR2_EXTERNAL is changed.
 # support/scripts/br2-external -k -o "/home/frank/test/buildroot/buildroot-2018.02.1/output/build/.br2-external.in"
 .PHONY: $(BUILD_DIR)/.br2-external.in
 $(BUILD_DIR)/.br2-external.in: $(BUILD_DIR)
     $(Q)support/scripts/br2-external -k -o "$(@)" $(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