openwrt构建过程探索

参考网站：http://wiki.openwrt.org/doc/howto/buildroot.exigence

需要下载必要的库文件，编译器等。。。

1 首先要获得openwrt的源码，参考openwrt.org官方网站的内容 https://dev.openwrt.org/wiki/GetSource

其中trunk为开发版本，最新的稳定版为12.09 branch (Attitude Adjustment)。

使用git获得：git clone git://git.openwrt.org/12.09/openwrt.git

如果要更新源码则运行git pull即可。

使用svn获得：svn co svn://svn.openwrt.org/openwrt/branches/attitude_adjustment

2 下载完源码之后

获取包列表：

./scripts/feeds update -a

将包选项加到menuconfig中去：

./scripts/feeds install -a

3 make menuconfig

在此菜单中选择要编译的模块并生成依赖

3.1

我们打开openwrt根目录下的Makefile文件，发现并没有找到menuconfig这个目标，这个目标是在

include $(TOPDIR)/include/toplevel.mk

所指的toplevel.mk中定义的，如下图：

它的依赖是scripts/config/mconf和prepare-tmpinfo FORCE

• scripts/config/mconf是一个已经存在的可执行文件；
• prepare-tmpinfo是本文件中的一个目标，等会再阐述；
• FORCE尚还不清楚它的作用和来源；

我们先看看menuconfig中的命令

    if [ \! -e .config -a -e $(HOME)/.openwrt/defconfig ]; then \
        cp $(HOME)/.openwrt/defconfig .config; \
    fi
    $< Config.in

这是一句shell脚本，意思是：如果不存在.config而且存在$(HOME)/.openwrt/defconfig，则拷贝$(HOME)/.openwrt/defconfig为.config

$<是什么？The automatic variable ‘$<’ is just the first prerequisite，即是指scripts/config/mconf。
把这两个字符串连起来看就知道什么意思啦：scripts/config/mconf Config.in

你也可以直接到openwrt目录下去试运行一下这个指令，如下图，正是我们运行make menuconfig时出现的画面（下图我已经关闭了menuconfig）：

3.2

好！现在我们回头去理prepare-tmpinfo的帐，并且看看能不能把Config.in这个文件搞懂是怎么回事。

prepare-tmpinfo: FORCE
    mkdir -p tmp/info
    $(_SINGLE)$(NO_TRACE_MAKE) -j1 -r -s -f include/scan.mk SCAN_TARGET="packageinfo" SCAN_DIR="package" SCAN_NAME="package" SCAN_DEPS="$(TOPDIR)/include/package*.mk $(TOPDIR)/overlay/*/*.mk" SCAN_DEPTH= SCAN_EXTRA=""
    $(_SINGLE)$(NO_TRACE_MAKE) -j1 -r -s -f include/scan.mk SCAN_TARGET="targetinfo" SCAN_DIR="target/linux" SCAN_NAME="target" SCAN_DEPS="profiles/*.mk $(TOPDIR)/include/kernel*.mk $(TOPDIR)/include/target.mk" SCAN_DEPTH= SCAN_EXTRA="" SCAN_MAKEOPTS="TARGET_BUILD=1"
    for type in package target; do \
        f=tmp/.$${type}info; t=tmp/.config-$${type}.in; \
        [ "$$t" -nt "$$f" ] || ./scripts/metadata.pl $${type}_config "$$f" > "$$t" || { rm -f "$$t"; echo "Failed to build $$t"; false; break; }; \
    done
    ./scripts/metadata.pl package_mk tmp/.packageinfo > tmp/.packagedeps || { rm -f tmp/.packagedeps; false; }
    touch $(TOPDIR)/tmp/.build

3.2.1

两个变量

_SINGLE在顶层Makefile中定义：

_SINGLE=export MAKEFLAGS=$(space);

NO_TRACE_MAKE的-/include/verbose.mk中定义：

ifeq ($(NO_TRACE_MAKE),)
NO_TRACE_MAKE := $(MAKE) V=s$(OPENWRT_VERBOSE)
export NO_TRACE_MAKE
endif

这里的命令先是去make V=xx -j1 -r -s -f include/scan.mk（分别Verbose，单线程，没有内建规则，指定Makefile文件）。所以我们再打开include/scan.mk文件看看怎么回事。最终目标是：

all: $(TMP_DIR)/.$(SCAN_TARGET)

3.2.2

这时scan.mk先定义了一个叫做PackageDir的“函数”（命令序列，后面将会使用）：

define PackageDir
  $(TMP_DIR)/.$(SCAN_TARGET): $(TMP_DIR)/info/.$(SCAN_TARGET)-$()
  $(TMP_DIR)/info/.$(SCAN_TARGET)-$(): $(SCAN_DIR)/$()/Makefile $(SCAN_STAMP) $(foreach DEP,$(DEPS_$(SCAN_DIR)/$()/Makefile) $(SCAN_DEPS),$(wildcard $(if $(filter /%,$(DEP)),$(DEP),$(SCAN_DIR)/$()/$(DEP))))
    { \
        $$(call progress,Collecting $(SCAN_NAME) info: $(SCAN_DIR)/$()) \
        echo Source-Makefile: $(SCAN_DIR)/$()/Makefile; \
        $(NO_TRACE_MAKE) --no-print-dir -r DUMP= -C $(SCAN_DIR)/$() $(SCAN_MAKEOPTS) >/dev/null || { \
            mkdir -p "$(TOPDIR)/logs/$(SCAN_DIR)/$(2)"; \
            $(NO_TRACE_MAKE) --no-print-dir -r DUMP= -C $(SCAN_DIR)/$() $(SCAN_MAKEOPTS) > $(TOPDIR)/logs/$(SCAN_DIR)/$()/dump.txt >&; \
            $$(call progress,ERROR: please fix $(SCAN_DIR)/$()/Makefile - see logs/$(SCAN_DIR)/$()/dump.txt for details\n) \
            rm -f $$@; \
        }; \
        echo; \
    } > $$@ || true
endef

3.2.3

这个命令系列的用法可以看下面的$(call progress, Colleting....)，progress也正是scan.mk文件中定义的一个命令序列：

$(TMP_DIR)/.$(SCAN_TARGET): $(TARGET_STAMP) $(SCAN_STAMP)
    $(call progress,Collecting $(SCAN_NAME) info: merging...)
    -cat $(FILELIST) | awk '{gsub(/\//, "_", $$0);print "$(TMP_DIR)/info/.$(SCAN_TARGET)-" $$0}' | xargs cat > $@ >/dev/null
    $(call progress,Collecting $(SCAN_NAME) info: done)
    echo

具体progress的定义是这样的：

ifeq ($(IS_TTY),)
  define progress
    printf "\033[M\r$(1)" >&;
  endef
else
  define progress
    :;
  endef
endif

所以，调用它之后会输出“<[M Collecting package info : merging... ”"....info: done"类似这样的信息（重定义到2，标准错误输出），$(1)表示第一个参数的意思

中间则输出awk信息，来研究下这个语句

-cat $(FILELIST) | awk '{gsub(/\//, "_", $$0);print "$(TMP_DIR)/info/.$(SCAN_TARGET)-" $$0}' | xargs cat > $@ >/dev/null

处理过程：

1. -cat $(FILELIST)，-cat最头的-表示如果出错也不提示如意思；
2. cat得的数据输出通过awk的解析

   awk '{gsub(/\//, "_", $$0);print "$(TMP_DIR)/info/.$(SCAN_TARGET)-" $$0}'

3. awk得的数据输出通过xargs cat（分小段输出给$@，也就是$(TMP_DIR)/.$(SCAN_TARGET)自己！），而错误输出的定义到null

看上面的过程，这部分主要问题是要搞清楚$(FILELIST)和awk的用法：

先上$(FILELIST)

$(FILELIST):
    rm -f $(TMP_DIR)/info/.files-$(SCAN_TARGET)-*
    $(call FIND_L, $(SCAN_DIR)) $(SCAN_EXTRA) -mindepth  $(if $(SCAN_DEPTH),-maxdepth $(SCAN_DEPTH)) -name Makefile | xargs grep -HE 'call (Build/DefaultTargets|Build(Package|Target)|.+Package)' | sed -e 's#^$(SCAN_DIR)/##' -e 's#/Makefile:.*##' | uniq > $@

这儿的FIND_L命令序列实在x/tmp/.host.mk中定义的（该mk文件由x/include/host.mk生成）

FIND_L=/usr/bin/find -L $()

因而这个命令就演变成了系统指令find/xarg&grep/sed/uniq的用法了。

1 find查找$(SCAN_DIR)中的叫做Makefile的文件（搜索深度1~5）；

2 xargs grep会展开各个Makefile文件，-H为显示时makefile名字，-E为启用后面跟着的正则表达式；

这儿call (Build/DefaultTargets|Build(Package|Target)|.+Package)会匹配到call Build/DefaultTargets或者BuildPackage或BuildTarget或者_任意多个字符_Package等三种情况的字符串（以行为结束）；

3 sed

4 uniq

最后获得的文件写到了FILELIST := $(TMP_DIR)/info/.files-$(SCAN_TARGET)-$(SCAN_COOKIE)中；

spidev_test
hostapd
opkg
fuse
hotplug2
ppp
...
feeds/xwrt/webif-iw-lua-openssl
feeds/xwrt/webif-netsukuku
feeds/xwrt/webif-mesh
feeds/xwrt/webif-fonheartbeat
robocfg
comgt
rssileds
madwifi
grub
libjson-c
odhcp6c
rotary-gpio-custom
ead
rtc-rv5c386a
sierra-directip
button-hotplug
grub2
kexec-tools
linux-atm
util-linux
xfsprogs
pjsip
ltq-tapidemo
owsip
fbtest
gpioctl
uboot-omap4
i2c-gpio-custom
ltq-tapi
ltq-vmmc
uboot-lantiq
swconfig
uhttpd
trelay
iptables
switch
owipcalc
ltq-kpi2udp

3.2.4

$(TMP_DIR)/.$(SCAN_TARGET)的信赖，条件

• $(TARGET_STAMP)

• $(SCAN_STAMP)

4 编译得的bin文件在bin目录中。

使用make menuconfig --debug -w --just-print命令，不执行操作仅调试，结果为：

 GNU Make 3.81
 Copyright (C)   Free Software Foundation, Inc.
 This is free software; see the source for copying conditions.
 There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
 PARTICULAR PURPOSE.

 This program built for x86_64-pc-linux-gnu
 Reading makefiles...
 Updating goal targets....
  File `menuconfig' does not exist.
     Target `scripts/config/mconf_check' is double-colon and has no prerequisites.
     Must remake target `scripts/config/mconf_check'.
 make: Entering directory `/home/tf/projects/openwrt'
 { [ -f "scripts/config/mconf_check.1" ] && mv "scripts/config/mconf_check.1"; /home/tf/projects/openwrt/scripts/timestamp.pl -x "*/.svn*" -x ".*" -x "*:*" -x "*\!*" -x "* *" -x "*\#*" -x "*/.*_check" -x "*/.*.swp"  -n scripts/config/mconf scripts/config && {  touch -r "scripts/config/mconf" "scripts/config/mconf_check"; } } || {  touch "scripts/config/mconf_check"; }
     Successfully remade target file `scripts/config/mconf_check'.
    Prerequisite `scripts/config/mconf_check' is newer than target `scripts/config/mconf'.
   Must remake target `scripts/config/mconf'.
 export MAKEFLAGS= ;umask ; cmd() { >/dev/null >& make -s $* < /dev/null || { echo "make $*: build failed. Please re-run make with V=s to see what's going on"; false; } } >& >&; cmd -s -C scripts/config all CC="gcc"
   Successfully remade target file `scripts/config/mconf'.
    File `prepare-tmpinfo' does not exist.
      File `FORCE' does not exist.
     Must remake target `FORCE'.
     Successfully remade target file `FORCE'.
   Must remake target `prepare-tmpinfo'.
 mkdir -p tmp/info
 export MAKEFLAGS= ;make V=s -j1 -r -s -f include/scan.mk SCAN_TARGET="packageinfo" SCAN_DIR="package" SCAN_NAME="package" SCAN_DEPS="/home/tf/projects/openwrt/include/package*.mk /home/tf/projects/openwrt/overlay/*/*.mk" SCAN_DEPTH= SCAN_EXTRA=""
 export MAKEFLAGS= ;make V=s -j1 -r -s -f include/scan.mk SCAN_TARGET="targetinfo" SCAN_DIR="target/linux" SCAN_NAME="target" SCAN_DEPS="profiles/*.mk /home/tf/projects/openwrt/include/kernel*.mk /home/tf/projects/openwrt/include/target.mk" SCAN_DEPTH= SCAN_EXTRA="" SCAN_MAKEOPTS="TARGET_BUILD=1"
 for type in package target; do \
         f=tmp/.${type}info; t=tmp/.config-${type}.in; \
         [ "$t" -nt "$f" ] || ./scripts/metadata.pl ${type}_config "$f" > "$t" || { rm -f "$t"; echo "Failed to build $t"; false; break; }; \
     done
 ./scripts/metadata.pl package_mk tmp/.packageinfo > tmp/.packagedeps || { rm -f tmp/.packagedeps; false; }
 touch /home/tf/projects/openwrt/tmp/.build
   Successfully remade target file `prepare-tmpinfo'.
 Must remake target `menuconfig'.
 if [ \! -e .config -a -e /home/tf/.openwrt/defconfig ]; then \
         cp /home/tf/.openwrt/defconfig .config; \
     fi
 scripts/config/mconf Config.in
 Successfully remade target file `menuconfig'.
 make: Leaving directory `/home/tf/projects/openwrt'